DISTRIBUTION AND FEEDING OF 



THE HORSESHOE CRAB, LIMULUS POLYPHEMUS, ON 



THE CONTINENTAL SHELF OFF NEW JERSEY 1 



Mark L. Botton 2 and Harold H. Haskin 3 



ABSTRACT 



The horseshoe crab, Limulus polyphemus , population was assessed during hydraulic dredge surveys of 

 the surf clam resource in the inshore 5.5 km (3 nautical miles) of the continental shelf off New Jersey 

 from 1976 through 1979. Frequency of occurrence and abundance was higher off the southern half of the 

 state, which may be a function of its proximity to Delaware Bay, a principal spawning site. Horseshoe 

 crabs consumed various benthic organisms, primarily bivalves, arthropods, and polychaetes. Surf 

 clams, Spisula solidissima, were important in the diet of Limulus; individual valves ranged in length 

 from < 1 mm to about 35 mm. In the laboratory, horseshoe crab predation was observed on surf clams as 

 long as 46 mm. 



This report describes the distribution of the horse- 

 shoe crab, Limulus polyphemus, on the inshore 

 continental shelf off New Jersey, and the diets of a 

 sample of these animals. Previous studies of the 

 horseshoe crab on the continental shelf are limited 

 to distributional records (Wolff 1977; Shuster 

 1979) or tagging studies conducted close to es- 

 tuarine spawning areas (Baptist et al. 1957; Rud- 

 loe 1980), although crabs have been found at 

 depths as great as 200 m according to National 

 Marine Fisheries Service surveys (J. W. Ropes 4 ). 

 Since the early 1960's, an intensive surf clam, 

 Spisula solidissima, fishery has developed along 

 the New Jersey coast (Ropes 1982). The junior au- 

 thor (Haskin) and his colleagues have inven- 

 toried the surf clam resource in the New Jersey 

 waters, to 5.5 km (3 nmi) offshore yearly since 

 1972. All macroinvertebrates, including L. 

 polyphemus, captured in hydraulic dredge hauls 

 from 1976 through 1979 were counted. Since a 

 percentage of the horseshoe crab population mi- 

 grates from the continental shelf to estuaries and 

 back again (Shuster 1982), we analyzed both tem- 



poral and spatial variability. Separating these ef- 

 fects was difficult because the sampling program 

 was designed primarily to inventory a sessile clam 

 resource, rather than a migratory one. However, 

 the data, based on over 1,100 stations, still repre- 

 sent the most systematic survey of L. polyphemus 

 distribution on the inshore continental shelf, and 

 since exploitation of these crabs for biomedical 

 research and bait is increasing (Pearson and 

 Weary 1980), our study provides baseline informa- 

 tion should future population assessment studies 

 be warranted. 



Information on the feeding biology of horseshoe 

 crabs is limited (Lockwood 1870; Fowler 1908; 

 Shuster 1950; Smith and Chin 1951; Smith 1953: 

 Smith et al. 1955; Botton 1981). In this study, 

 stomach contents from 36 horseshoe crabs from 

 the continental shelf were examined to supple- 

 ment a more intensive study of the food habits of 

 animals from Delaware Bay (Botton 1982); in Au- 

 gust 1980, predation by crabs on surf clams about 4 

 cm long was examined in the laboratory. 



MATERIALS AND METHODS 



'No. D-32503-1-83 of the New Jersey Agricultural Experiment 

 Station, Rutgers University, Piscataway, N.J. 



2 Department of Biological Sciences and Oyster Research 

 Laboratory, New Jersey Agricultural Experiment Station, Rut- 

 gers University, Piscataway, N.J.; present address: Excel Divi- 

 sion. Fordham University, The College at Lincoln Center, New- 

 York, NY 10023. 



department of Biological Sciences and Oyster Research 

 Laboratory, New Jersey Agricultural Experiment Station, Rut- 

 gers University, P.O. Box 1059, Piscataway, NJ 08854. 



4 J. W. Ropes, Northeast Fisheries Center Woods Hole Labora- 

 tory, National Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543, pers. commun. February 1983. 



Manuscript accepted October 1983. 

 FISHERY BULLETIN: VOL. 82, NO. 2, 1984. 



Population Survey 



Stations were sampled with a hydraulic dredge 

 (Meyer et al. 1981), adjusted to retain surf clams 

 >88 mm. This gear retained both adult and sub- 

 adult horseshoe crabs. Catch data, as number of 

 animals per tow, were normalized for dredge width 

 and tow time. The standard tow (ST) is defined as a 

 5-min haul using a 152 cm knife (width of dredge). 



383 



