Wild salmon policy status, limit reference point, and candidate escapement goals for Okanagan Sockeye Salmon

Abstract

Canadian Okanagan Sockeye salmon (Oncorhynchus nerka) are geographically and genetically distinct from all other Sockeye salmon in British Columbia, as they spawn in the Canadian portion of the Columbia River Watershed, the Okanagan Basin. This migratory route through the United States (U.S.) also causes them to have a unique history, primarily driven by the construction of nine mainstem Columbia River hydroelectric dam structures along their migratory route. Although Okanagan Sockeye salmon have provided an abundant source of food and trade for the Syilx people since time immemorial, as early as the late 19th century the health of the stock has been constrained by fish fences, dams, habitat degradation, and water flow regulation issues, among other threats. Despite this history, the stock showed signs of recovery in the early 2000’s, driven in part by improvements in freshwater flow management and dam passage, as well as habitat restoration projects, and hatchery supplementation aimed at re-establishing populations in previously inaccessible habitats. Therefore, harvesting was allowed to resume in some areas both in the U.S. and Canada. Okanagan Sockeye salmon are lake-rearing, and until 2009 they had access only to Osoyoos Lake (the southernmost lake in the Canadian portion of the Okanagan River Basin). In the last 15 years, restoration of passage at Okanagan River mainstem dams, and targeted hatchery programs, have facilitated the establishment of a population in Skaha Lake, while efforts are ongoing to also establish a population in Okanagan Lake, which is the largest lake in the Okanagan River basin. These changes in accessible range and population structure require the revision of reference points (both for management and conservation) and stock status. In this document, we consider three alternative methods for establishing reference points: 1. estimating total spawner capacity based on habitat attributes for all three lake populations, 2. estimating total rearing capacity based on the results of bioenergetic models of lake food webs, which was possible only for Skaha and Osoyoos lakes, and 3. population dynamics (spawner-recruit and spawner-smolt) modelling for the Osoyoos Lake population. Habitat-based estimates of spawning capacity were found to be the most useful approach for determining biological benchmarks in order to assess status under the Wild Salmon Policy and therefore to determine status relative to the Limit Reference Point, and to identify candidate management targets. Wild Salmon Policy status was assessed based on data combining Osoyoos and Skaha lakes. Lower and upper benchmarks for the relative abundance status metrics were identified at 20% and 40% of estimated median spawner capacity, respectively (20% of habitat-based Smax: 28,603; 40% of habitat-based Smax: 57,207). The final status of the Osoyoos-Skaha-Okanagan Sockeye salmon Conservation Unit (CU) for 2023 was assessed as Amber with high confidence. However, the CU faces serious threats from climate change and is at high risk of declining into Red status in the near future. The Okanagan Sockeye salmon Stock Management Unit (SMU) contains a single CU which is currently not of Red status. Therefore, the SMU is above the status-based Limit Reference Point (LRP) under the Fish Stock Provisions of the modernized Fisheries Act. Habitat-based estimates of the number of spawners that maximize juvenile recruitment (i.e., Smax, corresponding to full use of the available spawning habitat) were summed for all three lakes and were used to identify candidate management targets for the Okanagan Sockeye salmon SMU. A candidate target range of 96,000-135,000 spawners would approximate an escapement goal based on SMSY (as 50-70% Smax). A candidate target range of 192,000- 231,000 spawners could be used to represent a goal of maximizing total production (100-120% Smax). Escapement goals specific to each lake population are also estimated and provided.