On behaviour of some commercial crabs (Crustacea: Decapoda, Brachyura, Majidae; Anomura, Lithodidae) with special reference to snow crab (Chionoecetes opilio)

Movements, defensive and threat postures of the tanner crab (zuwai crab) Chionoecetes opilio were studied on deck of fishing vessels in the Sea of Okhotsk and the Bering Sea in 1995. The study was based on the assumption that crabs, even being out of water, realize natural behavioural stereotypes developed for stress conditions during their evolution. The obtained data were supplemented with the results of observing other species of tanner (spider) crabs and lithodid (king) crabs in these seas in 1991, 1992 and 1994 and those in the Sea of Japan in 1988. Five defensive and threat postures of the tanner crabs and the posture for fast movement on the desk were described and figured. The crabs did not expose any preference to ''right-'' or ''left-handedness'' in locomotor behavior. Moving fast sideward, the crabs bent their chelipeds and pressed their claws to the frontal part of cephalothorax, or, at least, bent the front cheliped and run with the bent ''elbow'' directed forward. This posture results in decreasing the water drag. Moving slowly the crabs stretched their 1st legs and opened their claws. About 20 percent of the crabs observed tries to move backward. This movement was likely to be an attempt of burying. Some comments on autotomy of tanner crabs are given.