Wednesday, January 20, 2010



Stray steelhead are recognized as a problem, but why and what is their effect on wild steelhead? Natural stray rates (one or two fish per year) are low compared to stray rates form some hatchery programs that can have stray rates of more than 60% of a run.

The problems that have been identified are associated with naturally spawning hatchery strays, for when they breed with wild fish there is a loss of reproductive success and can lead to reduced fitness in the wild population. Hatchery fish spawn successfully but their survival is poor compared to wild steelhead. Crosses between hatchery and wild fish produce progeny that have a lower survival rate and the result is fewer adult fish produced from the affected naturally produced wild population. Even if hatchery fish do not interbreed with wild fish, the progeny they produce have an impact for they occupy rearing space and are competitive with wild fish for food. They can also be predators on wild fish, attract predators, and spread disease. One study shows a remarkable 50% reduction in wild smolt production caused by the ecological impacts of hatchery fish on the wild population.

Some might assume that the naturally spawning hatchery fish enhance the number of adult fish returning to the river and available to the fishery, but they would be wrong, for hatchery smolt-to-adult survival is poor and few adults return.

This effect is not just a short term problem, for genetic changes caused by maladapted hatchery fish can change the basic productivity of a wild population so that its survival is jeopardized.

Over the last 150 years of fish management in the Northwest there have been many assumptions made about hatchery fish spawning naturally with wild fish ranging from “it doesn’t matter” to “no naturally spawning hatchery fish at all.”

In 1978 researchers tested the survival of hatchery and wild steelhead in the Deschutes River, Oregon to determine if there is a difference between them in the natural stream and hatchery environments. The results clearly pointed to wild fish surviving better than hatchery fish in streams than hatchery fish. The reverse was true in the hatchery. When wild and hatchery fish were crossed their progeny survival was better in streams than pure hatchery fish but inferior to wild fish. Wild fish produced more adult spawners than hatchery fish and a naturally spawning population of wild and hatchery fish reduced the reproductive success of the wild population.

During the 1980s and 1990s further research confirmed this initial research in other rivers. During this time concerns about mixing hatchery and wild fish in streams became the subject of concern, leading to scientific recommendations for how many naturally spawning hatchery fish could safely spawn with wild fish.

In 1997 NMFS invited an international group of scientists to discuss the effect of stray rates on native fish from non-native hatchery fish.

They concluded, “based on estimates of gene flow from allozyme frequencies in natural populations, a value of 5% gene flow is much higher than that generally occurring between non-local salmon populations. Also based on what is known about the strength of selection in other animals, this amount of gene flow would quickly lead to the replacement not only of neutral genes, but also of locally adapted ones. Most genes in natural populations probably have selection coefficients less than 5% and would thus be subject to loss if gene flow occurred at this level. The panel found no genetic justification for allowing gene flow from non-native fish at levels as high as 5%.”

“There are no ‘safe’ levels of hatchery straying. Any level of long-term straying will change the structure of local populations.”

In 2001, NMFS determined that “levels of gene flow from out-of-ESU hatchery stocks into natural upper Columbia steelhead populations should be less than 1% and patterns of straying and gene flow among the natural populations should be free from human-caused alterations.”

In 2002, the Oregon Department of Fish and Wildlife adopted the Native Fish Conservation policy that allows a 10% stray rate for hatchery fish of any origin.

Native Fish Conservation Policy 2002, page 6.
“(5) Reproductive Independence – At least 90% of the spawners within a population must be naturally produced and not hatchery produced fish, unless the department determines the hatchery produced fish are being used in a short-term experimental program to help restore a population in its natural habitat or otherwise directed by a court order.”

From 2001 to 2009, the Hatchery Scientific Review Group (HSRG) reviewed hatcheries in Puget Sound and the Columbia basin saying:

“…the traditional practice of replacing natural populations with hatchery fish to mitigate for habitat loss and mortality due to hydroelectric dams is not consistent with today's conservation principles and scientific knowledge. Hatchery fish cannot replace lost habitat or the natural populations that rely on that habitat.”

The HSRG recommended that hatchery fish be isolated from wild fish (segregated hatchery) or integrated with wild fish using a formula that incorporates wild fish into the egg take and allows a proportion of the naturally spawning fish to be of hatchery origin.

The HSRG program would allow hatchery fish to reproduce naturally with wild fish based on a formula that is aimed at controlling genetic introgression and reproductive fitness in the wild stock. It does not address ecological effects of adding hatchery fish to wild fish populations for natural breeding. In addition, the benefits of this practice are theoretical and have not been tested.

The fish management agencies in Oregon and Washington have embraced the HSRG formula and have developed native broodstock hatcheries before they have been evaluated to determine their effect on wild salmonids.

The integrated hatchery program has finally been evaluated and results published in 2007 through 2009.

The poor reproductive fitness – the ability to survive and reproduce – of the wild-born offspring of hatchery fish means that adding hatchery fish to wild populations may ultimately be hurting efforts to sustain those wild runs, scientists said. The study found that a fish born in the wild as the offspring of two hatchery-reared steelhead averaged only 37 percent the reproductive fitness of a fish with two wild parents, and 87 percent the fitness if one parent was wild and one was from a hatchery.

"The effect is so strong that it carries over into the first wild-born generation. Even if fish are born in the wild and survive to reproduce, those adults that had hatchery parents still produce substantially fewer surviving offspring than those with wild parents. That's pretty remarkable."

“The implication,” Blouin said, “is that hatchery salmonids – many of which do survive to reproduce in the wild– could be gradually reducing the fitness of the wild populations with which they interbreed. Those hatchery fish provide one more hurdle to overcome in the goal of sustaining wild runs, along with problems caused by dams, loss or degradation of habitat, pollution, overfishing and other causes.”

"The message should be clear," the researchers wrote in their report's conclusion. "Captive breeding for reintroduction or supplementation can have a serious, long-term downside in some taxa, and so should not be considered as a panacea for the recovery of all endangered populations."


We now know that naturally spawning hatchery fish have a negative effect on the reproductive fitness and success of wild salmonids whether they are of native origin or strays from some other population. We also know that they have an ecological impact on wild fish through competition for spawning and rearing space, disease transfer, predation, and the attraction of predators. We know that fisheries directed at hatchery fish cause the over harvest of wild fish reducing the number of spawners in our streams. Even though we know hatchery fish degrade the reproductive success of wild salmonids, allowance is still being made for mixing naturally spawning hatchery and wild fish.

Fish management agencies are continuing to contribute to the decline and extinction of wild salmon and steelhead, and that contribution combined with the determined degradation of salmonid habitat by land, water and energy management agencies has created a crisis in the Northwest.


Blouin, Michael: This research, which was just published in Biology Letters, was supported by grants from the Bonneville Power Administration and the Oregon Department of Fish and Wildlife. It was based on years of genetic analysis of thousands of steelhead trout in Oregon's Hood River, in field work dating back to 1991.

Ford, Michael, et al. 2001. Upper Columbia River Steelhead and Spring Chinook Salmon Population Structure and Biological Requirements. National Marine Fisheries Service, Northwest Fisheries Science Center. Seattle, WA .


ODFW. 2002. Oregon Native Fish Conservation Policy.

W. Stewart Grant (editor). 1997. Genetic effects of straying of non-native fish hatchery fish into natural populations: proceedings of the workshop. U.S. Dep. Commer., NOAA Tech Memo. NMFS-NWFSC-30, 130p.

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