'School-mix feedback': a different way to think about low frequency variability in large mobile fish populations

A conceptual perspective is introduced which appears to convey substantial explanatory power with respect to some prominent current issues in fisherie s ecology, including evident regime shifts in resource productivity and/or in species dominance. Underpinning the proposed perspective are two key ide as. These are the 'school trap' concept and the notion of 'affinities' to s pecific ocean features or locations that may characterize individual fish. These two ideas lead to a mechanism, here termed 'school-mix feedback', by which mobile fish populations may automatically track low frequency environ mental and ecosystem variability and make particularly rapid adaptive adjus tments of behaviors and migratory tendencies to the associated changes in c onditions. However the mechanism also appears to involve the possibility th at a fish population could thereby fall into a short-period analog to an ev olutionary feedback trap, from which it may not easily extricate itself wit hout undergoing population collapse. Analogous adaptive responses to geogra phically-biased fishery exploitation may upset the integrity of naturally-e volved systems and potentially lead to chronic suppression of resource prod uctivity. Possibilities for innovative adaptive management actions are sugg ested. Both heuristic and real explanatory examples are cited, in most case s dealing with pelagic fish stocks and upwelling ecosystems. (C) 2001 Elsev ier Science Ltd. All rights reserved.