Terms of Reference

Stock-specific Fraser River Sockeye Salmon Run Size Determination

Regional Peer Review - Pacific Region

May 27-29, 2024

Vancouver, BC

Chairpersons: Laura Tessier and Nicholas Komick

Context

Each year the management of Fraser River Sockeye Salmon (Oncorhynchus nerka) relies on a series of abundance estimates of adult returns (i.e., recruits per year) to the start of the coastal fisheries by stock or stock aggregations, commonly referred to as run size estimates. There are three temporal run size estimation processes:

1. preseason estimates of run size for 27 select stocks are generated by Fisheries and Oceans Canada (DFO) for fisheries planning purposes (Grant et al. 2010);
2. in-season estimates of run size for four run-timing groups (i.e., stock aggregates used for management) are generated by Pacific Salmon Commission (PSC) to determine total allowable catch by country for each timing group (Michielsens and Martens 2022); and
3. postseason estimates of run size for 28 stocks are generated via an expert-driven process involving members from DFO, PSC, and PSC’s Fraser River Panel Technical Committee (Robinson et al. 2014; Robinson and Patterson 2015).

Postseason run size estimates are used to calculate productivity and stock status for use in future harvest planning (Grant et al. 2011), to aid in recovery planning (DFO 2020a,b), and to evaluate factors limiting survival, such as en route mortality (Martins et al. 2011; Hinch et al. 2012; Doutaz et al. 2023). Despite the importance of postseason run size estimates for these analyses, there has been no consistent documentation and evaluation of the main contributing components—catch, spawning escapement, and en route mortality—and their summation.

Deteriorating freshwater migration conditions and declines in stock status expedited the need to closely examine estimates of spawning escapement, catch and en route mortality postseason at a stock-specific level. Starting with the 2009 return year, numeric adjustments to stock-specific run size components were initiated, called run size adjustments or RSAs, based on postseason updates to spawning escapement or catch not reflected in near final estimates, as well as explicit estimates of en route mortality component (Macdonald et al. 2010; Martins et al. 2011; Hinch et al. 2012). Historically, postseason run size estimates did not explicitly include estimates of en route mortality, a combination of natural mortality and human induced mortality, excluding landed catch (Patterson et al. 2017; Bett et al. 2020). The addition of postseason en route mortality can substantially alter estimates of abundance, productivity, and exploitation for salmon stocks. Failure to include high en route mortality will lead to underestimates of productivity and overestimates of harvest impact. Conversely, overestimating mortality will lead to overestimates of productivity and underestimates of harvest impact. However, the inclusion of postseason en route mortality estimates, along with postseason adjustments to spawning escapement and catch, has resulted in two different run size datasets with different time series of exploitation rates and stock-recruit data. With increased concern about current and future high levels of en route mortality (Hague et al. 2011; Hinch et al. 2021) and the associated implications for harvest, productivity, and stock status, it has become important to clearly articulate the current expert-led process and suggest improvements to future generation of postseason stock-specific run sizes for Fraser River Sockeye Salmon.

Fisheries and Oceans (DFO) Fisheries Management has requested that Science Branch provide review and documentation of the postseason methods currently used to estimate stock-specific run size for Fraser River Sockeye Salmon. This work will also provide recommendations for improvements, including alternative methods for generating run size estimates, as well as guidance on the use and interpretation of run size estimates and associated derivatives (e.g., en route mortality estimates, exploitation rates). The outputs from this process and advice arising from this Canadian Science Advisory Secretariat (CSAS) Regional Peer Review (RPR) will be used to inform run size forecasts and stock status assessments.

Objectives

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

Robinson, K.A. et al. Determination of stock-specific run size estimates for Fraser River Sockeye Salmon. 2024. CSAP Working Paper. Request ID 252.

Patterson, D.A. et al. Recommendations and guidance for run size estimation for Fraser River Sockeye Salmon. 2024. CSAP Working Paper. Request ID 252.

The specific objectives of this review are to:

1. Provide background on run size estimation and sensitivity to input uncertainty.
2. Document and review current methods for postseason stock-specific run size estimation.
3. Recommend improvements to stock-specific run size estimation methods.
4. Provide guidance on use of different datasets related to the generation of run size estimates.

Expected Publications

• Science Advisory Report
• Research Document

Expected Participation

• Fisheries and Oceans Canada (Ecosystems and Oceans Science, Fisheries Management, Ecosystem Management Branch)
• Carleton University
• Committee on the Status of Endangered Wildlife in Canada
• Fraser River Technical Committee
• Fraser Salmon Management Council
• LGL Limited
• Lower Fraser Fisheries Alliance
• National Oceanic and Atmospheric Administration
• Northwest Indian Fisheries Commission
• Pacific Salmon Commission
• Pacific Salmon Foundation
• Simon Fraser University
• Tulalip Tribes
• University of British Columbia
• University of Northern British Columbia
• Upper Fraser Fisheries Conservation Alliance
• Washington Department of Fish and Wildlife

References

• Bett, N.N., Hinch, S.G., Bass, A.L., Braun, D.C., Burnett, N.J., Casselman, M.T., Cooke, S.J., Drenner, S.M., Gelchu, A., Harrower, W.L. and Ledoux, R., 2020. Using an integrative research approach to improve fish migrations in regulated rivers: a case study on Pacific Salmon in the Seton River, Canada. Hydrobiologia. 849:385–405.
• DFO. 2020a. Recovery Potential Assessment – Cultus Lake Sockeye Salmon (Oncorhynchus nerka) (2019). DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2020/011.
• DFO. 2020b. Recovery Potential Assessment for Fraser River Sockeye Salmon (Oncorhynchus nerka) – Nine Designatable Units – Part 1: Probability of Achieving Recovery Targets. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2020/012.
• Doutaz, D., Huang, A.-M., Decker, S., Vivian, T. 2023. Recovery Potential Assessment for Fraser River Sockeye Salmon (Oncorhynchus nerka), Nine Designatable Units Part 2: Biology, Habitat, Threats, Mitigations and Allowable Harm – Elements 1-11, 14, 16-18, 22. DFO Can. Sci. Advis. Sec. Res. Doc. 2023/003. xiii + 250 p.
• Grant, S.C.H., Michielsens, C.G.J., Porszt, E.J., and Cass, A. 2010. Pre-season run size forecasts for Fraser River Sockeye salmon (Oncorhynchus nerka) in 2010. DFO Can. Sci. Advis. Sec. Res. Doc. 2010/042. vi + 125 p.
• Grant, S.C.H., MacDonald, B.L., Cone, T.E., Holt, C.A., Cass, A., Porszt, E.J., Hume, J.M.B., 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.
• Hague, M.J., Ferrari, M.R., Miller, J.R., Patterson, D.A., Russell, G.L., Farrell, A.P., and Hinch, S.G., 2011. Modelling the future hydroclimatology of the lower Fraser River and its impacts on the spawning migration survival of sockeye salmon. Glob. Ch. Biol. 17: 87–98.
• Hinch, S.G., Cooke, S.J., Farrell, A.P., Miller, K.M., Lapointe, M., and Patterson, D.A. 2012. Dead fish swimming: a review of research on the early migration and high premature mortality in adult Fraser River sockeye salmon Oncorhynchus nerka. J. Fish Biol. 81:576–599.
• Hinch, S.G., Bett, N.N., Eliason, E.J., Farrell, A.P., Cooke, S.J. and Patterson, D.A., 2021. Exceptionally high mortality of adult female salmon: a large-scale pattern and a conservation concern. Can. J. Fish. Aquat. Sci. 78:639–654.
• Macdonald, J. S., Patterson, D.A., Hague, M.J., and Guthrie, I.C. 2010. Modeling the Influence of Environmental Factors on Spawning Migration Mortality for Sockeye Salmon Fisheries Management in the Fraser River, British Columbia. Trans. Am. Fish. Soc. 139:768–782.
• Martins, E.G., Patterson, D.A., Cooke, S.J., and Miller, K.M. 2011. Effects of river temperature and climate warming on stock-specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka). Glob. Ch. Biol. 17:99–114.
• Michielsens, C.G.J. and Martens, F.J. Editors. 2022. Overview of pre-season and in-season assessment methods for Fraser River sockeye salmon. Pacific Salmon Comm. Tech. Rep. No. 49, 217 p.
• Patterson, D.A., Robinson K.A., Lennox, R.J., Nettles, T.L., Donaldson, L.A., Eliason, E.J., Raby, G.D., Chapman, J.M., Cook, K.V., Donaldson, M.R., Bass, A.L., Drenner, S.M., Reid, A.J., Cooke, S.J., and Hinch, S.G. 2017. Review and Evaluation of Fishing-Related Incidental Mortality for Pacific Salmon. DFO Can. Sci. Advis. Sec. Res. Doc. 2017/010. ix + 155 p.
• Robinson, K.A., Patterson, D.A., and McKay, D. 2014. Improvements to Determining Post-Season Run Size for Fraser River Sockeye Salmon. Pacific Salmon Commission Southern Endowment Fund Final Report. vii + 91 p.
• Robinson, K.A., and Patterson, D.A. 2015. Pacific Salmon Commission Southern Endowment Fund Final Report. ix + 53 p.