A production modeling approach to the assessment of the horseshoe crab (Limulus polyphemus) population in Delaware Bay


Davis, Michelle L., Jim Berkson, and Marcella Kelly
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Horseshoe crab (Limulus polyphemus) is harvested commercially, used by the biomedical industry, and provides food for migrating shorebirds, particularly in Delaware Bay. Recently, decreasing crab population trends in this region have raised concerns that the stock may be insufficient to fulfill the needs of these diverse user groups. To assess the Delaware Bay horseshoe crab population, we used surplus production models (programmed in ASPIC), which incorporated data from fishery-independent surveys, fishery-dependent catch-per-unit-of-effort data, and regional harvest. Results showed a depleted population (B2003/BMSY=0.03−0.71) and high relative fishing mortality (F2002/FMSY=0.9−9.5). Future harvest 2002 strategies for a 15-year period were evaluated by using population projections with ASPICP software. Under 2003 harvest levels (1356 t), population recovery to BMSY would take at least four years, and four of the seven models predicted that the population would not reach BMSY within the 15-year period. Production models for horseshoe crab assessment provided management benchmarks for a species with limited data and no prior stock assessment.