The impacts of longline and gillnet fishing on biodiversity and ecosystems, and known mitigative measures, both from international and Canadian experience, are summarized to support a Canadian Science Advisory Workshop on the topic.
Biodiversity issues are mostly framed as bycatch in the literature.
For longlines, a combination of net-sleeves, weighted mainlines, and bird-scaring lines, supplemented by dyed bait, offal control, and night setting can now be very effective in reducing bird bycatch. Zero-offset circle hooks, the use of fish rather than squid as bait, improved de-hooking protocols, training of practitioners, and fishing in colder water appear reduce turtle bycatch and mortality. Net sleeves appear to reduce marine mammal bycatch, but avoidance of whale concentrations remain the main effective mitigative strategy.
For gillnets, mitigation of bycatch through gear modifications is not as far advanced. Recovery boxes to improve survival of released fish bycatch, and some species-specific net modifications are used regularly in salmon gillnet fisheries. Coloured net panels to deter bird bycatch and acoustic deterrents to dissuade interactions with marine mammals show some promise, but are not widely used. Best strategies to avoid bycatch are management of areas, depths, or times the gear is utilized.
“Ecosystem impacts” are generally interpreted as impacts on habitats. Both pelagic gillnets and longlines have minimal impacts on habitat. Demersal applications of the gear, however, have some demonstrated impacts through entanglement and breakage of bottom features such as corals. The main concerns are with impacts on seamount ecosystems, deep-sea coldwater coral, and sponge communities. The prime mitigation strategy is avoidance of most sensitive areas. International protocols including precautionary management, closed areas, and protection for corals are pending.
“Ghost fishing” by lost gillnets and longlines is also of concern. Improved technology, regulations, and awareness of users is reducing rates of loss and improving recoveries, the only effective mechanisms so far for this problem.
An increased broader public concern has helped to drive many changes. Healthy discourse with conflicting points of view and collaborative development of policies and practices by managers, users, and other interested parties appear to be key elements for success for improved responsibility and sustainability of fisheries.
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