Trawl excluder devices are purpose-built mesh barriers or grids which are inserted between the entrance and the end (codend) of the trawl net. The grid is secured in at an angle, directing large marine animals (such as marine mammals and elasmobranchs) towards an escape hole – much like a skylight – in the top of the net. This allows large, non-target animals to be “excluded” from the catch in the end of the net.
Careful design of trawl excluder devices is paramount to ensure that catch of the target species is not also excluded. The design of the grid and size of the escape hole must ensure the target species can move easily into the end of the trawl net whilst ensuring the non-target species are excluded by the grid from the trawl net.
Although monitoring and research is ongoing, trawl excluder devices are widely accepted as an effective tool in reducing wildlife bycatch. Different designs, tailored to exclude different bycatch species, have been developed in recent years.
One such device, the Sea Lion Excluder Device (SLED) has been used to mitigate bycatch on squid trawlers in New Zealand, and became a legal requirement in the Southern Blue Whiting Fishery following a stint of sea lion fatalities. In 2017, an excluder device for both seals and sea lions became mandatory in the Falkland Islands Patagonian squid fishery, resulting in falling almost to a very low level, in comparison to the size of the populations. A similar device, designed to allow turtles to escape from trawl nets, has long been a legal requirement in the United States South Atlantic and Gulf of Mexico shrimp fisheries.
Whilst excluder devices have been shown to be effective at reducing seal, turtle, and elasmobranch bycatch, their success in reducing cetacean bycatch remains uncertain. A technical review for the Australian government suggests this may be due to dolphins’ lower manoeuvrability once within the confines of the net. Further investigation into their suitability for UK fisheries is required.
This page was last updated on 20.12.22.
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