Fishing: Catch quotas cause fish populations to fluctuate more

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Fishing: Catch quotas cause fish populations to fluctuate more
Fishing: Catch quotas cause fish populations to fluctuate more
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Catch quotas make fish populations more volatile

Restricting fisheries to large animals as a protective measure could have the opposite effect: taking away the reproductive fish leads to dangerous population fluctuations, marine biologists from Great Britain and the USA warn.

George Sugihara of the Scripps Institution in San Diego and his colleagues were able to directly compare the fish stocks of two areas in the Pacific with and without fishing as part of the "California Cooperative Oceanic Fisheries Investigations". The densities of the fish larvae over a period of fifty years served as the data basis for the population dynamics.

As expected, fewer animals lived in the fished region than in the unaffected one. However, the fished stocks showed strong population fluctuations from year to year. The researchers suspect that the capture of particularly large fish increases natural population fluctuations. This is because the reproductive animals that normally secure the stock are missing. In addition, the remaining juvenile fish are particularly sensitive to environmental changes such as periodic El NiƱo events, further weakening populations.

The current fisheries management should therefore be reconsidered, the scientists demand: not only stock densities, but also age structures of the fished stocks must be taken into account in order to avoid overfishing.

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