Assessment of the Maine Lobster Fishery with Surplus Production Models

Abstract

A long series of catch and effort data was available for assessment of the impact of fishing on the American lobster (Homarus americanus) population off the coast of Maine and the data indicated both the ascending and descending limbs of the equilibrium stock production curve. The logistic and the Fox surplus production models were applied and both models accounted for most of the observed variation in yield in terms of variation in fishing effort and stock biomass. Although the catch data appear to indicate a developing fishery, both models indicated that stock biomass was severely depleted in 1928 when continual collection of annual catch and effort data began. There was little difference between the equilibrium stock production curves of the two models below the optimum level of exploitation but, for high levels of effort, the logistic model predicted a rapid decrease in equilibrium yield with increasing effort whereas the Fox model predicted a slow decline in equilibrium yield with increasing effort. The data were not adequate to clearly identify which model more accurately describes the fishery. Although the models account for most of the variation in yield, additional factors such as a changing environment and changes in regulations also may be important.