Spatial and temporal variation of size at maturity in an intensive crustacean fishery with limited management

The edible crab Cancer pagurus supports a valuable northeast Atlantic fishery, but concerns have been raised about declining catches and its management relies heavily on minimum landing sizes (MLSs). Furthermore, few data are available on spatial and particularly temporal variation in maturity of this and other crab species. Here we estimated size at maturity for C. pagurus in the Irish and Celtic Seas (north and south Wales, UK, respectively, around 200 km apart) caught during 2020-2021 and compared these to the Wales-wide MLS of 140 mm carapace width (CW) and results of a similar study six years earlier. Using a standard scenario where only stage 1 gonads are considered immature, CW50 (50 % of individuals are mature) for all Wales (north and south pooled) was 88 and 107 mm (males and females respectively), in line with regional literature. We found significant spatial variation, with significantly smaller gonadal CW50 in north Wales compared to south Wales, for both males (83 cf. 94 mm) and females (98 cf. 114 mm). By 119 mm CW, a high proportion (99 % males, 50-95 % females) were gonadally mature (standard scenario), morphologically mature (most sex and area combinations), and the smallest functionally (ovigerous) and behaviourally mature females had been recorded. We only found evidence for a significant decline in size at maturity since the previous study using a more conservative gonadal scenario, where stages 1 and 2 are considered immature. This found declines for both sexes in north Wales (and all Wales pooled) and females in south Wales. Our results suggest the MLS adequately protects immature individuals, but further management measures may be needed to address reported declines.