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Research Document 2021/043

Recovery Potential Assessment for Fraser River Sockeye Salmon (Oncorhynchus nerka) – Nine Designatable Units: Probability of Achieving Recovery Targets - Elements 12, 13, 15, 19-22

By Huang, A-M., Pestal, G., Guthrie, I.


Ten Designatable Units (DUs) of Sockeye salmon that spawn in the Fraser River watershed in British Columbia were designated as Endangered (EN) or Threatened (TH) by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2017). The eight Endangered DUs (common name and DU number in parentheses) are: Bowron-ES (Bowron DU2), Cultus – L (Cultus DU6), Takla-Trembleur-EStu (Early Stuart DU20), Harrison (U/S)-L (Weaver DU10), Seton-L (Portage DU17), Quesnel-S (Quesnel DU16), Takla-Trembleur-Stuart-S (Late Stuart DU21), and Taseko-ES (Taseko DU22). The two Threatened DUs are: Widgeon (River-Type) (Widgeon DU24) and North Barriere-ES (Upper Barriere, previously Fennell DU14). A further five DUs were assessed as Special Concern (SC): Kamloops-ES (Raft DU11), Lillooet-Harrison-L (Birkenhead DU12), and Francois-Fraser-S (Stellako DU7), Harrison (D/S)-L (Misc. Lates DU9) and Nahatlatch-ES (Nahatlatch DU13). The Recovery Potential Assessment (RPA) of the Endangered Cultus DU was covered in a separate document (DFO 2020). SC DUs were not included in the Terms of Reference for this report. However, some of the modeling results showed similar outcomes to the EN and TH DUs and have been included in this report. SC DUs are identified with an asterisk (*). This document covers RPA elements 12, 13, 15, 19-21 (i.e., quantitative analysis of recovery targets, probability of achieving recovery targets, and mitigation effects) and summarizes how these elements could contribute to element 22 (i.e., allowable harm) for the remaining 9 EN/TH DUs and the three SC DUs (i.e., Raft*, Birkenhead*, and Stellako* DU 11, 12, 7) that have a time series of stock-recruit estimates (DFO 2014). The allowable harm assessment in this document does not include the elements covering habitat, threats, and limiting factors and should not be interpreted as being the final allowable harm statement for these DUs.

Two nested recovery targets are proposed for the DUs, with Recovery Target #1 approximating the objective that a DU would not be characterized as Endangered or Threatened by COSEWIC or as the Red biological status of the Wild Salmon Policy (WSP) and Recovery Target #2 approximating the objective of COSEWIC for Not At Risk or WSP Green. Stock-specific stock-recruit models that account for recent productivity were used in a simulation model to evaluate the likelihood of DUs reaching the two Recovery Targets over the next three generations (12 years) over a wide range of mortality rates. A method for evaluating impacts of the Big Bar landslide on the six impacted DUs was explored, and the impacts from a range of future changes in productivity were modelled for all DUs.

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