COSEWIC assessment and status report on the Sockeye Salmon Oncorhynchus nerka Sakinaw population in Canada
- Assessment Summary
- Executive Summary
- COSEWIC Mandate, Membership and Definitions
- Lists of Figures and Tables
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Supplementation and Restoration
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Acknowledgements and Literature Cited
- Biographical Summary of Contractor
Summary of Status Report
Sakinaw Lake sockeye salmon (Sakinaw sockeye) warrant designation as an Evolutionarily Significant Unit (or COSEWIC Nationally Significant Population) based on the two-part test developed to define salmonid “species” under the US Endangered Species Act. Protein electrophoresis and molecular DNA analyses indicate that Sakinaw sockeye are substantially reproductively isolated from other populations. Their distinctive life history characteristics (early and protracted river-entry timing, extended lake residence prior to spawning, small body size, low fecundity and large smolt size) suggest that they are also evolutionarily distinct from other sockeye populations in the Pacific Northwest and Alaska. The evidence for very restricted gene flow between Sakinaw and other populations and the distance to the nearest extant sockeye population both confirm that there is virtually no possibility of natural rescue from neighbouring sockeye populations. All previous attempts to transplant sockeye to Sakinaw Lake have almost certainly failed. Consequently, we cannot be optimistic about prospects for re-establishing a sockeye run to Sakinaw Lake should the native population be lost.
The persistence of Sakinaw sockeye is threatened by two primary factors: mortality from fisheries, and degradation of freshwater habitat. At present, fishing mortality is probably the single greatest threat. Overfishing can be considered the proximate cause of decline in the sense that fishing effort was not reduced significantly until 1998, and Sakinaw sockeye continue to be killed in fisheries despite the observed decline in spawning escapements to Sakinaw Lake that began in 1987. Sakinaw sockeye are captured together with sockeye and pink salmon from more productive populations in mixed-stock fisheries during their return migration through Johnstone and Georgia straits. It is evident that “passive management” and (limited) artificial supplementation have been inadequate to restore Sakinaw sockeye in the face of this fishing mortality. Further changes to fisheries will be necessary to promote recovery.
Sakinaw sockeye likely became increasingly vulnerable to overfishing in mixed-stock fisheries as their natural productivity was eroded by habitat degradation within Sakinaw Lake. The spawning beaches have been degraded by historic logging, milling and booming. The lake was dammed at the outlet to transport logs to the ocean, and log storage near the outlet has sometimes blocked adult salmon migration. Development of residential lots and recreational boating along the shore of Sakinaw Lake has more recently degraded spawning beaches further as stream flows have been diverted to prevent flooding and a boat ramp was constructed through the middle of one of the major spawning beaches. Domestic water use throughout the drainage contributes to reduced summer flows that can adversely affect adult migration into the lake; low water levels remain a serious concern. However recent attempts to restore spawning beaches and to improve fish passage at the dam appear to have set the stage for recovery.
If present trends continue, the Sakinaw sockeye will likely go extinct in the near future. The trend in smoothed escapement data from 1988 to 2002 indicates a reduction of 99% over 3 generations (12 years). The total number of mature individuals (all of which die after spawning) has averaged less than 80 (range 14 to 122) over the last full generation (4 years; 1999-2002). Adult numbers averaged 5000 individuals historically. Thus, the reduction to less than 80 adults is drastic, and there is no margin for further decline.
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