Science Advisory Report 2020/012
Recovery Potential Assessment for Fraser River Sockeye Salmon (Oncorhynchus nerka) – Nine Designatable Units – Part 1: Probability of Achieving Recovery Targets
- Ten Designatable Units (DUs) of Sockeye salmon that spawn in the Fraser River watershed in British Columbia were designated as Endangered or Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2017). Nine of them are the subject of this report (DU name followed by common stock name and DU number in parentheses):
- Endangered: Bowron-ES (Bowron DU2), 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), Taseko-ES (Taseko DU22)
- Threatened: Widgeon-River (Widgeon Slough DU24), North Barriere-ES (Upper Barriere, previously Fennell DU14).
- The tenth: Cultus-L (Cultus DU6); Endangered, has a separate recovery potential assessment (DFO 2020).
- A further five DUs were categorized as Special ConcernFootnote 1, and the three with a stock-recruit time series are also included in this analysis: Kamloops-ES (Raft DU11)*, Lillooet-Harrison-L (Birkenhead DU12)*, and Francois-Fraser-S (Stellako DU7)*. The remaining two are: Harrison (D/S)-L (Miscellaneous Lates DU9)* and Nahatlatch-ES (Nahatlatch DU13)*.
- Stock-recruit time series do not exist for two of the DUs (Widgeon Slough and Taseko DU 24, 22) so the type of quantitative analyses conducted for the other DUs were not possible.
- Productivity has been declining since at least the 1990s for all Endangered, Threatened, and Special Concern stocks with stock-recruit time series.
- Two related recovery targets are proposed:
- Recovery Target #1: approximates the objective for a DU that would not be characterized as Endangered or Threatened by COSEWIC or in the Red biological status of the Wild Salmon Policy (WSP).
- Recovery Target #2: approximates the objective of COSEWIC for Not At Risk or WSP Green.
- Stock specific stock-recruitment models were used to estimate the percentage of projections that would reach the two recovery targets in three generations (12 years) under scenarios using plausible population dynamics conditions across a range of mortality rates and productivity levels, including recent ones (brood years 2010-2013).
- In the summer of 2019, a large landslide was discovered in the Fraser River mainstem. The Big Bar landslide blocked virtually all of the natural migration of Fraser sockeye until 26-August. Six (Early Stuart, Late Stuart, Bowron, Quesnel, Taseko, and Stellako* DU 20, 21, 2, 22, 7) out of the twelve assessed DUs were affected by the landslide. Of those, Early Stuart, Bowron and Taseko (DU 20, 2, 22) were most affected since they were migrating upstream at a time when passage was completely blocked.
- A method to account for potential impacts of the Big Bar landslide was developed using the very preliminary information available in early August 2019 and used to make the projections.
- Assuming current productivity levels will continue, the projections were:
- Unlikely to Very Unlikely (0-33%) to reach Recovery Target #1 even at low mortality rates (e.g., 10% or less) for Early Stuart and Bowron. (DU 20, 2)
- As Likely As Not (34-65%) to reach Recovery Target #1 at low mortality rates for Upper Barriere, Portage, Weaver, Raft*, Late Stuart and Birkenhead*. (DU 14, 17, 10, 11, 21, 12)
- Likely or Very Likely (66-100%) to reach Recovery Target #1 at low mortality rates for Quesnel, and Stellako*. (DU 16, 7)
- This report covers 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 would contribute to element 22 (i.e., allowable harm). 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.
- Recognizing that activities in support of the survival and recovery of a DU (e.g., stock assessment, research, conservation, or mitigation activities) could potentially cause mortalities, all sources of harm should be reduced to the maximum extent possible for Early Stuart and Bowron DUs in order to provide the best opportunity for the survival of these DUs. (DU 20, 2)
- Recognizing that activities in support of the survival and recovery of a DU (e.g., stock assessment, research, conservation, or mitigation activities) could potentially cause mortalities (e.g., stock assessment, research, conservation, or mitigation activities), all sources of harm should be reduced to the maximum extent possible for Weaver, Raft*, Birkenhead*, Portage, Late Stuart and Upper Barriere DUs in order to provide the best opportunity for the DUs to meet Recovery Target #1. (DU 10, 11, 12, 17, 21, 14)
- Preliminary results are presented for Quesnel and Stellako* DUs, but no allowable harm statement can be made at this time. Additional information will be available in the next four months to provide empirical estimates of the immediate impacts of the Big Bar landslide and support additional modeling that can be incorporated into the final allowable harm statement. (DU 16, 7)
- For Taseko and Widgeon DUs, the available data does not allow for total allowable harm to be assessed using the methods described in this report. However, using the other small stocks assessed in this report as proxies, all sources of harm should be reduced to the maximum extent possible for Taseko and Widgeon. (DU 22, 24)
This Science Advisory Report is from the October 7-10, 2019 regional peer review on Recovery Potential Assessment – Fraser River Sockeye Salmon (Oncorhynchus nerka) – Ten Designatable Units. 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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