UW Aquatic & Fishery Sciences Quantitative Seminar

Kari Fenske

Washington Department of Fish and Wildlife

How do you slice the pie? Methods for evaluating ABC apportionment options for a highly mobile Alaska sablefish population.

Abstract

Alaska sablefish are highly mobile and are assessed annually using a single-area stock assessment model which assumes that the population is well mixed. Each year the model-estimated Acceptable Biological Catch (ABC) must be apportioned into the 6 spatial regions used for management. At present, the accepted approach for apportionment is based on a 5-year exponentially weighted moving average of survey and fishery abundance indices in each region; with the intent that this approach would adequately track changes regional biomass and reduce variability in interannual apportionment. However, in recent years interannual variability in the survey has been high in some regions leading to large annual changes in apportionment, and as a result, apportionment has been fixed at the 2013 values for two years. We are investigating new apportionment options using simulation-based MSE-type approach and a newly developed spatial assessment model. We will be presenting our methods with the hope of gaining feedback on the overall approach and more ideas for potential ways to apportion ABC.