Table 1. — Distribution of horseshoe crabs in clam 

 surveys, 1965-83; 1,640 animals enumerated at 

 535 stations. Number of crabs over (number of sta- 

 tions with one or more individuals) in each row. 



FISHERY BULLETIN: VOL 85, NO. 4 

 Inshore Offshore 



ginia and New Jersey (Table 1). Thus, horseshoe 

 crabs were most abundant along the continental 

 shelf from Virginia to southern New Jersey in 

 both groundfish and ocean clam surveys. 



Seasonal and Annual Variations 

 in Standing Stock 



On the New Jersey-Virginia continental shelf, 

 average abundance and biomass were highest 

 during spring and fall cruises, lower in summer, 

 and lower still (based on limited sampling) in 

 winter (Fig. 1, Table 2). Horseshoe crabs were 

 present in more than half the inshore tows 

 throughout the year. Frequency of occurrence did 

 not fluctuate as widely as abundance or biomass, 

 and was consistently higher inshore than off- 

 shore. 



Population estimates show considerable an- 

 nual variation, with highest recorded catches in 



Table 2. — Average of seasonal variation in horseshoe crab abun- 

 dance and biomass on the continental shelf, northern New Jersey 

 to southern Virginia, based on groundfish surveys from 1975 to 

 1983. Strata shallower than 27 m were defined as inshore, and 

 strata deeper than 27 m were defined as offshore. 



Winter Spring Summer Fall 



Inshore 



Mean no. per trawl 0.41 7.44 3.26 4.54 



% occurrence 56 76 61 78 



Population (X 106) 0.410 3.103 1.258 1.881 



Biomass (metric tons) 93 3,626 2,075 2,969 



Offshore 



Mean no. per trawl ' — 1.03 0.10 0.42 



% occurrence — 29 30 22 



Population (X 106) — i,445 0.129 0.530 



Biomass (metric tons) — 1,975 231 972 



1975 

 1976 



1977 



1978 



1979 



1980 



1981 

 1982 

 1983 



F 

 S 



F 



S 



Su 



F 

 W 



s 



Su 



F 



S 



Su 



F 



S 



Su 



F 



S 

 Su 



F 



S 



F 



W 



s 



F 



-• 





' ' I ' I I I I I I I'l [IT 



2 4 6 8 10 12 14 16 18 2 4 6 8 



Mean No. per Tow 



Figure 2. — Mean number of horseshoe crabs per tow (with 95% 

 confidence Hmits) on the continental shelf from New Jersey to 

 Virginia, based on NEFC groundfish trawl data from 1975 to 

 1983. W = winter; S = spring; Su = summer; F = fall; In- 

 shore = all tows within sampling strata shallower than 27 m; 

 Offshore = all tows within sampling strata deeper than 

 27 m. Where no confidence limit is shown, calculated limit 

 was smaller than the width of the datum point. 



spring of 1976 and 1981 (Fig. 2). However, no 

 clear trends in standing stock between 1975 and 

 1983 were evident. We estimate, based on the 

 more complete fall and spring surveys, a mini- 

 mum inshore population ranging from 1.8 to 3.1 

 million individuals (2,969 to 3,626 t), and a mini- 

 mum offshore population ranging from 0.5 to 1.4 

 million individuals (972 to 1,975 t) (Table 2), for 

 a total of some 2.3-4.5 million individuals. Coeffi- 

 cients of variation, based on individual stratum 

 catches, ranged from 11.6 to 41.6 for individual 

 inshore survey estimates, and from 23.6 to 87.5 

 for offshore estimates. 



Bathymetric Distribution 



Horseshoe crabs were taken at stations be- 

 tween the inshore sampling limit, 9 m, and 290 m 

 depth (Fig. 3). Seventy-four percent of the total 

 number caught in bottom trawl surveys were 

 taken from stations shallower than 20 m; and 

 92% were caught at depths <30 m. This trend was 

 not an artifact of sampling effort. Offshore sta- 

 tions (>27 m) comprised approximately 73% of 

 the sampling effort but produced <10% of the 



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