Effects of release size and location on the early survival of Chinook salmon on the west coast of Vancouver Island
Thornton Creek Enhancement Society has partnered with Tom Balfour of Central Westcoast Forest Society as he pursues research for his masters thesis on Toquaht River Chinook salmon. Tom is interested in filling in the knowledge gaps regarding the relationship between fry release size, timing, and location on subsequent habitat use, growth rates and survival. Tom joined our field crew in September and October of 2020 to collect broodstock from Toquaht River chinook to be used in this study. We will start PIT-tagging these fry this spring and releases will begin in May 2021. Below is Tom’s executive summary for his thesis:
“Population abundances of Chinook salmon (Oncorhynchus tshawytscha) are heavily influenced by early life stages. Growth during the early critical periods is known to play a major role in dictating marine survival and returns to freshwater as adults. However, the relationships between length of freshwater migration, body-size and timing of outmigration and early life survival are not well understood.
Widespread declines in Chinook Salmon populations throughout their North American range in recent decades have spurred a significant effort to further our understanding of early life survival of both wild and hatchery-produced Chinook salmon. Much of this work has been done on the Salish Sea, Puget Sound, and Columbia River populations. While many commonalities have been found in marine survival rates of Chinook salmon from different regions between years, local characteristics have also been identified as important drivers of survival variability within years (eg. Pinniped, avian and trout predation in Cowichan river populations, contaminates in Puget Sound estuaries, food web limitations in the Salish Sea, or hydroelectric dams in the Columbia river basin).
Chinook salmon originating from the west coast of Vancouver Island (WCVI) have received much less attention than neighbouring regions, despite also facing drastic population declines. Applying lessons learned from the Salish Sea Marine Survival Project, this project intends to use PIT-tag technology to better understand migration timing and behavior of hatchery origin Chinook in the Toquaht River – a small WCVI river, representative of the 100+ Chinook producing rivers in the WCVI region. This work plans to evaluate the relationship between body-size, release location, and subsequent early-life survival in both freshwater and during estuarine and early residency in coastal waters. By following the outmigration and sampling frequently throughout the spring and summer and across habitats, I aim to identify when and where growth opportunities and size‐selective mortality occur within the study site, furthering our understanding of the early life of both hatchery and wild Chinook Salmon in the Toquaht Watershed, with implications for the WCVI region more broadly.
The goals of this project are:
1) to quantify the relationship between fish size and release location on freshwater survival of hatchery Chinook salmon
2) to describe the migration timing and behavior of Toquaht Chinook salmon
3) to describe patterns in habitat occupancy by both wild and hatchery origin Chinook salmon in the Toquaht estuary and nearshore waters
4) to describe changes in fork length (mm) and weight observed across habitats and time; and relationships to release location
5) to evaluate the evidence for size‐selective mortality, hatchery-wild interactions and/or carry-over effects associated with freshwater residency.
By helping develop a fine-scale and region-specific understanding of how and when size‐selective mortality operates on a population, we can gain insight into growth dynamics and size‐selective ecological processes affecting Chinook salmon. This work has the potential to further our understanding of the early life of Chinook salmon, inform local hatchery strategies, and guide future Chinook salmon conservation and management practices.”
We are very excited to report our findings later this year, and hope that this research partnership continues into the future! A huge thank-you to Tom Balfour for initiating this incredible project and for working so hard to better our understanding of local Chinook, as well as to the Clayoquot Biosphere Trust and Pacific Salmon Foundation for providing funding.