Steelhead trout. (Photo: NOAA)
Study reveals strong juvenile trout drop in the ocean
Tuesday, June 27, 2017, 03:00 (GMT + 9)
A new study tracking 35-year trends for more than 40 steelhead populations determined that declining numbers of steelhead trout in the rivers flowing through British Columbia, Washington state, and Oregon are linked to poor survival of young fish in ocean environments.
The research study, carried out by scientists at the Washington Department of Fish and Wildlife and published in the Canadian Journal of Fisheries and Aquatic Sciences (CJFAS), reveals that declining survival of juvenile steelhead in the ocean is strongly coupled with significant declines in the abundance of adults.
"We were able to compile data from multiple reports and databases to document survival in the ocean of Oregon, Washington, and BC steelhead trout and show that these trends paralleled declines in adult abundance and also differ among populations originating from different areas," says Dr. Neala Kendall, lead author of the study.
These researchers point out that populations with particularly concerning declines were those in the Lower Columbia River and in Puget Sound, an inlet of the Pacific Ocean and part of the Salish Sea that extends north and south of Seattle, Washington.
The study found that among populations in Puget Sound, ocean survival of juvenile steelhead in the 2000s has declined by 77 per cent on average compared to the 1980s; survival averaged 3.1 per cent in the 1980s but dropped to 0.7 per cent in the 2000s.
The research found parallel trends in adult abundance. Specifically, numbers of adults in Puget Sound steelhead populations in the 2000s have declined by 53 per cent on average compared to the 1980s.
The declines in juvenile survival "likely contributed to these fishes' low abundance," says Kendall; abundances are so low that Puget Sound steelhead were listed for protection under the Endangered Species Act in 2007.
Steelhead populations in British Columbia included in the study also have all declined in abundance and ocean survival since the 1980s.
Declines in survival of juvenile steelhead in ocean environments were not as drastic for populations along the coasts of Washington and Oregon which are not listed under the Endangered Species Act.
Survival and abundance trends, like those generated in this study, can enhance current tools being used to predict changes in steelhead populations.
To best conserve steelhead in the Pacific Northwest, especially recovery efforts for Puget Sound populations, "stakeholders and concerned citizens want to better understand why these populations have been struggling and how marine survival has contributed," Kendall says.
The research is part of the Salish Sea Marine Survival Project, a US-Canada collaboration of more than 60 organizations conducting research to understand why salmon and steelhead are dying in the Salish Sea.