A Model of the Population Dynamics of the Blue Crab in Chesapeake Bay

This study has particular application to the blue crab fisheries in Chesapeake Bay, an economically important industry whose successful management has been hindered by relatively poor understanding of the population dynamics. Recent biological studies have indicated a systematic spawning behavior which seems designed for ejection of larvae seaward from the bay entrance where they spend their pre-metamorphosis stages in the neuston. A physical mechanism for retention of the larvae in sufficient proximity to the bay entrance for their return at the proper time which involves the action of wind stress in shallow waters is proposed. Since the supply of blue crabs in the bay may be dependent upon this action, the abundance of crabs is related to the variability of the wind stress. The consequences of a simple mathematical model of the population dynamics are described. Cohorts must originate on time intervals which are no longer than approximately one month because longer time intervals obscure critical aspects of the life cycle. Different instantaneous rates of mortality must be applied to the cohorts in order to reach numerical equilibrium. Relative abundance at equilibrium and the age structure of the population depend on whether the terminal molt hypothesis or the maximum fishable life span hypothesis is used to calculate post-recruitment total mortalities. The application of wind stress as a driving force in the life history model produced a decrease in harvest. Current levels of information about the population dynamics of this commercially important species are too poor to permit the formulation of rational harvest control regulations in Chesapeake Bay