Contributors (in alphabetical order)
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Smallmouth bassSmallmouth bass is one of the more abundant and widely distributed species in the lower Snake River reservoirs (Bennett et al. 1997) and an important sport fish (Normandeau Associates et al. 1998a). However, limited research has been conducted on the life history of smallmouth bass in the Lower Snake River. Two known estimates of the absolute abundance of smallmouth bass have been conducted in lower Snake River reservoirs. Anglea (1997) conducted multiple-census estimates during 1994 in Lower Granite Reservoir and reported 20, 911 bass greater than 174 millimeters (6.8 inches) (95% CI -17,092 to 26,197). Using an estimate of 0.47% survival, Anglea (1997) estimated that the population abundance of smallmouth bass greater than 70 millimeters (2.8 inches) in Lower Granite Reservoir was 65,400 (95% CI -61,023 to 71,166). Standing crop was estimated at 0.75 kilogram/hectare (0.44 lb/acre) for bass greater than 199 millimeters (7.8 inches), and density was 3.4 smallmouth bass/hectare (1.4 bass/acre) throughout the entire reservoir. More recently, Naughton (1998) estimated the absolute abundance of smallmouth bass in the Lower Granite Dam tailwater (Little Goose Reservoir), the forebay, Clearwater River, and Snake River arms of Lower Granite Reservoir. He found that densities were highest for smallmouth bass greater than 174 millimeters (6.8 inches) in the forebay of Lower Granite Reservoir (12.7 bass/hectare), followed by the Clearwater River Arm (12.5 bass/hectare [5.1 bass/acre]). His estimates of standing crop compared closely to those of Anglea (1997). Although absolute abundance has not been estimated for Lower Monumental and Ice Harbor reservoirs, studies by Zimmerman and Parker (1995) have shown that Lower Granite Reservoir supports the highest density and relative abundance of smallmouth bass among Snake River reservoirs. However, these estimates of abundance of smallmouth bass are generally lower than those reported by investigators for other geographical areas. For example, Paragamian (1991) reported densities of 2 to 911 smallmouth bass/ha (0.8 to 369 bass/acre) for 22 waters throughout Iowa, and Carlander (1977) reported densities no less than 16 smallmouth bass/ha (6.5 bass/acre). These findings demonstrate that smallmouth bass are comparatively low in abundance in lower Snake River reservoirs compared to other waters throughout their range. The spawning season of smallmouth bass in lower Snake River reservoirs is generally later than reported elsewhere. Bratovich (1983) reported on the reproductive cycle of smallmouth bass from examination of gonads in Little Goose Reservoir in 1979 and 1980. The largest ovaries were measured in April, and the reported time of spawning based on ovarian condition was in May, June, and July. In contrast, Pflieger (1975) reported smallmouth bass spawning in Missouri as early as the first of April. Henderson and Foster (1957) observed smallmouth spawning in the Columbia River until the latter part of July. Bennett et al. (1983) suggested a spawning period of longer than 60 days, similar to that reported for Missouri (Pflieger 1975). Other observations suggest spawning largely occurs in June and July, based on attainment of suitable water temperatures of about 15.9°C (60.6°F) (Coble, 1975). Bennett et al. (1983) observed spawning to occur over a range of temperatures from 14 to 19.6°C (57 to 67°F), within the full range of water temperatures reported in the literature (12.8 to 26.7°C [55 to 80°F]); Henderson and Foster 1957; Reynolds 1965) for smallmouth bass. Others have reported spawning temperatures of 15 to 18.3°C (59 to 65°F) (Turner and McCrimmon 1970; Coble, 1975; Pflieger 1975; Coutant 1975). Habitat used for spawning is largely gravel substrate, highly abundant along the shorelines of the lower Snake River reservoirs. Substrate used by smallmouth bass for spawning in Little Goose Reservoir was similar to that reported in the literature (Bennett et al., 1983). All observed smallmouth bass spawning activity in Little Goose Reservoir was on low-gradient shorelines of sand and/or gravel, with 85% of spawning nests on gravel 6 to 50 millimeters (0.25 to 2.0 inches) in diameter. Spawning areas in Little Goose Reservoir were frequently found in gulch and embayment habitats in the lower reservoir. The areas were generally protected from direct wind and wave action with little to no perceptible current. In the upper reservoir, smallmouth bass nests were more commonly observed in shoal areas that were usually exposed to wind and wave action and/or higher water velocities. Differences in habitats used were attributed to the paucity of gulch and embayment habitats in the upper reservoir (Bennett et al., 1983). Bennett and Shrier (1986) reported that smallmouth spawning nests were located in Lower Granite Reservoir from the confluence of the Snake and Clearwater rivers downstream nearly to Lower Granite Dam. Highest nest abundance was in the lower part of the reservoir where water velocities were lowest. Fluctuating water levels and water temperatures may adversely affect smallmouth bass in Lower Granite Reservoir. Bennett et al. (1994) suggested from their research that cold upstream water releases from Dworshak Reservoir in 1991 and 1992 probably had only a minimal effect on smallmouth bass growth and survival and, consequently, year-class strength. However, operational water level fluctuations up to 1.5 meters (5 feet) in Little Goose Reservoir may affect the vertical distribution of spawning activity by smallmouth bass. Most spawning activity of smallmouth bass (and other centrarchid fish) occurs in water of 2 meters (6.6 feet) or less (Bennett 1976). Most bass nests have been reported in water from 0.3 to 2 meters (1 to 6.6 feet) (Scott and Crossman 1979; Coble 1975), although smallmouth have been reported to spawn at depths of 6.7 meters (22 feet) in clear water (Trautman 1981). The deepest smallmouth bass nests reported for Little Goose Reservoir were 5.3 meters (17.4 feet) (relative to full pool), although 84% were located at depths of 2 meters (6.6 feet) or less. In 1980, Bennett et al. (1983) found that 27% of all nests located were desiccated by fluctuating water levels in Little Goose Reservoir, although 75% of all spawning nests were located within the 1.5-meter (5-foot) fluctuation zone. Bennett et al. (1983) suggested that periods of high, stable water levels during the spawning season, followed by pronounced reduction in water levels, may have deleterious effects on the spawning success of smallmouth bass in Little Goose Reservoir. Vertical fluctuations of similar magnitude can also occur in Lower Granite Reservoir, whereas those in Lower Monumental and Ice Harbor reservoirs are about 0.5 meter (1.6 feet) lower (i.e., limited to about 0.9 meters [3 feet]). Spawning of smallmouth bass in the latter reservoirs has not been investigated. Food items of smallmouth bass have been intensively examined in Little Goose and Lower Granite reservoirs. Bennett et al. (1983) found that smallmouth bass (n=484) consumed crayfish, fish, and terrestrial and aquatic insects in decreasing order of importance in Little Goose Reservoir during 1979 and 1980. Crayfish accounted for 72% by volume of the food items eaten and appeared in 64% of all bass stomachs. Fish consumed accounted for 25.4% by volume and were found in 32% of the smallmouth bass stomachs that contained food. Fish eaten were sculpin, white crappie, redside shiner, northern pikeminnow, catfish, bluegill, yellow perch, chinook salmon, bridgelip sucker, and pumpkinseed. Anglea (1997) examined food items from over 4,000 smallmouth bass in Lower Granite Reservoir. Crayfish were consistently the dominant food item in Lower Granite Reservoir in 1995, although salmonids and other fish accounted for nearly 50% of the diet in the spring. He found that fish were the most important food item, by weight, from April to June 1994 and 1995, whereas crustaceans and insects increased in abundance after June. As others have reported, larger smallmouth bass consumed a higher proportion of fish. Crayfish were the most abundant food item by weight for smallmouth bass from 175 to 249 millimeters (6.9 to 9.8 inches), while finfish and crayfish were equally important for bass from 250 to 389 millimeters (9.8 to 15.3 inches). Fish were the dominant food item of smallmouths greater than 389 millimeters (15.3 inches). Bennett and Naughton (1998) examined greater than 8,500 smallmouth bass stomachs from the tailwater, forebay, and Snake and Clearwater River arms of Lower Granite Reservoir in 1996 and 1997. They found that non-salmonid fish were the most abundant prey item by weight in the tailrace (46.9%), tailrace BRZ (71.6%), forebay BRZ (51.5%), and Clearwater River arm in 1996. In contrast, during 1997, crayfish were clearly the dominant food item by weight in the tailrace (73.4%), tailrace BR (60.8%), forebay (58.8%), and Snake River arm (50.3%). Monthly differences in food items were low within study sites. From these findings, it is obvious that smallmouth bass in Lower Granite, Little Goose, and probably other lower Snake River reservoirs consume a large number of crayfish, similar to that reported in the literature for other river and lake systems. The 1997 sport fishing catch (kept and released) of smallmouth bass was highest in Lower Granite (greater than 10,000 fish) and Little Goose (greater than 8,000 fish) reservoirs, while the sport harvest (kept only) of smallmouth bass varied more than fourfold among reservoirs. Lower Monumental and Little Goose reservoirs yielded the largest smallmouth bass harvests (2,802 and 2,762 bass, respectively), whereas anglers in Ice Harbor Reservoir harvested less than 700 fish (Table 36). Table 36. Estimated sport fishing harvest of selected fish in Lower Snake River reservoirs from April to November 1997 (Corps 1999).
CrappieBlack crappie and white crappie are two of the more important sport fish in backwater habitats in the lower Snake River reservoirs (Knox 1982; Normandeau Associates et al. 1998a). They are highly habitat-specific in the reservoirs and are chiefly limited to embayment areas off the main channel. The species co-occur throughout the reservoir system, but only in Little Goose Reservoir was there apparent dominance by white crappie (Bennett et al. 1983). The white crappie is more tolerant of turbidity and siltation than other centrarchid fish, although it is less competitive in clear waters (Carlander 1977). Limited life history information has been collected on crappie, primarily in Little Goose Reservoir (Bennett et al. 1983). Relative abundance of crappie has been determined for each of the lower Snake River reservoirs, and absolute abundance was determined for Deadman Bay in Little Goose Reservoir. Crappie ranged from about 20% of the fish community in Little Goose Reservoir to about 5% in Lower Granite Reservoir. Their relative abundance is directly related to habitats sampled during the abundance surveys. Crappie attains highest abundance in backwaters and, therefore, attained highest relative abundance in Little Goose Reservoir. Bennett et al. (1983) conducted the only known population dynamics studies on crappie in lower Snake River reservoirs. A multiple-census population estimate in Deadman Bay found that white crappie was the most numerous species (Table 37). Density and biomass estimates for white crappie ranged from 158 to 200 fish/hectare (64 to 81 fish/acre) and 26.7 to 33.8 kilogram/hectare (23.8 to 30.2 lb/acre), respectively, while those for black crappie were about 85% less. Catches of black crappie were higher in the main channel areas of Little Goose Reservoir, while catches were higher for white crappie in backwaters. Table 37. Estimates of population density (Number/Area) and standing crop (Biomass/Area) for selected centrarchid fish in Deadman Bay, Little Goose Reservoir (Corps 1999).
Growth increments and condition factors of crappie from the lower Snake River reservoirs were similar or better than those for comparable geographical areas (Bennett et al. 1983). Growth increments were not significantly different among reservoirs, although growth of black crappie was slightly slower than that of white crappie. Differences in growth between white and black crappie were attributed to higher water temperatures in backwaters where white crappie predominate, as well as the greater consumption of fish by white crappie. Food of white crappie in the lower Snake River reservoirs was similar to that reported in the literature. Cladocerans were the dominant food item of white crappie in the summer, and fish became more important in the fall in Little Goose and other lower Snake River reservoirs (Bennett et al. 1983). Dietary items of black crappie were similar to those of white crappie. Time of spawning for crappie is typically later in the north than in the south (Hardy 1978). Bratovich (1983) found white crappie in the lower Snake River reservoirs in spawning condition from June into August, similar to Nelson et al. (1967), who found the white crappie spawning season extended from mid-May through mid-July in Lewis and Clark Lake, Missouri River, on the Nebraska-South Dakota border. Hjort et al. (1981) reported white crappie spawning ranged from late May to late July in John Day Reservoir on the Columbia River. From late May to late July, water temperatures in the lower Snake River reservoirs ranged from 15.8 to 20.4°C (60 to 69°F) (Bennett et al. 1983). Published reports generally consider 16 to 21°C (61 to 70°F) optimal for white crappie spawning (Nelson et al. 1967; Siefert 1968). Spawning times for black crappie in the lower Snake River reservoirs were June and July, compared to early May to mid-July in John Day Reservoir (Hjort et al. 1981). Water temperatures in the lower Snake River reservoirs during the time when black crappie were in spawning condition ranged from 15.8 to 19.6°C (60 to 67°F). These water temperatures were a little cooler than those generally reported suitable for black crappie spawning (19 to 20°C [66 to 68°F]); Scott and Crossman 1979). The most recent sport harvest data for crappie varied among reservoirs by more than two orders of magnitude. The largest harvest was in Little Goose Reservoir (15,523 fish), compared to an estimated 204 crappie harvested from Ice Harbor Reservoir. SuckersSuckers are the most abundant fish in the lower Snake River reservoirs (Bennett et al. 1983; 1987; 1990). Largescale suckers are about two times more abundant than bridgelip suckers in Little Goose and Lower Monumental reservoirs and two orders of magnitude higher in Lower Granite and Ice Harbor reservoirs. The high abundance of suckers throughout the reservoirs suggests that both species are habitat generalists. The greater overall abundance of largescale sucker relative to bridgelip sucker suggests that habitat requirements for bridgelip sucker might be somewhat narrower than for largescale sucker. Bridgelip sucker was classified as a mesotherm, with narrower temperature requirements than largescale sucker, although their generalized distribution within a river continuum was similar (Li et al. 1987). The seasonal distribution of suckers in Lower Granite Reservoir can be inferred from data presented by Bennett et al. (1993), although spring catches are dissimilar with findings in Little Goose Reservoir (Bennett et al. 1983). Both species were primarily sampled in shallow waters in Lower Granite Reservoir during the spring of 1990. In 1980, however, captures of bridgelip sucker were highest in deepwater areas of Lower Granite Reservoir in the spring, while largescale suckers were more evenly distributed among deepwater areas and shallower shoal and gulch habitat. Both species were widely distributed throughout the water column in summer and fall based on gill net captures at deepwater stations. Bennett et al. (1983) also showed a tendency of both bridgelip and largescale suckers to move to the tailwaters of Lower Granite, Little Goose and Lower Monumental dams in the fall. Bennett et al. (1983) conducted the only known estimates of absolute abundance of suckers in the lower Snake River reservoirs. They estimated about 9,000 largescale suckers in Deadman Bay of Little Goose Reservoir in 1980, with a density of 172 fish/ha (70 fish/acre) and estimated standing crop about 156 kilograms/hectare (139 lb/acre). Little information is available on the spawning of bridgelip or largescale suckers in the northwest. Dauble (1980) found that bridgelip suckers spawn from March to June, with most spawning in the Columbia River occurring during April. Water temperatures in the lower Snake River reservoirs that coincided with the presence of ripe bridgelip suckers ranged from 10.2 to 12.2°C (50.4 to 54°F) (Bennett et al. 1983). Dauble (1980) reported spawning from 6 to 13°C (43 to 55°F) in the Columbia River. Bennett et al. (1983) found largescale suckers in spawning condition in May and June, similar to that reported by Scott and Crossman (1979) for British Columbia. MacPhee (1960) reported that largescale suckers spawn in the North Fork Payette River, Idaho, in mid-to late June, whereas Hjort et al. (1981) reported largescale sucker spawning from early May to early August in the lower Columbia River. Water temperatures in the lower Snake River reservoirs were 12.2 to 15.8°C (54 to 60°F) compared to 7.8 to 8.9°C (46 to 48°F) for stream-spawning largescale suckers in British Columbia (Scott and Crossman 1979). Food of suckers has been reported to be primary producers such as diatoms and filamentous green algae and benthic invertebrates (Carlander 1977; Li et al. 1987). Bennett et al. (1983) conducted stomach analyses of bridgelip and largescale suckers and found predominantly diatoms and green and blue-green algae in the stomachs of each species. Macroinvertebrates were relatively minor food items. Few seasonal differences were found, although detritus and blue-green algae increased in abundance from spring to winter. Anglers usually catch suckers only incidentally while fishing for other species. A few anglers, more typically in the mid-Snake River upstream of Asotin, catch suckers for bait for white sturgeon (Normandeau Associates et al. 1998b). Northern PikeminnowThe northern pikeminnow is a species of great interest in the Columbia River basin because of its predatory habits pertaining to downstream migrating juvenile salmonids (Poe et al. 1991). There has been substantial recent work detailing the food habits (Zimmerman and Ward 1997), predatory role (Zimmerman and Ward 1997), exploitation rates (Friesen and Ward 1997), and population and growth parameters (Parker et al. 1995; Knutsen and Ward 1997) for this important species in Snake River reservoirs. However, limited life history information exists relative to spawning and reproduction. Smith (1996) recently completed an analysis of the incidence of chiselmouth x northern pikeminnow hybrids in the Lower Snake River. F1 hybrids are present in the system, with 33% of the hybrids having chiselmouth maternity and 67% having northern pikeminnow maternity. His work demonstrated how morphological characteristics could be used to assess accurate species identification. The northern pikeminnow spawns from mid-May to late June in lower Snake River reservoirs (Bennett et al. 1983), somewhat earlier than reported by Hjort et al. (1981) for John Day Reservoir, Columbia River (June to August). In other areas, northern pikeminnow reportedly spawn from May to early July (Carl et al. 1959), both in lakes and tributary streams (Jeppson and Platts 1959; Patten and Rodman 1969). In Cascade Reservoir, central Idaho, Casey (1962) reported that northern pikeminnow spawn during June, with peak spawning activity in the latter part of June. Water temperatures at the time of spawning in Snake River reservoirs ranged from 14.0 to 20.4°C (57.2 to 68.7°F), similar to those reported by Casey (1962, 14.5 to 16.7°C [58.1 to 62°F]) and Stewart (1966, 18.0°C [64.4°F]). Other than the time of spawning, little other information is available on spawning habits of northern pikeminnow in any of the Snake River reservoirs. Bennett et al. (1994) and Cichosz (1997) have emphasized the importance of the early rearing period to year-class strength and recruitment. Cichosz (1997) examined what factors limit the abundance of northern pikeminnow in Lower Granite Reservoir. He found that their abundance is probably determined in the egg-through-larval stage, although juvenile mortality is also important. Density independent factors were most important in controlling egg-through-juvenile survival. Timing of water temperature conditions was most important in predicting survival of northern pikeminnow. Survival was also positively related to growth. Dresser (1996) examined the influence of habitat factors on fish assemblages in Lower Granite Reservoir. Through the use of multivariate analysis, he reported that the northern pikeminnow selected shallow, vegetated habitats with substrate sized less than 2.0 millimeters (0.08 inches). These findings were considerably different from those of Dupont (1994) who found that the northern pikeminnow in the Pend Oreille River, Idaho, selected rocky shorelines with deeper depths and higher water velocities. Dresser (1996) believed differences in selected habitats could be attributed to interactions with other species, particularly smallmouth bass. Smallmouth bass are not present in the Pend Oreille River. Habitat types occupied by the northern pikeminnow in the Pend Oreille River are occupied by smallmouth bass in Lower Granite Reservoir. Further, some evidence supports the hypothesis that predation on northern pikeminnow by smallmouth bass may account for differences in habitat use. Werner et al. (1997) reported that predation on small size classes may result in habitat segregation. Pollard (Idaho Department of Fish and Game, retired, personal communication, Portland, Oregon) observed that the abundance of northern pikeminnow decreased following the introduction of smallmouth bass into Anderson Ranch Reservoir, Idaho. He further suggested that similar habitats inhabited by the northern pikeminnow in Brownlee Reservoir, Idaho, were void of them following the introduction of smallmouth bass. Since most northern pikeminnow collected by Dresser (1996) were 120 to 250 millimeters (4.7 to 9.8 inches), and the smallmouth bass ranged in length from 100 to 520 millimeters (3.9 to 20.5 inches), his explanation seems plausible. The influence that northern pikeminnow have on downstream migrating salmonids has been a concern for over a decade in the Columbia River system. A number of studies have been conducted to investigate northern pikeminnow predation in the lower Snake River reservoirs. Chandler (1993) provided the initial quantification of actual predation on downstream migrating salmonids in Lower Granite Reservoir. Chandler (1993) found that salmonids were the most abundant food item (by weight) consumed by northern pikeminnow during spring from 1987 to 1991. Crayfish were second in importance. Year-to-year variation in salmonid consumption was high. Ward et al. (1995) found that northern pikeminnow abundance and consumption of salmonids were higher in the lower Columbia River than in the Snake River. Among Snake River habitats sampled, the consumption index was higher in the Lower Granite Reservoir forebay and in tailwaters of Ice Harbor, Lower Monumental, and Little Goose reservoirs. Ward et al. (1995) correlated biological characteristics of northern pikeminnow populations and found a significant correlation only of density with relative fecundity, implying that northern pikeminnow populations were not limited by density. Sport anglers pursue northern pikeminnow largely in Lower Granite Reservoir, mostly due to the bounty paid by the sport reward program (Freisen and Ward 1997). Harvest in Lower Granite Reservoir was approximately 1,500 fish (although most were in the Snake River arm), and less than 260 fish in the other reservoirs. White SturgeonLimited information exists on the white sturgeon in the lower Snake River system. No known information exists on spawning activities of white sturgeon in the lower Snake River reservoirs. However, Parsley and Beckman (1994) quantified spawning habitat in three of the lower Columbia River reservoirs by using a geographic information system. They showed that spawning habitat was available downstream of each of the dams, although the quantity of available habitat was affected by flow variability. Rearing habitat for age 0 and juvenile white sturgeon was also quantified and found to be more available in the impounded river than in the unimpounded reach below Bonneville Dam. Samples of numerous juvenile white sturgeon (less than 16 centimeters [6.3 inches]) suggest that juvenile rearing habitat is probably highly abundant in Lower Granite Reservoir (Bennett et al. 1993). Additionally, Bennett et al. (1994) concluded that the flowing water section of the Snake River above Lower Granite Reservoir may provide spawning habitat and ultimately could be a recruitment source for downstream reservoirs. Data collected in 1992 before and after the test drawdown indicated white sturgeon moved from Lower Granite Reservoir to the upstream portion of Little Goose Reservoir. However, Bennett et al. (1994) could not determine whether this movement was stimulated by the drawdown or occurred following the drawdown. Rearing habitat for white sturgeon seems to be linked to water velocity. Apperson (1990) suggested that white sturgeon in the Kootenai River, Idaho, were found at water velocities between 0.05 and 0.56 meters/second (0.2 and 1.8 feet/second). Velocities in this range were found exclusively in the upper portion of Lower Granite Reservoir, the reach with the highest abundance of white sturgeon. Deep, slack water in Lower Granite Reservoir, and probably in other lower Snake River reservoirs, did not provide suitable habitat, and captures have been consistently low. Lepla (1994) conducted the most comprehensive study on white sturgeon in the lower Snake River reservoirs on Lower Granite Reservoir, including the only known population estimate among the reservoirs. He estimated that 1,524 (95% CI -1,155 to 2,240) white sturgeon greater than 40 centimeters (15.7 inches) (fork length) inhabited Lower Granite Reservoir. White sturgeon density was estimated at 0.38 fish/hectare (0.15 fish/acre), or 12 to 45 sturgeon/rkm (19 to 73 sturgeon/rm). The density estimate was generally similar to that of Lukens (1985; 24 sturgeon/rkm 39 sturgeon/rkm) but lower than those of Coon et al. (1977) who reported 35 to 53 sturgeon/rkm (56 to 85 sturgeon/rm) between Lower Granite and Hells Canyon dams. Lepla (1994) sampled nearly 1,000 white sturgeon and examined habitat use. He found that 94% of the white sturgeon in Lower Granite Reservoir were less than 125 centimeters (49 inches) total length (TL) with the majority in the 0 to 8 age group. Lepla (1994) developed a stepwise discriminate model to explain white sturgeon distribution but could account for only 26% of the variation in distribution using habitat data. However, he found 56% of all fish sampled were from a 5.5-kilometer (3.4-mile) reach near Clarkston, Washington, (Port of Wilma to Red Wolf Crossing) in upper Lower Granite Reservoir. Catches in the mid-to-lower reservoir were consistently low. Coon (1975) also suggested the importance of moving water to white sturgeon, based on tracking fish with sonic tags. Implanted white sturgeon moved to the upstream portion of Lower Granite Reservoir during the impoundment process and resided in the same area near Clarkston, Washington, as the majority of fish sampled by Lepla (1994). Crayfish relative abundance has been quantified in Lower Granite Reservoir and its distribution appears very similar to that of white sturgeon (Bennett et al. 1993; Lepla, 1994). Crayfish are reportedly an important food item of white sturgeon in the Snake River (Coon et al. 1977; Cochanuer 1983). Bennett et al. (1993) could not ascertain whether higher crayfish abundance in up-reservoir areas was responsible for the upstream abundance of white sturgeon, or whether both species had similar habitat preferences. The sport harvest of white sturgeon is largely restricted to Little Goose Reservoir (Normandeau Associates et al. 1998a). Nearly 600 were caught, but estimated harvest was 40 individuals. Channel CatfishReasonably good information exists on the relative abundance of channel catfish in the lower Snake River reservoirs, although absolute abundance is unknown. Bennett et al. (1983) recorded the first known estimates of abundance from samples collected in 1979 and 1980. Their study indicated that channel catfish attained highest relative abundance in Ice Harbor Reservoir (5.8%), followed by Little Goose (2.8%) and Lower Monumental (2.5%) reservoirs. Abundance in Lower Granite Reservoir was considerably lower than in the other three reservoirs. The abundance of channel catfish in Little Goose Reservoir was significantly correlated with the abundance of several other species. The highest correlation of channel catfish abundance was with brown bullhead and bluegill, suggesting its abundance in backwater habitats is highest where these other species attain high abundance. Bennett et al. (1983) reported seasonal differences in the relative abundance of channel catfish. In the spring, 71% of the channel catfish in Little Goose Reservoir were collected from the Lower Granite Dam tailwater, whereas in the summer and fall, channel catfish were more highly abundant in lower embayment and gulch habitats. In general, the smallest catfish were collected from embayment habitats whereas the largest individuals were captured in the tailwater of Lower Granite Dam. Channel catfish distribution was not greatly different among habitats in Lower Granite (n = 8), Lower Monumental (n = 227), and Ice Harbor (n = 467) reservoirs from spring to fall, although seasonal differences may have obscured any habitat preferences. Growth of channel catfish in Little Goose Reservoir was deemed comparatively rapid (Bennett et al. 1983). Growth was more rapid during the first 6 years of life than in subsequent years. Bennett et al. (1983) suggested that growth increments increased since 1969, possibly a result of higher vulnerability of salmonid smolts downstream of Lower Granite Dam. Growth increments of channel catfish were significantly smaller in Ice Harbor Reservoir than either Lower Monumental or Little Goose reservoirs. The growth increments reported were similar to those for channel catfish in the midwestern United States, which was surprising because of below optimum Snake River water temperatures. Kilambi et al. (1970) reported 32°C (89.6°F) as the optimum temperature for growth, whereas the highest water temperatures in the lower Snake River reservoirs are typically 5-10°C (9 to 18°F) lower. These temperatures were taken in slack water areas and are higher than average high temperatures in the main reservoirs. Food of 452 channel catfish (92 to 649 mm [3.6 to 25.6 inches]) was also examined by Bennett et al. (1983). They found that fish, aquatic insects, crayfish, wheat, and cladocerans were the more important food items. Food items varied with sampling location. Seasonally, fish was the predominant food item in the spring. Predation on downstream migrating juvenile steelhead and chinook salmon was high in the spring, especially in samples taken from the Lower Granite tailwater. In the summer, crayfish, cladoceran zooplankton, and aquatic insects were important food items. More recently, Bennett et al. (1988) examined food items of channel catfish in Lower Granite Reservoir. They found that fish constituted 42% by weight of the food items during spring 1987. Rainbow trout, presumably juvenile steelhead, comprised 38% of the weight of fish consumed and juvenile chinook salmon about 1%. Chironomidae comprised about 29% of the remaining items of the diet in spring and 60 and 85%, respectively, of the channel catfish diet in the summer and fall. Juvenile salmonids comprised about 1% of all food items in the fall. The highest sport harvests of channel catfish in 1997 occurred in Little Goose (5,654 fish) and Ice Harbor (5,607 fish) reservoirs. In contrast, the harvest in Lower Granite Reservoir was estimated at only 228 fish. Bull TroutSeveral subpopulations of bull trout occur upstream of the reservoir influence of Lower Granite Dam. Representatives from these subpopulations have the capability of freely moving to and from Lower Granite Reservoir. These groups include fish from Asotin Creek, and the Grande Ronde, Imnaha and Salmon rivers. There is little evidence to suggest these populations use habitat associated with the reservoirs in the Lower Snake River. Radio tracking data from Elle et al. (1994) and Elle (1995) showed that adult migrants from the Rapid River subpopulation typically overwinter in the main stem Salmon River as far downstream as Whitebird, but a few may move as far as Mahoney Creek. None of these fish have been observed in the Snake River. Buchanan et al. (1997) suggested that some migrants from the Grande Ronde still utilize the Snake River. Recent observations of radio-tagged bull trout from the Grande Ronde River verified the use of the Snake River by those fish as far down as RM 146, just upstream from Asotin, WA (Shappart, ODFW, personal communication, 2000). Underwood et al. (1995) suspected that radio tagged fish migrated from the Tucannon River to the Snake River, but they could not locate the fish in the reservoir. In the lower reaches of the Imnaha River, large migrant sized bull trout are incidentally caught by steelhead anglers each year, and ODFW believes these fish are migrants that use the Snake River seasonally (Knox, ODFW, personal communication, 2000). The most compelling evidence is data from the Idaho Fish and Game smolt trap at Lewiston. It indicates the capture of an occasional bull trout (Basham, in litt. 2000), but the catch rates have been no more than one bull trout annually. Other FishesSeveral species of fish in the Snake River reservoirs occur in lower relative abundance than the key species. Some of these are native fish, while many others were introduced into the Snake River. The native fish are largely from two fish families: Cyprinidae and Cottidae. Of the cyprinids, chiselmouth and redside shiners are the most abundant. From limited sampling, chiselmouth seem to be equally abundant between Little Goose and Ice Harbor and between Lower Granite and Lower Monumental reservoirs, although differences in relative abundance may be more related to habitats sampled (Bennett et al. 1983). In Lower Granite Reservoir, Bennett and Shrier (1986) reported that chiselmouth were collected in highest abundance at the confluence of the Snake and Clearwater rivers and immediately downstream of the riverine portion of the Clearwater River. Data presented by Bennett et al. (1993) and Bennett et al. (1988) suggest that chiselmouth movements occur throughout the year. In the spring, abundance is higher at shallow water locations, whereas in the winter they are found in deeper waters. Time of spawning is similar to northern pikeminnow, based on the presence of hybrids (Smith 1996). Redside shiners are about equally abundant in the upper three reservoirs compared to their higher relative abundance in Ice Harbor Reservoir. Redside shiners have been sampled in highest abundance in the spring in the impounded portion of the Clearwater River arm (Bennett and Shrier 1986) and in shallow water stations in Lower Granite Reservoir (Bennett et al. 1988). Few were collected in the summer through the fall. The common carp is an introduced species and most abundant in Little Goose Reservoir, probably because of the extensive backwater habitats. Peamouth and speckled dace, both native cyprinids, have consistently been collected in low abundance in the lower Snake River reservoirs. Limited information exists on the species composition and relative abundance of various species of cottids in the lower Snake River reservoirs. Bennett et al. (1983) listed three species of cottids. Prickly sculpin, Piute sculpin and mottled sculpin were all identified, although all were treated as an assemblage throughout their work. No other known information has been collected on sculpins, especially their species composition and relative abundance in the lower Snake River reservoirs. Little life history information exists on these species in the lower Snake River reservoirs, although general life history information is available on each of these species from other systems (Simpson and Wallace 1978; Blair et al. 1968). The species complex of introduced ictalurids, other than channel catfish, has been consistently low (less than 1% of the total fish community) in relative abundance in the lower Snake River reservoirs (Bennett et al. 1983). Brown, black, and yellow bullheads have been found along with tadpole madtoms and a low number of flathead catfish. Brown bullheads have been the most abundant of the bullheads in Lower Granite Reservoir, although they comprise only 10 to 20% of the catch of channel catfish (Bennett et al. 1988, 1993). Tadpole madtom is a common species to the middle Snake River reservoirs above Hells Canyon (Dunsmoor 1990). They consumed similar food items as juvenile smallmouth bass in Brownlee Reservoir, Snake River, Idaho, with the bulk of their energy coming from cyclopoid microcrustaceans and freshwater shrimp. Species comprising the Snake River ictalurid complex are generally late-spring or summer spawners in areas out of the current with adequate bottom cover (Bratovich 1985). The centrarchid and percid assemblage consists of all introduced fish in the Lower Snake River. Centrarchid fish are largely found in backwater areas out of the current. A general characteristic of this habitat is finer substrate and the presence of aquatic vegetation. The exception to this generalization is smallmouth bass, which is common throughout the reservoirs. Pumpkinseed is the most abundant "sunfish" other than crappies and smallmouth bass. Yellow perch are included in this complex because of their use of similar habitat as the centrarchid fish. Yellow perch are almost exclusively found in conjunction with aquatic macrophytes in the lower Snake River reservoirs (Bennett et al. 1983). They have consistently been found in relatively low abundance and only achieve higher abundance in backwater habitats that characteristically have finer substrates, low velocity, and aquatic macrophytes. All of the centrarchid and percid fish are spring and summer spawners in shallower water on substrates that are protected from the current. Yellow perch in the lower Snake River reservoirs are the earliest spawners, and some of the centrarchids are the latest (Bratovich 1985). Sunfish (bluegill and pumpkinseed) and yellow perch were important components of the sport harvest only in Ice Harbor Reservoir. More than 10,000 yellow perch and more than 4,800 sunfish were harvested from Ice Harbor Reservoir in 1997 (Normandeau Associates et al. 1998a). These data suggest that as the lower Snake River reservoirs have aged, habitat for the centrarchid and percid fish, except smallmouth bass, has increased. River lamprey, margined sculpins, Umatilla dace, and leopard dace may exist in the Snake River mainstem, or some of the tributaries to the Snake River. These species are listed as State Candidate or Sensitive Species in Washington, but they have not been verified in the Snake River. Anadromous FishSalmon populations in the Snake River have been listed under provisions of the U.S. Endangered Species Act (ESA). The pertinent listed species are Snake River sockeye salmon (Oncorhynchus nerka, listed as endangered in 1991), Snake River spring/summer and fall chinook salmon (O. tshawytscha, both listed as threatened in 1992), and Snake River steelhead (O. mykiss, listed as threatened in 1998). Because of these listings, there is a need to consider management options that might mitigate the threats to these populations and assist in their recovery. The Snake River historically was and presently is one of the most important drainages in the Columbia River System for producing salmon. More broadly, salmon in the entire Columbia River system at one time numbered between 10 and 16 million fish; this drainage once contained the largest chinook salmon population in the world. Estimating specific historical population levels and trends of particular stocks of salmon in the Snake River Subbasin of the Columbia River is more difficult. But it is clear that all salmonid stocks in the Snake River were much more abundant at the end of the nineteenth century than they are now and that these stocks have undergone major fluctuations. Declines in Columbia River salmon populations began at the end of the last century as a result of overfishing; by early in the 20th century, however, environmental degradation from mining, grazing, logging, and agriculture caused further declines. Before construction of the first mainstem hydroelectric dams on the lower Columbia River (Bonneville Dam was completed in 1938), aggregate pounds of chinook salmon caught in the Columbia River had declined by approximately 40% since the beginning of the century (Netboy 1974). More recent historical decreases in Snake River stocks coincided with an intensive period of change from 1953 to 1975 in the middle and Lower Snake River and the lower Columbia River. In addition to construction of the impassible Hells Canyon complex of dams, four dams which allowed varying degrees of passage were built in the Lower Snake River and three in the lower Columbia River. The completion years during this period were 1954 (McNary Dam), 1957 (The Dalles Dam), 1958 (Brownlee Dam), 1961 (Ice Harbor and Oxbow Dams), 1967 (Hells Canyon Dam), 1968 (John Day Dam), 1969 (Lower Monumental Dam), 1970 (Little Goose Dam), and 1975 (Lower Granite Dam). The seven new dams on the Lower Snake and Columbia rivers inundated 227 and 294 kilometers (141 and 182 miles) of mainstem habitat, respectively. This changed the lower mainstem river from a mostly free-flowing body into a series of reservoirs covering about 70% of the distance between Lewiston, Idaho, and the Pacific Ocean. The slow-moving reservoirs decreased the rate of downstream travel for juvenile fish and increased the amount of habitat favorable to occupation by exotic and predator species. The construction of new dams was one of a suite of major changes in the Columbia Basin ecosystem. Other major changes that had potentially significant impacts on salmonid populations included: the emergence of industrial-scale hatchery production, the introduction of exotic species, major shifts in oceanic conditions, and dramatic seasonal shifts in water storage and flow regulation (National Research Council 1996b). Spring/Summer ChinookThis species was listed as threatened in 1992. Spring and summer Chinook migrate through the mainstem Snake River, but no spawning or rearing is known to occur there or in any of the minor tributaries in this subbasin, except the Tucannon River where an endemic stock persists. (see Tucannon subbasin summary). No spring chinook fishery has occurred in the Snake River since a jack fishery was terminated in the mid-1980’s. Fall ChinookFall chinook salmon were listed as threatened under the Endangered Species Act in 1992. Fall chinook salmon are unique in that they spend the entire freshwater portion of their life cycle in main-stem habitats. Historically, the majority of Snake River fall chinook salmon apparently spawned in the mainstem near Marsing, Idaho (Haas 1965; Irving and Bjornn 1981). Construction of the Hells Canyon complex (1958-1967) and the Lower Snake River Dams (1961-1975) eliminated or severely degraded 530 miles of spawning and rearing habitat for fall chinook in the Snake River (Mendel 1998). Historically, fall chinook salmon runs averaged 72,000 fish between 1938-1949, with highs of up to 120,000 (Irving and Bjornn 1981). By the 1950s these runs had decreased to an average of 29,000. Fall chinook continued to decline, and by the late 1960s and 1970s the average run was only 5,100 fish at Ice Harbor Dam. The average annual runs have remained at 4,700-5,500 fish in the 1980s and the 1990s. Spawning escapement in the Snake River is probably lower than Ice Harbor Dam counts would indicate. A radio telemetry study in the early 1990s found that a high percentage of fall Chinook that cross Ice Harbor Dam apparently “dip into” the Snake River and return to the Columbia or Yakima rivers to spawn (Mendel and Milks 1997). Today, spawning is restricted to the Hells Canyon Reach and to the tail-races of Lower Snake River dams (Dauble et al. 1999) and in the Clearwater River, Idaho. Juvenile fall chinook salmon rear along mainstem shorelines for 2-4 months before migrating seaward in the summer. Juvenile fall chinook salmon use the Lower Snake River as a migration corridor and begin passing Lower Granite Dam in June, peak passage occurs in July, and the migration is protracted into September. Many juveniles are transported, primarily by trucks, from Lower Granite, Little Goose, and Lower Monumental dams to below Bonneville Dam where they are released. The migrant population of fall chinook salmon is composed of natural fish produced in the Hells Canyon Reach and hatchery fish released from Lyons Ferry Hatchery. Fall chinook fisheries have been closed for many years in the Snake River. Lower Columbia River fisheries have targeted upriver bright fall chinook destined primarily for the Hanford Reach of the Columbia River. However, these mixed stock fisheries have harvested Snake River fall chinook at high rates during many years, especially prior to ESA listing in 1992. CohoWild coho are extinct in the Snake River basin since the early to mid 1980s. Hatchery coho are being reintroduced in the Clearwater River by the NPT. Also, there may be stray coho from the Umatilla, and possibly the Yakima reintroduction efforts in the Snake River. Some of these fish are recovered at Lyons Ferry Hatchery or in the Tucannon River since about 1997. SteelheadInformation on Snake River steelhead is limited because it is difficult to develop stock-specific estimates of abundance and survival. Additionally, it is nearly impossible to obtain accurate redd counts for Snake River steelhead because of their spawning locations and timing. The result of these limitations is a more qualitative than quantitative analysis. Nonetheless, some insight regarding hydrosystem options and the future prospect for survival and recovery of steelhead is possible from comparisons to spring/summer chinook salmon (noting both similarities and contrasts). In particular, to the extent that steelhead respond like spring/summer chinook salmon, the limited quantitative data for steelhead can be supplemented with the spring/summer chinook salmon PATH analyses and inferences. There are, of course, extrapolation limitations from spring/summer chinook salmon to steelhead. Biologically, steelhead are divided into two basic run-types based on the state of sexual maturity at the time of river entry and duration of spawning migration (Burgner et al. 1992). The stream-maturing type, or summer steelhead, enters fresh water in a sexually immature condition and requires several months in fresh water to mature and spawn. The ocean-maturing type, or winter steelhead, enters fresh water with well-developed gonads and spawns shortly after river entry (Barnhart 1986). Snake River steelhead are all classified as summer steelhead. Inland steelhead of the Columbia River Basin, especially the Snake River Subbasin, are commonly referred to as either A-run or B-run. These designations are based on observation of a bimodal migration of adult steelhead at Bonneville Dam and differences in age (1-ocean versus 2-ocean) and adult size among Snake River steelhead. Adult A-run steelhead enter fresh water from June to August; as defined, the A-run passes Bonneville Dam before 25 August (Columbia Basin Fish & Wildlfife Authority, CBFWA 1990; Idaho Department of Fish & Game, IDFG 1994). Adult B-run steelhead enter fresh water from late August to October, passing Bonneville Dam after 25 August (CBFWA 1990; IDFG 1994). Above Bonneville Dam, run-timing separation is not observed, and the groups are separated based on ocean age and body size (IDFG 1994). A-run steelhead are defined as predominately age-1-ocean, while B-run steelhead are defined as age-2-ocean (IDFG 1994). Adult B-run steelhead are also, on average, 7.5-10 cm larger than A-run steelhead of the same age; this difference is attributed to their longer average residence in salt water (Bjornn 1978; CBFWA, 1990; Columbia River Fisheries Management Plan Technical Advisory Committee 1991). It is unclear, however, if the life history and body size differences observed upstream are correlated with the groups forming the bimodal migration observed at Bonneville Dam. Furthermore, the relationship between patterns observed at the dams and the distribution of adults in spawning areas throughout the Snake River Basin is not well understood. Unlike Pacific salmon, steelhead can spawn multiple times before death. However, it is rare for steelhead to spawn more than twice before dying; most that do so are females (Nickelson et al. 1992). Prior to construction of most lower Columbia River and Lower Snake River dams, the proportion of repeat-spawning summer steelhead in the Snake and Columbia rivers was less than 5% (3.4% (Long and Griffin 1937); 1.6% (Whitt 1954)). The current proportion is unknown, but is assumed near zero. The Snake River Evolutionarily Significant Unit generally matures after 1 year in the ocean. Based on data from purse seine catches, juvenile steelhead tend to migrate directly offshore during their first summer from whatever point they enter the ocean, rather than migrating along the coastal shelf as do salmon. During fall and winter, juveniles move southward and eastward (Hartt and Dell 1986). Oregon steelhead tend to be north-migrating (Nicholas and Hankin 1988; Pearcy et al. 1990; Pearcy 1992). The average return of wild steelhead to the Snake River Basin declined from approximately 30,000 to 80,000 adults in the 1960s through mid-1970s to 7,000 to 30,000 in recent years. Average returns during 1990 through 1991 and for the 1995 and 1996 return years was 11,465 fish. The general pattern has included a sharp decline in abundance in the early 1970s, a modest increasing trend from the mid-1970s through the early 1980s, and another decline during the 1990s. The sharp decline in steelhead numbers during the early 1970s parallels the similar sharp decline in spring/summer chinook salmon populations during the same time period. However, whereas the wild steelhead population in the Snake River doubled from 1975 (13,000) to 1985 (27,000), the spring/summer chinook salmon did not show an increase. In addition, much of the initial steelhead decline in the 1970s may be attributed to the construction of Dworshak Dam in 1973. This dam cut off access to the North Fork of the Clearwater River, which was an important spawning and rearing area for B-run steelhead. Some natural production of steelhead occurs in minor tributaries such as Alpowa Creek, Alkali Flat Creek, Almota Creek, Steptoe Creek., Deadman and Meadow creeks, etc. Steelhead are also produced from the Tucannon River (see Tucannon subbasin). Spawning and rearing by steelhead is limited in the mainstem because of the Snake River Dams and reservoirs. Most tributaries that maintain summer water flows and do not have barriers are suspected of being used by steelhead. The mainstem Snake River provides some of the largest steelhead harvests in Washington (Table 38). Wild or naturally produced (not fin clipped) steelhead must be released and only hatchery fish can be retained. Many anglers fish for hatchery produced steelhead near dams or at the mouth of the Tucannon River. Table 38. Steelhead harvest estimates from catch cards for the Snake River from its mouth to Clarkston, WA (WDFW harvest data). Run Year Harvest
American ShadAlthough American shad are an anadromous fish in the Snake River, their abundance may indirectly affect resident predatory fish. Other than estimates of abundance from passage counts at dams, little American shad life history information exists in the Columbia River basin. American shad in the Snake River are most abundant in the lower reservoirs, while few adults are observed upstream of Lower Granite Dam (Bennett et al. 1988). Some biologists have hypothesized that American shad may assist in maintaining fish predator populations at artificially high levels. Research is needed to determine if this hypothesis has merit. Where juvenile American shad are most abundant, such as in lower Columbia River reservoirs, they may constitute a protein source for predators that enables them to maintain higher population levels than could occur without shad. However, their role as prey is insignificant in Lower Granite Reservoir for smallmouth bass (Curet 1994; Anglea 1997; Naughton 1998) and northern pikeminnow (Chandler 1993). Further, it is unlikely that juvenile shad currently constitute a major prey item in predator diets in the lowermost Snake River reservoirs, based on recent passage estimates of 5,000 to 14,000 adults at Ice Harbor Dam during 1996 to 1998 (Corps data). | |||||||||||||||||||||||||||||||