MEPS 226:45-61 (2002)  -  doi:10.3354/meps226045

ABSTRACT: Conservation of exploited marine populations requires knowledge of interannual variation in the characteristics of and relationships between the spawning stock and recruitment, which determine population resilience and persistence. We examined relationships between spawning stock abundance, postlarval recruitment, larval abundance, and female size of the blue crab in Chesapeake Bay, both within the spawning grounds over a 13 yr interval (1988 to 2000) and within lower-bay tributaries over 20 yr (1979 to 1998). Our findings establish that there has been a concurrent, persistent and substantial reduction in the spawning stock, recruitment, larval abundance, and female size. Specifically, in 1992 to 2000: (1) spawning stock abundance declined by 81%, female size by 8%, and spawning stock biomass by 84%; (2) mean size at maturity (L_m) diminished by 9%; (3) larval abundance and postlarval recruitment were lower by approximately 1 order of magnitude compared with earlier years. The decrease in these variables was rapid, occurring over 1 to 2 yr, and therefore indicative of a phase shift in the spawning stock and recruitment, rather than a progressive diminution. We propose that the initial descent resulted from poor recruitment in 1991, despite high spawning stock and larval abundance, and that the poor recruitment in 1991, in concert with high fishing and natural mortality, subsequently led to a diminished spawning stock in 1992 and thereafter. We further suggest that the spawning stock, larval abundance, and recruitment are unlikely to rebound to former high levels without significant reductions in fishing and natural mortality along with enhanced environmental conditions conducive to successful recruitment. The key consequences of a diminished spawning stock and recruitment are a heightened probability of recruitment failure and reduced resilience to demographic and environmental stochasticity. In addition, the relationships between spawning stock abundance (SSA) and larval abundance, SSA and postlarval recruitment, and SSA and female size were positive and significant. The demonstration of a concurrent decrease and significant association between spawning stock abundance and recruitment, larval abundance and female size is unique for the blue crab and for marine invertebrates in general, and indicates an urgent need to conserve the spawning stock for long-term sustainable exploitation and population persistence.

KEY WORDS: Conservation · Blue crab · Callinectes sapidus · Spawning stock · Recruitment · Larval abundance · Exploitation