Contributors (in alphabetical order)
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Fish and Wildlife StatusFishReservoirs (Corps 1999)Eighteen native species and 17 introduced fish comprise the current resident ichthyofauna of the reservoirs. A list of resident fish species compiled from several sources with common and scientific names is shown in Table 32. The white sturgeon is a state species of concern in Idaho. Bull trout are listed as a threatened species in the Snake River Basin. Current information on the relative abundance of resident fish in the lower Snake River reservoirs suggests that fish community structure is generally similar among reservoirs (BPA 1995). Bennett et al. (1983) conducted seasonal sampling in each of the four lower Snake River reservoirs and extensive sampling in Little Goose Reservoir in 1979 and 1980. Bridgelip sucker, redside shiner, largescale sucker, smallmouth bass, and northern pikeminnow were the age one and older fish in highest relative abundance, based on sampling with multiple gear types in Little Goose Reservoir (Table 32). These five species accounted for about 80% of all fish sampled in 1979 and 1980. All of these fish but smallmouth bass are native species in the Snake River. Species of lesser abundance were a mixture of native and introduced fish. Chiselmouth, another native cyprinid species, was moderately abundant in the lower Snake River reservoirs, while native peamouth, sculpins, and white sturgeon were less abundant. Introduced crappies, yellow perch, and some sunfish were highly abundant in off-channel habitats. Other introduced fish such as catfish and bullheads were present, but in lower abundance. Non-migratory salmonid fish were generally rare, seasonal in occurrence, and typically associated with a tributary confluence. Relative abundance of fish varied among habitats sampled. In general, introduced centrarchid fish were more abundant in lentic backwater habitats while native suckers and redside shiners were more abundant in the more lotic up-reservoir stations (e.g., tailwater and upper shoal). For example, Bennett et al. (1983) reported that redside shiner and bridgelip sucker dominated the catch in the Lower Granite Dam tailwater of Little Goose Reservoir during 1980. These two species combined represented over 60% of the fish caught by multiple gear types. A tendency also existed to have higher abundance of selected species in the older downstream reservoirs. These species, all introduced, included channel catfish, largemouth bass, and carp. In contrast, non-native smallmouth bass, pumpkinseed, and white crappie were more abundant in upriver reservoirs. Table 32. Composite resident fish species list and sources of data for the Lower Snake River (Corps 1999).
Bennett et al. (1983) also showed variation in abundance among similar habitats in different reservoirs. For example, the abundance of chiselmouth and northern pikeminnow was considerably higher at an embayment station in Lower Monumental Reservoir than in embayment habitat in either Little Goose or Ice Harbor reservoirs. Also, the abundance of chiselmouth was higher at main channel stations on Lower Monumental and Lower Granite reservoirs than in Ice Harbor Reservoir (Table 33). Table 33. Species composition of fish collected with multiple gear types in Lower Snake River reservoirs during 1979 to 1980 (Corps 1999).
Although these differences in the fish community were apparent, overall similarities in relative abundance persisted as determined by correlation analysis (Table 34). The relative abundance of fish among reservoirs showed high similarities with correlations ranging from r = 0.74 (Lower Granite and Little Goose reservoirs) to r = 0.94 (Lower Granite and Ice Harbor reservoirs). This cursory analysis shows that from 54 to 87% of the variation in fish communities is accounted for by differences in reservoirs. These correlations are largely driven by the species in higher abundance among each of the reservoirs. A number of other fish were collected, but all were generally lower in abundance in each of the lower Snake River reservoirs. Because of the general similarities in fish community structure, we believe a more specific analysis by habitat best describes the fish within the lower Snake River reservoirs. Table 34. Correlation coefficients of relative abundance among Snake River reservoir resident fish communities (Corps 1999).
Subsequent research has provided updated or refined estimates of relative abundance among reservoirs or among macrohabitat types for selected species deemed important in predator-prey relationships or sport fisheries. ODFW sampled fish with multiple gear types throughout the Lower Snake River in 1991 and 1994 to 1996 as part of an investigation of predator dynamics, distribution, and abundance (Zimmerman and Parker 1995; Ward and Zimmerman 1997; Zimmerman and Ward 1997). Reporting of results was limited to three piscivorous species. Smallmouth bass density (CPUE) in 1991 was reportedly highest in mid-reservoir and forebay reaches of Snake River reservoirs. Additionally, smallmouth bass relative abundance and density in Lower Granite Reservoir was more than twice that in other lower Snake River reservoirs, and density decreased in a downstream direction. Follow-up sampling in the upper reservoir reach of Lower Granite Reservoir showed a trend of decreasing abundance of smallmouth bass from 1994 to 1996, but other areas in Lower Granite Reservoir or other reservoirs were not sampled from 1994 to 1996 for comparison. Trends in channel catfish abundance and density were generally opposite those for smallmouth bass. The density and relative abundance of channel catfish in Ice Harbor Reservoir were more than twice that in any other reservoir, and catfish were least abundant in Lower Granite Reservoir. Further, the highest density of channel catfish among reservoir macrohabitats was in mid-reservoir and tailrace reaches, especially in tailrace BRZs. Northern pikeminnow density among reservoir macrohabitats was highest in tailrace BRZs. Density was highest in tailrace BRZs of Little Goose and Lower Monumental reservoirs (i.e., below Lower Granite and Little Goose dams). Mid-reservoir densities were lower, but the overall abundance was higher due to the large size of mid-reservoir areas relative to other habitats. Comparable sampling during the 1994 to 1996 period in the tailraces of Lower Monumental and Little Goose reservoirs and upper reservoir habitats in Lower Granite Reservoir showed declines in abundance of northern pikeminnow greater than 250 millimeters (9.8 inches) due to operation of a sport reward program that paid bounties for removal of large-sized individuals by angling (Friesen and Ward 1997). Qualitative assessments of distribution and abundance within reservoir macrohabitats for other Snake River fish sampled by electrofishing during 1991 are shown in (Table 35) (Tom Poe, U.S.G.S., B.R.D., unpublished data). Species such as chiselmouth, carp, northern pikeminnow, suckers, and smallmouth bass were widely distributed among reservoirs and habitats, and abundance of these species was reported as common in most locations. Only northern pikeminnow and suckers were recorded as abundant in some reservoir macrohabitats. Species either less abundant or more narrowly distributed included mountain whitefish, brown bullhead, pumpkinseed, bluegill, crappie, and yellow perch. Of these, all but mountain whitefish were most abundant in embayment or gulch habitats as reported in Bennett et al. (1983), which may illustrate the results of different sampling protocols or gear types. Table 35. Qualitative relative abundance estimates of resident fish determined by electrofishing in macrohabitats of Lower Snake River reservoirs in 1991(Corps 1999).
Several species were mostly reported as rare (one or two individuals per collection) in 1991 samples. These included redside shiner, sandroller, bull trout, and sculpins. Bull trout was only reported above the reservoir influence in the mid-Snake river, but are also infrequently reported passing the dams. Sculpins and sandrollers are occasionally seen in stomach samples of reservoir predators, rather than in standard fisheries collections (David H. Bennett, University of Idaho, personal communication). Mosquitofish are only found in levee ponds in Lewiston (David H. Bennett, University of Idaho, personal communication). More recently, the spatial trends in catch and catch rates among reservoirs determined by 1997 sport fishing surveys (Normandeau Associates et al. 1998a) corroborated trends in species density and abundance estimates for major Snake River predators as portrayed by Zimmerman and Parker (1995). For example, the highest smallmouth bass sport angling catches and catch rates occurred in Lower Granite Reservoir, whereas sport angling catch, harvest, and catch and harvest rates for channel catfish were highest in Ice Harbor Reservoir. The catch and catch rates of northern pikeminnow by anglers were highest in Lower Granite Reservoir, particularly in the more lotic Snake River arm of the upper reservoir. Recent sport fishing catches may also illustrate recent spatial trends in distribution among reservoirs for several other species not targeted by specific management studies or activities. Sport catch and harvest of crappie were substantially higher in Little Goose Reservoir than in other reservoirs, especially in Ice Harbor Reservoir where crappie catch was nearly two orders of magnitude lower than in Little Goose Reservoir (Normandeau Associates et al. 1998a). Similarly, the white sturgeon sport catch was highest in Little Goose Reservoir. Yellow perch and sunfish (Lepomis spp.) sport catches were substantially higher in the downstream reservoirs, especially in Ice Harbor Reservoir. The sport catch of bullheads was highest in Lower Granite Reservoir. In summary, recent documentation of the status of Lower Snake River reservoir resident fish communities has focused primarily on a small group of species, mostly non-native, and that information on the current status of most native species (other than northern pikeminnow and white sturgeon) is lacking. Thus, the work by Bennett et al. (1983) shortly after the last reservoir was completed in 1975 represents the only quantitative information available on most resident fish that likely remain quite abundant and widely distributed. These species include largescale and bridgelip suckers, redside shiner, and other native cyprinids and cottids. In spite of the recent information on the relatively high-profile species, the overall similarities in community composition and relatively limited information on specific fish abundance of most species in each reservoir suggest that the four lower Snake River reservoirs should be treated as one reservoir system with an analysis of the fish community inhabiting each of the principal macrohabitats in the reservoirs. Our analysis of expected impacts will be based on examination of the characteristic fish communities in the forebay, tailrace, mid-reservoir, and specific backwater/embayment habitats common to all reservoirs in the system. This type of analysis will facilitate subsequent descriptions of expected impacts to reservoir fish communities for the various alternatives under consideration. Six species or congeners have been identified for individual treatment as ecologically key, or important, species. The native northern pikeminnow, for example, is important in predator-prey dynamics of the reservoirs (Ward et al. 1995) and is the focus of population reduction efforts via a sport reward program that pays bounties for removal of large individuals (Friesen and Ward 1997). Largescale and bridgelip suckers are native species that were highly abundant throughout the reservoirs during comprehensive sampling efforts in 1979 and 1980 (Bennett et al. 1983). White and black crappie, smallmouth bass, and channel catfish represent introduced species that are highly sought by sport anglers throughout the reservoir system (Normandeau Associates et al. 1998a). Smallmouth bass and channel catfish also have been the focus of predator-prey investigations (Zimmerman and Parker 1995; Ward and Zimmerman 1997), along with northern pikeminnow. White sturgeon is a native species that has declined in abundance due to continued harvest and isolation and loss of flowing water habitats by dams. White sturgeon is a Species of Concern in Idaho (BPA 1995). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||