CANNIBALISM IN THE SNOW CRAB, CHIONOECETES-OPILIO (O-FABRICIUS) (BRACHYURA, MAJIDAE), AND ITS POTENTIAL IMPORTANCE TO RECRUITMENT

Density-dependent cannibalism, either on early benthic instars or on l ate prerecruits, has been hypothesized to regulate recruitment in the snow crab Chionoecetes opilio (O. Fabricius). However, there is little direct empirical or experimental evidence to support these hypotheses . We examined the stomach contents of 1218 C. opilio of 12-135 mm cara pace width (CW) for evidence of cannibalism. Crabs were collected by b eam trawl in 1993 and 1994 in the estuary and northwest gulf of the Sa int Lawrence River (Canada). Complementary laboratory experiments serv ed to constitute a library of digested crab body parts for reference i n the identification of stomach contents, and to evaluate the possibil ity and size-specificity of cannibalism on C. opilio instar I (settler s: 3 mm CW). The natural diet of C. opilio changed with increasing bod y size, with smallest crabs feeding mainly on amphipods and ophiuroids , while the largest crabs fed mainly on annelids, crustacean decapods and fish. Overall, conspecifics other than exuviae occurred in the sto machs of 7.2% of wild caught C. opilio and were probably derived throu gh predation rather than scavenged. Non-exuvial conspecifics were foun d most frequently in the stomachs of adult males (sperm-producing, che lae differentiated), with occurrence declining significantly from 22% to 6% of adult males by 10 mm CW size class over the range of 50-120 m m CW. Conspecific prey ranged in size from 3.9-48.8 mm CW, but most we re immature crabs belonging to molt instars V(approximate to 15 mm CW) , VI (approximate to 20 mm CW) and VII (approximate to 28 mm CW). In t he laboratory, instar I crabs were cannibalized by males of 8-50 mm CW , but not by males of 51-130 mm CW. Based an laboratory and field resu lts, there are relative lower and upper size thresholds for vulnerabil ity of intermolt crabs to cannibalism, which vary with predator size. We conclude that intraspecific predation may reduce cohort strength ma inly over the first 4 years following settlement. (C) 1997 Elsevier Sc ience B.V.