In conjunction with Cambrex, a biomedical company that utilizes horseshoe crabs for the production of Limulus Amoebocyte Lysate (LAL), a study was conducted to investigate movement patterns and population distributions of horseshoe crabs to increase understanding of mid-Atlantic horseshoe crab populations. In addition, areas of the shoreline of Tom's Cove, Assateague Island, Virginia were investigated as possible locations for annual spawning surveys. Twelve thousand five hundred horseshoe crabs were tagged and released in Chincoteague, Virginia and Ocean City, Maryland as part of a movement study; 431 (3.45%) were reported as resights. The mean distance between site of release and site of recapture for all resighted crabs was 68.3 km; maximum distance moved was 493.7 km. During 1999-2004, demographic data were collected from horseshoe crabs harvested in Chincoteague, VA and Ocean City, MD. The proportion of females (p < 0.0001) and juveniles (p < 0.0001) sampled varied from year-to-year, but no trends were observed. This study also showed that a greater proportion of females were observed in the juvenile cohort sampled compared to the adults sampled (p < 0.0001). The spawning survey revealed that spawning activity in Tom's Cove varied between years. On May 30th, 2003, 1,192 horseshoe crabs were observed spawning on the northern shoreline of Tom's Cove. The maximum number of horseshoe crabs observed spawning in the same area in 2004 was 94. This study provides no evidence for isolated subpopulations in Chincoteague, VA or Ocean City, MD. It also shows that horseshoe crab sex and age ratios fluctuate annually, therefore requiring a long time series of data to detect trends. / Master of Science

Horseshoe crabs (Limulus polyphemus) have been harvested along the east coast of the United States since the 1800s, however a Fishery Management Plan (FMP) was only recently created for this species. To date, there have not been any studies that have attempted to identify or quantify bycatch in the horseshoe crab trawl fishery. A horseshoe crab trawl survey was started in 2001 to collect data on the relative abundance, distribution, and population demographics of horseshoe crabs along the Atlantic coast of the United States. In the present study, species composition data were collected at sites sampled by the horseshoe crab trawl survey in 2005 and 2006. Seventy-six different taxa were identified as potential bycatch in the horseshoe crab trawl fishery. Non-metric multidimensional scaling (NMS) was used to cluster sites and identify the spatial distribution of taxa. Sites strongly clustered into distinct groups, suggesting that species composition changes spatially and seasonally. Species composition shifted between northern and southern sites. Location and bottom water temperature explain most of the variation in species composition. These results provide a list of species that are susceptible to this specific trawl gear and describe their distribution during fall months throughout the study area. Identifying these species and describing their distribution is a first step to understanding the ecosystem-level effects of the horseshoe crab trawl fishery. / Master of Science