An individual based model (IBM) of the female brown crab Cancer pagurus population exploited off South Devon, UK is described. Size dependent movement rules are ascribed to individuals based on previous observations of predominantly westward migration down the English Channel. Two additional versions of the movement rules explored whether the empirically derived rule was necessary to model the temporal and spatial distribution of crabs. Local crab movement was dependent on substrate type and water depth. Females prefer a soft substrate in which they can bury when temperatures are low or they have eggs to incubate. Crabs have size dependent depth preferences with larger crabs preferring greater depths. Two recruitment functions are used which relate the number of incoming crabs to the sea surface temperature five years earlier. Model outputs were tested against 10 years of logbook data from three crab fishers and against data from a year-long sampling programme on eight of the vessels exploiting the area. The model reproduces the long-term pattern which is mostly temperature driven. Spatial variation in catch is captured effectively by the model with more crabs being caught in the east of the area than the west and more caught offshore than inshore. The significance of the results is discussed in relation to the crab life cycle, management of the fishery and the potential effects of increasing temperatures.

Size-at-maturity, often used by fisheries managers to specify reference points, was estimated for Cancer edwardsii, the most intensely exploited brachyuran crab in Chile, using morphometric data and observation of the gonadal cycle. Sampling was conducted in Chiloé Island, the principal landing region. Several morphometric measurements of secondary sexual characters were recorded for both sexes. Their size-dependence was investigated in search of ontogenetic allometric changes. Six stages of maturity were established for females, and four for males, on the basis of macroscopic and histological observation of the reproductive system, allowing distinction between adults and juveniles. Females and males, on average, attained full development of secondary sexual characters at 106 and 118 mm carapace width (CW) respectively. The CW at which 50% of females and males have gonads of adult appearance was around 101 mm. Current minimum legal size is 120 mm CW, seemingly high enough for conservation purposes. This management control, however, is unlikely to provide effective protection due to the high proportion of crab of sub-legal size in the landings. Traps with escape vents could be introduced in this fishery in order to ensure its sustainability.