The Issue
Bottom trawling has been described as the most destructive of all fishing practices, comparable to forest clear cutting and agricultural ploughing on land.
WWF Report: Fish Dish – exposing the unacceptable face of seafood (pdf 1.2MB)
© WWF
© WWF
Norway lobster live in burrows dug into soft, muddy sediments on the seafloor. Although there is much more to learn about these muddy habitats, a diverse group of creatures are known to live here, including other burrowing crustaceans, burrowing worms and fish, seapens, starfish, brittlestars, and shellfish.
These muddy habitats form in areas where the seafloor is relatively undisturbed by waves and other external factors. This makes them particularly sensitive to bottom trawling, the main method used to catch Norway lobster.
Fishing for Norwegian Lobster is extremely destructive
The heavy otter and beam trawls scrape and plough into the mud, to a depth of 30cm or more.
The trawls can leave deep, lasting furrows up to 6m wide; flatten out natural contours; and compact sediments. In addition to the marine life caught by the net, animals living on the seafloor are crushed or buried as the trawl passes, while those living in the sediment can become exposed.
The trawls also resuspend large quantities of mud into the water - around 112kg of particles per second. This sediment can smother filter feeders such as seapens, which are related to corals. It can also reduce the light available for photosynthetic organisms and have negative effects on animals’ feeding and metabolic rates.
Small wonder that bottom trawling has been described as one of the most destructive fishing practices, comparable to forest clear cutting and agricultural ploughing on land.
And the damage occurs over vast areas.
The entire area of Irish Sea has been intensively bottom trawled for Norway lobster, as well as for other species such as plaice, sole, cod, haddock, whiting, saithe, and monkfish. The North Sea is also intensively bottom trawled for these species, with some areas being trawled 3 or 4 times a year. And nowadays fishermen use not one trawl, but 4 or 6 per vessel.
Changes what can live and what can be produced
The effects of a bottom trawl are immediate. Significant decreases in the number of species, biomass, species richness, and diversity have been documented 24 hours after otter trawling for Norway lobster in the Irish Sea.
Long-term effects are more difficult to assess — mainly because there are very few untrawled areas left for comparison in the two areas most studied, the Irish Sea and the North Sea.
One study of the Irish Sea, however, concluded that there are significantly fewer individuals and reduced biomass in areas trawled for Norway lobster than in areas around nearby shipwrecks that have not been trawled. Populations of burrowing urchins and mudshrimp have also been shown to be severely impacted by these trawls.
By disrupting burrowing animals, bottom trawling can also alter the complexity and oxygenation of muddy sediments on the seafloor, leading to further impacts on seafloor communities.
In general, stronger, mobile, and/or fast-growing animals are believed to recover from bottom trawling more quickly than fragile, non-mobile, and/or slow-growing ones.
There is speculation that bottom trawling also leads to a reduced body size for organisms living in intensely trawled areas.
In addition, the large numbers of dead and dying animals on the seafloor - due to both the trawl passing as well as the unwanted bycatch discarded overboard - may also alter seafloor communities by, for example, attracting increased populations of “scavenger” species that feed opportunistically on the dead animals.
Overall, seafloor communities may never recover to their original condition while trawling continues. Trawling on muddy habitats is likely to be the most serious threat to these unique, fragile communities - where species are vanishing faster than they are being discovered.
Side dishes
Lobster on the sideYour plate of Norway lobster comes with another plate that was discarded. Large numbers of Norway lobster are thrown overboard, either because they are smaller than the minimum landing size or because the market prefers larger individuals.
In the North Sea, 30% of caught individuals are discarded, while in the Bay of Biscay the figure rises to 50–60%. Norway lobster caught by trawls suffer frequent and often severe damage, and the vast majority of discarded individuals do not survive.
Baby fish on the side
Your plate of Norway lobster also comes with a plate of discarded baby fish - including commercial species such as cod, sole, plaice, haddock, whiting, and hake.
The small mesh size of Norway lobster trawl fisheries means that considerable numbers of fish are caught as bycatch, up to 70% of which are discarded as the fish are below the minimum landing size.
In the Skagerrak, for example, 61% of the total cod catch by Norway lobster trawls was discarded between 1995 and 2000. In some cases, the amount of discarded fish is greater than the Norway lobster catch.
A significant proportion of discarded fish do not survive. Even young fish that escape through the net can die from the injuries they sustain. The high level of juvenile fish mortality caused by most Norway lobster fisheries has led to concerns about the potential impact of these fisheries on the recovery of cod populations, as well as the sustainability of whiting and haddock populations.
Starfish and shellfish on the side
The waste doesn’t stop with edible seafood: huge amounts of invertebrate species (such as worms, starfish, and shellfish) are also discarded from bottom trawl nets. In North Sea fisheries alone, 150,000–180,000 tonnes of invertebrates are discarded each year.
Say Yes to sustainable seafood
Take a stand against unsustainable fishing and pledge to buy MSC certified seafoodIf you can't find seafood with the MSC label in your local store, please ask for them. Businesses do listen to their customers.
If they think there is enough demand for MSC certified seafood they will stock it.
