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Open Seas

Promoting sustainable seafood from Scotland's Seas

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Bottom dragging.

Scotland’s coastal fisheries are focused on shellfish. Scallops and Nephrops (otherwise known as Dublin Bay prawns, langoustine or Norway lobster – we’ll call them prawns), caught mostly for the European export markets, make up the majority of fish and shellfish coming from this area. Although both species can be caught in a few different ways, most scallops are caught by dredging, and most prawns are caught from bottom trawling, normally otter or twin rig.

Dredging and bottom-trawling are unsustainable, whether because of the scale and impact of the direct damage they cause to the seabed or through the knock-on impact of suppressing recovery of fish populations due to bycatch. We explore these impacts in detail below.

This unsustainability has been widely accepted for a long time, but neither Scottish Government nor the seafood and fishing industries appear able or willing to resolve the issues. Here are just a handful of occasions when they have committed to change and then failed to follow through:

  • In May 2017, the Scottish Government’s Environment Minister Roseanna Cunningham promised to limit the damaging impact of bottom-trawling and dredging on seabed habitats throughout Scotland’s inshore waters via the ‘Priority Marine Feature Review’. Implementation of fishing measures were promised by Mairi Gougeon (now Minister for Rural Affairs) by the end of 2019. This protection has yet to be delivered.
  • The main scallop dredge lobby group (the Scottish Whitefish Producers Association) acknowledged problems of illegal and damaging fishing following what happened in Loch Carron, and said publicly that its fishing members had “volunteered to avoid certain areas of known sensitive marine habitats in recognition of their importance” and was producing maps. These maps have never been published despite requests. Open Seas suspects they do not exist. We continue to see legal damage to areas known to hold sensitive habitats.
  • The Scottish Government promised to implement vessel tracking by 2019. Vessel tracking has yet to be rolled out across the Scottish scallop dredge fleet. Currently just 14 Scottish scallop dredgers have had the kit fitted and there are only 100 or so vessels. No progress has been made at all on the bottom-trawl fleet, despite a Scottish Parliament motion voting for robust, tamperproof tracking for all fishing vessels in 2018.

There are always opportunities to make these fisheries more sustainable – for example avoiding sensitive areas of our seas or switching to alternative, lower impact methods. Technical changes to fishing gears to avoid bycatch and habitat damage might also have a role to play. However, we have yet to see the necessary leadership from industry or government to take these opportunities.

Dredge the bed.

Scallop dredging is known to have the most severe ecological effect of all UK marine fisheries because of the damage and mortality it causes to the seabed habitat and species that live there.

Scallop dredgers in the UK use heavy toothed dredges that can weigh more than two tonnes and penetrate between 3 – 10 cm into the seabed. They are an inefficient way of capturing scallops so dredgers tend to repeat tows within the same area, exacerbating the initial impacts they have on the seabed. With powerful engines and heavy wires, they can be towed over most seabed types including areas of rocky reef, but mostly target areas of sands, gravels and cobbles where the scallops are found in greatest abundance. In some cases dredgers target areas which were once biogenic reefs where scallops live in small patches between the now damaged reef.

The amount and severity of damage and the rate at which the seabed and ecosystem can recover is considered to depend on habitat type and can range from 1 to more than 10 years.

Biogenic reefs (such as shell, sponge and coral beds) and other biogenic habitats (like kelp and seagrass beds) are normally considered the most sensitive. Unfortunately the sand, gravel and cobble seabeds where these occur (or formerly occurred) are also where scallops are found and dredging takes place.

Coral-like maerl is amongst the most vulnerable with 70% removed from an area by a single dredge tow, recovery takes many decades. Sponges, like the Elephant hide sponge also suffer and, in places where dredging is permitted in the Sound of Jura and Firth of Clyde, have nearly all been damaged. These (and other) slow growing sponges and soft corals can take up to 8 years to recover from a single dredging event. Mollusc species like Flame shells are capable of building large reefs and beds important for the wider ecosystem but again, a single pass can entirely remove a flame shell bed and recovery has been recorded at only 12% a year. The extent, density and overall biomass of seagrass beds is reduced by dredging, and this can take up between 6 – 20 years to recover, even in areas which are already considered wave, exposed and naturally disturbed. Unfortunately just one pass with a dredge can be just as damaging as persistent dredging.

Sandy habitats in areas with lots of wave and current action are thought to be of lower sensitivity due to their adaptation to natural disturbance. In the offshore sands and gravels of Cardigan Bay, studies have found that there are few differences between the species living on the seabed inside and outside a dredge closure. That said, decreases have been recorded in larger and immobile species in these habitats and, as acknowledged by the studies, the study may not have covered a long enough time period to actually observe changes. In similar Scottish “high energy coast, shallow and very exposed to wave action” habitats mollusc and crustaceans were also adapted to disturbance, yet large numbers of crabs and sandeels and other species were still killed by dredge tows.

Rocky reef areas are peripheral fishing grounds for scallop dredgers but in Scottish areas where dredging is permitted, they held 30% less fauna living on the rocky reefs than in areas where it is banned. That said, bedrock reefs can also sometimes provide protection. In Lyme Bay they appeared to shelter fragile pink sea fan, which persisted in areas despite dredging.

Whilst some of these habitats are protected from dredging pressure others, such as the reefs of Eagamol or even the Small Isles Marine Protected Area remain open to the damage despite concerns raised by local communities. Many other areas will have also been home to these habitats up until the main expansion of the dredge fishery (about 40 years ago) and still have the potential to recover. The science now shows that, despite the (albeit limited) protection of Marine Protected Areas, biogenic habitats are in decline in Scotland.

Sadly, even those areas which are protected have been damaged by the behaviour of illegal fishing. Over the past few years we have documented at least eight instances of illegal fishing.

Initially, Government and industry’s response was that illegal dredging was a small issue, perpetrated by only a few rogue individuals. Sadly this is not true. Recently the chairman of Scotland’s largest (SWFPA’s) scallop association was found guilty of illegal scallop dredging and fined £187,000.

Fishermen in Scotland who have been investigated for similar offences have anonymously accepted Fixed Penalty Notices, paying just £2,000. In many cases the damage they have caused will last for decades to centuries, resulting in a loss to society well in excess of £2,000.

Trawl the bottom.

Where dredgers operate on the sands and the gravels, trawling for prawns occurs on the muds and muddy, bouldery habitats. These habitats hold less fragile biogenic reefs, but in Scotland’s inshore seas they are often a lot less dynamic (i.e. they naturally receive much less wave and tidal disruption), making them less able to adapt to change.

Prawn trawls are wide-mouthed nets, weighted to fall to the seabed, and often fitted with ‘rock-hoppers’ (heavy rubber disks that act kind of like wheels) to help them run along seabeds without snagging on rocks. To address some of the issues regarding unwanted catch (discussed below), nets are often fitted with escape and sorting panels to improve ‘selectivity’.

Whilst scallop dredging is considered to be the most damaging UK marine fishery, prawn trawling is considered second. Modelling estimates that Scottish prawn trawls cause a larger amount of disruption beneath the top 2cm of seabed (per unit effort) than any other European demersal fishery.

The impact of trawl on the species that live in and on the seabed has been well studied and argued about since at least the 14th century. Intensive trawling simplifies the ecosystem, reducing the diversity and abundance of marine life. In the North Sea trawling has changed the biomass and species richness and diversity. Species like seapens and molluscs suffer the worst, whereas species like polychaete worms actually benefit. The species and habitats can and do recover, but only when there is sufficient time between trawls.

Trawling is patchily distributed and focuses on some highly productive grounds. This means that there are some areas which are very heavily impacted, but it also means that there is potential to protect those areas on the periphery.

The Risk to Recovery.

As well as having an immediate impact, damaging or removing species living on the seabed, dredge and trawl fisheries have the potential to alter seabed habitats in ways that impact the way the ecosystem works.

The diversity of the seabed habitat is important for many species’ reproduction; dead shells, rock crevices and maerl reef act as shelters for small mobile animals including small but important fish prey species such as mud lobsters, and provide ‘essential fish habitat’ for many fish species. Dredging generally leads to a flattened, less varied habitat and removes essential fish habitat function and performance.

In experiments significantly fewer juvenile cod survived on seabeds that resembled dredged ones, than on others where sponge habitats were present. The abundance of these species living in and on the seabed significantly reduces the mortality of year old Atlantic cod and these juveniles actively select seagrass beds as nursery grounds which can hold an entire order of magnitude more juvenile cod than bare sandy areas. Similar preference for biologically complex habitats has also been found in the Firth of Clyde for haddock, and in fact has just been further supported by very recent research showing the abundance of whiting and cod is correlated with the diversity of the seabed. Herring distribution in Shetland is also closely linked to the nature of the seabed, and their spawning is associated with maerl and gravels shallower than 100m.

This functional structure can be fundamentally changed by long-term trawling. Impacts are cumulative, and can lead to profound changes in benthic communities with potentially far-reaching implications for the integrity of marine food webs. Damage to fish prey caused by trawling has been found to decrease the condition (health and size) of the plaice themselves through increased competition. Similar effects are thought to be experienced by dab and whiting, but are somewhat masked by the fact that these two species are bycaught or caught in such numbers that there is no competition. In general, intense trawling can cause major changes to habitats, in turn affecting the fish populations and changing ecosystems.

Prawn trawling also has a significant impact on marine ecosystems through the amount of fish, shellfish and other marine species accidentally caught (known as bycatch) (Seafish, 2016). The scale of bycatch problems is different in different areas. In the Clyde studies have found that between 66 – 80% of the catch (by weight) was unwanted, in other areas only 12% of the original catch was kept. Much of the fish being discarded are potentially commercially valuable, edible species such as hake, sole, plaice, cod, whiting and haddock. Scientific advice from ICES states that stocks of west coast cod and whiting will not recover until this bycatch problem is reduced.

Discarding was made illegal in 2019. However, it is widely accepted to continue, the Head of Fisheries for Scottish Government stated so in evidence to the House of Lords and imagery we have been provided shows fish thrown overboard. There is also a clear mismatch between the amount of fish recorded in catches by fisheries observers, and the amount of fish which lands to Scottish ports. When we have inquired about how this law is being enforced we have been told by Marine Scotland that “we need to make it easy for fishermen to comply with the law”. Scottish Government have therefore been attempting to ‘derogate’ discarding of species like cod, to make it legal. Ultimately this may make it easier for compliance but it certainly will not help the health of our seas.

Trawler skippers, the industry and others have been trying – and continue to try – to catch fewer unwanted fish, with improved net designs and other innovations. However, approaches have not been entirely successful or broadly adopted to date and so the risk to the inshore ecosystem remains significant.

Coastal Margins

It’s not just about protection for the environment’s sake. Sustainability is about assessing the entire system and working out what’s in society’s best interests.

Around the world, companies are thinking about their operations in terms much broader than just the economic bottom-line, hardwiring sustainability and reporting on financial and non-financial performance.

The current intensity and distribution of bottom-towed fishing around our shores is unsustainable, not just ecologically, but economically and socially. We’ve seen similar things happen in the past; the boom of inshore herring lasted for well over a century but eventually crashed and was entirely banned in 1977. This seriously affected the villages that were built upon it or which had grown to depend on it.

Intensive bottom-trawling and dredging may have been commercially viable for the past 40 years, but many communities and some within the broader fishing industry are waking up to the tell-tale signs that this intensive method of bottom-towed fishing is not in the long-term good.

In the past few years we are fishing much harder but for fewer fish and lower profits. Scallop landings per unit effort grew to a peak in the late 2000s and early 2010s, but have been falling in the past few years. Income, operating costs and total profits have all declined, in some areas by as much as 92% for larger vessels.

In many cases, lower impact fishing methods provide better returns; creel-caught prawns yield both higher value and profits than those caught by trawls for example. However, as stated by a Report to Select Committee in 2004, “Trawling is now completely dominant [and] reduces the ability of other fishing methods to continue.” This opportunity cost is rarely considered in policy decisions.

It is also important to consider the impact damaging fishing might have on other sectors and communities. Fishing in Scotland (including both inshore and offshore) is estimated to generate about £215m (a further £461m if you also include all fish processing). Meanwhile spending on sea angling, wildlife watching, hotels and other aspects of the coastal economy are estimated at  around £3.7 billion per year. Many communities have already raised concerns about their reliance on healthy seas and the impact of damaging fishing.

Stand still or make a change

The issues here are significant, and have been around for a long time. However, we have an opportunity to do better.

Some have recommended that fisheries and habitat conservation can both be achieved through an appropriate use of total and partial exclusion of bottom-towed fishing gears, avoiding displacement onto other sensitive areas. Others contend that switching from trawling to lower impact creels would allow Nephrops landings to continue without damaging wider fish stocks. Elsewhere in the UK, zoned fisheries management has allowed commercially viable fishing to continue whilst also protecting the benthic ecosystem and its function. Recent collaboration between seafood retailer, foodservice, leading academics and members of the fishing industry concluded that better understanding of the distribution of sensitive habitats is needed to improve the trawl fisheries.

Protection of the most biologically diverse and vulnerable parts of our inshore seas is needed, but we must acknowledge that current management does not consider fully the wider ecosystem services provided by our entire inshore area. Marine Protected Areas may cover roughly 20% of the inshore, but dredging and trawling can still legally take place in the vast majority (96%) of our inshore waters.

Government commissioned reviews have made similar recommendations. In 2013, a review of the entire Scottish scallop fishing industry concluded that the current system did not provide sufficient protection to sensitive areas of the seas (“priority marine features”), and recommended reserves and night time curfews on fishing in the inshore. Similar analysis, on a UK-wide basis, concluded that the costs of managing scallop dredging are outweighed by the benefits. Moreover a report investigating economic opportunities for the inshore found that there were significant opportunities to improve profitability in the inshore by moving away from damaging fisheries in sensitive areas. In 2018 the West Coast Regional Inshore Fisheries Group commissioned another review, this again found that closed areas and better monitoring was needed. These were again overlooked.

Annual advice from the UK’s Seafood Authority states that “dredging must be done only with full understanding of the fisheries concerned, together with a practical application of mitigating measures”. In 2009 the UK Scallop Industry Good Practice Guide agreed commitments to reporting, avoiding and maintaining a protection zone around areas where sensitive species are encountered and observed. Unfortunately it appears this good practice is not being followed in Scotland.

Perhaps most importantly, collaboration between seafood retailer, foodservice, leading academics and members of the fishing industry concluded that better understanding of the distribution of sensitive habitats is the highest priority knowledge gap if we are to better understand the consequences of bottom trawling and dredging and to appropriately protect our seas.

We’re interested in protecting our marine environment and the things that live in it. We’re interested in buying and eating sustainable fish and shellfish. We can do much better, why don’t we?

Why should we care?

About 5 million seabirds come to breed in them every summer, 24 species of whale and dolphins have been sighted off the West Coast, and extremely rare seabed species like serpulid reefs exist in our sheltered sealochs (other than two lochs in Ireland, and a coastal lagoon in Italy, these exist nowhere else in the world.)

The seabed is the foundation of a healthy marine ecosystem and Scotland’s is a mosaic of different habitats. The east coast Firths like the Firth of Forth, once held massive oyster beds and are now shallow muds and gravels. Further offshore are sandbanks which provide the perfect habitat for flat fish and sandeels, a keystone species underpinning the food web for a wide range of species.

All along the west coast and in Shetland and Orkney to the North, the different rocks, the currents and waves and the impact of the last ice age have meant the seabed is more varied. Deep sealochs hold steep shelves of shells, sponges and coral-like species above the muddy depths. Beyond the mouths of these sheltered waters, sands and gravels surround the islands and can be important spawning grounds for fish like herring, whilst the strong tidal currents provide vital feeding grounds for basking sharks that visit in the summer. Jutting out from islands and in deeper waters, submerged rocky reefs are vital habitats for crabs and lobsters.

The seas are by no means in a natural state. The oyster beds mentioned above have been almost entirely removed from our seas by industrial harvesting. Similarly whaling, seabird hunting and fishing have all played a part in changing the range of life in the seas today. Some ecosystems have been fundamentally transformed because of these human impacts: herring no longer run up the west coast of Scotland in huge numbers as they once did. Others ecosystems have absorbed the change or adapted to it and rebounded.

Each habitat plays a part in the mosaic of Scotland’s seabed, and yet of these biogenic habitats are in decline. Will we be the generation that stands up for change?

Members of:

Scottish Rewilding Alliance
Our Seas coalition
Slow Food Scotland
Scottish Food Coalition
UKELA Scotland
Stop Climate Chaos Scotland