236 
Fishery Bulletin 107(2) 
crabs harvested in Delaware and Virginia waters were 
converted to biomass using conversion factors derived 
from fishery-independent and fishery-dependent data 
(i.e., Delaware: 1.05 kg/male, 2.32 kg/female, 1.69 kg/ 
combined catch; Virginia: 1.8 kg/horseshoe crab or 
2.27 kg/horseshoe crab depending on the composition 
of the catch). The landing data from all other states 
were converted to pounds using a NOAA Fisheries 
conversion factor (i.e., 1.21 kg/horseshoe crab). These 
data have since been used to generate estimates of 
total landings, to set state-by-state quotas, and to 
manage the stock (Fig. 1). 
Once the horseshoe crab fishery management plan 
was initiated, all landings were required to be re- 
ported by sex, harvest method, and the number and 
pounds of harvested horseshoe crabs. However, many 
fishermen reported their catch in numbers of har- 
vested horseshoe crabs, and state agencies used con- 
version factors to convert harvests from numbers to 
pounds. Because of the uncertainty in these conver- 
sion factors and resulting biomass estimates, state 
agencies are no longer required to report the pounds 
of horseshoe crabs landed. The Atlantic States Marine 
Fisheries Commission (ASMFC) and state agencies 
now assess and manage stocks using only the number 
of horseshoe crabs (not pounds) harvested. 
ASMFC currently uses trend analysis to manage 
horseshoe crab populations, but numerous prediction 
models are being developed for future, more accurate 
management. For some of these models, landing data 
are required to be reported in pounds, not numbers. 
Because all state landings are currently reported by 
numbers of landed horseshoe crabs, conversion fac- 
tors need to be derived to estimate pounds of landed 
horseshoe crabs. The availability of accurate conversion 
factors will serve as a factor in choosing an appropriate 
model to better manage horseshoe crab populations. 
The objective of our study was to derive prosomal- 
width-to-weight equations to calculate alternative sex- 
specific conversion factors based on the average width 
of horseshoe crabs from each state. We also tested 
the NOAA Fisheries conversion factor by comparing 
the observed total biomass of horseshoe crabs to the 
total biomass that was estimated with the conversion 
factor. 
Materials and methods 
Data collection 
Data were collected during three spawning surveys in 
the Mid-Atlantic (i.e., Delaware Bay, NJ, sampled in 
1997 and 2000 [n = 379]; Raritan Bay, NJ, sampled in 
1988 [/r = 297] ) and southern New England (i.e., Great 
Bay, NH, sampled in 1988 [/r = 131]) and from the Del- 
aware commercial fishery (i.e., Delaware Bay, DE, 
sampled in 1999, 2003, and 2004 [n = 348]) (Fig. 2). 
The sex, prosomal width (PW; to the nearest 1 mm), 
and weight (to the nearest 10 g) were recorded from a 
sample of individuals that were collected from the vicin- 
ity of each breeding beach. During spawning surveys, 
animals were collected as either mated pairs (a male 
coupled to a female) or as unpaired (or satellite males) 
because previous studies (Botton and Loveland, 1989) 
have shown that there is no significant size difference 
between unattached males within a population. The 
majority of the samples collected from the commercial 
fishery were harvested by hand 
during spawning events. All 
samples were mature individu- 
als because only mature horse- 
shoe crabs visit beaches during 
spawning events. 
Measurements also were re- 
corded for horseshoe crabs in 
coastal waters (i.e., within 12 
nautical miles from shore) be- 
tween New York and Virginia 
(Fig. 2). In September, Octo- 
ber, and November of 2005 and 
2006, 743 individuals were col- 
lected and measured during the 
Horseshoe Crab Research Center 
(HCRC) trawl survey (for meth- 
ods see Hata and Berkson, 2004). 
In June of 2006, an additional 
182 horseshoe crabs were sam- 
pled aboard a commercial trawl 
vessel harvesting crabs for a bio- 
medical company off the coast of 
Ocean City, Maryland. Trawling 
gear, specifically a flounder net, 
was used to collect all horseshoe 
