The decapod crab species Cancer pagurus is currently the most valuable crab fishery in UK waters. Fecundity is the reproductive rate of crabs measured by the number of eggs she produces; which is important for fisheries managers, as it is used to calculate the reproductive potential of a stock. Together with information on survival between life stages it is possible to estimate the expected number of recruits entering each life stage and then into the fishery. To date no published studies report the fecundity for Welsh C. pagurus; although there are a number of published studies on C. pagurus from the North Sea. A total of 96 gravid female C. pagurus were obtained from the static gear fishery in Welsh waters in 2014. Morphometric measurements were taken and external eggs were staged, measured and counted. Crabs were then dissected and internal ovary structure and condition was noted and hepatopancreas was removed and weighed to determine an index of body condition. The state of the female prior to capture was noted and each crab was assigned a condition index depending on which limbs and how many were missing (and were beginning to heal or regrow, thus were not lost during capture, transport or storage). Fecundity increased with carapace width; however, the strength of relationship varied with region and between this and other published research. Total fecundity varied between 26,590 and 2,836,000 eggs per female from crabs sized between 116 and 198 mm carapace width; this is within the range of other published research for this species. Most females carried eggs at an early stage of development (early gastrula) and as such, they were all approximately 400 μm in size. Morphologically more eggs are carried on the two proximal pleopod pairs, and significant differences of egg numbers between pleopods were observed. Crabs that had lost one claw and other limbs also had much lower fecundity and a variable ratio of eggs between the pleopods; though sample size of damaged females was too small for this trend to be significant. The hepatosomatic index decreased with increasing fecundity indicating that producing more eggs required more energy, regardless of animal size.
This research highlights the complexity in energetic trade-offs between condition, fecundity and energy reserves. Research is currently underway to determine if crab condition effects the level of energy provided to each individual egg; which would in turn determine the survivability of the larvae.