Commercial fishermen are now harvesting "food" fishes, severely affecting the marine food web
scientists and marine biologists have warned that catching of species that other fishes prey on will lead to collapse of marine ecosystems in the years to come. In eastern Canada, fisherfolk generally fish cod. As cod populations are depleting, they have resorted to catching shrimp, the cod's natural prey. In Europe, herring -- once considered a trash fish -- is increasingly being harvested.
Although it was long believed by fisheries experts that such a shift was taking place, a study conducted by David Pauly, fisheries biologist at University of British Columbia in Vancouver, Canada, has provided enough evidence for this. The study combined two sets of data. One was the fisheries statistics obtained from the United Nations Food and Agricultural Organisation ( fao ), while the other one was the analysis of food web.
Pauly and his colleagues assigned each marine species to one of the four different levels in the food web. On level four are predators like sharks, swordfish and tuna. On level one, at the bottom, are the grass, detritus and algae.
By combining the fao 's statistics on worldwide catches with the data of the position of each species against the scale of one to four, they concluded that overall global fish catch declined to 3.4 from 3.7 in the 1950's. Pauly said that "many marine food webs will be collapsing on themselves in three or four decades", meaning that in the years to come, the marine food chain will be disrupted severely.
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