By-catch

Bycatch, in the fishing industry, is a fish or other marine species that is caught unintentionally while catching certain target species and target sizes of fish, crabs etc. Bycatch is either of a different species, the wrong sex, or is undersized or juvenile individuals of the target species. The term "bycatch" is also sometimes used for untargeted catch in other forms of animal harvesting or collecting.

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". Bycatch contributes to fishery decline and is a mechanism of overfishing for unintentional catch.

The fisherman bycatch issue originated due to the “mortality of dolphins in tuna nets in the 1960s”

There are at least four different ways the word "bycatch" is used in fisheries:

Given the popularity of recreational fishing throughout the world, a small local study in the US in 2013 suggested that discards may be an important unmonitored source of fish mortality.

The highest rates of incidental catch of non-target species are associated with tropical shrimp trawling. 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. They found discard rates (bycatch to catch ratios) as high as 20:1 with a world average of 5.7:1.

Shrimp trawl fisheries catch 2% of the world total catch of all fish by weight, but produce more than one-third of the world total bycatch. American shrimp trawlers produce bycatch ratios between 3:1 (3 bycatch:1 shrimp) and 15:1(15 bycatch:1 shrimp).

Trawl nets in general, and shrimp trawls in particular, have been identified as sources of mortality for cetacean and finfish species. When bycatch is discarded (returned to the sea), it is often dead or dying.

Tropical shrimp trawlers often make trips of several months without coming to port. A typical haul may last 4 hours after which the net is pulled in. Just before it is pulled on board the net is washed by zigzagging at full speed. The contents are then dumped on deck and are sorted. An average of 5.7:1 means that for every kilogram of shrimp there are 5.7 kg of bycatch. In tropical inshore waters the bycatch usually consists of small fish. The shrimps are frozen and stored on-board; the bycatch is discarded.

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