Spatial variability in velvet crab populations: a possible candidate for real time fisheries management.

Recent work has shown that there is variability in the pattern of moulting in velvet crabs around Shetland. As a result of this, alternate closed seasons on the east and west coast have been implemented to protect stocks. Recent studies and reports from fishermen have shown that the patterns of moulting are variable between years, as well as between areas, and this has resulted in the closed seasons being ineffective, in some cases displacing effort from areas where crabs are hard-shelled to areas with a high proportion of soft-shelled crabs. Previously, total closure of the fishery has disrupted supply to the market, and presented an economic challenge to inshore fishermen who may not be able to diversify locally to other species for the period of the closure. This report details an investigation into the variability in velvet crab moulting around Shetland during the closed period of the fishery in 2007 and 2008. The aim of this work was to gather together data to determine the practicality of implementing real time closures for this fishery.

This work has identified a successful method for the identification of soft crabs at sea which could be implemented through fishers reporting and observer trips to inform the management system. Data collection on the presence of soft crabs within the Shetland fishery has shown that the closed season did not match the periods of moulting within the velvet crab population in either 2007 or 2008. This resulted in displacement of fishing effort to areas with a relatively high proportion of soft crabs. This would allow closures to be synchronised with the moult cycle of the velvet crab. The data collected in 2008, however, indicated that the soft crabs were present in all areas simultaneously which, with a real time closure system, would have resulted in the complete closure of the fishery, with associated supply problems. Market forces have a strong influence on the velvet crab fishery in Shetland and therefore this process was approached with caution by fisheries managers.

For Shetland’s fisheries it is recommended that reporting of soft crabs should be used to determine the start of the closed season, and, should the moult occur simultaneously in all areas, that the first closure each year is rotated between east and west coasts, so that the displacement of effort into areas of soft crabs is not always on the east coast of Shetland. The identification of soft crabs by fishermen as a tool for implementation of closed areas could be used in the management.