700 



Fishery Bulletin 102(4) 



Rock crab 



Hudson-Rantan Estuary 



New York 





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qp ° 





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None 

 o 1-9 

 o 10-49 

 O 50-99 

 O 100-249 

 O 2 250 



Figure 5 (continued) 



The diets of lady crabs and rock crabs were significantly 

 different in two taxa: M. lateralis for lady crabs and M. 

 edulis for rock crabs. 



Within the crab size ranges sampled adequately by 

 our gear, we found some ontogenetic differences in di- 

 ets (Fig. 9). Notably, amphipods and shrimp were con- 

 sumed by smaller sizes of all three predators. Certain 

 mollusks, such as N. trivittatus and the Atlantic jack- 

 knife clam (Ensis directus), increased in occurrence in 

 foreguts with increasing crab size. Smaller lady crabs 

 primarily fed upon M. lateralis, but larger ones broad- 

 ened their diets to include other mollusks such as slip- 

 persnails (Crepidula spp.) and M. edulis. Blue and rock 

 crabs exhibited two peaks in consumption of M. edulis: 



the foreguts of small crabs contained recently settled 

 mussels, whereas those of large crabs contained shell 

 fragments and meat of larger mussels. Xanthidae and 

 Paguridae, small in body size, were eaten mostly by 

 intermediate-size predators. 



Mann-Whitney tests showed that amphipods were 

 the only prey significantly different (P<0.01) between 

 maturity classes for all three crab species. 



Spatial variability in diets 



Cluster analysis of the diets by species and stratum 

 defined six groups at 50% similarity (Fig. 10). Group A 

 consisted of lady and rock crabs caught at oceanward 



