Stock Assessment Model Evaluation for St. Matthew Blue King Crab

Stock Assessment Model Evaluation for St. Matthew Blue King Crab

J. Zheng, D. Pengilly, R. Foy, and D. Barnard

Stock Assessment Model Evaluation for St. Matthew Blue King CrabThis is part of Biology and Management of Exploited Crab Populations under Climate Change
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Description

A catch-survey analysis was developed with trawl survey data from 1978 to 2009, triennial pot survey data from 1995 to 2007, and commercial catch data from 1978 to 2009 to assess St. Matthew Island blue king crab abundances. A maximum likelihood approach was used to estimate abundance and recruitment. Because of the sharp decline of survey abundance in 1999, five model scenarios with different combinations of natural mortality (M) and trawl survey catchability were evaluated. The evaluation criteria include likelihood ratio tests and fits of abundance and biomass. Scenarios 1-3 with estimating M separately for 1999 resulted in a significant improvement in fit from scenarios 4 and 5 with a constant M. Among the five scenarios, with a p-value of 0.05, scenario 1 with fixed M for both 1978-1998 and 2000-2008 (M = 0.18 per year) and trawl survey catchability (Q = 1) with M estimated by the model in 1999 is the best model, and scenario 4 with a fixed constant M = 0.18 per year for the whole time series is the worst one.

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