État en vertu de la politique concernant le saumon sauvage, point de référence limite et objectifs d'échappée potentiels pour le saumon rouge de l'Okanagan

Abstract

Okanagan Sockeye salmon make up a single stock management unit (SMU), which contains a single conservation unit (CU) with three distinct spawning populations; these rear in Osoyoos Lake, Skaha Lake, and Okanagan Lake. Naturally returning spawners were re-established in Skaha Lake in 2011 and in Okanagan Lake in 2022, due to modifications to access barriers that allowed passage. The current escapement goal for Okanagan Sockeye salmon was set at 35,500 based on Hyatt and Rankin’s (1999) study, but that target has since been exceeded in 12 of the past 20 years for the Osoyoos Lake population alone (2004-2023). Furthermore, improvements in water management, changes in stock assessment, habitat restoration, and range reintroduction due to improved fish passage have fundamentally changed the structure of, and our understanding of, the stock. Therefore, it no longer reflects the capacity of the habitats available to Sockeye salmon in the Okanagan basin. Estimates of current habitat capacity, and potential reference points, were explored using three alternative approaches: (1) spawning habitat capacity estimates based on detailed habitat mapping of flow and gravel sizes (all three lakes); (2) rearing habitat capacity estimates based on in-lake sampling (e.g., stomach contents) and food web modeling (Osoyoos and Skaha Lakes); and (3) estimating reference points based on spawner-recruit models (Osoyoos Lake). Estimates of spawning habitat capacity were found to be the most appropriate approach for determining population status and candidate management reference points, because consistent and reliable estimates could be developed for all three populations. Median spawning habitat capacity for all three populations combined ranged from 180,754 to 205,588. Wild Salmon Policy (WSP) status was evaluated for the combined spawner time series for Osoyoos and Skaha lakes, based on four standard metrics (relative abundance, absolute abundance, long-term trend and percent change over three generations) and associated benchmarks using established methods. The final status 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 SMU, which contains one CU that is not currently Red status, is considered to be above the Limit Reference Point (LRP) under the Fish Stock Provisions of the modernized Fisheries Act. Habitat-based estimates of the number of spawners that maximizes recruits (SMAX; corresponding to full use of the available spawning habitat) for all three lakes were used to identify candidate management targets for the Okanagan Sockeye 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. Okanagan Sockeye salmon are already being impacted by climate change. Climate change effects will likely increase the frequency of adverse conditions throughout their lifecycle (e.g., thermal barriers during adult return migration, increased egg mortality due to freezing). Preserving diverse phenotypes may increase long-term resilience and should be considered as part of management planning.