Towed underwater camera sled system for sale

Marine Bio-images towed underwater camera sled for sale.

Marine Bio-images towed underwater camera sled being deployed from the stern of a survey vessel in Persian Gulf.

Marine Bio-images towed underwater camera sled being deployed from the stern of a survey vessel in Persian Gulf.

The camera sled

The camera sled in constructed out of tubular stainless steel and comes with 150 metres of ROV armoured umbilical cable and removable weights.  It has been successfully deployed to 90 metres depth (limited by umbilical length) for pipeline corridor surveys in the Persian Gulf and the Black Sea.  It is currently configured to use independent, battery-powered lighting.  No camera is currently assigned as this is job dependent.

Marine Bio-images underwater camera sled in storage.

Camera sled in storage on pallet

stainless steel underwater camera sled.

stainless steel underwater camera sled

150 metre ROV umbilical

Umbilical EO wet connector

The camera sled system for sale.

The system comprises a tubular stainless camera sled with a platform for mounting stills and video cameras. Steel weights are attached to the underside (to ensure the sled stays on the seabed while being towed).  Floats are attached to the topside (to ensure the sled lands on the seabed right way up). There are attachment points for fixing strobe and video lights. A stainless steel bridle for towing is attached at the front end.  Total weight (including all steel weights) is approximately 80-90kg.  Note. the system for sale does not include camera or lights.

The system is currently stored in Exeter, UK.  It is pallet mounted and can be delivered worldwide. Email us for more details.

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Albatross: Ocean navigators par excellence.

Albatross: Ocean navigators par excellence.

I’ve spent many an hour of the deck of fishing boats, hauling and emptying nets, sorting fish and filling fish boxes. I’ve always been amazed at how, as soon as we start hauling the net, seabirds appear from nowhere across an empty sea.  One of the joys of spending time at sea in the higher latitudes of the South Pacific, is watching albatross track across the ocean.  On a couple of occasions, I have gone out in small boats specifically to watch albatross. Off the Kaikoura, on New Zealand’s South Island, large numbers of albatross congregate.

Two wandering albatross squabbling over food. © Colin Munro Photography

Wandering Albatross squabbling

Albatross are pretty much unmistakeable.  Huge seabirds that appear to soar effortlessly at sea, hardly moving so much as a wingtip. They belong to the family Diomedeidae, and like their relatives the petrels and shearwaters, they have distinctive tube-shaped nasal passages, which scientists believe help them find food at sea through a keen sense of smell.  Albatross are phenomenal travellers.  Individual birds will circumnavigate the earth, travelling as much as 500 miles in a day and often flying at a steady 50 miles an hour.  Once they are fledged, they remain at sea without ever touching land again for the next five or six years.  They are found in the North and South Pacific, and in the South Atlantic, but not the North Atlantic. Quite why they don’t occur in the North Atlantic is still a subject of debate amongst scientists. We know they used to occur there from fossil records. Short-tailed albatross, which are now confined to the North Pacific, bred as recently as are 400,000 years ago in Bermuda.  The current evidence suggests that a combination of factors may have been responsible.  The closing of the Central American Seaway, connecting the Atlantic with the Pacific between North and South America, approximately 2.5 million years ago, and a period of global warming and interglacial sea level rise of several metres (some scientists suggest as much as 20 metres rise in Bermuda).  The closure of the seaway effectively isolated the North Atlantic populations from others of the same species in the North Pacific, rendering smaller populations more vulnerable to extinction. It is also thought that sea level rise probably destroyed many nesting grounds.  At this point you may be thinking ‘They fly vast distances, why didn’t they simply spread north from the South Atlantic?’  Unfortunately, it’s not that simple.  While they appear to fly effortlessly, albatross need wind to generate lift and to steer.  The sailors among you will be familiar with the doldrums, areas of ocean where only light winds or no wind at all occurs, and sailboats can be stuck for many days.  The doldrums, more properly known as the Inter-Tropical Convergence Zone (ITCZ), forms a band that encircles the earth, extending roughly 5 degrees either side of the equator.  Here the north-easterly and south-easterly trade winds collide, resulting in still, slowly rising air that leaves the sails of trans-Atlantic yachts gently flapping. In you are a bird designed to soar on the wind, this is no use at all.  Albatross cannot sustain flight by flapping their enormous wings for long.  At roughly 10 degrees of latitude wide, the doldrums form a band around 600 nautical miles wide. This is too far for albatross to travel without the aid of wind, and so those born in the southern hemisphere will normally remain in the southern hemisphere all their lives.  Occasionally one does cross, perhaps during storm winds.  They are then trapped in the northern hemisphere.  The Bass rock, a small rocky remnant of ancient volcanos, off the east coast of Scotland, supports the largest colony of northern gannets in the World, but in May 1967 an unusual visitor nicknamed ‘Albert’ arrived. Albert was a black-browed albatross, a species that belongs in the southern hemisphere, more at home surfing the roaring 40s between New Zealand and Chile.  It’s thought that Albert was blown off course during a storm in 1967, and was then marooned in the northern hemisphere.  In subsequent years Albert was seen further north in the Shetland Isles, and in 2004 a black-browed albatross, believe to be Albert, took up residence among another gannet colony on the remote rocky outcrop of Sula Sgier.   In recent years black-browed albatross continue to occasionally turn up around the British coast.  In February 2019 one was spotted off Cornwall, while in July 2020 one was seen resting on cliffs amongst a gannet colony in Yorkshire.

A Salvin's Albatross taking off. Kaikoura, New Zealand. © Colin Munro Photography.

A Salvin’s Albatross taking off. Kaikoura, New Zealand.

This is still a very rare occurrence. The majority of albatross spend years at sea, traversing tens of thousands of miles, then successfully navigate back to the same colony. Wandering albatross, in particular, are famed for the vast distances they cover and their navigation abilities. Because raising chicks is such a long and demanding process for albatross, in most species the adults will breed only every second year, the intervening time being known as their sabbatical year.  One study published in Nature (Weimerskirch Et al., 2015) found that some birds breeding in the Crozet and Kerguelen Islands (remote Antarctic and sub-Antarctic Island groups) will circumnavigate Antarctica twice or even three times, covering up to 120,000 kilometres during this sabbatical year, before returning to these remote specks of land in the Southern and Indian Oceans.  The short answer is we really don’t know how albatross navigate so precisely. Sensitivity to the Earth’s magnetic fields has been suggested, but other studies have shown that disrupting these fields (by attaching tiny magnets to birds’ heads) make no difference to their ability to navigate. Using their sense of smell to detect traces of gases or compounds is another possibility.  Albatross are tubenoses, they have distinctive tubular nostrils believed to help funnel smells as an aid to foraging. Studies have shown that wandering albatross are able to detect and follow faint food smells from at least 20 kilometres away. The olfactory bulbs, the part of the forebrain that processes information on smell, makes up around 37% of the brain space of albatross, so this sense is obviously hugely important in their interpretation of the world around them. Where smells are faint and patchy, albatross will fly upwind in zigzag patterns, presumably working out where the odours are strongest. Recent research is providing growing evidence that ocean-going seabirds may rely not on magnetic patterns but olfactory, or smell cues, and may be producing brain, odour maps of the oceans, possibly similar to our nautical charts of ocean currents, to successfully navigate across thousands of miles of empty ocean and return home.

Gabrielle A. Nevitt, Marcel Losekoot, Henri Weimerskirch. Evidence for olfactory search in wandering albatross, Diomedea exulans. Proceedings of the National Academy of Sciences Mar 2008, 105 (12) 4576-4581; DOI: 10.1073/pnas.0709047105

Anna Gagliardo, Joël Bried, Paolo Lambardi, Paolo Luschi, Martin Wikelski, Francesco Bonadonna. Oceanic navigation in Cory’s shearwaters: evidence for a crucial role of olfactory cues for homing after displacement. Journal of Experimental Biology 2013 216: 2798-2805; doi: 10.1242/jeb.085738

J. Mardon, A. P. Nesterova, J. Traugott, S. M. Saunders, F. Bonadonna. Insight of scent: experimental evidence of olfactory capabilities in the wandering albatross (Diomedea exulans). Journal of Experimental Biology 2010 213: 558-563; doi: 10.1242/jeb.032979

Reynolds Andrew M., Cecere Jacopo G., Paiva Vitor H., Ramos Jaime A. and Focardi Stefano 2015Pelagic seabird flight patterns are consistent with a reliance on olfactory maps for oceanic navigation. Proc. R. Soc. B.28220150468

Weimerskirch H, Delord K, Guitteaud A, Phillips RA, Pinet P. Extreme variation in migration strategies between and within wandering albatross populations during their sabbatical year, and their fitness consequences. Sci Rep. 2015;5:8853. Published 2015 Mar 9. doi:10.1038/srep08853

This blog was first published on my other website: I’ve shared this here due to the marine biology content.

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Scallop dredging: how we approach marine habitat protection from entirely the wrong direction.

Scallop dredging is a crude, inefficient, non-selective, and hugely destructive means of collecting shellfish.  It is akin to using a bulldozer to collect mushrooms. If you were to plough through the top few inches of soil with a bulldozer bucket, pushing forward for a mile or so through grassland and scrub, then you will probably collect quite a few mushrooms.  Of course you will leave a trail of destruction in your path; saplings will be uprooted, countless small invertebrates will be broken and killed, wild flowers will be killed, many decades of slowly maturing habitat will be destroyed in less than an hour.  In the bulldozer path a wasteland will remain.  But this is only part of the damage.  Most of the mushrooms, the actual target species to be collected, will also be destroyed in the path of the bucket; many more will be collected but be unusable due to damage as they are rolled and tumbled along with all the other debris in the bucket.  Now image that process being repeated week after week, until all the land has been disturbed, the copses had been flatten and all the trees within destroyed. All the wildflowers gone, their place taken by sparse clumps of fast-growing weeds.  With most of the cover species removed, soil erosion will proceed at a rapid pace with nothing to buffer the wind and rain. Gone will be almost all the slow moving and delicate invertebrates that that are the lifeblood of a diverse ecosystem.  Once this degraded state is achieved and the number of mushrooms collected is no longer economically viable, then the bulldozers just move to a new patch, and the process begins again.  That is precisely how scallop dredging works.

Lyme Bay Closed Area Monitoring. An area of cobble reef within Lyme Bay badly damaged by scallop dredging. Scallop dredges, when used over rocky reefs leaves the area largely devoid of life with large amounts of broken rock. Even a single pass by such gear can cause large amounts of damage and recovery may take many years.

An area of cobble reef within Lyme Bay badly damaged by scallop dredging. Scallop dredges, when used over rocky reefs leaves the area largely devoid of life with large amounts of broken rock. Even a single pass by such gear can cause large amounts of damage and recovery may take many years. Photograph © Colin Munro.

Scallop dredging is not simply hugely destructive to the environment.  It is also highly inefficient and destructive to scallops.  Diver surveys have found that the heavy, steel-toothed dredges kill between 13 and 17 percent of the scallops they pass over but fail to pick up in the dredges (Caddy, 1973).  Yet more are damaged within the dredge chain-mesh bottomed bags as they are dragged along the seabed and tumbled with other scallops, stones and small boulders.

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.

The environmental impacts of scallop dredging on underwater reef habitats is nothing short of catastrophic. I have personally dived on and witnessed first hand reef areas where all attached life has been decimated in a matter of hours by scallop dredgers: boulders lifted out of the sediment and rolled until all attached life was crushed, sponges shredded, soft corals ripped of the rock and rolling about the seabed, sea fans snapped off, calcareous ‘ross coral’ bryozoans smashed until they resemble cornflakes scattered across the rocks.  If this wre happening on land it would, of course, be banned as soon as people saw the damage. Herein lies the problem.  Scallop dredging happens beneath the sea, where few will witness the destruction.  Secondly, it often happens in areas not hugely favoured by recreational divers; the lower profile reefs within larger areas of sand, gravel and boulders, rather than the dramatic limestone or granite rock walls.  But these areas are just as  important, and often far more extensive, than the few ‘scenic’ reefs favoured by divers, and often support ther own unique communities of species.  Whist a set of scallop dredges cannot be dragged across high rock pinnacles or up steep rock walls, they will easily bounce across boulder reefs and low rocky outcrops.

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 above diagram illustrates the damage caused to boulder reef habitats by a scallop dredge.  For a more detailed explanantion of scallop dredge design and action read my previous blog here.

Lane’s Ground

Lane’s Ground Reef is a low lying area of stones and small boulders a little offshore from Lyme Regis, Lyme Bay, Southwest England.  It’s a narrow strip of reef, a few hundred metres wide by around a kilometre long.

A diagram of Lane's Ground Reef, Lyme Bay, before damage from scallop dredging.

Lane’s Ground Reef, Lyme Bay.

I first dived Lane’s Ground in 1999. Back then it supported one of the richest asssemblages of marine sponges I’d ever encountered.  Almost every dinner-plate sized boulder was festooned with life: long delicate fingers of sponges, including several species only rarely recorded in other parts of the UK,  large Phallusia seasquirts, and occasional seafans.  But these small boulders were no impediment to scallop dredgers. So when the supply of scallops within the sand and gravel seabed areas surrounding Lane’s Ground was exhausted, the scallopers began working across it.

Lane's Ground Reef, Lyme Bay. A small patch of relatively pristine reef remaining in 2009. € Colin Munro

Lane’s Ground Reef, Lyme Bay. A small patch of relatively pristine reef still remaining in 2009.

Now of course this is far from ideal seabed to drag dredges across in the hope of catching scallops.  The dredges will bounce and fly, they will push stones and boulders in front of them, some of with will end up in the dredges damaging the scallops already caught.  But when everywhere else nearby is depleted, for some, it became a worthwhile excercise. The structure of many of the sponges you see in the image above is no more robust than marshmallow.  It doesn’t require much imagination to appreciate the damage that a tonne of metal dredges pulled by over 3000 horsepower will cause.

But even back in year 2000, Lane’s ground had started to change.  Scallop dredgers had began to chip away at the edges, gradually working deeper and deeper across the reef.  By 2008, the reef was no longer a continuous reef , but more a scattering of ‘islands’ of reef remained, surrounded by plains of sand and barren boulders, where vessels had repeatedly dragged dredge gear across.

As vessels worked deeper and deeper across Lane’s Ground, tracks of barren boudlers and sand grew in number, breaking up the reef.

One of several factors leading to greater exploitation of reefs has been the ever increasing power of the under 10 metre vessels working close in shore. In 2001 the average power of an under 10m vessel was around 2000KW (~2.6k horsepower). By 2011 this has risen to almost 14,000KW (UK Marine Management Organisation, cited in Poseidon Aquatic Resource Management Ltd. 2013).  This allows them to drag gear over rocky seabeds they could not work in the past, simply because they have the power to force the gear over rocky obstructions, but causing massive destruction in the process. Under 10m vessels are also generally allowed to work closer to shore than larger vessels, this is also where more rocky seabeds with fragile attached species are found.  Other factors that have played in to this include the fact that scallops have not been (in the UK) subject to similar catch restrictions as fish species, encouraging more skippers to switch gear and dregde for scallops.  Improvements in electronic natigation aids (GPS and higher resolution echo sounders) have allowed vessels to more accurately point-point seabed obstructions they need to avoid, so allowing them to work ever closer to one rocky outcrop, or one very large bouder, they need to avoid.  The combination of these factors has been a lethal cocktail for many fragile reefs.

The Exeters

The ‘Exeters’ was a reef  known for the life it supported and popular with local dive clubs, including that of Exeter University nearby.  The was in relatively shallow water, and only a few miles out from the port of Exmouth.  It consisted of a series of low sandstone ledges, supporting ross corals (Pentapora fascialis) large numbers of branching sponges and sea squirts.  Unfortunately its low relief and proximity to the fishing port of Exmouth made it easy scallop dredging ground.  It was one of the first to disappear. By the early 2000s, when I first dived it, all that remained was a slight rise in the seabed, with a few quickly colonising, opportinistic, sea squirts and hydroids.  The relavitely soft nature of the rock had meant that not only had all attached life been removed, the very rock had been broken down and worn smooth by the action of the fishing gear.

Zoned Management

Things have changed in the past ten years.  We now have bottom fishing mobile gear (scallop dredges and bottom trawls) excluded from much of Lyme Bay through the enactment of the Lyme bay Closed Area.  Lamlash Bay in the Clyde Estuary (where I also conducted some of the early survey and monitoring work) is now the second area in the UK closed by law to scallop dredgers.  But this is approaching the problem from entirely the wrong end.  Any rational person would consider it madness to say ‘Okay, you’re not allowed to work this National Park, or that one up in Scotland, but everything else, feel free to drive your bulldozers across it’. But that is more or less the approach taken in our seas. Increasingly we are recognising that zonation is necessary in our increasingly crowded seas; in many estuaries and coastal areas activities such as waterskiing and using of jet skis are restricted to clearly defined areas, based on management plans and assessment of impacts.  One cannot lay a pipeline across an area of seabed without a long and detailed assessment of the impacts on marine life, pollution and other marine activities, yet in much of our coastal seas you can rip all the life of the seabed, no questions asked. Destructive methods of fishing cannot be exempt from such considerations simply because ‘we’ve always done it’.  That is not even valid in it’s own terms, as the destructive capacity has increased enormously in recent decades through increasing vessel power and other technological improvements.  Rather than fighting for a few small areas where destructive fishing practices are prohibited, the fishing industry must be required to follow the same rules as mining, construction, oil and gas, and every other development and industry that disturbs the land or seabed.  If scallop dredging is to continue its impacts need to be assessed, and zones allocated for this method of fishing.  There is no reason why these areas cannot be quite large, if the impacts are considered low for extensive areas.  Creating bounded zones would also address the serious problem of vessels simply working an area hard, to extract as much as possible without concern for the stocks long term viability, then moving on to a new area.  There are simply far too many fragile areas for all to be protected individually, and this is far too destructive a method of fishing to allow it to continue to occur in areas where the potential damage has not been assessed.

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Nitrogen narcosis, Rapture of the Depths, what do we really know about it?

Rapture of the Deep

Two scientific divers wearing full face Aga masks communicate underwater. @Colin Munro Photography @Marine-Bio-Images

Nitrogen narcosis can be a real problem for working divers breathing air at depth

Many years ago, I was diving off the west coast of Scotland with a group of friends.  Our planned dive for that morning was a deep wall dive.  I was paired up with a new diver to our group, relatively inexperienced but who been trained by our group leader who was confident of her abilities.  Despite initial concerns, I was persuaded she was ready for a comparatively advanced dive like this.  We agreed we would stay within no decompression stop limits, head straight down to 50m, and begin our slow ascent back up the wall.  Allowing for our descent time, this would give us no more than a couple of minutes at 50m, but that was fine as the main purpose of the dive was to enjoy the marine life on the wall as we ascended.  Buddy checks were completed, on the skipper’s signal we jumped off the dive boat, swum the short distance to the edge of the wall and began to descend.  As we dropped steadily down, I continued to check on my dive buddy; she appeared relaxed and signalled all was fine.  At around 46m we slowed, and I signalled to stop at just over 49m.  After again checking all was okay I re-checked my dive computer; with one minute no stop bottom time remaining, I signalled for us to start ascending and my buddy confirmed.  We rose about a metre together, but then my buddy stopped ascending.  I dropped back down, made eye contact, signalled okay – which was confirmed – and again signalled up.  After ascending maybe 30cm, my buddy again slowed and stopped.  A second time I dropped back down, checked all was okay and signalled up, pointing to my dive computer and indicating we needed to keep moving.  This seemed clearly understood, but as I ascended my buddy began to slowly descend.  Dropping back down for a third time I decided it was time for positive action. We were over our planned maximum depth and over our no-stop time.  I firmly grasped the collar of her buoyancy jacket, squirted a little extra air into my own and gave a little kick to start us moving.  We continued up like this until we had ascended to around 30m depth and were back well inside our no-stop time. We then continued with our dive as planned.  Once back on the surface, aboard our dive boat, my buddy was far from happy with me.  Why had I spoiled the dive, grabbing hold of her like that, she wanted to know.  It quickly became apparent that she had no memory of our start-stop ascent, or awareness that she had started to re-descend to beyond 50m.  It took several minutes explaining and examining our computers’ dive log to convince her.

It is a well-known fact among divers that their ability of to recall observations made during a dive is worse than their recall of similar observations made while on land.   Part of this appears to be due to having gather data underwater, then recall it in a completely different environment (dry land).  That this can be a problem was demonstrated in a classic experiment by two British psychologists at the University of Stirling in Scotland, Duncan Godden and Alan Baddeley, back in the 1970s (Godden and Baddeley, 1975).  Using volunteers from two local Scottish Sub Aqua clubs (including the Stirling University club) they had them recall words learned underwater, and words learned on land. Interestingly they found that words learned underwater were recalled less well on land (than if they had been learned on land) but were recalled equally well underwater as words learned and recalled on land.  But this change of environment is not the entire reason.  When diving on deep walls, recording species, I, and many other marine biologists I know, have had the experience of not being able to recall the name of a species we know well, when we are at depth (i.e. below 30 metres).  Yet the name will suddenly pop in to our heads as we ascend to shallower depth.  I have often resorted to drawing little sketches of the species on the side of my writing slate; ten metres shallower the scientific name would miraculously come to me, and I could replace the drawing with a proper name. In fact, I was merely demonstrating a known phenomenon. Experimenting with divers in recompression chambers. In 1975, Canadian reserachers Barry Fowler and Kenneth Ackles found that memory recall of previously learned words was disrupted under hyperbaric air conditions equivalent to significant depth.   This, we know, is due to the narcotic effect of the nitrogen component of air. As depth, and so pressure, increases, so does the partial pressure of the 79% nitrogen in air, gradually introducing the effects of nitrogen narcosis.

A scientific diver writes up notes on a slate as she ascends at the end of a dive. © Colin Munro Photography © Marine Bio-Images

Scientific diver Kat Brown writes up notes on a writing slate as she ascends at the end of a dive.

The term l’ivresse des grandes profondeurs, translated to English as rapture of the great depths, has been credited to Jacques Cousteau, after his and Fredric Dumas’s vivid accounts of diving to over 200 feet (60 metres) in occupied France during WW2.  Through his hugely popular book, and later film, The Silent World, Cousteau made the wider public aware of the ‘rapture of the depths’, but despite what you will read in many popular articles and some textbooks, it was not Cousteau that discovered the narcotic effects of breathing elevated levels of nitrogen.

The Silent World, by jacques cousteau and Frederic Dumas (1953).

Through its use as an anaesthetic, nitrogen’s narcotic effect was recorded as far back as 1799 by the Cornish chemist Humphrey Davey.  Creating nitrous oxide by heating ammonium nitrate crystals, he collected the gas in a silk bag, from which he would then inhale, describing the sensations as ‘sublime emotion connected with highly vivid ideas’, an experience he appeared to become rather addicted to, spending hours alone in his laboratory inhaling large amounts of the gas. Fortunately, he maintained his scientific rigour and carefully described the effects (Davy H. Researches, chemical and philosophical, chiefly concerning nitrous oxide, or dephlogisticated nitrous air, and its respiration, 1800).  Around 100 years later, German pharmacologist Hans Meyer and British physiologist Charles Overton independently, in 1899 and 1901, developed what is now known as the Meyer-Overton theory, linking the anaesthetic potency of gases (including nitrogen, but also others) to their solubility in lipids.  In 1906 British Navy captain Guybon Damant dived to 64 metres in Loch Striven in West Scotland, setting a World record for the deepest dive outside a diving bell. This dive was conducted as part of Damant’s collaboration with Scottish scientist John Scott (J.S.) Haldane when the latter was working towards developing the World’s first diving decompression tables for the Royal Navy. Fortunately for Damant, most of Haldane’s experiments were conducted on goats, though he wasn’t above experimenting on himself or his son.

John Scott Haldane in 1910. Source Wikipedia under Creative Commons License (photographer unknown).

The following year Damant went on to become the Royal Navy’s Inspector of Diving and in 1917 he led the salvage operation on the SS Laurentic, a British ocean liner that had struck mines and sunk, with 43 tons of gold on board, in January of that year. His interest in science did not dim however and in 1930 he published an article in the journal Nature, entitled Physiological Effects of Work in Compressed Air.  The bulk of the article dealt with the effects of physical work on nitrogen absorption and release (and the potential for decompression sickness to occur) drawing on his experience of operations such as the Laurentic salvage, and ‘dry’ experiments done using a Siebe Gorman Davis hyperbaric chamber.  However, in an interesting aside, Damant described how some divers, during deep hyperbaric chamber dives (equivalent to over 300ft (91m) depth) would become ‘abnormal mentally, or emotionally’ under high pressure, yet have no memory of it upon return to atmospheric pressure.  With wonderful British reserve, Damant described the discovery of this phenomenon as ‘unexpected and rather awkward’ and only a few lines were devoted to it in the article.  Though he and his co-workers were unaware of the cause of these changes, he was undoubtedly describing nitrogen narcosis.

As a young military diver in the late 1970s, I was a beneficiary of much of this early research.  The first dive tables I dived on were Royal Navy Physiological Laboratory (RNPL) 1972 tables, developed by the laboratories’ superintendent Val Hempleman, building on the original work of Haldane and Damant.  I learned these at the British Army’s diving school in Marchwood, near Southampton, England.  Classroom learning was a bit of a hit and miss affair, as much of the training was devoted to physical endurance and discipline.  One of the favoured punishments for minor misdemeanours was having to wear a latex rubber diving hood during classes. Hot, uncomfortable and humiliating, it also meant you heard very little, so left the classroom in a blissful haze as ignorant as you had entered.  Uncomfortable as it was however, this punishment was preferable to the alternative, carrying a four-foot length of telegraph pole on your shoulder as you jogged between classes.

Ongoing practice and training is very much part of any military regime.  Once established as part of the regimental dive team in northern Germany our training continued in lakes, flooded quarries and industrial rivers, the blacker water the better as far the Army was concerned.  As part of this training we sometimes travelled to Kiel, to dive in the Baltic, generally in mid-winter when a thin film of ice covered the sea.

Colin Munro preparing to dive as an British Army diver 1978.

A rather younger version of me preparing to dive, Keil, North Germany, 1977-78.

During one of these visits I, along with about nine of my fellow divers, were allowed to complete a chamber dive in the nearby German military’s recompression chamber.  We were blown down to 70 bar pressure (equivalent to 60 metres depth) on air.  This resulted in much hilarity and laughter among my equally young and inexperienced colleagues.  I however, felt completely clear headed and, watching my friends with mild amusement, was convinced that they were suffering from marked nitrogen narcosis (true) and that I was not (not quite so true).  We were then asked to complete a short and simple arithmetic test, on sheets of paper handed out by our instructor.  This was indeed very simple, consisting of a drawing of a lake and several small dinghies and questions such as: how many dinghies are in the lake; how many are beside the lake; how many dinghies are there in total?  And so on.  Imagine my shock, upon receiving my test paper back after exiting the chamber, to find that I had scored the lowest mark of anyone, with over 50% wrong.  Yet I had been convinced that I was totally unaffected and clear headed.  This was a salutary lesson for me. Nitrogen narcosis can often leave us believing we are performing as efficiently and thinking as clearly as if we were on dry land when in fact we are anything but.

Fast-forward a couple of decades, and I found myself running a scientific study looking at the population dynamics on an offshore reef off the south coast of England.  The study reef was in 27-29 metres, so within the depth range where subtle effects of narcosis start to occur.  It was also an ideal depth for the use of nitrox, air where the oxygen percentage is increased and the nitrogen percentage lowered.  So I reconfigured our filling station to mix nitrox, and this became the gas of choice for most dives.  The prime reason was the extended bottom time available on nitrox 32 or 36 (i.e. 32% or 23% oxygen, as opposed to 21% air) at this depth, which vastly improved our efficiency.  It meant that around double the amount of work could be completed in one days’ diving compared to the same operation breathing air.  But I am also of the opinion that the quality of our data improved because of this switch. I personally felt more clear headed during a dive and less fatigued following a days’ diving, despite being in the water far longer.  This was not, of course, a controlled experiment, but there was definitely a sense among us that we were sharper and operated more efficiently when breathing nitrox. Thinking back to the chamber dive arithmetic test I performed as a teenage army diver, the key point is that I was completely unaware that I was being affected by narcosis and that my calculations were so wrong.  For so much scientific diving data collection, where reliance is placed on divers counting, measuring, or otherwise visually assessing, and then recording these data on underwater writing slates, the potential for error is, in my opinion, significant when you are working (breathing air) below 25 metres depth.

Working in dark and turbid water at depth appears to increase our susceptibility to nitrogen narcosis. Scientific diver lexie Munro working on our seafan study at around 28 metres. 2000.

Deeper than 34 metres the situation becomes more complex.  The benefits of nitrox are limited, as the correspondingly increased partial pressure of oxygen (PPO2) becomes the limiting factor (e.g. nitrox 32 gives a PPO2 of 1.4bar at 34 metres depth, 1.4bar being considered the safe maximum to avoid the potential effects of oxygen toxicity).  For deeper depths the gradual replacement of nitrogen by other inert gases (most commonly helium) is frequently used.  Controlling the oxygen levels to prevent toxicity, and reducing decompression penalties by utilising inert gases that have faster saturation and desaturation speeds, are the main goals for these alternative breathing gas mixtures, but limiting the narcotic effects (at depth) of the breathing mix is also an essential consideration. Indeed, calculating the equivalent narcotic depth (END), i.e. the depth at which the same level of narcosis would be experienced if breathing compressed air, is part of the process of determining the most suitable mix for deep dives. Thus helium is the nitrogen replacement gas of choice not only because it has the fastest desaturation rate of all inert gases (apart from hydrogen which is generally discounted due to its flammability and risk of explosion) but also because it has the lowest narcotic effect of all tested noble (inert) gases.

So what exactly causes nitrogen narcosis? Among the first studies designed to measure and investigate the effects of high pressure nitrogen were those of Dr. Peter Bennett, working at the Royal Navy Physiological Laboratory in the late 1950s and early 1960s (Bennet would go on to become the first CEO of the DAN network, and to develop trimix for deep SCUBA at Duke University).  But back the late 1950s Bennett was head of a small team working on inert gas narcosis at the Royal Navy Physiological Laboratory in Portsmouth.  Here he and colleagues demonstrated that breathing air at depth (trialled at 30 and 60m) the normal electrical activity of the brain altered.  At atmospheric pressure, when asked to perform mental arithmetic or other complex tasks, Alpha waves (associated with restful states of mind) will normally stop as the brain fires in to action.  But at both 30m and 60m this did not occur.  As they described it, the Alpha-blocking response was stopped.  More interestingly, what varied with pressure was not the severity of the response, but the time lag before it occurred. So typically Alpha-blocking stopped after about 3 minutes at 7bar abs. pressure (60m equivalent depth) but took 12 minutes at 4bar abs. (30m equivalent).  Having the men perform arithmetic test at 45m equivalent pressure resulted in a 12% increase in incorrect answers (Bennett and Glass, 1960).  Some of the volunteer subjects were switched to breathing oxy-helium mixes during the chamber dives.  With these it was found that the normal Alpha-blocking returned within a few minutes, demonstrating that nitrogen at high pressure was the cause of these changes.

This early work of Bennet’s was taken up by Ralph Kiessling of the U.S. Navy Experimental Diving Unit, and Clinton Maag at US Office of Navy Research.  They confirmed that divers’ ability to complete complex tasks was significantly impaired as depths as shallow as 30 metres, and the more complex the task the greater the degree of impairment.  However, their data indicated that there was no real time lag between arriving at depth and impairment setting in.  This suggested that the delayed Alpha-blocking detected by Bennet and Glass was maybe not the driver of the effects of narcosis, but simply another effect.  It is often said that divers can learn to reduce the effects of narcosis. Before conducting deep dives, we will conduct a series of work up dives to prepare us.  But does that actually reduce the effects of narcosis?  Work done by Hamilton, Laliberté and Fowler in the mid-1990s suggest that we simply learn to cope with the effects rather than reduce them, in particular reaction time did not improve over time. In recent decades the concept of nitrogen absorption into the bi-lipid layer of neural cell membranes, disrupting communication between nerve cells.

Of course nitrogen is not the only inert gas used in diving.  Helium replaces nitrogen in deep, technical diving, and hydrogen and neon have been used to replace nitrogen in experimental dives.  The level of narcosis induced varies markedly between these gases, and it correlates well with their solubility in lipids, thus supporting the bi-lipid layer absorption theory (e.g. hydrogen is less soluble than nitrogen, but more soluble than helium; hydrogen is also less narcotic than nitrogen, but more narcotic than helium).  This theory has been popular for a long time; essentially a refinement of the Meyer-Overton theory developed at the start of the previous century and later refined as the ‘critical volume theory’. This proposes that gas molecules accumulate in the cell membrane lipid layers, causing it to swell and distort. It is not, however, the only theory in in town.  Double Nobel Prize winner Linus Pauling (so clearly someone we should pay attention to) developed an aqueous phase theory that would require several pages to attempt to explain, so I won’t.  More recently the ‘protein theory’ where inert gases bond to protein sites through as yet unclear mechanisms is gaining traction as supporting evidence grows. There has also been some fascinating work recently demonstrating the suppression of release of certain neurotransmitters, in particular dopamine, under high partial pressure of nitrogen.  Studies conducted on rats (Lavoute, et al. 2012) demonstrated that a small number of repeated exposures to narcosis inducing levels of nitrogen at high pressure appeared to cause long-lasting changes in the brain’s neural pathways and neurotransmitter receptors.  The implications for divers is not yet known, but it raises the possibility that the effects of regularly getting ‘narked’ may not be confined to ones that disappear as soon as you surface. Bosco et al (2023) found that chamber dives to equivalent 48 metres seawater, while induced marked narcosis effects on study subjects, also produced significantly lowered circulating levels of glutamate (the major excitatory neurotransmitter in the brain), dopamine and BDNF (Brain-derived neurotrophic factor). BDNF influences a wide number of processes within the brain, playing an important role in neuronal survival and growth, and serves as a neurotransmitter modulator.  The study found that these levels remained low at least ten minutes after the divers had returned to surface pressure.

For longer term effects, without complete understanding of the mechanism, it is not possible to differentiate between effects due to narcosis-inducing changes and effects due to other factors such as micro-bubble formation during decompression.  In recent years a number of studies have demonstrated lowered cognition abilities correlating to having conducted a large number of dives (e.g. Coco et al, 2019) and evidence of micro-lesions on the myelin sheath (essentially the insulating layer around nerve cells). Whether this is due to changes in brain chemistry, microbubbles, or both (or an as yet unknown mechanism) remains an open question.

Nearly 70 years on from Cousteau and Dumas’s Silent world, 90 years since Damant’s nature article, and 320 years on from Davy’s treatise, we still do not really understand the biochemical and physiological changes that cause nitrogen narcosis.


Bosco, G., Giacon, T.A., Paolocci, N. et al, 2023. Dopamine/BDNF loss underscores narcosis cognitive impairment in divers: a proof of concept in a dry condition. Eur J Appl Physiol 123, 143–158 (2023).

Coco M, Buscemi A, Perciavalle V et al, 2019. Cognitive deficits and white matter alterations in highly trained scuba divers. Front Psychol 10:2376.

DAMANT, G. C. C. 1930. Physiological effects of work in compressed air. Nature (Lond.) 126: 606–608.

Fowler B, Ackles KN. Effect of hyperbaric air on long-term memory organization and recall. Aviat Space Environ Med. 1975;46(5):655‐659.

Godden, D. & Baddeley, A.D., 1975. Context dependent memory in two natural environments on land and underwater. British Journal of Psychology, 66, 325-331.

Hamilton K, Laliberté MF, Fowler B. Dissociation of the behavioral and subjective components of nitrogen narcosis and diver adaptation. Undersea Hyperb Med. 1995;22(1):41-49.

Kiessling, R. J., & Maag, C. H. 1962. Performance impairment as a function of nitrogen narcosis. Journal of Applied Psychology, 46(2), 91–95.

Lavoute C, Weiss M, Risso JJ, Rostain JC. Mechanism of action of nitrogen pressure in controlling striatal dopamine level of freely moving rats is changed by recurrent exposures to nitrogen narcosis. Neurochem Res 37(3): 655-664, 2012. doi: 10.1007/s11064-011-0657-1.




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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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