A study conducted by researchers at Oregon State University has found that first-generation, wild-born descendants of hatchery-origin Chinook salmon in the McKenzie River show improved fitness compared to their hatchery-origin counterparts. Fitness was measured by the number of adult offspring a fish produces, with higher fitness leading to more offspring. The study, based on data collected over 13 years, provides encouraging news for Chinook salmon recovery efforts. While previous studies have shown that hatchery-origin salmon have lower reproductive success in the wild, this research suggests that reproductive success may improve in the wild as quickly as it declines in the hatchery.
Spring Chinook salmon in the Upper Willamette River are listed as threatened under the federal Endangered Species Act. The McKenzie River has historically supported a large population of spring Chinook salmon and still supports a significant portion of the natural-origin spring Chinook salmon in the Upper Willamette Basin. The construction of Cougar Dam on the South Fork McKenzie River blocked historical spawning habitat, but an adult fish collection facility constructed in 2010 allowed for the collection and reintroduction of adult Chinook salmon above the dam.
The researchers collected fin samples from salmon at the collection facility to determine parent and offspring relationships and quantify their numbers. By creating family trees for each fish, the researchers were able to trace the ancestry of nearly 10,000 fish in the system. They found that first-generation, wild-born descendants of hatchery-origin fish produced significantly more adult offspring than hatchery-origin salmon that spawned alongside them in the river. These first-generation descendants also produced similar numbers of offspring to natural-origin fish, suggesting that naturally spawning Chinook salmon populations can be established from hatchery-origin salmon, with potential generational increases in fitness as they spawn in the wild.
The study did not determine what led to the increase in fitness between the first generation, wild-born salmon, and the hatchery-origin salmon. Questions remain about whether the increase is due to genetics, the environment, or a combination of both. Concerns also exist over the risk hatchery-origin salmon pose to the genetic integrity and productivity of natural populations. However, careful management of interbreeding between hatchery-origin and natural-origin salmon could help prevent a decline in overall fitness for the natural-origin fish.
The researchers caution that their conclusions may not apply to other river systems with reduced natural production or historical transfers of non-local origin salmon stock. Additionally, the findings may not apply to other species, such as steelhead. The study’s authors suggest that practices specific to the McKenzie River hatchery may have maintained adaptive genetic diversity and the capacity for increased fitness among the wild-born descendants of hatchery-origin salmon. Overall, the findings offer promising news for the use of hatchery salmon in conservation and recovery efforts.
The study’s lead author, David Dayan, now works for the U.S. Fish and Wildlife Service, while the senior author, Kathleen O’Malley, directs the State Fisheries Genomics Lab at Oregon State University. The study was published in the journal Evolutionary Applications and included contributions from researchers affiliated with OSU’s Coastal Oregon Marine Experiment Station and the College of Agricultural Sciences. Coauthors from other institutions were also involved in the research, emphasizing the collaborative nature of the study and its implications for future conservation efforts.
