'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 fisheries ecology, including evident regime shifts in resource productivity and/or in species dominance. Underpinning the proposed perspective are two key ideas. These are the 'school trap' concept and the notion of 'affinities' to specific 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 environmental and ecosystem variability and make particularly rapid adaptive adjustments of behaviors and migratory tendencies to the associated changes in conditions. However the mechanism also appears to involve the possibility that a fish population could thereby fall into a short-period analog to an evolutionary feedback trap, from which it may not easily extricate itself without undergoing population collapse. Analogous adaptive responses to geographically-biased fishery exploitation may upset the integrity of naturally-evolved systems and potentially lead to chronic suppression of resource productivity. Possibilities for innovative adaptive management actions are suggested. Both heuristic and real explanatory examples are cited, in most cases dealing with pelagic fish stocks and upwelling ecosystems. (C) 2001 Elsevier Science Ltd. All rights reserved.