The HCRC, headquartered at Virginia Tech University, is the only multi-investigator, multi-institutional research unit dedicated to providing the essential information needed for sustainably managing the horseshoe crab Since its creation in 2001, the HCRC has produced a steady stream of information useful for scientific and management purposes for conserve this resource that is central for protection of public health and worth more than $100 million annually the economy. Here, we briefly highlight studies conducted by the HCRC and their importance.
Management of the horseshoe crab continues to be the focus of controversy. There is increasing evidence that the horseshoe crab population is declining. The diversity of interests involved (birders, environmentalists, commercial fishers, biomedical companies, coastal residents, and the ecotourism industry) makes management especially challenging. With improved information and management, the horseshoe crab population likely could provide the LAL needed to protect public health, and also meet the needs of all users, including fishers and shorebirds (Berkson and Schuster 1999).
The most critical unknown factors in management of the horseshoe crab resource are its abundance and population dynamics. A trawl survey specifically targeting horseshoe crabs is needed for gathering that information. We developed standardized methods for conducting trawl surveys for horseshoe crabs (Hata and Berkson 2004). After demonstrating the method in the Delaware Bay (Hata and Berkson 2003), we extended it to Rhode Island and the Carolinas. We used these data to develop a surplus production model of the population (Davis et al., in review) that managers will use to assess key population reference points, providing the basis for sustainable harvest.
Because horseshoe crab sex and age ratios fluctuate annually, we have collected six years of demographic information off Chincoteague, VA (Walls 2001, Grogan 2004). In addition, a study of the movements of 12,500 crabs marked and released at Chincoteague, VA provided information on population structure (Grogan et al., in review).
The traditional method for indexing horseshoe crab abundance is by counts of breeding crabs. Klopfer et al. (2004) investigated the feasibility of a remote-sensing approach to supplement or replace these labor-intensive ground surveys. Using digital aerial photography, by comparing counts made by trained observers to actual ground-based counts, we found that interpreters tended to underestimate numbers of crabs when breeding density was high. Although this technique shows promise, it will require additional work on image acquisition and interpretation techniques.
Spawning of horseshoe crabs provides a super-abundant food resource that is believed critical for migratory shorebirds, including protected species such as red knot. In order to test this hypothesis, we first had to develop a statistical test to show that locations of individual birds are indeed independent observations (Karpanty et al., in review a). We found that presence of horseshoe crab eggs was the most significant factor determining the use of sandy beaches by red knots (Karpanty et al., in review b).
The biomedical industry bleeds horseshoe crabs to produce LAL, a product used to test the sterility of medical and pharmaceutical products. The effect of blood extraction was unknown until we showed that the differential mortality rate of bled and unbled crabs was 7.5% (Walls and Berkson 2003). Crabs utilized by the industry are subject to both bleeding and handling stress; our studies showed that transport and handling had a larger effect on mortality than the blood extraction (Hurton, Berkson, and Smith 2006; Hurton and Berkson, in review). Smith et al. (in review) showed that basic blood and immunological parameters of horseshoe crabs vary with their external environment, developmental stage and reproductive status.
Although harvest models for horseshoe crabs are based on the assumption that the harvest is comprised of one stock, results of a preliminary population genetic survey (King et al. 2003) suggest that several more-or-less distinct stocks of horseshoe crabs live along the Atlantic coast. Our group is collaborating with the Biological Resources Division of the U.S. Geological Survey to extend the range and intensity of population genetic sampling. Separate management plans will have to be developed for each genetic stock.
The fishery for horseshoe crabs, like any fishery, includes bycatch of other, untargeted species. Although the bycatch may pose issues for other valued fisheries, its composition has never been characterized. An ongoing project is characterizing the species composition of the horseshoe crab harvest.
HCRC scientists are participating members of both the horseshoe crab scientific and management communities. All work with the key scientists, managers, and agencies in prioritizing, conducting, and presenting its research. The HCRC regularly works with the Atlantic States Marine Fisheries Commission, the agency responsible for horseshoe crab management on a regular basis. The HCRC annually brings research plans and results to ASMFC's Technical Committee, where the HCRC and its research benefit from the Technical Committee's oversight and participation. Research results are provided to the ASMFC Management Board by both the Technical Committee Chairman and by regularly requested briefings by HCRC scientists.
Important HCRC collaborators include the states of Delaware and New Jersey; Cambrex, Inc., the worldwide leading producer of LAL; other universities, including Delaware State University; the U.S. Geological Survey - Biological Resources Division, and a number of non-governmental organizations including the Ecological Resources Development Group.
