CONICET | Buscador de Institutos y Recursos Humanos

Density-dependent cannibalism, either on early benthic instars or on late prerecruits, has beenhypothesized to regulate recruitment in the snow crab Chionoecetes opi/io (0. Fabricius).However, there is little direct empirical or experimental evidence to support these hypotheses. Weexamined the stomach contents of 1218 C. opilio of 12-135 mm carapace width (CW) forevidence of cannibalism. Crabs were collected by beam trawl in 1993 and 1994 in the estuary andnorthwest gulf of the Saint Lawrence River (Canada). Complementary laboratory experimentsserved to constitute a library of digested crab body parts for reference in the identification ofstomach contents, and to evaluate the possibility and size-specificity of cannibalism on C. opi/ioinstar I (settlers: 3 mm CW). The natural diet of C. opilio changed with increasing body size, withsmallest crabs feeding mainly on amphipods and ophiuroids, while the largest crabs fed mainly onannelids, crustacean decapods and fish. Overall, conspecifics other than exuviae occurred in thestomachs of 7.2% of wild caught C. opilio and were probably derived through predation ratherthan scavenged. Non-exuvial conspecifics were found most frequently in the stomachs of adultmales (sperm-producing. chelae differentiated). with occurrence declining significantly from 22%to 6% of adult males by 10 mm CW size class over the range of 50-120 mm CW. Conspecificprey ranged in size from 3.9-48.8 mm CW, but most were immature crabs belonging to moltinstars V (= 15 mm CW). VI (= 20 mm CW) and VII (= 28 mm CW). In the laboratory, instar Icrabs were cannibalized by males of 8-50 mm CW. but not by males of 51- 130 mm Cw. Basedon laboratory and field results, there are relative lower and upper size thresholds for vulnerabilityof intermolt crabs to cannibalism. which vary with predator size. We conclude that intraspecificpredation may reduce cohort strength mainly over the first 4 years following settlement

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