Size-at-maturity of Brown Crab (Cancer pagurus) in Scottish waters based on gonadal and morphometric traits

Minimum landing sizes (MLS) are commonly used to manage crustaceans and are generally set above the size at first maturity to ensure that some protection is afforded to exploited stocks. Despite the economic importance of the brown crab fishery in Scotland, the species is considered data-poor and only limited information is available on size-at-maturity. This study provides, for the first time, estimates of the size-at-maturity of brown crab on the east and west coasts of Scotland using gonadal and morphometric criteria. Gonadal maturity was determined from female ovary and male testes, which were classified macroscopically into development stages and their relationship with body size modelled using a logistic regression. Body morphometric maturity was studied by analysing morphometric changes in growth in the male chelae and female abdomens using generalized additive models and regression models to estimate the size at which changes in allometric relationships occur. Estimates of size-at-maturity using gonad development were 101-106 mm carapace width (CW) for males and 127-128 mm for females. Size-at-maturity based on the morphometric characters were 120-148 mm CW for males and 131-142 mm for females. Results show that brown crab maturity is likely to occur at lower sizes than the current MLS in Scotland, implying that crabs may be able to reproduce at least once before being harvested. Regional variations in local populations should be considered when setting a MLS and this study suggests that the current MLS of 150 mm is appropriate for both areas considered.