Évaluation du potentiel de rétablissement de neuf unités désignables du saumon rouge (oncorhynchus nerka) du fleuve Fraser – partie 2 : habitat, évaluation des menaces, atténuation et dommages admissibles

Abstract

This is the second of two parts of a Recovery Potential Assessment (RPA) for 9 Designatable Units (DUs) of Fraser River Sockeye Salmon (FRS). The objective for this portion of the RPA was to assess threats that may be limiting the survival and recovery of these DUs, discuss scenarios for mitigation of these threats, and to provide recommendations for allowable harm based on the collective results from both parts of the RPA. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assessed twenty-four FRS DUs in 2017. Ten DUs were assessed as either Threatened or Endangered. This RPA addresses nine of those DUs; one DU was assessed in a separate RPA process (DU6 Cultus-L). Declining trends in abundance have continued for these DUs since the COSEWIC assessment. The following DUs were assessed: DU2 Bowron-ES (Endangered) DU10 Harrison (U/S)-L (Endangered) DU14 North Barriere-ES (Threatened) DU16 Quesnel-S (Endangered) DU17 Seton-L (Endangered) DU20 Takla-Trembleur-EStu (Endangered) DU21 Takla-Trembleur-S (Endangered) DU22 Taseko-ES (Endangered) DU24 Widgeon-RT (Threatened) 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). A threats calculator based on the International Union for Conservation of Nature (IUCN) threats classification system was used to estimate the population-level impacts over the next three generations from many ongoing and future anthropogenic threats. The overall threat ranking ranged between High to Extreme for all DUs based on the number and severity of the threats. Common threats to all DUs were climate change, geological events, fishing, pollution, ecosystem modifications, problematic species, and hatchery competition. Individual DUs are experiencing a unique combination of threats based on the location of spawning grounds and migration timing that resulted in different overall threat rankings. The landslide in the mainstem Fraser River near Big Bar poses a specific threat to five Endangered DUs that spawn above the slide: DU2 (Bowron-ES), DU16 (Quesnel-S), DU20 (Takla-Trembleur-EStu), DU21 (Takla-Trembleur-S), and DU22 (Taseko-ES). The challenging migratory conditions created by the landslide has led to high levels of adult en route mortality, particularly for the earliest-timed DUs (i.e. DU2, DU20, DU22). Even with appropriate mitigation, DU2, DU20 and DU22 face persistent challenges into the future. Impacts of the landslide on juvenile salmon out-migration are being investigated. Regulatory responsibilities for mitigations lie with multiple jurisdictions. Mitigating the numerous complex, and often interrelated, threats facing these DUs will be extremely challenging, especially as many threats are exacerbated by climate change. Based on the collective results from Part 1 and 2 of this RPA, the following allowable harm statements were made: for DU2 Bowron-ES and DU20 Takla-Trembleur-EStu, the only activities allowed that cause mortality should be those that are in support of the survival of the DU, and all sources of anthropogenic harm should be reduced to the maximum extent possible. for DU10 Harrison (U/S)-L, DU14 North Barriere-ES, DU16 Quesnel-S, DU17 Seton-L, DU21 Takla-Trembleur-S, and DU22 Taseko-ES, the only activities allowed that cause mortality should be those that are in support of the survival and recovery of the DU, and all sources of anthropogenic harm should be reduced to the maximum extent possible. for DU24 Widgeon-RT, this population is naturally at low levels and is susceptible to harm even if steps are taken to minimize mortality. As such, the only activities allowed that cause mortality should be those that are in support of the persistence of the DU, and all sources of anthropogenic harm should be limited to the maximum extent possible.