Bottlenecks Weekly Summary Report
Jamieson Atkinson RPBio BC Conservation Foundation
2024-03-14
Introduction
Recent declines in the abundance and productivity of Chinook (Oncorhynchus tshawytscha) salmon, coho salmon (O. kisutch), and steelhead trout (O. mykiss) in the Salish Sea have resulted in ecological, economic, and cultural impacts in British Columbia (BC). Reduced abundance of these species resulted in the closure of targeted commercial troll fisheries in the Strait of Georgia in the 1990s (Ryall & Shardlow 1991); similarly, marine recreational fishery effort, formerly representing 90% of effort in BC, decreased by 90% between the 1980s and 2000s (Strongitharm 2006). This decline represents a large loss of potential economic benefit given that marine recreational fisheries in BC generate over $700M in annual revenue (Government of Canada 2023). Chinook salmon are also the primary prey of the endangered Southern Resident Killer Whales (SRKW; Orcinus orca), which have been listed as an endangered species in both the United States and Canada (COSEWIC 2008; NOAA 2022). It is believed that the poor health of SRKW is related to dwindling populations of Chinook salmon. Beginning in 2019, the critical conservation status of Chinook salmon in Southern BC led to unprecedented restrictions on commercial, recreational, and First Nations food, social, and ceremonial fisheries (Department of Fisheries and Oceans (DFO) 2020; Government of Canada 2018).
There is a growing consensus that the first year in the marine environment plays a key role in regulating Pacific salmon productivity (Beamish and Mahnken 2001). The Province of British Columbia frequently invests in freshwater habitat enhancement projects, but this approach has limited ability to offset low marine survival. Predation, competition, climate change, and fishing mortality are the dominant hypotheses to account for poor steelhead returns, but the relative contributions of each are neither well estimated nor understood (Kennedy et al. 2022; Wade et al. 2013). Understanding the factors limiting Chinook, coho, and steelhead productivity is a key cultural, economic, and ecological priority for BC.
As wild salmon and steelhead abundance continue to decline or remain at historic lows, there is growing recognition that traditional hatchery mitigation is not meeting conservation and recovery objectives for wild stocks (Naish et al. 2008). In 2019, the Province released the BC Wild Salmon Advisory Council Recommendations for a Made-in-BC Wild Salmon Strategy, which identified investment in and support for salmon enhancement activities that are strategic, science-based (Strategy 1.5), and key to wild stock recovery (WSAC 2019). For salmon enhancement programs to effectively contribute to harvest and conservation, the performance (i.e., survival and fitness) of hatchery fish must be high relative to wild fish.
A project implemented under the Pacific Salmon Foundation’s (PSF) Salish Sea Marine Survival Project (SSMSP) by the British Columbia Conservation Foundation (BCCF), used passive integrated transponder (PIT) tags to mark cohorts of juvenile Cowichan River Chinook as a novel approach to studying both freshwater and marine survival; in-river PIT tag arrays were installed to detect tags as the fish passed over on their outward or return migrations (PSF 2018). PIT tags are tiny electronic tags that are cost-effective, easily applied, and have a 12-digit unique code. The tag can be automatically detected and decoded as the fish crosses an antenna, eliminating the need to handle or kill fish to determine its origin.
PIT tags provide information on fish at the individual level. Furthermore, PIT tags are two orders of magnitude less expensive than other types of electronic tags (e.g. radio and acoustic tags), allowing economical marking of thousands of individuals. The landmark Cowichan PIT tag study highlighted the importance of the link between freshwater flows and in-river mortality, and indicated there is likely high mortality after the first marine summer, and the much lower survival of hatchery-produced salmon over wild fish (Pearsall et al. 2021). These findings prompted decisions by the DFO-Salmon Enhancement Program (SEP) to change their hatchery release locations for Cowichan Chinook, resulting in higher survival of hatchery fish and providing the impetus to address minimum ecological flows. However, hatchery Chinook on the Cowichan still exhibit a third to half of the survival of their wild counterparts, and data collated to date suggest that the difference may be established over the first winter (Pearsall et al. 2021).
Study Areas
The Salish Sea is an inland sea encompassing Puget Sound, the Strait of Juan de Fuca, and the Strait of Georgia (Figure 1). The area spans from Campbell River on Vancouver Island to the Olympic Peninsula. The Salish Sea is home to 37 species of mammals, 172 species of birds, 253 fish species, and more than 3,000 species of invertebrates (Gaydos and Pearson 2011; Brown and Gaydos 2011). Multiple threatened and endangered species as listed under the Canadian Species at Risk Act and the United States Endangered Species Act, call the Salish Sea home; these species include the SRKW and ecologically significant units of Pacific salmon, such as the Nanaimo and Puntledge river’s summer-run Chinook.
Our study area is concentrated in the Strait of Georgia, the northeastern portion of the Salish Sea and includes 14 rivers across 13 watersheds (Figure 1 and Figure 2), including two west coast watersheds, the Stamp/Somass rivers and the Toquaht River.
