The incidence of autotomy in an estuarine population of the crabCarcinus maenas

The incidence of autotomy is described for a discrete population ofCarcinus maenasin the Yealm Estuary over a period of one year. During this time the crabs showed seasonal trends in distribution whereby during the summer months they congregated at the top of the estuary. This seasonal migration up and down the estuary corresponded with peak rates in the rate of change in temperature of the bottom water. Recruitment occurred in June, July and August. Overall, there were more female than male crabs although the ratio varied throughout the year. All sizes and sexes of crabs autotomized limbs but although autotomy increased with the size of the crabs it showed no obvious relationship with other population parameters. Significantly more chelipeds than walking limbs were lost. There were more multiple autotomies than would be expected if autotomy was a random event. Autotomy is shown to be a rare event for sexually matureCarcinusbut essential to the survival of immature crabs. The means by which crabs may regulate the incidence of autotomy is discussed.