Restratification of red king crab stock assessment areas in southeast Alaska

Restratification of red king crab stock assessment areas in southeast Alaska

J.E. Clark, S. Hinkley, and T. Koeneman

Restratification of red king crab stock assessment areas in southeast AlaskaThis is part of Crabs in Cold Water Regions: Biology, Management, and Economics
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Description

The red king crab (Paralithodes camtschaticus) stock assessment survey is a pot survey which is used to estimate abundance in surveyed areas and set guideline harvest levels. Studying the spatial patterns of crab catches in these pots contributes to a better understanding of the distribution and interactions of different population segments in an area, refinement of survey design, and improvement in accuracy of abundance estimates. We developed a process to stratify survey areas and to evaluate the impact of this stratification on the precision of average catch per pot-day estimates. This process involves determining the best method and optimum distance interval over which to average catches to better predict the catch for a specified location. Relative catches (catches divided by overall average catch for an area and year) are estimated for all locations, and the survey area is divided into strata based on these estimates. A resampling simulation evaluates the impact of this new stratification on precision. Application of this process to red king crabs in Deadman Reach, Southeast Alaska,resulted in the variance of average catch estimates decreasing to 45% of the variance of randomly allocated survey effort across the entire area,and to 58% of the variance using the 1986-2000 stratification.

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