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Temporal and Spatial Variability of Alaska Red King Crab Fecundity, and Accuracy of Clutch Fullness Indices in Estimating Fecundity

Temporal and Spatial Variability of Alaska Red King Crab Fecundity, and Accuracy of Clutch Fullness Indices in Estimating Fecundity

K.M. Swiney, J.B. Webb, G.H. Bishop, and G.L. Eckert

Temporal and Spatial Variability of Alaska Red King Crab Fecundity, and Accuracy of Clutch Fullness Indices in Estimating FecundityThis is part of Biology and Management of Exploited Crab Populations under Climate Change
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Description

Stock assessment and management of the Alaska red king crab, Paralithodes camtschaticus, will be improved by incorporating information on egg production in the development of biological reference points; therefore, an understanding of spatial and temporal variability in fecundity is needed. Here we compare summer fecundity estimates in red king crab, taking into account differences in female size, from three time periods in Bristol Bay, Alaska (1980s, 2007, 2008) and from four areas in southeastern Alaska in 2008. Fecundity of likely primiparous (<105 mm CL) Bristol Bay females was significantly greater in 2007 followed by the 1980s and 2008. Among likely multiparous females (≥105 mm CL), fecundity was greater in 2007 and 2008 (which did not differ) than in the 1980s. Fecundity of crabs in southeastern Alaska did not vary significantly among areas sampled. Red king crabs in Bristol Bay were more fecund than crabs in southeastern Alaska. The temporal and spatial variability in fecundity observed in this study should be considered in development of biological reference points and fishery stock assessments. A second objective of this study was to assess the current methods for estimating egg production on crab abundance and distribution surveys and by observers onboard commercial vessels. We compared quantitative measures of fecundity with clutch fullness indices (CFI), which score egg clutches by a visual estimate of egg clutch size relative to abdomen size in either 10% or 25% fullness increments. Significant differences in fecundity were not detected between consecutive CFI scores, suggesting that current CFI methods are not exact estimators of fecundity. More precise and easily executed methods to estimate egg production are needed.

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