Fishing throws targeted species off balance, Scripps s...( Fishing activities can provoke volat...)

Fishing activities can provoke volatile fluctuations in the populations they target, but its not often clear why. A new study published in the journal Nature by scientists at Scripps Institution of Oceanography at UC San Diego and colleagues has identified the general underlying mechanism.

Research led at Scripps with a distinguished team of government and international experts (including two chief scientific advisors to the United Kingdom) demonstrates that fishing can throw targeted fish populations off kilter. Fishing can alter the age pyramid by lopping off the few large, older fish that make up the top of the pyramid, leaving a broad base of faster-growing small younglings. The team found that this rapidly growing and transitory base is dynamically unstablea finding having profound implications for the ecosystem and the fishing industries built upon it.

The data show that fished species appear to be significantly more nonlinear and less stable than unfished species, said Professor George Sugihara of Scripps. We think the mechanism involves systematic alteration of the demographic parametersand especially increases in growth rates that magnify destabilization in many wayswhich can happen as fishing truncates the age structure.

Imagine a container of water with a 500-pound fish. With food, it grows a little bigger. Without food it gets a bit smaller. Imagine the same container with 500 one-pound fish. They eat, reproduce and the resulting thousands of fish boom, quickly outstripping the resources and the population crashes. These many smaller fishwith the same initial biomass as the larger fishcant average out the environmental fluctuations, and in fact amplify them through higher turnover rates that promote boom and bust cycles.

The study that included academic and government scientists from Alaska, Asia and Great Britain is based on data from the California Cooperative Oceanic Fisheries Investigations (CalCOFI),
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