Bycatch

In 1997, the Organisation for Economic Co-operation and Development (OECD) defined bycatch as "total fishing mortality, excluding that accounted directly by the retained catch of target species".

In 1997, the Food and Agriculture Organization of the United Nations (FAO) documented the estimated bycatch and discard levels from shrimp fisheries around the world.

[12] Another sampling of the same fishery over a two-year period found that rock shrimp amounted to only 10% of total catch weight.

This bycatch issue has been one of the reasons of the growing ecolabelling industry, where fish producers mark their packagings with disclaimers such as "dolphin friendly" to reassure buyers.

[21] One of the main threats is commercial longline fishing,[22] because albatrosses and other seabirds which readily feed on offal are attracted to the set bait, after which they become hooked on the lines and drown.

A research study examined the impact of illegal longline fishing vessels on albatrosses, by using environmental criminology as a guiding theoretical framework.

[23] These findings provide strong grounding that illegal longline fishing poses a particularly serious threat to the survival of seabirds.

Estimates indicate that thousands of Kemp's ridley, loggerhead, green, and leatherback sea turtles are caught in shrimp trawl fisheries in the Gulf of Mexico and the US Atlantic annually[24] The speed and length of the trawl method is significant because, "for a tow duration of less than 10 minutes, the mortality rate for sea turtles is less than one percent, whereas for tows greater than sixty minutes the mortality rate rapidly increases to fifty to one hundred percent".

In the US Atlantic, the interactions were greatest for loggerheads, followed in order by Kemp's ridley, leatherback, and green sea turtles.

The incidental catch is not limited to only fish species: dolphins, sea turtles, and seabirds are also victims of bycatch.

Longlines, trawls and purse seine nets are driving factors in the endangerment of no fewer than fifteen shark species.

Longlines with bait hook attachments can potentially reach lengths of dozens of kilometres, and, along with gill nets in the water and bottom trawls sweeping the sea floor, can catch essentially everything in their path.

[27] Hook-and-line fishing could limit bycatch to a certain extent as the non-target animals can be released back to the ocean fairly quickly.

Temporary area closures are common in some bottom trawl fisheries where undersized fish or non-target species are caught unpredictably.

[29][30] In 1978, the National Marine Fisheries Service (NMFS) started to develop turtle excluder devices (TED).

The development and testing of modifications to fishing gear to improve selectivity and decrease impact is called "conservation engineering".

In March 2006, the Hawaiʻi longline swordfish fishing season was closed due to excessive loggerhead sea turtle bycatch after being open only a few months, despite using modified circle hooks.

[4][33] Seabirds get entangled in longlines by flocking around vessels, this eventually leads to drowning because they try to catch baits on the hooks.

Fisheries had been using "streamer lines" as a cost effective solution to mitigate this type of bycatch, and it has dramatically reduced seabird mortality.

These streamer lines have bright colors and are made of polyester rope, they are positioned alongside the longlines on both sides.

Their bright colors and constantly flapping of water frightens the seabirds and they fly away before reaching the baited hooks.

Sometimes bycatch is sorted and sold as food,[34] especially in Asia, Africa and Latin America, where cost of labour is cheaper.