Science Advisory Report 2020/023
Recovery Potential Assessment for 11 Designatable Units of Fraser River Chinook Salmon, Oncorhynchus tshawytscha, Part 1: Elements 1 to 11
- This is the first of two parts of a Recovery Potential Assessment (RPA) for 11 Designatable Units (DUs) of southern BC Chinook Salmon that spawn in the Fraser River watershed. The primary focus of this portion of the RPA was to assess threats that may be limiting the survival and recovery of these DUs.
- DUs were assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in November 2018, and four of which were designated as Threatened and seven were designated as Endangered. Declining trends in abundance have continued for these DUs since the COSEWIC assessment. The assessed DUs are:
- Lower Fraser River Ocean Fall (DU2)
- Lower Fraser River Stream Summer - Upper Pitt (DU4)
- Lower Fraser River Stream Summer (DU5)
- Middle Fraser River Stream Spring - Nahatlatch (DU7)
- Middle Fraser River Stream Fall - Portage (DU8)
- Middle Fraser River Stream Spring (DU9)
- Middle Fraser River Stream Summer (DU10)
- Upper Fraser River Stream Spring (DU11)
- South Thompson Stream Summer - Bessette (DU14)
- North Thompson Stream Spring (DU16)
- North Thompson Stream Summer (DU17)
- Redds, the spawning nests constructed by Pacific salmon and other fish species, meet the definition of a "residence" under the Species at Risk Act (SARA).
- For each DU the COSEWIC threats calculator was used to assess 33 ongoing and future threats on population trends over the next three generations. The highest ranked anthropogenic threats to all assessed DUs were climate change, modification to ecosystems, pollution, and fishing.
- The overall threat ranking for all DUs was either Extreme or Extreme–High based on the number and severity of the threats.
- Climate change is anticipated to negatively impact all DUs through changes to physical and biological processes in both marine and freshwater environments and through interactions with other threats.
- There was a wide range in the threat risk posed by fishing-related mortality on population trends due to uncertainty about future fishing-related mortality, implementation uncertainty, and effects of other threats on productivity. In Part 2 of the RPA, quantitative modelling will be used to assess the impacts of fishing and other threats on population trends.
- For all DUs, and in particular for the Middle Fraser River Stream Spring and South Thompson Stream Summer (Bessette) DUs, threats posed by ecosystem modifications to both catchment surfaces and streamflow due to water withdrawals, fire, logging, and agricultural and urban development are expected to adversely affect population trends.
- Pollution from many diverse sources was assessed to be a pervasive threat for all DUs, but the cumulative effect on population trends was identified as a knowledge gap.
- The 2018 Big Bar landslide in the mainstem Fraser River poses an additional threat to three DUs (Middle Fraser River Stream Spring, Middle Fraser River Stream Summer, Upper Fraser River Stream Spring) that spawn upstream of the slide. These DUs are unlikely to persist if this barrier is not removed.
- Information gaps identified during the threats assessment were the main cause of difficulty in assessing the magnitude of impact of many threats.
This Science Advisory Report is from the December 10-12, 2019 regional peer review on the Recovery Potential Assessment – Fraser River Chinook Salmon (Oncorhynchus tshawytscha) – Eleven Designatable Units (Elements 1 to 11). 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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