Extending statistical age-structured assessment approaches to Gulf of Alaska rockfish (Sebastes spp.)

Extending statistical age-structured assessment approaches to Gulf of Alaska rockfish (Sebastes spp.)

D.L. Courtney, J.N. Ianelli, D. Hanselman, and J. Heifetz

Extending statistical age-structured assessment approaches to Gulf of Alaska rockfish (Sebastes spp.)This is part of Biology, Assessment, and Management of North Pacific Rockfishes
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Description

Modern age-structured stock assessments typically involve use of a complex "packaged" model or programming of a customized model. For Gulf of Alaska (GOA) rockfish, a customized model has been developed for use with four rockfish species: northern rockfish (Sebastes polyspinis), Pacific ocean perch (S. alutus), dusky rockfish (S. variabilis), and rougheye rockfish (S. aleutianus). Each species has particular differences in fishery, survey, and biology, and changes to the customized model structure have allowed for the additional data types and special fishery and biological characteristics. Compared with large, more feature-rich packaged programs, the software developed for GOA rockfish is efficient and relatively straightforward to implement. We describe the customized model and compare differences in model structure among the four applications, the relative impact of different data sources, and factors affecting the uncertainty of key parameter estimates. Modifications needed to adapt the customized model to the different rockfish species were relatively minor, and comparisons among assumptions were easy to compile. Comparison of diagnostics of model fits and estimates of uncertainty in key parameters among species indicated that the variance specified for most data components was consistent with characteristics of the data and the biological aspects unique to each rockfish species. The development of a customized age-structured model for several rockfish species proved to be adaptable for evaluating uncertainty and the information content of diverse types of data.

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