• Changes in embryonic development, hatching, and zoeae of snow crab with variation in incubation temperature

      Webb, Joel Benjamin (2005-08)
      The effect of incubation temperature on duration of embryonic development and morphology, weight and energetic content of post-hatch zoeae was described for snow crab, Chionoecetes opilio, from the eastern Bering Sea held at -1, 0, 1, 3, and 6° C in the laboratory from collection to hatch. The mean incubation time increased with decreasing temperature by 32% (113 d) between 6 and -1° C. Extrusion success of females at 6° C was lower versus 0 or 3° C, but the duration of hatching did not vary significantly with incubation temperature. A one-year cycle of embryo incubation was observed, indicating that switching from one to two-year duration of embryo incubation may occur early in development. The energy content and individual weights of post-hatch zoeae were not significantly affected by temperature, indicating that longer incubation periods may not have an energetic cost. The rostro-dorsal length of zoeae incubated at 6° C was smaller than those from cooler temperatures. Conversely, the length of the 3rd abdominal somite increased significantly with decreasing temperature, perhaps serving as an indicator of incubation temperature in field collected zoeae. The consequences of varying incubation temperature appear on post-hatch zoeae appear to be limited between -1° and 6° C.
    • Reproductive potential of snow and tanner crab in Alaska

      Webb, Joel Benjamin; Kruse, Gordon; Eckert, Ginny; Woodby, Douglas; Sainte-Marie, Bernard (2014-12)
      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.