Oregon Coastal Salmon Restoration Initiative |
Salmon have declined to a small fraction of their historic abundance in Oregon. Society recognizes the immediate crisis, namely, too few salmon. This crisis is actually a symptom of many factors acting over a broad scale of space and time to reduce salmon production, including but not limited to:
Risk Agents
Risk agents consist of natural processes or human activities that place sustainability of salmon at risk. Fishing, artificial propagation, alteration of spawning and rearing habitats, and introduction of exotic species are examples of risk agents related to human activities.
Some risk agents are natural and would exist if humans were not present in the region. Natural risk agents include short- and long-term variation in freshwater, estuarine, and oceanic environments. Examples include short-term droughts, freezing, and floods, as well as long-term trends of cooling, warming, low rainfall, high rainfall, and high or low oceanic productivity. Volcanic eruptions, earthquakes, landslides, fire, ice ages, and the like, are also natural risk agents that have and will affect the sustainability of salmon populations and species.
Other risk agents are largely related to the activities of people. These risk agents have often been categorized as related to fishing (harvest), artificial propagation (hatcheries), and landscape alteration (habitat). Dams and hydropower structures may be considered a subset of habitat alteration.
The harvest risk agent category includes all activities related to fishing, including direct and indirect effects on any life stage in freshwater or the ocean. Salmon are a commodity that has been exploited by various fishing methods in the Pacific Northwest for well over a century. The problems of over exploiting less productive stocks and species in mixed-stock fisheries and of selectively fishing populations and species have been widely recognized but poorly resolved by society. Mortality associated directly and indirectly with fishing can eliminate populations, reduce numbers within populations, alter or eliminate life history patterns, reduce fitness, and mask population trends. All of these effects may adversely affect the sustainability of wild salmon populations and should be evaluated in an assessment of extinction risk.
The hatchery risk agent category includes all genetic and ecological interactions related to the use of artificial propagation. Many parameters may be useful in evaluating whether hatcheries are adversely affecting sustainability of wild populations, including numbers and sizes of fish stocked, species stocked, release locations, evidence of residualism, genetic characteristics, disease history, homing fidelity to a recapture facility, occurrence of hatchery fish in natural spawning populations, and so on.
The habitat risk agent category includes all activities that alter the nature of freshwater and estuarine landscapes in a way that affects sustainability of wild salmon. This is the most complex risk-factor category, because salmon use watersheds from the headwaters to the coast at some time throughout their life cycle.
For restoration to be effective, it is important to identify the effect of risk agents on the populations. These effects are sometimes referred to as factors for decline that are the result of risk agents. The factors for decline are responsible for causing population declines or impeding recovery. Separate status reviews for Oregon coho salmon previously prepared by NMFS and ODFW discussed risk agents and factors for decline for coastal coho; part of this discussion is taken from these previous works. The purpose of this section is to provide a brief discussion of the major risk agents that have been identified for Oregon coastal coho salmon. Factors for decline are described in Chapter 17.
Harvest rates can, both directly and indirectly, influence extinction risk. Harvest mortality can directly affect spawner numbers and trends. Harvest in mixed stock fisheries managed for optimal production of more abundant stocks will overexploit the less productive stocks contributing to the fishery. This can diminish both the range and the genetic diversity of the species as a whole. Harvest can also produce strong selective pressure for smaller size at maturity which can compromise the species' adaptive ability by reducing numbers of eggs and by influencing spawning habitat selection. In responding to changes in abundance, trends in harvest rates can also mask trends in stock productivity. By masking trends in productivity, harvest can affect the perception of risk resulting from other factors, and thus delay response to other threats to the survival of the species.
Coho salmon from both of the Oregon coastal ESUs are harvested in mixed stock ocean fisheries and in terminal recreational fisheries. Fishery-related mortality on Oregon coastal coho salmon has probably been in the 70-80 percent range from the 1950s through the early 1980s. These rates are higher than rates considered sustainable, based on Oregon's Coho Salmon Management Plan. Productivity of coastal populations, as measured by recruits per spawner, has been declining since the mid-1970s.
Although habitat degradation and declines in ocean productivity have contributed to a decline in productivity, harvest has also played a major role in declines in coho production. In hindsight, harvest rates that Oregon coastal coho were exposed to over the last two decades were excessive, especially considering the adverse ocean conditions that were limiting productivity during the same period. Harvest management traditionally has attempted to maximize sustainable yield in mixed stock fisheries, and in some years, exceeded harvest rate targets thought to be sustainable for smaller groups of populations. As a consequence, it is likely that less productive and smaller populations have been reduced to levels where loss of genetic diversity is a concern. Although data do not clearly demonstrate outright extirpation of small populations or range reductions, these phenomena may be masked by a low, natural level of straying by wild and hatchery populations nearby.
Artificial propagation may affect wild salmonid populations in a number of ways. For example, occurrence of hatchery fish in spawning populations of wild fish may mask declines in natural populations, making it difficult to detect changes in abundance and to determine whether the wild fish are self-sustaining. Also, artificial propagation presents the potential for genetic and ecological risks to natural populations that may affect their productivity. Stock transfers that result in interbreeding of hatchery and natural fish (or hatchery programs that lead to high levels of straying) can cause loss of fitness in local populations and loss of diversity among populations.
Actual impacts of hatchery programs on wild coho populations in the Oregon coastal region have not been assessed. It is common, however, to assess other aspects of hatchery management programs and also to consider these populations as surrogates that permit inference of potential impact on wild populations. Features that provide a basis for evaluating the potential level of impact include:
Hatchery production of coho salmon in the Oregon portion of the ESU that is shared with California has been at a relatively low level and has only occurred in recent years. In the California portion of this ESU, larger numbers of hatchery coho are released, more transfers occur between hatcheries, and some hatchery coho have been imported from sources outside the ESU.
The vast majority of hatchery coho production in the southern Oregon ESU occurs at one Rogue River hatchery and was developed from native fish in the mid-1970s.
Data are not available to establish the proportion of hatchery fish that are present in spawning areas with wild coho in the southern Oregon portion of the ESU, although some marked hatchery coho have been detected at non-parent hatcheries and in non-native basins.
Hatchery production of coho salmon in the northern Oregon ESU has been at a higher level and of extended duration. ODFW hatchery programs in this region typically released 3 to 6 million smolts and 1 to 4 million coho fry annually during the 1980s. Private hatcheries in this region released variable numbers of coho during the 1980s that approached 20 million annually. Transfers of coho salmon between ODFW hatcheries typically used stocks from within the area. In contrast, private hatcheries in this region imported Puget Sound stocks, which were later mixed with Oregon coastal stocks. Private hatcheries are not presently in operation. Since the 1970s, outplants of coho salmon into Oregon coastal rivers using stocks from outside the Oregon coast have been rare.
Recoveries of marked fish and detection of distinct scale patterns provided clear evidence of straying by private hatchery coho, both within and between basins, when they were operating. Several locations have been noted where hatchery coho are known or expected to be common, including the North Nehalem, Trask, Salmon, and Siletz Rivers. At face value, scale data are a basis for concern regarding the possibility that significant proportions of several naturally spawning populations are actually composed of hatchery coho. Some marked hatchery fish have been detected in natural spawning areas, but recoveries have been at a level insufficient to confirm or refute the scale analysis data. Hatchery coho appear to be relatively rare in some basins, notably the lake systems and populations in the southern portion of the northern Oregon coast ESU.
In the future, the proportion of stray coho among natural spawning populations will be more clearly established by sampling in spawning areas because all hatchery fish will be marked.
Coho salmon evolved in freshwater ecosystems that were historically characterized by flood plains, braided channels, and off-channel areas-all of which contained considerable structural complexity, such as large wood debris and debris jams. Human activities have simplified and degraded freshwater habitats utilized by anadromous salmonids in Oregon and throughout the Pacific Northwest. These activities include timber harvest, mining, water withdrawals, stream cleaning, livestock grazing, road construction, stream channelization, dredging and other navigation improvements on rivers, diking and filling of wetlands, waste disposal, gravel removal, farming, urbanization, and splash dam logging.
Habitat reduction and degradation probably have reduced the resiliency of coho salmon to withstand natural variability in biological and physical factors, such as low spawner abundance, severe hydrologic events (high or low flows), and variability in ocean productivity. Habitats that have been altered by human activities are more likely to suffer degradation from disturbance events such as severe winter storms. For example, the frequency and magnitude of debris torrents increases with activities such as logging and road building. While debris torrents are recognized as potential sources of woody debris that may ultimately be beneficial to salmon production, such events may have a disastrous effect on salmon production in the short term.
Although some habitat functions can be readily restored through habitat improvement projects, other functions (e.g., production and recruitment of large woody debris into streams or transportation of fine sediments out of spawning gravels) may require decades or centuries to recover. Also, instream habitat restoration work can only be conducted in a relatively small proportion of watersheds. A considerable lag time may be expected between initiation of some corrective actions and restoration of significantly improved habitat function.
Degradation of coho freshwater habitats along the Oregon coast is extensive. All human activities have contributed to habitat changes. Contemporary habitats in coastal river basins are usually characterized by a combination of the following features:
Winter habitat is thought to be a primary factor limiting coho salmon production in many coastal Oregon watersheds. In localized stream reaches, subbasins, and watersheds, however, other habitat features may be dominant limiting factors to coho production.
Natural risk agents that are also thought to contribute to the decline of Oregon coho include ocean conditions and predation by birds and marine mammals.
Ocean Conditions
Cyclic variation in the ocean environment is thought to be a major determinant of
stock size and productivity of Oregon coastal coho. Climate conditions are
known to have changed recently in the Pacific Northwest, and Pacific salmon
stocks have been affected by changes in ocean production that occurred during the
1970s. Climate factors affecting ocean conditions are large-scale processes that
also affect terrestrial and freshwater environments. Logically, climate factors that
affect the productivity of the ocean environment may have simultaneous effects
on the productivity of the freshwater and estuarine environment. These climate
conditions are thought to be cyclic in nature, but it is not possible to accurately
predict whether conditions will return to more favorable conditions in the near
future. Changes in ocean productivity since 1976 are thought to be a major
determinant of the recent decline in coho return ratios.
Predation by Birds and Marine Mammals
Birds and marine mammals eat salmon. The magnitude of this predation on
regional coho production remains a matter of intense debate. Scientific studies and
recent reviews of Pacific Northwest salmon by the National Research Council in
the Botkin Report have tended to assert that predation by coastal bird and marine
mammal populations, except in unusual, isolated locations, is not a major,
underlying cause of the decline in coho or other regional salmonid populations.
Based on the comments received at Oregon coastal county fairs in 1996 and public
comment on the August 1996 draft of the Conservation Plan, however, many
people believe that seals and sea lions, and to a lesser degree, cormorants, are
primarily responsible for the decline in Oregon's coho populations.
Seals and sea lions (pinnipeds) are predatory animals that depend almost exclusively on fish for their diet. As such, pinnipeds have long been viewed as competitors of humans for marine fish resources. For most of the first part of this century, seals and sea lions were hunted and killed as part of bounty programs in an attempt to keep these animals out of coastal bays and rivers, and to reduce their numbers overall. Although bounty programs were based on the idea that reducing pinniped numbers would result in increased fish populations, no scientific data proved this assumption.
In 1972, the federal government passed the Marine Mammal Protection Act (MMPA), which removed all management authority for pinnipeds from the states and vested it with the National Marine Fisheries Service (NMFS). Increases in pinniped numbers in the Pacific Northwest over the past 20 years have raised new concerns about the potential impacts of seal and sea lion predation on depleted fish resources. The concern for pinniped predation is more significant when fish populations are depressed and/or when estuary habitat has been simplified. If a localized situation exists where fish numbers are abnormally low, barriers to fish migration exist, and local predator numbers are high, then predation by seals and sea lions may have a significant adverse effect on individual salmonid populations.
NMFS will work with Oregon and other states to address the issue of growing pinniped populations and their potential effects on depressed salmonid stocks in the Pacific Northwest. Currently, Oregon is working with California and Washington, as well as NMFS, to identify areas with potentially significant impacts of pinniped predation on salmonids. NMFS has expressed a concern about potential effects of growing pinniped populations on depressed salmon populations in the Pacific Northwest. In specific areas, pinniped predation could be hindering the rebuilding of salmon populations. Additional research is necessary to determine the extent of actual impacts on salmonid populations. Where predation is determined to be a significant problem, management actions consistent with the ESA and MMPA can be taken to reduce salmon mortality. NMFS will seek funding to assess pinniped interactions with salmon populations at critical sites and initiate appropriate management actions to minimize predation where assessments indicate such action is needed.
Many human activities and natural processes, individually, can cause a decease in salmon populations, in the productive capacity of populations, and in the productive capacity of their supporting habitats. Interactions of risk agents can compound these effects. The Oregon coho situation presents an example of interactions among risk agents. A period of high ocean productivity stimulated an expansion of coho fisheries and hatchery programs during the 1960s. When the oceanic productivity declined after the mid 1970s, hatchery programs were maintained at high levels and fishery harvest rates remained at levels that, in hindsight, were greater than the coho populations could sustain. The harvest rates alone were capable of causing a decline in coho populations similar to what has been observed in the last two decades. The actual effects are not known for (1) recent alterations in the productivity of freshwater habitat, (2) interactions with hatchery fish, and (3) predation by marine mammals on the production of Oregon coastal coho.
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