BOTTON and ROPES: POPULATIONS OF HORSESHOE CRABS 



1979 to 655 in 1966). Catches were not expanded 

 into stock estimates, as for the bottom trawl sur- 

 vey data. 



To analyze broad latitudinal variations in 

 abundance and frequency of occurrence, catch 

 and sampling effort were grouped by 1-degree lat- 

 itude and longitude blocks. For example, stations 

 at lat. 38°06'N, long. 74°02'W and 38°45'N, 

 74°50'W were both grouped together as 38°N, 

 74°W. Bottom trawl and ocean clam survey 

 data were analyzed separately, because strati- 

 fication schemes differed and the efficiencies of 

 the two types of sampling gear cannot readily 

 be compared. 



RESULTS 



Latitudinal Distribution 



During groundfish surveys, 7,035 crabs were 

 taken at 983 stations distributed from 33°N to 

 41°N; 75^^ of the crabs were caught between 37°N 



and 40°N (Fig. 1, App. Table 1). Highest abun- 

 dance and frequency of occurrence was found on 

 the shelf nearest the mouth of Delaware Bay. The 

 maximum number of individuals per tow, 99, was 

 obtained on 22 March 1976, from a station located 

 off Assateague Island, VA, at 38°00'N, 75°14'W, 

 in 13 m of water. Mean number per tow generally 

 decreased with increasing distance from shore 

 (Fig. 1). 



Horseshoe crab abundance decreased both 

 north of 40°N and south of 37°N (Fig. 1). Crabs 

 were absent northeast of Montauk Point, Long 

 Island (41°N, 72°W), and no crabs were found on 

 or north of Georges Bank despite intensive sam- 

 pling effort. Fewer than 2% of all horseshoe crabs 

 collected were found south of 35°N (Cape Hat- 

 teras), and only one animal was caught south of 

 34°N. 



The observed latitudinal distribution of horse- 

 shoe crabs in ocean clam surveys paralleled the 

 above trends. A total of 1,640 animals was taken 

 at 535 stations clustered primarily between Vir- 



FlGURE 1.— Continued ~hy T latitude and longitude blocks, based on NEFC groundfish trawl data from 1975 to 1983. 



807 



