Trawl Excluder Device
WHAT IS A TRAWL EXCLUDER DEVICE?
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.
Source: Hamilton & Baker 2019
CURRENT RESEARCH & USE
Although monitoring and research is ongoing, trawl excluder devices are widely accepted as an effective tool in reducing bycatch of seals and sea lions, turtles, and sharks, skates, and rays. Different designs, tailored to exclude different bycatch species, have been developed in recent years. Most recently, a novel shark excluder device (SED) based on a hard aluminium grid was found to be effective when trialled in a Mediterranean multispecies bottom trawl fishery – although it did reduce catch rates of some target fish species, leaving some participating fishers with concerns about potential commercial losses.
The use of trawl excluder devices has been made mandatory in some fisheries. This includes New Zealand’s commercial southern squid trawl fishery and southern blue whiting fishery, where a Sea Lion Excluder Device (SLED) has significantly reduced sea lion bycatch. Likewise, the mandatory use of an excluder device for both seals and sea lions in the Falkland Islands Patagonian squid fishery has seen bycatch events fall to a negligible level, relative to population sizes. 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.
The effectiveness of trawl excluder devices in reducing cetacean bycatch remains much more uncertain, with a technical review for the Australian government suggesting this may be due to dolphins’ lower manoeuvrability once within the confines of the net. Collaborative European project CetAMBICion is currently trialling prototype cetacean excluder devices (CEDs) in Spanish waters, with initial results indicating that these are effective in enabling short-beaked common dolphins to escape trawl nets; although it is caveated that such CEDs must be tailored to the specific fishery in which they are implemented.
This page was last updated on 04.12.24.
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