Genetic variation in Irish Sea brown crab (Cancer pagurus L.): implications for local and regional management

Understanding demographic processes over multiple spatial scales is vital for the optimization of conservation/management strategies, particularly for commercially harvested taxa such as the brown crab (Cancer pagurus L). Brown crab population genetic structure was investigated at (i) a local scale within the Irish Sea, which included comparisons with the Lundy No Take Zone (NTZ) and (ii) across the NE Atlantic. The results indicate that the brown crab does not exhibit strong spatial structure either within the Irish Sea or at the regional level, suggesting high gene flow within and among the Irish Sea, English Channel and North Sea. Comparisons between the Lundy NTZ and harvested areas revealed similarly high levels of genetic diversity. An intriguing result was that the Lundy NTZ sample exhibited a degree of genetic patchiness (ephemeral geographically unpatterned differentiation) which may indicate elevated recruitment skews within the NTZ. Overall, the results support the view that brown crabs within the sampled area belong to a single genetically panmictic stock and that if breeding stock sizes are maintained genetic drift will not be strong enough to reduce neutral genetic diversity. The highly connected nature of this species requires international cooperation for sustainable management, an important component of which will be the application of more powerful population genomic approaches to assess finer scale aspects of stock structure as well drivers of genetic patchiness reported for the species. This is a timely consideration in light of potential future misalignments between biological and geopolitical stock boundaries in the Irish Sea following Brexit.