Sixteen lessons from a 40-year quest to understand the mysterious life of the grey triggerfish

Abstract

Abstract Fish stock assessments based solely on energy flow through the ecosystem are not good predictors of population dynamics. To accurately forecast the response of populations within one or more ecological regimes, consideration must be given to non-trophic mechanisms allowing interactions inside the system, and fish behaviour in response to changes in their habitats. The example of the grey triggerfish (Balistes capriscus) in West Africa shows that fisheries biology is unable to model satisfactorily the life of a fish population. The Ecosystem Approach to Fisheries improves the models but does not overcome this fundamental limitation. Data from direct observations of fish biology and behaviour must be added to the catch and environmental data to help to design energetic-cybernetic models in order to anticipate non-linear and chaotic dynamics. This requires adding data collected by fishers (e.g. underwater acoustics) to scientific data bases, conceiving environmental indicators (e.g. habitat), and using scenarios to anticipate the reactions of populations to regime shifts. It also requires a good understanding of the population structures and strategies. We developed the concept of “pelagic metapopulation” which, through comparative analysis with the jack mackerel (Trachurus murphyi), allowed us to propose a hypothesis explaining the history of the grey triggerfish population.