Reports & papers By category Symposium on Ocean Conditions

Consideration of ocean conditions in the management of salmon

Gustavo A. Bisbal and Willis E. McConnaha
Northwest Power Planning Council
Fish and Wildlife Division
Portland, Oregon

Introduction

On September 12, 1996, the U.S. Congress enacted the first and only amendment to the Northwest Power Act of 1980 (Northwest Power Planning and Conservation Act, section (4)(h)(10)(D) 1996). The original federal law authorized the states of Idaho, Montana, Oregon and Washington to form the Northwest Power Planning Council (the Council) and called for the Council to develop the Columbia River Basin Fish and Wildlife Program (NPPC 1994). The program addresses the restoration of fish and wildlife affected by hydroelectric development in the Columbia River Basin. The recent amendment directed the Council to "?consider the impact of ocean conditions on fish and wildlife populations?" during the implementation of its program. Consideration of ocean conditions has its most direct impact on anadromous fish populations, such as salmon and steelhead. In this paper, we will suggest how the consideration of ocean conditions can be incorporated into salmon management, especially as it relates to the Council's mission in the Columbia River.

During their anadromous life cycle, Pacific salmon utilize riverine and stream environments, but spend most of their lives at sea. Management of salmon populations, however, has typically stressed manipulations of elements in the freshwater phase of this cycle. In general, the forces and processes affecting salmon in the marine environment have been largely ignored (Hare and Francis 1995). The ocean has been regarded as a virtually inexhaustible pasture for juvenile fish produced through actions taken in the freshwater environment (Pearcy 1992). Hatcheries and other approaches in fresh water have been implemented to compensate for habitat deterioration, to increase numbers of fish produced and to smooth out natural fluctuations in abundance (Lichatowich 1997). Failure to maintain adult salmon abundance through these controlled actions indicates that ocean conditions are, in fact, highly variable and major determinants of the fate of entire fish runs. For some, the pendulum has shifted to the conclusion that management actions during the freshwater phase of salmon life are relatively futile in the face of the mortality and variability experienced by salmon during the marine phase of their life.

In this paper, we suggest the need for a more holistic view of the salmon ecosystem that encourages a new perspective on the importance of ocean conditions and their inclusion in the management of salmon. Both ocean and freshwater conditions ? and their variability ? are now accepted as integral components of the salmon ecosystem (NRC 1996; Williams et al. 1996). We now have a greater appreciation for the impact of the ocean on salmon abundance and the degree of variation in the marine environment. Throughout their life cycle, salmon negotiate environmental variability by having a broad array of biological characteristics within and between populations. This diversity provides different options for salmon to cope with the mortality they experience during their life cycle in general, including their marine residence. Because management actions taken in fresh water can restrict biological diversity, consideration of ocean conditions in the management of anadromous fish will require relaxation of those constraints that lead to environmental and biological simplification.

Interaction between salmon and environmental variability

Many factors can potentially affect the growth and survival of salmon at sea. Physical events, such as extreme environmental conditions, and biological interactions like competition and predation can result in substantial variability in salmon recruitment (Pearcy 1992). In addition to natural fluctuations of environmental conditions, salmon encounter elements introduced by man. These impacts are particularly acute in the estuary and river plume. Human actions can affect estuarine and coastal-ocean conditions through pollution, river operations, hatcheries, harvest or habitat changes. The response of salmon to such environmental challenges differs according to important biological features including life stage, body size, age, growth rate, and previous exposure to specific conditions. Extensive contributions by several authors provide ample information on the factors and sources of variability that challenge salmon as they enter the ocean (Sherwood et al. 1990; Pearcy 1992; Beamish and Bouillon 1993; Weitkamp 1994; Mantua et al. 1997).

Variation within the marine environment is particularly important in determining the success of individuals, populations and species of anadromous salmonids, because they spend most of their life in the ocean. Salmonids can be quite plastic in their response to environmental change and can accommodate this variability by a relatively high degree of genotypic and phenotypic diversity (Adkison 1995; Healey and Prince 1995; Thompson 1991). Within salmonids, features such as spawning, dispersal, morphology, maturation, and patterns of growth are all life-history traits that define the "fit" of individuals to their environment. Each life history represents a suite of characteristics that defines the episodes of birth, reproduction and death of individuals, and the dynamics of populations over evolutionary time.

Variation in life histories represents different biological solutions to intrinsic environmental variability. In a natural ecosystem, life history strategies evolve through natural selection, operating under anatomical, behavioral and genetic constraints, to match key characteristics of the environment. When confronted with variable environmental conditions, however, no one solution is always optimal. Hence, depending on the particular environmental template (sensu Southwood 1977) encountered by individuals, certain life histories are more successful than others and convey a reproductive advantage and increased fitness (Thompson 1991). The environmental template varies in time and space and determines the range of possible life histories needed to maintain fitness through time (Southwood, 1977).

Human interventions add important hurdles to the ability of salmonids to maintain their biological diversity and, hence, their ability to withstand environmental variation. Anthropogenic forces may act as agents of artificial selection (Sheridan 1995), favoring some life-history traits over others, and can modify the generalized anadromous life cycle of Pacific salmon. Fish husbandry practices, for example, can select against behaviors and morphologies that may be advantageous in the wild, but that are less conducive to the operations and goals of hatchery programs (Reisenbichler 1997). Harvest, hydroelectric dam operations, flow manipulations and many other human-driven perturbations can act synergistically with variable environmental conditions to alter the biological structure of salmonid populations. Under favorable environmental conditions, salmon populations show a higher tolerance to human perturbations. When environmental factors are restrictive, the relative importance of human factors increases and the capacity of salmon populations to tolerate external disturbances becomes very limited (Fogarty et al. 1991).

Intensively regulated freshwater systems tend, in general, to reduce environmental variation (Stanford et al. 1996). Floods are reduced, banks are stabilized and biological components are adjusted to fit within the needs of a heavily engineered river redesigned through human technology. For example, in the Columbia River, a variety of actions are taken to enhance survival of juvenile fish during their downstream migration. These include seasonal flow augmentation, controlled spill at hydroelectric dams and physical transport of fish around dams in barges and trucks (Ebel et al. 1989). Many of these actions are designed to force a particular biological configuration that minimizes the conflict with other human uses of the river. Because these actions are expensive, their implementation tends to be optimized on the basis of juvenile fish abundance rather than on the natural diversity of salmon life histories. Based on the relationship between the habitat template and ecological strategies (Southwood 1977), simplification of the environment and its variability also should result in a decrease in biological diversity (Stanford et al. 1996).

The interaction between environmental variability and biological diversity is illustrated in Figure 1. Environmental variability is depicted on the left as a template (Southwood 1977) with variously shaped indentations representing combinations of spatial and temporal environmental conditions encountered by salmon over the course of their life cycle. This variability promotes the development of adaptive mechanisms that maintain relative fitness in salmon populations and shapes the evolution of life history traits (Thompson 1991). Different life histories are represented by correspondingly shaped pieces on the right. As an adaptive mechanism influencing reproductive success and fitness, the correspondence between the life histories and the environmental template must ultimately embrace the entire life cycle. The environment at each life stage, however, is realized by salmon at different scales and offers its own unique set of factors and circumstances (Levin 1992). Thus, it is possible to imagine a different template for the environment encountered at each life stage. For purposes of this discussion, the templates in Figure 1 illustrate the variability in the ocean environment encountered by populations of juvenile salmon entering from the freshwater (in this case the Columbia River). Five general scenarios are discussed below, focusing on variation in ocean conditions, life histories, and their significance to salmon survival.

Figure 1A represents an ideal scenario where favorable ocean conditions provide adequate survival and growth opportunities to a broad range of salmon life histories. Due to the complex and dynamic nature of the environmental template, however, even "favorable" conditions can be better described as some average state tracked by the bulk of available life histories. In this ideal case, variation in the shape of the template results in varying degrees of match and mismatch between some life histories and the environmental template. Different life histories may be favored according to random circumstances and decadal or longer environmental cycles. Therefore, the evolution of a rich mosaic of life history strategies provides salmon with their characteristic resilience to a variable environment.

Figure 1B depicts an extreme condition where the environmental window of biological opportunity is severely narrowed, perhaps as a result of an El Ni? episode or other climatic event. While some of the available life histories fit the template, many others are disfavored, resulting in decreased salmon abundance. In fact, the persistence of some life histories may be in jeopardy; however, as the environmental template varies again, these life histories may reappear to take advantage of new opportunities. Over time, a biologically diverse array of life histories exists to accommodate adverse environmental demands.

As discussed above, human interactions with the ecosystem tend to reduce biological diversity. This makes the natural mechanism for incorporating environmental variability less effective. This situation is depicted first in Figure 1C where a reduced set of life histories fits segments of the environmental template. The outcome of this scenario is probably a reduced abundance relative to the situation in Figure 1A or even 1B, although artificial augmentation can bolster abundance under favorable conditions. However, some might conclude that any reduction in fish abundance is simply a necessary sacrifice towards progress and point to the apparent success of mitigation efforts directed at the reduced set of populations. A strategy of this kind, however, may prove risky and result in serious ecological imbalances, as illustrated in the next two scenarios.

For example, it is possible that a much reduced set of life histories can thrive during a period of generally unfavorable ocean conditions if there happens to be a fortuitous fit between the available life histories and the ocean conditions (Figure 1D). Then the end result parallels the outcomes described for Figure 1C. The apparent success of a management strategy that focuses on customizing fish populations to the assumed "normal" ocean condition, masks the serious risks of environmental variation.

If the environment shifts away from the situation depicted in Figure 1D, then the limited set of life histories may fail to fit the template of ocean conditions (Figure 1E). This mismatch translates into a disastrous recruitment collapse. Because there are no alternative life histories to exploit the prevailing environment, abundance declines, perhaps precipitously. Some populations can be extirpated, and, without a rich source of biological alternatives, recolonization can be slow or non-existent.

Taking ocean conditions into consideration

The question of how ocean conditions can be taken into account for salmon management revolves around how we view the relationship between marine and freshwater environments and their relative significance to salmon. Figure 2 illustrates three different possibilities for this relationship, each of which results in an alternative approach to salmon management. While no individual or entity necessarily ascribes fully to any of these hypothetical views, elements of one or more of them form the basis for many salmon management decisions in the Columbia River Basin and elsewhere. These explanations for ? and proposed responses to ? the fluctuations in salmon abundance have polarized numerous interest groups, administrative entities, and segments of the public involved in the architecture and implementation of salmon recovery programs.

A. Freshwater Dominance

The first view (Figure 2A), which characterizes traditional salmon management for most of this century, suggests that fluctuations and declines in salmon abundance are largely the result of deterioration of the freshwater environment due to development activities. While acknowledging that a large part of the mortality that occurs over the course of the salmon life cycle takes place in the ocean, the implied assumption is that the ocean is a relatively stable environment where salmon mortality affects a constant proportion of smolts entering the ocean. It then follows that fluctuations in the production of adult salmon can be dampened and declines can be reversed through the manipulation of the smolt output (Bottom 1997). From this "freshwater dominance" perspective, management actions in fresh water areas above the estuary have a direct impact on overall salmon production. According to this argument, a management course that relies heavily on artificial production and technological innovations, for instance, is generally correct. Hatcheries, hydroelectric operations and harvest are managed to provide a standard "product" with the focus of increasing the number of juvenile fish entering the ocean. Augmenting the number of juveniles released from hatcheries is the strategy of choice to increase numbers of fish available for harvest or returning to the river, independent of variation in ocean conditions (Bottom, 1997). Ironically, continued declines in fish runs do not provide the much needed evaluation of the strategy, conceptual criticism or rejection of program activities. Instead, they seem to provide the necessary justification for a more aggressive implementation of the current technological fixes (Meffe 1992; Stanford et al. 1996; Lichatowich 1997).

B. Marine Dominance

The second view pervading the political environment of salmon management ascribes most of the variability in salmon abundance to conditions in the marine environment (Figure 2B). In many ways, this is the opposite of the first view. This "marine dominance" perspective views the ocean as the ultimate controller of fish populations. In this scenario, environmental changes in the ocean control the number of fish, and the freshwater environment is reduced in importance.

Because many sources of mortality affecting salmon during their freshwater phase are under management control, compared to very few in the marine environment, both the efficacy of freshwater actions as well as the importance of salmon mortality during their seawater residence are reevaluated under this view. Failure to observe simple cause-and-effect relationships between augmented smolt abundance in fresh water and eventual returns of adult fish suggests that variation in the abundance of salmon runs can be attributed to factors outside human control. It then follows that freshwater actions may assist downstream migrants and returning adults, but are relatively less important in the face of large and variable ocean conditions. The significance behind this argument is that if changes in the ocean climate dominate changes in salmon biomass, then actions to improve conditions in the river or its tributaries are relatively futile, particularly in years when ocean conditions are unfavorable. This view could lead to the conclusion that recovery efforts and funding for them may be wasted because ocean conditions negate the effect of any improvements in the freshwater environment.

C. Holistic

The first two perspectives view the freshwater and marine environments as distinct and separable habitats. Fundamentally, they differ in regard to the relative importance placed on either area as determinants of salmon abundance. In recent years, the continued decline of salmon from the Columbia River has called into question the wisdom underlying both of these management arguments. More recent thinking about ecosystems and their importance to species of interest, such as salmon, as well as a greater understanding of the ocean, leads to a third conceptual alternative (NRC 1996; Williams et al. 1996). Under this view, freshwater and marine areas are integral components of a larger ecosystem within which salmon exist (Figure 2C). Hence, the abundance of salmon reflects the overall condition of the entire ecosystem and variation in both the freshwater and marine environments. This view reflects a greater appreciation of the ecological context of fisheries management (Bottom 1997). Variation in the environment, including ocean conditions, is a natural feature of the ecosystem to which salmon have adapted through a diverse array of biological traits. The shift of management focus toward the entire salmon ecosystem, recognizes that even though the ocean is variable, management actions ? particularly those in freshwater systems ? are critical in promoting the conservation of this diversity over time (Lawson 1993).

This "holistic" view of the ecosystem can be summarized in the following points:

1. The ocean is not a constant environment. Ocean conditions and carrying capacity vary and can be limiting.
2. Freshwater and marine environments are not independent. There is evidence that variations in the two environments are linked via large-scale atmospheric processes and that both are integral parts of the salmonid ecosystem.
3. The estuary is an important transition between these two portions of the ecosystem. Conditions in the estuary can be an important determinant of early ocean survival of salmon.
4. Environmental variability is an inherent feature of the ecosystem of salmon. Salmon accommodate this variability through a similar variety in life history traits.

The proposed management response

Although the causes of salmon mortality in the marine environment are difficult to study, our understanding of how ocean conditions affect long- and short-term variation in salmon populations has increased over the last several years. In the northeastern Pacific, in general, and the more localized realm of the Columbia River estuary and discharge plume, both natural phenomena and human interventions have modified environmental conditions and their rate of change. Although salmon tolerate a wide range of environmental conditions and disturbances, many factors may be lethal or cause physiological stress. The integration of these factors into management policies is based on our perception of the whole salmon ecosystem - a wide area that spans marine and freshwater domains.

Based on an understanding of the mechanism salmon use to cope with environmental variation (Figure 1) and an holistic view of salmonid ecosystem (Figure 2C), fish and wildlife managers may employ two primary approaches to influencing salmon survival in the ocean. The first approach is through the improvement of estuarine and nearshore conditions. The Columbia River estuary and nearshore plume are important to salmon production, particularly because of their impact on survival of juvenile fish making the transition to the ocean environment. Like many estuaries, these areas have been, and continue to be, negatively affected by upstream flow regulation, construction of dams, and local habitat change. Hatchery operations may also result in ecological imbalances, competitive interactions and competition for food and space by smolts during their estuarine and plume residence.

Based on these points, consideration of ocean conditions could include evaluation of flow regulation, river operations and habitat management in regard to their impacts on the estuary and nearshore marine areas. For example, efforts in the Columbia River to restore the seasonal hydrograph through release of stored water during the spring have generally been conceived as a way to assist downstream migrating salmon and steelhead (e.g. NPPC 1994). A more holistic view of the salmonid ecosystem suggests a broader biological role for flow including estuarine habitat and food web development and establishment of a river plume that approximates the condition under which Columbia River salmon evolved. Flow regulation to affect estuarine and nearshore areas may require volumes and schedules different from those used for upriver biological purposes. Estuarine habitats lost to past efforts to stabilize riparian areas and land reclamation can be reclaimed. In several Northwest rivers, for example, estuarine habitat has been re-established by breaching dikes to allow normal tidal flooding of estuarine areas (Simenstad and Thom 1996). The key role of these areas in the critical freshwater-marine transition suggests the need for examination of these possibilities in the Columbia River as well.

The second management approach available to resource administrators, is to address environmental variability ? whether freshwater or marine ? through the preservation of life-history diversity in salmon, a natural survival mechanism that evolved in response to changing conditions (Thompson 1991). Fluctuations in the ocean climate are an integral component of the overall environmental variability encountered by salmon. Salmon and steelhead in the Columbia River and elsewhere accommodate environmental variability through the development of a wide range of biological traits and behaviors that have been selected to permit survival within this ecosystem. However, management actions often restrict the natural expression of salmon life-history diversity. Actions that target limited time periods (e.g., restricted flow augmentation, spill, transportation and hatchery release schedules), select for particular physical characteristics of the fish (e.g., harvest and hatcheries), or reduce complexity of habitats (e.g., reduction of seasonal flows and channelization), can restrict biological diversity. For instance, the current operation of bypass systems at dams, smolt transportation, flow augmentation and spill, generally occurs within a relatively short time period from about April 15 to July 31, in the Snake River, and from May 1 to August 31 in the Columbia River (NPPC 1994). However, the juvenile fish migration extends appreciably before and after this period. Some bypass measures select for some physiological and morphological conditions over others (Muir et al. 1990). To the extent that these actions enhance passage conditions for the majority of the migrating population, they select against life histories that migrate outside this window of time or are not captured by the actions. The result is a focusing of the migration within a narrow time interval and a selection against the wide range of migration strategies that might occur naturally. Therefore, a major option for taking ocean conditions into account involves ensuring that restoration strategies are designed and evaluated in regard to their potential to restrict or enhance the natural expression of biological diversity in salmon populations.

The hypothetical scenarios described in Figure 1 have significant implications for the management of salmon, specifically those that limit salmon diversity. It is possible to take advantage of favorable ocean conditions and dampen negative ones by addressing potential settings of the ocean environment in a proactive, rather than a reactive or even a resigned, manner. An appropriate management response to environmental variability in general, and ocean variability in particular, is to relax anthropogenic pressures that inhibit or restrict development of a natural range of biological diversity.

From this premise, a primary means for taking ocean conditions into consideration in salmon management in general, and for the implementation of the Council's program in particular, it to evaluate recovery actions and their impact on biological diversity. Hatchery practices, for example, should need to minimize selection that restricts or skews the distribution of biological diversity. The role of hatcheries within a functioning salmonid ecosystem needs to be developed to allow populations to express diversity levels that enhance long-term survival (White et al. 1995). In the Columbia River, the use of smolt transportation, flow augmentation, spill and other juvenile migrational aids should be managed to provide benefits to the entire spectrum of migrants rather than the central majority of the run. Restoration efforts need to move from the paradigm of management for the average biological condition to management for the range of potential biological variation (Williams et al. 1996). Common to these scenarios is that biological diversity is not "fixed" or engineered in a mechanical sense but is allowed to increase to the appropriate level by relaxation of anthropogenic constraints. The appropriate level of biological diversity is not static, if indeed it is even quantifiable or predictable, but varies according to short and long term trends in the environment.

In the debate over innovative approaches to salmon management, it is questioned whether current capabilities to forecast changes in the marine environment are sufficient to adjust management decisions (Pulwarty and Redmond 1997). In general, resource managers are concerned with anticipating ocean and atmospheric conditions to manage their coastal waters and resources. The advent of modern remote sensors and electronic instrumentation has expanded significantly the ability to sample ocean conditions, fish distributions and ecosystems over multiple scales of space and time. Based on this progress, it has been argued that the impacts of future atmospheric and oceanic conditions on salmon populations could be modeled and, to some degree, predicted (Simpson 1994). With sufficient predictive power, it might be argued that hatchery releases and other practices could be managed in real time to maximize the fit between biological traits and the environment (Figure 1). However, the accuracy and precision of these predictions still require much improvement before management decisions can be implemented according to forecasts of ocean conditions (Walters and Collie 1988). Furthermore, a potential danger associated with this is continuation of the implicit belief that we can engineer biological systems to simultaneously meet the goals of multiple use, sustainability, and fish and wildlife as well. Predictive power aside, practical difficulties associated with managing production areas often located several hundred miles upriver from the ocean and the need to manage and protect the remaining wild populations and genetic resources, argue against the hope that fish might be engineered in response to real-time environmental predictions. While new technologies can be useful tools for ecosystem managers, caution should be exercised to avoid a "predict-and-control" approach as a surrogate to implementing sound ecological principles (Stanley 1995).

The ideas presented in this article argue against the default notion that salmon management activities are futile in the face of variable ocean conditions. If attention is focused on that portion of the marine environment that includes the estuary and near-shore plume at the mouth of the Columbia River, then there are important ways to directly address ocean conditions through the restoration of estuarine habitats. Specifically, we call for a significant re-assessment of management strategies that directly affect these environments. We further suggest that ocean conditions be taken into account by promoting the naturally evolved strategy that salmon use to accommodate environmental variability. We propose that policy directives and management actions be geared to estuarine habitat restoration and to promoting the conservation of salmon biological diversity. Improving the understanding of these actions and the ways they force biological changes in salmon life histories can enhance the management of Pacific salmon. Certainly, restoration of habitats and modification of actions and strategies to foster development of a natural expression of life history diversity within Columbia River salmon will likely conflict with other uses of the river and involve potentially costly tradeoffs. Thus, the management questions confronting policy-makers require an understanding of the impact of ocean and freshwater factors on salmon and a willingness to devise necessary adjustments to meet these challenges.

References

Adkison, M.D. 1995. Population differentiation in Pacific salmon: local adaptation, genetic drift, or the environment? Can. J. Fish. Aquat. Sci. 52: 2762-2777.

Beamish, R.J., and Bouillon, D.R. 1993. Pacific salmon production trends in relation to climate. Can. J. Fish. Aquat. Sci. 50: 1002-1016.

Bottom, D.L. 1997. To till the water : A history of ideas in fisheries conservation, p. 569-597. In Pacific salmon and their ecosystems: Status and future options. Edited by D.J. Stouder, P.A. Bisson, and R.J. Naiman. Chapman and Hall, New York.

Fogarty, M.J., Sissenwine, M.P., and Cohen, E.B. 1991. Recruitment variability and the dynamics of exploited marine populations. Trends Ecol. Evol. 6: 241-246.

Hare, S.R., and Francis, R.C. 1995. Climate change and salmon production in the Northeast Pacific Ocean. In Climate change and northern fish populations. Edited by R.J. Beamish. Can. Spec. Publ. Fish. Aquat. Sci. 121: 357-372.

Healey, M.C., and Prince, A. 1995. Scales of variation in life history tactics of Pacific salmon and the conservation of phenotype and genotype. In Evolution and the aquatic ecosystem: Defining unique units in population conservation. Edited by J.L. Nielsen. Am. Fish. Soc. Symposium 17: 176-184.

Levin, S.A. 1992. The problem of pattern and scale in ecology. Ecology 73: 1942-1968.

Lichatowich, J. 1997. Evaluating salmon management institutions: The importance of performance measures, temporal scales, and production cycles. In Pacific salmon & their ecosystems: Status and future options. Edited by D.J. Stouder, P.A. Bisson and R.J. Naiman. Chapman & Hall, New York. pp. 69-87.

Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M., and Francis, R.C. 1997. A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Meteor. Soc. 78: 1069-1079.

Meffe, G.K. 1992. Techno-arrogance and halfway technologies: Salmon hatcheries on the Pacific Coast of North America. Cons. Biol. 6: 350-354.

Muir, W.D., McCutcheon, C.S., Giorgi, A.E., Zaugg, W.S., Hirtzel, S.R., and Beckman, B.R. 1990. An assessment of the relationship between smolt development and fish guiding efficiency at Lower Granite Dam, 1989. Annual Report to U.S. Army Corps of Engineers (Contract DACW68-84-H-0034) and Coastal Zone and Estuarine Studies Division, National Marine Fisheries Service, 19p.

Northwest Power Planning and Conservation Act, section (4)(h)(10)(D) 1996. 16 United States Code, section 839b (h)(10)(D).

NPPC (Northwest Power Planning Council) 1994. Columbia River Basin Fish and Wildlife Program. Portland, Oreg.

NRC (National Research Council) 1996. Upstream: salmon and society in the Pacific Northwest. National Academy Press, Washington, D.C.

Pearcy, W.G. 1992. Ocean Ecology of North Pacific Salmonids. University of Washington Press, Seattle, Wash.

Pulwarty, R.S., and Redmond, K.T. 1997. Climate and salmon restoration in the Columbia River Basin: The role and usability of seasonal forecasts. Bull. Amer. Meteor. Soc. 78: 1-17.

Reisenbichler, R.R. 1997. Genetic factors contributing to declines of anadromous salmonids in the Pacific Northwest. In Pacific salmon & their ecosystems: Status and future options. Edited by D.J. Stouder, P.A. Bisson and R.J. Naiman. Chapman & Hall, New York. pp. 223-244.

Sheridan, A.K. 1995. The genetic impacts of human activities on wild fish populations. Rev. Fish. Sci. 3: 91-108.

Sherwood, C.R., Jay, D.A., Harvey, R.B., Hamilton, P., and Simenstad, C.A. 1990. Historical changes in the Columbia River Estuary. Prog. Oceanog. 25: 299-352.

Simenstad, C.A., and Thom, R.M. 1996. Functional equivalency trajectories of the restored Gog-Le-Hi-Te estuarine wetland. Ecol. Appl. 6: 38-56.

Simpson, J.J. 1994. Remote sensing in fisheries: a tool for better management in the utilization of a renewable resource. Can. J. Fish. Aquat. Sci. 51: 743-771.

Southwood, T.R.E. 1977. Habitat, the templet for ecological strategies? J. Animal Ecol. 46: 337-365.

Stanford, J.A., Ward, J.V., Liss, W.J., Frissell, C.A., Williams, R.N., Lichatowich, J.A. and Coutant, C.C. 1996. A general protocol for restoration of regulated rivers. Regul. Riv. 12: 391-413.

Stanley, Jr., T.R. 1995. Ecosystem management and the arrogance of humanism. Cons. Biol. 9: 255-262.

Thompson, J.D. 1991. Phenotypic plasticity as a component of evolutionary change. Trends Ecol. Evol. 6: 246-249.

Walters, C.J., and Collie, J.S. 1988. Is research on environmental factors useful to fisheries management? Can. J. Fish. Aquat. Sci. 45: 1848-1854.

Weitkamp, L.A. 1994. A review of the effects of dams on the Columbia River estuarine environment, with special reference to salmonids. Report to the Bonneville Power Administration (Contract DE-A179-93BP99021) and National Marine Fisheries Service, 148 p.

White, R.J., Karr, J.R., and Nehlsen, W. 1995. Better roles for fish stocking in aquatic resource management. Am. Fish. Soc. Symposium 15: 527-547.

Williams, R.N., Calvin, L.D., Coutant, C.C., Erho, M.W., Lichatowich, J.A., Liss, W.J., McConnaha, W.E., Mundy, P.R., Stanford, J.A., and Whitney, R.R. 1996. Return to the river: Restoration of salmonid fishes in the Columbia River Ecosystem. Northwest Power Planning Council (NPPC 96-6), Portland, Oreg.

Figure 1. Interaction between ocean conditions and salmon life-history diversity. Five possible scenarios (A-E) illustrate the relative definition of failure and success of salmon management as determined by the fit between different salmon life histories (shapes on the top right) and the variability in ocean conditions (template on the top left).

Figure 2. Different theoretical perspectives on the relative impact of freshwater and ocean environments on salmon production: A) Freshwater dominance, B) Marine dominance, and C) Holistic. In each case, the box on the left represents the freshwater environment, while that on the right represents the marine environment. The horizontal arrows through the boxes illustrate movement of juvenile salmon during their life cycle, from fresh water to the ocean. Vertical arrows on either the freshwater or marine boxes indicate were adjustments may occur in order to affect the number of fish returning. These adjustments can be natural, in the form of environmental variability, or human-caused, resulting from management actions to increase numbers of fish, or other activities that reduce their abundance.

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