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Assessment of Hatchery Chinook Salmon Straying in Southern British Columbia

Regional Peer Review - Pacific Region

September 12-13, 2023
Nanaimo, BC

Chairperson: Nicholas Komick


Fisheries and Oceans Canada (DFO) Salmonid Enhancement Program (SEP) hatcheries produce approximately 40 million juvenile Chinook Salmon for release annually into southern British Columbia (BC) marine waters (south of Cape Caution), of which the majority are identifiable to their hatchery of origin by an internal or external mark. Although the majority of Chinook Salmon are known to exhibit strong homing behaviour to their stream of origin or natal streams as returning adults, straying (i.e., adults returning to non-natal streams) is also known to occur naturally in Chinook populations. To date, the magnitude of straying resulting from hatchery production and its effect on wild populations in southern BC has not been assessed.

Straying in hatchery Chinook Salmon has been identified as a potential risk to wild populations, due to an expected reduction in fitness as a result of outbreeding with hatchery fish that have a lower relative reproductive success (Christie et al. 2014). An Independent Panel’s Report recommended that an evaluation of hatchery stock-specific stray sources, abundance and rates be conducted (Riddell et al. 2013).

The majority of hatchery-released Chinook Salmon smolts are marked by one of the following: thermally marked otoliths, coded wire tags (CWT), parentage-based genetic tagging (PBT), and/or adipose fin clips (AFC), primarily for fisheries and stock management purposes. Data collected through the various marked fish recovery programs can also be used to assess the magnitude and extent of hatchery Chinook Salmon straying.

Fisheries and Oceans Canada (DFO) Salmon Enhancement Program (SEP) has requested that Science Branch provide an evaluation of the magnitude and extent of straying in hatchery Chinook Salmon in southern BC. Information and data related to the recovery of thermally marked and CWT hatchery Chinook Salmon will inform the assessment of the magnitude and extent of straying. An examination of the genetic effects of straying and implications for hatchery reform has been completed (Withler et al. 2018) and will inform discussion on the potential risks and impacts of straying in southern BC.


The following draft research document will be reviewed and provide the basis for discussion and advice on the specific objectives outlined below.

Jacob Weil, Wilf Luedke, Ruth Withler, Erin Porszt, Nick Brown, and Jessy Bokvist. The Magnitude and Extent of Chinook Straying from Hatcheries in Southern BC. 2023. CSAP Draft Research Document. Request ID 775.

The specific objectives of this review are to:

  1. Provide a working definition of what constitutes a Chinook “hatchery stray” and compile available sampling data for the purposes of assessing hatchery stock straying, including metadata about the sampling program (e.g., spatial coverage and sampling purpose);

  2. Provide estimates of mean stray rates, the magnitude of straying, and spatial and temporal patterns of straying by stock and release strategy of Chinook from hatcheries in southern BC, using a. Available CWT recovery data, and b. Available thermally marked otolith recovery data.

  3. Where possible, provide annual estimates of the contribution of hatchery strays into recipient spawning populations of sampled rivers in southern BC (i.e., produce annual estimates for proportion of hatchery-origin fish on the spawning grounds (pHOS), proportion of natural-origin parents in the hatchery broodstock (pNOB), proportion of local hatchery-origin fish on the spawning grounds (pHOSlocal), proportion of stray hatchery-origin fish on the spawning grounds (pHOSstray), proportionate natural influence (PNI), using CWT and thermally marked otolith recovery data.

  4. To the extent possible, identify and discuss potential sources of bias and uncertainties associated with the estimates of hatchery straying on natural spawners.

Expected Publications

Expected Participation



Participation to CSAS peer review meetings is by invitation only.

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