Science Advisory Report 2018/001

Review of genetically based targets for enhanced contributions to Canadian pacific Chinook Salmon populations

Summary

• Hatchery production in the Salmon Enhancement Program of DFO is used as a management tool for the conservation of small or endangered natural populations, fish production (harvest), stock assessment, and stewardship/education objectives. The presence of hatchery-origin salmon poses risks to the fitness and genetic diversity of wild fish spawning in the natural environment and therefore has implications for the conservation of wild salmon.
• Canadian enhancement programs have been developed as ‘integrated’ populations in which natural- and hatchery-origin salmon spawn in both the hatchery and wild environments, with the gene flow between the two spawning components slowing the process of domestication (adaptation to the hatchery rather than the wild environment) that would occur in a segregated hatchery system.
• The proportionate natural influence (PNI) and associated metrics developed by the U.S. Hatchery Scientific Review Group (HSRG) have been assessed as appropriate metrics to evaluate, classify and monitor levels of hatchery influence and genetic risk to the natural adaptive state in Canadian integrated Chinook Salmon hatchery populations.
• A population classification system informed by the Wild Salmon Policy for Canadian Pacific Salmon has been developed to reflect the adaptive state of integrated hatchery populations based on proportions of natural- and hatchery-origin fish. Increased genetic risk is associated with population designations that have increasing hatchery influence and decreasing proportions of wild and/or naturally-spawned fish.
• The impacts of three management measures (hatchery size, proportion of hatchery fish visually marked, and proportion of marked fish selectively harvested) on the genetic risk metrics for integrated hatcheries were evaluated using a demographic model of a Chinook Salmon population that incorporated genetic impacts on fitness from hatchery spawning and rearing.
• The model demonstrated that each management option can be used to manage genetic risk. Limiting hatchery size was a consistently effective approach to reduce genetic risk and, in some cases, combinations of high rates of visual marking, selective broodstock composition, and selective removal of hatchery-origin fish from the natural environment were also effective in reducing genetic risk.
• Genetic risk associated with higher levels of hatchery production can be lowered by reducing the proportions of hatchery-origin fish included in the hatchery broodstock and/or allowed to spawn in the natural environment. However, selectively increasing the proportion of natural-origin salmon in both environments depends on visual external marking to enable differentiation of fish based on origin prior to spawning.
• Minimizing genetic risk to wild salmon populations to maintain consistency with WSP conservation goals requires limitation of the number of local and stray hatchery-origin fish in natural spawning environments, creating a trade-off between genetic risk and hatchery production for socio-economic purposes. Higher levels of genetic risk may be warranted for populations that are in immediate danger of extirpation as a result of demographic risk.
• Measures proposed to manage risk to fitness and genetic diversity of wild Canadian Chinook Salmon populations are consistent with the hatchery management principles outlined by the HSRG: 1) develop explicit biological goals for hatchery-influenced populations, 2) implement scientifically defensible hatchery programs and 3) undertake adaptive management of hatchery programs within a documented experimental approach.
• Minimizing genetic risk from hatchery production to wild populations requires maintaining the productivity of natural habitat and controlling the presence of hatchery-origin fish therein. This necessitates a comprehensive approach to monitoring and assessment among enhancement, stock assessment, fishery management, and habitat restoration activities.
• There is uncertainty about the degree of, and the mechanisms underlying, loss of fitness in hatchery-influenced Pacific salmon populations.  There is no information on the magnitude and timeframe of fitness restoration for a population in which hatchery influences are removed.

This Science Advisory Report is from the August 31-September 1, 2017 Evaluation and update of biologically-based targets for enhanced contributions to Chinook populations. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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