The impact of pelagic fish behaviour on fisheries
T.J. Pitcher

This paper details the mismatch between human fisheries and the behaviour that has evolved to fit pelagic fishes to their niche. Behavioural adaptations of pelagic fishin feeding, spawning, migration and schooling are driven by the opportunity to exploit high levels of planktonic production: the highest levels are intrinsically patchy. On an annual scale, the mismatch generates volatility, range reduction and catchability-led stock collapse (CALSC). On a time scale of decades, the human response to uncertainty in pelagic fisheries has been to develop ever more effective levels of fish catching technology. Three quantitative models of catchability collapse are explored. The nonequilibrium Schaefer surplus production model is used for baseline comparisons: catch-per-unit-effort is directly proportional to stock abundance and the catchability of fish is constant. This model is remarkably resilient against rapid stock collapse. In the Csirke-MacCall model, catchability increases with decreasing abundance and the stock is led into a CALSC at catch rates only slightly above the Schaefer MSY. This paper introduces a new model in which catch-per-unit-effort is constant while catchability is directly proportional to stock size, the opposite of standard fishery theory but congruent with the effects of high-technology fisheries. In this model CALSC can occur very rapidly. The social behaviour that makes CALSC possible is a behavioural response that can act, in concert with adverse environmental change, to exacerbate stock collapse. Management of pelagic fisheries must recognise that the behaviour of pelagic fishes, tuned by evolution for persistence in this volatile niche, can make human exploitation of this resource a fragile enterprise.

Keywords: Pelagic fishes, schooling behaviour, stock collapse, fisheries management.
Contents of this volume Sci. Mar. 59(3-4) : 295-306 Back PDF
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