BASIC MOVEMENT PATTERN AND CHEMO-ORIENTED SEARCH TOWARDS BAITED POTS IN EDIBLE CRAB (CANCER-PAGURUS L.)

The basic (natural) movement pattern and gear-induced behaviour of fem ale edible crab Cancer pagurus L. were studied by means of a stationar y positioning system. Nine crabs were tagged with ultrasonic transmitt ers and their positions were monitored approximately every third minut e for 9-24 days. Because the crabs sometimes hid, the signals were oft en received improperly, resulting in inaccurate position fixes, and a computer program to distinguish between movement and inactivity was de veloped. Edible crabs showed a nocturnal activity cycle. During the da y crabs were in hiding as indicated by less accurate position fixes. T here were variations in activity levels both between and within indivi duals. Three crabs hardly moved at all during the study, while the oth ers were active during some, or all nights. The crabs did not return t o the same place after movement, but stayed close to the hydrophone tr iangle (290 x 350 x 175 m) throughout the study. The activity and move ment patterns are discussed in relation to optimal foraging behaviour and predator avoidance. Six baited pots were set in the area on seven nights. Four of the crabs located baited pots during the study. Three crabs located pots more than once, resulting in a total of nine locali sations. Three of the tagged crabs were caught. The localisations of b aited pots were divided into four categories on the basis of the curre nt direction at the start of the localisation and whether the crab was caught or not, in order to suggest the probability of the localisatio n being chemically stimulated. At least six of the localisations seeme d to be induced by chemical attraction to the bait. Pots were always l ocated during night at the time of high activity. The searching distan ces ranged from 12 to 48 m. Speed of movement during searching was hig her than speed during basic movement.