Research Document 2018/014

By Authors: Kim Hyatt, Ruth Withler, and Kyle Garver

Abstract

The Columbia River Basin supports a Sockeye Salmon (Oncorhynchus nerka ) aggregate that is composed of three Sockeye Salmon populations. 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. 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. This work was initiated to determine the potential risks, impacts and uncertainties associated with variable scale introductions of Sockeye Salmon fry into Okanagan Lake – through bioenergetics or food-web disruption, pathogen transfer, or genetic impacts. Based on results from an introduction experiment in a nearby lake (Skaha Lake), and data from nearby lakes (acknowledging differences in lake size, depth, and productivity, and scaled to account for O. nerka proportion of total pelagic fish biomass), the impact of Sockeye Salmon fry introductions on Okanagan Lake and especially its’ populations of resident kokanee salmon were considered. Sockeye Salmon fry introductions, across the range of abundance currently proposed for Okanagan Lake, are considered unlikely to induce detectable changes to pelagic food-webs (i.e. phytoplankton and zooplankton), or to sensitive aquatic biota (all ages and size classes of pelagic fish) within Okanagan Lake. The transfer of bacterial, parasitic, and viral pathogens to the watershed from hatchery-origin Sockeye Salmon fry were considered as part of the impact evaluation. Due to their capacity to spread from mother to offspring, viruses such as infectious pancreatic necrosis virus (IPNV) and infectious hematopoietic necrosis virus (IHNV) were noted of concern. Nevertheless, based on results from the Skaha Lake introduction, and the use of egg disinfection and containment procedures employed by the applicant, the potential transfer risk of these pathogens is low, as no detection of IPNV, IHNV or other cell culture replicating agents has occurred in fry since the inception of the hatchery program in 2003. Genetically distinct ecotypes may arise within a species when there is more than one selective niche to occupy in the environment and there exists within the species sufficient genetic diversity to respond to the divergent selective forces through an adaptive process of ecotype development (Wellborn and Langerhans 2015). The process of ecotype development and maintenance is not always stable and irreversible, especially in the face of environmental change. Little genetic impact on the kokanee populations, including ecotype formation and persistence or degradation, would be expected to result from a one-time introduction of 750,000 Okanagan Sockeye Salmon fry to the lake, while an ongoing release of between 0.75 and 3.5 million Okanagan Sockeye Salmon fry would be expected to result in hybridization between residual Sockeye and kokanee in Okanagan Lake; the results of which cannot be predicted.

Complete document (PDF, 805 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.