215 



Abstract — Horseshoe crab {Liiuuhis 

 polyphemus) is harvested commer- 

 cially, used by the biomedical indus- 

 try, and provides food for migrating 

 shorebirds, particularly in Delaware 

 Bay. Recently, decreasing crab popula- 

 tion trends in this region have raised 

 concerns that the stock may be insuf- 

 ficient to fulfill the needs of these 

 diverse user groups. To assess the Del- 

 aware Bay horseshoe crab population, 

 we used surplus production models 

 (programmed in ASPIC), which incor- 

 porated data from fishery-independent 

 surveys, fishery-dependent catch- 

 per-unit-of-effort data, and regional 

 harvest. Results showed a depleted 

 population (B._,|,„3/B;^,gY=0.03-0.71 ) 

 and high relative fishing mortality 

 <^2002'^MSV=0-9-9-5). Future harvest 

 strategies for a 15-year period were 

 evaluated by using population projec- 

 tions with ASPICP software. Under 

 2003 harvest levels (1356 t), popula- 

 tion recovery to B,,,,.,- would take at 

 least four years, and four of the seven 

 models predicted that the population 

 would not reach Bi/sy within the 15- 

 year period. Production models for 

 horseshoe crab assessment provided 

 management benchmarks for a spe- 

 cies with limited data and no prior 

 stock assessment. 



A production modeling approach to the assessment 

 of the horseshoe crab iUmulus polyphemus) 

 population in Delaware Bay 



Michelle L. Davis 



Department of Fisheries and Wildlife Sciences 

 Virginia Polytechnic Institute and State University 

 210 Cheatham Hall 

 Blacksburg, Virginia 24061-0321 

 Email address midavistSvtedu 



Jim Berkson 



National Marine Fisheries Service RTR Unit at Virginia Tech 

 100 Cheatham Hall 

 Blacksburg, Virginia 24061-0321 



Marcella Kelly 



Department of Fisheries and Wildlife Sciences 

 Virginia Polytechnic Institute and State University 

 210 Cheatham Hall 

 Blacksburg, Virginia 24061-0321 



Manuscript submitted 25 January 2005 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 10 August 2005 by the Scientific Editor. 



Fish. Bull. 104:215-225 (2006). 



The horseshoe crab {Limulus poly- 

 phemus) has become a source of con- 

 troversy on the Atlantic coast of the 

 United States (Berkson and Shuster, 

 1999; Walls et al., 2002). This species 

 is commercially harvested for use as 

 bait, is used by the biomedical indus- 

 try, and is an important source of food 

 for a large number of species, includ- 

 ing migrating shorebirds. However, 

 population trends in the Delaware Bay 

 region in recent years have indicated 

 a possible decline in horseshoe crab 

 abundance, raising concerns that the 

 population may be unable to fulfill 

 the present and future needs of these 

 diverse user groups. 



Horseshoe crabs are harvested 

 commercially for use as bait in the 

 American eel (Anguilla rostrata), 

 whelk, and conch (family Melongeni- 

 dae) pot fisheries (ASMFC). Histori- 

 cally, horseshoe crabs were considered 

 "trash fish" of little commercial value 

 and were used primarily as fertilizer 

 or animal feed. When the bait fish- 

 ery began, there were few restrictions 

 on harvest and no harvest-reporting 

 requirements. A maximum reported 

 coastwide harvest of about 2 million 

 crabs (3100 metric tons [t]) occurred 

 in 1998 (ASMFC2). Commercial har- 



vest has decreased in recent years 

 owing to the adoption of state-by- 

 state quotas in 2000 (ASMFC'') and 

 the increased use of bait-saving de- 

 vices for the eel and conch fisheries, 

 both of which have reduced the de- 

 mand for crabs. 



Horseshoe crabs are also used by 

 the biomedical industry. The blood 

 of horseshoe crabs contains Limulus 

 Amebocyte Lysate (LAL), a substance 

 used to detect the presence of endo- 

 toxin contamination in injectable and 

 implantable drugs and devices (No- 

 vitsky, 1984). The Food and Drug Ad- 

 ministration estimated that 260,000 

 horseshoe crabs were bled for LAL 

 in 1997. After bleeding, the animals 

 were released at the capture site, and 



1 ASMFC (Atlantic States Marine Fisher- 

 ies Commission). 1998. Interstate fish- 

 ery management plan for horseshoe crab, 

 57 p. ASMFC, 1444 Eye Street, NW, 

 Sixth Floor, Washington, DC 20005. 



- ASMFC. 2004. Horseshoe crab 2004 

 stock assessment report, 87 p. ASMFC, 

 1444 Eye Street, NW, Sixth Floor, Wash- 

 ington, DC 20005. 



■' ASMFC. 2000. Addendum I to the fish- 

 ery management plan for horseshoe crab, 

 9 p. ASMFC, 1444 Eye Street, NW, 

 Sixth Floor, Washington, DC 20005. 



