Science Response 2024/032

Scientific Evidence to Inform Spawning Practices at Fisheries and Oceans Canada Salmon Hatcheries in the Pacific Region

Context

Release of Pacific salmon from hatcheries to support or enhance natural populations creates potential risks to the genetic integrity, genetic diversity, and fitness of wild salmon. Under Canada’s Policy for Conservation of Wild Pacific Salmon, wild salmon are defined as salmon that have spent their entire lives in the wild and are the offspring of naturally-spawned parents (DFO 2005). The genetic risks to wild salmon associated with hatcheries are mitigated and minimized through genetic management of broodstocks. The Fisheries and Oceans Canada (DFO) Salmonid Enhancement Program (SEP) currently uses guidelines developed in the 1980s to direct broodstock collection and spawning within their hatchery lines (DFO 2016; see Appendix A). In recent years there have been substantial advances in scientific knowledge regarding the effects of hatcheries on wild salmon. A review of the genetic management of broodstock guidelines is timely to ensure operations are consistent with current science advice.

A recent Canadian Science Advisory Secretariat (CSAS) research document, Genetically Based Targets for Enhanced Contributions to Canadian Pacific Chinook Salmon Populations (Withler et al. 2018), established proportionate natural influence (PNI) designations for Canadian salmon populations to facilitate management of genetic risks associated with hatchery selection and domestication. The application of these designations is currently being developed for SEP’s hatchery lines, which have objectives spanning harvest, assessment, rebuilding, conservation, and education/stewardship. Therefore, it is also essential to evaluate if the general broodstock collection and spawning guidelines require modifications depending on the particular management objective or PNI designation of a line enhanced by SEP.

DFO SEP has requested science advice on updates to the broodstock collection and spawning practices at SEP operated and supported hatcheries in the Pacific Region. This assessment and the advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR) process will be used to update both the SEP genetic management guidelines (DFO 2016) and the SEP risk management framework for enhancing Pacific salmon (DFO 2013).This Science Response Report results from the regional peer review of March 5, 2024 on Scientific Evidence to Inform Spawning Practices at Fisheries and Oceans Canada Salmon Hatcheries in the Pacific Region.

The specific objectives of this report are to:

1. Assess potential genetic impacts of existing hatchery broodstock collection guidelines regarding the proportion of the escapement removed for broodstock, and the relative use of natural- versus hatchery-origin spawners compared to their representation in the escapement.
2. Examine published scientific knowledge to provide advice on best practices for maintaining genetic diversity in hatchery broodstock depending on broodstock size and enhancement objectives, particularly with reference to the use of males, cryopreserved milt, sex ratios, and matrix spawning.
3. Evaluate the potential consequences of random versus intentional selection of hatchery spawners based on fitness-related traits (e.g., size, age, or run timing) with dedicated consideration of the use of jack males in hatchery broodstocks.

The information reported here is presented specifically in the context of Pacific salmon populations enhanced by hatcheries operated and supported by SEP. However, the underlying basic principles also have relevance to other hatchery operations involving Pacific salmon, other salmonids, and other species more generally.

Science Response 2024/032 (PDF, 2,212 KB)

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