ROPES: FOOD HABITS OF FIVE CRAB SPECIES 



Table 1. — Numbers of crabs caught in dredge tows at Pettaquamscutt River, Rl, 1955-57. 



'Stomachs not examined. 



food. Empty stomachs were omitted from all calcu- 

 lations. 



Since most food consisted of crushed or frag- 

 mented remains, hard structures were relied upon 

 for food identification. To assign a food to a definite 

 species category was not always possible, but it 

 could usually be included in a general taxonomic 

 group. Thus, not all major taxonomic groups are the 

 sum of specific items. Mollusk shells, and especial- 

 ly the hinge structure of pelecypods, could be most 

 readily recognized. Annelids were identified by their 

 jaws (whole worms were rarely found). Arthropods 

 could rarely be identified to species, but were 

 separated into three general groups: 1) crabs, 

 which consisted of heavy pigmented exoskeletal 

 remains, 2) small crustaceans, which consisted of 

 translucent exoskeletal remains of amphipods, 

 isopods, and small shrimp, and 3) barnacles (shells 

 and bodies). Many stomachs contained food re- 

 mains that were too fragmented or digested for 

 identification. These were classified as unidentified 

 remains. 



Analysis of food habits by sex, molting condition, 

 egg bearing, and mating were not possible due to 

 the small numbers of each species collected. In a 

 study of nearly 4,000 green crabs, Ropes (1968) 

 found that feeding habits by sex were inconsistent 

 and that feeding habits by premolt and very soft- 

 shelled crabs (not included in the present study) 



were arrested. Similarly, o\'igerous green crabs ex- 

 amined by Ropes (1968) tended to feed less than 

 nonovigerous crabs, and the stomachs of mated 

 pairs were nearly empty. Thus, analyses in the pres- 

 ent study focused only on general food habits of the 

 five species. 



RESULTS 



Although a few blue crabs were caught in 1955, 

 none were taken in 1956 (Table 1). They were most 

 numerous in the 1957 samples. The mean number 

 per tow varied from to 12.4. Green crabs were 

 caught during every collection trip, except 8 August 

 1957, and were usually more numerous than the 

 other crab species. The 6 September 1955 collection 

 was unusual: 90 green crabs <10 mm CW (carapace 

 width), 6 crabs <20 mm, and 1 crab 58 mm were 

 caught entangled in decaying algae. It was the only 

 collection containing such a large number of small- 

 sized crabs. The mean number of green crabs caught 

 per tow varied widely (0 to 21.7). Other crab species 

 were caught infrequently and then in relatively low 

 numbers. 



Blue crabs ranged from 20 to 160 mm CW (Fig. 

 2). Although none exceeded 105 mm in 1955, 35% 

 were larger in 1957. No size group was dominant; 

 most ranged from 40 to 109 mm. Green crabs 

 ranged from 4 to 70 mm, with most between 20 



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