The month that saw the passing of David Cushing, perhaps Britain's leading marine fisheries ecologist, also saw evidence in Nature for his little-known theory of stochastic regulation of fish stocks.
Coilín Minto and his colleagues show that both the survival and variability of fish larvae increases as the size of the population declines to give a density-dependent regulation (C. Minto, R. A. Myers and W. Blanchard Nature 452, 344–347; 2008). Christian Anderson and his co-workers further explain how changes in the demographics of populations can generate these effects, which are magnified by fishing (C. N. K. Anderson et al. Nature 452, 835–839; 2008).
Almost 20 years ago, Cushing and John Shepherd speculated that increased variability in larval survival provides the strong regulation that allows intensive fishing, and demonstrated the effects through modelling (J. G. Shepherd and D. H. Cushing Phil. Trans. R. Soc. Lond. B 330, 151–164; 1990).
At the time, the hypothesis was left as plausible, likely even, but unresolved, as examinations of data proved inconclusive. The recent metadata analyses in Nature provide support for more variability when the population is small and so confirm at least a role for stochastic regulation in fish stocks. The analyses also reveal little or no clear increase in variability in many fish stocks, including many cod stocks. Other regulatory mechanisms might also exist.
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Horwood, J., Shepherd, J. Analyses support theory of stochastic regulation of fisheries. Nature 453, 586 (2008) doi:10.1038/453586d