( Systematic overfishing of fresh waters ...)Overfishing in inland waters reduces biodiversity and threatens health

Although the status of inland waters and their fish species should be of broad concern, threats to freshwater fisheries and associated biodiversity have received scant attention from conservation groups and the media, according to author J. David Allan of the University of Michigan and his colleagues. Allan and colleagues refer to the relative lack of attention to fresh waters as a "dangerous" imbalance, since freshwater ecosystems are by some accounts more threatened than marine ecosystems.

Fishing is a crucial source of livelihoods in developing nations, and in 2000 constituted an estimated 15.3 percent of human consumption of animal protein. About 1 billion people rely on fish as their primary protein source. Landings from inland waters have increased more than fourfold since 1950, mainly in developing nations, though in developed countries, in contrast, catches have decreased. But catch statistics are difficult to interpret for inland species because they may exclude recreational and illegal fisheries, and because landings are dispersed. Moreover, overfishing may not immediately cause declines in the total catch––and its weight may even transiently increase. Overfishing leads to numerous changes in both the target species and other species. Larger individuals and species are often successively replaced in the catch by smaller ones. At the same time, some fish populations respond to fishing pressure with reductions in mean size at maturation.

Allan and colleagues identify two main types of overfishing. One leads to marked declines in catch per unit effort and size of individuals captured. The second type is characterized by sequential declines of species and depletion of individuals and species of large size, e
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Source:American Institute of Biological Sciences