Global review of peer-reviewed research documents harmful impacts of salmon, trout and char hatcheries on wild populations

Trout Unlimited fisheries scientists and prominent coauthors reviewed fifty years of research across salmonid species, including both freshwater and marine environments.

ARLINGTON, Va.– For over a century, fish hatcheries across the world have produced salmonids (salmon, trout, and char) to supply fisheries, mitigate habitat loss and boost depleted stocks. A newly published review of scientific literature examining the impacts of these programs on wild (i.e., naturally produced) salmonids shows that over 80 percent of global, peer-reviewed research on the topic has found that hatchery fish have adverse effects on wild salmonid populations in freshwater and marine environments.

Brought together by Trout Unlimited, a team of prominent American and Canadian researchers led by John McMillan and Helen Neville published their findings this summer in the peer-reviewed journal Fisheries Management and Ecology. The literature review, the product of four years of work, provides a comprehensive resource for decision-makers and fishery managers so they can fully weigh the consistent scientific findings when evaluating when, where, and to what extent hatcheries should be used, and how to minimize their impacts on wild salmonid populations if they are.

The new paper, “A global synthesis of peer-reviewed research on the effects of hatchery salmonids on wild salmonids” is openly available at the Wiley Online Library.

From the beginning, the coauthors sought a transparent, comprehensive approach. They first established a rigorous protocol that followed a globally accepted framework for literature review and synthesis to evaluate thousands of peer-reviewed publications. They identified 206 papers published between 1970 and 2021 that met framework-aligned criteria for inclusion in the literature review. These publications were assembled into a new, publicly available database, which will continue to be updated by science staff at Trout Unlimited as new research becomes available.

While research into the effects of hatchery salmonid production is often limited to specific regions or species, this literature review was global in scope to ensure a thorough collection of the scientific research of hatchery effects on wild salmonid populations worldwide. Notably, this included studies analyzing the impact of extensive releases of hatchery chum and pink salmon into the Pacific Ocean.

While the coauthors found that 83 percent of the publications reviewed found some level of adverse effects on wild salmonids from hatchery salmon, trout and char, a small percentage of the literature reviewed (3 percent) found beneficial effects. For example, some studies showed benefits when wild populations were highly depleted and close to extinction, suggesting the potential for a short-term boost.

The coauthors noted that the literature review did not consider instances of successful reintroductions of extirpated salmonid stocks, as the focus of was on research documenting impacts to existing wild populations.

John McMillan, Science Director for The Conservation Angler (formerly Science Director for Trout Unlimited’s Wild Steelhead Initiative): “It is important to take stock of the totality of existing information from time to time, particularly for complex topics that span several species and multiple continents. Considering the volume of research and the tendency of managers and scientists to operate in regional or species-specific silos, we thought there was value in conducting a global review to fully evaluate the body of literature and determine what the weight of evidence says about effects of hatchery salmonids on wild salmonids, and ultimately, to create a database that allows people to easily access information they may not have been previously aware of.

We found that the vast majority of studies reported some level of adverse hatchery effects, which echoes similar prior reviews by Miller et al. (1990) and Araki and Schmid (2010). The consistency in results over time suggests the science has matured to a point where we have a true, long-term understanding that hatchery salmonids harm wild salmonids much more often than benefit when they interact in nature.” 

Helen Neville, Trout Unlimited Senior Scientist: “Our goal was to provide an open and transparent resource summarizing the global research that others could build on and that could be updated in the future as new science comes out. Our findings closely mirrored, and thus corroborated, earlier, more geographically limited reviews. They also revealed several key areas where more recent science, particularly related to competition in the ocean and the fast-moving field of genetics, has advanced our understanding of how hatcheries impact wild salmonid populations.

Informed by the global science, we hope this work will motivate and support a deeper consideration of when and where hatcheries may, or may not, be an acceptable or effective tool, and how we can minimize harmful impacts to wild salmonid populations when they are justifiably used for compelling reasons.

Although this report is global in nature, we recognize that hatcheries play a significant role in specific regions where wild salmon and steelhead remain on the brink of extinction because of habitat degradation, including places where dams have drastically reduced wild production. In such places, hatchery salmon and steelhead, for instance, often serve as a vital lifeline to the lives, cultures, and well-being of tribal nations, and Trout Unlimited looks forward to continuing to work with tribes and others toward essential actions, including dam removal, that can recover healthy and harvestable populations of wild salmon and steelhead.”

Rob Masonis, Trout Unlimited Vice President for the Pacific Region: “This comprehensive analysis of peer-reviewed research underscores the need to make sure hatcheries are used judiciously for clearly defined purposes and with appropriate safeguards. Across the world, many salmonid hatcheries were built decades ago to support fisheries and replace natural salmonid production lost to dams and habitat destruction. Unfortunately, back then, managers lacked the scientific understanding we now have about the harmful impacts of hatcheries on the wild, naturally reproducing populations the hatcheries were intended to boost. If we are going to succeed in recovering depleted wild salmonid populations – which are more productive and resilient to climate change than hatchery fish – we need to make sure hatchery operations are aligned with wild population recovery goals. Without that alignment we risk undermining the enormous investments we are making in habitat restoration and other recovery actions, in addition to the wild fish themselves.” 

Trout Unlimited (www.tu.org) is the nation’s oldest and largest coldwater fisheries conservation organization dedicated to caring for and recovering America’s rivers and streams so our children can experience the joy of wild and native trout and salmon. Across the country, TU brings to bear local, regional, and national grassroots organizing, durable partnerships, science-backed policy muscle, and legal firepower on behalf of trout and salmon fisheries, healthy waters and vibrant communities. 
As one of the nation’s foremost aquatic conservation organizations, Trout Unlimited works to ensure its efforts to protect, reconnect, restore, and sustain coldwater fisheries and their watersheds are based on the best available science. Our science staff promote science-based policies, guide where and how the organization conducts its conservation efforts, provide tools for more effective conservation planning and groundwork, and conduct original research with a host of collaborators. 

About: Fisheries Management and Ecology
Fisheries Management and Ecology is a journal that aims to serve as a forum for applied studies and reviews of fishery management and ecology from across the world. Studies can span from small-scale artisanal fisheries to large-scale industrial fisheries in developing and developed countries.  Studies of fishery management practices (harvest, habitat, or population manipulations), effects of fish stocking on management of fisheries, ecology and population dynamics of fish stocks that support fisheries, and fish stock assessments and associated methods are invited, if they are presented in an appropriately broad geographical, biological, or methodological scope to be of interest and utility for an international audience of fishery managers and ecologists.