Tom's Cove, Virginia Horseshoe Crab Tag Recovery Study: Interim Results

Hallerman, Eric

I conducted a pilot mark-recapture study to examine the hand fishery for horseshoe crabs (Limulus polyphemus) for bait in Tom's Cove on Assateague Island, Virginia. The objectives of this study were: ( 1) to infer the geographic origins of spawners, (2) to estimate the number of spawners in the population, (3) to characterize the harvest, ( 4) to track post-spawning dispersal, and, in light of all these findings, ( 5) to frame recommendations for discussion by horseshoe crab managers. Over seven thousand crabs were tagged during new and full moons in May and June 2008. Only eight crabs spawning or harvested had already been tagged; six were marked in Delaware Bay and two off of Ocean City, Maryland. Of the crabs marked in this study, 1,019 were recaptured in the commercial fishery. The estimated size of the spawning population was 69,500 individuals, although there were issues of violations of assumptions underlying mark-recapture studies. After spawning, horseshoe crabs dispersed. Fifty-eight marked crabs subsequently were collected in offshore biomedical and research trawls, and 57 marked crabs were observed and reported by members of the general public. Resighted crabs most frequently were observed in Tom's Cove or the Ocean City, Maryland areas, although some dispersed further to the northeast. The picture emerging from this study, building upon earlier mark-recapture and genetics studies, is that the Tom's Cove, VA population is linked demographically to the Delaware Bay population. Findings will be shared with the Horseshoe Crab Technical Committee of the Atlantic States Marine Fisheries Commission and with relevant state and federal marine resources management agencies.