708 



Fishery Bulletin 102(4) 



of their chelae cannot match those of blue crabs. As 

 they grow, Cancridae and Portunidae undergo shifts in 

 diet, and may be divided into ontogenetically distinct 

 trophic units (Laughlin, 1982; Stevens et al., 1982: 

 Stoner and Buchanan, 1990; Rosas et al.. 1994). In 

 our study, larger crabs dropped amphipods and shrimp 

 from their diets, but otherwise only minor changes 

 occurred in prey identity and relative volumes of prey 

 taxa among size classes (Fig. 9). An interesting ontoge- 

 netic shift was in the size of prey eaten: small crabs ate 

 small individuals of prey taxa, such as M. edulis, and 

 Xanthidae, and large crabs ate large individuals of the 

 same taxa. Thus in our study the influence of physical 

 structure upon diet was greater as body size increased 

 within a species than among species. 



Spatial variability and overlap in diets 



The three predators were scattered throughout the 

 cluster diagram of diet among strata of the estuary 

 (Fig. 10), yet crabs from inner and outer groups of strata 

 usually clustered separately. We concluded that loca- 

 tion influenced diet more than did predator identity. 

 The inner, outer, and channel strata differ in depth, 

 sediment type, currents, and mean temperature, and 

 therefore in benthic and epibenthic prey assemblages. 

 Our results support the concept that these species are 

 mainly opportunistic in diet, as was suggested for blue 

 crabs (Laughlin, 19821, and rock crabs (Hudon and 

 Lamarche, 1989). The Hudson-Raritan and other nearby 

 coastal and estuarine areas from Long Island Sound to 

 Chesapeake Bay are crossroads where blue, lady, and 

 rock crabs share space and resources. 



Acknowledgments 



We thank those who helped design and carry out the 

 Hudson-Raritan Estuary trawl surveys, especially Stuart 

 Wilk, Anthony Pacheco, and Eileen MacHaffie. We also 

 thank Fred Farwell, Sherman Kingsley, and the NOAA 

 Corps captains and crew. Suellen Fromm was instru- 

 mental in obtaining data from NEFSC trawl surveys. 

 We thank the scientists who shared their opinions and 

 unpublished data. We are indebted to colleagues Mary 

 Fabrizio, Clyde MacKenzie, John Manderson, Carol 

 Meise, Frank Steimle, Allan Stoner, and anonymous 

 reviewers who helped improve the manuscript. This 

 paper is dedicated to the memory of Tony Pacheco. 



Literature cited 



Auster, P. J., and R. E. DeGoursey. 



1994. Winter predation on blue crabs, Callinectes sapi- 

 dus, by starfish Asterias forbesi. J. Shellfish Res. 

 13:361-366. 

 Azarovitz, T. A. 



1981. A brief historical review of the Woods Hole Labora- 

 tory trawl survey time series. In Bottom trawl surveys 



(Doubleday. W.G., and D. Rivard, eds.), p. 62-67. Can. 

 Spec. Publ. Fish. Aquat. Sci. 58. 

 Barshaw, D. E„ and K. W. Able. 



1990. Deep burial as a refuge for lady crabs. Ocalipes 

 ocellatus: comparisons with blue crabs, Callinectes 

 sapidus. Mar. Ecol. Prog. Ser. 66:75-79. 

 Behrens Yamada, S., and E. G. Boulding. 



1998. Claw morphology, prey size selection and foraging 

 efficiency in generalist and specialist shell-breaking 

 crabs, j. Exp. Mar. Biol. Ecol. 220:191-211. 

 Birchard, G. F., L. Drolet. and L. H. Mantel. 



1982. The effect of reduced salinity on osmoregulation 

 and oxygen consumption in the lady crab. Ocalipes ocella- 

 tus (Herbst). Comp. Biochem. Physiol. 71A:321-324. 

 Block. J. D., and S. Rebach. 



1998. Correlates of claw strength in the rock crab. 

 Cancer irroratus (Decapoda, Brachyura). Crustaceana 

 71:468-473. 

 Blundon. J. A., and V. S. Kennedy. 



1982. Mechanical and behavioral aspects of blue crab, 

 Callinectes sapidus (Rathbuni, predation on Chesapeake 

 Bay bivalves. J. Exp. Mar. Biol. Ecol. 65:47-65. 

 Briggs, P. T. 



1998. New York's blue crab I Callinectes sapidus) fisheries 

 through the years. J. Shellfish Res. 17:487-491. 

 Choy, S. C. 



1986. Natural diet and feeding habits of the crabs Lio- 

 carcinus puber and L. holsatus I Decapoda. Brachyura. 

 Portunidae). Mar. Ecol. Prog. Ser. 31:87-99. 

 Clarke, K. R.. and R. M. Warwick. 



1994. Change in marine communities: an approach to 

 statistical analysis and interpretation, 144 p. National 

 Environmental Research Council, UK. 

 Coch. N. K. 



1986. Sediment characteristics and facies distributions 

 in the Hudson system. In Sedimentation in the Hudson 

 system: the Hudson River and contiguous waterways iN. 

 K.Coch and H. J. Bokuniewicz, eds. I, p. 109-129. North- 

 eastern Geology (spec, issue) 8. 

 Colwell, R. K., and D. J. Futuyama. 



1971. On the measurement of niche breadth and overlap. 

 Ecology 52:567-576. 

 de Lestang, S., N. G. Hall, and I. C. Potter. 



2003. Reproductive biology of the blue swimmer crab 

 {Portunus pelagicus, Decapoda: Portunidae) in five 

 bodies of water on the west coast of Australia. Fish. 

 Bull. 101:745-757. 

 Drummond-Davis, N. C, K. H. Mann, and R. A. Pottle. 



1982. Some estimates of population density and feeding 

 habits of the rock crab. Cancer irroratus, in a kelp bed in 

 Nova Scotia. Can. J. Fish. Aquat. Sci. 39:636-639. 

 Eggleston. D. B. 



1990. Functional responses of blue crabs Callinectes 

 sapidus Rathbun feeding on juvenile oysters Crassostrea 

 virginica (Gmelin): effects of predator sex and size, and 

 prey size. J. Exp. Mar. Biol. Ecol. 143:73-90. 

 Eggleston, D. B.. J. J. Grover, and R. N. Lipcius. 



1998. Ontogenetic diet shifts in Nassau grouper: tro- 

 phic linkages and predatory impact. Bull. Mar. Sci. 

 63:111-126. 

 Elner, R. W., P. G. Beninger. L. E. Linkletter. and S. Lanteigne. 

 1985. Guide to indicator fragments of principal prey taxa 

 in the stomachs of two common Atlantic crab species: 

 Cancer borealis Stimpson, 1859 and Cancer irroratus Say, 

 1817. Can. Tech. Rep. Fish. Aquat. Sci. 1403:1-20. 



