Research Document 2021/009
Recovery Potential Assessment for the Okanagan Chinook Salmon (Oncorhynchus tshawytscha) (2019)
By Mahony, A., Challenger, W., Robichaud, D., Wright, H., Bussanich, R., Sharma, R., and Enns, J.
Abstract
Okanagan Chinook Salmon (Oncorhynchus tshawytscha) are the only Columbia River population in Canada and are genetically distinct from all other Canadian Chinook Salmon populations. Okanagan Chinook (Ntytix) are considered a “first food” and of high importance to the Syilx Okanagan Nation. These fish were formerly the subject of an important First Nations food fishery and commercial trade, but today few persist in the wild. The Okanagan Nation Alliance (ONA) has been actively involved in the study and conservation of Okanagan Chinook Salmon, and has been enhancing Chinook Salmon spawning habitat by installing spawning beds at Oliver and Penticton, and by working to remove migration barriers at dams and in tributaries.
The minimum spawner abundance of Okanagan Chinook Salmon averaged ~9 individuals from 2008-2012, and then increased to an average of ~50 individuals from 2013-2017 (with a maximum estimate of 61 in 2015). In 2018, the number of spawners returned to 2008-2012 levels (10 spawners). In addition to the above, there is new evidence that a Spring Chinook Salmon population is present in the Okanagan watershed, this paper considers only the Ocean-type Summer Run Okanagan Chinook.
Currently, there is enough spawning habitat in the Okanagan River to accommodate a maximum of 1,460 spawning pairs. Considering the numbers of returning Okanagan Chinook Salmon are in the 10’s of fish, it is unlikely that physical habitat availability will be a constraint in the near future, though the successful return of hatchery-derived adults could eventually impact the availability of habitat to wild fish. Cold water refugia, such as those in tributary areas, are noted as being important, especially given the warming climate.
Numerous threats were identified, including impacts due to resource use, climate change, dams, ecosystem modifications\habitat loss, and invasive species. Rescue potential from other populations is considered unlikely. Under the current conditions, Population Viability Analysis (PVA) indicates that the population will not reach the recovery target of 1,000 spawners. Even with the complete cessation of all fishery-related mortality the population would still require aggressive management interventions (habitat improvements and/or a hatchery supplementation program) to meet the recovery target. If no other management actions were implemented, a supplementation program of ≥ 250,000 smolts released per year would be required to meet recovery targets with a high likelihood (assumes equal fitness between wild and hatchery-derived smolts; if fitness of hatchery fish is lower, larger numbers would need to be released to compensate). Hatchery supplementation programs could be reduced (e.g., 150,000 full-fitness hatchery smolts per year) if combined with other management actions that reduce juvenile or adult mortality.
Restoration initiatives are underway, and include, among others: returning channelized portions of the river to a more natural state; creation of spawning beds in Penticton channel; improving fish passage at dams; and hatchery production.
There remain a number of gaps in the understanding of basic life history characteristics for Okanagan Chinook Salmon. In particular, studies are needed to assess the importance of juvenile rearing habitat for the survival or recovery of a Canadian population, including the impact of invasive species. A comprehensive habitat update should be undertaken to assess the location and importance of groundwater input and estuary use. Moreover, limitations from temperature and oxygen regimes should be investigated as part of a habitat and dam passage assessment.
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