Establishing a Baseline

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Science  09 Jul 2004:
Vol. 305, Issue 5681, pp. 149
DOI: 10.1126/science.305.5681.149a

There is abundant evidence that fish stocks are being exploited at unsustainable rates in many sectors of the world's oceans. In order to gauge the extent of human impacts, it is necessary to assess where stocks stood in prefishery times; however, accurate analyses are hampered because records did not begin until many years, and often centuries, after initial exploitation.

Jennings and Blanchard have devised a method for estimating what fish abundances would be in the absence of fishing, using macroecology theory that relates abundance, biomass, predator-prey mass ratio, and efficiency of energy transfer between trophic levels in an ecosystem. Applying it to the North Sea fishery, they estimate that the current biomass of fishes larger than 4 kg is only about 2.5% of its pretrawling level, and the total biomass of all fishes is nearly 40% lower than it would have been. These effects are larger than those predicted from existing time-series data, and this approach may provide a useful basis for comparing the impacts of fishing across different ecosystems and different fish communities. — AMS

J. Anim. Ecol. 73, 632 (2004).

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