Status Review of Pink Salmon from Washington, Oregon, and California
Jeffrey J. Hard, Robert G. Kope, W. Stewart Grant,
National Marine Fisheries Service
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The Endangered Species Act (ESA) allows listing of distinct population segments of vertebrates as well as named species and subspecies. The policy of the National Marine Fisheries Service (NMFS) on this issue for anadromous Pacific salmonids is that a population will be considered distinct for purposes of the ESA if it represents an evolutionarily significant unit (ESU) of the species as a whole. To be considered an ESU, a population or group of populations must 1) be substantially reproductively isolated from other populations, and 2) contribute substantially to ecological/genetic diversity of the biological species. Once an ESU is identified, a variety of factors related to population abundance are considered in determining whether a listing is warranted.
In March 1994, in response to a petition seeking protection under the ESA for two populations of pink salmon in Washington State, NMFS initiated a status review of pink salmon in Washington, Oregon, and California, and formed a Biological Review Team (BRT) to conduct the review. This report summarizes biological and environmental information gathered in that process.
1) Even-year pink salmon. The only persistent population of even-year pink salmon in Washington occurs in the Snohomish River. Although several attempts were made in this century to transplant even-year pink salmon from Alaska and British Columbia to the Puget Sound region, there is no indication that these attempts were successful. Furthermore, life history and genetic information for Snohomish River even-year pink salmon is consistent with the hypothesis that this population resulted from a natural colonization event. The nearest even-year pink salmon populations occur in British Columbia, at least 130-150 km away. On the basis of available information, the BRT could not resolve with any degree of certainty the extent of the ESU that contains the Snohomish River even-year pink salmon population. After considering all available information, about half of the BRT members concluded that the Snohomish River even-year population is in an ESU by itself, whereas half judged that the ESU also included populations from British Columbia. In any case, the BRT unanimously agreed that any conclusion about the extent of the even-year pink salmon ESU should be regarded as provisional and subject to revision should substantial new information become available.
2) Odd-year pink salmon. The BRT considered several possible ESU scenarios for odd-year pink salmon. The majority of BRT members concluded that all odd-year pink salmon populations in Washington are part of a single ESU. This ESU includes populations in Washington as far west as the Dungeness River (or the Elwha River, if that population is not already extinct) and in southern British Columbia (including the Fraser River and eastern Vancouver Island) as far north as Johnstone Strait. A minority of BRT members concluded that populations from Washington rivers draining into the Strait of Juan de Fuca are members of a separate ESU. All members agreed that, collectively, odd-year pink salmon in Washington contain a considerable amount of genetic and life history diversity, with populations from the Dungeness, Nooksack, and Nisqually Rivers being the most distinctive in this regard. Several small odd-year populations occur on southwestern Vancouver Island, but little information is available to ascertain the relationship of these populations to the proposed odd-year ESU. Additional information on these populations is needed to resolve the question of whether odd-year pink salmon in Washington and southern British Columbia are in one or more ESUs.
The ESA (section 3) defines the term endangered species as any species which is in danger of extinction throughout all or a significant portion of its range. The term threatened species is defined as any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. According to the ESA, the determination whether a species is threatened or endangered should be made on the basis of the best scientific information available regarding its current status, after taking into consideration conservation measures that are proposed or are in place. In this review, the BRT did not evaluate likely or possible effects of conservation measures and, therefore, did not make recommendations as to whether identified ESUs should be listed as threatened or endangered species; rather, the BRT drew scientific conclusions about the risk of extinction faced by identified ESUs under the assumption that present conditions will continue. The resulting conclusions for each ESU follow.
1) Even-year pink salmon. The BRT was unanimous in concluding that this ESU is not presently at risk of extinction. Nevertheless, nearly all BRT members expressed concerns about the status of this ESU. Although available escapement data suggest that the even-year pink salmon population in the Snohomish River has been increasing since 1980, the low abundance and isolation of this population--when coupled with the lack of variable age structure in pink salmon--suggest that the population is at some risk due to demographic or environmental fluctuations. All BRT members agreed that this population should be closely monitored, even if it is determined to be part of a larger ESU.
2) Odd-year pink salmon. The BRT was unanimous in concluding that this ESU as a whole is not presently at risk of extinction. Most populations appear to be healthy, and overall abundance appears to be close to historical levels. The two most distinctive Puget Sound populations (from the Nooksack and Nisqually Rivers) both show nonsignificant trends in recent abundance, and no other factors were found that would suggest that either of these populations is at immediate risk. However, most BRT members expressed concerns about the status of certain populations within this ESU. For odd-year pink salmon, two of the three U.S. populations along the Strait of Juan de Fuca are in steep decline, and the third may already be extinct. The population nearest to these three occurs in northern Hood Canal and is also declining. However, the remaining odd-year populations in the United States, as well as most of those in southern British Columbia, show no evidence of sustained declines, and many are increasing in abundance. In addition, the other U.S. populations that are the most distinctive based on genetic and life history characteristics appear to be healthy. The majority of BRT members therefore concluded that the odd-year pink salmon ESU is not presently at risk of extinction or endangerment. However, BRT members unanimously expressed concern about the status of the marginal populations along the Strait of Juan de Fuca, and concern that further erosion of these populations might eventually pose risk to a significant portion of the ESU as a whole. In addition, evidence exists for a recent decline in body length of odd-year Washington pink salmon, which increases risk to these populations by limiting their ability to respond to perturbation. A similar decline has also been observed in pink salmon from southeastern Alaska.
The status review for west coast pink salmon was conducted by a team of researchers from the National Marine Fisheries Service (NMFS). This biological review team relied on information in the Endangered Species Act Administrative Record for West Coast Pink Salmon, which was developed pursuant to this review and includes comments, data, and reports submitted by the public and by state, tribal, and federal agencies. The authors acknowledge the efforts of all who contributed to this record, especially the Washington Department of Fish and Wildlife, Oregon Department of Fish and Wildlife, California Department of Fish and Game, U.S. Fish and Wildlife Service, and Northwest Indian Fisheries Commission.
In addition, the authors are grateful to several fishery scientists and managers for assembling and providing information that aided the development of this report and for providing critical reviews of our analyses of this information. Much of the information provided was previously unpublished and represents the most comprehensive body of biological information available on pink salmon in North America south of Alaska and northern British Columbia. Several of these scientists and managers provided their recommendations on the reliability and utility of this information. In particular, the authors thank Jim Ames, Don Hendrick, Dr. James Shaklee, Jim Uehara, and Sewall Young of the Washington Department of Fish and Wildlife; Gary Graves and Keith Lutz of the Northwest Indian Fisheries Commission; Dr. Anthony Gharrett and Dr. William Smoker of the University of Alaska; Dr. Terry Beacham, LeRoy Hop Wo, and Wilf Luedke of the Canadian Department of Fisheries and Oceans; and Frank Thrower of the NMFS Alaska Fisheries Science Center.
The biological review team for this status review included: Dr. Stewart Grant, Dr. Jeffrey Hard, Dr. Robert Iwamoto, Dr. Orlay Johnson, Dr. Robert Kope, Dr. Conrad Mahnken, Dr. Michael Schiewe, William Waknitz, Dr. Robin Waples, and Dr. John Williams, all from the NMFS Northwest Fisheries Science Center (NWFSC), Dr. Peter Dygert from the NMFS Northwest Region, and William Heard from the Auke Bay Laboratory of NMFS s Alaska Fisheries Science Center.
Several NWFSC staff made substantial contributions to the preparation of this status review. JoAnne Butzerin, Sharon Damkaer, and Dr. Robert Iwamoto edited earlier versions of this report and made numerous suggestions to improve its presentation. Peggy Busby and Laurie Weitkamp provided much of the environmental information presented in this review, information that they collected during their preparation of status reviews for west coast steelhead and coho salmon, respectively. Kathleen Neely drafted the maps and assisted in editing the other figures.
Scope and Intent of the Present Document
Pink salmon (Oncorhynchus gorbuscha) is a widespread species of Pacific salmon, occurring regularly in most major river basins around the Pacific Rim from Washington State to North Korea, and occasionally in rivers as far south as northern California and the Japanese island of Hokkaido (Heard 1991). Recently published investigations have reported that several local populations of pink salmon in Washington and California have become extinct or are at high risk of extinction, and that the abundance of others is depressed (e.g., Nehlsen et al. 1991, Moyle et al. 1995). These declines led to public concern that some of these populations of pink salmon be listed as threatened or endangered species under the U.S. Endangered Species Act (ESA; technical terms and abbreviations such as ESA are defined in the glossary in the Appendix). Under the ESA, the term species is defined rather broadly to include subspecies and distinct population segments of vertebrates (such as salmon) as well as taxonomic species.
The National Marine Fisheries Service (NMFS) was petitioned in March 1994 by the Professional Resources Organization-Salmon (PRO-Salmon) to list Elwha River and fall-run Dungeness River pink salmon as threatened or endangered species under the ESA (PRO- Salmon 1994). At about the same time, NMFS also received petitions for several additional populations of Pacific salmon in the Puget Sound area. In response to these petitions and the more general concerns for the status of Pacific salmon throughout the region, NMFS (1994) announced that it would initiate ESA status reviews for all species of anadromous Pacific salmonids. These comprehensive reviews will consider all populations in the states of Washington, Oregon, California, and Idaho and are scheduled for completion in 1996. This proactive approach should facilitate more timely, consistent, and comprehensive evaluation of the ESA status of Pacific salmonids than would be possible through a long series of reviews of individual populations.
This document considers environmental and biological information for pink salmon populations in Washington, Oregon, California, and southern British Columbia (Fig. 1). These populations will be collectively referred to in this document as west coast pink salmon. The scope of this review thus encompasses, but is not restricted to, the two populations identified in the PRO-Salmon (1994) petition.
Because the ESA stipulates that listing determinations should be made on the basis of the best scientific information available, NMFS formed a team of scientists with diverse backgrounds in salmon biology to conduct this review. This Biological Review Team (BRT) discussed and evaluated scientific information presented at two public meetings held in Seattle in December 1994 and February 1995 as well as information gathered independently by the authors of this report. The BRT also reviewed additional information submitted to the ESA administrative record for pink salmon. This document represents the findings and conclusions of the BRT on the status of west coast pink salmon under the ESA.
In determining whether a listing under the ESA is warranted, two key questions must be addressed:
1) Is the entity in question a species as defined by the ESA?These two questions are addressed in separate sections of this report. If it is determined that a listing(s) is warranted, then NMFS is required by law (1973 ESA Sec. 4(a)(1)) to identify one or more of the following factors responsible for the species threatened or endangered status: 1) destruction or modification of habitat; 2) overutilization by humans; 3) disease or predation; 4) inadequacy of existing regulatory mechanisms; or 5) other natural or human factors. This status review does not formally address factors for decline, except insofar as they provide information about the degree of risk faced by the species in the future.
2) If so, is the species threatened or endangered?
The Species Question
As amended in 1978, the ESA allows listing of distinct population segments of vertebrates as well as named species and subspecies. However, the ESA provides no specific guidance for determining what constitutes a distinct population, and the resulting ambiguity has led to the use of a variety of approaches for considering vertebrate populations. To clarify the issue for Pacific salmon, NMFS published a policy describing how the agency will apply the definition of species in the ESA to anadromous salmonid species, including sea-run cutthroat trout and steelhead (NMFS 1991). A more detailed discussion of this topic appeared in the NMFS Definition of Species paper (Waples 1991a). The NMFS policy stipulates that a salmon population (or group of populations) will be considered distinct for purposes of the ESA if it represents an evolutionarily significant unit (ESU) of the biological species. An ESU is defined as a population that 1) is substantially reproductively isolated from conspecific populations and 2) represents an important component of the evolutionary legacy of the species.
The term evolutionary legacy is used in the sense of inheritance --that is, something received from the past and carried forward into the future. Specifically, the evolutionary legacy of a species is the genetic variability that is a product of past evolutionary events and that represents the reservoir upon which future evolutionary potential depends. Conservation of these genetic resources should help to ensure that the dynamic process of evolution will not be unduly constrained in the future.
The NMFS policy identifies a number of types of evidence that should be considered in the species determination. For each of the two criteria (reproductive isolation and evolutionary legacy), the NMFS policy advocates a holistic approach that considers all types of available information as well as their strengths and limitations. Isolation does not have to be absolute, but it must be strong enough to permit evolutionarily important differences to accrue in different population units. Important types of information to consider include natural rates of straying and recolonization, evaluations of the efficacy of natural barriers, and measurements of genetic differences between populations. Data from protein electrophoresis or DNA analyses can be particularly useful for this criterion because they reflect levels of gene flow that have occurred over evolutionary time scales.
The key question with respect to the second criterion is, If the population became extinct, would this represent a significant loss to the ecological/genetic diversity of the species? Again, a variety of types of information should be considered. Phenotypic and life history traits such as size, fecundity, migration patterns, and age and time of spawning may reflect local adaptations of evolutionary importance, but interpretation of these traits is complicated by their sensitivity to environmental conditions. Data from protein electrophoresis or DNA analyses provide valuable insight into the process of genetic differentiation among populations but little direct information regarding the extent of adaptive genetic differences. Habitat differences suggest the possibility for local adaptations but do not prove that such adaptations exist.
The Extinction Risk Question
The ESA (section 3) defines the term endangered species as any species which is in danger of extinction throughout all or a significant portion of its range. The term threatened species is defined as any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. NMFS considers a variety of information in evaluating the level of risk faced by an ESU. Important considerations include 1) absolute numbers of fish and their spatial and temporal distribution; 2) current abundance in relation to historical abundance and carrying capacity of the habitat; 3) trends in abundance, based on indices such as dam or redd counts or on estimates of recruit-to-spawner ratios; 4) natural and human-influenced factors that cause variability in survival and abundance; 5) possible threats to genetic integrity (e.g., selective fisheries and interactions between hatchery and natural fish); and 6) recent events (e.g., a drought or a change in management) that have predictable short-term consequences for abundance of the ESU. Additional risk factors, such as disease prevalence or changes in life history traits, may also be considered in evaluating risk to populations.
According to the ESA, the determination of whether a species is threatened or endangered should be made on the basis of the best scientific information available regarding its current status, after taking into consideration conservation measures that are proposed or are in place. In this review, we do not evaluate likely or possible effects of conservation measures. Therefore, we do not make recommendations as to whether identified ESUs should be listed as threatened or endangered species, because that determination requires evaluation of factors not considered by us. Rather, we have drawn scientific conclusions about the risk of extinction faced by identified ESUs under the assumption that present conditions will continue (recognizing, of course, that natural demographic and environmental variability is an inherent feature of present conditions ).
NMFS policy (Hard et al. 1992, NMFS 1993) stipulates that in determining 1) whether a population is distinct for purposes of the ESA, and 2) whether an ESA species is threatened or endangered, attention should focus on natural fish, which are defined as the progeny of naturally spawning fish (Waples 1991a). This approach directs attention to fish that spend their entire life cycle in natural habitat and is consistent with the mandate of the ESA to conserve threatened and endangered species in their native ecosystems. Implicit in this approach is the recognition that fish hatcheries are not a substitute for natural ecosystems. Nevertheless, artificial propagation is important to consider in ESA evaluations of anadromous Pacific salmonids for several reasons.
First, although natural fish are the focus of ESU determinations, possible effects of artificial propagation on natural populations must also be evaluated. For example, stock transfers might change the genetic or life history characteristics of a natural population in such a way that the population might seem either less or more distinctive than it was historically. Artificial propagation can also alter life history characteristics such as smolt age and migration and spawn timing.
Second, artificial propagation poses a number of risks to natural populations that may affect their risk of extinction or endangerment. These risks are discussed below in the Assessment of Extinction Risk section. In contrast to most other types of risk for salmon populations, those arising from artificial propagation are often not reflected in traditional indices of population abundance. For example, to the extent that habitat degradation, overharvest, or hydropower development have contributed to a population s decline, these factors will already be reflected in population abundance data and accounted for in the risk analysis. The same is not true of artificial propagation. Hatchery production may mask declines in natural populations that will be missed if only raw population abundance data are considered. Therefore, a true assessment of the viability of natural populations cannot be attained without information about the contribution of naturally spawning hatchery fish. Furthermore, even if such data are available, they will not in themselves provide direct information about possibly deleterious effects of fish culture. Such an evaluation requires consideration of the genetic and demographic risks of artificial propagation for natural populations. The sections on artificial propagation in this report are intended to address these concerns.
Finally, if any natural populations are listed under the ESA, then it will be necessary to determine the ESA status of all associated hatchery populations. This latter determination would be made following a proposed listing and is not considered further in this document.
This section briefly summarizes information presented by the petitioner (PRO-Salmon 1994) to support its arguments that two populations of pink salmon on Washington s Olympic Peninsula qualify as a threatened or endangered species under the ESA. We discuss this information and related issues in the following sections, and we evaluate the status of west coast pink salmon in the conclusions of the Assessment of Extinction Risk section.
Distinct Population Segments
A petition to list two pink salmon populations as protected species under the ESA was received by NMFS from PRO-Salmon on 14 March 1994. The status of these two populations, in the lower Dungeness River and the Elwha River, was characterized as critical by WDF et al. (1993). In the planned revision of the Washington State Salmon and Steelhead Stock Inventory (SASSI), the Washington Department of Fish and Wildlife (WDFW) is likely to recommend that Elwha River pink salmon be reclassified as extinct (J. Ames). Both petitioned populations are odd-year populations that spawn or have spawned in systems draining into the Strait of Juan de Fuca from the northern side of the Olympic Peninsula. No other rivers along the Strait of Juan de Fuca appear to support persistent pink salmon populations (Williams et al. 1975, WDF et al. 1993).
With respect to the two criteria established by NMFS to define a species of Pacific salmon, the petitioner argued that the lower Dungeness and Elwha River populations of pink salmon were both reproductively isolated from other pink salmon populations. Reproductive isolation was inferred primarily on the basis of distance to nearest neighboring population; for lower Dungeness River pink salmon, this distance is approximately 10 km (to the upper Dungeness River population), and for Elwha River pink salmon, this distance is about 25 km (to the lower Dungeness River population). According to the petitioner, genetic data, in the form of allozyme variation, support a hypothesis for at least partial reproductive isolation of the lower Dungeness River population (Shaklee et al. 1991), but no genetic data exist for the Elwha River population (WDF et al. 1993, J. Shaklee).
In its petition, PRO-Salmon provided little information that addresses the evolutionary significance criterion. The petitioner argued that spatial and temporal isolation of the lower Dungeness River population from the upper Dungeness River population, due to differences in run timing and spawning location, contribute to the distinctiveness of the lower river population. No quantitative data are available to support a hypothesis for the distinctiveness of the Elwha River population.
The petitioner noted that the run size for lower Dungeness River pink salmon declined from about 11,000 spawners per year between 1969 and 1979 to 6,600 fish in 1981, following severe flooding in January 1980. (The recorded historical high was 210,000 fish in 1963). Recent abundance has ranged from less than 150 to more than 750 spawners, about 5% of pre- flood levels and 0.1% of the historic high (WDF et al. 1993, PRO-Salmon 1994). The run size for Elwha River pink salmon crashed from about 4,800 spawners per year (1969-79) to an estimated 200 fish or less since 1981, following severe flooding in January 1980. (The recorded historical high was 40,000 fish in 1963.) Since 1981, less than 35 pink salmon have been observed in the Elwha River over all of the odd-numbered years combined, and only 4 fish have been observed since 1989 (PRO-Salmon 1994, J. Uehara).
Causes of Decline for Pink Salmon
The petition identified several threats to the viability of lower Dungeness River pink salmon: water withdrawals from the lower river during the holding and spawning periods in late summer and fall, habitat degradation due to increased urbanization along the river, diking for flood control, and possible sewage contamination. Any or all of these factors may be inhibiting natural recovery of pink salmon. In addition, timber harvest near the river and artificial propagation of coho salmon at Dungeness Hatchery may impede recovery (PRO- Salmon 1994; Hiss 1994, 1995).
Finally, harvest in mixed-stock fisheries, especially in fisheries that target Fraser River pink salmon in the Strait of Juan de Fuca, may limit the ability of this population to recover naturally (estimated total exploitation rate on the lower Dungeness River population = 47%, PRO-Salmon 1994). The petitioner suggested that similar factors threaten the viability of Elwha River pink salmon, although urbanization and timber harvest are apparently less significant factors in this drainage, and hatchery production on the river includes chinook salmon and steelhead as well as coho salmon. Unlike the Dungeness River, the Elwha River is obstructed by two dams, the Elwha and Glines Canyon Dams. These structures prevented access by pink salmon to 35 km of the river early in this century, and pink salmon spawning is currently limited to the lowest 5 km of the river. However, the petitioner noted that the Elwha River population did not decline to extremely low levels until the late 1970s (PRO-Salmon 1994). Nevertheless, based on the petitioner s information, the abundance of this population apparently has been depressed since at least the late 1960s.
The spawning populations of west coast pink salmon that are the focus of this review are presently distributed over a small region of the contiguous 48 United States, in northwestern Washington from its border with British Columbia (49°N) south to the Nisqually River (48°N) in southern Puget Sound. Although climatic features do not vary markedly in this region, diverse patterns of vegetation, weather, soils, and water quality exist there. This section summarizes environmental and biological information relevant to determining the nature and extent of ESUs for pink salmon in this region (see also Weitkamp et al. 1995).
Physiography and Geology
Pink salmon inhabit areas in northwestern Washington and southern British Columbia that are represented by several physiographic regions: the Coast Range Province, which extends in the United States from the Strait of Juan de Fuca southward to the Klamath Mountains and from the Pacific Ocean eastward to the lowlands west of the Cascade Mountains, and in Washington includes the Olympic Mountains and Willapa Hills; the Puget- Willamette Lowland, which covers Puget Sound and the Willamette River Valley in the United States; the Coast Mountains of British Columbia, which include in Washington the Cascades North and Cascades South areas; the Coastal Trough, which covers the area surrounding the Strait of Georgia and Johnstone Strait; and the Outer Mountains of Vancouver Island (McKee 1972, Lasmanis 1991). These regions are geologically diverse. Most of the encompassed area, with the exception of the Olympic Mountains and higher elevations in the Cascade Mountains, was glaciated during the Pleistocene Epoch (Booth 1987).
As a result of Pleistocene glaciation, the Puget Sound lowlands contain a thick layer of moraine. The North Cascades along northern Puget Sound and southwestern British Columbia are composed of a wide spectrum of metamorphic rock types. Like the Olympic Peninsula, the coastal mountains of British Columbia are composed of basalt and sedimentary rock as well as volcanic and nonvolcanic rock (McKee 1972). The most unique aspect of the Olympic Peninsula is its massive foundation of marine basaltic flow (McKee 1972). The northern coastal area where pink salmon presently spawn has been heavily influenced by marine sedimentation, as have other lowland areas in the region. In present-day Washington and southern British Columbia, the lowlands surrounding Puget Sound probably have the most complex hydrologic history because of their repeated exposures to alternating glaciation and deposition of marine sediment.
Temperature, Precipitation, and Hydrology
Climate varies primarily with latitude along the west coast of North America, and this region exhibits south-to-north gradients of increasing average precipitation and declining average temperature. The coastal region has a mild climate with warm, relatively dry summers and cool, wet winters.
Pink salmon typically enter fresh water and spawn at a time of year when streamflow is low and water temperature is relatively high. Streamflows are lowest in August and September, and there is some tendency for streamflows to reach their lowest points later in rivers on the Strait of Juan de Fuca and in Hood Canal than in systems on Puget Sound. Water temperatures in northwestern Washington are generally highest in July and August (Hydrosphere Data Products, Inc. 1993). Because run timing and spawn timing are sensitive to these factors, streamflow patterns determine the temporal availability and suitability of spawning and incubation habitat for pink salmon.
The Olympic Peninsula is much wetter (160-380 cm precipitation/yr) than the rest of Washington, with considerable snowfall (over 150 cm/yr) at higher elevations. The abundant precipitation results at least partially from the relatively high elevation of the Olympic Mountains (1,000-2,000 m). Persistent spawning populations of pink salmon are found only in watersheds draining the northern and eastern sides of the Peninsula. Maximum and minimum air and water temperatures are cooler in the Olympic Peninsula than farther south, reflecting effects of both latitude and elevation. Annual maximum and minimum water temperatures are 10°C to 14°C and 2°C to 4°C, respectively, whereas annual maximum and minimum air temperatures are approximately 21°C and 2°C, respectively.
The wet climate of the Olympic Peninsula continues north along the west coast of Vancouver Island and along the British Columbia mainland north of Vancouver Island. Limited hydrographic data (Farley 1979) indicate that water-flow patterns in this area are similar to those on the Olympic Peninsula, with relatively high flows throughout the year. Summer air temperatures generally decrease with increasing latitude--the Olympic coast is a few degrees warmer than the southwestern coast of Vancouver Island, which is a few degrees warmer than the northwestern coast and the mainland north of Vancouver Island.
A smaller gradient of decreasing average precipitation exists from west to east in northwestern Washington. East of the Olympic Peninsula, precipitation rapidly decreases because of the rainshadow caused by the Olympic and Vancouver Island Mountains to the north, and the Willapa Hills to the south. The rainshadow, which becomes apparent along the northern coastline of the Peninsula west of the Elwha River, continues through lowland Puget Sound, up the lowlands bordering the Strait of Georgia, to the south end of Queen Charlotte Strait. Most Washington streams that support pink salmon are found in Puget Sound. Most of this area receives less than 120 cm rain per year, with some areas receiving as little as 50 cm per year (U.S. Dep. Commerce 1968).
A slight summer temperature cline appears to exist within the northern rainshadow region; average maximum air temperatures in Puget Sound and Hood Canal (20°C-24°C) are slightly higher than those in the Strait of Georgia (16°C-20°C), which in turn are higher than those in areas inside Vancouver Island farther north (14°C-16°C). In contrast, winter air temperatures are more uniform and average 0°C-5°C throughout the area. Stream temperatures in the area are generally cool, with a maximum of 12°C-20°C in summer and 0°C-4°C in winter (Hydrosphere Data Products, Inc. 1993).
No major variations in upwelling patterns occur along the coasts of British Columbia and Washington (Smith 1983, Landry et al. 1989). Upwelling in this region is primarily wind driven (Bakun 1973, 1975; Thompson 1981). One exception to this pattern has been observed off the southwestern corner of Vancouver Island where consistent and strong upwelling appears to occur throughout the year (Denman et al. 1981). Upwelling in this area is thought to be caused by current-driven as well as wind-driven events, a condition that leads to relative temporal and spatial stability.
Vegetation patterns in Washington and southern British Columbia are affected by precipitation gradients. Coastal regions in Washington and British Columbia are forested with a Sitka spruce (Picea sitchensis)-dominated floral community, which also includes western hemlock (Tsuga heterophylla), western red cedar (Thuja plicata), red alder (Alnus rubra), and Douglas fir (Pseudotsuga menziesii) as major species. This vegetation type is restricted to coastal regions and river valleys extending a few kilometers inland over coastal plains, and to elevations above 150 m in areas immediately adjacent to the ocean (Franklin and Dyrness 1973).
Sitka spruce forests are replaced by western hemlock-dominated forests along the Strait of Juan de Fuca to the north and east. This vegetation type also includes western hemlock, Douglas fir, red alder, and western red cedar. The transition between Sitka spruce and western hemlock along the Strait of Juan de Fuca occurs at about the Elwha River on the Olympic Peninsula and Sooke Inlet on Vancouver Island. Because of Puget Sound's lower precipitation and glacial soils, drought-tolerant western white (Pinus monticola), lodgepole (Pinus contorta), and occasionally ponderosa (Pinus ponderosa) pines, occur more frequently here than elsewhere in the western hemlock zone.
Along the east coast of the North Pacific Ocean within the range considered in this status review, a distinct faunal boundary for marine fishes occurs off the northern tip of Vancouver Island (approximately 50°N) (Allen and Smith 1988). Within the range of pink salmon in the Pacific Northwest, only one major freshwater ichthyogeographic region has been described: the Columbia (McPhail and Lindsey 1986, Minckley et al. 1986). Thus, no pattern of variation in marine fishes associated with pink salmon is evident in Washington and southern British Columbia.
Estuarine fish assemblages show regional differences based on presence or absence of species, but only a single group exists in northwestern Washington (Monaco et al. 1992). This group, the Fjord Group, occurs within inland estuaries of Puget Sound and Hood Canal. Other estuary groupings are less evident and seem to depend more on characteristics of individual estuaries than on geographic location.
The distribution of marine invertebrates shows transitions between major faunal communities similar to those of marine fishes (Hall 1964, Valentine 1966, Hayden and Dolan 1976, Brusca and Wallerstein 1979). The primary cause of this zonation has been attributed to geographic variation in temperature (Hayden and Dolan 1976), but other abiotic (Valentine 1966) and biotic (Brusca and Wallerstein 1979) factors may also influence invertebrate distribution patterns.
The distributions of many amphibians appear to begin and end at several common geographical areas within the range of pink salmon in Washington; the Strait of Georgia and Vancouver Island are the northern extent of many amphibian distributions (tailed, Ascaphus truei, and red-legged, Rana aurora, frogs; Pacific giant, Dicamptodon ensatus, western long- toed, Ambystoma m. macrodactylum, western red-backed, Plethodon vehiculum, Oregon slender, Batrachoseps wrighti, and brown, Ambystoma g. gracile, salamanders) (Cook 1984). In addition, several amphibians are restricted to the Olympic Peninsula (Olympic torrent, Rhyacotriton olympicus, and Van Dyke's, Plethodon vandykei, salamanders), whereas other species occur in most areas in western Washington and Oregon except in the Olympic Peninsula (Pacific giant and Dunn's, Plethodon dunni, salamanders) (Leonard et al. 1993).
The U.S. Environmental Protection Agency has developed a system of ecoregion classification based on perceived patterns of factors such as climate, topography, potential natural vegetation, and soils (Omernik and Gallant 1986, Omernik 1987). Under this system, the range of pink salmon in Washington covers two ecoregions that border on salt water: the coast range ecoregion, which extends from the Strait of Juan de Fuca to Monterey Bay, from the ocean to about the crest of the coastal mountains; and the Puget lowland ecoregion, which begins in Washington at about the Dungeness River near the eastern end of the Strait of Juan de Fuca and extends through Puget Sound to the British Columbia border.
The above information indicates that the Olympic Peninsula is environmentally distinct from the rest of northwestern Washington. However, the gradients in temperature and precipitation within the range of pink salmon in Washington and southern British Columbia are not sharp ones, and, on the basis of the physical and biological factors examined here, the precise geographic boundary separating these two areas is not well defined.
Distribution and Life Cycle
Pink salmon occur around the Pacific Rim of Asia and North America north of about 40°N to greater than 70°N (Neave et al. 1967, Takagi et al. 1981). However, the spawning distribution of pink salmon is much more restricted, ranging from 48°N (Puget Sound, Washington) to 64°N (Norton Sound, Alaska) in North America and from 44°N (North Korea) to 65°N (Anadyr Gulf, Russia) in Asia (Heard 1991, Mathisen 1994; Fig. 2). In North America, pink salmon populations regularly occur in marine waters as far south as Washington State and spawn in this area as far south as Puget Sound and the Olympic Peninsula (Williams et al. 1975, WDF et al. 1993; Fig. 1). Between 70 and 80% of the Washington pink salmon spawning escapement occurs in northern Puget Sound (WDF et al. 1993, Big Eagle & Assoc. and LGL Ltd. 1995).
Pink salmon spawn during the late summer and fall in both large and small rivers; they prefer clean, coarse gravel in shallow (10-100 cm) pools and riffles exposed to moderately fast (30-150 cm/s) currents. These fish generally avoid spawning in deep, slow-moving water or on muddy, sandy, or heavily silted substrate (Heard 1991). Water temperatures during peak spawning activity range from about 5°C to 15°C and are generally higher in southern populations. This species tends to spawn closer to tidewater than other species of Pacific salmon, generally within 50 km of a river mouth (Heard 1991, WDF et al. 1993). However, populations returning to large systems such as the Fraser River and Skeena River watersheds in British Columbia migrate up to 500 km upstream to spawn, and a substantial fraction of other populations may spawn intertidally (Hunter 1959, Noerenberg 1963, Jones 1978). Pink salmon mature at the smallest average size of any species of Pacific salmon (1.0-2.5 kg) and show marked sexual dimorphism (Davidson 1935, Pritchard 1937, Beacham and Murray 1985). Spawning populations throughout much of the range of pink salmon may be extremely large, often exceeding hundreds of thousands of adult fish (Heard 1991, WDF et al. 1993).
Mortality of juvenile pink salmon in fresh water is high, ranging from about 75% to over 99%, and most of this mortality occurs before emergence from the gravel (Hunter 1959, McNeil 1966). Upon emerging from the gravel, pink salmon alevins migrate rapidly downstream, generally in schools and usually in darkness (Heard 1991). Juveniles grow most rapidly during their residence in the nearshore marine environment (up to approximately 1 mm per day and 5-6% body weight per day). Preferred prey are small crustaceans, especially euphausiids, amphipods, and cladocerans (McDonald 1960, Bailey et al. 1975). After a few weeks to a few months in estuaries and nearshore habitat, pink salmon move offshore, where they migrate at sea for 12-16 months (Heard 1991). Tagging studies suggest that southern populations from Washington and British Columbia have a more restricted oceanic migration than Alaskan populations (Takagi et al. 1981, Ogura 1994; Fig. 3).
Pink salmon do not presently occur in Idaho (Heard 1991); it is unknown whether the species occurred there historically. Along the coasts of Washington, Oregon, and California, persistent populations of pink salmon have been documented only in Washington (Ayers 1955, Herrmann 1959, Heard 1991, Mathisen 1994, H. Weeks), although pink salmon have been observed spawning in rivers in central and northern California in the past (Scofield 1916, Evermann and Clark 1931, Snyder 1931, Taft 1938, Smedley 1952, Hallock and Fry 1967). Nehlsen et al. (1991) described pink salmon from the Klamath and Sacramento Rivers in California as extinct and pink salmon from California s Russian River as at high risk of extinction.
Recent observations of pink salmon in California have been rare. No pink salmon have been observed spawning in the Russian River in recent years, but a few adult fish are observed occasionally in the Klamath River system (Moyle et al. 1995, P. Moyle). In the last 20 years, only one fish was observed in the Garcia River, and only one or two fish have been caught annually for several years in the Klamath River. Over this same period, three male pink salmon were collected from the American River, and an additional fish was observed there (Moyle et al. 1995). The capture of seven juvenile pink salmon on the Sacramento-San Joaquin River system in March 1990 is evidence that some pink salmon spawned successfully there (Moyle et al. 1995).
Adult pink salmon are rarely observed in Oregon coastal rivers, and none have been recorded in the last several years (H. Weeks). Nevertheless, successful spawning of pink salmon in Oregon has been documented in the past through the collection of juvenile pink salmon from Yaquina Bay near Newport in the late 1950s (C. Bond).
Along the north coast of the Olympic Peninsula and on the outer Washington coast, adult pink salmon are also relatively rare. Small escapements (10-100 adults) have been observed occasionally in the Sekiu, Hoko, and Lyre Rivers. As late as the early 1970s, adult pink salmon were caught in Native American setnets on the Quillayute and Hoh Rivers in both even and odd years, and some spawning (less than 500 adults) was observed a few decades ago in the Quillayute River below the confluence of the Bogachiel and Soleduck Rivers (Williams et al. 1975). At about this same time, relatively large numbers (< 1,500) of adults were observed spawning annually on riffles on both the Queets and Quinault Rivers (the length of this period is unclear). Small numbers have also been observed in several streams in the Chehalis River Basin (Williams et al. 1975).
Pink salmon are rare in the Columbia River Basin, especially upstream of Bonneville Dam. However, adult pink salmon have been observed migrating up the Columbia River past Bonneville and The Dalles Dams in small numbers (Table 1). According to the Army Corps of Engineers Fish Passage Reports for the Columbia River Basin, no adult pink salmon have been counted at dams upstream of The Dalles Dam (U.S. Army Corps of Engineers 1994). However, Basham and Gilbreath (1978) stated that several adult pink salmon were observed in 1975 at John Day Dam (45) on the Columbia River and at Little Goose Dam (12) and Lower Granite Dam (1) on the Snake River. In the same year, Basham and Gilbreath (1978) recovered five pink salmon carcasses (4 female, 1 male) from the lower Tucannon River between October 18 and November 1. The females appeared to have spawned due to the few remaining eggs in their body cavities and the erosion of the lower lobes of their caudal fins.
In 1991, a record 550 adult pink salmon were observed migrating past Bonneville Dam, and minimum pink salmon abundance for the lower Columbia River that year was estimated at nearly 1,700 adults (H. Fiscus). In that year, approximately 225 pink salmon redds were observed by Washington Department of Fisheries (WDF, now the Washington Department of Fish and Wildlife (WDFW)) biologists in the Cowlitz River, a lower Columbia River tributary. Also in 1991, 32 pink salmon were observed at Cascade Hatchery on the lower Columbia River, and one was observed in the Clackamas River.
Pink salmon have been recovered occasionally in ocean fisheries off the coasts of Oregon and southern Washington (Hubbs 1946, Bonar et al. 1989). At least some of these fish are apparently stray fish from Puget Sound streams (e.g., Van Hyning 1959). A recent review of Pacific salmon populations in Washington (WDF et al. 1993) concluded that pink salmon populations do not exist outside Puget Sound and the northern Olympic Peninsula.
This information suggests that spawning populations of pink salmon no longer occur regularly south of northwestern Washington. The remainder of this report therefore focuses on the status of pink salmon in Washington and southern British Columbia.
|The Dalles |
In addition to their small size, extreme sexual dimorphism, and lack of extended residence in fresh water as juveniles, pink salmon differ from other species of Pacific salmon in another important respect. Because essentially all pink salmon mature at 2 years of age (Gilbert 1914, Anas 1959, Bilton and Ricker 1965, Turner and Bilton 1968), this species lacks variable age structure. Two broodlines result from generations spawning in alternate years. Throughout much of the range of this species, many rivers that support pink salmon populations produce both even- and odd-year broodlines which may have arisen independently and have presumably been genetically isolated for hundreds or thousands of generations (Aspinwall 1974, Gharrett and Smoker 1991, Heard 1991). Although 1- and 3-year-old adults have been recorded (Anas 1959, Foster et al. 1981, Alexandersdottir and Mathisen 1983), almost all pink salmon are 2 years of age at maturity (Gilbert 1914, Bilton and Ricker 1965, Turner and Bilton 1968). Fish in the broodline that matures in even-numbered years are referred to as even-year pink salmon; fish in the other broodline, which matures in alternate, odd-numbered years, are referred to as odd-year pink salmon (Aspinwall 1974, Johnson 1979, McGregor 1982, Beacham et al. 1985). Even distinct broodlines in the same river differ for a variety of life history as well as genetic characteristics (Heard 1991).
The geographical distributions of these two broodlines are not random. At the southern extent of the pink salmon range in North America, odd-year pink salmon are most abundant (Atkinson et al. 1967, WDF et al. 1993). Pink salmon in southern British Columbia, including the Fraser River, are dominated by odd-year fish (Aro and Shepard 1967). British Columbia populations north of the Fraser River support both odd- and even-year populations, as do those in southeastern Alaska (Heard 1991). Even-year pink salmon dominate runs in the Queen Charlotte Islands and become more abundant than odd-year pink salmon in western Alaska (Neave 1952, Aro and Shepard 1967, Ricker and Manzer 1974). In Asia, even-year pink salmon generally become more abundant than odd-year pink salmon as latitude increases (Heard 1991). The reasons for this variation in broodline dominance remain a major unsolved problem in pink salmon biology (Ricker 1962, Heard 1991).
The relative abundance of these broodlines can fluctuate dramatically over time, even within the same system (Neave 1952, Ricker 1962). In recent decades, pink salmon south of central British Columbia have been dominated by odd-year fish (Aro and Shepard 1967, Beacham et al. 1985), and even-year fish are almost completely absent from Washington (Atkinson et al. 1967, WDF et al. 1993). Even-year pink salmon in Washington are known only from the Snohomish River on Puget Sound, where spawning escapements have ranged from a few hundred to over 2,000 fish over the last decade (WDF et al. 1993).
With the exception of those in the Fraser River, the sizes of even- and odd-year pink salmon populations in British Columbia generally increase with latitude. In odd-numbered years, large populations (100,000 spawners or more) also occur in some rivers on the east side of Strait of Georgia and Johnstone Strait (Stefanson et al. 1993); in even-numbered years, however, the largest populations occur primarily along Johnstone Strait and farther north (Aro and Shepard 1967; Gould et al. 1988; Stefanson et al. 1989, 1991). Several small populations (less than a few hundred to a few thousand spawners) of pink salmon occur in southern British Columbia, including southern Vancouver Island. On the east coast of Vancouver Island south of the Puntledge and Tsolum Rivers, populations spawning in odd-numbered years are relatively small and probably only rarely exceed a few thousand fish. On the west coast of the island, populations spawning in odd-numbered years probably rarely exceed this size south of Nootka Sound. However, escapement estimates for these populations are probably not very reliable (L. Hop Wo, W. Luedke).
Several small populations of pink salmon in southern British Columbia are not well characterized. The even-year pink salmon populations nearest to the Snohomish River appear to spawn in Vancouver Island rivers at least 130-150 km away (and perhaps considerably further), possibly in the lower Fraser River (T. Beacham), along Stuart Channel in the western Strait of Georgia, or between Sooke Inlet and Port San Juan on southwestern Vancouver Island (Aro and Shepard 1967). These areas also support the odd-year populations that appear to be nearest to Washington pink salmon populations (Aro and Shepard 1967).
Pink salmon populations vary in timing of adult migration and spawning but often lack the distinct seasonal runs observed in several other species of Pacific salmon. The return of maturing pink salmon to fresh water occurs from June to September and tends to advance with increasing latitude (Neave et al. 1967). In North America, pink salmon spawn primarily from August to October, with spawning becoming progressively later at lower latitudes (Heard 1991). Pink salmon runs in some areas can be divided into early and late components, and sometimes these components exhibit spatial separation as well (e.g., southeastern Alaska: Royce 1962, Sheridan 1962, Smoker et al. in press; Fraser River, British Columbia: Ward 1959; Asia: Ivankov 1968).
Davidson et al. (1943) characterized two general strategies of upstream migration and maturation in pink salmon: 1) immediate entry into the stream, where final maturation occurs, and a consequent delay until spawning, and 2) final maturation in the estuary, subsequent entry into the stream (often contingent on flow variation), and immediate spawning. These strategies of maturation show some evidence of being genetically based (Davidson et al. 1943; see also Smoker et al. in press). Because spawn timing may influence outmigration timing in pink salmon, and because some evidence indicates that outmigration timing affects marine survival (Taylor 1980, Mortensen et al. 1991), spawn timing is likely to be an important component of local adaptation in pink salmon as well as in other species of Pacific salmon.
In Washington and southern British Columbia, river entry occurs from July to October, and spawning is generally observed from August to October (Neave 1963, Heard 1991, WDF et al. 1993). In Washington, timing of river entry and spawning are generally earliest in northern Puget Sound and in the upper Dungeness River on the Olympic Peninsula (WDF et al. 1993).