Moulting synchrony in green crabs (Carcinus maenas) from Prince Edward Island, Canada

The growth and spread of non-indigenous green crabs (Carcinus maenas) in Atlantic Canada is of concern to the sustainability of shellfish resources, particularly in areas recently invaded. Commercial green crab fishing has been initiated on Prince Edward Island to help control this species and provide a new resource for inshore fishermen. Developing a soft-shell crab product modelled after the Venetian ‘Moleche’ would provide an economic incentive beyond the existing hard-shell crab bait market. However, answers to questions such as the timing and characteristics of green crab moulting are required. A pilot study conducted in 2014–2015 collected seven groups of crabs and held them in individual compartments for 2–4 weeks to record moulting rates and physical characteristics. We found that a synchronized ‘moulting window’ occurs during July for male crabs. Field experiments in 2015 had an average moulting rate of 34%, with group-specific rates as high as 60%. The same cohort of crabs held in the laboratory had an average moulting rate of 48%, with group-specific rates as high as 75%. We observed a gradual increase in moulting rates from early to mid-July, after which all crabs caught had recently moulted, with evidence of new carapaces on all crabs. In 2015, the moulting window followed a 5°C increase in water temperature. Regarding morphology, the presence of a ‘halo’ on the episternites of the carapace was an indicator that a crab would soon moult. These promising results represent the first step in assessing the feasibility of a soft-shell, green crab industry.