Great whites sharks, makos or sailfish, what is the fastest fish?

A great white shark charges forward.

My only encounters with a great white were on a cage diving trip, many years ago.  Two of us at a time would enter the cage and wait, cameras poised.  This was around Isla Guadalupe, 250km west of Baja Peninsula, Mexico.  The water was around 30metres deep and the water clarity stunning.  As we stood in the cage, breathing through hookah (surface-supplied) diving regulators, heavily weighted to keep us firmly planted, I would get in to a rhythm, look left… look right…. look left…look right, gently swinging my head and shoulders.  Shoals of yellowfin tuna would constantly glide past, so there was always something to see.  Occasionally a massive great white would cruise in to view, and we would both try and position ourselves to get the perfect shot.  That’s where my problems began.  The guy I was normally paired up with – a great guy who’s name I’m afraid I now forget – was easily 6’5″.  Those who know me know I am not especially tall. No matter which way I turned it seemed like his arms and camera were stretching out in front of me, always edging in to the frame of my pictures.  Time and again my shots included a forearm or a big, meaty fist and camera in front of the shark.  My frustration grew and silently I seethed!  I watched the great whites slowly cruise and then gently turn and wheel.  If only I could get outside this (expletive deleted) cage and get a couple of clean shots.  This thought went around and around in my head.  As the days past the novelty of seeing great whites close up, and standing still in cool water for two hours at a stretch, faded a little for some.  This meant that those of us – the ones who were there to try and get the shot – were able to spread out a little.  So in the latter part of the trip I would often be in a cage on my own.  But still I was not satisfied. Those damn cage bars! When a shark cruised past, checking me out, and I would track its path – only to have a couple of cage bars creep into the edge of the picture. So once again, standing in the cage looking left, looking right, looking left …. staring out in to the incredibly clear blue water for maybe an hour, and seeing nothing.  If only I could have gotten out of the cage, to have a little look around with no obstructions. Look left, look right, look le… and there – directly in front of me, maybe two metres away, from out of nowhere, was a massive great white.  Suddenly I lost all interest in getting out of the cage.  Seconds previously I had looked in that direction and seen nothing, then suddenly this enormous fish was right there – in my face.  I could not believe it had moved so fast.  Great whites are famous for their vertical attacks on fur seals, where they swim directly up, slamming in to the intended victim which such speed and power that both predator and prey breach clear of the water.  This got me thinking recently, just how fast are these sharks, and how do they achieve such speeds?

When we think of sharks tend to think of sleek, powerful predators that appear to cruise effortlessly, but are capable of dazzling bursts of speed when they attack prey.  This image of the shark is exemplified by the shortfin mako (Isurus oxyrinchus).  We know makos are fast,they are often described as the fastest of all sharks, but how fast?  Reliable measurements of swimming speeds of large fish are notoriously difficult to achieve; most scientific data out there are estimates based on things such as tail beat frequency, white muscle contraction speeds and sometimes measurements of speed of juveniles under test conditions.  Trouble is, we known maximum speed tends to increase with overall length but white muscle twitch speed decreases with size, so extrapolations are full of caveats.  Look online and you will find incredible speeds ascribed to makos, often on reputable websites; 60mph is cited on some pages, 74km per hour on many others.  Trouble is, finding out where these figures actually come from is pretty damn tricky.  Wikipedia until recently quoted 74kmph as the maximum speed of makos; so I kinda suspect that many article authors in a hurry simply googled and went to Wikipedia (ahh, we’d all done it).  In the current Wikipedia version (2020/06/06) the figure is revised down to 68km per hour (42mph).  Unfortunately, the referenced paper for this figure (Graham, et al., 1990) doesn’t mention this speed, or indeed any maximum speed, for full grown makos (sorry Wikipedia, you are terrific most of the time).  Other pages cite anecdotal accounts of makos, hooked by fishermen, covering 30m in 2 seconds, but … we all know about fishermen’s tales.  So the bottom line is, we don’t really have much in the way of solid data on how fast they can swim, but they are pretty damn fast.

A Mako shark make a half-hearted attempt to grab a cape petrel.

So let’s look a bit more widely at the problem. It is generally believed the fastest of all fish in the ocean are billfish (sailfish, swordfish etc.).  Esteemed organisations such NOAA (The U.S. National Oceanic and Atmospheric Administration) on their Ocean Facts web page, state that the sailfish (Istiophorus platypterus) reaches a blistering 70mph (113kmph) ( accessed 7th June 2020).  However, a 2015 study lead by Stefano Marras, from the Institute for Marine and Coastal Environment, Oristano, Italy, and Takuji Noda, Kyoto University, Japan, suggested the truth was a little more sedade.  Using high speed videography and data loggers with built in accelerometers attached to the fish (rather than the adrenaline-fuelled anecdotes of big-game fishermen) they found that the maximum speeds burst speeds recorded by sailfish chasing prey were between 8.19 and 9.77 metres per second (that’s 29.5 – 35kmph), with average burst speed between 19 and 26kmph (these ranges for top and mean speeds reflect differences between the two recording methods).

As it turns out, a second study the following year, also looking at sailfish maximum speeds, but using very different techniques, produced very similar results.  Morten Svendsen and others (Svendsen et al 2016) looked at four different species of fish, all noted for their speed, including sailfish.  The limiting factors, they determined, are maximum tail speed movement based on muscle contraction values, and bubble cavitation.  Bubble cavitation is essentially the water boiling as pressure drops.  Physics tells us that the temperature at which the vaporisation point of a body of liquid is reached varies as the pressure varies.  This is why, were an astronaut take a glass of water on a spacewalk, the water would instantly vaporise because there is almost no pressure in space (it does not, unfortunately, tell us why he would do something as pointless as that).  It is also why mountaineers cannot make a decent cup of tea at altitude, because at the lowered atmospheric pressure water will boil at less than 100 degrees C, which as any tea drinker will tell you is far from ideal.  Bubble cavitation is a phenomenon well known to small powerboat drivers.  As a propeller turns it creates dramatic pressure drops behind the blades.  This, in turn, causes microbubbles to form (the plume of bubbles one can see behind the prop of a speedboat) as some of the water vaporises.  As these bubbles hit higher pressure water they collapse, often violently, creating pressure waves. These pressure waves will, over time, destroy the material of the propeller.  So what has all this got to do with fish swimming?  Well exactly the same physics apply.  Between 10-15 metres per second (36-45kmph) significant cavitation will start to occur around the tailfin of fast swimming fish or marine mammals, but pain is likely to set in a little below that speed.  Interestingly tuna, another fast swimming group of fish, have bony tails without nerve endings.  It is therefore possible they may be able to exceed the speed threshold that other fish species cannot, and in fact lesions have been on the tails of tuna, which it is thought might be cause by bubble cavitation.  Bubble cavitation lessens at depth (as temperature drops and pressure increases) but maximum speed will still be limited by muscle contraction speed and ‘tail stall’ when the pressure differential is too great.

So where does this leave us with mako sharks?  Well, a reasonable assumption is that their top speed is probably only slightly slower than that of sailfish.  So that puts them just under 30kmph mark.  That may not sound quite so exciting, but it’s still almost four times faster than a top Olympic swimmer.  The French champion swimmer Frédérick Bousquet set a 50 metre dash world record in 2009, with an average speed of 8.6km per hour.

Now swimming fast requires a lot of energy; and it requires muscles to move fast.  That’s pretty self-evident. But we know that cold blooded (ectothermic) animals can’t move fast when their muscles are cold, because the chemical reactions, e.g. the production and utilisation of Adenosine triphosphate (ATP) for muscle contraction, occur more slowly.  That’s why no reptiles are active during winter months in temperate regions, and in summer lizards will bask in the morning sun to warm up before becoming active.  But you can’t do that underwater, the sea temperature does not heat up daily, nor sunlight’s warmth penetrate beneath the waves.  And, as Herman Melville wrote ‘Of all nature’s animated kingdoms, fish are the most unchristian, inhospitable, heartless, and cold-blooded of creatures‘.  So how do these ultra-fast fish species overcome this problem? Well we now know that quite a few different fish species have evolved their own way to become warm-blooded, after a fashion.  Shortfin mako, porbeagle, salmon and great white sharks have all been found to be capable of maintaining their body temperature several degrees above that of the surrounding water.  In 1969, Francis Carey and Jim Teal, of Woods Hole Institute, published a paper showing that porbeagles and makos were able to maintain their body temperature 7-10 degrees Centigrade above the surrounding water. They are able to do this through a mechanism known as the rete mirabilia (from Latin, meaning wonderful net).  We now know that not only these shark species, but several other fast swimming species such as tuna, all have this mechanism for raising body temperature.  A rete mirabilia is essential a network of arteries and veins lying close to one another and acting as a countercurrent exchange system.  In these species of shark, large powerful red muscle generate heat deep within the body as they swim.  The rete mirabilia surrounds these muscles, with many side branches looping down into the muscle, and heat is transferred.  Bands of alternate arteries and veins transfer heat, which is carried to the white ‘fast twitch’ muscle.  This ability to warm the body, or parts of the body, above that of the surrounding water temperature probably serves multiple purposes.  For salmon sharks, porbeagles and great whites, it probably helps them to function and hunt in chilly waters; porbeagles occur off Northern Norway; great whites congregate around Fiordland and Stewart Island, Southern New Zealand.  Having been snorkelling in both areas without a wetsuit I can tell you that after 15 minutes I was barely functioning and only just able to pull myself back in to the boat.  Recent studies have shown that blue marlin, swordfish and makos and porbeagles, heat the blood supply to their eyes and brains.  This has been demonstrated to dramatically improve the response of their retinas to light stimuli, and so probably improves their visual acuity for hunting at depth.

I’ve yet to encounter a living porbeagle at sea. Despite ranging widely around the western shores of the British Isles, they are essentially an offshore, deeper water species, and so rarely encountered by divers.  The closest I have come was working, many years ago, on a Cornish fishing vessel.  This was a Newlyn Netter, setting bottom nets for highly prized hake around deep wrecks in the middle of the Irish Sea.  In two teams the crew would work around the clock; travelling is a great circle we would set nets for twelve hours then, arriving at our start wreck, haul nets for twelve hours.  Hauling nets at night, we pulled up porbeagle, unfortunately.  This happened years ago but, unfortunately, accidental bycatch remains one of the biggest threats to porbeagles.  Broad and powerfully built, they look much like small great whites, although they are predominantly fish eaters and not considered dangerous.  Porbeagles are thought to be second only to the closely related salmon shark in terms of thermoregulation. This probably explains their ability to tolerate colder water better than most shark species.  A recent study off Nova Scotia found that most were caught at depths where the water temperature was only 5-10 deg. C. That’s a colder preferred range than pretty much any other highly active shark species.

Porbeagle shark, Lamna nasus, caught as bycatch, on the deck of a fishing vessel, Irish Sea, UK.

My first encounter with a mako was an entirely unexpected one, along the East Coast of New Zealand, off Kaikoura (this story is told in more detail on my photography blog here).  Kaikoura, is a small town on the north east coast of New Zealand’s South Island.  It is famous as one of the best places in the World for whale watching, especially sperm whales.  Kaikoura may be most famous for whales, but it is also a fantastic place to see many species of albatross up close. Whilst the big whales grab most of the international headlines, the sheer drama of seeing several species of albatross up close – really close – soaring, wheeling and plunging down to feed, is pretty hard to beat.  Once well out to sea, the water was chummed to bring the albatross in. however, it not just the albatrosses and giant petrels that noticed the food in the water.  The scent of chum attracted in predators from below.  A dark triangular fin broke the surface and began weaving through the wary seabirds.  The shark was a juvenile mako, approximately 5-6ft (1.5-1.8m) long. Whilst clearly drawn towards us by the fish scraps in the water, it then became interested in the birds splashing around.

The great albatrosses eyed the shark with a mixture of wariness and belligerence; with a wingspan probably exceeding the length of the shark they may have seemed a little large to tackle.  The smaller petrels were more anxious.  It made a grab for one cape petrel that did not move out of its path fast enough, but the attack seemed have hearted and the petrel skittered away easily enough.  There was probably enough fish remains floating in the water to keep the shark happy. Makos will occasionally take seabirds, but mostly feed on pelagic fish species such as mackerel, herring and anchovies.  Larger individuals have been found to have young seals and even common dolphins in their stomachs, as well as billfish such as marlin.  Common dolphins and marlin are both renowned for their speed, so whilst it is possible that these were injured individuals snapped up by the mako, it is also these fell prey to the makos lightning speed.  I have yet to get in the water with a mako; however, should I be lucky enough to find myself snorkelling or diving with one, I’m not going to try and outswim it.

So to finish off, lots return to the beginning.  I still haven’t answered the question about great whites.  All other things being equal, absolute speed tends to increase with overall length.  So how do the much larger great whites compare with makos? When they turn the power on, and come swim vertically up, what speed is a 2.5 tonne shark doing when it bursts clear of the water’s surface like a cruise missile?  A 2011 paper by R. Aiden Martin and Neil Hammerschlag looked at exactly that.  They were interested in the predator prey relationship between great whites and cape fur seals (Arctocephalus pusillus pusillus).  Great whites use sheer speed and surprise to kill or incapacitate fur seals.  If they are unsuccessful in the first attack, the greater maneuverability of the fur seal favours them.  Using towed bouys to entice sharks to strike, they then analysed video footed to determine exit speed. One such attack was calculated at 35kmph. Analysis of underwater footage of actual attacks on seals suggests even faster speeds, (though the margin for error is probably greater).  So on that basis, the great white shades out the mako, maybe even the sailfish.  But, until even is compared using similar methodologies, the jury is still out.

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The Grind. Is campaigning for it to stop or condemning it on social media hypocritical?

A grind, Torshavn, Faroe Islands, May, 2019

A grind, Torshavn, Faroe Islands, May, 2019

The grind, or grindadrap, is a non-commercial, community based whale and dolphin drive in the Faroe Islands. Around 840 pilot whales and white sided dolphins are killed every year. This is done by local boats driving them in to designated beaches (there are 26 around the Faroe Islands. Grinds occur spontaneously, when pilot whale pods are sighted. It can only be initiated by sightings from land. The whales are driven by small boats on to the beaches, where local people gather and kill the whales using a specially designed lance that severs the spinal chord. The meat is not sold, but distributed equally and freely to all households in the Faroes. It is bloody, some say barbaric, affair. There are widespread calls in Europe and North America for it to be halted. Most prominent among the groups opposing the grind is Sea Shepherd, who have an ongoing campaign, Operation Bloody Fjords, to stop or disrupt the grind.

I was in the middle of writing a completely different blog when the topic of the Grind started resurfacing on social media posts. The post most frequently reposted, and commented upon, that I saw, was one from Sea Shepherd calling upon cruise ships to stop visiting the Faroe Islands until the Grind is stopped. Published on the Sea Shepherd UK website, this has been shared on Facebook and other social media platforms, as widely reposted and commented upon, including by several friends and work colleagues. In this, Sea Shepherd UK has written to 16 cruise ship companies (12 th August 2019) calling on them postpone visits the Faroe Islands until the hunting of pilot whales and dolphins is stopped.

This is part of a larger campaign by Sea Shepherd UK, known as Operation Bloody Fjords, aimed at halting or disrupting the grind in the Faroes. This is something I have given a fair bit of thought to and so, at the risk of alienating quite a few people, I decided to write this blog.

So to firstly declare my own interest in this matter. I consider myself a conservationist; for most of my professional career I worked as a freelance marine biologist/environmental consultant. I have a particular interest in the effects of fisheries on the marine environment, having worked for over 20 years collecting data on the effects of benthic mobile fishing gear on seabed marine life and habitats, and working to establish no fishing zones and monitoring their effectiveness.

Secondly, I work — as a self-employed contractor, on small cruise ships and have more than once been to the Faroes on such ships (though this is entirely a personal blog and represents solely my own views).

Thirdly, I have witnessed a grind, in 2018, and have talked to quite a few Faroese about it the grind and their views on the subject.

I should also add I am no fan of Sea Shepherd, or their founder Paul Watson. I consider them overly aggressive and confrontational with little or no science behind any of their activities, largely ineffective in terms of conservation, and that the prime (often sole) beneficiary of their activities are the finances of Sea Shepherd and their media profile. Sea Shepherd also prominently bills itself as a conservation body, but nowhere in their letter to cruise companies, or on their website campaign information, do they mention conservation. The most obvious reason for this is that the grind has no real impact on the conservation of pilot whales and their campaign has nothing to do with conservation. But more of that later.

I am genuinely conflicted regarding the grind. There is no doubt that pilot whales and white-sided dolphins are highly intelligent social animals. So I absolutely do not like to see them killed. Reposting and commenting on social media is quick and easy. It requires little effort and, unfortunately, often little thought. It can however have significant effect if done by a large number of people. For me, the core questions are proportionality, effectiveness and comparison of the action I am considering condemning with my own actions. We don’t want to spend our lives endlessly condemning things on social media to little effect, so it is a question of priorities — what is really important and what is not. Equally we should not be hypocritical: condemning things where our own personal deleterious impact is actually greater. With the Faroese pilot whale and dolphin hunt I believe the key questions are, sustainability and cruelty, so I will attempt to address these before returning to the question asked at the top of this blog.


The number of pilot whales killed annually in the Faroes is around 840 — since detailed records began over 300 years ago, and around 640 per year (2000–2017). All the science suggests this is a sustainable fishery. The Central and N.E. Atlantic population of pilot whales is estimated over 750,000 (Buckland et. al, 1989) although that figure is now quite old. A more recent assessment of the Faroese pilot whale hunt (NAMMCO 2013) found that, for the grind to be sustainable, a population (in Faroese waters) of 50–80,000 pilot whales was required. The current estimation puts the Faroese population at over 100,000. Unless this is a significant overestimate, then the pilot whale hunt is sustainable, with around 0.1% being killed annually. The most recent study (Pike, et al, 2019) looking at data between 1987 and 2015, indicates that the pilot whale population in the North East Atlantic is relatively stable during this period, with no long term trend of increasing or decreasing.

This is not something to be considered lightly — few British fisheries, for example, could be considered anything like as sustainable. It is also one of the best regulated fisheries in the World. Each year every single whale or dolphin killed is recorded, along with location and species. Very few other fisheries have such accurate records.

If one compares the pilot whales grind to fisheries in the UK (which I am very familiar with) or other developed countries:

1. it does not destroy the seabed habitat and all animals living there — unlike many of our fisheries where one hour of fishing will devastate a vast area of seabed, often for decades;

2. there is normally no bycatch; many other fisheries kill far more non-target than target species, which are simply dumped back into the ocean.


Cruelty is, almost by definition, a highly emotive issue, and not one easily quantified or compared. However, think about this hypothetical question.

Before being born you are given two choices for your life:

  1. You will be born into captivity. You will be separated from your mother when still very young. If male, you will be castrated before puberty. You will never be allowed to live naturally, in a natural environment, forage naturally, eat a natural diet, live in natural family groups, mate and reproduce, care for your offspring. You will be slaughtered when a few months old. Your natural lifespan would have been 15–20 years.
  2. You will be born in a total natural environment, surrounded by family members. Your mother will care for you, and as you grow you will play, be protected, and learn from other family members. You will hunt, feed, socialise, reproduce and raise offspring in a family group in totally natural conditions. You may live 45–50 years, all in a completely natural environment. Each year, there is a one in a thousand chance that you might be killed.

So if you had to choose one, which would you chose? I would be very surprised in anyone chose the first. I suspect most people would consider the first a truly horrific fate. Yet that is the fate of around 25 Million pigs — every single week — globally. That’s 1.5 thousand million pigs every year. Pigs are also highly intelligent, long-lived, social animals. There is no scientific evidence that I am aware of that suggests that pigs are in any way less susceptible to experiencing pain, fear, loss or loneliness that are pilot whales, nor any rational reason why that should be so. It is frequently said that ‘ I can be against keeping farmed animals and against the grind’. That is perfectly true, but think of the scale. If you accept that the life of a wild pilot whale is far preferable to the life imposed on most farmed pigs, then can you really argue that campaigning against the ‘cruelty’ imposed on around 640 pilot whales demands equal effort to campaigning against the greater individual cruelty imposed on 1.5 billion pigs? The differences in scale of suffering are almost unimaginably vast. Yet it is not the fate of farmed animals that gets the greatest high profile media attention, or the most reposts and comments on social media. It is the killing of around 640 pilot whales in the Faroe Islands. If the scale of campaigning was correlated to the scale of the suffering, then we should be reposting, commenting and campaigning over a million times for every single time we repost or campaign against pilot whales being killed in the Faroes. But of course that does not happen, reality is closer to the converse.

There is another aspect to this. For most people the Faroes are simply a group of small, remote islands somewhere in the North Atlantic. To vilify them online, to call for tourists to not go there, costs us nothing. We make zero personal sacrifice, but it makes us feel good, and righteous (something Sea Shepherd are well aware of). Conversely, giving up all farmed meat, campaigning against the meat farming industry would, for most of us, involve dramatic changes to our lifestyle and significant personal sacrifices. So instead we take the easy option of targeting something that has no effect on our own lives.

Sea Shepherd

As Sea Shepherd is the organisation driving this campaign, it is worth examining their record and modus operandi. I make no secret of the fact I am not terribly impressed by the group. A couple of illustrative examples may help explain this. Sea Shepherd was founded by Paul Watson after he was expelled from Greenpeace in 1977 for his ‘aggressive’ approach and distain for Greenpeace’s non-violent methods. That following year (1978) he gave an interview broadcast by the Canadian Broadcasting Association (CBC) about the Canadian harp seal cull, claiming the profitability of the campaign was why Greenpeace campaigned against the cull: ‘ Well it’s definitely because it’s easier to make money and because it’s easier to make a profit because there are over a thousand animals on the endangered species list, and the harp seal isn’t one of them’ stated Watson in the radio interview. He then added ‘ and now we have a dozen people this year from Greenpeace California — I mean they’re coming from the highest standard of living region in North America — they’re traveling to the place with the lowest income per year on this continent telling them not to kill seals because they’re cute but not endangered species. ‘ A year later his new organisation, Sea Shepherd, began their direct action campaign against the Canadian seal cull, recruiting celebrities like Brigitte Bardot and Pierce Brosnan to pose next to baby seals on the ice for publicity purposes.

More recently (2010) Sea Shepherd hit the news again when their 24m racing trimaran the MY Ady Gil collided with a Japanese whaling support vessel the MV Shonan Maru 2. The bow of the Ady Gil was badly damaged and she sunk the following day. Both parties blamed the other; the official inquiry found that both were at fault for the collision. Paul Watson first blamed the Japanese vessel for the collision, then blamed the Ady Gils captain, Peter Bethune, after falling out with him. Sea Shepherd claimed that the Ady Gil sunk the following day as she took on water while being towed. Peter Bethune subsequently claimed that Paul Watson had ordered him to deliberately scuttle the Ady Gil for publicity purposes, something Watson denied. The owner of the MY Ady Gil (the millionaire animal rights supporter Ady Gil) then took legal action against Sea Shepherd and Watson under the Racketeer Influenced and Corrupt Organizations Act. He won. The court in New York ruled that Sea Shepherd had indeed intentionally scuttled the vessel for publicity purposes and awarded compensation of half a million dollars. In the ruling the Arbiter described Watson as ‘“ highly evasive, internally contradictory, or at odds with his own prior written statements, and in certain areas simply lacking the basic indicia of genuineness that instinctively inspires confidence and trust.” She ruled that the order to scuttle her by opening the sea cocks came from Paul Watson and that the accounts given on the Whale Wars reality TV show were false and the sinking staged to maximise publicity. Sea Shepherd tried to keep the court ruling secret from the public, but failed in this. I described these two events as I think they give insight into the personality of Paul Watson and the aims of Sea Shepherd. I have no doubt that many Sea Shepherd staff and volunteers are well meaning, idealistic and honest, but the basic philosophy behind the organisation appears to be to generate conflict and drama and to maximise publicity and profits. There is very little science behind their campaigns and not a great deal of evidence of their long term effectiveness; rather they often antagonise local people and entrench views to resist change.

Sustainability — wider aspects

If we consider the wider aspects of the sustainability argument, the comparison between the grind and meat farming is even more damning. One is totally unsustainable. It destroys huge amounts of the World’s natural resources, and is directly responsible for the extinction, or imminent extinction, of a great many species. It is a major contributor to climate change and is a major polluter of land and waterways. It is also one of the greatest threats to the survival of tens of millions of humans around the planet through the large scale use of antibiotics, leading to drug resitant bacterial infections. And that one is not the killing 640 pilot whales each year. Meat farming is one of the largest causes of deforestation and habitat destruction around the World. It causes even greater habitat loss through the growing of crops specifically for animal feed. Habitat loss and fragmentation are probably the biggest causes of species extinction globally.

As far as I know there is no evidence that the grind has any measurable long term environmental impact whatsoever, and the available evidence suggests it is quite sustainable.

Last year, Sea Shepherd UK wrote to cruise companies asking them to cease visiting the Faroe Island until the grind is ended (covid-19 restrictions have made this request irrelevant for 2020). Sea Shepherd identifies itself as a conservation organisation. It is pretty clear that, while the grind is bloody and upsetting for many to watch, it is not a conservation issue. As someone involved in the cruise ship industry I am well aware that this is a far from perfect industry. It does indeed have major environmental issues. The amount and type of fuel burned by cruise ships is one. The air miles flown by joining and departing passengers is another. But this is also a heavily regulated industry and one where all involved — especially those in the small ‘expedition ship’ more likely to visit the Faroes — are deeply concerned and very aware of the issues. These are regularly discussed and ways sought to reduce our plastics use, our carbon footprint and our impact on the environment in general. One of, if not the biggest, impact is flying. You need to get your passengers to and from departure and arrival ports. This is a problem for all cruise ships not exclusively operating in local waters, and a huge problem for the tourism and travel industry in general. It is pretty indisputable that climate change is the biggest environmental threat to our planet at the moment. Currently, civil aviation accounts for around 2.5% of all energy-related CO2 emissions, and 4–5% of all energy-related greenhouse gas emissions. However, emissions from air travel grew 40% between 1990 and 2010. Air travel is predicted to grow at around 4% a year. Even with improvements in technology and carbon trading (i.e. buying carbon credits from less polluting industries) there is a still a real disconnect between air travels targets for reductions in greenhouse gases required to have a realistic chance of keeping climate change to the 2 oC rise target set as part of the IPPC’s Paris Agreement. In most Western developed countries, flying is the biggest single contributor to our carbon footprint. The UK’s carbon emissions are now (latest figures 2018) around 5.6 tonnes per person. But for one return flight (economy class) from London to Perth, Australia, releases around 5 tonnes of greenhouse emissions. So one long haul flight a year can effectively double one’s impact on climate change. That is a pretty sobering statistic. So let’s return to Sea Shepherd UK’s call for cruise ship companies to boycott the Faroes. Were Sea Shepherd really a conservation organisation one might think, when targeting a particular sector, they would look at that sector’s activities and choose the most environmentally damaging and attempt to persuade them to reduce or mitigate the damaging effects of that activity. So if the target industry is the cruise ship industry, then campaigning for a boycott of the Faroe Islands makes zero sense, in terms of conservation. If, instead, the target is the marine environmental impacts of the Faroese islanders and Government, then targeting the grind still makes zero sense in conservation terms. Now that is not to say that there are that there are no significant conservation issues with Faroese fisheries. There are; currently, and for some years, both cod and haddock stocks within Faroese waters are severely depleted, with cod stocks at historic lows, largely due to a combination of overfishing, over-capacity and poor regulation. So were Sea Shepherd looking at marine conservation issues, that would be valid issue to campaign on. It probably would not command anything like the same media attention though.

Threats to pilot whale populations

If we are concerned about the conservation of pilot whales, we need first to identify what the main threats are to pilot whales in the NE Atlantic, and globally. Undoubtedly one of the biggest threats is the amount of plastic waste in the oceans. And not just to pilot whales but a great many other marine mammals and marine life in general. On June 1st 2018, a short fin pilot whale found floating off the coast of Thailand took five days to die. Hours before it died it started vomiting up bits of plastic. An autopsy found 80 plastic bags in its stomach. In March 2019, a Cuvier’s beaked whale washed up dead on the Philippines coast; an autopsy found 40kg of plastic bags in its stomach. In April 2019 a pregnant sperm whale washed up on the Sardinian coast and was found to have over 20 kg of plastic in its stomach. In May 2019 a dead young sperm whale washed up on the coast of Italy; again its stomach was found to be full of plastic rubbish. This is clearly the tip of the iceberg. Undoubtedly many toothed whales (possibly the majority) will have plastic rubbish in their stomachs and be suffering sub-lethal effects. Equally, many will die at sea and their plastic burden will go unrecorded. Studies have shown that pilot whales have very high levels of mercury in their tissues. Sea Shepherd uses this fact as part of their argument to halt the grind. A more conservation-minded approach might be to ask why they have such high levels of mercury contamination, and what can be done about it. The main sources of organic mercury (methylmercury) in the marine environment are anthropogenic; particularly coal burning power plants, chlorine production and gold mining. The levels of organic mercury in pilot whales is among the highest recorded for marine mammals (although it is also high in polar bears, belugas, ring seals and many other top marine predators). In pilot whales the concentrations are considered high enough to produce neurological changes in them, along with liver and kidney abnormalities and changes in lymphocytes affecting their ability to fight infections. Yet another likely big impact on pilot whales (and many other cetaceans) is noise pollution from ship traffic and seismic survey activities. Like most cetaceans, pilot whales rely on vocalisation for communication over distance, for navigation and for hunting. Anthropogenic sources of marine noise, which have grown massively in the past hundred years (and which cruise ships contribute to) has been implicated in in many adverse effects on cetaceans, including displacement and avoidance behaviour, changes in vocalisation and mass strandings. The above all have real, profound and sometimes catastrophic effects on pilot whale populations and much other marine life besides, yet Sea Shepherd campaigns focus on none of the above. Instead, they chose to focus on an activity for which there is no evidence that it has any significant effect on pilot whale populations, on other marine species or on the wider marine environment. But it is one that garners Sea Shepherd a great deal of publicity.

The questions posed by this blog title was: is it hypocritical to campaign for the end of the grind or to criticise it on social media? Ultimately that depends, I believe, on your own personal lifestyle. If you eat farmed meat, if you use disposal plastics at all (recycling doesn’t count — most ‘recycled’ plastics are shipped to Third World countries of sit around in waste collection centres) if you travel by air at all, then the answer is ‘yes’ it is hypocritical, because your own negative impacts on the environment are almost certainly greater than those of the grind. I certainly do not meet that standard, which is one reason I would be very reluctant to criticise it. The grind is likely to slowly die out as younger peoples attitudes change; less likely as long as outsiders aggressively condemn the Faroese over it. In my view criticising and supporting campaigns to stop the grind are, and best, simply a distraction. They divert attention, time and energy away from environmental issues that are genuinely important, and the real threats to whale and dolphin populations.

Originally published at on August 27, 2019.

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Cornwall’s blue sharks

An account of photographing blue sharks off Cornwall, Southwest Britain, a few years back, and a link to buying fine art prints of these amazing hunters of of the oceans at

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

A Blue shark, Prionace glauca, swims leisurely through clear blue water off Cornwall, UK.

On a clear July morning I stumbled out of my bunk (I was living on a boat at the time) at 5.30am, forced out my the insistent buzzing of my phone alarm. One hour, and one strong coffee later, I squeezed my dive bag into the back of Ritchie’s car and we were off. We had over a hundred miles to cover, and a boat to catch.

Charles Hood runs the best, and most successful, blue shark snorkelling operation in the UK. His boat, a large rigid-hulled inflatable (RIB) operates out of Penzance, almost at southwesternmost extremity of the British mainland, so that’s where we were headed. The boat is a fast open boat, perfect for getting us 10 miles offshore quickly, but small and devoid of any shelter from the elements. So we changed in to wetsuits on the quayside, packed our camera gear in dry bags carefully padded with towels and sweatshirts for the bouncy ride out, and we were off.

Blue sharks have often been called the most beautiful of all sharks. It’s easy to see why.

Each year blue sharks arrive off the coast of Southwest Britain, normally sometime in mid-June and remaining until mid-October. Blues are true oceanic sharks; they inhabit deep water, only infrequently venturing on to shallower, continental shelf waters. They are found in tropical and temperate oceans around the globe. However, in the tropics they tend to stay in deeper, cooler water but are often observed in surface waters in temperate seas. They feed on fast moving prey such as squid and schooling fish. Much of their feeding appears to be done in deeper waters. We know this partly from studies looking at gut contents, identifying the hard tissue remains of the prey species, and knowing where those prey species live, and partly from small data loggers, recording depth profiles, that are attached to sharks and then recovered at a later date. Below 100 metres, it seems they predate mostly on squid, in particular those belonging to the Histioteuthidae family, more commonly known as cock-eyed squid. Cock-eyed squid are bizzare creatures that inhabit the twilight zone of the oceans, so-called because their left eye is around twice the size of their right. Observations with deep water remotely operated vehichles (ROVs) have shown that they swim with the left eye facing upwards, and the right facing down. It’s believe the the huge left eye is used to pick up the faint sunlight coming from far above; the smaller right eye, staring into the depths, serves a quite different purpose. It picks up bioluminecent glows and flashes from prey (or predators below). But blue sharks are not fussy eaters. Studies off the coast of Brazil have found they eat large numbers of oilfish (a deepwater member of the mackerel family) but will also sometimes grab seabirds such as shearwaters. Those off Southern Brazil were found to be mostly scavenging on dead baleen whales. But I have digressed somewhat from our trip. Some ten nautical miles out Charles stopped the RIB and allowed us to drift. Sure we were a fair way from shore, and in pretty deep water, but still well within continental shelf depths, probably 50-70 metres, as we drifted. The 100 depth contour was still over 20 miles distant. So what tempted the blues, normally oceanic species, this close inshore? As we drifted Charles began to prepare the chum bag that hopefully would draw nearby sharks to our boat. A small hessian sack was filled with chunks of mackerel and mackerel guts, including some caught angling off the stern of his RIB. Tied just off the side of the RIB, a slick of fish oil drifted away down current. This is the clue to why blue sharks arrive in coastal waters of southern and western Britain. Mackerel also arrive around British coasts during the summer months, often found in huge shoals numbering thousands of fish. Like their deeper water relatives, the oilfish, mackerel are an oily fish, so a high energy food source for any predator fast enough to catch them. And the blue shark is just that; generally a sedate swimmer it can move with lighting bursts of speed.

Once our bag of chum was positioned, and final checks on cameras completed, all we then had to do was wait. Charles dug out his fishing rod and started supplementing our chum supply with a few extra mackerel. And we waited. There was no wind, and just a slight, rolling swell on the sea. The sun was hot and the sky a clear blue, so it was not extactly a hardship. The sun climbed to its zenith, then slowly fell westward as morning gave way to afternoon. We were woken from our torpor when, around 2pm, a group of three sunfish drifted close. Sunfish are odd-looking disc shaped fish. They feed on There was a flurry of activity as we grabbed cameras and donned fins, but they were skittish and disappeared in seconds. We settled back in to watching and waiting. At around 3.30pm Charles announced that we should start heading back to shore at 4pm. The minutes ticked by; 4pm arrived and still no blues. Charles apologised but, as we were well aware, there is never any guarantee with wildlife. He announced we would give it another 20 minutes. At 4.15 the first blue arrived. Rather than leap in immediately, we gave it time to settle and get used to the boat. A couple of minutes later a second arrived. Charles had been very clear on the safety aspect, wearing gloves, no shiny jewellery. The necessity for this was made abundantly clear when one of the sharks managed to grab to chum bag. Its razor sharp teeth ripped through it like paper, and bits of mackerel guts spilled out into the water. The bag was quickly quisked out of the sea and we gave it a minute for the cloud to disperse. Once Charles was confident the sharks were no longer likely to disappear immediatly, we, one by one, slowly slide over the side of the boat and in to the water.

Blue shark, Prionace glauca. A female blue shark swimming close to the surface swims underneath a snorkeller off Southwest Cornwall, UK.

Richie fires off a couple of snaps as a blue passes beneath him.

Once in the water I dipped my head to check all around me, then slowing finned away from the RIB. Once around 8 metres away I stoppped finning, and started checking around. I could clearly see my three companions at this stage, floating 5-10 metres away from me. Every so often a shark would cruise in, swimming below or between us, to to check out us or the RIB. The water was clear, visibility a good 15-20 metres, but the sun was now low in the sky. When the sun is overhead, and light hits the waters’ surface more or less perpendicular, then much of that light penetrates the surface; but late afternoon, when the sun is low and its rays hit the water at a shallow angle then most of that light bounces off the surface and it becomes markedly darker just below than above. My photographic problems were two-fold. The reduced light levels made focussing a little trickier, and when a blue shark came fast out of the expanse of blue water, the camera would struggle to pick up contrast and focus quickly. I fiddled with the settings, pre-focussed using my colleagues as targets, fired off test shots and again readjusted my settings. All the time keeping looking around me. A RIB, with its large surface area above the water, will drift with wind and tide, but a swimmer, around 90% below the water’s surface, will drift with the tide alone. So as I floated I was aware that the distance between was growing. This was not a concern; conditions were perfect and I knew Charles would be fully aware of our positions. On the contrary, it gave me space around me. As I drifted I also became aware that one of the sharks had become interested in me, and was moving with me, not steadily but zig-zagging. It would pass close, then swim off , to turn and pass close again.

Blue shark, Prionace glauca. A female blue shark swimming close to the surface off Southwest Cornwall, UK.

A curious blue checks me out; maybe checking its reflection in my camera dome port?

This was not in a threatening or aggressive manner, but rather one of curiosity. A couple of times it would swim straight towards me, only to stop maybe 18 inches in front of me. Whether it was seeing reflections in the large glass dome port of my camera housing I am not sure. Whatever the reason it provided me with more perfect photo oportunities than I could have hoped for. Thirty minutes passed in what seemed like three, and Charles was recalling us to the RIB. We may have had to wait, but performace at the end far exceeded our expectations.

Fine Art Prints and Wall Art

I have made two of my images from this trip available as fine art prints and wall art. These are available to be purchased in a wide range of media and sizes directly from my Colin Munro Images website. media available include traditional giclée prints, stretched and flat mounted canvas, metal prints (dye directly infused on sheet aluminium) and acrylic, from 8 inches up to 48 inches across. My prints are produced by Bay Photo Labs in Santa Cruz, California. I choose bay Photo Labs for the excellence of their quality, with over 40 years providing printing services to professional photographers, their constant innovation, combining the latest technology and innovation with the finest traditional techniques, and their committment to the highest environmental standards using green technology. You can buy my prints directly here at If you are outside of North America, and would prefer a printer in your region, please contact me directly. I will be adding printers in Europe and S.E. Asia soon.








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The extraordinary life cycle of the lion’s mane jellyfish

Jellyfish, or sea jellies as they are now often called (clearly they are not fish) are amongst the most ancient of multi-organ animals.  Fossils of jellyfish (or scyphozoans, to give them their scientific name) are found only rarely as they contain no hard structures within their bodies, which are 95% water.  However, under the right conditions fossils of soft bodied creatures will form; current fossil evidence suggests they first evolved at least 500 million years ago.

Lion's mane jellyfish, Cyanea capillata, underwater clearly showing tentacles trailing in many directions. Colin Munro Photography

The lion’s mane jellyfish, Cyanea capillata, is the largest known species. The bell of individuals in colder northern waters can reach two metres across.

The lion’s mane jellyfish (Cyanea capillata) common throughout the North Atlantic, epitomises this image of a large, slowly pulsing, gelatinous bell (or medusa) and long trailing tentacles that pack a powerful sting, but this is in fact only one stage of a complex life cycle.  Lion’s mane medusae begin to appear in April or May in the Northern Atlantic, but are quite tiny at that stage.  These jellies are voracious predators and grow rapidly through the summer.  By August the medusae are commonly one third to half a metre across, with trailing tentacles many metres long.  However there is considerable variability;  large specimens have been reported at over two metres across with tentacles up to 37 metres long, though these generally occur within the more northern parts  of their range.  As they grow large in late summer they will often drift, under the influence of wind and tides, in to sheltered bays where they may aggregate in large numbers. This is when sperm is release and egg fertilisation takes place.  In common with most scyphozoans (the taxonomic group to which jellyfish belong) the sexes are separate; lion’s mane jellies are either male or female.  Sperm is released from the mouth of male jellies and drifts in the current, some reaching female jellies, where the eggs are fertilised. Fertilised eggs are stored in the oral tentacles of the female, where thy develop in to tiny planulae larvae. Once fully developed the planulae larvae detach and, after drifting for a short time, settle on the seabed.  Here they metamorphose into a polyp, not dissimilar to tiny sea anemones or coral polyps (both of which are relatives of jellyfish).  These polyps then grow, taking on a layered appearance until they resemble a stack of wavy-edged pancakes.  Each one of these ‘pancake layers’ will then separate from the parent polyp, once again becoming free living and drifting with the currents.  The ‘pancakes’, more properly ephyra larvae, will grow throughout the summer into the giant lion’s mane jellies and the cycle is complete.  With a lifespan on only one year, during which they can grow to be as long (possibly even longer) than blue whale, lion’s mane jellies need to catch and consume considerable amount of prey.  Each trailing tentacle is packed full of vast numbers of stinging cells, known as nematocysts.  When touched these cells fire out a harpoon-like structure which pumps toxins in to the hapless victim (this is what causes the painful sting from jellyfish).  These toxins incapacitate the prey, which is then drawn up towards the mouth of the jellyfish.  A large lion’s mane may have over 1,000 tentacles trailing far behind them.  Many SCUBA divers in Scotland and Scandinavia have experienced the situation where, having completed their dive on a sunken wreck and returned to the buoy line they planned to ascent to the surface, only to look up and see numerous lion’s mane jellies strung out along the line.  As the current sweeps the jellies along so their tentacles catch on the buoy line, leaving the divers with the unpleasant prospect of ascending through thousands of jellyfish tentacles.

A diver warily watches a large lion's mane jellyfish (Cyanea capillata) drift past. Isle of Arran, West Scotland.

A diver warily watches a large lion’s mane jellyfish (Cyanea capillata) drift past. Isle of Arran, West Scotland.

Not every creature lives in fear of lion’s mane jellies however.  Leatherback turtles, the only species of marine turtle that can tolerate the cold waters these jellies inhabit, consume them with relish, apparently oblivious to the stinging tentacles.  Lion’s mane jellies can make up 80-100% of a leatherback’s diet.  When you consider that a full grown leatherback weighs up to 800kg and may consume up to its own weight in jellyfish daily (bear in mind jellyfish are 95% water) then that equates to pretty large numbers of jellyfish being eaten.

As summer wanes and autumn approaches the lion’s mane jellies begin to die.  This provides a feeding bonanza for many scavengers.  On the surface seabirds will peck away at the gelatinous bell, whilst those that sink are often torn to shreds by shore crabs (Carcinus meanus) and velvet swimming crabs (Necora puber).

Dying lion's mane jellyfish (Cyanea capillata) that has sunk to the seabed being eaten by a velvet swimming crab (Necora puber).

Dying lion’s mane jellyfish (Cyanea capillata) that has sunk to the seabed being eaten by a velvet swimming crab (Necora puber).

At the other end of the scale these deadly tentacles can provide refuge to some unlikely creatures.  Juvenile whiting (Gadus melangus) have long been known to swim underneath the bell of lion’s mane jellies, apparently unconcerned by the curtain of tentacles they weave between. In fact they have been observed to rush into the mane of tentacles when startled by predators.  A series of fascinating experiments by the Swedish zoologist Erik Dahl in the late 1950s showed that, compared to other fish species, juvenile whiting were able to adapt their movements such that even when surrounded by tentacles they rarely came in to contact with them.  Also, unlike other fish species, when they did brush against them it seemed to cause them little concern. Biopsies of the tissue of whiting where they had contacted tentacles showed that very few if any stinging nematocysts had fired into the fish’s body; this compared to hundreds per square millimetre for other fish species.  We still don’t understand the mechanism behind this protection. So does the lion’s mane get anything in return for the refuge afforded the young whiting?  Well another creature found on lion’s mane jellies is the tiny planktonic amphipod (a type of crustacean) Hyperia galba. Hyperia is, for the jellies, a rather irritating ectoparasite. It lives on the outside of the jellies’ bell, nibbling away at it.  Now whiting don’t appear to like the taste of lion’s mane jellies, instead they are rather partial to planktonic crustaceans; in particular (you’ve guessed this already) Hyperia galba.   It is these elegant little symbiotic collaborations that make nature so beautiful.

This article was originally published on my photography website blog, but I’ve reproduced it here because it is essentially a marine biology blog.

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Scallop dredging: why is it considered so damaging to reefs?

I first wrote this blog back in 2012.  If moved off-site for several years, but in 2020 I’ve reinstated it, with a few very minor changes.  Lyme bay now has statutory protection from scallop dredging, and all towed bottom fishing gear. However the majority of the UK’s coastal seas, and indeed coastal seas around the World, do not.  Scallop dredging is still conducted around the World: Iceland, Ireland, Faeroes, North America , to name just a few. So I believe this is still a relevant piece in relation to the massive amounts of damage caused to reef, boulder and indeed all seabed habitats. 
Colin Munro April, 2020.

I’ve written this in relation the the Lyme Bay Closed Area (see my earlier blogs about this: Part 1 and Part 2) and the concerns about the impacts of scallop dredging on the nearshore reefs that lead to this statutory closure. There are numerous studies identifying damage on seabed habitats from scallop dredging, and much indeed about the impacts in Lyme Bay in particular. But why exactly is scallop dredging so damaging on reef communities compared to other forms of bottom fishing? There is probably not spelled out as clearly as possible; those familiar with the gear perhaps assuming it is obvious. So I’ve decided to post this article for those who may have heard about scallop dredging being very destructive on sensitive habitats but are maybe rather hazy as to why this is. Much of the following I have actually lifted from a report I wrote for the Devon Wildlife Trust about twenty years ago (An investigation into the effects of scallop dredging in Lyme Bay, 1992) and although there is much that I have had to update, it is depressing how much remains unchanged.

A scallop, Pecten maximus, lying buried in gravel, with only its tentacles visible. Lyme Bay.

A scallop dredge in basically a weighted rectangular bag dragged across the seabed. the upper part of the bag is made from a synthetic fibre stretched mesh; the underside has to withstand constant abrasion as it travels across the seabed. To withstand this abrasion it is composed of heavy interlinked steel rings, each about 8cm diameter. This is the chain belly of the dredge. The mouth of the bag is a letterbox shaped steel frame, which then connects to a towing eye. The individual dredges are then attached to a dredge beam, a heavy steel tube with bobbin wheels at either end. This in turn is connected to a steel wire bridle, and then a towing warp which will normally be deployed from a beam. beams are set either side of the boat (just as in a beam trawler); with this set a typical scallop dredger will tow up to sixteen dredges, eight either side (four to six either side is the norm). Now all this chain, wire and metalwork makes the gear very heavy, so clearly if this is dragged across fragile habitats it’s going to do a lot of damage. One feature not yet mentioned is the tooth bar. Scallops, unlike the otter and beam trawls, are trying to catch relatively static animals (scallops do move, but not that readily) that mostly live half buried in sediment. Scallops will try and dig themselves into the seabed until their flat upper shell is flush and covered with a fine layer of sand or gravel, only the line of fine tentacles around the rim of the shell betrays its presence. Even a heavy chain bellied dredge will simply pass straight over the scallop as it clamps its two valves shut and sits tight. So the scallop has to be, quite literally, dug out of the seabed. To do this scallop dredges are fitted with a tooth bar. This is bolted to the framework at the bottom of the dredge bag mouth, the teeth, about 9-10cm in length, are downward pointing rake through the seabed as the dredges are pulled along. Now of course this tends to lift partially buried stones and small boulders into the dredge as well as scallops. Indeed when they work particularly stony areas the dredges have to be hauled regularly to empty out the stones that have filled up the dredges. If instead they were fishing for bottom dwelling fish (like traditional trawls) then of course the boats simply couldn’t work such areas as the fish caught would end up so badly damaged they couldn’t be sold for anything other than fish paste, but scallops are tough blighters and are encased in a pretty heavy duty shell (check out those ash trays or soap dishes) so can withstand being smacked and clattered about in a bag fill of stones for thirty minutes or so until hauled. Even so, the main reason (apart from being far more environmentally friendly) that diver caught scallops command a much higher price is that they look better; no-one wants to pay top dollar in a plush restaurant for scallops served up in a shell all broken around the edges or looking like it’s been opened using a lump hammer. In fact scallop dredging is known to pretty inefficient. many scallops are missed as the dredges bounce along, many are also fatally damaged as dredge teeth coming down hard smash through the shell leaving them broken on the seabed for scavengers to feed on (see the pictures of broken shells below).
A modification to this design occurred in the late 1960s. Instead of having rigidly fixed teeth, the tooth bar was spring-loaded (the Newhaven dredge). A problem with the fixed tooth design was that if it hit something very hard, like a raised outcrop on rocky ‘hard ground’ it tended to come fast or damage the teeth. By contrast when the spring loaded teeth are hit hard against an immovable object the teeth will pivot backwards against the springs, allowing the dredge to lift over the obstruction. This is sometimes erroneously interpreted as being less damaging to reef habitats since the teeth spring back. When I say hit hard I mean HARD, we’re taking about maybe a ton of ironwork being slammed against a rock at maybe 3-4 knots by a vessel of maybe 200 or more horsepower). For any sponge, soft coral, sea squirt or seafan that happens to be attached to the outcrop in question it’s rather akin to saying it’s okay because the sledge hammer that just pulverised you has a spring-loaded handle. What it did allow though was for scallop dredgers to work areas of low rocky ledges, boulder reefs and low rock outcrops that previously had been off limits due to the risk of snagging or damaging gear. The law of unintended consequences: suddenly reef habitats and their associated life that had been more or less undisturbed for thousands (perhaps millions) of years had massive steel structures being dragged across them. By the very fact that that had been untouched by mechanical disturbance, species with delicate growth forms flourished: large delicate diaphanous feeding apparatus and colonies forming marshmallow soft cushions, eggshell brittle plates and slender fragile branching structures carpet such tide swept but undisturbed reefs; until the passing of a scallop dredger sweeps them away.

A scallop dredger, with five dredges aside, hauling its dredges.

Illustration showing the key parts of a spring-loaded scallop dredge and how it works on the seabed, including how it affects marine life on boulder reefs. Colin Munro Photography

Illustration showing the key parts of a spring-loaded scallop dredge and how it works on the seabed, including how it affects marine life on boulder reefs.

The comparison to loggers clearing virgin rainforest is compelling, and also quite valid. From the available evidence many of the species occurring in such habitats are long lived, the soft coral Alcyonium digitatum (aka dead men’s fingers) is known to live for at least 28 years and with colonies changing little in that time, so its actual lifespan is probably much longer, the pink seafan (Eunicella verrucosa) also appears to have a lifespan of several decades, some axinellid sponges (e.g. Axinella dissimilis) occurring in these habitats also appear to change little over many years study. We are very much in the infancy of our understanding of the ecology of species living in the temperate rocky reef habitats but it appears that they are mostly species well adapted to competing for space and resources in a very stable environment. They are not (or at least unlikely to be) adapted to rapid recolonisation following major physical disturbance. So the likelihood is (borne out by the evidence on the ground) that when these habitats are disturbed these long lived species do not come back any time soon, instead they are replaced by short lived rapid colonisers (the weeds of the reef, if you like). And if disturbance continues, they do not come back at all.

Relatively undisturbed boulder reef, Lyme Bay, rich in branching sponges and large Phallusia tunicates (sea squirts).

A final question that needs to be addressed is ‘why do scallop dredgers work reef areas in the first place?’ Scallops are pretty widely distributed, but their preferred habitat is not rock but sand or gravel where they can hide by partially burying themselves. Scallop fishermen are not unpleasant people (contrary to the views of some conservationists) with a burning desire to destroy the environment. Nor is working over reef areas risk free; there is always the chance that dredges are going to come fast and the vessel being unable to free them. This may result in the boat losing the gear (more than once I have come across old dredges lying abandoned, firmly wedged under a rocky ledge). Worse still, the gear catching on one side will cause the boat to slew sharply and list violently to that side; once seas start pouring over the gunwales the vessel can sink in minutes. This can and does happen (for example, the 12 metre scalloper Guyona that went down in exactly this manner off the Channel Islands in 2008, with all crew plunged in to the water before they had a chance to get out a Mayday or even grab their life jackets, fortunately all were picked up safely). A third consideration is that when dragged across rocky ground the dredges are often bouncing over the rocks and small boulders. Any scallops present will generally be located in the sand or gravel accumulations in hollows between outcrops; dredges will literally bounce over many of them.

An area of ‘worked’ boulder reef in Lyme Bay. Almost all larger and slow growing species have been removed. Broken scallop shells and a live scallop buried in a sediment hollow can be seen.

Empty and broken scallop shells swept in to a pile, possibly due to the raking action of dredges, on a heavily worked area. Lyme Bay.

Empty and broken scallop shells swept in to a pile, possibly due to the raking action of dredges, on a heavily worked area. Lyme Bay.

So apart from being highly damaging to the seabed fauna, scalloping on rocky ‘hard ground is a risky and inefficient business. And yet it happens. The reasons are simply that there are insufficient scallops on the surrounding sandy or gravelly ‘clean ground’ to support the number of vessels. As scallops are a non-quota species, there are no set limits on the numbers that can be landed, so vessels will switch to non-quota species, such as scallops, when quotas for other fished species are exhausted. When scallopers clean out most of the scallops on sandy seabeds, the temptation is then to start working around the edges of the rocky ground, working ever closer. As they work the boulders are rolled away, the ledges are ground down, and so the following year they can work that much further into the reef areas. And so it goes.
This was essentially the point we were at in 2008, when the statutory closed area was established in Lyme Bay, protecting the nearshore reefs. How that has changed things in the four years since will be the subject of another blog.

Related blog: Lyme Bay, what makes it special?
All images and text (C) Colin Munro/Marine Bio-images.



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Marine Environmental Impact Assessment

The relevant legislation for Environmental Impact Assessment (EIA) in the marine environment can be tricky to keep up with.  Within UK waters, licensing is now generally controlled by the Marine Management Organisation (MMO).

A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme. West Scotland. Colin Munro. Marine Bio-images

A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme. West Scotland.

The requirements for Marine licensing and Environmental Impact Assessment are set within the Marine Works (Environmental Impact Assessment) Regulations under Part 4 of the Marine and Coastal Access Act 2009, and the 2011 amendment.  Essentially what this means is that, before a license can be issued for a given development or activity, the MMO will determine whether an EIA is required; this assessment is based on the type, scale, location and potential environmental impacts of the proposal.  There is a three stage process to the license application:

  1. screening
  2. scoping
  3. environmental review and submission

Up to two hours of advice is given free by the MMO during the initial screening process.  During this process the MMO will determine whether an EIA is likely to be required.

If it is determined that an EIA is required, then the scoping process will identify the sensitivities and issues that will need to be addressed in the impact assessment, and the type of information that will need to be included in the Environmental Statement.  The scoping process is likely to require advice from other statutory bodies, such as Natural England (NE), in particular where there is likely to be a requirement for a Habitat Regulation Assessment or where the proposal may potentially impact on European Protected Species.  The Environmental Statement should include all aspects of the EIA, including a detailed description of the development, an assessment of the information required to properly assess the effects of the development and any proposed mitigation or alternative proposals.

Marine Bio-images is able to assist in all aspects the marine EIA and Environmental Statement production. This includes liaising with statutory bodies, guidance on likely impacts, conducting surveys and data collection and Environmental Statement production.

For more information please email Marine Bio-images or telephone us on +44(0) 7926478199+44(0) 7926478199.






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Remote Camera Surveys

Remote camera surveys – drop down video, towed video and combined video and stills drop-down or towed systems – have been a major component of our underwater survey work for over a decade.  Remote camera surveys can often be used to identify and map underwater species and features.  They are much faster and generally less expensive than diver surveys (although in some situations diver surveys are required).  They can also be combined with spot dives: towed or drop camera transects providing rapid, wide coverage then targeted spot dives adding detail.

Marine Bio-images drop stills camera and video system being deployed from a RIB as part of our monitoring of Lamlash Bay no-take zone

Marine Bio-images drop video and stills camera system being deployed from our rigid inflatable boat as part of our monitoring of Lamlash Bay no-take zone

At Marine Bio-images we operate lightweight systems that are ideal for deployment from small vessels.  Our drop camera system has proved very successful for mapping seagrass beds (we have used this at many locations in UK waters, off the Mediterranean coast of Southern Europe and North Africa).  The system can be configured as video only or as a combined video and high resolution stills system. Key advantages are the lightwieght, compact size and modular construction.

Diagram illustrating Marine Bio-images' drop/towed camera system in operation.

Diagram illustrating Marine Bio-images’ drop/towed camera system in operation.

This allows the system to be taken as personal baggage on flights, removing the delay of waiting for freight.  The system is also entirely self-contained and can operate without external power with a fully waterproof surface unit.  This makes it idea for operation from small open vessels such as inflatables and RIBs.

Still from our drop camera system taken during a seagrass (Zostera marina) survey

Still from our drop camera system taken during a seagrass (Zostera marina) survey

Our towed camera sled is ideally suited for extensive surveys over sedimentary seabeds.  Like our drop down system this can be configured with both video and high resolution stills.  This has proved particularly successful in pipeline corridor surveys; we have used it in depths of 80-100 metres in the Persian Gulf and Black Sea as a tool to help map benthic species and biotopes within proposed pipeline corridor routes.

Marine Bio-images' towed video sled being deployed along a pipeline corridor off Iran, Persian Gulf.

Marine Bio-images’ towed video sled being deployed along a pipeline corridor off Iran, Persian Gulf.

If you would like to know more about our remote camera systems, or discuss your survey requirements, please email marine bio-images or call +44 (0)7926478199+44 (0)7926478199.

Marine Bio-images are based in Exeter, Devon, UK.  We are available to undertake marine environmental surveys locally and world-wide; recent contracts have included marine environmental surveys in Devon, Cornwall, Dorset and Hampshire, and further afield in Scotland, Italy, Black Sea Bulgaria, UAE and Libya.


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How to buy bad science.


Lyme Bay Closed Area was a first for British waters.  The very first statutory closed area established for conservation reason, protecting fragile reefs and associated species from the effects of bottom-fishing trawls and scallop dredges.  It was a long process to get there, 16 years of surveys, reports and campaigning.  That it was established is an unqualified success.

Since it was established, annual surveys have been conducted and reports produced by Plymouth University’s Marine Institute describing the phenomenal re-growth that has occurred since the protection was introduced. I was directly involved in these studies, running a specific component (diving surveys 2008-2010).  The study was a DEFRA Science and Research project:

DEFRA Science and Research Projects. Lyme Bay – A Case-study: Measuring the effects of benthic species and assessing potential – MB0101.

The findings reported here suggest that the Closed Area has benefited the marine species living on the rocky reefs to a far greater degree than anyone could have possibly hoped. It seems too good to be true.

What if it is too good to be true?  What if much of the data is not real?

Increasingly concerned about aspects of the study, and after much deliberation, I wrote to the key scientists within Plymouth University’s Marine Biology and Ecology Research Centre and requested that my name as an author on the Lyme Bay study be removed from the final scientific report submitted to DEFRA. This was the first time in 25 years as a marine biologist I have felt it necessary to take such actions.

There are, in my view, three fundamental problems with the study:

  • the study design is such that the comparative areas outside the Closed Area are in no way comparable; they were never likely to support similar species assemblages;
  • the methodology used is highly unlikely to be capable of detecting the type of changes expected within the study timescale, or capable of detecting many of the species claimed to have been detected, indeed it is highly unlikely that some of the species reported as being recorded actually exist in the locations surveyed;
  • the key changes highlighted simply could not have happened; they fly in the face of everything we know about the species and taxonomic groups involved.

I wrote to the key researchers and suggested the report be withdrawn until these points were addressed.  This was rejected.  Aspects of our own study have been incorporated into the final report.  The interpretation of our data is not one I or others working on the diving was involved in, nor one I would concur with.  Our own study was to be published by Natural England as a separate report.  Days before this was due to happen the process was halted.  When querying this I was informed that this was because they were too busy.  More than two years later it has still not been published by Natural England.  It is fair to say that our findings and recommendations do not all concur with those of Plymouth University’s marine biologists.

These issues are troubling. Of greater concern is the opacity of the underlying data on which these findings are based and the apparent lack of interest in both Natural England and DEFRA over very obvious flaws in the study.  This is best illustrated by examples; although this was an imaging based study (species counts through analysis of images collected by remote camera) almost no stills images have been made available, even as part of the study reviews.  Although never made clear, the photographs of species and habitats used in the study reports were not obtained by the camera system employed, nor collected as part of the study and some are clearly not from Lyme Bay.  Attempts to seek confirmation on issues such as the resolution of the camera system employed (which appears to be less than one megapixel) and clarification as to how claimed data extraction could have occurred given turbidity and low camera resolution problems have not been successful.  Comparative data sets between the camera system used by Plymouth University and divers have never been seen nor the results published. Statements made and comparative images depicting the findings of the study, shown on the Plymouth University website research page dedicated to this study are, at best, highly misleading.  Species reported as being recorded by the remote camera system on subtidal (approximately 20-27 metres depth) reef systems in the study area include species normally associated with rockpools and intertidal waters, small species normally requiring microscopic identification never previously recorded in Lyme Bay and small species normally found underneath rocks, yet many common species were not recorded.  It appears that further years funding was awarded to the study without any of these questions being addressed or any raw data ever being seen despite regular meetings with Natural England and DEFRA and interim reports produced.

Why does this matter?

From a scientific viewpoint a unique opportunity was lost.  The significant changes within species assemblages on the reefs within Lyme Bay are very unlikely to have occurred within the first 2-3 years; they will mostly likely occur during the 5-15+ years following cessation of mobile bottom fishing.  If we cannot trust the data collected in the first few years we have no benchmark against which we can measure change.  Currently there is no raw data available to provide this benchmark and even were the raw data made available we cannot be sure what is accurate and what is not.

This was a four year study, costing the best part of half a million pounds. Despite all meetings and interim reporting, it appears that there was a lack of critical analysis.  There is a danger that similar studies may be inclined to reach conclusions preferred by the client rather than one that reflect reality.   A number of marine protected areas (MPAs) have been designated recently in UK waters, with (hopefully) more to come.  These will require monitoring and initial consultations are already taking place.  It is stating the obvious to say that we need accurate and transparent data if we really want to understand the changes that occur in these protected marine habitats.

1. Tread carefully

DEFRA Science and Research Projects. Lyme Bay – A Case-study: Measuring the effects of benthic species and assessing potential – MB0101.

A cobble reef in Lyme Bay, approximately 22 metres depth.  This illustrates typical visibility (~4-5 metres) in the central part of the bay.  Note the survey diver (holding a white monitoring quadrat) only just visible, approximately 4 metres away from the camera. (c) Colin Munro, Marine Bio-images

A cobble reef in Lyme Bay, approximately 22 metres depth. This was one of the diver monitoring stations. This illustrates typical visibility (~4-5 metres) in the central part of the bay. Note the survey diver (holding a white monitoring quadrat) only just visible, approximately 4 metres away from the camera.

For those of us working primarily on the conservation side of marine environmental monitoring and impact assessment, it is important that the work we do, and the data we present, is as robust, evidence-based and open to scrutiny as we expect that of developers, oil and gas industries and fishery industries to be. If not, how can we hold them to account should they fail to meet such standards?  As scientists, it is important that we bear in mind at all times that we are being paid to tell clients what they need to know, and that is not necessarily the same as what they want to hear.  Yet public criticism of the work of other scientists is not an action that should be undertaken lightly, and only after other avenues have been exhausted. One needs to carefully consider both the likely consequences of such actions and one’s own motives for doing so.   For those reasons I have deliberated for over a year before publishing this article.  I suspect I am unlikely to be offered another contract by Natural England in the near future.  That is a pity, but if contracts continue to be administered in this manner it is probably mutually beneficial if I am not.  I should also point out that, before deciding to publish this article, I consulted quite widely with marine biologist colleagues including independent scientists and others working within conservation organisations.

Study of the ecology of Lyme Bay has occupied a fair amount of my professional life. I have been diving and conducting surveys in Lyme Bay since the early 1990s; I ran the first studies investigating the impacts of scallop dredging on the reefs in the Bay and have run or participated in a great many since. So no-one was more pleased than I when statutory protection for the reefs in Lyme Bay was introduced in 2008 through a 60 square nautical mile exclusion zone for mobile bottom fishing.

To determine how well and how quickly the reefs would recover following cessation of disturbance by mobile fishing gear a three year study was commissioned by DEFRA (Department of Environment, Food and Rural Affairs) with the science being overseen by Natural England (NE) Marine Monitoring specialists.  The protection had been introduced due to the concern over (and evidence of) the destruction and decline in the more fragile and slow-growing species that occurred on these reefs, in particular the erect branching sponges, the octocorals Eunicella verrucosa (pink seafans) and Alcyionium digitatum (dead man’s fingers).

Once the statutory protection had been established, it was important to monitor the changes that occurred on the reefs.  There was little doubt that change would occur once such a major disturbance ceased, but how would it happen?  The important questions were how quickly would it occur, which species would re-establish first and how long would it take for species that were typical of undisturbed reefs (the erect sponges, seafans and dead mens’s fingers) to start to recolonise?

Between 2008 and 2011 I collaborated on a DEFRA /Natural England funded study to determine the changes that occurred on the deeper water reef communities within Lyme Bay Closed Area. Specifically I ran a study looking at changes occurring on boulder reef communities lying between 20 and 22 metres depth (chart datum). This work was conducted by a small team of highly experienced marine biologists/divers. The study was a sub-contract, conducted as a discrete, but ideally complimentary, study within the main contract investigating these changes. The main contract had been awarded to the University of Plymouth who were primarily using remote (towed) video (a camera system towed above the seabed, termed the ‘flying array’) to investigate these changes. Our work ran concurrently and was, at the start of the contract, to be published as one final report.

During the course of the study my colleagues and I became increasingly concerned about the reliability of the main towed video study.  So much so that, in late 2011 during the preparation of the final report, we requested our report be published separately as a stand-alone report. We also requested that we conduct our own data analysis rather than providing Plymouth University with our data, to be analysed by them. Our feelings concerning this were so strong that we conducted all analysis and write up on a unpaid basis.  In November 2012, after much deliberation, I wrote to the scientists within Plymouth University’s Marine Biology and Ecology Research Centre who had run the university’s three year study, and requested that my name as an author be removed from the final scientific report submitted to DEFRA. This was the first time in 25 years as a marine biologist I have felt it necessary to take such actions. Our own, separate, report was completed, reviewed, and then, after considerable pressure to modify certain conclusions (which I declined to do) accepted for publication.  It was never published by Natural England or DEFRA.

There were also other discrete components of the over-arching project, in particular a socio-economic study.  My comments here apply only to the benthos study, specifically the ‘flying’ towed video study which formed by far the largest part of the project. I have no knowledge of the socio-economic component or expertise in this area and have no reason to believe it is anything other than excellent.  Nor do I intended these comments as any criticism of Plymouth University’s science in general, which again I have no reason to assume is other than first rate.  I also stress that, before writing this, I wrote several times to the scientists involved in the Flying towed video study, explaining these problems in considerably more detail than below. I asked that any misunderstandings in my interpretation be corrected. After some delay I received a very brief response explaining that I ‘clearly did not like our study‘ and that they could not help me further.

2. Key problems

From Plymouth University website:

As soon as the SI was enforced in 2008 the team undertook the first baseline survey and have monitored the bay annually since then. At first the reefs were slow to respond but in 2010 the results were impressive (see videos from 2008 and 2011 below)

Presenting all the problems of this multi-year study cannot be done concisely, nor can the key problems, without first explaining a little about the ecology of Lyme Bay, the legislation introduced and the study design. However, a snap-shot of the study is presented on Plymouth University’s Marine Biology and Ecology Research Centre’s website, where a page is dedicated to the study. This provides an indication of the sorts of concerns I had. The page is titled Marine Protected Areas: monitoring the Lyme Bay exclusion zone and can be accessed here.

Plymouth University Marine Biology and Ecology Research Centre's Marine Protected Areas web page.

Plymouth University Marine Biology and Ecology Research Centre’s Marine Protected Areas web page.

The page summarises the importance of Lyme Bay, the aims of the study, the methods used and the findings of the three year study. Here is the study description from the web page:

The team developed a non-destructive, cost-effective and time-effective technique for monitoring vast areas of the sea bed in Lyme bay. The technique involves flying a towed HD camera above the seabed to capture video footage of the reef communities that can be analysed back in the laboratory. As soon as the SI was enforced in 2008 the team undertook the first baseline survey and have monitored the bay annually since then. At first the reefs were slow to respond but in 2010 the results were impressive (see videos from 2008 and 2011 below)

(The underlining of the last sentence describing the changes recorded are mine, not from the web page.)

Immediately below this text are two video clips, one entitled ‘Video footage of Lyme Bay reef taken in 2008’ the other ‘Video footage of Lyme Bay reef taken in 2011’. The differences between the two clips are indeed impressive; the 2008 clip (10 seconds) shows a rather barren area of rocky reef with little attached marine life; the 2011 (28 seconds) shows rocky reef supporting a range of larger marine species, the most obvious of which are numbers of large pink seafans (Eunicella verrucosa), a large yellow boring sponge (Cliona celata) and a large ross coral (Pentapora fascialis). Below are two, fairly representative, frame grabs I have taken from each clip, illustrating the differences between them.

Frame grab from video clip entitled 'Video footage of Lyme Bay reef taken in 2008'

Frame grab from video clip entitled ‘Video footage of Lyme Bay reef taken in 2008’


Frame grab from video clip entitled 'Video footage of Lyme Bay reef taken in 2011'
Frame grab from video clip entitled ‘Video footage of Lyme Bay reef taken in 2011’

The differences between the 2008 and 2011 clips are indeed striking, and if this is the change that has occurred on that area of reef between 2008 and 2011 it is quite spectacular. However, what you think you are seeing is not necessarily what you really are seeing. Reading the web page, one might assume that we are looking at the same area of reef at two different points in time. We are not. We are looking at two different reef areas. Nor are we looking at two areas representative of the change that occurred in this three-year time period; the large pink seafans visible in the 2011 clip are all at least 15 years old, most probably between 15 and 30 years old. We know this because of their size and ramification (degree of branching) and from what we already know about pink seafan growth rates from earlier studies conducted in Lyme Bay and elsewhere. Pink seafans grow slowly; estimates put this between one and three centimetres per year (e.g. Munro and Munro, 2003, Sartoretto and Francour, 2012). It is also highly unlikely that the Ross coral (Pentapora fascialis) and yellow boring sponge (Cliona celata) colonies visible in the 2011 frame grab could have grown to such size in three years.

Change at anything approaching the rate implied by the two video clips simply does not happen.  This is way beyond the growth rates for any known gorgonion species. To make a terrestrial comparison, this is akin to the 2008 video showing an area of barren wasteland following a major construction programme, with the 2011 video showing ‘the same’ area populated by 10 metre tall birch trees that have sprung up in the intervening three years. Unfortunately this is simply a rather graphic example of much within presentations given and the technical reports published on the DEFRA website.

The statutory closure of such a large area of seabed for conservation purposes was a first for England. It was high profile and highly contentious. It was also likely to be a trial, a test bed to see how well such areas worked in terms of facilitating regeneration and how quickly it could occur. This was a four year study, costing the best part of half a million pounds, easily the most expensive study conducted on the ecology of the reefs in Lyme Bay and probably costing significantly more than all the other studies in the previous sixteen years combined. It was also the most intensively scrutinised study; overseen by Natural England marine monitoring specialists, where annual interim progress reports were produced and quarterly meetings involving DEFRA, Natural England, Plymouth University and myself (as Marine Bio-images consultancy) were held with presentations on study progress given and questions asked. There are two obvious questions here.  Firstly, how did this happen, and secondly, could something so obviously wrong escape notice? Is it possible that no-one was aware these findings could not possibly be correct?

Fundamental problems

There were, I believe, three fundamental problems with the study.

1. The study design the study design is such that the comparative areas outside the Closed Area are in no way comparable; they were never likely to support similar species assemblages; thus differences between the still-fished and now protected areas could not be attributed to the differences in fishing pressure. Indeed it seems clear that this is not the most significant factor in differences between the treatments.

2. The image resolution of the the towed camera system employed is too low to accurately detect recently settled colonies of the species of interest on the reef, and the sled design exacerbates this problem. If this cannot be done then change and ‘recovery’ cannot be recorded.

3. Key changes highlighted simply could not have happened; they fly in the face of everything we know about the species and taxonomic groups involved, yet there has been no attempt to address this.

All studies have problems. The important thing is that they are identified and addressed. Thus the real issues here are not what the problems were but how they were, or were not dealt with. However before that can be properly discussed a little more detail on the nature of the problems is necessary. I am not going to attempt to describe all issues with the study; rather I will select one problem, image resolution, as the issues with this are simpler to explain in non-technical terms and it is fairly representative of how they were dealt with.  I will then briefly describe some of the study design issues.

Image resolution.

The prime means of data collection was by towed high definition (HD) video camera (as described on the University’s web page, image 2, above). The analysis is summarised in the biodiversity final report (Attrill et al, 2012)

Analysis of the video transects was conducted in two stages (Sheehan et al., 2010). Firstly, species counts were made from each entire video transect for infrequent organisms (all mobile taxa) and conspicuous sessile fauna. Secondly, frame grabs were extracted from the video to quantify the encrusting, sessile species, some abundant, free-living fauna and metrics of infaunal density and bioturbation such as burrow densities.

Thus pretty much all new growth and newly settled colonies’ data were gained from frame grabs from the video footage. However, there is a problem here. Video frame grabs are not a good way to produce stills. The maximum possible resolution of the frame grab stills extracted from the video is less than one megapixel (0.92 megapixels to be precise; the video format used was 720 Progressive scan, i.e. each frame was 1280 x 720 pixels, equalling 921,600 pixels). To put this in to context, this is only a fifth of the resolution of the cheapest smartphone camera one can buy and around a 1/20th of the resolution of a good quality digital SLR. In fact this is lower resolution than any consumer digital stills camera one can buy (or has ever been made; the first commercially produced DSLR, the Kodak DCS 100, released in 1991, had a resolution of 1.3 megapixels).  The system was adapted from one used in the clear and well-lit waters of the Great Barrier Reef where, for mapping corals such systems work quite well. The much darker and more turbid waters of Lyme Bay are a quite different scenario. One must also remember the task was not to map or count the presence large colonies, the aim of the study was recording colonisation and early growth of sponges, seafans, dead men’s fingers soft corals and ross coral bryozoans. These are all long-lived, slow growing species (the first three in particular) thus in the first 2-3 years one is recording colonies that are likely to be only millimetres tall. The problem was actually worse than the camera resolution alone would suggest. The camera system was designed to ‘fly’ above the reef. This again may work well in very clear bright waters; in the relatively turbid conditions such as those that prevail in Lyme Bay; the image resolution is further degraded by the considerable distance between the subject and the camera system, far greater than we would normally consider acceptable when collecting similar data using a high resolution camera. The camera to subject distance is around twice what would normally be considered the maximum one would try to extract such data from a much higher resolution stills camera.

Correlating the actual camera resolution with that required to record settlement and growth of small colonies would appear to be impossible; I have seen no coherent explanation as to how it was achieved. There is a bigger problem however when using such a flying towed camera system in Lyme Bay. Lyme Bay waters are far from gin clear; the seabed here is largely sedimentary with significant levels of suspended particles. It is also prone to strong plankton blooms which can reduce underwater visibility to less than one metre. However, and this is the important point, the level of turbidity is not constant. It changes constantly from hour to hour as tidal streams vary in strength, day to day and week to week as gales pass through and plankton blooms come and go. These changes in turbidity dramatically affect the amount that can be seen (and recorded). This is a problem for anyone working in this environment; the only solution being to avoid really bad conditions and to get close as possible to the seabed and the species of interest, thus reducing the amount of water (and suspended particles) between the viewer and subject. Ideally this distance should be no more than 0.25- 0.3metre (as is the case for diver surveys or most towed camera sleds).

The camera to subject distance of the ‘flying’ towed video used is around a metre or more from the subject (taking into account the angular distance as the camera is not looking straight down) these changes in turbidity will create enormous differences in what can be seen on the seabed. Individual organisms that will be clearly identifiable on some occasions will become completely invisible to the camera following relatively minor changes in turbidity. These changes in what is visible will almost certainly be of far greater magnitude than any actual changes occurring in species abundances. This means that improvements and changes in abundances that are not real will appear to occur. It also means that improvements and increases in abundance that are real may not be recorded and even if they are, there will be no reliable way to separate them from apparent, non-real changes.

Positional accuracy

This is not a resolution issue, but is a further confounding factor for image interpretation. The flying towed video’s position cannot be precisely controlled and is never accurately known.  Towed behind a slow moving boat (0.5kt) pushed by wind and tide, repeat surveys of the same transect will never cover exactly the same area of seabed, often being 10-20 metres off the previous year’s track.  The distribution of rocky reefs and associated life is very patchy in Lyme Bay and varies markedly over distances of only a few metres, thus two parallel track lines 10 metres apart (e.g. the same transect recorded at two sampling intervals) will most likely record quite different numbers of target species without any real change in numbers occurring. This is not a big problem for descriptive surveys, but is a huge problem for time-series monitoring.

Examples of image resolution

The problems associated with image resolution are probably best understood by showing examples. As mentioned earlier, recently settled seafans are extremely small, on average no more than 90mm tall three years after settlement. How difficult this would make recording recently settled seafans is clearly illustrated in the images below.  The image immediately below shows a full frame grab (1280 x 720 pixels) taken from one of the Plymouth Universities video tows (this is a typical image; I extracted several for comparison) reduced slightly in size to fit here. The white rectangle shows the area of 900 x 600 pixels on the full 1280 x 720 pixel image.

A 1280 x 720 (full resolution of the camera) frame grab from Plymouth University's towed video, reduced to 900 x506 pixels for display purposes.  The white box shows the area of 900 x 600 pixels at full resolution.

A 1280 x 720 (full resolution of the camera) frame grab from Plymouth University’s towed video, reduced to 900 x506 pixels for display purposes. The white box shows the area of 900 x 600 pixels at full resolution.

The next image (below) shows a fairly low resolution digital SLR camera image (a 6 megapixel camera; modern equivalents are 12-24 megapixel). Again, for the purposes of direct comparison, the white rectangle here also shows the area covered by 900 x 600 pixels on the full resolution image.

A still from an older, 6 megapixel, Digital SLR camera, reduced to 900 x 602 pixels for display purposes. The white box shows the area of 900 x 600 pixels at full resolution.  Note also the differences in contrast, colour saturation and image sharpness with the previous image.

A still from an older, 6 megapixel, Digital SLR camera, reduced to 900 x 602 pixels for display purposes. The white box shows the area of 900 x 600 pixels at full resolution. Note also the differences in contrast, colour saturation and image sharpness with the previous image.

The next image shows shows the 900 x 600 (white rectangle) area from towed video sled image, displayed at full resolution.  As can be seen this is fine for recording larger conspicuous species such as common starfish (Asterias rubens), large seafan and deadmen’s fingers colonies.

A 900 x 600 crop from the above towed video still (white box) displayed at 100%.  This illustrates typical resolution obtained from such a towed video system camera.

A 900 x 600 crop from the above towed video still (white box) displayed at 100%. This illustrates typical resolution obtained from such a towed video system camera.

The next image is the 900 x 600 crop (white rectangle) taken from the 6 megapixel digital SLR image, also displayed at 100% so allowing direct comparison. Note the recently settled pink seafan near the bottom right of the image. This is likely to be that year or the previous year’s recruitment; I estimate it is 10-20mm tall. It would therefore seem unlikely that many such recently settled seafans would be recorded using the towed camera system, let alone reliable counts made.

900 x 600 pixel crop from the 6 megapixel DSLR image from Lyme Bay, displayed at full resolution.  Note the recently settled (1st year) pink seafan in the bottom right of the image.

900 x 600 pixel crop from the 6 megapixel DSLR image from Lyme Bay, displayed at full resolution. Note the recently settled (1st year) pink seafan in the bottom right of the image.

What happened when people became aware of this problem.

The camera resolution was not immediately obvious.  It was not mentioned in the paper describing the system, not in any of the technical reports.  No extracted stills from the towed video were ever shown at any of the quarterly meetings, nor were any used in any of the interim or final reports.  In fact images from other studies (including our own) were used to illustrate their reports, including some images that clearly did not originate in Lyme Bay.  I estimate that around 1000 or more stills were analysed.  This leaves one asking; given so much was made of the capabilities of this system why were none of the images captured by it ever shown?

I personally queried DEFRA, Natural England and the lead author of Plymouth University’s study, pointing out the resolution of the camera.  DEFRA made no direct response; Natural England’s response was that they didn’t know whether this was true (about the camera resolution).  Given that the study was totally dependent on the resolution of the images being good enough to reliably detect new growth amongst key species then Natural England and DEFRA’s indifference to this seems more than a little surprising, particularly so given that funding for the study was to be extended by another year shortly after. It would have taken around 30 seconds to confirm the resolution on Google, or they could simply have asked Plymouth’s team. I emailed the lead author at Plymouth University, including comparative images and my interpretation of the maximum resolution of the still’s extracted from the towed video, asking how they achieved detection of newly settled colonies. This was forwarded to more junior personnel within the team, and I received a reply that neither confirmed or denied my calculation of the camera’s resolution; instead I was informed that special ‘professional’ software was used. Unfortunately this software was not named, nor what it did explained. No examples of improved or enhanced stills were provided.  I am aware of no software in existence capable of enhancing electronic images to anything like the degree that would be necessary. To the best of my knowledge there has never been any clarification of the camera’s resolution, nor have Natural England or DEFRA asked to see any stills images .

How does the data stack up?

So how does the above assessment of the camera’s resolution square with the actual data recorded?  Evaluating the collected data is not straightforward; no raw data has been provided (fundamental rule of any monitoring study, you must provide raw data; only by comparing raw data can we understand what is going on when we find anomalies, without raw data apparent change can simply be subtle changes in analysis or interpretation when different workers are involved).  Reading the final reports we find that the frame grabs from the towed video produce some inexplicable identifications; e.g. rare encrusting sponges never before confirmed in Lyme Bay before and normally only identified after microscopic examination by specialists; small spider crabs that are normally extremely well camouflaged and difficult to identify at much higher resolutions; small crab species that normally live hidden under rocks and fish and starfish species that are normally found in intertidal rockpools rather 20-30 metre deep reefs. Many small, well-hidden species were identified by frame grabs that were never recorded by our dive team (a table listing a few of the anomalous records is provide at the end of this article.)  It is well beyond the bounds of probability that these species really were recorded during the study by flying towed video

How did the video data compare with that collected by our diver monitoring study?

Direct comparison is not possible.  Our study design and survey stations were different.  However, we were commissioned to undertake a a week’s diving survey work on small sections of a subset of of the flying towed video transects.  The purpose of this was to compare the species counts by divers with that obtained by towed video in order to calibrate the video.  So what were the findings of this comparison?  That is a good question.  We provided our data, and the comparison was never seen; the data simply disappeared.  When I queried this in meetings I received no answer.

How did the key, long-lived, slow growing species data look?

This is probably the most important consideration as this was what the study was all about.  If the flying towed video was accurately recording change then what we would expect to see is that the numbers of larger sponges, dead man’s fingers and seafans would remain largely unchanged (given their slow growth and longevity) in both the newly protected area and also in the older established voluntary protected areas lying within it.  We might possibly start to detect increasing numbers of small, recently settled  colonies as colonisation occurred on previously disturbed areas.  However, if the system was simply recording spatial heterogeneity in mature colony distribution (resulting from the fact the camera transects were never in exactly the same place from year to year) and variations in the number of large colonies detected (due to the system’s limited resolution and variable underwater visibility) then we might expect to detect very few small colonies and unexplained large random variations in the numbers of large, mature colonies recorded.  So what was found?

Interpreting the data is a little tricky, as no raw numbers have been provided. However, if one looks at the processed data provided in the final reports owe then essentially we find large, random variations in the numbers of these key species.  This include apparent dramatic increases and crashes between years in species we would expect to be extremely stable (e.g. dead man’s fingers in the longer-established protected areas) and dramatic fluctuations in the numbers of large (i.e. more than 10 years old) seafans within the protected areas.  How are these crashes and fluctuations explained? Well mostly they are simply not.  Increases that support the notion of rapid and dramatic improvements are described and identified as possible signs of recovery; population crashes (sometime larger in magnitude) are generally not explained.  For example, looking at the Alcyonium digitatum (dead man’s fingers) relative abundance data the most striking change is an apparent crash in numbers within the longer, established voluntary protected areas (2009-2010) with a simultaneous large increase in numbers within the new protected area. This was followed in 2010-2011 by the opposite, a rise in numbers within the older voluntary protected areas coupled with a fall in numbers in the newly protected area.  These findings are, at best, highly unlikely (especially when one considers that the longer established voluntary areas lie scattered within the newly protected area, see diagram below) and should prompt closer inspection of the data, particularly given that older voluntary areas all lie within the newly protected area, evenly scattered across it.

Diagram showing the location of the three different 'treatments', 1. the New Statutory Closure, 2. the Pre-existing Voluntary Closures and 3. the still-fished Nearby Sites.

Diagram showing the location of the three different ‘treatments’, 1. the New Statutory Closure, 2. the Pre-existing Voluntary Closures and 3. the still-fished Nearby Sites.

If we turn to pink sea fans we see that the most pronounced change in numbers were in the pre-existing voluntary closures where between 2009 and 2009 the relative abundance dropped by about 2/3; at the same time the relative abundance appeared to be rising within the newly protected area. This was followed by an even larger change, a four-fold increase in relative abundance between 2009 and 2010 within the older voluntary protected areas.  At this stage someone should be asking serious questions about the data.  If we look at size class data it appears that the number of large seafans (<18cm or roughly <10 years old) increased by about 1/3 between 2008-2009, then decreased by about 1/3 between 2010-2011 in the newly protected area.   It would also appear that only tiny numbers of small seafans have been recorded (again, as we would expect given the resolution of the system); Frequency graphs are produced at very small scale so difficult to read accurately, but it appears that less than 20 seafans smaller than 60mm tall was recorded in every treatment in every year; with less than 5 recorded in most years in all treatments. Given that 60mm tall seafans are likely to be around 2-3 years old, this is an extremely small data-set and, even if accurate, little could be read in to it in terms of interpreting the changes that are occurring within the Bay.

Study design

I will briefly touch on the study design. The study was designed to test the following hypothesis.

Over time, species assemblages within sites in the new statutory closure but outside the pre-existing voluntary closures would change to more closely resemble those in the pre-existing voluntary closures but similar change would not occur within nearby sites where fishing by towed bottom gear was still permitted.

This means that the rocky seabed habitats within the new protected area would start out resembling the areas just outside, then gradually change to resemble the rocky seabed areas within the longer established voluntary protected areas.  This could not happen. The  seabed habitats and environmental immediately outside of the new statutory closure were very different from that within the new statutory closure.  That is the very reason that the boundary to the closure was originally set.  The light levels, current regimes, turbidity, amount of rocky habitat, structure of rocky habitats, amount of river water flowing in and the species present were all very different.  In short the areas outside of the protected area did not support the same species assemblages as the reef area within the protected area and never would irrespective of whether they were fished or not. As an example, the ‘still-fished’ control area to the west of the protected area has much weaker tides, has the River Exe and Otter flowing in (no major rivers flow in within the protected area) the water is markedly more turbid, the seabed much more sedimentary and composed of finer material, the rocks present are mostly low-lying sandstone as opposed the harder and more rugged-relief limestone within the protected area.  There are no seabed areas within the still-fished area to the west that remotely resemble the rugged and extensive reefs within the voluntary protected areas.  As a result of these differences the still-fished area to the west support very few sponges and dead-men’s fingers and almost no seafans.  This was explained to all,  in detail, several times at meetings.  I went as far as preparing Powerpoint presentations with graphics depicting current regimes, river inflows and seabed sedimentology, with supporting photographs of reefs from different locations.  Not a single question was asked or comment made at the end of the presentation.

What did the two 2008-2010 monitoring studies find?

As expected, our study found that there were possible, very early, indicators of recovery but that only future monitoring would identify whether these were real. We also (as predicted) found that the areas outside of the protected areas were fundamentally different from protected area itself  in all years, i.e. they started out very different and remained very  different thus these differences could not be attributed to the cessation of trawling and scallop dredging within the protected area (note, this is different from saying that changes within protected were not due to cessation of trawling and dredging, some almost certainly were, it is simply pointing out the irrelevance of making comparisons with non-comparable areas) .  The flying towed video study reported more positive indications of recovery.  Their frequency graphs for most key species indicated that the ‘still-fished’ controls were very different from the protected areas, in all years, however this was not noted in the report text and comparisons were made between both treatments that would suggest these were essentially similar treatments apart from one being fished and one not.  In our report we noted that the still-fished were not similar to the protected area and therefore could not be considered comparative controls.  I was repeatedly asked to remove this from the executive summary of our report. I declined as I considered that to do otherwise would fundamentally misrepresent the findings of the study.

Is it possible that these problems were simply not noticed?

For that to be possible we would have to accept that NE and DEFRA never noticed that, for three years they had seen no data and no extracted frame grabs from an imaging-based study.  One would also have to accept that, when NE and DEFRA were shown video clips of ‘new growth’ , growth that NE specialists recognised was at least a decade old, they assumed this was not somehow not relevant.  If one accepts that these lapses in critical analysis then I will simply state that all of these problems were explained clearly, verbally and in writing, and even in Powerpoint presentations to all relevant personnel.  I have little doubt that everyone was under great pressure from above and that may, in part, explain the reluctance to question the work in more detail.

Why did it happen?

This may be the most important question.  A number of factors combined here.  Firstly there was a lack of experience of working in these sort of conditions coupled with the use of equipment designed for a different purpose and quite different conditions. Secondly, there was an almost complete focus on statistics and statistical design, to the point that basic ecology was completely ignored.  Thirdly, the most obvious questions were never asked and key data, indeed almost all data, was withheld.  There was also very pronounced pressure for the studies to produce the ‘right’ answer.  Recall that there was no interest in whether the towed video camera system was even capable of detecting colonisation.  The findings of our own study differed significantly from that of Plymouth University and it was decided that this needed to be resolved before publication.  Now one might think that looking at both sets of data might be useful here; I proposed it several times however the data was never provided.  Instead it decided that our statistical analysis would be reviewed.  At the start of the meeting I was informed that Plymouth University’s report had already been approved and so was not open to discussion.  Thus in order to resolve the differences between the two studies review and changes to one study (ours) was permitted.

 Why does any of this matter?

Apart from the obvious,  that we should always aim for the best science, why does this matter?  One could argue that the changes described are almost certainly going to happen anyway, not in the time scale of this study and maybe not as neatly as the study suggests, but in 10 to 15 years it is perfectly possible that areas of recently protected reef will look as described in this study.  So what’s the harm?

From a scientific viewpoint a unique opportunity was lost.  The significant changes did not occur in the first 2-3 years; they will mostly likely occur during the 5-15+ years following cessation of mobile bottom fishing.  We do not know how exactly how the reefs will look then; nor do we have a benchmark against which we can measure change.  There is no raw data available to provide this benchmark and even were the raw data made available we cannot be sure what is accurate and what is not.

Talking in generalities for a moment, I think most scientists and environmentalists would agree that a client disinclined to question study findings provided the findings conform to a preferred agenda, and a contractor inclined to mold findings to suit the preferred agenda, is a toxic mix that is lethal to good science and to the development of policy that actually changes conditions in the real World.  Suppose for a moment that, once the closed area had been established, the eventuality of positive change  in the benthic environment of Lyme Bay was not quite the certainty that we believe it to be.  Would that have changed the findings of this study?  Given that the findings appear to be decoupled from what was actually happening on the protected reefs then the answer is ‘probably not’.  Suppose the client was a developer rather than a conservation agency, and that their preferred findings were for their development to have minimal impact and require minimal mitigation measures. This could be contentious, highly politicised issues (as was Lyme Bay Closed Area) for example dredging a shipping channel and removing live maerl beds in the process. If ever the central aim becomes to please the client by providing the ‘right’ answers rather than accurate answers then we are on a very slippery slope indeed.

It also matters in as much as this is being pushed, all flaws airbrushed out of the  presented material, as a shining example of how to monitor Marine Protected Areas in conferences, DEFRA reports and published articles.

Specifically addressing the Lyme Bay Closed Area, this was an experiment on a grand scale, the like of which we have not seen in UK waters before. It was a phenomenal opportunity to record how species colonise disturbed areas of seabed once this disturbance ceases. Data like this simply does not exist. Lyme Bay was in many ways the ideal candidate; it was easily accessible, all within diving depths, and had been well studied for nearly two decades so we already knew a great deal about the species that existed there, the habitats and locations where they were found and which ones had declined in number. Relatively rare within reef habitats, much of it was fairly level seabed, so the establishment of fixed monitoring stations was far easier than would be the case in many other areas. Unfortunately this opportunity has been lost.

There is also the question of what else has been missed. As mentioned earlier, we were commissioned to undertake a series of dives on a subset of Plymouth University’s towed video transect stations in order to provide comparative data (never seen). This was simply a snap-shot, one off visit where we looked at short sections of a few of the flying towed video transects.  However, at some of these stations we found significant damage, tracks several metres wide swept bare of life and almost certainly due to recent mobile fishing gear operating there. These were photographed and the images presented at meetings with DEFRA, NE, Plymouth University.  Perhaps surprisingly no-one asked why this was not being picked up by the towed video system. This would seem to be a fairly important question, as if it is not picking up fairly major signs of habitat degradation then how can it be detecting more subtle signs of improvement.

It is possible that Lyme Bay Closed Area monitoring was an anomaly, possibly due to the high profile and the level of political expectation as regards the outcome. The evidence suggests otherwise. The last Natural England contract I was invited to tender for, some 18 months back, was an extremely challenging survey requiring 3 dimensional mapping, counting and monitoring of very small animals (e.g. individual coral polyps only millimetres in diameter) living within submerged sea caves along an exposed stretch of coast where underwater visibility was normally very low. Moreover, the study was to be conducted in mid-winter, when storms were most frequent, underwater visibility at its lowest and darkness falling at 4 or 5pm. After carefully reading the tender and calling NE staff to discuss this with them I emailed informing them I would not be tendering and why. My reasons were that, in order to do the job properly (by that I mean to have any chance of generating data that was remotely meaningful) was simply far too dangerous at the time of year they required the fieldwork to be conducted and I would not consider risking the lives of survey team members in this way. Secondly, the weighting given to evaluation if different aspects of each bid was helpfully provided: 50% of overall weighting was given to cost; 5% was given to the expertise and experience of the team with regard to the work to be undertaken.  To put this in as polite terms as possible, this is madness. The message this sends out is pretty clear; you can have no experience whatsoever in this field, nor any expertise within the team relevant to the fieldwork, but provided you are cheap enough the contract is yours. This was hammered home further by a maximum of 15% weighting being given to the estimation of the survey actually being successful, so a starting assumption of ‘little chance of success’ even within the very loose adopted definitions of ‘successful outcomes’ is no barrier to being a successful bidder.  This is not only a pointless squandering of money, producing meaningless reports solely to meet targets, it is also dangerous and may lead to fatalities if this approach continues.

Perhaps the most important reason it matters is that a number of marine protected areas (MPAs) have been designated recently in UK waters, with (hopefully) more to come.  These will require monitoring and initial consultations are already taking place.  The worst possible scenario is that we continue along the path of devaluing expertise and placing ever more weight on low cost.  This is actually worse than doing nothing at all, as it inevitably generates bad data, and bad data we think is accurate is worse than knowing we have no data. This could also be a wonderful opportunity to not only monitor the condition of these MPAs; systems could be established whereby comparative data collected from locations around the UK could provide information about changes on a larger scale.  I am aware that there are many dedicated biologists within Natural England who would love to see contract survey and monitoring work conducted to the highest standard and generating real, useful and pertinent data.  I am also aware that front line staff are under enormous pressure from above and that many of these decisions are no longer within their power to make.

An alternative approach

A network of permanently marked fixed monitoring stations could have been established across the newly protected site and monitored annually for a fraction of the cost of the towed video study. High quality photographs from precisely the same position can be taken year after year. These fixed stations can also be used as structures from which to ‘hang’ physical data loggers (temperature, ambient light etc.) allowing correlation of change in the physical environment with biological change.

 It is true that data from permanently fixed stations are not amenable to testing by the most powerful statistical tests, but for working in the marine environment they have one overwhelming advantage, year on year data is directly comparable. Rocky seabeds in UK waters are simply too heterogeneous, in terms of spatial distribution of species, for random sampling. Moreover this spatial variability is evident over distances of tenths of a metres or less. We simply do not have the technology yet to relocate stations to this level of accuracy within realistic budgets unless we physically mark them. We actually do have a small number of marked stations within Lyme Bay closed area (created and surveyed for our diver-based boulder reef study). These are now abandoned and the data gathering dust. These stations could, with a little effort, be relocated regularly and comparative data collected in five, ten and twenty years time. The principle could also be expanded over a much wider geographical area. With a little imagination in the appropriate bodies a network of low-cost subtidal monitoring stations could be established. These could not only be used to collect data on the condition of marine protected areas but could also be collecting data time-series data that would inform us of local and regional changes in species and habitats.

Table 1. Some of the more unlikely species identified from video frame grabs

Species Taxonomic group Comments Recorded by
Grantia compressa Sponge A small flattened purse sponge generally found attached to other species or under overhangs Video frame grab
Sycon ciliatum Sponge A small purse sponge up to 50mm tall generally attached to other species Video frame grab
Actinothoe sphyrodeta Anthozoan A small anemone found on rock faces identified by dark patches at the base of tentacles Video frame grab
Ebalia granulosa Crustacean A small crab (around 10mm across) found on gravel seabeds Video frame grab
Porcellana platycheles Crustacean A small flattened crab (around 15mm across) generally found on rocky shores underneath boulders Video frame grab
Asterina gibbosa Echinoderm A small starfish (up to 50mm across) normally found in rock pools and shallow rock – never found on any dive surveys in Lyme Bay we are aware of Video frame grab
Ocnus planci Echinoderm A rare sea cucumber – small (up to 80mm) difficult to identify without detailed inspection Video frame grab
Aplidium elegans (?) Tunicate Assume this is meant to be Sidnyum elegans – a small (about 50mm) red colonial tunicate requiring detailed inspection to identify Video frame grab
Diademnum coriaceum Tunicate An encrusting colonial sea squirt – very difficult to identify from appearance alone (not previously known in Lyme Bay) Video frame grab
Lissoclinum perforatum Tunicate An encrusting colonial sea squirt – tricky to identify positively (similar to other Didemnid sea squirts) Video frame grab
Molgula manhattensis Tunicate A small (up to 30mm) solitary sea squirt often encrusted with sand and shells- very tricky to spot and identify with certainty Video frame grab
Lipophrys pholis Fish Shanny – a fish normally found in intertidal rockpools Video frame grab


Munro C.D., Munro L. 2003. Eunicella verrucosa: investigating growth and reproduction from a population ecology perspective. PHMS Newsletter 13: 29-31.

Sartoretto S. and Francour P. 2012. Bathymetric distribution and growth rates of Eunicella verrucosa (Cnidaria: Gorgoniidae) populationsalong the Marseilles coast (France). Scientia Marina, vol. 76(2): 349-355.

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Benthic survey versus monitoring, a comparison of aims and methodologies

The terms survey and monitoring are often used interchangeably when collecting data on the marine environment. More worryingly there is sometimes a blurring of the differences between the aims and methods required for descriptive surveys and data collection as part of a time-series monitoring programme.

In general, the approach to benthic survey differs from that taken to monitoring in a couple of important aspects. In descriptive survey, more emphasis is put on identifying what organisms and habitats are present rather than precisely how many of them are there. Conversely, monitoring often does not give full descriptions of sites, it may only look at a sub-set of organisms, but requires greater precision in recording the number of individuals or colonies or colonies present, or more precise measurement of the condition of the organisms present. The reasons are fairly obvious; with monitoring you are concerned about recording change in numbers, so your numbers need to be pretty accurate and you need to be pretty confident about the identities of what you are recording. This means that we have to be fairly careful when designing or selecting the format in which data is collected. For example, the UK’s Joint Nature Conservation Committee’s Marine Nature Conservation Review’s recording forms are based of the SACFOR Abundance Scales (apologies for all the acronyms). These SACFOR* scales are widely used for marine survey work around the UK today. They have the advantage that they are well known, widely accepted and can be applied to all marine habitats and all marine marcoflora and fauna. They are very useful for descriptive surveys; they give a good feel for the composition of species assemblages and with experience broad comparisons can be made between different sites. Unfortunately they are also sometimes used for time-series monitoring, something for which they are pretty useless. As they use a logarithmic scale each abundance category is an order of magnitude up or down from the next, thus you need in the region of a ten-fold change in abundance to register as change on the scale. For most species change is abundance will be very obvious long before a ten-fold change in abundance occurs, thus recording only SACFOR abundance values will mean that quite large impacts (e.g. a 50% reduction in a key species abundance, or the doubling in numbers of an invasive species) may go un-noticed. This scenario happens all to easily, especially where one organisation is contracted to undertake repeat monitoring and compare data with that collected by a different organisation (something I have often had to do) or when different staff undertake monitoring on different years.

A corollary of this is that you also need a good idea of what your margin of error is and what are your sources of error. These sources of error are particularly important to know if they are variable or intermittent. Again the reasons are fairly self-evident. If you have sources of error that affect the data they need to be identified and recorded if erroneous records of change or false conclusions are to be avoided. A good example of this in diver or remote camera recording is underwater visibility. The waters off Southern England are prone to strong plankton blooms during the summer months. These blooms vary in timing and duration. Sometimes they arrive in late April and linger for months; sometimes the do not arrive until mid-May and disappear after a few weeks. They also vary in intensity and distribution. When the plankton is thick visibility can be 0.5 of a metre or less, often the plankton occurs in patches, so that visibility is less than a metre at one location but several metres only a few miles away. This patchiness can vary from day to day and from hour to hour as the tides sweep in water from upstream locations. Similarly storms and string tides can lift sediment in to the water column, similarly reducing near seabed visibility to a fraction of what it was days before. This can make visual comparisons between different points in time extra-ordinarily difficult. This is particularly true of comparisons between photographs taken as part of a time series. When the visibility is reduced through plankton blooms, strong tides or following poor weather this can dramatically reduce the number of individuals counted within a fixed area when no change in numbers has actually occurred. Thus it is vitally important for monitoring studies that the raw data (i.e. photographs or log sheets with condition records) and not simply numerical count data is available to those tasked with interpretation of the data.

Because we need greater precision and numerical accuracy for monitoring there are differences in the appropriate methods. Video, either diver operated or remote, can be really useful for broad-scale survey as it collects a lot of spatial data quickly and cheaply and can be very useful for identifying habitats and some conspicuous species or flora/fauna types (e.g. for identifying biotopes as hydroid/bryozoan turf or red algal turf or kelp forest). It can also useful for counting larger, conspicuous and widely spaced individuals (e.g. estimating densities of mature seafan colonies), though stills photography sampling or mosaics are normally a much a better option. Video is rarely suitable for monitoring smaller faunal turf species (such as sponges, soft corals, anemones, hydroids, tunicates etc.) as, although quality is steadily improving, video still does not have the image resolution for accurate identification and accurate counts. This is not to say it will never see some of them; rather it may possibly see some but exactly how many in relation to how many are actually there will vary considerably so the data generated will be unreliable.

Suspended sediment and plankton will dramaticallly reduce visibility. Sediment settling out after a storm may also temporarily coat rock surfaces making smaller species difficult to see.

Suspended sediment and plankton will dramaticallly reduce visibility. Sediment settling out after a storm may also temporarily coat rock surfaces making smaller species difficult to see.


A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme. West Scotland. Colin Munro. Marine Bio-images

A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme. West Scotland. Visibility here will vary between less than 2m to more than 10m (as in this picture).



Species for monitoring.

For any given study we will select target species for monitoring based on a criteria such as known or expected sensitivity to the variable (e.g benthic filter feeding organisms may have a know or presumed sensitivity to increased suspended particulates and sedimentation rates due to nearby dredging or spoil dumping). However, there are some fundamental criteria that apply to nearly all monitoring studies.

  1. We must be able to find the species using the selected methodology (e.g. if using remote towed or drop cameras, species that tend to live of hide in crevices or under rock overhangs are generally unsuitable because they are only likely to be recorded by chance and so numbers are likely to be unreliable)
  2. We must be able to accurately identify the selected species using the selected methodology;
  3. The species must be evenly distributed across the habitats in question (e.g rare species confined to a small area within the total study area are unlikely to yield useful data, especially where a study involves treatment and control areas).
  4. The species must occur in numbers sufficient to generate statistically usable data;
  5. The methodology employed must be able to accurately count the selected species otherwise error or bias will occur.
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Lyme Bay, Lane’s Ground Reef: sponge species recovery and opportunities lost

As part of a small study looking in to gear impacts on seabed species, we recently conducted a few dives attempting to record HD video of bottom trawls and crab pots working on the seabed. Unfortunately we picked a period of one of the thickest plankton blooms this year (either very late or very early for thick plankton, but this has been rather a strange summer, weather-wise). Hanging on to a moving trawl net holding a bulking camera in 0-2 metres visibility certainly keeps you alert! However, it’s not really conducive to great images, so we’ll be trying again once the waters clear.

One very useful aspect of this however was a checkout dive on Lane’s Ground Reef. As described in previous blogs (Lyme Bay, what makes it special, Lyme Bay Closed Area Pts 1 and 2)., Lane’s Ground Reef previously supported rich and diverse sponge assemblages, which largely disappeared as scallop dredging intensified within Lyme Bay. Co-incidentally we dived on an area of lane’s Ground Reef that I had surveyed 17 years ago, before scallop dredgers and other mobile fishing gear had significantly degraded the reef, and again in 2007, immediately prior to the implementation of statutory protection from bottom fishing mobile fishing gear within the Lyme Bay Closed Area (within which Lane’s Ground Reef lies). In 2007 the condition of the reef appeared very poor. Although not a detailed survey (as was the 1995 study) the visual appearance was of far fewer sponge species and much lower densities of sponges and ascidians (sea squirts), with many other attached species appearing to have dramatically declined. (See blog: Scallop dredging: why is it so damaging to reefs for more info on effects)

Lane's Ground Reef, a circalittoral boulder reef rich in sponges and ascidians, within Lyme Bay Closed Area, Lyme Bay, southwest England. Colin Munro Photography

Lane’s Ground Reef, an undisturbed patch of reef rich in sponges and ascidians.

Our three year monitoring, funded by Natural England as part of the study to look at whether the reef habitats recovered following cessation of scallop dredging, centred around Lane’s Ground Reef (Report here as PDF). One reason being it was one of the hardest hit of all vulnerable reefs within Lyme Bay but was also one where the basic reef structure (small boulders on mixed sand and gravel) remained intact, thus the potential for recovery was there. Another reason was that Lane’s Ground Reef, of all the reefs in Lyme Bay, was the one reef highlighted as previously supporting particularly rich sponges assemblages and that these rich sponge assemblages were, probably more than any other feature, what made the reefs of such high conservation importance, with many unusual or rare species and others not yet fully identified. We knew that sponges, being soft-bodied filter feeding organisms, were particularly vulnerable to physical impact (i.e. the passing of a scallop dredge would completely destroy them). The available evidence from other monitoring studies (e.g. Lundy Island Marine Nature Reserve and Skomer Marine Nature Reserve) also indicated that many of these sponge species reproduced and grew very slowly indeed (some colonies being decades old and with little or no recruitment over many years). Thus recording and measuring recovery in the sponge assemblages within Lane’s Ground Reef would seem one of the top priorities for assessing recovery of the reefs species assemblages in Lyme Bay Closed Area after scallop dredging and bottom trawling has stopped. It would also provide invaluable information of rates of recruitment and growth of these species during recovery following prolonged disturbance. At the end of our three years of monitoring (summer 2010) we believed we were just starting to detect such a recovery in sponges on Lane’s Ground. The change was small, and not (at least then) statistically significant, but given the expected slow recovery of sponges this was hardly surprising. That we might, after three year just be starting to see a recovery was therefore extremely encouraging. Unfortunately Natural England decided not to fund further years work. In my view this was a serious error of judgement; in essence they have paid for all the set up and groundwork, then said ‘Ok, let’s stop there and not bother getting the meaningful data’. The closure of 60 square nautical miles of Lyme Bay to mobile bottom fishing gear for conservation purposes is unprecedented in U.K. waters and provided a unique opportunity to study the changes that occurred following the removal of these impacts. The uniqueness of this opportunity also lay in the fact that so there was so much existing diver-collected survey and monitoring data for Lane’s Ground; including accurately positioned data going back to the early 1990s. Thus, probably more than just about anywhere else one could think of in Southwest British waters, we knew what they area had been like prior to intensive scallop dredge and trawling; not just anecdotal diver observations but detailed survey reports and quantitative species counts by experienced marine biologists.

Three years monitoring would, at best, only lay the foundations for detecting recovery by providing a baseline against which recovery of the most impacted, slower growing species could be measured. Real change is far more likely to be observed over a 5-10 year period. We hope to start limited monitoring again in 2013, on a self-funded basis, because we believe that understanding the changes that occur on these boulder reefs is crucial to our understanding of how the reef species assemblages are recovering. As the prime reason that for establishing the Closed Area was to protect these reef assemblages and allow their recovery, and was also the driver behind a 16 year campaign (notably by the Devon wildlife Trust) to achieve this, then it seems to me a little absurd not to measure whether this is actually achieving the desired effect. Currently there is no study running that is capable of detecting these subtle changes in species such as sponges, ascidian and other small turf-forming species that create the richness and diversity of species for which these reefs were previously known.

I bring this up now because, during our brief dives on Lane’s Ground last week, our observations did suggest that quite significant recovery, especially within the sponge assemblages, was indeed now occurring. Unfortunately these dives were not on any of our 2008-2010 monitoring stations as this was not practical, so direct comparison is not possible.

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