Science Response 2017/031

Review of potential impacts associated with recent and proposed Okanagan Sockeye Salmon fry introductions to Skaha and Okanagan Lakes

Context

The Columbia River Basin supports a Sockeye Salmon (Oncorhynchus nerka) aggregate that is composed of three Sockeye Salmon populations including: the Okanagan population from British Columbia (BC), Canada, the Wenatchee Lake population from Washington State, and a small population from Redfish Lake in Idaho that is listed under the United States Endangered Species Act (ESA). On average, the Okanagan population has accounted for greater than 80% of all Sockeye Salmon returning to the Columbia Basin in the most recent decade.

Anadromous Sockeye Salmon and freshwater-resident kokanee are two ecotypes within Oncorhynchus nerka that occur frequently as sympatric paired populations sharing a common nursery (juvenile-rearing) lake.  The closely related ecotypic pairs typically develop naturally, with the presence of Sockeye Salmon believed to give rise to the subsequent development of kokanee. Okanagan Lake currently provides no access to Sockeye Salmon but contains shore- and stream-spawning kokanee that display limited morphological and genetic differentiation and may constitute incipient ecotypes. Okanagan Lake has experienced extensive environmental perturbation over the past 100 years and the evolutionary trajectory of the kokanee ecotypes (stable, increasing or decreasing genetic differentiation) is not known.

As part of a program to introduce Sockeye Salmon into Okanagan Lake, the Okanagan Nation Alliance (ONA) initiated introductions of hatchery-origin Sockeye Salmon to Skaha Lake as an initial, 12-year experiment to provide results to inform future introductions to Okanagan Lake. The ONA conducted an evaluation phase on Skaha Lake from 1999 to 2003; and then began introducing hatchery-origin Sockeye Salmon fry to rear in Skaha Lake, as part of a collaborative “Skaha Re-introduction Project”. Observational data to assess both disease and other ecological impacts have been gathered on an ongoing basis by the ONA and subjected to annual review by the three-party (ONA, DFO, BC-FLNRO) Canadian Okanagan Basin Technical Working Group since the program’s inception (Alexander and Hyatt eds. 2015). A recent genetic study suggests that significant introgression has occurred in the Skaha Lake Sockeye/kokanee Salmon populations since the introduction of Sockeye Salmon in 2004 (Veale and Russello 2016); with unknown long term consequences on resident kokanee salmon.

In British Columbia, a federal – provincial Introductions and Transfers Committee (ITC) reviews applications to introduce or transfer cultured aquatic species to assess risks for possible disease, ecological and genetic effects on native species and ecosystems, and to ensure that the licensing requirements of s. 56 of the Fishery (General) Regulations are met. When issuing a licence, the ITC may also prescribe certain measures to minimize risks associated with transfer activities (e.g. egg disinfection, quarantine of stock). Specifically, the ITC can recommend the Minister issue a licence if:

1. the release or transfer of the fish would be in keeping with the proper management and control of fisheries;
2. the fish do not have any disease or disease agent that may be harmful to the protection and conservation of fish; and
3. the release or transfer of the fish will not have an adverse effect on the stock size of fish or the genetic characteristics of fish or fish stocks.

The ONA has applied to release up to 750 000 Sockeye Salmon fry into Okanagan Lake in 2017, and has indicated that their hatchery facility has the capacity to rear 7 million fry; with maximum single-year introductions estimated at 3.5 million fry. To provide a recommendation regarding whether or not to authorize the release application, the ITC requires science advice on potential ecosystem disruption, pathogen transfer, or genetic interference impacts associated with the proposed release. Consequently, DFO Aquaculture Management Division has requested that DFO Science review the literature and results from the ongoing assessment of the Skaha Lake experimental re-introduction program, as well as other applicable sources of information, and provide advice regarding the potential risks, impacts and uncertainties associated with variable scale introductions of Sockeye Salmon fry into Okanagan Lake. The assessment and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR) will be used to assist in arriving at a regulatory authorization decision.

This Science Response Report results from the Science Response Process of May 2017 Review of proposed Okanagan Sockeye fry introduction to Skaha and Okanagan Lakes: history, uncertainties, and implications.

Complete document (PDF, 300 KB)

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