2016 Assessment of the Sablefish Stock in Alaska
New data included in the assessment model were relative abundance and length data from the 2016 longline survey, relative abundance and length data from the 2015 longline fishery, length data from the 2015 trawl fisheries, age data from the 2015 longline survey and 2015 fixed gear fishery, updated catch for 2015, and projected 2016 -2018 catches.
The 2016 Center for Independent Experts (CIE) review panel had a number of recommendations to improve aspects of the reference model. We present the reference model and seven alternatives that sequentially address some of the key recommendations made by the panel. The first five alternative models address the data inputs described above. We consider the first two of these alternatives to be minor model changes (incorporating the area sizes and variance estimates for the domestic longline survey). The next three incorporate corrections of the domestic longline survey and longline fishery for whale depredation, which we consider to be a benchmark change that was recommended by the CIE.
The final two models address the CIE panel’s concern that the model provided “overlyprecise” estimates of management quantities. These models reweight the abundance indices relative to obtaining a standard deviation of normalized residuals of one for the domestic longline survey abundance index, while maintaining a value of one for the previously tuned age and length compositions. These two models increase the uncertainty around estimates of spawning biomass and other key management results. Finally, the recommended model estimates natural mortality with a prior distribution, which further propagates uncertainty. In addition, the recommended model has the best retrospective performance of all models considered.