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.
Brown crab (Cancer pagurus) is a widely distributed crustacean that occurs around the British coastline supporting important commercial fisheries. The habitat preferences of brown crab around Scotland are poorly documented and for the purposes of stock assessment, the species is considered data-poor. Based on an analysis of dredge and trawl surveys taking place in the North Sea (2008–2018), we describe the spatial distribution of brown crab and for the first time, develop abundance and recruitment indices for the species. We make use of geostatistical methods and apply generalized additive models to model catch rates in relation to a number of explanatory variables (depth, distance to the coast, sediment type and year). The dredge and trawl abundance indices were correlated showing a similar trend of increasing catch rates in the early years of the time series up to 2016 and a subsequent reduction. The recruitment index showed a gradual increase in captured juvenile crabs up to 2014 followed by a steep decrease with 2018 being the lowest value estimated. The derivation of robust indicators of stock abundance will contribute to the stock assessment of this species and enable the provision of improved fisheries management advice for brown crab around Scotland.
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