The International Pacific Halibut Commission adopted a coastwide stock assessment methodology at its 2008 Annual Meeting. This methodology accommodates movement of halibut at all ages and determines a single coastwide estimate of exploitable biomass. This single coastwide estimate is then apportioned into IPHC regulatory area estimates using data from the fishery-independent IPHC setline stock assessment survey and estimates of bottom area from each regulatory area. This apportionment resulted in a different distribution of the exploitable biomass than had been estimated with the previous closed-area stock assessments.

At the 2008 Annual Meeting, the IPHC Commissioners and industry endorsed the coastwide stock assessment methodology but wished to have further investigation of methods for apportioning the coastwide exploitable biomass estimate into IPHC regulatory area estimates of biomass and catch limits. In addition, the Commission requested that the staff update industry on the most recent results and understanding of halibut movements arising from Commission tagging programs, particularly the PIT-tag experiment. This workshop addressed both of these issues.

Questions on the workshop can be directed to either Laura Black or the IPHC office at (206) 634-1838.

• Apportionment Workshop summary

• Questions and Comments at the Workshop

• Outline of proceedings  

• Presentations 

  • The IPHC Stock Assessment, Harvest Policy, and Exploitable Biomass Apportionment (4.3 MB pdf)

  • IPHC PIT tagging study (1.6 MB pdf)

  • Exploring Effects of Fishing and Migration on the Distribution of Pacific Halibut (2.4 MB pdf)

  • Presentation slides for Area 2C regional meetings (2 MB pdf)

• News Release

Using IPHC Widgets

Widgets are a type of graphical user interface (GUI) that can be used to display information changeable by the user, such as a window or a text box. One of the advantages of a widget is to provide a single interactive tool to manipulate data, specify data inputs, model characteristics and view results. The International Pacific Halibut Commission developed two widgets for the 2008 IPHC Biomass Apportionment Workshop, one to illustrate alternative apportionments and another one to illustrate the effects of migration and fishing on the distribution of biomass. An updgraded version of the migration/fishing widget was used at the Biomass Apportionment Workshop II.

Documents relevant to the Biomass Apportionment Workshop 

• IPHC Scientific Report 83, which describes the assessment model and harvest policy
• Aims of study, external technical review, tagging protocol, holding experiments, and scanning experiments (2002)
• Initial work in 2001 on tagging location, holding studies, and a exploration of a state-space approach to analysis
• Tagging protocol, summary of 2003 shedding studies, recoveries, and preliminary analysis
• Simulation of the effect of migration and uneven fishing effort on the selectivity and harvest rate estimates (2004)
• 2004 releases, tag-loss summary, and summary of 2004 sampling and recoveries
• A simple recovery model presented in a paper analyzing the 2004 PIT recoveries
• A somewhat more complicated model accounting for non-commercial removals of marked fish presented in the paper analyzing the 2005 PIT recoveries
• Analysis of recoveries through 2005 (2005 RARA pp. 123-134)
• Summary of 2005 sampling and recoveries (pp 253-276); tag loss (pp 279-284); and examination of cause for low recoveries (pp 285-292) in the 2005 RARA
• Analysis of recoveries through 2006 (pp 129-138) and causes of low recoveries (pp 139-144) in the 2006 RARA
• Summary of 2006 sampling and recoveries (2006 RARA pp 277-298)
• Fine-scale modeling of migration from tagging data (includes estimation of scanning rates by statistical area) (pp 245-258) and analysis of recoveries through 2007 (pp 259-274) in the 2007 RARA
• Summary of 2007 sampling and recoveries (2007 RARA pp 399-426)
• Summary of 2007 assessment, peer review, and migration effects
• Examination of survey catch rates, fishery-survey interactions, modeling migration, harvest policy
• Summary of 2008 recommended catch limits (2008 Bluebook pp 105-110)