Fisheries Impacts on North Atlantic Ecosystems: Models and analyses
Part1. Analysis of biomass trends
Ecosystems of the past: how can we know since we weren't there?
Villy ChristensenAbstract
Most reconstructions of historic abundances for marine organisms have been done on a species by species basis. It is argued here that assembling such reconstructions and working at the ecosystem level makes it more feasible to evaluate the consistency of historic estimates. If we construct ecosystem models of past ecosystems based on present ecology and historic exploitation patterns, we can use information about system form and function to evaluate past abundances. This can in turn be used to describe the parts of the systems for which we do not have information. A modeling approach, Ecopath, which has been used for such ecosystem reconstructions is presented, and it is discussed how it can be used for historic and pre-historic reconstructions. Application is exemplified through a case study of the Strait of Georgia ecosystem, British Columbia, Canada, where ecosystems models were constructed to represent the present, a hundred, and five hundred years ago. The model construction was part of a multidisciplinary project, including fisheries ecologists, marine historians, archaeologists, economists, along with fishers and others with local knowledge of a system and its history who, jointly parameterized, evaluated and discussed the models and the ecosystems they represented. The reconstruction serves to provide a baseline for evaluation of present day ecosystems and the human impact on these.