Terms of Reference

Estimates of a Biologically-Based Spawning Goal and Biological Benchmarks for the Canadian-origin Taku River Coho Stock Aggregate

Regional Peer Review Process – Pacific Region

November 3-4, 2014
Nanaimo, BC

Chairperson: Jeffrey Lemieux

Context

The Taku River is a large, trans-boundary river in northwestern British Columbia with approximately 90% of the 19,000 km2 drainage area occurring in B.C. The drainage is ecologically and physiographically diverse characterized by three dominant aquatic regions, based primarily on geomorphological features: the dynamic, highly braided and glacially influenced streams and Taku mainstem in the lower river; the lake dominated and glacially influenced streams on the eastern slopes of the Boundary Ranges; and, the high elevation streams and small lakes of the Stikine Plateau.

With the signing of the Pacific Salmon Treaty (PST) (Canada 1985) bilateral investigations into the Chinook, Coho and Sockeye Salmon of the Taku drainage were begun. Estimation of Coho Salmon escapement began in 1987 and smolt enumeration and coded-wire tagging was begun in 1991.  The annual total run size of Coho Salmon originating from the Canadian portion of the Taku River drainage over the past decade has been in excess of 185,000 fish with an average exploitation rate of roughly 49%.  Most of the harvest (approximately 89%) is taken by the US primarily in marine troll and net fisheries; the remainder is harvested in a small in-river commercial gillnet fishery in Canada. Coho rear and spawn throughout the drainage and likely are diverse in their utilization of habitat. The diverse ecotypology of the drainage underlies the three Coho Conservation Units for this system.

Taku River coho salmon are managed in the aggregate under provisions of Chapter 1, Annex IV of the PST. The most recent provisions of the Pacific Salmon Treaty call for the development of a bilaterally-agreed spawning goal for Canadian-origin Taku River coho salmon set at SMSY. The aim was to have this in place for the 2010 fishing season.  Considerable work in this regard was undertaken and presented in an exploratory draft to CSAP in the fall of 2010. Reviewers of the paper acknowledged the complexity of the work undertaken, but provided feedback that the work should be more focused on the spawner-recruitment and smolt-recruitment relationships, and less focused on separating the analyses into apparent productivity regimes.  Due to changes in personnel, the work was not completed or accepted for publication.

In addition to the above PST obligations, as part of implementing Strategy 1 of the Wild Salmon Policy (WSP), Fisheries and Oceans Canada (DFO) is required to identify biological benchmarks to assess the status of WSP Conservation Units (CUs) for Pacific salmon.  Benchmarks have not been estimated for Taku River Coho CUs, and this work cannot be completed at this time because of data deficiencies at the CU level.

Fisheries Management Branch has requested that Science Branch provide advice respecting a biologically-based spawning goal for Taku River Coho Salmon and the estimate of WSP biological benchmarks.

This assessment will attempt to estimate the lower WSP benchmark (Sgen) of the abundance metric for the aggregate of the three Taku Coho CUs. The upper WSP benchmark for abundance is 85% SMSY and follows from the estimate of the spawning goal. Note, however, that this Working Paper will not present the other WSP status metrics (trends, distribution), and will not comment on the status of Taku Coho CUs. Also note that the Working Paper will only estimate the spawning goal given the current definition in the PST, and not evaluate the implications of this management approach (e.g. expected trajectory relative to the WSP benchmarks). Methods utilized to estimate biological benchmarks will be based on the approaches and criteria previously developed and applied for other Pacific Salmon CUs (Holt 2009a, Holt 2009b, Grant 2011).

Results of the assessment, and advice arising from this Regional Peer Review process, will be used by Canadian and United States management to develop a revised integrated management plan for Taku Coho Salmon and may potentially affect calculations of TAC which could change harvest levels of the Parties.  Advice respecting WSP biological benchmarks will contribute to a future assessment of status to meet WSP commitments.

Objectives

The following working paper will be reviewed and provide the basis for discussion and advice on the specific objectives outlined below.

Pestal, G. and Johnston, S.  Estimates of a Biologically-Based Spawning Goal and Biological Benchmarks for the Canadian-origin Taku River Coho Stock Aggregate. CSAP Working Paper 2014-15/SAL01

The specific objectives of this review are to:

1. Review coho production, escapement and fry abundance data for the Taku River;
2. Develop biological benchmarks at the aggregate level including the number of spawning adults that would produce a maximum sustainable yield of Coho Salmon using various models;
3. Examine and identify uncertainties in the data and methods;
4. Comment on future data needs and considerations which would allow development of biological benchmarks at the CU level.

Expected Publications

• Science Advisory Report
• Proceedings
• Research Document(s)

Participation

• Fisheries and Oceans Canada (DFO) (Science, Fisheries Management)
• Alaska Department of Fish and Game
• Taku River Tlingit FN
• Academia

References

Fisheries and Oceans Canada. 2005. Canada's Policy for Conservation of Wild Pacific Salmon. Fisheries and Oceans Canada, Vancouver, BC. 34 p.

Grant, S.C.H., MacDonald, B.L., Cone, T.E., Holt, C.A., Cass, A., Porszt, E.J., Hume, J.M.B., and Pon, L.B. 2011. Evaluation of uncertainty in Fraser Sockeye (Oncorhynchus nerka) Wild Salmon Policy status using abundance and trends in abundance metrics. DFO Can. Sci. Advis. Sec. Res. Doc. 2011/087. viii + 183 p.

Holt, C.A. 2009a. Evaluation of benchmarks for Conservation Units in Canada's Wild Salmon Policy: technical documentation . DFO Can. Sci. Advis. Sec. Res. Doc. 2009/059. xii + 50 pp.

Holt, C.A., Cass, A., Holtby, B., and Riddell, B. 2009b. Indicators of status and benchmarks for Conservation Units in Canada's Wild Salmon Policy. DFO Can. Sci. Advis. Sec. Res. Doc. 2009/058. vii + 74 p.

Production of coho salmon from the Taku River, 2003-2007.  Alaska Department of Fish and Game, Fishery Data Series No. 12-12, Anchorage.