Reproductive potential of snow and tanner crab in Alaska

Abstract

Fisheries for snow (Chionoecetes opilio) and Tanner (C. bairdi) crab in Alaska are managed with large male only harvest regulations. Management of sex-selective crab fisheries could be enhanced by improved understanding of the functional relationship between male harvest and female reproductive potential. This research advances knowledge of factors associated with variation in reproductive potential by characterizing factors influencing female sperm reserves for Tanner crab, identifying factors associated with variability in fecundity for female snow crab in the eastern Bering Sea (EBS), and developing refined indices of egg (embryo) production and recruitment for snow crab that revealed a positive functional relationship that has not been previously described for this stock. Sperm reserves of female Tanner crab varied with mature female ontogeny, sex ratio, and harvest. Increasing exploitation rate is associated with decreased average sperm reserves of primipara (first reproductive cycle) while increased availability of large, sexually-dominant, adult males, was associated with increased cumulative sperm reserves for multipara (second or greater reproductive cycle) among Tanner crab stocks. A white-layer of fresh ejaculate in the spermathecae (sperm-storage organ) was a robust indicator of increased sperm reserves in both primiparous and multiparous females and is likely a useful tool for evaluating risk of sperm limitation in Chionoecetes. Fecundity of female snow crab in the EBS was influenced by both intrinsic and extrinsic factors. Fecundity increased with increasing female size and decreased for older multipara likely due to senescence. Variability in fecundity-at-size was higher among multipara than primipara and this may be associated with contrasting mating dynamics, tempo of reproduction, maternal age, or environmental influences on maternal condition. Mating success may also influence fecundity of multiparous females; females with fresh ejaculate had higher fecundity (~10%) than those that did not. Substantial embryo loss during brooding was not observed for snow crab, and embryo quality did not vary with female size or age relative to maturity. Refining indices of female reproductive potential with demographic and fecundity information resulted in reduced estimates of reproductive output. A positive functional relationship between reproductive potential and recruitment was detected at a lag of four years due to coherence between high reproductive output in the late 1980s and strong recruitment in the early 1990s. Stock productivity reached a minimum thereafter, preceding a rapid decline in mature abundance.