Are supertrawlers bad for marine biodiversity?

“Supertrawler” is the kind of word that journalists love. It sounds unimaginably huge, capable of senseless damage and more than a little menacing. This hyperbole is well-earned: the world’s biggest fishing vessel – Poland’s Annelies Ilena ­– is 144 metres long; that’s nearly five times larger than a blue whale (generally, a supertrawler is any fishing vessel 130m or greater in length). The sight of such vessels steaming through crowded coastal waters is undoubtedly significant, but does their presence – as recent newspaper reports suggest – mean the ocean is being “plundered” and marine ecosystems “destroyed”?

As ever, the reality is more complex than the headlines. Firstly, not all high-volume, large-scale fishing leads to collapsing fish populations. When a fishing vessel’s target species are reduced to critical levels, this undermines the health of the entire ecosystem and its ability to function and supertrawlers have been repeatedly linked to fishing on species populations that are depleted or on the brink of collapse (i.e. overfishing). However, while vast catches may look apocalyptic to a bystander, some of the world’s largest (and most market-approved, sustainability-certified) catches come from enormous fishing boats, so-called factory vessels that catch, fillet, package and freeze thousands of tonnes of fish in a single trip, all while at sea. Fishing in a large vessel isn’t inherently unsustainable, as long as the biologically safe limit of exploitation for targeted species is known and everyone involved sticks to that limit.

Without proper management, stocks of commercial fish, such as Atlantic cod, are at risk. Credit: Joachim S. Müller/Flickr

Secondly, supertrawlers can, of course, cause harm to other marine species that they don’t intend to catch – i.e. through bycatch of marine turtles, sharks, rays, whales, dolphins and so on. But this risk is common to any form of fishing, at any scale. That risk is increased for a vessel that fishes longer, further and with larger nets than a smaller vessel. However, the possibility of adapting an enormous supertrawler net to avoid this risk – for example by fitting escape hatches for turtles, dolphins etc. – may be higher than in, let’s say, a small-scale gillnet vessel (in which these bycatch species can’t be filtered out and instead need to be deterred using light or noise, for example). Whether supertrawlers actually employ these adaptations is a different question and one that depends on the laws of the places they fish in, as well as the extent to which they comply with those laws (more on that later).

Finally, not all trawlers interact with marine habitats in the same way. Very broadly, there are those that fish for species that live in the middle of the water column (known as “midwater” or “pelagic” trawlers, targeting species such as mackerel, anchovies and tuna) and those that fish for species that live on, or in, the seabed (known as “bottom” or “demersal” trawlers, targeting groundfish such as cod, and crustaceans such as shrimp).

Responsible for 27% of the world’s fish catch, bottom trawling is a fishing technique designed to come into contact with the seabed. With its associated risk of permanent degradation to – and even wholesale removal of – marine habitats, this fishing practice is arguably (from a biodiversity perspective) the most controversial means of mass-producing food from the ocean. Almost all of the world’s supertrawlers are pelagic rather than bottom trawlers and, therefore, do not pose this risk. If we are concerned about trawlers and biodiversity, we should be focusing first and foremost on the ones that harm the seabed.

Though they may be much smaller than supertrawlers, bottom trawlers cause serious damage to the seabed. Credit: Otto Mejía

Illegal fishing complicates this picture. While supertrawlers may not inherently cause seabed damage, bycatch or overfishing, as soon as there is any question of the legality of these vessels’ operations, risks to biodiversity are higher. Eliminating the environmental impacts of fishing depends on the rule of law – governing where and how fishing takes place (in order to avoid sensitive habitats and minimise risk to bycatch species) and how much you can take (via catch limits and quotas). It is absolutely true to say that many supertrawlers have a patchy legal record; their ability to stay at sea for long periods means they can (and do) evade detection, change identities and launder their catch, providing the ideal smokescreen to quietly, illegally take the fins of sharks or catch more fish than allowed. It should be noted, however, that the supertrawlers of recent focus in the UK are (at least visibly) operating legally, with government-granted licences.

Essentially, although very large fishing vessels can (and do) threaten biodiversity (sometimes contravening fishing law), much of the public and media concern over the presence of supertrawlers in coastal waters is social in nature – it is about fairness, sovereignty and our sense of place and identity. These things matter when we consider the future of the world’s fisheries. Perhaps the most troubling aspect of supertrawlers is that they perfectly represent the globalised, inequitable and commodified nature of industrial fishing; a long way from the well-worn image of the plucky artisanal fisher in an undecked wooden boat.

For a biodiverse ocean, we need to limit the role of bottom trawling, adapt fishing so that we only catch what we’re targeting and establish (and enforce) precautionary, evidence-based catch limits; where fisheries are high-volume, they pose higher risks. It may not be true to say that supertrawlers and industrial fishing vessels are inherently bad for biodiversity, but fundamentally making fishing a fairer business – driven by the people and communities that need it the most, rather than the owners of vast, floating factories – represents a vital and necessary step in ensuring a thriving marine environment for future generations.