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What is bycatch in commercial fishing?

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A worker in dark clothing inspects large frozen tuna lined up on the floor at Tsukiji fish market in Tokyo, Japan, using a tool to check the fish. — commercial fishing Worker in the Tsukiji fish market, Tokyo.

Bycatch refers to any fish, mammal, bird, or other marine life captured unintentionally by the commercial fishing industry while harvesting targeted species.1

Because large-scale fishing gear—such as trawls, gill nets, and longlines—cannot discriminate between species, it often captures all marine life in its path. This process is considered an unavoidable consequence of large-scale fishing, and the nontargeted animals are frequently killed or injured by the trauma of being hauled in nets. These carcasses are often cast back into the ocean as "discard," though discard can also include commercially relevant species that are thrown away to make room for higher-quality catch or to comply with regulatory limits.1

Bycatch is a significant environmental concern, as it threatens many species with extinction. Efforts to mitigate this include the development of technological solutions like turtle excluder devices and acoustic pingers, as well as international legal frameworks aimed at reducing the use of indiscriminate gear like large-scale drift nets.1