Movement of adult edible crab ( Cancer pagurus L.) at the Swedish West Coast by mark-recapture and acoustic tracking

Abstract

Movements of the edible crab Cancer pagurus were investigated from mark-recaptures in the Skagerrak and Kattegat. Crabs were released in 1968–1973 and in 2003 from six main areas along the Swedish west coast, and from one offshore bank in the Kattegat. Recaptures were reported for up to 7 years after the release. Sex-specific differences in migration were found: females migrated significantly longer distances than males, and higher proportions of males stayed within the area of release (60 and 48% of males versus 28 and 19% of females) were recaptured within 1 km of the release site: initial and recent mark-recapture studies, respectively. The movement direction varied with sampling location, however females tended to move in a net southerly direction. The range of mean rates of movement within the first month were 325–345 m d −1 for females and 202–299 m d −1 for males. Over longer time periods mean rates of movement were significantly lower. There was no significant impact of size class on the distance migrated. Short-term (2 months) movements of nine male edible crabs were studied with acoustic transmitters and active tracking. The movement pattern varied among individuals: some stayed in the same area for weeks whereas some made regular movements every day during the tracking period. The difference in migration pattern of females and males, and the largely southward migration of females is consistent with the hypothesis that the migration is related to reproduction. By moving to the south to release their larvae, females may compensate for larval dispersion in the northbound current along the Swedish west coast. The observed migration pattern indicates advisable management options in Sweden for this commercially fished species: protection of areas with high proportion of egg-bearing females from fishing, especially in the Kattegat. Significantly, local management only on a small spatial scale is not recommended as the resource is seasonally shared, if not the effect on the crab population is monitored.