Coastal Cutthroat Trout (Oncorhynchus clarki clarki)

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1 Coho Salmon (Oncorhynchus kisutck) Coho salmon are native to coastal streams of western North America and range throughout temperate waters of the northern Pacific Ocean. Prior to the 1900s, naturally produced coho salmon were widespread in the Columbia River basin, with a historical center of abundance in the lower Columbia River (Fulton 1970). Coho salmon supported tribal, commercial, and sport fisheries. Now there are essentially no naturally spawning fish in the basin. Because their naturally spawning numbers are low throughout their range in California, Oregon, and Washington, coho salmon have been petitioned for listing under the Endangered Species Act and are now under status review by the National Marine Fisheries Service. Early literature, reports, and accounts reveal some major historical production areas for coho salmon in the middle and upper Columbia and Snake rivers (map 4.43) (Fulton 1970; Mullan 1984). The Yakima, Wenatchee, and Methow rivers in the upper Columbia River and the Grande Ronde River system in the Snake River were major natural production areas (Fulton 1970; Mullan 1984). Fulton (1970) and Mullan (1984) also report some substantial runs in the Hood, John Day, Entiat, Okanogan, and Spokane rivers. Other reports appear to verify that historic coho runs in the Snake River also occurred in the Clearwater, Lochsa, Touchet, Tucannon, and Walla Walla rivers (Fulton 1970; Schoning 1947b). u In the Grande Ronde River, the Wenaha, Wallowa, Minam, and Lostine rivers, and Catherine Creek historically supported runs of coho salmon. Other accessible tributaries in the Columbia and Snake River systems with low gradients and sufficient water in September through November probably 'Also, personal communication Stacy Gebhards, Idaho Department of Fish and Game, Boise, Idaho. 2 Also, personal communication Chuck Huntington, Clearwater BioStudies, Inc., Portland, Oregon. supported small runs of coho salmon. The longest distance coho salmon are known to have migrated in the Columbia River was to the Spokane River, about 1,125 kilometers from the ocean (Fulton 1970). Chapman (1986) estimated the peak 5-year average of adult coho salmon that annually entered the Columbia River before 1900 was 618,000 fish, of which somewhere around 30 percent or upwards of 200,000 fish spawned in the middle and upper Columbia and Snake rivers (Mullan 1984). Wahle and Pearson (1987) indicated that less than 25,000 coho salmon were spawning naturally in the Columbia River Basin by the early 1980s. This number remained the same into the late 1980s (CBFWA 1990). Naturally spawning fish included feral hatchery fish that spawned in streams near hatcheries, returns from hatchery outplants to streams away from hatcheries, and naturally produced fish. Currently, natural coho salmon production (including hatchery spawning fish) in the Columbia River Basin above Bonneville Dam occurs in the Wind, Big White Salmon, Klickitat, Yakima, and Wenatchee rivers in Washington and the Hood, Deschutes and Grande Ronde rivers and Lindsey, Viento, Mosier, Chenowith and Mill creeks in Oregon (Johnson and others 1991). The current abundance is less than 6 percent of historic abundance (Johnson and others 1991). The in-river harvest of Columbia River coho salmon reached a peak of about 880,000 fish in 1925 (Beiningen 1976). Thereafter, an almostcontinuous decline in the fishery occurred until the 1960s, when a widespread hatchery enhancement program was initiated. Since the 1960s, the vast majority of coho salmon returning to the Columbia River have been of hatchery origin (CBFWA 1990). Habitat requirements for coho salmon were reviewed by Bjornn and Reiser (1991). Coho salmon migrate upstream at water temperatures ranging from 7.2 to 15.6 C. Spawning and egg incubation occur at water temperatures from 4 to 13 C. Adults spawn in as sorted gravels. After 1284 Aquatics

2 emergence, coho fry move into available rearing space, especially areas with lower velocities, such as stream margins and off-channel habitat. As fry grow, they rear in deeper pool habitats. Preferred summer water temperatures for rearing are 12 to 14 C, with upper lethal temperatures near 26.0 C. During winter rearing, young coho salmon seek areas with more cover, such as woody debris, root wads, and overhanging vegetation and lower velocity areas such as side channels, sloughs, and beaver ponds. Key Factors Influencing Status Human activities have profoundly influenced the past and present status of coho salmon in the mid and upper Columbia and Snake River systems. These activities have resulted in lost spawning and rearing habitat, migration delays, passage mortality, predation, diseases, water pollution, genetic introgression, and overfishing (Homer and Bjornn 1981). Habitat degradation has resulted from water withdrawals for irrigation, increased water temperatures caused by removal of riparian vegetation, and excessive sediment and simplification of stream channels from accelerated land use activities. The National Marine Fisheries Service has essentially determined that mid and upper Columbia and Snake River wild stocks of coho salmon are below levels necessary for long-term survival (Johnson and others 1991). Commercial exploitation, dams, and degradation of spawning and rearing habitat, beginning around the 1890s, dramatically reduced natural spawning populations and resulted in extirpations in much of the historical range. All middle and upper Columbia River and Snake River runs were drastically reduced or destroyed by construction of impassable mill dams, unscreened irrigation diversions, habitat loss, and over-harvest, prior to completion of the Grand Coulee Dam in 1941 (Mullan 1984). However, the advent of extensive artificial propagation in hatcheries "rebuilt" some runs to or above historic levels. In the process, coho salmon runs once dominated by naturally spawning fish have changed to predominately hatchery-maintained runs. Coastal Cutthroat Trout (Oncorhynchus clarki clarki) Historically abundant and widespread, the coastal cutthroat trout is particularly sensitive to environmental disturbance and is now in decline throughout its historic range (Trotter 1989). The coastal cutthroat trout includes both anadromous and resident forms that support popular sport fisheries. The American Fisheries Society identified all remaining populations of coastal cutthroat trout in the Columbia River as at high risk of extirpation (Nehlsen and others 1991). In July 1994, the National Marine Fisheries Service proposed to list the coastal cutthroat trout in the Umpqua Basin, Oregon as threatened. Listing was finalized in August Also in Oregon, it is listed as a state critical species by the Oregon Department of Fish and Wildlife and a sensitive species by the BLM. Coastal cutthroat trout are distributed along the Pacific Coast from northern California's Eel River to Gore Point, Kenai Peninsula, Alaska (Behnke 1979). In Oregon and Washington, they extend to the east slopes of the Cascade Mountains and in British Columbia and Alaska to the crest of the coast range. Their distribution rarely extends inland more than 160 kilometers. This geographical pattern corresponds closely with the distribution of the coastal rain forest belt in the Pacific Northwest. In Oregon, coastal cutthroat trout are distributed in almost all rivers from the Winchuck River north into the Columbia River system (map 4.44). In the Columbia River Basin, coastal cutthroat trout resided in tributaries east to Fifteenmile Creek in Oregon and Rock Creek in Washington, including the Willamette Basin to its headwaters. The abundance of sea-run cutthroat trout in the lower Columbia Basin appears to have significantly declined in recent years. Although these populations are not routinely monitored, angler surveys have shown decreases from catches of around 5,000 fish in the 1970s to catches as low Aquatics

3 Map Historical and current distribution of coho salmon. Aquatics

4 Map Historical and current distribution plus introduced sites of coastal cutthroat trout. A q u at i c s 1287

5 as 50 in the 1980s. Effective as of 1994, all wild cutthroat trout caught in the Columbia River by anglers must be released unharmed. Sea-run cutthroat trout are believed to be extirpated in the Wind and Klickitat rivers of Washington. The stocks in the Hood River of Oregon and Rock Creek in Washington are listed as at high risk of extinction. All populations in small tributaries in the lower Columbia Basin below Bonneville Dam are identified as at moderate risk of extirpation (Nehlsen and others 1991). Both anadromous and resident coastal cutthroat trout are present in the mainstem Hood River and its tributaries, including the East Fork. In the Fifteenmile Creek drainage, cutthroat trout are known to be present in Fivemile Creek and are thought to be present in Eightmile Creek. Coastal cutthroat trout exhibit diverse patterns in life history and migration. Populations of coastal cutthroat trout show marked differences in their preferred rearing environments (river, lake, estuary, or ocean), size and age at migration, timing of migrations, age at maturity, and frequency of repeat spawning. Four distinct life history patterns have been described for the subspecies: anadromous (sea-run) populations migrate to the ocean or estuary for usually less than a year before returning to freshwater; fluvial populations undergo in-river migrations between small spawning tributaries and main river sections downstream; adfluvial populations migrate between spawning tributaries and lakes or reservoirs; and nonmigratory (resident) forms occur in small headwater streams and exhibit little instream movement. Spawning occurs in riffles 15 to 45 centimeters deep in pea-sized, clean gravel in low gradient stream reaches. Spawning sites are located near or in shallow areas of deep pools close to escape cover (Hunter 1973). Newly emerged fry move into low-velocity stream margins, backwaters, and sidechannels adjacent to main channel pools and riffles (Moore and Gregory 1988). Selection of small tributaries for spawning and first-year rearing serves to isolate sea-run cutthroat trout and minimize their interactions with other salmonids. There is evidence of negative interactions among juvenile cutthroat trout, coho salmon, and steelhead during this life history stage (Bisson and others 1988; Glova 1984, 1986) which may limit sea-run cutthroat trout population size. Generally in spring, young fish move downstream into mainstem rivers and, with the onset of winter freshets, often move back upstream into smaller tributaries. In the Columbia River, smolts remain in a large estuary during their first migration. The Columbia River plume provides a large, near-shore area for feeding in the ocean. Some sea-run cutthroat trout overwinter in salt water, but most return to freshwater in the same year they migrate (Johnston 1981). Resident cutthroat trout are primarily drift feeders and reside at the head of pools (Wilzbach and Hall 1985). In forested streams, large woody debris creates productive habitat by forming pools, meanders, secondary channels, and undercut banks (Bisson and others 1987). Pools formed by large wood support more and older resident cutthroat trout, and also provide winter refugia during high flows (House 1995). Campion (1981) and Campton and Utter (1987) found genetic differences among coastal cutthroat trout stocks at four locations in Washington. If this genetic variation holds true throughout the subspecies range, then the total subspecies gene pool could be composed of literally hundreds of genetically distinct breeding units (Trotter and others 1993). Key Factors Influencing Status There are three main factors that contribute to coastal cutthroat trout declines (Trotter and others 1993): present or potential destruction, modification, or blockage of habitat by logging, urban and rural development, or mainstem passage; overharvest from recreational fishing; and negative interactions with hatchery stocks and/or introduced species. Aquatics

6 Lahontan Cutthroat Trout (Oncorhynchus clarki henshawi) The Lahontan cutthroat trout is native to the Pleistocene Lake Lahontan Basin of northwestern Nevada, northeastern California, and a small adjacent portion of southeastern Oregon. This subspecies is federally listed as threatened pursuant to the Endangered Species Act throughout its native range. It has been introduced elsewhere in southeastern Oregon and eastern Washington. Lahontan cutthroat trout are native to the McDermitt Creek drainage, a Quinn River tributary of the larger Lahontan Basin, in southeastern Oregon (map 4.45). In 1991, genetic analyses of cutthroat trout in Willow and Whitehorse creeks, also in southeastern Oregon, found the inhabitants to be genetically indistinguishable from O. c. henshawi (Williams 1991). During the 1970s, trout from Willow and Whitehorse creeks were introduced into Denio, Van Horn, Pike, Mosquito, Little McCoy, Big Alvord, Little Alvord, Cottonwood, and Willow creeks in the adjacent Alvord Basin. Surveys conducted in 1991 confirmed that Lahontan cutthroat trout still persist in many Alvord Basin streams. 3 Trout from Willow and Whitehorse creeks were also introduced into Guano Creek in 1957 (Hanson and others 1993). Lahontan cutthroat trout also have been introduced into Oregon's Mann Lake although recent information questions their genetic purity.* In addition, the Washington Department of Fisheries has widely introduced Lahontan cutthroat trout into eastern Washington. Optimal riverine habitat for Lahontan cutthroat trout is characterized as clear, cold water with an average maximum summer temperature of less than 22 C; an approximate 1-to-l poohriffle ratio; well-vegetated, stable stream banks; at least 25 percent of the stream area providing cover; a relatively stable water flow regime; and a relatively silt-free rocky substrate in riffle-run areas (USFWS 1993a). Key Factors Influencing Status Habitat degradation, especially loss of riparian vegetation, is identified as a key factor in declining Oregon stream populations. Loss of vegetation has resulted in stream temperatures that have far exceeded those considered optimal for the subspecies. Dissolved oxygen levels in such reaches are too low. Drought conditions coupled with extremely low temperatures during winter have caused stream segments to freeze completely. Loss of vegetation has resulted in the loss of forage organisms and cover (Hanson and others 1993). Excessive turbidity and sedimentation also contribute to habitat degradation problems because of their effects on food production, spawning areas, and feeding ability (Hanson and others 1993). Water diversions and the introductions of non-native salmonids are also key factors. Because native populations of Lahontan cutthroat trout in southeastern Oregon are naturally small and isolated, they are at risk. Many introduced populations are especially vulnerable because the number of founding fish was less than 30. 'Personal communication Wayne Bowers, Oregon Department of Fish and Wildlife, Hines, Oregon. Personal communication of unpublished data. ^Personal communication Ron Wiley, Bureau of Land Management, Portland, Oregon. Aquatics 1289

7 Map Historical and current distribution plus introduced sites of Lahontan cutthroat trout Aquatics

8 Sunapee Char (Salvelinus alpinus oquassa) The Sunapee char, a landlocked Arctic char endemic to Sunapee Lake, New Hampshire, was extirpated from New Hampshire in the mid-1900s as a result of competition with introduced species (Kircheis and others 1995). In 1925, prior to extirpation from Sunapee Lake, Sunapee char were introduced into two high elevation and fishless lakes in Idaho's Sawtooth Mountain Range (Kircheis and others 1995) where they established reproducing populations. The fish stocked in Idaho were not "rediscovered" until 1978 (IDFG 1991). To help protect the taxon, no further information on the location of introduction sites is provided. The American Fisheries Society listed the Sunapee char and blueback trout (a phenotypically distinct form endemic to Maine) as threatened (Williams and others 1989). Because the subspecies is introduced, Idaho does not list it as a state species of special concern. However, protection of the fish and its habitat is suggested as a priority because of its unique genotype (IDFG 1991). Sunapee char differ from other North American lacustrine char in their unique coloration, large size, and use of a mid-lake spawning shoal (Kircheis and others 1995). Kircheis and others (1995) recently examined the genetic identity of 17 Sunapee char collected from one Idaho lake. The samples displayed four haplotypes, three of them uniquely divergent from other landlocked arctic char and the other similar to a blueback char haplotype. The authors reported that the divergent portion of the Idaho char population represented a distinct, native population formerly in Sunapee Lake. Despite the unique haplotype, Kircheis and others (1995) recommended against using Idaho arctic char to restock New Hampshire waters because of the potential for dilution of the gene pool by brook trout, which were stocked in the Idaho lakes in the 1940s. The authors, however, presented no data assessing the degree of introgression with brook trout. Pygmy Whitefish (Prosopium coulteri) The pygmy whitefish may have been widely distributed across North America during the last ice age, however, once the glaciers receded only isolated populations remained. Little is known about the species in the southern range of its distribution, including Washington, Idaho, and Montana. The pygmy whitefish is listed as a Washington state monitor species. The pygmy whitefish has a discontinuous distribution in the Columbia River system. No reports have found this species to be present below Grande Coulee Dam on the Columbia River (map 4.46). In Montana, the pygmy whitefish is found in Bull Lake and Lake MacDonald and their tributaries, Flathead, Little Bitterroot, Ashley, Swan and Seeley lakes and Hungry Horse Reservoir. In Washington, the fish has been reported in Diamond Lake near Spokane and Lake Roosevelt. In Idaho, the pygmy whitefish occurs in Lake Pend Oreille and Priest Lake. No estimates of abundance are available. The pygmy whitefish inhabits lakes and cold streams. All reported data are from lakes. In Canada, fish were found in depths ranging from 4.6 to 36.6 meters (McCart 1963). The upper limit may coincide with the depth of the warmer epilimnial water. Shallower distributions in some lakes may be the result of low dissolved oxygen levels on the bottom (McCart 1963). There is no evidence of horizontal or vertical movements or change in depth distribution in pygmy whitefish with seasonal changes (Scott and Grossman 1973). Aquatics 1291

9 Key Factors Influencing Status Little is known about the distribution and abundance of the species or its ecology. One factor that may influence species abundance is chemical treatment of lakes. Increased eutrophication of lake environments, through nutrient additions from increased human development and sediment input from watershed practices, could negatively influence the species persistence. Lack of information on species distribution, abundance, and ecology at the southern edge of its range leads to a cautionary approach. If pygmy whitefish are isolated to a few lakes in the Columbia River Basin, species persistence is at risk. Burbot (Lota lota) The burbot, a freshwater member of the cod family and a popular sport fish, has a holarctic distribution that includes Alaska, much of Canada, and the northern portion of the United States from die Columbia River Basin to Maine (Scott and Grossman 1973). Within the assessment area, they are native to the Kootenai and Columbia rivers, and scattered deep lakes of eastern Washington, which represent the southern extent of their distribution in the Pacific Northwest. Burbot in the Kootenai River, Idaho, are listed as threatened by the State and as sensitive by Region 1 of the Forest Service. In Washington, Wydoski and Whitney (1979) reported burbot from the Columbia River and deep lakes in the Columbia River Basin, including Kachess, Keechelus, Banks, and Cle Elum (map 4.47). In Idaho and the Columbia River drainage of Montana, burbot are native only to the Kootenai River system, where they provided a popular winter game fishery until numbers began to decline in 1965 (Simpson and Wallace 1978). According to the Idaho Chapter of the American Fisheries Society (IDAFS 1995), Idaho Fish and Game personnel could fill trap nets set for burbot and individual anglers could catch up to 50 per night during the 1950s. Traditional Idaho spawning tributaries included Deep, Snow, Caribou, Parker, Smith, Mission, Boundary, and Myrde creeks. Stocking of burbot in Clark Fork River, Montana, has resulted in introduced populations in the Clark Fork drainage of Idaho and Montana as well as in Lake Pend Oreille. Burbot prefer clear, cold water (15.6 to 18.3"C) lakes or large rivers. In summer, they move into deeper pools or hypolimnion areas of lakes. Spawning occurs in midwinter, typically in water between 0.6 and 1.7 C. Young burbot may occur in shallow areas of lakes, large rivers, or smaller cold water streams. As burbot increase in size, they prefer deeper water and become nocturnal. Key Factors Influencing Status Populations of burbot in the Kootenai River dropped precipitously in numbers following completion of Libby Dam in Montana and associated changes in the river's hydrograph (IDAFS 1995). In the Pacific Northwest, dam construction typically leads to collapse of burbot populations below the dams, although populations may persist in the reservoirs. Impoundments and changes in river hydrographs appear to disrupt historic spawning patterns and result in reduced recruitment (IDAFS 1995). Most burbot populations in the Columbia River drainage suffer from reduced recruitment, low population densities, and fragmented populations. Sand Roller (Percopsis transmontana) The sand roller is an uncommon, poorly understood species that is endemic to larger rivers of the Columbia River system. It is a species of special concern in Idaho, and a monitor species in Washington. Historic distribution has not been fully documented but sand roller were known to occur from the Columbia River at Horseshoe Island Slough (about 40 kilometers from the mouth of the Columbia River) upstream to West Bar south of Wenatchee on the Columbia River and in the Snake River to the. Aquatics

10 lower Clearwater River in Idaho (map 4.48) (Gray and Dauble 1979). The sand roller is currently uncommon throughout its range. Within its historic range in the assessment area, it occurs in the Yakima River upstream to Ellensburg and the Umatilla and Walla Walla rivers (Pratt and Whitt 1952). It is unlikely that the fish presendy occurs in Idaho. Because of its seclusive behavior during the day, the sand roller is a difficult species to sample and may be more abundant than it appears. Little information is available to assess its current range and population size. Sand rollers seem to prefer large rivers in areas with low water velocities. Because of their seclusive nature, large numbers of sand rollers have only been observed when they enter shallow open waters to feed at night. During the day, they inhabit quiet areas near exposed roots and undercut banks with depths greater than 15 meters. Key Factors Influencing Status Several non-native predators now occupy waters in the historic and current ranges. Walleye, smallmouth bass, channel catfish, and native squawfish are known to prey on sand rollers. For instance, sand rollers were found to be the primary food of walleyes between 350 and 550 millimeters in length (Poe and others 1991). Alterations of larger rivers may degrade habitat preferred by the native species. Northern Roach (Hesperoleucus symmetricus mitrulus) The northern roach is native to Oregon and California and was classified as a subspecies of the California roach in 1948 (Murphy 1948). The California roach occurs in the Sacramento River Basin (Moyle 1976). The northern roach is currently listed as sensitive by the BLM and as sensitive (peripheral/rare) in Oregon. Historically, the northern roach was found in the upper Pit River system and tributaries to Goose Lake (map 4.49) (Moyle 1976). In the Goose Lake Basin, the fish was known only from tributaries in the Oregon side, although the actual extent of their historic distribution is poorly known. They were known to occur in Cottonwood, Drews, and Muddy creeks and were thought to be introduced in Deep and Mud creeks in the Warner Valley (ODFW 1992). Outside the Goose Lake Basin, the distribution of die northern roach has been reduced in the Pit River system (Moyle and Daniels 1982). Surveys conducted in 1983 and 1988 revealed a limited distribution of the northern roach, with populations still occurring in Thomas and Dent creeks and possibly Cottonwood Creek. 5 Northern roach have also been introduced as bait fish into Summer and Harney lakes and tributaries of die Chewaucan River (Bills 1977). The northern roach was abundant in Spring Creek, tributary to Cottonwood Creek, but is rare in odier areas. Presendy, populations are considered stable (ODFW 1992). Northern roach are generally found in small, intermittent streams with silty bottoms and containing frequent isolated pools. Water temperatures ranged from 5.5 C in March to 29 C in July. Spawning occurs from March to June (Moyle 1976). Fry remain in interstitial spaces until they are freeswimming and then move into shallow areas with moderate flow and gravel or rubble substrate. Key Factors Influencing Status Northern roach in the Goose Lake Basin are very rare. Their rarity and apparent lack of use of the lake limit their ability to recolonize extirpated streams. Conditions that would negatively affect existing stream populations include loss of surface water during extreme drought, timing of water diversions, construction of reservoirs, and introduction of non-native fishes. 'Personal communication Jack Williams, Bureau of Land Management, Boise, Idaho. Personal communication of unpublished data. Aquatics 1293

11 Map Historical and current distribution of pygmy whitefish Aquat ics

12 Map Historical and current distribution plus introduced sites of burbot. Aquatics 1295

13 Map Historical and current distribution of sand roller Aquatics

14 Map Historical and current distribution of northern roach. Aquatics

15 Alvord Chub (Gila alvordensis) Alvord chub are endemic to the Alvord Basin of southeastern Oregon and northwestern Nevada. The American Fisheries Society considers the Alvord chub to be a species of special concern (Williams and others 1989). The Alvord chub was described in 1972 based on specimens collected from Trout Creek in the Alvord Basin, Harney County, Oregon (Hubbs and Miller 1972). The species is restricted to the Alvord Basin of southeastern Oregon and northwestern Nevada, where it is widely distributed within springs, creeks, and lakes (map 4.50). Williams and Bond (1983) reported Alvord chubs from 16 localities within the basin, including Serrano Pond, Trout Creek, Alvord Lake, and Pueblo Slough in Oregon, as well as Bog Hot Creek, Bog Hot Reservoir, Thousand Creek Spring, Thousand Creek, Continental Lake, Warm Spring, Dufurrena Ponds, Gridley Springs, and West Spring in Nevada. The Alvord chub may be absent from the pluvial lake remnants of Alvord and Continental lakes during drier years. The current distribution of this species has apparently changed little during the past 100 years except for a recent report of Alvord chubs in Juniper Lake, Oregon (Bond 1974), where they were introduced and subsequently disappeared, and the extirpation of the Alvord chub population from Thousand Creek Spring. Within the Alvord Basin, the Alvord chub occurs in a wide variety of available habitats such as isolated springs, cool- and warm-water creeks, reservoirs, and lakes. Within the principal creek systems in the Alvord Basin, Trout Creek in Oregon and the Thousand-Virgin Creek system in Nevada, chubs occur commonly in the mid and lower elevation sections, but are rare or absent entirely from high elevations. Within spring systems, the Alvord chub occupies a variety of spring habitats except springs with water temperatures above 31 C. Alvord chubs are absent from Bog Hot Springs, which is fishless, and from Borax Lake, which is occupied by the Borax Lake chub (G. boraxobius). Key Factors Influencing Status Alvord chubs appear capable of occupying a wide range of habitat conditions as long as relatively clean water persists that is free of introduced species. The Alvord chub has been eliminated from Thousand Creek Spring because of the presence of introduced guppies (Poecilia reticulata). Alvord chubs are absent from some ponds at Dufurrena, which are dominated by introduced centrarchids (Williams and Bond 1983). Introductions of non-native fish and diversion of stream flows pose the greatest immediate risk to populations. Maintenance of the integrity of aquifers that feed surface waters in the Alvord Basin is critical to the long-term persistence of this species. Borax Lake Chub (Gila boraxobius) The Borax Lake chub is a small cyprinid fish restricted to the Borax Lake ecosystem of southeastern Oregon. Because of its restricted distribution and threats to its remaining habitat, it is listed as an endangered species by the U.S. Fish and Wildlife Service and State of Oregon. This species is known only from Borax Lake and associated waters in Harney County, Oregon (map 4.51). The Borax Lake chub is a sister taxon of the Alvord chub (Gila alvordensis) from which it became isolated as the waters of pluvial Lake Alvord receded (Hubbs and Miller 1972; Williams and Bond 1980). The Borax Lake chub occurs in Borax Lake, its associated outflows including Lower Borax Lake, surrounding marsh, and pools. Aquatics

16 Map Historical and current distribution of Alvord chub. Aquatics 1299

17 Map Historical and current distribution of Borax Lake chub.

18 From 1986 to 1988, population estimates for the Borax Lake chub ranged from 3,934 to 13,319 depending on the year and season (Williams 1995). 6 ' 7 Based on water conditions, hundreds of chubs also may occur in outflow creeks and, during wet years, up to a few thousand also may occur in Lower Borax Lake. 6 ' 7 The Borax Lake chub is restricted to the thermal waters of Borax Lake and its outflows. Waters flow out from the elevated rim of Borax Lake in many directions, but more typically to the southwest, where they enter a marsh and then flow into Lower Borax Lake (a reservoir). Reproduction is limited to Borax Lake; Borax Lake chubs in other habitats gain access through interconnected outflows and marshes. In Borax Lake, the species occurs throughout the lake except in hot spring inflows, where temperatures exceed approximately 34 C. Key Factors Influencing Status Threats of geothermal energy exploration and manipulation of surface flows from Borax Lake were the primary factors that resulted in the 1980 listing of the species by emergency provision under the Endangered Species Act. Changes in thermal flows that enter the lake could cause slight temperature increases or decreases that would be detrimental to the species. Alterations in surface flows from Borax Lake could isolate subpopulations adjacent to the lake causing their desiccation. Because of the restricted size of the lake, threats also exist from introductions of chemicals or nonnative species. Protection of the fragile salt crusts that maintain water level at Borax Lake is also critical (USFWS 1987). Livestock grazing and physical damage from off road vehicles and hu- 6 Also, personal communication Jack Williams, Bureau of Land Management, Boise, Idaho. Personal communication of unpublished data. 7 Also,The Nature Conservancy Unpublished data. Portland, OR: The Nature Conservancy. mans are the primary risks to shoreline salt crusts. The species is also at risk because of its highly restricted range and specialized habitats. CatlowTui Chub (Gila bicolorssp.) Catlow tui chub are endemic to the Catlow Valley of southeastern Oregon. Because of their restricted distributions and threats to remaining habitat, the subspecies is considered of special concern by the American Fisheries Society (Williams and others 1989). Historically, Catlow tui chubs occurred in three streams (Threemile, Skull, and Home creeks) that drain the west flank of the Catlow Rim and in Rock Creek along the western edge of Catlow Valley (map 4.52) (Bills 1977; Kunkel 1976). The Catlow tui chub has a restricted range, but appears to be locally abundant in streams and in Threemile Reservoir. An exception is Rock Creek, where only a few were found in Little is known about the habitat relationships of the Catlow tui chub. Their preference for low gradient reaches of Skull, Threemile, and Home creeks suggests an affinity for low velocity habitats, which is typical of most tui chubs. They also appear to be well-adapted to Threemile Reservoir, at the downstream end of Threemile Creek. Catlow tui chubs occur in streams occupied by redband trout (Kunkel 1976). Key Factors Influencing Status Diversions of creek flows for irrigation reduce Catlow tui chub habitat. The low gradient reaches that it prefers are also subject to degradation from livestock overgrazing. Because of the Catlow tui chub's restricted distribution, disturbances such as drought or fire and human land use practices place populations at risk. "Oregon Department of Fish and Wildlife Unpublished data. Hines, OR: Oregon Department of Fish and Wildlife. Aquatics

19 Map Historical and current distribution of Catlow tui chub Aquatics