2018 Assessment of the Northern Rockfish Stock in the Gulf of Alaska
Gulf of Alaska (GOA) rockfish are assessed on a biennial stock assessment schedule. In 2017, the scheduled frequency for some stock assessments was changed in response to the National Stock Assessment Prioritization effort. Prior to 2017, Gulf of Alaska (GOA) rockfish were assessed on a biennial stock assessment schedule to coincide with the availability of new trawl survey data. Under the new schedule, full assessments for northern rockfish will be conducted in even years and partial assessments will be presented in odd years, resulting in the same frequency of assessment but age compositions from the most recent survey being available to each full assessment. For 2018, we present a full stock assessment document with updated assessment and projection model results. In this full assessment, we update the 2015 assessment model with new data available since 2015 and present a new model fitting to a model-based index of abundance from the NOAA GOA bottom trawl survey created using a Vector Autoregressive Spatio-temporal (VAST) model.
As in 2015, the general model structure for GOA northern rockfish is a separable age-structured model, and this same model structure is used for Gulf of Alaska Pacific ocean perch, dusky rockfish, and rougheye/blackspotted rockfish. This consists of an assessment model, which uses survey and fishery data to generate a historical time series of population estimates, and a projection model, which uses results from the assessment model to predict future population estimates and recommended harvest levels.