U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications

NOAA Tech Memo NMFS NWFSC-30:
Genetic Effects of Straying of Non-Native Hatchery Fish into Natural Populations


STRAYING AND GENETIC DIFFERENCES BETWEEN HATCHERY AND NATURAL POPULATIONS

Gary Graves

Northwest Indian Fisheries Commission
6730 Martin Way East
Olympia, WA 98516-5540, USA

I appreciate the opportunity to address this workshop. I feel the workshop is especially timely because of the recent activities by NMFS to address ESA concerns, and because it is particularly relevant to the activities of the State of Washington and the Indian tribes in their efforts to recover wild salmon stocks. For the last several years, the tribes and State have been involved in an effort referred to as the Wild Stock Restoration Initiative. One of the activities under this initiative has been the successful development of the Salmon and Steelhead Stock Inventory for the State of Washington. We are currently undertaking the development of recovery plans for all "critical" stocks identified in the inventory. We are also just beginning work on a statewide salmon habitat inventory, and for about the past year, we have been working on the development of a Wild Salmonid Policy for Washington State. The framework of this policy includes habitat restoration and conservation, harvest management, and hatchery programs, but also includes genetic conservation. One major concern within genetic conservation is the effect of straying of genetically dissimilar hatchery fish into wild populations, and how and when this straying should be limited.

I would like to focus on two questions being addressed by the workshop panel. The first is, How do the effects of straying depend on genetic differences between hatchery and natural populations, and how can these differences be measured? In developing a Wild Salmonid Policy, we have explored several alternatives to these questions in our deliberations. One is to limit the amount of straying that would be permissible based on the amount of genetic dissimilarity between the hatchery population and the natural populations receiving hatchery strays. The key problem, however, is how to measure the genetic differences between hatchery stocks and natural populations. How do we measure differences in characteristics that are important in predicting the effects that interbreeding will have on natural populations? The approach we have taken is that if hatchery and natural populations are genetically dissimilar, then the amount of allowable straying should be very small or none at all. If the hatchery and natural populations are similar, then some level of straying can be allowed. We are uncertain, however, how to predict what effects that a particular amount of straying would have and how to measure genetic differences between hatchery and natural populations. How do measurable genetic differences, allozyme frequency differences, for example, relate to fish size, fecundity, or more importantly, to productivity and survival? How do genetic interactions between non-native hatchery fish and natural spawners affect the potential for the future productivity of the resource?

The second important question is, What research should be undertaken to resolve the uncertainties of this issue? The effects of straying of non-native hatchery fish into natural populations are uncertain, and I think it is unlikely a consensus of opinion exists on the subject in the scientific community. State and tribal agencies can develop a Wild Salmonid Policy for genetic conservation that is based on population genetics theory and our best scientific opinions, but unless we have direct empirical evidence that the expected genetic consequences are actually taking place, we are not going to have much luck in getting these policies adopted. Some of the possible restrictions on levels of straying that we have considered could make major changes in how hatchery fish are produced in the State of Washington. I can envision some scenarios that would cause us to reduce radically or to alter hatchery production in Puget Sound. It will not be easy to sell a policy that might reduce hatchery production by 60-70%, unless there is good evidence to show that it is necessary to prevent the loss of future sustainable productivity. The question the State and tribal managers will ultimately be most concerned about is, How does this policy affect the ability of the fish resource to produce harvest in the future?

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