|Author(s)||Morizur Yvon, Caillart B, Tingley D|
|Source||Encyclopedia of Life Support Systems (Eolss), 1999|
|Keyword(s)||Marine, Wastage, Overview, World, Social, Economic, Ecology, Biology, Impact, Target, Species, Gear, Fishery, Bycatch, Catch, Discards|
|Abstract||Introduction : It is now clear that the world's fishery resources are being subjected to exploitation at or above their capacity to produce maximum sustainable yields. At the same time as these trends are being felt, there is a very large wastage of fishery resources from discarding unwanted catches at sea. At the end of each fishing operation a part of the catch is often returned to the sea after sorting by the fishermen. A 1994 FAO report provided an estimate of global discards in commercial fisheries of 27 millions of tons per year compared to 50 million tons of direct human consumption. A more recent FAO document estimated that discards were in the order of 20 million tons in 1997.
The majority of the world's fisheries are multi-species in nature and consequently it is difficult to optimize management measures for all the species caught. Management measures are most often decided from the target species perspective. However, total catches are a compound of commercial species and also non-commercial and prohibited species. In addition, catches often contain juvenile commercial species. The use of selective gears attempts to avoid capture of these young, small-sized fish. Normally the technical regulatory measures include gear characteristics (e.g. mesh size in nets) and also minimum landing sizes in an attempt to ensure fishermen use the most appropriate gears and so limit discards.
Discards that cause the most problem are of species or individuals which do not survive when they are returned to the sea. The survival rate depends on the combination of species and fishing practice (e.g. gears). Towed gears generate low survival rates whilst at the other end of the spectrum, fixed gears do not generally damage individuals and so have very low discard mortality rates. Crustaceans, for example, have a higher survival rate after release than many fish species.
Morizur Yvon, Caillart B, Tingley D (1999). The problem of discards in fisheries. Encyclopedia of Life Support Systems Open Access version : https://archimer.ifremer.fr/doc/00000/1237/