Competition Between Marine Mammals and Fisheries—Can We Successfully Model This Using ECOPATH with ECOSIM?

摘要

Perceived conflicts between marine mammals and fisheries targeting common sources of food have come increasingly to the fore in recent years. Escalating pressures on shared resources are expected in the future because of both increasing marine mammalpopulations and the needs of an increasing human population. Hence there is an urgent need for scientific evaluations to estimate the existence and extent of possible competition in a reliable manner. In particular, there is a need to critically review the modeling methods used to attempt to quantify the predicted effects of marine mammal reductions on fisheries and, conversely, the effects of increases or decreases in fishery catches on marine mammal populations. Given that the ECOPATH with ECOSIM (EwE) modeling approach is currently dominating attempts world-wide to provide information on how ecosystems are likely to respond to changes in fishery management practices, the applicability of this approach to answering three questions in this context isdiscussed. The extent to which the assumptions underlying this approach are appropriate and either predetermine or have implications for the results obtained is considered. Specific examples discussed are the hake-seal-fishery interactions off the west coast of South Africa, the postexploitation recoveryof whale stocks off Antarctica, and Antarctic predator requirements for krill off Antarctica. EwE has limited predictive capability in these contexts due inter alia to the high residual variability in these systems, the important role of abiotic and biotic mesoscale (o [100 km]) processes, life history handling and insufficient flexibility in the preset model structure to simulate hypothesized causative mechanisms adequately. However, EwE applications based on good data and that adequately reflect uncertainty have an important role to play in exploring broader aspects of ecosystem structure.