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Fishing down the food web
Fishing down the food web is the process whereby fisheries in a given ecosystem, "having depleted the large predatory fish on top of the food web, turn to increasingly smaller species, finally ending up with previously spurned small fish and invertebrates."〔Pauly, Daniel and Watson, Reg (2009) ("Spatial Dynamics of Marine Fisheries" ) ''In:'' Simon A. Levin (ed.) ''The Princeton Guide to Ecology''. Pages 501–509.〕
The process was first demonstrated by the fisheries scientist Daniel Pauly and others in an article published in the journal ''Science'' in 1998.〔Pauly D, Christensen V, Dalsgaard J, Froese R and Torres F (1998) ("Fishing down marine food webs" ) ''Science'', 279: 860-863.〕 Large predator fish with higher trophic levels have been depleted in wild fisheries. As a result, the fishing industry has been systematically "fishing down the food web", targeting fish species with trophic levels that are progressively decreasing.
The trophic level of a fish is the position it occupies on the food chain. The article establishes the importance of the mean trophic level of fisheries as a tool for measuring the health of ocean ecosystems. In 2000, the Convention on Biological Diversity selected the mean trophic level of fisheries catch, renamed the "Marine Trophic Index," as one of eight indicators of ecosystem health. However, many of the world's most lucrative fisheries are crustacean and mollusk fisheries.〔 ("Global fishery development patterns are driven by profit but not trophic level" )〕
==Overview==
Over the last 50 years, the abundance of large predator fish, such as cod, swordfish and tuna, has dropped 90 percent.〔Myers RA and Worm B (2003) ("Rapid worldwide depletion of predatory fish communities" ) ''Nature'' 423: 280-283.〕 Fishing vessels now increasingly pursue the smaller forage fish, such as herrings, sardines, menhaden and anchovies, that are lower on the food chain.〔 “We are eating bait and moving on to jellyfish and plankton” says Pauly.〔(UBC PublicAffairs: News ) 5 October 2006.〕 Beyond this, the overall global volume of fish captured has been declining since the late 1980s.〔Watson, R and Pauly D (2001) ("Systematic distortions in world fisheries catch trends" ) Nature 414: 534-536.〕
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