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NOAA-NMFS-NWFSC TM-33: Sockeye Salmon Status Review (cont)
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INFORMATION RELATING TO THE SPECIES QUESTION

Environmental Features2

Spawning populations of west coast sockeye salmon that are the focus of this review are presently distributed over the northwest region of the contiguous United States, from the Washington-British Columbia border (49oN) south to the Deschutes River (44oN) in Oregon's interior. Climate and geological features vary markedly over this region, with diverse patterns of vegetation, weather, soils, land use, and water quality. This section summarizes environmental and biological information that may be relevant to determining the nature and extent of ESUs for sockeye salmon in Washington and Oregon.

Physical Features of the Freshwater Environment

The following discussion includes climate data from USDOC (1968) and Farley (1979), calculations of river flow patterns using U.S. Geological Survey (USGS) data from Hydrosphere Data Products, Inc. (1993), and information from Forstall (1969). Because some populations of sockeye salmon spawn and undergo early development in small tributaries, egg-alevin survival and, to a lesser degree, river- and lake-entry timing and spawn timing are sensitive to patterns in river flow. In this respect, river flow patterns and seasonal water temperature help define both early survival success and the temporal availability of access to lake habitat for these populations. Water temperatures in all regions of Washington and Oregon are generally highest in July and August (Hydrosphere Data Products, Inc., 1993). Run-timing and spawn-timing are sensitive to these factors.

Along the west coast of North America, climate varies primarily with latitude; this coastal 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. Climate in the interior basins, east of the Cascade Mountains, is greatly affected by topography and is influenced by continental air masses that bring much warmer, dryer summer conditions and colder winters than coastal areas influenced by maritime air to the west.

Columbia River Basin

Rivers draining into the Columbia River have their headwaters in increasingly dryer areas moving from west to east, as the Columbia River cuts through the 500­1,000-m-high Coast Range/Willapa Hills and the 1,000-2,000-m-high Cascade Mountains farther inland. Rivers draining into the lower Columbia River have a single peak in flow in December or January and relatively low flows in summer and fall. Rivers draining into the mid-upper Columbia River experience peak flow in spring associated with snow melt. Occasionally, rain-on-snow events in the fall give rise to widespread flooding.

Precipitation levels in the Willamette Valley in Oregon (100-120 cm/year) are much lower than those on the coast (120-240 cm/year) or in the Cascades (120-280 cm/year). Precipitation in the interior Columbia River Basin ranges from about 85 cm/year on the eastern slope of the Cascade Mountains, to between 25 and 36 cm/year in the dry central basin, and between 23 and 70 cm/year in the Snake River drainage. Water and air temperatures also reflect the more extreme climate east of the Coast Range. Maximum water temperatures in rivers draining into the Columbia River are slightly warmer (13-25oC) and minimum temperatures are slightly cooler (3-6oC) than those along the coast. Similarly, maximum (around 27oC) and minimum (around -1oC) air temperatures during the summer and winter are warmer and cooler, respectively, than along the coast. The Willamette Valley receives 2,000-2,200 hours/year sunshine, the lower Columbia River less than 2,000 hours/year, and the mid-Columbia River between 2,200-2,800 hours/year.

Olympic Peninsula

The Olympic Peninsula is much wetter (160-380 cm precipitation per year) than areas farther east and receives considerable snowfall (over 150 cm/year) at higher elevations (1,000-2,000 m). Currently, persistent spawning populations of sockeye salmon on the Olympic Peninsula are found only in watersheds draining the peninsula's western side. Many of the rivers draining the western Olympic Peninsula derive much of their water from snow and glacier melt that causes a second flow peak each year. These rivers have relatively high flows even in summer and have comparatively high annual flows. 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 10-14oC and 2-4oC, respectively, while annual maximum and minimum air temperatures are approximately 21oC and 2oC, respectively. Annual sunshine along the Olympic Peninsula coast is the lowest of anywhere in the continental United States, averaging less than 1,800 hours/year.

Coastal British Columbia

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 river flow patterns in this area are similar to those on the Olympic Peninsula, with relatively high flows throughout the year, although glacial melt-water does not contribute as much to this flow on Vancouver Island as it does on the Olympic Peninsula and mainland coastal British Columbia. There is a general decrease in summer air temperatures with increasing north latitude; the Olympic Peninsula coast is 3-5oC warmer than the southwest coast of Vancouver Island, which is 3-5oC warmer than the northwest coast and the mainland north of Vancouver Island.

Inland waters

East of the Olympic Peninsula, precipitation rapidly decreases because of the rainshadow caused by the Olympic and Vancouver Island Mountains to the north, and 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. Several Washington streams that support sockeye salmon are found in Puget Sound. This area receives rainfall of less than 120 cm/year, with some areas receiving as little as 50 cm/year. Mountains to the east and west of this rainshadow receive high precipitation (up to 280 cm/year) and have an annual snowfall of 500-1,020 cm/year. Due to snow, and in some cases glacier melt in their headwaters, rivers draining into Puget Sound, Hood Canal, and the southeastern Strait of Juan de Fuca have relatively high flows in summer and two annual high flow peaks. These flow patterns are similar to those of rivers on the western Olympic Peninsula, and limited data from western British Columbia rivers indicate similar flow patterns (Farley 1979). Occasionally, rain-on-snow events in the fall-winter give rise to widespread flooding. There appears to be a slight summer temperature cline within the northern rainshadow region; average maximum air temperatures in Puget Sound and Hood Canal (20-24oC) are slightly higher than in the Strait of Georgia (16-20oC), which in turn are higher than areas inside Vancouver Island farther north (14-16oC). In contrast, winter air temperatures are more uniform and average 0-5ooC throughout the area. Stream temperatures in the area are fairly cold, with a maximum of 12­20oC in summer and 0­4oC in winter. The greater Puget Sound area receives 2,000-2,200 hours/year of sunshine.

Physiography and geology

Sockeye salmon inhabit areas in Washington, Oregon, Idaho, and southern British Columbia that are represented by several physiographic regions: 1) the Coast Range Province, which extends in the U.S. from the Strait of Juan de Fuca south to the Klamath Mountains and from the Pacific Ocean east to Puget Sound; 2) the Puget-Willamette Lowland, which encompasses Puget Sound and the Willamette River Valley in the U.S.; 3) the Cascade Mountain Range of Washington and Oregon; 4) the Columbia Plateau, which incorporates the Columbia and Okanogan River valleys between the Cascade and Rocky Mountains in Washington; 5) the Northern Rocky Mountains in Idaho; 6) the Coast Mountains of British Columbia; 7) the Coastal Trough, which constitutes the area surrounding the Strait of Georgia and Johnstone Strait; and 8) the Vancouver Island Mountains of Vancouver Island. These regions are geologically diverse (Easterbrook and Rahm 1970, McKee 1972).

Glaciation events during the Pleistocene were instrumental in the formation of many lakes that were historically used or continue to be used as rearing habitat by sockeye salmon. Terminal moraines left behind by retreating glaciers created Quinault, Ozette, Wenatchee, Cle Elum, Kachess, Keechelus, and Wallowa Lakes; glacial scouring deepened existing river valleys that allowed formation of Okanagan,3 Osoyoos, Washington, Sammamish, and Upper and Lower Arrow Lakes (Easterbrook and Rahm 1970, McKee 1972).

Pleistocene Ice Age glaciation in the form of gigantic continental ice sheets and local alpine glaciers had a profound impact on the topography of the North Cascades, the Puget Lowland, the Olympic Peninsula section of the Coast Range Province, and the northern Columbia Plateau. Changes in climate during the Pleistocene caused several advances and retreats of the ice, and northern Washington was probably glaciated in every ice age. In the North Cascades, alpine glaciers were inundated by later advance of the continental ice sheet, whereas the South Cascades were not overwhelmed by large ice sheets, and the effects of alpine glaciers are more evident in this region than they are farther north (Easterbrook and Rahm 1970). During the last major continental glaciation event west of the Cascades, the Fraser Glaciation, the ice sheet split into two lobes; the Juan de Fuca Lobe, flowing westward, and the Puget Lobe, flowing south. This continental glaciation scoured out the deep troughs of Puget Sound and left behind extensive morainal deposits in the Puget Lowlands. The Juan de Fuca Lobe and Puget Lobe of the Fraser Glaciation heavily impacted the northern and eastern flanks of the Olympic Mountains, up to an altitude of about 915 m, but the southwestern side of the Olympics was beyond the continental glacier's reach, and evidence of the extent of alpine glaciation in river valleys of the southwestern Olympics is much clearer there. The southwestern Olympics were glaciated at least four times during the Pleistocene. Valley glaciers extended to at least the mouth of the Hoh River, to near Taholah on the Quinault River, and to near Queets on the Queets River during the Pleistocene (Easterbrook and Rahm 1970, McKee 1972). During the last, or Late Wisconsin, glaciation on the east side of the Cascades, the Okanogan Lobe of the continental ice sheet extended down the Okanogan and Columbia River Valleys to south of Lake Chelan (Easterbrook and Rahm 1970).

Physical and chemical characteristics of sockeye salmon nursery lakes

Juvenile sockeye salmon typically spend 1 or more years in the limnetic zone of a nursery lake prior to smoltification. Growth and survival while in the lacustrine environment depend on the morphological and limnological conditions of the nursery lake. Factors affecting a lake's productivity may be grouped into three major categories: morphometric, edaphic, and climatic (Rawson 1952, Northcote and Larkin 1956). Morphometric factors include lake area, volume, mean and maximum depth, and drainage area, while edaphic factors are defined by the abundance of dissolved nutrients, measured as concentrations of chlorophyll-a, total phosphorus, total nitrogen, and total dissolved solids. Climatic factors include effects of temperature, wind, and solar radiation. Values for a number of these parameters, together with distance from the sea, altitude, transparency (as measured by Secchi-disk depth), and dissolved oxygen from lakes in the Pacific Northwest are listed in Appendix Tables B-1 and B-2.

Lakes may be classified as oligo-, meso-, or eutrophic based on the relationships between nutrient concentrations, algal abundance, and water clarity (USEPA 1974). Lakes with a Secchi-disk depth greater than 3.7 m, and with less than 10 µg/L total phosphorus and less than 7 µg/L chlorophyll-a are classified as oligotrophic. Lakes with a Secchi-disk depth between 2.0 and 3.7 m, and concentrations of total phosphorus between 7-12 µg/L and chlorophyll-a between 10-20 µg/L, are classified as mesotrophic. Lakes with a Secchi-disk depth less than 2.0 m, and concentrations of chlorophyll-a and total phosphorus of greater than 12 and 20 µg/L, respectively, are classified as eutrophic (USEPA 1974). Oligotrophic lakes generally have greater diversity, but smaller populations of algal, zooplankton, and fish species, than eutrophic lakes (Brenner et al. 1990).

Lakes in the Pacific Northwest typically develop a summer thermocline resulting from solar heating, with water below the thermocline remaining colder and denser than the lighter water above it. Surface water in a thermally stratified lake is termed the epilimnion, whereas water below the thermocline is termed the hypolimnion. The hypolimnion may become depleted in oxygen as a result of natural decomposition of plant and animal matter on the lake bottom, if mixing is inhibited by thermocline formation. Lakes in the Pacific Northwest also undergo a single mixing event of the epi- and hypolimnion in the fall or winter in a process called turnover and are therefore referred to as monomictic (Brenner et al. 1990). Phosphorus is particularly important in limiting the abundance of phytoplankton, and thus zooplankton food for juvenile sockeye salmon, in Pacific Northwest lakes (Edmondson 1977b).

Several indices of fish production in lake environments have been developed, including the morphoedaphic index (MEI) (Ryder 1965, Henderson et al. 1973), the plankton-acre index (IPSFC 1972, Blum 1988), the mean-depth index (Rawson 1952), the bio-index (Northcote and Larkin 1956), the lake-surface-area index (Youngs and Heimbuch 1982), the chlorophyll-a index (Oglesby 1977), and indices based on phosphorus concentration or macrobenthos biomass divided by mean depth (Hanson and Leggett 1982). The morphoedaphic index is the most widely used index of potential fish production and is derived by dividing a lake's total dissolved solids (mg/L), or its conductivity, by its mean depth in meters to provide a metric expression of the MEI (Henderson et al. 1973). The mean depth of a lake is usually derived by dividing the lake's volume by its surface area. The level of total dissolved solids (TDS) is thought to be proportional to one of the limiting nutrients such as phosphorus or nitrogen, whereas mean depth depicts the extent of a lake's euphotic-littoral zone to some degree (Henderson et al. 1973). Relatively unproductive lakes have a low MEI, great depth, occupy U-shaped basins, and are located on firm igneous substrate, whereas productive north-temperate lakes have a high MEI, often have restricted depths, and are underlain by rich sedimentary deposits (Henderson et al. 1973). Available MEI values for selected Pacific Northwest lakes containing sockeye salmon are listed in Appendix Table B-2.

Ecoregions: Vegetation and Land Use

The U.S. Environmental Protection Agency has developed a system of ecoregions, based on the perceived pattern of factors such as climate, topography, natural vegetation, land use, and soils (Omernik and Gallant 1986, Omernik 1987). Under this system, the range of sockeye salmon in Washington, Oregon, and Idaho covers two ecoregions that border on salt water and three interior ecoregions. The Coast Range Ecoregion (containing the SASSI sockeye salmon stocks Ozette, Pleasant, and Quinault (WDF et al. 1993)) extends north and south from the Strait of Juan de Fuca to Monterey Bay, and east from the ocean to approximately the crest of the coastal mountains. The Puget Lowland Ecoregion (containing the three SASSI sockeye salmon stocks in the Lake Washington watershed (WDF et al. 1993)) begins in Washington at approximately the Dungeness River near the eastern end of the Strait of Juan de Fuca and extends through Puget Sound to the British Columbia border and up to the Cascade foothills. The Cascades Ecoregion (containing the SASSI stocks Baker River and Wenatchee (WDF et al. 1993) and the original lake habitat of Deschutes River, Oregon sockeye salmon) includes the high mountains and deeply dissected valleys of the Cascades Mountain Range in Washington and Oregon. The Columbia Basin Ecoregion (containing the SASSI sockeye salmon stock Okanogan (WDF et al. 1993)) is bordered on the west by the Cascade Mountains, on the east by the foothills of the Rocky Mountains, on the south by the Blue Mountains of Oregon, and extends north to the Canadian border through the Okanogan River valley. Finally, the Northern Rockies Ecoregion (containing Redfish Lake sockeye salmon) is comprised of the sharp ridges and steep slopes of the northern portion of the Rocky Mountains in Idaho and Montana between elevations of about 400 and 2400 m.

The Coast Range Ecoregion is forested with dense stands of Douglas fir, western hemlock, Sitka spruce, western red cedar, big-leaf maple, and red alder. Forest understories consist of herbaceous vegetation and shrubs such as rhododendron, vine maple, willow, salmonberry, and evergreen huckleberry (Omernik and Gallant 1986). Timber harvesting and logging road construction has occurred extensively throughout the northern section of the Coast Range Ecoregion, with consequent hill slope and stream bank erosion and increased stream sedimentation (Omernik and Gallant 1986).

The Puget Lowland Ecoregion is forested with Douglas fir, western hemlock, western white pine, lodgepole pine, ponderosa pine, western red cedar, big-leaf maple, and red alder. Localized habitats include prairie, oak woodland, northwestern paper birch, quaking aspen, and swamp and bog communities. Timber harvest, agriculture, and urban development are important land uses in this ecoregion. Stream water quality is affected by industrial and municipal wastes, increasing urbanization, and erosion resulting from timber harvest and road construction (Omernik and Gallant 1986).

The Cascades Ecoregion, located at an altitude between 600 and 2100 m, is densely forested with Douglas fir, noble fir, Pacific silver fir, western white pine, western hemlock, and western red cedar. Forest understories in this region consist of shrubs such as Oregon grape, salal, vine maple, rhododendron, oceanspray, huckleberry, and blackberry. At higher elevations, mountain hemlock, subalpine fir, whitebark pine and Englemann spruce predominate. Land uses are predominantly timber harvest, wildlife habitat, and recreation. Stream degradation is exacerbated by timber harvest, logging, and recreational road construction that, coupled with periods of heavy rainfall and rapid snowmelt, lead to scouring and disruption of stream habitat (Omernik and Gallant 1986).

Natural vegetation in the steppe and grassland habitat of the Columbia Basin Ecoregion consists of sagebrush, wheatgrass, and smaller amounts of bluegrass and fescue. Dryland wheat and irrigated vegetable, fruit, and pasture agriculture, together with cattle grazing, are the primary land uses in this ecoregion. Water withdrawals for irrigation and agricultural runoff, coupled with low annual precipitation, impact the quality and amount of water available to local streams (Omernik and Gallant 1986).

Natural vegetation in the Northern Rockies Ecoregion consists of stands of lodgepole pine, western white pine, western red cedar, western hemlock, western larch, Douglas fir, subalpine fir, Englemann spruce, and Ponderosa pine, with understory vegetation consisting of forbs and grasses. Wheatgrass, fescue, and needlegrass occur in localized prairie habitats. Major land uses include timber harvesting, recreation, wildlife habitat, mining, and livestock grazing on lower elevations. Stream water quality is affected by timber harvest, logging road construction, and mine waste runoff (Omernik and Gallant 1986).

Ocean Upwelling

Ocean upwelling (the movement of cold, nutrient-rich subsurface water to the surface) along the coasts of British Columbia, Washington, and Oregon is primarily wind driven (Bakun 1973, 1975). Upwelling in the area is both seasonal and episodic because winds that cause upwelling are more frequent in the spring and summer, but do not occur uniformly during those times (Smith 1983, Landry et al. 1989). Wind-driven upwelling also occurs within the Strait of Georgia, where it is similarly limited both spatially and temporally (Thompson 1981). One exception to this pattern has been observed off the southwest 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, leading to relative temporal and spatial stability.

Zoogeography

Patterns of marine and freshwater species' distributions indicate changes in the physical environment that are shared with sockeye salmon. These environmental differences may affect salmon habitat and provide different selective pressures in different areas to which salmon must adapt.

Marine fishes

Along the east coast of the North Pacific Ocean within the range considered in this status review, there is one distinct faunal boundary for marine fishes off the northern tip of Vancouver Island (approximately 50oN) (Allen and Smith 1988). Marine fishes north of 50oN are primarily cold-water, subarctic species, whereas those between 50oN and 34o30'N are primarily temperate species.

Marine invertebrates

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). Invertebrate faunal boundaries along the west coast of North America occur at approximately Dixon Entrance (between Prince of Wales Island, Alaska and the Queen Charlotte Islands, B. C.) and the Strait of Juan de Fuca (between Vancouver Island and the Olympic Peninsula). The primary cause of this zonation is attributed to temperature (Hayden and Dolan 1976), but other abiotic (Valentine 1966) and biotic (Brusca and Wallerstein 1979) factors may also influence invertebrate distribution patterns.

Freshwater fishes

Freshwater fishes in south/central British Columbia, Washington and most of coastal Oregon are of Columbia River origin (McPhail and Lindsey 1986, Minckley et al. 1986). Variations in the makeup of freshwater fish communities in these areas reflect the varied dispersal patterns of fishes between river basins. The Stikine River in northern British Columbia is the point at which freshwater fishes from the north displace the Columbia River fish fauna (McPhail and Lindsay 1986). Thus, there is no evident pattern of variation in freshwater fishes associated with sockeye salmon in Washington and southern British Columbia.

Estuarine fishes

Estuarine fishes also show regional differences based on presence or absence of species and can be roughly divided into four groups in Washington and Oregon (Monaco et al. 1992). Two groups were identified in Washington: the Fjord Group, which is restricted to Puget Sound and Hood Canal, and a second group, which is found in Grays Harbor, Willapa Bay, and the Columbia River estuary. Two other large groups, with considerable geographic overlap, extend from Willapa Bay in Washington to the Eel River estuary in California. Other estuary groupings are less evident and seem to depend more on characteristics of individual estuaries rather than geographic location.

Freshwater mollusks

Freshwater mollusks and anadromous salmonids share similar freshwater habitat and water quality requirements, while the distributions of salmonids, large prosobranch snails, and freshwater mussels are similarly constrained by the requirement for continuous waterways for dispersal (Clarke 1981). Small sphaeriacean clams and small freshwater snails are not good indicators of zoogeographic regions, as they may be dispersed when attached to bird feathers, or imbedded in mud attached to the feet of water birds. The distribution of freshwater mussels, whose larvae (glochidia) parasitize the gills or fins of fish and require fish hosts to complete their life cycle, may be particularly dependent on the distribution of host fish. Certain bivalve glochidia rely on specific species of fish as hosts, whereas others tolerate a wide range of fish hosts. Within the range of west coast sockeye salmon, glochidia of the Yukon floater mussel Anodonta beringiana parasitize the gills of sockeye and chinook salmon, while glochidia of the western pearlshell Margaritifera falcata parasitize the gills of chinook salmon and other fishes (Clarke 1981). The host fishes for other species of freshwater mussels in this region are unknown, but likely include juvenile sockeye salmon.

Five recognized species of freshwater mussels occur within the range of west coast sockeye salmon: Anodonta beringiana (Yukon floater), A. nuttalliana (winged floater), A. kennerlyi (western floater), Margaritifera falcata (western pearlshell), and Gonidea angulata (western ridgemussel). Dall (1905), Zhadin (1965), and Clarke (1981) record A. beringiana from Kamchatka to central Alaska and into the upper Yukon drainage, whereas Henderson (1929) and Ingram (1948) extend this species' range south into Oregon and include several western Washington lakes in this species' distribution including Whatcom, Samish, Washington, and Crescent. Anodonta nuttalliana (which has been synonymized with A. oregonensis and A. wahlamatensis) occurs in the Fraser and Columbia Rivers south into central California (Clarke 1981) and east into Idaho in the Snake and Spokane Rivers (Henderson 1929). It has been recorded from Shuswap, Nicola, Sumas, and Chilliwack Lakes on the Fraser River; Okanagan Lake, The Dalles, and Astoria in the Columbia River Basin; Nootka Sound on Vancouver Island; Lakes Whatcom, Sammamish, Union, and Washington in the Puget Sound lowlands; Upper Klamath Lake in Oregon; and the Sacramento and San Joaquin Rivers in California (Dall 1905; Henderson 1929, 1936; Ingram 1948; Clarke 1981). Anodonta kennerlyi occurs on the Queen Charlotte Islands south through the Skeena and Fraser Rivers, Vancouver Island, and into the Pacific drainage of Oregon. It has been seen in Quinault and Samish Lakes in western Washington, at Spokane and Yakima on the Columbia River, and in Eugene and just north of Coos Bay, Oregon (Henderson 1929, 1936; Ingram 1948; Clarke 1981). Margaritifera falcata ranges from California to the southern interior of British Columbia, to the Queen Charlotte Islands, and to Revillagigedo Island in Southeast Alaska (Clarke 1981). It has been recorded north to Naha Bay, Alaska (at 55oN); in the Fraser River; the Snake River in Idaho (Stanford 1942); at Spokane, Yakima, Walla Walla, The Dalles, and Portland on the Columbia River; in Lake Crescent and the Chehalis River on the Olympic Peninsula; in North Creek (Sammamish River drainage), Whatcom Creek, Samish River, and Snoqualmie River in the Puget Sound lowlands; in the Deschutes River (at Bend, Oregon); in the Umpqua and Coos Rivers in Oregon; and in the Sacramento River, California (Dall 1905; Henderson 1929, 1936; Ingram 1948; Clarke 1981). Gonidea angulata occurs from the upper Columbia River in British Columbia (Okanagan and Kootenai Rivers) south to southern California in rivers that drain into the Pacific. It has been recorded from Vaseux Lake on the Okanagan River; from Spokane, The Dalles, the Willamette River, and the Snake River (at Weiser, Idaho) all in the Columbia River drainage; and in California from the Klamath River south to Los Angeles (Dall 1905; Henderson 1929, 1936; Ingram 1948; Clarke 1981).

The combined range of A. beringiana, A. nuttalliana, and A. kennerlyi encompasses the range of sockeye salmon, as well as other Pacific salmon species, and may indicate either a close link in habitat requirements between this species complex of freshwater mussels and anadromous salmonids or a direct reliance by these mussels on Pacific salmonid juveniles as hosts for the larval glochidial stage. The range of M. falcata is likewise coincident with the range of sockeye salmon south of Alaska.

Three large freshwater prosobranch snails also occur within the range of west coast sockeye salmon: Juga plicifera, J. bulbosa, and J. hemphilli. The latter two species appear confined to the lower Columbia River (Burch 1989), whereas J. plicifera occupies the lower Columbia River and the Willamette and Santiam Rivers, as well as drainages on the southern Olympic Peninsula and south into northern California (Henderson 1929, 1936; Millimann and Knapp 1970; Clarke 1981; Burch 1989). Juga plicifera is the first intermediate host for the trematode Nanophyetus salminicola, which is the vector for the rickettsia-like organism Neorickettsia helminthoeca that causes "salmon poisoning disease" in dogs and other canids (Millimann and Knapp 1970).

Amphibians

Although most amphibians are not restricted to aquatic habitats, and therefore have little direct habitat overlap with sockeye salmon, many amphibian species have very restricted distributions, suggesting preferences for specific habitat types and environmental conditions. Because of this sensitivity, patterns of amphibian distributions may serve as indicators of subtle differences in environmental conditions.

The distributions of many amphibians appear to begin and end at several common geographical areas within the range of sockeye salmon in Washington; the Strait of Georgia and Vancouver Island are the northern extent of many amphibian distributions (tailed and red-legged frogs; Pacific giant, western long-toed, western red-backed, Oregon, and brown salamanders) (Cook 1984). In addition, several amphibians are restricted to the Olympic Peninsula (Olympic torrent and Van Dyke's salamanders), whereas other species occur in most areas in western Washington and Oregon except in the Olympic Peninsula (Pacific giant and Dunn's salamanders) (Leonard et al. 1993).



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