A Model Of Aggregate Biomass Tradeoffs

No abstracts are to be cited without prior reference to the author.

Multi-species and ecosystem based approaches to fisheries management provide alternate and complimentary views of fishery ecosystems. This work provides an example of the need to consider species interactions when evaluating and establishing management goals. Given the caveats of scale and variability, there is a finite amount of biological production within ecosystems. These carrying capacity limits to all levels of biomass production can lead to difficult choices about the allocation of production and biomass among commercially valuable finfish. I present a model based upon the functional guild approach to explore various scenarios for a hypothetical food web, roughly analogous to the finfish community of the U.S. northwest Atlantic. The model, an extension of simpler production models, has both ecological and abiotic constraints and accounts explicitly for predation, competition, and harvest. Model simulations show greater stability of biomass at the guild level when compared to the species level, irrespective of species composition within a guild. Individual species biomasses within a guild are typically much more dynamic. Fishing and abiotic conditions are the more dominant factors changing total guild biomass when compared to internal ecological dynamics. Scenarios with excessive fishing demonstrate a tendency to forego biomass relative to the potential carrying capacity in an ecosystem. These simulations mimic observations of the U.S. northwest Atlantic finfish community from the past 40 years. Using aggregate models such as the one presented here will generally provide more conservative harvest reference points and are likely to be valuable tools for further implementation of the precautionary approach.