A review of a model for qualitative evaluation of exploitation levels in multi-species fisheries

The fauna of inland waters, especially in the tropics, consist of complex assemblages of numerous species, which are not accessible to analysis by conventional stock assessment methods. The formulation of policies for management and conservation requires alternative models which are capable of predicting the ways in which such assemblages change in response to fishing or other stresses. Historically, models which group species according to simple parameters have proved adequate to provide the level of advice needed to indicate ecosystem health and sustainability of yield from the fishery. Such models have received relatively little attention, and can be profitably further developed and refined. The present review concludes that, out of the various explanatory variables, the mean length of fish caught is one of the most significant together with the numbers of species in the catch and the time taken for catches in fluctuating systems to respond to floods. More complex indicators are based on emergent characteristics of the system such as the production:biomass or predator:prey ratios. Three major strategies are identified for management based on responses of fish assemblages to increases in effort.