DEVELOPMENT OF LIFE-STAGE-SPECIFIC INDEXES OF RELATIVE ABUNDANCE AND STOCK-RECRUITMENT RELATIONSHIPS FOR THE DELAWARE BAY BLUE-CRAB STOCK

We analyzed 18 years of research trawl data from Delaware Bay to asses s the life history, stock-recruitment relations and trends in abundanc e of blue crabs. Six indices of relative abundance were developed: the young of the year index, the index of recruits, the index of large cr abs, the year-class index of large crabs, the index of spawning stock (ISS) and the index of spawning stock biomass (ISSB). The index of rec ruits and the index of large crabs were validated against commercial l andings data. The indices show that the stock was at relatively low ab undance for the first 7 years, then climbed to higher abundance in the mid-1980s. A positive trend in the index of recruits and the index of large crabs was detected during the Ii-year time series; there was no trend in the young of year (YOY) index. Over the last decade, the ind ices of spawning stock and spawning stock biomass have shown significa nt declining trends. The YOY index is a significant predictor of indic es of later life stages, with a curvilinear model producing the best f it, indicating that density-dependent mortality occurs between the YOY stage and the recruit and large crab stages. The index of recruits pr edicts the index of large crabs. No relation was detected between any index and the index of spawning stock biomass. Removal of one datapoin t gave a significant fit to both a linear regression of recruits on tw o measures of spawning stock size and a nonlinear Ricker stock-recruit ment model. These two models have significantly different management i mplications. We also discuss the implications of continental shelf dis persal of larvae for stock-recruitment relations.