Reproductive ecology of female snow crab (Chionoecetes opilio) in the Barents Sea. Maturation, fecundity and brooding

Abstract

The snow crab (Chionoecetes opilio, O. Fabricius 1788) relatively recently (first reports in 1996) established a population in the Barents Sea. Both the populations size and distribution area have drastically increased since then, and the species is now distributed over large parts of the northern and eastern Barents Sea, and further expansion northward and westward has been predicted. Despite an emerging fishery, the Barents Sea stock is poorly investigated with regards to basic biological properties important for fisheries management. The aim of this study was to describe several aspects of the reproductive ecology of female Barents Sea snow crab including estimates of fecundity, egg survival during brooding, size at maturity, and incubation cycle. In total, 4 133 female and male crabs were sampled between February 2006 and September 2017 from the central Barents Sea. Of these crabs, 1 803 were females with a size range of 10-100 mm carapace width (CW), and 2 330 were male crabs that ranged from 7-145 mm CW. About 54% (2 233) of all crabs (female and male) caught were between 15 and 20 mm CW. The size range of mature (and ovigerous) females was 48- 100 mm CW. Immature females ranged from 10 to 77 mm CW. The size of 50% maturity was estimated to be 62 mm CW. Most of the females (95%) had 100% clutch fullness. There was a significant positive relationship between fecundity (y) and carapace width (x) which can be described by the equation y = 0.24 * x 2.93. The modeled relationship gives an estimated fecundity of a 75 mm CW female (which was the mean size of mature females) of ~ 77 000 eggs in one reproductive cycle. From the observed fecundity and size frequency distribution it was deduced that more than 50% of the eggs in the Barents Sea population are produced by females between 65 and 79 mm CW. The categorization of primiparous and multiparous females based on exoskeleton condition was shown to be problematic. No evidence of egg mortality during brooding was found. Simultaneous occurrence of females with different developmental stages of the broods, and differences in ovary weight between these females at the same size suggest the existence of a biennial egg brooding cycle in the Barents Sea. Further research on the reproductive ecology and spatial dynamics of the Barents Sea snow crab population is advised.