Chapter 1b: Assessment of pollock (Theragra chalcogramma) from the Bogoslof Island Region James N. Ianelli and Steven J. Barbeaux Alaska Fisheries Science Center National Marine Fisheries Service Executive Summary In 1987 pollock catch peaked in the Bogoslof region (INPFC area 518) with over 370,000 tons reported. During the period from 1985 to 1991, a total of 932,996 t of pollock were caught in this region. NMFS subsequently closed this area to directed pollock fishing (1992-2005) due in part to agreements under the Convention on the Conservation and Management of the Pollock Resources in the Central Bering Sea. Under this convention, the Bogoslof spawning aggregations are linked to the abundance of pollock found in international waters of the Aleutian Basin. As part of the monitoring program for the Convention, 17 annual Echo Integration Trawl (EIT) surveys of Bogoslof pollock abundance have been undertaken since 1988. In 2005 an age-structured stock assessment was developed and presented to the Council for consideration. In 2006 this analysis was refined based on advice of the SSC by considering alternative assumptions about Donut Hole catches during the 1980s. The analysis showed sensitivity to these assumptions and since they seem equally plausible, acceptance of a model was considered premature until the exchange of pollock between the Bogoslof and Central BS regions stock could be more clearly understood. Since information to help resolve these issues is still lacking, any improvements to be made on the assessment model would be of limited value. Therefore, this assessment provides maximum permissible ABC estimates based on Tier 5. Additionally, an adjusted ABC is provided identical to the method that the Council has selected in past years. Changes in the assessment data, methodology, and results In the winter of 2007 an echo-integration trawl (EIT) survey was conducted and provides the biomass estimate used for this assessment. Maximum permissible ABC and OFL estimates for 2008 and 2009 under Tier 5 were used in place of an age-structured stock assessment model. This method relies exclusively on the NMFS survey biomass estimate. The 2007 survey biomass estimate of 292,000 t represents a 22% increase over the 2006 estimate. This results in a Tier 5 maximum permissible ABC value of 43,800 t (assuming M = 0.2). Using an alternative to this value (which includes a target stock size) gives 8,000 t. Response to SSC comments In their December 2006 minutes, the SSC commented: “This year the authors explored the effect of Donut Hole catches in the 1980s on the stock assessment results. They assumed that 75% of the Donut Hole catches came from the Bogoslof stock, which is in accord with past practices of international pollock workshops (which used a range from 60 to 80%). The authors and Plan Team have remaining concerns about this assumption and also about the degree of interchange between Bogoslof fish and central BS fish. The SSC encourages further work in this regard by exploring the sensitivity of the assessment to this percentage. Consequently, the SSC agrees with the Plan Team to postpone acceptance of the model until this research is done.” Additional research on evaluating the proportion of Donut Hole pollock catches to assign to the Bogoslof stock awaits additional data and resources to conduct analyses. It is likely that additional information, if it exists, would fail to reduce the uncertainty appreciably. Given this, the authors feel that any improvements over the age-structured model presented last year would be of limited value. Therefore the