Publication Abstract

Electronic data storage tags reveal the behaviour of free-ranging edible crab, Cancer pagurus L., in UK waters.

E. Hunter*, A. Riley*, D. Eaton*, C. Stewart*, A. Lawler*, A. Leocadio* & M. Smith*

The fishery for edible crabs (Cancer pagurus) is one of the most important commercial fisheries in England and Wales, yet there remain several important gaps in our understanding of their biology and ecology. Previous mark-recapture experiments carried out in the 1970s in the English Channel indicated some long distance movements, generally from east to west, particularly by mature females, and return movements by adults were not demonstrated. Since then, however, there have been significant changes in both the environment and the fishery.

Here we describe the first results from a large-scale application of archival electronic data storage tags (DSTs). One hundred and twenty-eight mature, fresh-shelled females (carapace width 138 – 288 mm), were released at 4 sites in the English Channel and Celtic Sea between August 2008 and June 2009. The tags allowed continuous records to be made of ambient pressure (depth) and temperature experienced by free-ranging crabs in their natural environment at 30 s intervals between the times of release and recapture.

To date, 35 DSTs (27%) have been returned through the commercial fishery, with data records ranging from 8 to 430 days. Observed migration patterns, reconstructed using the “tidal location method”, were essentially similar to those originally described from mark-recapture data, with no evidence of west-east migration in any location or at any time of year. Furthermore, the data have also provided valuable insights into habitat occupancy on local and regional geographical scales, and activity patterns related to diurnal, tidal and reproductive cycles, notably a period of inactivity associated with egg-brooding which lasted from December to June.

Understanding how, where and when crabs undergo large scale migrations is a key element of successful stock assessment and management and is important in identifying key life stages and periods that may be vulnerable to local fishing or other human activities. The results described above are therefore particularly relevant to marine spatial planning, and will contribute biological parameters to population dynamics models addressing management of crabs on a wider scale.