The last decade has seen an increasing awareness of the importance of considering genetic issues in the management of Pacific salmon (Oncorhynchus spp.) (Simon et al. 1986, Allendorf and Ryman 1987, Withler 1988, Waples et al. 1990, Riddell 1993, Park et al. 1994, Currens and Busack 1995, NRC 1996). At the same time, it has become clear that available scientific information is often insufficient to allow reliable predictions of the genetic consequences of different management actions, particularly those involving artificial propagation. One issue with both scientific and management implications is straying. Straying among, as well as homing to, natal populations is part of the evolutionary ecology of Pacific salmon. However, human manipulation of salmon and their ecosystems can also affect the nature and magnitude of straying. In particular, artificial propagation can result in higher rates of straying than would occur naturally and may also cause salmon to stray into areas that they would not normally reach.

Both scientific and management issues related to straying have been discussed for some time. Recently, this issue has been brought to a head as a result of two related developments in the Pacific Northwest. First, since 1990, several distinct population segments of salmon have been listed as threatened or endangered species under the federal Endangered Species Act (ESA) (see Waples 1995 for discussion). Under the ESA, the National Marine Fisheries Service (NMFS) has jurisdiction over marine and anadromous species, including Pacific salmon, steelhead (mykiss), and anadromous cutthroat trout (clarki). Guided by the ESA's emphasis on conserving species in their native ecosystems, NMFS has developed a policy on the use of artificial propagation in conservation and recovery and to limit the potential of hatchery fish to adversely affect listed natural populations (Hard et al. 1992). Although many of these effects have been known for some time, existing regulatory mechanisms have often failed to adequately protect natural populations. The ESA provides a much more powerful legal framework for conservation.

The second development is that empirical data have shown that non-native1 hatchery fish are straying in significant numbers into natural spawning areas for two ESA-listed species: Snake River fall-run chinook salmon (tshawytscha) and Snake River spring/summer-run chinook salmon. The articles in this volume by Crateau and Carmichael provide background and details for the hatchery programs and natural populations involved. For example, stray hatchery fish of non-native origin have made up the majority of natural spawners in many streams in the Grande Ronde Basin in recent years.

Straying from these hatchery programs has presented a major challenge to fishery managers. On the one hand, Sewall Wright showed long ago (Wright 1931) that only a few migrants per generation will prevent substantial divergence among populations due to genetic drift. Low levels of gene flow can also rapidly break down existing population genetic structure. Furthermore, even a small percentage of strays from a productive hatchery population can represent a substantial fraction of a depressed natural population.

On the other hand, the hatchery programs involved (Columbia River fall chinook salmon released into the Umatilla River and Rapid River stock spring chinook salmon released from Lookingglass Hatchery in the Grande Ronde Basin) were both initiated to satisfy tribal treaty obligations and to mitigate reductions in natural production caused by hydropower development on the Columbia and Snake Rivers. Stringent controls to limit straying could make it impossible to meet these legal obligations under current conditions.

In 1994, following ESA Section 7 consultations about the effects of straying by non-native hatchery fish from these two programs, NMFS established an interim standard to limit the proportion of stray, non-native hatchery fish to no more than 5% of any natural spawning population. This value was chosen in part arbitrarily, and in part as a compromise between several factors. There was a scientific basis for imposing some upper limit for straying, but exactly what that limit should be and how it should be applied was not clear. Some researchers thought that straying at a level of 5% per year was too high and would eventually erode the fitness of natural populations and alter their population genetic structure. Others thought that the level was too low and that it would seriously limit hatchery programs designed to meet other goals. Some believed that straying might be beneficial to depressed natural populations by increasing abundance and genetic diversity.

Because of the considerable interest surrounding this issue, NMFS proposed that a workshop be held to address the scientific evidence for the effects of straying by non-native hatchery fish. This workshop, which featured a panel of 12 experts in evolutionary biology and salmon biology, was held in Seattle, Washington on June 1-2, 1995. Panelists included Dr. Craig Busack, Washington Department of Fish and Wildlife; Mr. Richard Carmichael, Oregon Department of Fish and Wildlife; Mr. Kenneth Currens, Oregon State University; Dr. Joseph Felsenstein, University of Washington; Dr. Tony Gharrett, University of Alaska, Fairbanks; Dr. Michael Gilpin, University of California, San Diego; Dr. Michael Lynch, University of Oregon; Dr. Thomas Quinn, University of Washington; Dr. Nils Ryman, Stockholm University; Dr. Dolph Schluter, University of British Columbia; Dr. Eric B. Taylor, University of British Columbia; and Dr. Ruth Withler (Chairman), Department of Fisheries and Oceans, Canada. Dr. Stewart Grant, National Marine Fisheries Service, served as rapporteur. This volume is the proceedings of that workshop.

The panel was asked to consider a general scenario involving one-way straying of non-native hatchery fish into natural spawning areas at levels higher than would occur naturally. Increased levels of straying might occur if non-native stocks are imported and released near natural spawning areas, or if artificial propagation elsewhere leads to long-distance straying. Although the impetus for the workshop was concern for the listed Snake River populations of chinook salmon, the straying issue is more generally applicable to a wide range of hatchery programs for all species of anadromous Pacific salmonids throughout the region. Therefore, the panel was asked not to limit their evaluations to any species or geographic region.

The panel was also not expected to make management decisions or to formulate policy for NMFS or anyone else. Rather, the panelists were asked to consider the following fundamental question: What are the genetic consequences for natural populations of straying by non-native hatchery fish? The panelists were asked to consider both short- and long-term effects, and to consider these effects as they relate to population structure and diversity as well as to the fitness of natural populations. In evaluating this basic issue, the panelists were also asked to consider a variety of related questions. Some examples follow.

• Can effects of hatchery straying be predicted with any certainty? If so, how? If not, what are the ramifications of the lack of certainty?

• Can hatchery straying be beneficial for natural populations? If so, how and under what circumstances?

• Is any non-zero level of hatchery straying consistent with conservation of natural populations? If not, why not? If so, what level is acceptable?

• Do short-term and long-term effects of straying differ? If so, how and why?

• How do effects of straying depend on the following factors?

  • Magnitude of straying

  • Duration of straying

  • Genetic differences between hatchery and natural populations

  • (and how the differences are measured)

  • Number of natural populations affected

• Are the effects of hatchery straying likely to be permanent? If not, over what time frame would initial conditions be restored?

• What are appropriate units to consider in evaluating straying: the absolute number of stray fish, or the proportion of the population they represent?

• What research should be undertaken to help resolve uncertainties surrounding this issue?

The workshop did not attempt to address several related issues. For example, the panel was not asked to answer the question, Do hatchery fish stray? Empirical evidence makes it clear that some hatchery fish stray, and others do not. Rather, the panelists focused on evaluating the consequences of straying in those cases in which it does occur. Similarly, the workshop did not focus on the effects of fish culture per se; rather, the focus was on the effects of non-native fish that reach natural spawning areas because of artificial propagation. Finally, the panel did not attempt to evaluate the effects of supplementation programs that use local broodstock. These and other hatchery issues are important but were judged to be too complex to be dealt with in a single workshop.

This volume follows the organizational structure of the workshop, which attempted to balance two goals: encouraging interactions by having an open session to take advantage of the expertise of the approximately 140 fishery biologists in the audience, and allowing the panel time for intensive discussion on the various difficult issues they were asked to address. In the introductory session, representatives of various state, tribal, and conservation groups from the region were asked to provide background information, offer comments on scientific or management issues, and pose additional questions for the panel to consider. The rest of the first day was taken up with a series of six presentations by panel members on key issues in evolutionary biology and salmon biology. These presentations were intended to provide a common framework for addressing the key issues. Audience questions and discussion that followed these presentations are included in these proceedings.

On the second day, the panel met in closed session to discuss theoretical and empirical information relevant to the key questions. At the end of the day, the panel chairman, Dr. Ruth Withler, summarized the panel's conclusions to the audience, who had spent the second day discussing various strategies for dealing with the listing of hatchery fish under the ESA. A written summary of the panel's conclusions follows the proceedings.

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