Trawling: between polemics and provable facts

For centuries people have benefited from the wealth of the seas but today many worry that we are placing undue burdens on the marine ecosystems. This is not just about the overfishing of individual stocks but about where and how we catch fish. Criticism mainly centres around bottom trawls and the deep-sea fishery that allegedly cause severe damages to the marine environment and to fish stocks.

No one can deny that man puts pressure on the world’s oceans. We pollute them with plastic waste and toxic chemicals, we acidify them with our emissions into the atmosphere, we over-fertilize coastal waters with waste water from agriculture and municipalities, and we increase water temperature in the wake of global warming. In order to change this we would have to lower our sights a bit and change our lifestyle. But that would be uncomfortable and possibly explains why it is mostly fishing that we point our fingers at when searching for someone or something to blame for the damages to the marine environment. And there seem to be reasons enough for this… the overfishing of certain stocks, the share of by-catch which is still too high, the ongoing illegal fishing for lucrative fish species, apparent weaknesses of fisheries management and its practical implementation. And the list could be continued. It is deep-sea fishing, however, and the use of bottom trawls that bear the brunt of criticism.

It is claimed that bottom trawling leaves a trail of destruction, damaging the seabed and in just a few months or weeks destroying highly sensitive ecosystems that have taken centuries to evolve. Perhaps this reproach would be better directed at the farmers who plough their fields every year, tearing 30 centimetres deep into the topsoil and thereby destroying populations of creatures that live in and on the earth. Compared to agricultural monocultures, bottom trawling probably causes less severe damages. Although the fishing sector is looking for technical solutions to further reduce these damages it will probably never be possible to avoid them completely. Perhaps that is why environmentalists and other critics have got it in for the fishery and its trawls. Trawling was the “most destructive” fishing method, and one which could soonest be compared with the slash and burn clearance of the rain forest. This fishing method caused particularly severe damages in the highly sensitive habitats of the deep sea that often needed centuries for their regeneration because many of the life processes that take place there are extremely slow. Deep-sea fish species such as redfish or orange roughy grow very slowly, reach maturity late, and then only have relatively few offspring. This makes them particularly vulnerable to overfishing, particularly since deep-sea fishes are often faithful to their habitats and rarely leave the seamount ecosystems where they live. Once a fishing vessel has located swarms of fish there it is not difficult to fish them successfully. According to a report by the UN Secretary General, in 2006 95 per cent of the worldwide damages to the seamount ecosystems in the deep sea were caused by bottom trawling.

When a bottom trawl is dragged over the seabed it can indeed cause serious damages to the ecosystems and habitats there. The usually large and correspondingly heavy trawls act like huge planes on the seabed. At the sides the net is held open by the pressure caused by the heavy trawl doors that drag over the seabed during slow trawling and plough deeply through it. Fishermen used to hang heavy chains or weights onto the net opening at the bottom to keep it constantly close to the seabed. In the meantime these have mostly been replaced by gentler rubber rollers but even they are heavy enough to crush clams, crabs and other creatures on the seabed as they roll over them. Whether the damages caused by bottom trawls are “irreversible”, as is often claimed, remains questionable, however. Another point of criticism is the low selectivity of the fishing gear. Trawls did not only catch the target species but practically everything that finds itself in front of the net opening during trawling. Such by-catches, which in some fisheries can constitute as much as 90 per cent of the total catch, contribute to the reduction of biodiversity in the sea.

In a region where the sediment is constantly churned up and rearranged by the currents and tides the impact of bottom trawling can more easily be ignored than in areas with relatively static ecosystems that have developed over long periods without such influences.


Criticism of trawling not sufficiently differentiated

Although the criticism of trawls might be justifiable in individual cases a generalization of these allegations seems rather excessive, particularly since it does not only relate to otter trawls but also beam trawls which are mainly used to catch flatfishes and prawns, and dredgers with which mussels, clams, scallops and other molluscs are collected from the seabed. Sometimes even the use of pelagic trawls in shallow waters is denounced because the trawls sink down during slow trawling and can touch the seabed. None of these types of fishing gear is basically “good” or “bad” but strictly speaking only suitable or unsuitable for a certain marine region and the seabed found there. Bottom trawling on a densely populated hard seabed should be assessed differently from bottom trawling on a sandy or muddy bed. In a region where the sediment is constantly churned up and rearranged by the currents and tides the impact of bottom trawling can sooner be neglected than in areas with relatively static ecosystems that have developed over long periods without such influences. And of course there are also those highly sensitive areas where fishing – if at all – should only be allowed with great caution and sensitivity.

Trawling is carried out both in coastal areas using small open boats and in the deep sea using large factory vessels. When working with rigid fishing gear such as beam trawls or dredges, engines with just 30 or 50 horsepower are often sufficient. More powerful engines are usually necessary for larger trawls that are held open by the hydrodynamic effect of the trawl boards. A speed of four to five knots (seven to nine kilometres per hour) is usually sufficient, however, for catching the mostly demersal fish species. The impact of bottom trawling can only be assessed under the particular prevailing conditions, and a general condemnation or even a ban would not be appropriate for such a complex situation. Criticism of bottom trawls has to be carefully differentiated and that is often the weak point. Environmental associations and NGOs even do their best to dramatize the consequences of this fishery, probably to show how urgent a ban on trawling would be. Bottom trawls destroy the seabed, is the simple message; they leave behind a desert landscape and have a negative impact on biodiversity. It is not rarely even claimed that the damages to the seabed are irreversible, that some species would disappear irretrievably.

Photos or films are often used to support these allegations. They show bottom trawls in operation and the damages they cause. Anyone who looks up “deep-sea trawling” on the internet will get more than 1.5 million hits, most of them describing the negative aspects and devastating impact of this fishing method, frequently polemically presented. What is lacking, however, are objective scientific studies on the long-term consequences of the damages and the regeneration capacity of the different ecosystems on the seabed. What consequences trawls have for a given area depends on numerous different factors. For example, the seabed structures and the populations that live there, the size of the net, how often the area is fished and in what spatial density. If the assumed regeneration periods of many years are actually true for some areas then the investigations would have to be carried out over a period of many years, too. This is methodologically difficult, costs a lot of money and demands long-term research concepts that are hardly feasible today. In some respects the situation can be compared to that of discards, for which there were for a long time no reliable basic data. That is why many people relied on estimates by Greenpeace and other NGOs that spoke of 25 to 30 million tonnes of discards per year. It was not until the FAO presented more accurate information that an average discard volume of 6.8 million tonnes per year was determined (FAO Technical Paper T 470). That is of course a significant amount, too, but much less than had been speculated before.


Far too few meaningful scientific studies

Because there is a lack of scientific studies the door to speculation and exaggeration is wide open. A lot of statements concerning the risks of bottom trawling are perceived among the public as scientifically proven facts although they are strictly speaking no more than conjectures and hypotheses. The lack of evidence hinders an honest debate, particularly since critics of bottom trawling often reject any findings that do not fit in with their ideas. In 2010, when Donna Kline, a fish ecologist at the California State University in Monterey Bay, presented the first results of a five-year study on the impacts of bottom trawls on the seabed of Morro Bay between Los Angeles and Monterey in the New Scientist. She soon reaped the wrath of many environmentalists. Other than they had expected, the team of scientists around Donna Kline had found signs of a revival of the biotope rather than its destruction. Many more organisms than expected had survived the trawls rolling over the seabed. Already a short time later nature seemed to have largely regenerated and new forms of life had even settled there. Donna Kline sees the recovery of the ecosystem as a result of the better structure of the seabed: the bottom trawl had scratched furrows and small ditches into the seabed enabling invasive species to colonize there.

The scientists themselves limit the generalizability of their findings, however. It was much too early to view the results as secure and they could not be applied directly to other marine regions. What had led to the revitalization of the ecosystem in Morro Bay could have completely different effects elsewhere. It was not only the structure and colonization of the seabed that must be considered but also the size of the trawls and the frequency of fishing. In spite of these limitations the study is still noteworthy, however, because it does not demonize bottom trawls in principle and tries to come to an objective assessment of the fishery.

Fisheries experts and environmentalists are largely in agreement with regard to the vulnerability and need for protection of the seabed and its inhabitants in the deep sea. Here, where many life processes run in “slow motion”, any kind of intervention in the natural systems that have evolved over millennia will have long-term serious effects. In the year 2010 the International Council for the Exploration of the Sea (ICES) found that all the commercially exploited deep-sea fish stocks in the North East Atlantic were “outside safe biological limits”. Although there is often a lack of adequate data on many deep-sea species this is alarming because it is often precisely these species that take decades to regenerate. What makes matters worse is that bottom trawling in international waters outside of the national jurisdiction zones is practically not subject to any regulation. One of the few exceptions is the Antarctic region where the use of bottom trawls is greatly limited in accordance with the Convention for the Conservation of Antarctic Living Resources. The North East Atlantic Fisheries Commission (NEAFC) has also banned bottom trawling temporarily in some sensitive regions of their area of responsibility. Similar efforts are being made in the South Pacific where the South Pacific Regional Fisheries Management Organisation (SPRFMO) called on all fishing nations in May 2007 to stop bottom trawling in the deep-sea areas until scientific reviews and risk assessments were available for the affected areas. The necessary preventive measures were then to be initiated on this basis. But it remains open how these rules can be controlled in practice for the affected area of the South Pacific constitutes almost one quarter of the world’s oceans.

When a bottom trawl is dragged over the seabed it can indeed cause serious damages to the ecosystems and habitats there. However, whether the damage caused by bottom trawls is “irreversible”, as is often claimed, remains questionable.


Proposal to ban deep-sea bottom trawling initially failed in the EU

Many nations have taken measures for more effective protection of the deep-sea areas in their exclusive economic zones (EEZ). Norway, for example, has operated a study programme since 1999 that is to determine the dissemination of the cold-water coral Lophelia off the coast in order to close bottom trawling in these areas. In the same year Australia’s government banned the bottom trawl fishery in the southern Tasman Sea. In 2004 Australia also installed the world’s largest marine protective area, the Great Barrier Reef Marine Park, in which not only bottom trawling but any sort of fishing activities are prohibited. Canada protects its coral reef ecosystems off Nova Scotia. The Northeast Channel was closed for fishing in 2002, and two years later the Gully was declared a Marine Protected Area (MPA). The National Oceanic and Atmospheric Administration (NOAA) of the USA has prohibited bottom trawling since 2006 nearly everywhere off the Pacific coast, and since then also in other marine regions that are 3 to 300 nautical miles off the coast. Only these regions fall under federal US jurisdiction, the coastal zones within 3 nautical miles are the responsibility of the respective states. In 2006 Anote Tong, the President of the Pacific island state of Kiribati, announced the foundation of the world’s first deep-sea marine reserve “Phoenix Islands Protected Area”.

Compared to these efforts, Europe is currently still finding it difficult to implement similarly far-reaching bans. They did, however, for precautionary reasons close the sensitive Darwin Mounds off Scotland for bottom trawling in 2004. The FAO General Fisheries Commission for the Mediterranean (GFCM) banned bottom trawling in 2005 in all Mediterranean regions below 1,000 metres and as from January 2006 other ecologically sensitive regions off Italy, Cypress and Egypt have been closed for fishing, too. In mid-2012 the EU surprised people when the Commission made the historic proposal to ban bottom trawling in the deep sea for EU fishing vessels in the North East Atlantic. From an economic point of view that would probably be reasonable despite the fact that the EU is responsible for 75% of all catches of deep-sea species in this area and the member states possess about 100 vessels that are equipped with the technical gear for this special fishery. That is equal to about one third of the worldwide vessels suited to deep-sea fishing whose number was estimated in 2008 by the FAO at 285 vessels that are registered in 27 states. All the deep-sea species together account for only 1.2% of the EU states’ landed volume and 1.3% of landed value. The significance of the deep-sea species for the world fishery is similarly low. According to FAO statistics the catch volume of the 76 deep-sea species and species groups was in 2009 just 3.3 million tonnes or 4.1% of the total global catch. More than half of that were blue whiting (Micromesistius poutassou) and large-head hairtail (Trichiurus lepturus). Deep-sea fishing is technically demanding and expensive, and without subsidies most vessels would soon be unprofitable and would have to give up this fishery.

Underwater mountains

Seamounts and the abundant life there

In numerous marine locations steep rugged mountain ranges and individual peaks rise from the ocean floor: seamounts. They can rise 1,000 metres and more from the seabed. Although presumably not all their locations are yet known their number in the Atlantic is already estimated at more than 800, in the Pacific even over 30,000. In areas with hard floors veritable forests of cold water corals, sea pens, sponges and gorgonians grow on the mountain sides, and between them live crustaceans, spider crabs and other marine organisms. Some species such as orange roughy or deepwater dory also seek protection here from the strong underwater currents. On the slopes’ softer floors live various worms, mostly polychaetes, but also slipper lobsters and other species. The seamount ecosystems are particularly fragile and vulnerable to destruction because a lot of the species in the ice-cold depths only grow very slowly and the ecosystems take decades to regenerate once they have been disturbed.

That is why critics of bottom trawling and the deep-sea fishery hope that the EU will manage to come to a clear decision on the stronger protection of deep-sea fish stocks and eco-systems and announce a complete ban on bottom trawling in these regions. The vote was narrow and initially disappointing. With 342 to 326 votes and 19 abstentions the MEPs voted in the European Parliament on 10 December 2013 against a complete withdrawal from deep-sea trawling. The pressure on the ministers for this decision was huge. They had to weigh up the various aspects against each other: the protection of the marine environment and sustainable exploitation of fishery resources, the rising food demands of a growing world population, and incomes and jobs in the fish industry. Even if the EU ministers’ decision might seem incomprehensible to many there are now signs of new, much greater risks to the ecosystems in the depths of the ocean which make the danger from trawls seem almost petty. For a lot of states are now reaching out for other treasures that lie on the ocean floor: manganese nodules, polymetallic formations, the “truffles” of the deep sea. This industry promises much higher profits than could ever be achieved with fish. And with that it also has much greater technical possibilities and potential that could also become a danger to fish stocks and thus to the fishery. It is possible that environmentalists and the fish industry will have to join forces in the future to protect and enforce their basically similar interests against an economically much more powerful “opponent”.