Graduate Thesis Or Dissertation
 

Size classes, population structure, growth, sex ratio, and size and age at maturity of Chionoecetes tanneri Rathbun (Brachyura:Majidae) off the Oregon coast

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593tz73f

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  • During eleven cruises conducted off the Oregon continental slope from April 1973 to March 1975, approximately 1600 specimens of the majid crab Chionoecetes tanneri Rathbun were collected. A time sequence of size frequency histograms and bivariate plots of allometric measurements were used to determine size classes, population structure, growth and age at maturity of C. tanneri from the Oregon coast. Adult sex ratios and sex ratios for each of the juvenile size classes were computed. Bivariate plots of carapace width and cheliped length for males and carapace width and abdomen width for females defined nine size classes for juvenile males and eight size classes for juvenile females. The morphogenic relationship between differential cheliped length and gonad maturity in males and differential abdomen width and gonad maturity in females (Watson, l970a; Brown and Powell, 1972) allowed determination of minimum size at maturity of 118 mm carapace width for male C. tanneri and 85 mm carapace width for female C. tanneri. Mean carapace widths for adult males (142.7 mm) and adult females (102.5 mm) collected for this study compare well with those given by Pereyra (1972). Mean carapace width increase for each molt for all juvenile size classes was computed to be 26.14%. When size classes were equated to molt groups a linear regression (Time = -2.94 + 0.81 (Carapace width)), based on progression of carapace width modes through time, predicts age at maturity to be from five to six years. A highly significant departure from a 1:1 sex ratio for adults, of 2.41 females per 1 male, is consistent with reports for other members of the genus Chionoecetes (Hilsinger, 1975).
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