A recent literature review that analyzed over 200 studies focusing on the release of hatchery salmonids, which include species such as salmon, trout, and char, revealed hatchery releases often adversely affect marine and freshwater wild salmonid populations.
The research, “A global synthesis of peer-reviewed research on the effects of hatchery salmonids on wild salmonids," which appeared in Fisheries Management and Ecology, scoured over 50 years’ worth of publications published between 1970 and 2021. Over half the publications studied fisheries in the United States, with other countries studied including Canada, France, Spain, and Norway. The research primarily focused on the effects releases have on 15 species, such as brown trout, steelhead trout, Chinook salmon, and Atlantic salmon.
While the release of hatchery salmonids typically lead to an increase in stock abundance and overall aquaculture successes, those gains are often counterbalanced by genetic and ecological disruptions to wild populations. These disruptions are due to the fact that hatchery fish compete for the same resources and reproductive opportunities as wild salmonids and can introduce exponentially harmful maladaptive behaviors in future generations.
“Wild and hatchery fish are not the same creatures. Wild salmonids embody unique genetic characteristics and incredible ecological strategies developed over long evolutionary histories, and hatchery fish can erode these adaptations and reduce the resiliency of wild populations,” Helen Neville, one of the study co-author's and a senior scientist at Arlington, Virginia, U.S.A.-based nonprofit Trout Unlimited, said.
There are many bodies of water where hatchery fish now make up large swaths of overall populations. For example, over five billion hatchery fish are annually released into the Pacific Ocean, with over 40 percent of the salmon biomass in the Pacific now comprised of hatchery fish. Neville said these releases are helpful in certain instances but should not be used as a blanket solution to increasing salmonid populations.
“Hatcheries will remain a key part of fishery management in many watersheds, especially in places where habitat is degraded or populations are on the brink of extinction and to support critical needs like tribal rights to harvest,” Neville said. “Where these programs are used, managers should look to the best available science to guide the operation of these programs to ensure they meet the highest standards possible to reduce the risk to wild salmonids.”
Neville said though the raising and release of hatchery fish provides some benefits, such as subsidizing fisheries, mitigating habitat loss and overexploitation, and rebuilding depleted populations of wild salmonids, the risk of doing so can often outweigh the benefits. Namely, even when broodstock directly stem from a wild population, genetic issues such as inbreeding and reduced resistance to parasitic infections still arise.
“From that very basic genetic perspective, even if you’ve built your broodstock out to thousands of individuals, they’re all genetically representative of that first group that increasingly differentiates from the wild population over time,” Neville said. “Then, add strong selection for domestication in a hatchery, where individuals that perform well in the artificial hatchery environment do better in that setting but perform more poorly in the wild, and you end up with quite a different fish.”
Wild salmonids demonstrate substantial resilience to disease, but adapting rapidly to a hatchery environment inevitably leads to the loss of essential adaptations required for survival in natural environments, according to Neville. Once acclimated to hatchery conditions, salmon have trouble reverting to original traits, and the number of wild salmonids that have robust adaptations subequently dwindles.
“When the hatchery fish come out of this domesticated environment, they have lower success rates, and they have lower fitness, which includes both survival and relative reproductive success, compared to wild fish,” Neville said.
According to Neville, to properly conserve wild populations, there must be greater priority placed on habitat restoration and removal of habitat disruptions such as dams, which are often the original factors that limited wild populations and made hatchery releases necessary in the first place.
The paper concentrated solely on assessing the impacts of hatchery releases on existing wild populations, omitting successful reintroductions of locally extinct salmonid stocks. Such cases illustrate clearer and more significant benefits of hatchery releases in aiding conservation efforts and fulfilling tribal treaty rights and fisheries goals, presumably with less impact on wild populations.
“Ultimately, I hope [the research] provides fishery managers, decision-makers, and conservationists a considerable resource that elevates our understanding of these impacts and fosters science-based assessments of practices and rigorous monitoring so that where hatcheries are used, they do not undermine wild salmon and trout recovery,” Neville said. “This work can, and should, inform policy and budget decisions to better balance conservation and fishery goals.”
Trout Unlimited, which was originally established in the U.S. state of Michigan in 1959 to conserve and protect America’s coldwater fisheries and watersheds, provided financial support for the research.
Photo courtesy of Christina Dutkowski/Shutterstock
