Blue Crab Population Dynamics in Chesapeake Bay: Variation in Abundance (York River, 1972–1988) and Stock-Recruit Functions

Blue crab abundance in the York River, Virginia was analyzed for interannual, monthly and spatial variation at two stations sampled by bottom trawl from 1972–1988. Various stock-recruitment and recruit-stock functions were derived from trawl abundance and commercial fishery landings statistics. The key component of variation was due to interannual fluctuations in abundance, which remained consistently high or low for two or more years before changing, suggesting internal population feedback mechanisms, such as cannibalism, or long-term climatic control. In addition, significant cyclic patterns in residuals from stock-recruitment functions further indicated the existence of long-term variability in abundance. Peak seasonal abundance and lowest variation occurred from June–August. A significant year x month interaction effect was due to shifts in the time of highest seasonal abundance from summer during high-abundance years to late summer and fall in low-abundance years, suggesting differential dominance of successive year classes. Spatial variation was appreciable such that an upriver station had consistently higher catches than a downriver station, except for 2 of 17 years. A key finding concerned the significant and dome-shaped stock-recruitment relationship (Ricker model) for the trawl data. Re-examination of previous empirical and conceptual arguments against the existence of a significant stock-recruitment relationship for the blue crab indicates their invalidity. Significant surrogate effects were incorporated into the stock-recruitment relationship, including components representing prior recruiting year classes and spawning stocks, which may impact recruitment through alterations in food availability, growth and survival. A recruit-stock function was significant and indicated a correlation between juvenile abundance and a measure of spawning stock size. In concert with the preceding models, other recruit-stock functions indicate various biologically meaningful inter-relationships between different segments of the blue crab population in Chesapeake Bay.