Can Hatcheries Help Recover Coho Salmon?

Study Finds Even "Conservation" Hatcheries Offer Few Benefits, Real Recovery Depends on Improving Freshwater Habitat

The results of a study by independent scientists in Oregon, Gretchen Oosterhout and Charles Huntington, indicate that Oregon coast coho salmon populations are unlikely ever to be restored by fish hatcheries. The study underscores that recovery of dwindling salmon runs depends not on fish hatcheries, but squarely on the protection and restoration of freshwater habitat.

Oosterhout and Huntington adapted an existing widely-respected, peer-reviewed coho life-cycle model to enable computer simulation of interactions between wild and hatchery fish in the same river basin. The new model, CoRAS or "Coho Risk Assessment Simulation," incorporates available data from multiple studies of salmon survival across a full range of habitats. The newly adapted model allowed the scientists to simulate the potential effects of state-of-the-art "conservation" hatchery designs now being prescribed with the intent of reducing negative effects on wild fish while helping restore failing returns of salmon. Computer simulations were run to investigate the effects of tightly controlled, limited hatchery supplementation across a variety of freshwater and saltwater survival conditions, and to examine the effects of uncertain variables such as the relative survival and reproductive success of wild and hatchery fish, and the timing of poor and good ocean survival conditions.

The intent of the investigation was to answer to the question, Under what circumstances could hatchery fish stocking contribute to the recovery or viability of natural populations of Oregon Coast Coho salmon?  This key question goes to the heart of such policy issues as whether hatchery-origin fish must be considered as part of the protected population when wild salmon stocks are reviewed for endangered species protection. CoRAS is believed to be the first stochastic computer model to simulate population dynamics of interactions between Oregon coastal hatchery and wild coho salmon. Previous studies, on other salmonids, mainly have focused on genetic risks posed by hatchery fish culture and stocking.

Research Results: Hatchery Fish Pose Risk of Harm with Little or No Population Benefit

The results of the investigation were simple but important. Simulated supplementation of a coho population on the Oregon Coast -- even by an ideally-conceived-and-operated conservation hatchery -- rarely showed a net benefit to salmon abundance, and in those few instances that it did, benefits were marginal and short-lived (i.e., a few years). The results suggest that freshwater and near-shore ocean conditions cap the survival of both wild and hatchery-released salmon. Because wild fish tend to do well in freshwater habitat wherever it is of high enough quality, adding hatchery fish to the freshwater system can push out some wild fish, replacing wild fish with hatchery-origin fish that may pose a risk of compromising the genetic integrity of the wild population. Neither wild nor hatchery fish survive and reproduce well in poor-quality habitat. One clear implication of the study is that improvements in hatchery fish survival, much sought-after by management agencies in recent years, come at a cost. The more hatchery fish that survive after release to reproduce in the natural environment, the more they may act to displace wild fish, so that any short-term benefit the "improved" hatchery fish may confer to the total population may be offset by their displacement of wild individuals. The result is that some naturally-produced wild fish are traded away for costly hatchery fish.

Oosterhout and Huntington found that of the various management interventions simulated in the model runs, only freshwater habitat restoration offered significant and permanent gains in salmon abundance. In contrast to hatchery programs, habitat restoration poses no genetic or ecological risk to salmon populations. The model results consistently suggested that wild populations respond rapidly to improvements of their habitat without the addition of hatchery salmon.

The study was focused on Oregon coast coho salmon as an example. The extent to which the results directly translate to other salmon species or regions remains to be investigated. However, the basic tenets and conclusions of the study are clear and unambiguous, and they likely are broadly applicable to salmon conservation everywhere.

Conservation Implications: Wild Production and Habitat Restoration Determine Recovery

PRC believes the results of this study point toward three clear principles that provide a clear policy direction for salmon recovery:

1. Status determinations, recovery plans, and recovery goals for salmon should not assume that hatchery-origin salmon are an integral component of the wild population. Salmon released from hatcheries displace natural fish spawned in the wild, and likely contribute little or nothing to the survival and recovery of wild, natural salmon populations. Hatchery-origin fish should be explicitly considered as a threat, not a boon, to wild populations.
2. New, often very expensive "conservation hatchery" or "supplementation" programs likely will be, at best, only marginally more effective than past practices at benefiting natural fish populations. A chain of ecological (i.e., habitat) limitations caps the productivity of natural populations in ways that are not simply overridden by the release of hatchery-bred fish. Even when they are few, wild fish are fecund and adept at exploiting high-quality habitat. Neither hatchery fish nor wild fish can maintain populations in unsuitable habitat. When freshwater habitat appears good but wild fish are scarce there, most often this appears to be because of unsuitable habitat conditions later or earlier in the life cycle-conditions that are likely to harm hatchery fish as well as wild fish. The better habitat gets across the whole life cycle, the more productive wild populations are, and the less they need any "assistance" from hatcheries.
3. Protection and restoration of freshwater habitat are critical and necessary for the recovery of natural salmon populations. Habitat improvement is of lasting benefit to both wild and hatchery salmon. Neither wild nor hatchery fish do well in poor habitat. Unlike hatchery programs, which require permanent capital investment and output of fish to support even marginal fish populations, habitat restoration, once properly achieved, is self-sustaining and self-restorative.

The study was supported with funds from PRC and received technical input from numerous professional salmon biologists and research scientists at the design, development, and review stages.  The report was also updated to include more species, has been peer reviewed, and was printed in the Canadian Journal of Fisheries and Aquatic Sciences Volume 62 in 2005.

To download the journal publication, click here.

To download the full original report or to order a hard copy, click here.

For more information on the report, click here to read some questions and answers regarding the report and its implications.