2016 Assessment of the Rougheye and Blackspotted Rockfish Stock Complex in the Gulf of Alaska
Rockfish are assessed on a biennial stock assessment schedule to coincide with the availability of new trawl survey data. For Gulf of Alaska rockfish in off-cycle (even) years, we present an executive summary to recommend harvest levels for the next two years.
We use a statistical age-structured model as the primary assessment tool for the Gulf of Alaska (GOA) rougheye and blackspotted (RE/BS) rockfish complex which qualifies as a Tier 3 stock. This assessmentconsists of a population 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 population model to predict future population estimates and recommended harvest levels. The data sets used i n this assessmentinclude total catch biomass, fishery age and size compositions, trawl and longline survey abundance estimates, trawl survey age compositions, and longline survey size compositions. For an off-cycle year, we do not re-run the assessment model, but do update the projection model with new catch information. This incorporates the most current catch information without re-estimating model parameters and biological reference points.
Changes in the input data: There were no changes made to the assessment model inputs since this was an off-cycle year. New data added to the projection model included an updated 2015 catch estimate (550 t) and new catch estimates for 2016-2018. The 2016 catch was estimated by increasing the official catch as of October 8, 2016, by an expansion factor of 2.3%, which represents the average fraction of catch taken after October 8 in the last three complete years (2013-2015). This expansion factor decreased from last year’s expansion factor of 3.2% and resulted in an estimated catch for 2016 of 628 t. To estimate future catches, we updated the yield ratio to 0.52, which was the average of the ratio of catch to ABC for the last three complete catch years (2013-2015). This yield ratio was multiplied by the projected ABCs from the updated projection model to generate catches of 685 t in 2017 and 668 t in 2018. The yield ratio was slightly lower than last year’s ratio of 0.53.