235 
Prosomal-width-to-weight relationships 
in American horseshoe crabs 
( Limulus polyphemus ): examining 
conversion factors used to estimate landings 
Brian R. Murphy 1 
Email address for contact author: L|g85@cornell.edu 
1 Department of Fisheries and Wildlife Sciences 
Virginia Polytechnic Institute and State University 
100 Cheatham Hall 
Blacksburg, Virginia 24061 
Present address for contact author: New York Sea Grant 
Stony Brook University 
146 Suffolk Hall 
Stony Brook, New York 11794-5002 
2 Department of Natural Sciences 
Fordham University, College at Lincoln Center 
1 1 3 West 60 ,h Street 
New York, New York 10023 
3 Department of Ecology, Evolution, and Natural Resources 
Cook College, Rutgers University 
New Brunswick, New Jersey 08901 
Abstract — Horseshoe crabs ( Limu- 
lus polyphemus) are valued by many 
stakeholders, including the commer- 
cial fishing industry, biomedical com- 
panies, and environmental interest 
groups. We designed a study to test 
the accuracy of the conversion fac- 
tors that were used by NOAA Fish- 
eries and state agencies to estimate 
horseshoe crab landings before man- 
datory reporting that began in 1998. 
Our results indicate that the NOAA 
Fisheries conversion factor consis- 
tently overestimates the weight of 
male horseshoe crabs, particularly 
those from New England populations. 
Because of the inaccuracy of this and 
other conversion factors, states are 
now mandated to report the number 
(not biomass) and sex of landed horse- 
shoe crabs. However, accurate esti- 
mates of biomass are still necessary 
for use in prediction models that are 
being developed to better manage the 
horseshoe crab fishery. We recommend 
that managers use the conversion fac- 
tors presented in this study to convert 
current landing data from numbers to 
biomass of harvested horseshoe crabs 
for future assessments. 
Manuscript submitted 11 June 2008. 
Manuscript accepted 14 January 2009. 
Fish. Bull. 107:235-243 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Larissa J. Graham (contact author) 1 
Mark L. Botton 2 
David Hata 
Robert E. Loveland 3 
Horseshoe crabs ( Limulus polyphe- 
mus) are considered a multiple-use 
resource. They are valued by many 
stakeholders, including the commer- 
cial fishing industry, biomedical com- 
panies, and environmental interest 
groups (Berkson and Shuster, 1999). 
Horseshoe crabs are commercially 
harvested and sold as bait for whelk 
( Busycon spp. and Busycotypus spp.) 
and American eel (Anguilla rostrata) 
fisheries. This species is also gath- 
ered for biomedical companies because 
its copper-containing blood is used to 
create a pharmaceutical product, Lim- 
ulus amoebocyte lysate (LAL) that is 
used to detect pathogenic endotoxins 
on medical devices and in injectable 
drugs (Novitsky, 1984; Mikkelsen, 
1988; Levin et ah, 2003). The mor- 
tality associated with the handling 
and bleeding of horseshoe crabs is 
minimized (i.e., 8-20% [Rudloe, 1983; 
Kurz and James-Pirri, 2002; Walls 
and Berkson, 2003; Hurton and Berk- 
son, 2004]) because the animals are 
required to be returned to the water 
within 72 hours. Horseshoe crabs are 
ecologically important because their 
eggs serve as a food source for migrat- 
ing shorebirds most notably in Dela- 
ware Bay (Tsipoura and Burger, 1999; 
Botton et al., 2003; Karpanty et al., 
2006; Haramis et al., 2007). 
In 1998, a fishery management 
plan was developed for the horseshoe 
crab. However, before this plan, most 
states did not require the manda- 
tory reporting of harvested horse- 
shoe crabs. NOAA Fisheries collected 
commercial landing data by state, 
year, and gear type, but these data 
were incomplete and disjunct. To es- 
timate reference period (or a basis 
for reductions in landing data), the 
Horseshoe Crab Technical Commit- 
tee asked state agencies to provide 
their best estimate of the number 
of horseshoe crabs harvested before 
1998. These numbers were converted 
to pounds using various conversion 
factors. The number of horseshoe 
