Relative growth and size at onset of sexual maturity of the brown crab, Cancer pagurus in the Isle of Man, Irish Sea

In this study, the relative growth, size-weight relationships and size at onset of maturity of the brown crab Cancer pagurus were investigated in the Isle of Man. For the analyses of relative growth and size at onset of maturity, the samples were collected seasonally between autumn 2012 and spring 2013 using several methods: pot surveys, dredge and trawl surveys, market surveys and shore surveys. Results showed that allometric growth occurred in the chelipeds of males (n = 87) and in the abdomen of females (n = 222). Four different measures of maturity (behavioural, functional, morphometric and physiological) were examined. With respect to the behavioural maturity, the smallest female crab found with a sperm plug measured 110 mm CW, whereas in terms of functional maturity the smallest ovigerous female had a CW of 134 mm. Based on direct observations of gonad maturity, 50% of females were mature at 108 mm CW, whereas 50% of males were mature at 89 mm CW. The size at the onset of maturity measurements of female and male C. pagurus based on gonad development is smaller than the current minimum landing size (130 mm), and therefore this suggests that the current minimum landing size is an adequate management measure.