933 



Abundance of horseshoe crabs 

 (Limulus polyphemus) 

 in the Delaware Bay area 



David Hata 



Jim Berkson 



Department of Fisheries and Wildlife Sciences 

 Virginia Polytectinic Institute and State University 

 Blacksburg, Virginia 24061-0321 

 E-mail address (for J Berkson, contact author) iberksoniffivtedu 



III recent years, increasing commercial 

 landings of horseshoe crabs {Limulus 

 polyphemus) along the Atlantic coast of 

 the United States have raised concerns 

 that the present resource is in decline 

 and insufficient to support the needs 

 of its user groups. These concerns have 

 led the Atlantic States Marine Fisher- 

 ies Commission ( ASMFC ) to implement 

 a fishery management plan to regulate 

 the harvest (ASMFCM. In order to 

 properly manage any species, specific 

 management goals and objectives 

 must be established, and these goals 

 depend on the resource users involved 

 (Quinn and Deriso, 1999). Horseshoe 

 crabs present a distinct resource 

 management challenge because they 

 are important to a diverse set of users 

 (Berkson and Shuster, 1999). 



Horseshoe crabs lay their eggs on 

 sandy beaches in spring and summer, 

 and migrating shorebirds rely heav- 

 ily on the eggs to supply the energy 

 required to complete their migration 

 (Rudloe, 1980; Shuster and Botton, 

 1985; Castro and Myers, 1993; Botton 

 et al., 1994; Myers, 1996; Thompson, 

 1998; Tsipoura and Burger, 1999). 

 Biomedical companies catch horseshoe 

 crabs for their blood, from which they 

 produce Limulus Amebocyte Lysate 

 (LAL) (Novitsky 1984; ASMFCi). LAL 

 is used to detect contamination of in- 

 jectable drugs and implantable devices 

 by Gram-negative bacteria and is the 

 most sensitive means available for 

 detecting endotoxins (Novitsky, 1984). 

 Finally, horseshoe crabs are harvested 

 commercially for bait in the American 

 eel (Anguilla rostrata), catfish (Ictci- 

 lurus spp.), and whelk (Busycon spp.) 

 fisheries (ASMFC). 



The goal of the ASMFC fishery man- 

 agement plan is to ensure a sustainable 

 population level that will support the 

 continued use by these diverse ecologi- 

 cal, biomedical, and fishing interests 

 (ASMFC). Proper management of the 

 resource requires information on the 

 status and dynamics of the horseshoe 

 crab population (Berkson and Shus- 

 ter, 1999). However, the status of the 

 population is poorly understood, and 

 there is currently no reliable informa- 

 tion on which to base any management 

 scheme. Available fishery-independent 

 surveys were not designed for horse- 

 shoe crabs, and are of little or no value 

 in assessing their status (ASMFC'^). 

 Towards this end, the states of New 

 Jersey, Delaware, and Maryland in 

 conjunction with the ASMFC and the 

 National Fish and Wildlife Foundation, 

 funded a pilot benthic trawl survey for 

 the fall of 2001. Data collected during 

 this pilot trawl survey were used to es- 

 timate the horseshoe crab population 

 size in the Delaware Bay area. 



Methods 



This study was conducted in the vicin- 

 ity of Delaware Bay, which is the center 

 of abundance for horseshoe crabs on 

 the Atlantic coast (Shuster, 1982). The 

 study area extended from north of Cape 

 May, New Jersey, to south of Ocean City, 

 Maryland (39°10'N to 38°10'N), and 

 from shore out to 22,2 km (Fig. 1). The 

 area was divided into four strata based 

 on distance from shore and topography, 

 both of which influence crab distribu- 

 tion. Distance from shore was con- 

 sidered important because horseshoe 



crab abundance decreases with depth 

 (Botton and Ropes, 1987a). Therefore, 

 the area was split into an inshore zone 

 from to 5.6 km (0 to 3 nautical miles 

 [nmi] ) from shore and an offshore zone 

 from 5.6 to 22.2 km (3 to 12 nmi) from 

 shore. Topography was also consid- 

 ered important because commercial 

 fishermen stated that crabs are more 

 abundant in troughs (Burke^; Eutsler'*; 

 Munson^). For this study, troughs were 

 defined as at least 2.4 m deep, no more 

 than 1.8 km wide, and more than 1.8 

 km long. These dimensions are common 

 for troughs identified as important by 

 the fishermen. The inshore and off- 

 shore zones were both further divided 

 into trough and nontrough areas. The 

 resulting strata were inshore trough, 

 inshore nontrough, offshore trough, 

 and offshore nontrough. 



The study area was divided into grids 

 of one-minute latitude by one-minute 

 longitude. A grid was considered in- 

 shore if the majority of its area was in 

 water and inshore of the 5.6-km divid- 

 ing line. A grid was considered offshore 

 if the majority of its area was offshore 

 of the 5.6-km dividing line and inshore 

 of the 22.2-km boundary. A grid was 

 also considered a trough if the long ax- 

 is of a trough passed through the grid. 



• ASMFC (Atlantic States Marine Fisheries 

 Commission). 1998. Interstate fishery 

 management plan for horseshoe crab. 

 Fishery management report no. 32, 58 p. 

 Atlantic States Marine Fisheries Com- 

 mission. 1444 Eye Street, NW, Sixth Floor, 

 Washington, DC 20005. 



2 ASMFC. 1999. Horsehoe crab stock 

 assessment report for peer review. Stock 

 assessment report No. 98-01 (supplement), 

 47 p. Atlantic States Marine Fisheries 

 Commission, 1444 Eye Street, NW, Sixth 

 Floor, Washington, DC 20005. 



■* Burke, C. 2001. Personal commun. 25 

 Cove Drive, North Cape May, NJ 08204. 



■* Eutsler, J. 2001. Personal commun. 

 11933 Gray's Corner Road, Berlin, MD 

 21811. 



^ Munson, R. 2001. Personal commun. 

 Box 358, Newport, NJ 08345. 



Manuscript approved for publication 

 6 March 2003 by Scientific Editor 



Manuscript received 22 July 2003 at 

 NMFS Scientific Publications Office. 



Fish Bull. 101:933-938 (2003). 



