Terms of Reference

Science Information to Inform Consideration of Risks to Cultus Lake Sockeye Salmon in 2018

Science Response Process – Pacific Region

July 2018
Nanaimo, British Columbia

Chairperson: Mary Thiess

Context

Cultus Lake is a small (6.4 km²) coastal lake in the lower Fraser River watershed that is the natal home to a unique population of sockeye salmon (Withler et al. 2000). The population is significant to local First Nations and has contributed to non-native fisheries since the late 1800s. While highly variable, the historical generational (4-year) average abundance of spawners entering the lake was about 20,000 spawners. The population began to decline in the 1970s, and the current generational average is about 1,000 spawners.

The Cultus Lake population is one of five Wild Salmon Policy (WSP) conservation units (CUs) comprising the Late Run Fraser Sockeye Salmon aggregate that historically entered the Fraser River in September each year. Since 1996, Late Run CUs (including Cultus Lake) have started their upstream migration as early as early August. Of the five co-migrating CUs in the Late Run Fraser Sockeye Salmon aggregate, three (including Cultus Lake) are assessed as “Endangered”, one as “Special Concern”, and one as “Not At Risk” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Additionally, the COSEWIC assessments align with recent WSP biological status assessments for these CUs (i.e., three CUs are Red, one CU is Amber and one CU is Amber-Green; DFO 2012; DFO 2018). To date, none of the CUs have been listed under Species at Risk Act (SARA).

It is suspected that high exploitation rates particularly in the 1980s, predation in the lake, declining lake water quality, and elevated pre-spawn mortality since the mid-1990s have contributed to the decline in abundance of Cultus Lake Sockeye Salmon. Since 1988, management actions have been taken to constrain exploitation rates on the Late Run aggregate. Beginning in 2000, a number of recovery actions were implemented to increase the abundance of Cultus Lake Sockeye Salmon, including a predator control program in the lake and hatchery fish culture that included conventional supplementation and a captive breeding program, under the guidance of the Cultus Sockeye Recovery Team (CSRT 2009), and Wild Salmon Policy (DFO 2005). Results from the last DFO assessment of Cultus Lake Sockeye Salmon (DFO 2010) indicated that the decline in abundance appeared to have been halted, although the population still had not yet met any of the recovery objectives set by the CSRT, nor a lower benchmark proposed under the WSP. That assessment also projected that the population’s long term viability would depend on the relative reproductive success of hatchery fish in the wild–identified as a high priority information need that could inform significant changes to the enhancement program (DFO 2010).

In 2018, the Adams River stock (Shuswap Complex-L CU) (the component of the Late Run aggregate that is considered “Not At Risk” by COSEWIC) is expected to provide a large return of Sockeye Salmon. Although fishing plans for the 2018 season are currently under development, fishing opportunities on the Late Run aggregate are anticipated and, as a result, incidental mortalities of Cultus Sockeye Salmon are likely to occur. In the past, Fisheries Management has constrained fisheries on stronger stocks in order to protect weaker co-migrating stocks such as Cultus Lake Sockeye Salmon, resulting in lost opportunities for First Nations, commercial and recreational fishers. Recent estimates of freshwater survival rates for both wild and enhanced juvenile Sockeye Salmon in Cultus Lake show a decline to levels that are not sufficient for the stock to replace itself even in the absence of all fishery impacts.

DFO Fisheries Management Branch has requested that Science Branch provide an update of the state of knowledge for Cultus Lake Sockeye Salmon.  The advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response Process (SRP), will be used to inform fisheries management decisions in 2018, as well as to identify issues to be addressed over the longer term regarding appropriate Sockeye Salmon enhancement measures, and recovery plans and strategies for Cultus Lake Sockeye Salmon.

Objectives

The specific objectives of this review are to:

1. Summarize the current state of knowledge relating to survival of Cultus Lake Sockeye Salmon (focusing on the period since 2010), including survival of both natural- and hatchery-origin fish in both the lake and marine environments.
2. Discuss potential contributions of freshwater factors to observed declines in lake survival of Cultus Lake Sockeye Salmon and what measures might reverse this trend.  
3. Identify key uncertainties and knowledge gaps, including potential mitigating factors that may contribute to the short term reproductive success of the Cultus Lake Sockeye Salmon population.

Expected Publications

• Science Response

Expected Participation

• Fisheries and Oceans Canada (DFO): Science, Fisheries Management, Salmonid Enhancement Program

References

COSEWIC. 2003. COSEWIC assessment and status report on the sockeye salmon Oncorhynchus nerka (Cultus population) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa, Ont.

Cultus Sockeye Recovery Team (CSRT). 2009. National conservation strategy for Cultus Lake sockeye salmon (Oncorhynchus nerka). Can. Tech. Rep. Fish. Aquat. Sci. 2846: viii + 46 p.

DFO. 2005. Wild Salmon Policy.  57 pgs. Last accessed June 28, 2018.  https://waves-vagues.dfo-mpo.gc.ca/library-bibliotheque/315577.pdf

DFO. 2010. Assessment of Cultus Lake Sockeye Salmon in British Columbia in 2009 and Evaluation of Recent Recovery Activities. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2010/056.

DFO. 2018. The 2017 Fraser Sockeye Salmon (Oncorhynchus nerka) integrated biological status re-assessment under the Wild Salmon Policy. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2018/017.

Withler, R.E., K.D. Le, R.J. Nelson, K.M. Miller and T.D. Beacham. 2000. Intact genetic structure and high levels of genetic diversity in bottlenecked sockeye salmon, Oncorhynchus nerka, populations of the Fraser River, British Columbia, Canada. Canadian Journal of Fisheries and Aquatic Sciences 57: 1985-1998.