Standardizing CPUE from Aleutian Islands Golden King Crab Observer Data

Standardizing CPUE from Aleutian Islands Golden King Crab Observer Data

M.S.M. Siddeek, Jie Zheng, and Doug Pengilly

Standardizing CPUE from Aleutian Islands Golden King Crab Observer DataThis is part of Assessing and Managing Data-Limited Fish Stocks
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Fishery-dependent data are the only source for assessments of many data-poor stocks. Catch per unit effort (CPUE) is commonly used as a measure of relative abundance for those stocks. In the absence of surveys or biomass assessment models, nominal CPUEs from commercial pot fisheries have been used to monitor the stock status of golden king crab in Alaska’s Aleutian Islands. In this paper we develop an analytical technique to standardize the CPUE from observer data from the eastern Aleutian Islands pot fishery. We consider different time series of CPUE data (pre- and post-crab rationalization time periods and the whole time period) with a number of explanatory variables (categorical and continuous) and employ piecewise cubic spline and the negative binomial error distribution in the generalized linear model (GLM) framework for standardization. After crab fishery rationalization in 2005, both soak time and CPUE increased markedly, coinciding with a reduction in vessel participation. Because of that change, we fit separate GLM for pre- and post-rationalization CPUE time series and the whole time series. We identify non-interacting explanatory variable sets to standardize observer CPUE data, present post-fit diagnostic statistics and step plots, and compare standardized CPUE indices among different time series of data. Trends in standardized and unstandardized CPUE are similar during pre- and post-rationalization time periods and the whole time period, but standardized CPUE values are lower during the latter part of the time series. Residual diagnostic plots show no violations of model assumptions and support negative binomial error distribution for standardization.

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