Modeling the dynamics of ecosystem for the American lobster in the Gulf of Maine

The objective of this study is to evaluate impacts of different management scenarios for American lobster (Homarus americanus) and Atlantic cod (Gadus morhua) fisheries on the dynamics of ecosystem for the lobster in the Gulf of Maine (GOM). The GOM lobster supports one of the most economically valuable commercial fisheries in the northeastern United States. The GOM ecosystem has experienced a great change over the last two decades, switching from a groundfish-dominated ecosystem to a lobster-dominated ecosystem. An evaluation of the GOM ecosystem dynamics can help identify possible causes of such a change and improve our understanding of interactions between lobster and other species in the same ecosystem. In this study, we developed a 24-group Ecosim model to quantify the ecosystem dynamics in the GOM from 1985 to 2007. We developed a Monte Carlo simulation approach to incorporate uncertainties for 15 most sensitive vulnerabilities. We found that the GOM ecosystem dynamics could be generally well simulated using the Ecosim model compiled in this study. A high fishing mortality in cod could result in high lobster stock biomass, suggesting that higher fishing pressure on cod in the 1980s might contribute to the high lobster biomass in recent years. A higher fishing mortality for lobster would have led to a lower lobster biomass. The change in the fishing mortality of cod and lobster would also affect the biomass dynamics of other functional groups, indicating that the Atlantic cod and American lobster fisheries played an important role in the change of the GOM ecosystem in the last two decades.