Seasonal movements of Atlantic rock crab (Cancer irroratus Say) transplanted into a mussel aquaculture site

Approximately 73 000 Atlantic rock crab (Cancer irroratus) were captured in coastal waters and transferred to an estuarine mussel aquaculture site in Prince Edward Island, Canada, in an effort to control overgrowth by the invasive tunicate Ciona intestinalis. To assess whether transplanted crabs remained in the vicinity of mussel farms, acoustic tags were attached to 25 resident and 25 transplanted individuals (all males) and their movements were monitored for 1 year, from September 2006 to August 2007. Resident crabs tended to occupy (within 1.6 km) the middle estuary where the majority of mussel farms are located. They left this area during winter, possibly to reach upstream overwintering grounds, and most returned to the middle estuary in spring. In contrast, translocated crabs exhibited a marked downstream movement (<5.5 km distant) in autumn and winter and few returned into the middle estuary in spring. Results suggest that transplanting large numbers of additional rock crabs is not an effective means to reduce the effects of invasive tunicates on mussel farms.