Soft-shelled European green crab: an alternative use for an invasive species

Principal Investigators: Pedro A. Quijon & Sophie St-Hilaire

The growth of invasive European green crab populations in PEI threatens the sustainability of healthy aquatic systems, other shellfish species, and the livelihood of fishing communities that rely on these resources. There is an urgent need to develop mitigation and control measures to help sustain healthy shellfish and provide alternative sources of income to fishers. A green crab fishery may address this need, but its viability over time is uncertain due to the lack of a competitive market for harvested crabs. One attractive option is the development of a soft-shell green crab product, similar to the successful soft-shell crab industry in regions of Italy and the US. These industries rely on the identification and harvesting of “soft” moulting crabs that sell for over $60 CAD per kilogram in Venice, Italy.

The goals of this project were to explore the most promising methods for identifying moulting green crabs in PEI and to apply the sorting and holding techniques used in Italy to green crabs in PEI. Through study of the existing soft-shell fishery in Italy and local field studies, our goal was to lay the foundation for an industry to address the mitigation of an invasive species and the sustainability of healthy shellfish resources.

Our preliminary findings suggest that the moulting event is temperature-dependent, and we learned from the Italians how to identify crabs that are within ~3 weeks of moulting. Over the last two summer seasons, we have observed between 40 and 70% molting in male crabs held under both laboratory and field conditions. Research and development of a better handling system is required to improve the economics of this industry, but we have determined that, in 2014, it cost fishermen approximately $0.30 per lb to catch green crabs.

Our trip to Italy in the fall also revealed that female crabs are less likely to molt synchronously in the fall than are males in early summer. The Italians prefer to catch the females as hard-shell pregnant crabs in the fall and market them for the eggs. This could also become a new industry in Canada, and will require more research to determine the optimal time to harvest the crabs for the best quality roe.