242 
Fishery Bulletin 107(2) 
Table 4 
The aggregate observed weight and estimated weight using the NOAA Fisheries conversion factor (i.e., 1.21 kg per animal) of 
horseshoe crabs ( Limulus polyphemus) collected during spawning surveys. The percent that the NOAA Fisheries conversion 
factor overestimates weight is also listed. 
Location 
Sex 
Aggregate 
observed 
weight (kg) 
Aggregate 
estimated 
weight (kg) 
Percent 
weight 
overestimated 
New Jersey (Delaware Bay) 
Female (rz =168) 
446 
448 
0.3 
Male (n=211) 
237 
563 
58 
Total (n=379) 
683 
1011 
32 
New Jersey (Raritan Bay) 
Female (n = 102) 
231 
272 
15 
Male (n = 195) 
192 
521 
63 
Total (n =297 ) 
424 
793 
47 
Delaware (Delaware Bay) i 
Female (n=261) 
631 
697 
9 
Male (n = 87) 
90 
232 
61 
Total (rc=348) 
721 
929 
22 
New Hampshire (Great Bay) 
Female (n=12) 
7 
31 
77 
Male (« = 119) 
28 
309 
91 
Total (n = 131) 
35 
341 
90 
1 S. Michels. Unpubl. data. 1999, 2003, 2004. Delaware Fish and Wildlife, P.O. Box 330, Little Creek, DE 19961. 
species. According to our analyses, a New England har- 
vest, composed of mostly male horseshoe crabs, would 
be the worst-case scenario for overestimating landings 
data when measured in pounds. 
To more accurately estimate reference period land- 
ings, biomass should be recalculated using state-specific 
conversion factors for each sex. However, determining 
the male-to-female ratios from landing data may be a 
challenge. Before 1998, participants in the fishery were 
not required to record the ratio of males to females 
among landed horseshoe crabs. It has been suggested 
that eel bait fishermen prefer to harvest females, be- 
cause of a chemical attractant associated with the eggs 
(Ferrari and Targett, 2003). In contrast, both male and 
female horseshoe crabs were used, as available, for the 
whelk fishery. Unfortunately, no data are available on 
the percentage of horseshoe crabs landed as bait for eels 
versus whelks, from which one might be able to deduce 
the sex ratio in the early commercial catches. 
Future estimates of the biomass of harvested horse- 
shoe crabs should incorporate the sex and location of 
horseshoe crab harvests. Use of geographically-appro- 
priate conversion factors for each sex would provide 
an accurate estimate of biomass despite the differing 
regulations among states. Some states have already 
derived their own sex-specific conversion factors, and 
most seem to provide an accurate representation of the 
average weight for male and female horseshoe crabs. 
States that have used one conversion factor to estimate 
the weight of both female and male horseshoe crabs 
(i.e., Maine, Rhode Island, Virginia, South Carolina, 
and Florida) either underestimate the weight of female 
horseshoe crabs or overestimate the weight of male 
horseshoe crabs. Although state agencies are no longer 
required to report landings in number and pounds, the 
conversion factors that have already been derived by 
state agencies may serve as a useful tool for accurately 
converting data to be used in prediction models. For 
states that have not developed accurate conversion fac- 
tors, the PW-weight equations derived from this study 
can be used to develop conversion factors based on the 
average width of male and female horseshoe crabs from 
that area. Besides providing a more accurate estimate 
of biomass, use of state-specific and sex-specific conver- 
sion factors is feasible for management purposes be- 
cause states are already required to report the location, 
sex, and number of horseshoe crabs harvested. 
At present, only very limited size and weight data 
are available for horseshoe crabs from North Carolina 
through northern Florida. Our PW-weight relationships 
for both sexes are very robust across a wide range of 
sizes, but could be further improved by the inclusion 
of horseshoe crab populations from this part of their 
range. 
Conclusion 
It is important to provide accurate biomass estimates 
of harvest data for future management purposes and, 
therefore, accurate conversion factors should be devel- 
oped. From the results of this study, it seems that the 
most practical approach to estimating landing data is 
to use state-specific conversion factors, one for females 
and one for males, based on the average weight of horse- 
shoe crabs from that area. Researchers should continue 
