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.
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.
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.
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.
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 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.