2016 Assessment of the Pacific Ocean Perch Stock in the Gulf of Alaska
Rockfish are assessed on a biennial stock assessment schedule to coincide with the availability of new survey data. For Gulf of Alaska rockfish in alternate (even) years we present an executive summary to recommend harvest levels for the next two years. Please refer to last year’s full stock assessment report for further information regarding the assessment model (Hulson et al., 2015, A full stock assessment document with updated assessment and projection model results will be presented in next year’s SAFE report.
We use a statistical age-structured model as the primary assessment tool for Gulf of Alaska Pacific ocean perch which qualifies as a Tier 3 stock. 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 (18,733 t) and new estimated catches for 2016-2018. Normally in off-cycle assessments the current year’s catch (2016) is estimated with an expansion factor that is the average additional catch from the date of running the projection model (beginning of October) through the end of December from the previous three complete catch years (2013-2015). In 2014 the directed fishery for Pacific ocean perch in the Western Gulf did not occur until after October 15; in a typical year the large majority of TAC in the Western Gulf is caught by the end of August. This additional catch in October of 2014 resulted in an inflated expansion factor that estimated 2016 catch to exceed the gulfwide TAC by nearly 1,800 t. However, the catch of Pacific ocean perch as of October 8, 2016 remains nearly 1,350 t less than the gulfwide TAC, directed fishing has ceased in the GOA, and Pacific ocean perch has been placed on prohibited species catch (PSC) status in the Central Gulf. We find it highly unlikely that the 2016 catch will exceed the TAC by such an amount that is suggested by the expansion factor, thus, for this year’s projection model we have set the 2016 estimated gulfwide catch at the 2016 TAC of 24,437 t. We expect in the future to return to the use of the expansion factor once the 2014 anomaly in the Western gulf has moved out of the three year averaging window. To estimate future catches (2017-2018), we updated the yield ratio to 0.87, which was the average of the ratio of catch to ABC for the last three complete catch years (2013-2015) and resulted in the same yield ratio as used in the 2015 full assessment. This yield ratio was multiplied by the projected ABCs from the updated projection model to generate catches of 20,806 t in 2017 and 20,201 t in 2018.