Multi-Species And Ecosystem Models In A Management Context

The final decades of the 20th century saw the emergence and first applications of multi-species models of marine ecosystems along with a general recognition of the potential importance of taking into account multi-species interactions when managing fisheries.Multi-species effects can include biological and technical interactions. Technical interactions frequently are of concern, for example when discards of certain species are believed to be a consequence of the management system. Biological interactions may fundamentally change the perspective of how to utilize an ecosystem, since a fishery or a moratorium on a predator may completely change the survival of a prey and, conversely, fishing on a prey may affect the growth of a predator.Modern research on multi-species modelling is highly multidisciplinary in nature, drawing on expertise from fishery science, fish biology, ecology, hydrography, mathematics, statistics, economics, operations research and computer science. As the models become more detailed and complex, they are able to address more issues that are of concern to managers, but at the same time it becomes ever more difficult to interpret results.Fundamental issues are raised in the multi-species context, and particularly so when fishing is viewed in the light of the precautionary approach. Some multi-species research has indicated that heavier fishing with smaller mesh sizes may lead to more profits for the fishing industry, whereas most earlier single-species research has indicated that low fishing pressure, particularly on juveniles, would be beneficial for the resource and the fishery. Conclusions from other research have indicated that economic considerations such as maximum economic yield may not be applicable, and have failed to lead to sustained utilization, whereas the traditional view has been that long-term economic views generally will lead to sustainable use of the resources.This chapter seeks to resolve some of these apparent conflicts, drawing on the multi-disciplinary nature of fishery science. It is seen that almost all points of view lead to the conclusion that fishing with low fishing pressure is not only sustainable but in accordance with the precautionary approach. Further, almost all multi-species concerns strengthen the need for reduced fishing pressure.It is also argued that simple management measures such as quotas, effort control or areal closures alone may not suffice to maintain viable fisheries in multi-species ecosystems.