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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival 4 Environmental Influences on Salmon Columbia River basin salmon are among the world’s most intensively studied fish species. Quantitative and qualitative data regarding salmon species and their habitat have been gathered and evaluated for many decades. This information has increased understanding of Pacific salmon and their complex life histories. Given their responsibilities to help protect salmon, water management agencies in the Pacific Northwest have drawn heavily on this information and have consulted with fisheries scientists in designing strategies for preserving and enhancing salmon habitat and populations. Despite the extent of data and scientific knowledge regarding Pacific salmon, more precise understanding of salmon is inhibited by the complexities of salmon’s diverse anadromous (which refers to organisms that spend most of their adult lives in saltwater and then migrate to fresh water and lake to reproduce) life histories and the vast scale of the biomes they traverse during their life spans. In addition to the biological complexities of salmon species, within the impounded Columbia River they have been affected by an array of environmental conditions and changes, such as increasing water temperatures and changes to other water quality parameters, changes to water velocity through reservoirs, habitat degradation, changing turbidity, shifting seasonal patterns and volumes of river flows, passage effects at dams, and changes in predators and predation rates. Scientists and water managers have considered these issues when formulating fish passage strategies such as flow augmentation, construction of smolt (young salmon, generally two to three years in age) bypass systems, spill programs, smolt transportation programs, and the construction and upgrade of fish ladders. Collectively, these devices and strategies are designed to work in concert to increase survival rates of salmon migrating through the dammed river and
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival contribute to the productivity of anadromous fish populations. NOAA (National Oceanographic and Atmospheric Administration) Fisheries (formerly the National Marine Fisheries Service, or NMFS), the federal fishery agency responsible for the recovery of anadromous salmonid populations listed pursuant to the Endangered Species Act, embraces these strategies and calls for their continued improvement and use in fostering salmon recovery (NMFS, 2000). Even so, it is not known whether these actions alone can reverse or stall long-term declines in salmon populations. Much of the research identified in the 2000 Biological Opinion from the NMFS focuses on improving the implementation of these strategies and gaining a clearer understanding of the outcomes of management actions that are often confounded by environmental complexities. Furthermore, conditions in tributaries and in estuarine and marine habitats have pronounced effects on salmon productivity, as do harvest and hatchery programs. Large salmon returns in 2001 to 2003, for example, were viewed by many scientists as a function of favorable ocean conditions (NPCC, 2003), but ecological and biological complexities inhibit perfect understanding of cause and effect in such events. In any event, a 100-year snapshot of Columbia River salmon portrays long-term declines and provides a backdrop against which short-term events should be evaluated. This chapter reviews environmental variables that affect Columbia River salmon and examines competing hypotheses and models constructed to explain the relative importance of these variables. COLUMBIA RIVER SALMON Three species of anadromous salmonids commonly migrate through the middle and upper reaches (above Bonneville Dam) of the Columbia and Snake rivers in the State of Washington: Chinook (Oncorhynchus tshawytscha), steelhead (Oncorhynchus mykiss), and sockeye (Oncorhynchus nerka) all commonly migrate to spawning destinations well upstream from Bonneville Dam. Remnant wild and hatchery populations of coho salmon (O. kisutch) are also found in select locales in the upper Columbia basin. All these species have some population units that are listed as endangered or threatened under the Endangered Species Act (see Table 1-1). Additionally, chum salmon (O. keta), which
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival are also federally listed, and a vestigial population of pink salmon (O. gorbuscha), inhabit waters downstream from Bonneville Dam. Requirements for each stage of salmon life history can be generalized for all of the anadromous species. Spawning fish, returning from the ocean, require freshwater instream habitat with temperatures that ensure survival until they spawn. Spawning salmon seek species-specific gravels, water depths, and velocities to build redds (nests) in which they deposit their eggs. Egg survival depends on low sedimentation rates, adequate delivery of dissolved oxygen, and appropriate river temperatures to support egg development. Once the eggs hatch, some of the young fish (fry) maintain locations in the river to develop, while some fry grow while migrating downstream. During the post-fry stage (juvenile), these fish remain in the river from several months to more than two years, depending on the species or life history type. Growth is crucial during this phase, which supports the physiological transformation required for emigrating from fresh water, into brackish water, and then into saltwater. This transformation phase is called smoltification and during it the fish undergo a complex physiological process that prepares them for adaptation to seawater as they migrate downstream (as their names suggest, spring migrants experience smoltification during spring months, and summer migrating ocean-type Chinook go through smoltification mainly in July and August). Chinook Salmon Fishery managers traditionally divide Columbia River Chinook salmon into spring, summer, and fall runs. After spending much of their lives in the Pacific Ocean, spring Chinook salmon adults that spawned in high, cold tributaries in Idaho, Oregon, and Washington return to the Columbia River mouth from February through mid-May. Through olfactory homing instincts, they travel upstream and reach their natal tributary streams in June, move to spawning sites in August, and largely complete spawning by early September. Summer Chinook salmon, which use the Columbia River upstream from the mouth of the Snake River, enter the river mostly in May and June and spawn in September and early October in natal streams such as the Wenatchee
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival and Methow rivers. In the Snake River, summer Chinook salmon make up a later component of the spring Chinook salmon migration, spawning in late August and early September. Fall Chinook salmon enter the Columbia River in July and August and spawn in late October and November in the mainstem river (a small number also spawn in the Snake River between Lewiston and Hells Canyon Dam). Fall Chinook salmon today make up the largest segment of Chinook salmon runs. Hatchery and naturally produced fall Chinook salmon that use the lower Columbia River area are known as “tule” fall Chinook salmon. Relatively dark in color, they arrive in the river in September and October, then spawn in late fall. Fall Chinook salmon that spawn upstream from McNary Dam in both the Snake and Columbia rivers are known as “upriver brights.”1 They enter the Columbia River in August and spawn mostly upstream from McNary Dam. Upstream from Bonneville Dam, the (numerically) most important spawning area—a long, damless stretch of river known as “The Hanford Reach”—lies between Priest Rapids Dam and the head of McNary Dam pool. The shoreline-oriented behavior of subyearling fall Chinook salmon in flowing river segments, and their relatively slow rearing migration in the Snake and Columbia rivers, which occurs in early and midsummer, makes them potentially vulnerable to high water temperatures. Construction of mainstem hydroelectric projects, and the consequent slower river velocities, extended the passage period for subyearling (juvenile fish less than one year old) fall Chinook in the Hanford Reach (Chapman et al., 1994; Park, 1969). Reservoirs like McNary and Lower Granite pools, however, may serve as surrogates for estuarine rearing (Chapman et al., 1994). Fall run Chinook usually migrate to the ocean during their first spring and summer in fresh water. Most yearling spring Chinook salmon migrate in April and May and reach the estuary in early June of their second year in fresh water, thus evading the warmest Columbia River waters of early and midsummer. Fall run and spring run Chinook are often called ocean and streamtypes, respectively. Returns of spring Chinook and Snake River “summer” Chinook are dominated by hatchery-reared fish. Returns of fall Chinooks (upriver brights) are pri- 1 “Brights” also describes fall Chinook that spawn in the Lewis River, a Cowlitz River tributary, and in the Deschutes River.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival marily wild fish. Steelhead Columbia River steelhead are categorized according to two broad modes of behavior. Winter steelhead remain at sea until late fall or winter, then enter the Columbia River and tributaries as far upstream as Fifteen Mile Creek at The Dalles, which enters the Bonneville Dam pool. They spawn in late winter and early spring, and fry emerge from redds in late spring to July. Juveniles spend two winters in fresh water before migrating to sea in March to early June. Summer steelhead, by contrast, which use some tributaries downstream from Bonneville Dam (e.g., Kalama River) and virtually all suitable streams upstream from Bonneville, enter the Columbia River from May to early September. Adults spend the winter in the mainstem of the Columbia and Snake rivers and in large tributaries and spawn mostly in the period from March to May. Like winter steelhead, fry emerge from redds in late spring to midsummer and spend at least two winters in fresh water before migrating to sea as smolts. The smolts move seaward in spring. Returns of steelhead at the Columbia River estuary are dominated by hatchery-reared fish. Sockeye Salmon Sockeye salmon require a lake for juvenile rearing. Sockeye were once found in the upper Columbia River lake and tributary systems of the upper Columbia River upstream from Grand Coulee, in Suttle and Wallowa lakes in Oregon, in the chain of Okanogan River lakes and Lake Wenatchee, and in the Stanley basin lakes of the upper Salmon River in Idaho. They spawn in fall upstream from the two lakes, and fry move downstream soon after emergence from redds, rearing in the lake environment for mostly one but sometimes two years. As smolts they emigrate in April and May. Sockeye currently inhabit only Osoyoos Lake in Canada, Lake Wenatchee in Washington, and Redfish Lake in Idaho. Sockeye salmon return to the Columbia River estuary mostly in May and June. The bulk of these returns are wild fish.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Coho Salmon Coho salmon in the Columbia River mostly spawn (and juveniles rear) in tributaries downstream from The Dalles Dam. Hatchery-produced coho predominate. Wild coho formerly used a number of other tributaries, including some upstream from McNary Dam, like the Yakima, Methow, and Grande Ronde rivers. Most coho smolts move seaward in the spring. Variations in Migratory Patterns These different salmon and steelhead species and subspecies migrate downstream and upstream through the Columbia River system at different times of year. The greatest risks to the survival of migrating fish occur during periods when Columbia River temperatures are highest and during low-flow periods and in low-flow years. Species and life stages of listed fish that transit the Columbia River mainstem in summer months (June to August) include: Subyearling fall Chinook from the Snake River; Late-migrating steelhead (smolts); Snake River adult sockeye salmon (adults); . Snake River summer Chinook (adults); Snake and Columbia river steelhead (adults); Snake River fall Chinook (adults); and Bull trout. This report contains several references to the risks of survival of Columbia River salmonid stocks during critical periods. References to fish in the system during these periods do not apply to all salmon and steelhead species and subspecies but rather focus on the species listed here that transit the system during the critical June-August period. STATUS OF SALMON AND STEELHEAD STOCKS Historical perspectives of trends in Columbia River salmon abundance are essential to understanding the relative abundance
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival of recent and current salmon runs as well as long-term fishery trends. Many sources of data contribute to scientific knowledge of historical changes in the abundance of the Columbia’s anadromous salmon and steelhead. Because of their abundance (and their size) in the Columbia River, Chinook salmon have long attracted the attention of fishery scientists and have been intensively monitored and tracked over time. Fish counts at Bonneville, McNary, Priest Rapids, and Lower Granite dams for the period 1977 to 2002 (Figures 4-1, 4-2, and 4-3, for adult Chinook, adult steelhead, and adult sockeye, respectively) provide an overall picture of changes in the status of salmon populations over time. FIGURE 4-1 Counts of adult Chinook salmon at Bonneville, McNary, Priest Rapids, and Lower Granite dams on the Columbia River (1977 to 2002). SOURCE: Fish Passage Center (available online at http://www.fpc.org/adult_history/adultsites.html, last accessed November 17, 2003).
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Returns of Chinook from 2001 to 2003 greatly exceeded the 1993 to 2002 average returns (Figure 4-1) and generated a great deal of excitement in the Pacific Northwest. These record returns have generally been attributed to favorable ocean conditions. The Northwest Power and Conservation Council, for instance, asserted that “good ocean conditions are creating strong adult returns” and noted that “ocean conditions will change” (available online at http://nwppc.org/news/2003_11/3.pdf, last accessed December 2, 2003). It bears noting that the 2001 to 2003 returns of fall Chinook salmon, like in-river runs since the mid-1990s, also benefited from increased restrictions on ocean fishing. In addition to recent, comparatively large Chinook runs, steelhead returns also rose sharply relative to figures since the mid-1970s (Figure 4-2). Sockeye also experienced an increase in returns in the late 1990s (Figure 4-3). FIGURE 4-2 Counts of all adult steelhead at Bonneville, McNary, Priest Rapids, and Lower Granite dams on the Columbia River (1977 to 2002). SOURCE: Fish Passage Center (available online at http://www.fpc.org/adult_history/adultsites.html, last accessed November 17, 2003).
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival FIGURE 4-3 Counts of adult sockeye salmon at Bonneville, McNary, Priest Rapids, and Lower Granite dams on the Columbia River (1977 to 2002). SOURCE: Fish Passage Center (available online at http://www.fpc.org/adult_history/adultsites.html, last accessed November 17, 2003). Redd counts from Idaho’s Salmon River basin provide additional information regarding temporal trends of spring/summer Chinook salmon listed by the Endangered Species Act.2 Redd counts in 1957, the first year of systematic surveys, were inflated by completion of The Dalles Dam in the lower Columbia River (Figure 4-4). The reservoir behind the dam flooded the Celilo Falls, which was an important Indian fishing site. As a result of the loss of this important fishing site and an attendant reduction of harvests, Columbia and Snake river escapements of salmon and steelhead increased sharply. Later, as Indian fishers shifted to gillnets, fishing and harvest rates increased. 2 “Summer Chinook” salmon in Idaho, like spring Chinook salmon, spend one winter in natal tributaries before migrating to sea. They spawn principally in the South Fork Salmon River and upper Salmon River.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival FIGURE 4-4 Number of combined spring and summer Chinook redds (thousands) counted in Salmon River drainage, wild and natural/hatchery-influenced trend areas, 1957-2002. SOURCE: Fish Passage Center (available online at http://www.fpc.org/adult_history/adultsites.html, last accessed March 24, 2004). Figures 4-5 and 4-6 present a longer time frame of reference of salmon abundance and its changes, and they reflect a steady decline in the spring Chinook catch since the early 1940s (there are, however, some departures from this long-term trend, such as increases in landings in the mid-1980s). The harvest rate in the Columbia River between the river mouth and the upper limit of commercial fishing near the site of McNary Dam ranged from 40 to 85 percent before the 1960s, declined until 1974, and thereafter averaged less than 10 percent (Chapman et al., 1995). Numerical harvest in the post-Bonneville Dam era peaked in the 1950s, declined to 1974, and then remained negligible. Declines in salmonid stocks, and the variations in declines across stocks, have been described as follows:
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival FIGURE 4-5 Commercial landings of salmon and steelhead from the Columbia River in pounds, 1938 to 2000. SOURCE: WDFW-ODFW (2002). FIGURE 4-6 Commercial landings of salmon and steelhead from the Columbia River in numbers of fish, 1938 to 2000. SOURCE: WDFW-ODFW (2002).
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival not too severe, these types of transportation could be beneficial. If the effects of transport are pronounced, however, the passage strategy can put endangered stocks at risk. NOAA Fisheries is currently engaged in a multiyear research effort to help reduce mortality rates for key salmon populations in the Snake-Columbia river system associated with this type of transport. WATER TEMPERATURE AND FLOW MANAGEMENT Water temperature is an important factor in the life history of Pacific salmon, as it affects the rate of embryo development, juvenile growth rates, metabolic processes, and the timing of life history events such as spawning and migration (Brannon et al., 2002). In cold, high- elevation tributaries, newly emerged salmon fry must grow through the summer to obtain sufficient size to survive the lengthy downstream migration and the estuary and nearshore marine environment, then migrate to sea as yearlings. Farther downstream in the mainstem Columbia River, emergent ocean-type fry find more moderate temperatures and sufficient growth opportunities in the first spring and summer of their lives to reach sizes adequate for estuarine and marine survival during their first year or before their first year in seawater. Water temperature regimes have changed in the Columbia River (see Chapter 3), largely because of human activities. Some salmon populations have shown some ability to adapt to altered river thermal regimes. Fall Chinook salmon, for example, recently began spawning in a formerly unused site in a Snake River tributary, the Clearwater River, because water releases from Dworshak Dam3 warmed the Clearwater River during winter, providing a suitable environment for spawning and incubation. Similarly, releases of relatively warm water from Columbia River storage reservoirs (most importantly Grand Coulee and Chief Joseph), and operation of hydro dams downstream, have increased temperature units (TU)4 in spawning areas between the head of McNary Dam pool and Chief Joseph Dam. Adult sockeye salmon and American shad have gradually shifted the peak 3 Dworshak Dam impounds the North Fork Clearwater River just upstream from Orofino, Idaho. 4 Each 1°C for 1 day = 1 TU. Thus, for example, over 24 hours, an incubation temperature of 4°C equals 4 TU.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival of upstream migration forward about 10 days, responding to rising Columbia River water temperature (Quinn and Adams, 1996). More adult summer steelhead have tended to move later in the year, after river temperatures have peaked (Robards and Quinn, 2002). Although some adult migration and spawning times have shifted in response to lower late-spring and summer flows and warmer river temperatures, physiological responses of adult and juvenile salmon and steelhead to temperature very likely have not (Bell, 1973; Ordal and Pacha, 1963; Reiser and Bjornn, 1979a, b). High water temperatures delay the upstream migration of adult salmonids (Bjornn and Peery, 1992; Hallock et al., 1970; Major and Mighell, 1966). For example, Chinook salmon slow their movement when water temperatures approach 21°C or above (Bell, 1991; McCullough, 1999), a level already common in the Columbia River in summer (see Figure 3.8). Steelhead appear to delay migration when water temperatures exceed 21° to 22°C (Bjornn and Peery, 1992). Clearly-defined thresholds that affect salmon behavior are difficult to identify. For example, not all Chinook salmon completely stop moving when water temperatures exceed 21°C. Fish counts at Ice Harbor Dam on the Snake River between 1962 and 1992 showed that some fish continued to move when water temperature exceeded 23.3°C (Hillman et al., 2000). Increases in summer water temperatures in the mainstem Columbia River have led to more use of cool tributary refugia (e.g., Deschutes and Wind rivers) by fall Chinook (Goniea, 2002) and steelhead (High, 2002). Higher prespawning mortality rates and depletion of energy reserves can be expected in adult fish exposed to elevated water temperature during upstream migration (McCullough, 1999; Sauter et al., 2001). There do not appear to be any analyses, however, that support precise and reliable predictions of survival changes as related to water temperature. Within the Columbia and lower Snake rivers, summer water temperatures now reach levels that clearly impose risks to juvenile salmonids. During the summer, subyearling Chinook salmon rear and migrate downstream when river temperatures exceed 20°C (Giorgi and Schlecte, 1997). Temperature tolerance for juvenile fall Chinook has been reported to range from 5.5°C to 20°C (Groves, 1993). The young fish use more energy at high temperature, requiring either higher daily rations (that may not be available) or the consumption of stored energy.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Growth tends to decrease as water temperature approaches 19° to 20°C, which in turn can reduce the size of subyearlings at seawater entry. Disease incidence also increases with rising temperatures. Water temperature is also an important factor affecting predation-related juvenile salmon mortality rates. For example, Vigg and Burley (1991) developed a model which suggests that a decrease in water temperature from 21.5°C to 17°C could reduce the number of prey consumed by a northern pikeminnow from seven to four per day. This suggests that water temperature regulation measures that reduced Snake River water temperatures could indirectly and locally enhance survival prospects of juvenile fall Chinook. High water temperatures during the latter part of the spring migration of smolts pose physiological threats, especially to steelhead. As previously explained, the smoltification process involves a change in physical appearance as parr become leaner and turn a silvery color. During this process, smolts become physiologically more tolerant of saltwater. Smoltification continues during the seaward migration (Beeman et al., 1995; Zaugg, 1987). Higher temperatures during downstream migration, however, can impede the smoltification process such that fish are prevented from reaching the sea. An appropriate temperature threshold, above which smoltification is inhibited, appears to lie between 12° to 13°C (Adams et al., 1973; Zaugg et al., 1972; Zaugg and Wagner, 1973). It is not known whether actively migrating steelhead smolts that encounter temperatures greater than 14°C in the lower Columbia River, for example, would revert to parr status (for a more extensive review of temperature effects on smoltification, see http://www.deq.state.id.us/water/suface_water/temperature/ContractorReview_EPA_DraftGuidance.pdf, last accessed January 5, 2004). In 2001, when river flows were low and water temperatures high, survival rates of steelhead were extraordinarily low, as previously noted. And, as also noted earlier, it seems likely that the apparent “mortality” rates that year were due in part to reversion of smolts to parr status and a consequent cessation of seaward movement.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Restoration and Mitigation Measures Flow Augmentation In 2002, Giorgi et al. reviewed the status of flow augmentation evaluations published to date. The authors emphasized that establishing general relationships between flows and either migration speed or survival provides a rationale for entertaining flow augmentation as a strategy to improve survival. However, an evaluation of the biological benefits of providing additional water in any particular year has many facets and requires a more focused analysis. Few such detailed evaluations have been conducted. Even the 2000 NMFS Biological Opinion offered no assessment of benefits or risks associated with flow augmentation; rather, it specified volumetric (in millions of acre-feet) standards dedicated to flow augmentation and prescribed seasonal flow (in thousands of cubic feet per second, or kcfs) targets. However, no quantitative analysis describing the change in water velocity, smolt speed, or survival improvement was presented that can be attributed to the additional water provided by flow augmentation. Some studies that attempted to focus specifically on evaluating the effects of flow augmentation water delivery are discussed briefly below. A study in the late 1990s commented on the effectiveness of flow augmentation in changing water velocity and meeting the flow targets specified in the 2000 Biological Opinion (Dreher, 1998). It was found that the volumes of water in storage reservoirs currently earmarked for flow augmentation in the Snake River (1) provide only small incremental increases in average water velocity through the hydrosystem and (2) are insufficient to meet flow targets in all years. This analysis, however, was not intended to specifically evaluate flow augmentation strategies and thus offered no insight with respect to fish responses. The topic of summer flow augmentation has received increased attention in recent years. For example, Connor et al. (1998) conducted a study that had implications for summer flow augmentation in the Snake River. Using PIT-tagged juvenile fall Chinook that reared upstream from Lower Granite Dam, they regressed tag detection rates at the dam (survival indices) against flow and temperature separately. They found that over four years, the detection rate was positively correlated to mean sum-
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival mer flow and negatively correlated with maximum water temperature. They acknowledged that the predictor variables were highly correlated, limiting specific inferences regarding the effects of the individual variables. They also noted water temperatures at Lower Granite Dam dropped approximately 5° to 6°C during the period of flow augmentation from Dworshak Dam and the Hell’s Canyon Complex in 1993 and 1994. They concluded that summer flow augmentation, especially cooler water released from Dworshak Reservoir, could improve survival of juvenile fall Chinook, at least to arrival at Lower Granite Dam. Connor et al. (2003) further analyzed this stock of fall Chinook salmon using PIT tag-based data for the years 1998 to 2000. Survival rates decreased as temperatures warmed and as flows decreased through the course of the summer. It was concluded that flow augmentation increased survival rates of Snake River fall Chinook salmon to the first dam they encounter. Giorgi and Schlecte (1997) evaluated the effectiveness of flow augmentation in the Snake River for the years 1991-1995. They estimated the volume and temporal distribution of flow augmentation water delivered to the Snake River and evaluated the biological consequences to stocks listed by the Endangered Species Act. They then estimated incremental changes in water velocity and temperature that were attributable to the water delivered as flow augmentation. Using several smolt passage models, the incremental change in smolt migration speed for yearling Chinook salmon, steelhead, and fall Chinook salmon that may have resulted from flow augmentation water was estimated. It was concluded that Snake River flow augmentation increased water velocity through Lower Granite Pool an average of 3 to 13 percent during the spring. The increase was more pronounced during summers, with an increase of 5 to 38 percent change in water velocity attributable to augmentation water. Correspondingly, the change in smolt travel time predicted by the different passage models varied considerably. For example, decreases in travel time for yearling Chinook ranged from 5 to 16 percent over five years, or 0 to 5 percent depending on the passage model applied.
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Temperature Manipulation Several investigations have focused on the effectiveness of Snake River flow augmentation in reducing summer water temperature in the Lower Snake River, specifically considering the use of Dworshak Reservoir as a cold water source for decreasing water temperature in August and early September (Bennett et al., 1997; Karr et al., 1992, 1998). Karr et al. (1992) first presented results which indicated that strategic releases of outflow from Dworshak Reservoir could reduce water temperature in the Snake, at least to the vicinity of Lower Granite Dam. Bennett et al. (1997) modeled water temperature and monitored empirical data for 1991 to 1993. They established that the Corps of Engineers model (COLTEMP) provided reliable predictions of changes in water temperature associated with flow augmentation releases upstream. The reduction in Snake River water temperature associated with cold water releases from Dworshak Reservoir was greatest at Lower Granite Dam and diminished as water moved downstream to Ice Harbor Dam. Depending on the year and base flow characteristics, the change in temperature at Lower Granite Dam typically ranged from 1° to 4°F. However, the model predicted differences as great as 6° to 8°F, which extended for a period of several weeks. Here again, prediction depended on base flows and the volume released for flow augmentation. At Ice Harbor Dam the decrease in temperature was typically small, on the order of 1 to 2F. It was also reported that the cold water released upstream tended to sink toward the bottom of the reservoirs and mixed at the dams (Bennett et al., 1997). This suggests that deep cool water may be available as a refuge but that cooling of the entire water column cannot be achieved. Also, the extent of cooling decreases in the lower reaches of the river. Biological information has not yet been integrated with this or similar evaluations. Benefits and Risks to Other Species Water releases from storage reservoirs to increase mainstem flows or to reduce water temperatures alter conditions both in the storage reservoirs and in tributaries connecting with the Columbia and Snake rivers. These processes in turn have effects on
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival resident and anadromous fish inhabiting those waters, which introduces an additional, complex facet of flow augmentation. Risks associated with flow augmentation were addressed by the Independent Science Advisory Board’s publication Return to the River, which expressed concerns regarding risks associated with summer flow augmentation, in particular (ISAB, 1996): Underscoring these substantial uncertainties in flow augmentation rationale is the fact that summer drawdowns in upstream storage reservoirs, for example Hungry Horse Reservoir in Montana, to accomplish summer smolt flushing in the lower Columbia River has direct and potentially negative implications for nutrient mass balance and food web productivity in Flathead Lake, located downstream from Hungry Horse. The issue involves balancing expected benefits to anadromous fish with ecosystem functions and potential risks to other species. There is clearly a complex array of water management activities in the Columbia River basin today, and arriving at an appropriate balance among competing and complementary strategies is a venture that contains many considerations and uncertainties. Flow Management and the Estuary The ISAB (1996) stressed the importance of the estuary as a key regulator of overall survival and annual variation in abundance of salmon. The estuary (and nearshore Columbia plume and its interface with seawater) provides a physiological transition zone, potential refuge from predators, and forage (Simenstad et al., 1982). Rapid growth of juvenile salmon in this transition zone is important, as increased size lessens vulnerability to predation in this environment. For example, in the lower Sacramento River, the primary floodplain area provides better rearing and migration habitat for juvenile Chinook salmon than provided by adjacent river channels (Sommer et al., 2001). Anthropogenic effects on estuarine and plume dynamics derive from estuarine alterations such as diking and filling, and from flow and water quality alterations upstream (e.g., reductions in turbidity;
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Junge and Oakley, 1966). The Columbia River estuary has changed greatly since the early 1800s. Total volume of the estuary has declined by about 12 percent since 1868, and diking and filling have converted 40 percent of the original floodplain to various human uses (Sherwood et al., 1990). The annual spring freshet has been greatly diminished, thereby reducing organic and sediment inputs. The standing crop of organisms that feed on macrodetritus is only about one-twelfth as great as it once was (ibid.). The Northwest Power Planning Council’s ISAB (1996) assumed that a reduction in the food web supported by phytoplankton macrodetritus has negatively affected salmon. Changes in food web production have resulted in a more favorable environment for herring, smelt, and shad. Estuarine degradation and potential mitigation are further discussed in Bottom et al. (2002), Jay and Naik (2000), and Kukulka and Jay (2003). Hatchery-produced salmon and steelhead now pass through the estuary in large quantities, in temporal patterns dissimilar to historical patterns of the passage of wild fish. Effects of these large releases on estuarine ecology are not fully understood and quantified. Nonetheless, they are likely to negatively affect wild anadromous fish because of the diminished ecological opportunities offered by a smaller estuary that has experienced pronounced hydrologic and related changes. Tributary and Riparian Issues Potential exists to increase salmon stocks in the Columbia River system by restoring or rehabilitating riparian vegetation that has been altered by overgrazing, timbering, mining, and clearing for agriculture (Maloney et al., 1999; Meehan, 1991). For example, approximately 88 percent of the original presettlement forests occupying the floodplain of the Willamette River (a major tributary of the Columbia) have been removed (NRC, 2002a). A pristine riparian zone, unaltered by human activities, enhanced salmon spawning and rearing by )1) shading the stream and maintaining low water temperatures, (2) contributing coarse woody debris to provide cover and in-stream habitat heterogeneity, (3) filtering sediment and pollutants from runoff waters, and (4) producing many forms of organic matter to support stream productivity (Clinton et al., 2002; McIntosh et al.,
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival 1994; Naiman et al., 1992). Returning adult salmon themselves contribute to riparian zone and stream productivity by transporting marine-derived nutrients to their spawning grounds (Schindler et al., 2003). SUMMARY Columbia River salmon are anadromous and are affected by environmental conditions and variability not only within the Columbia River basin but also by conditions in the northern Pacific Ocean. Columbia River basin salmon have been in a general state of decline for decades, with these declines being driven by a variety of environmental changes. There have been departures from this long-term trend, the most recent being an increase in the returns of (mainly hatchery-reared) Chinook salmon in 2002 and 2003. This increase has generally been attributed to favorable ocean conditions. Although a positive development, these increased numbers still fall well short of what was once the world’s premier salmon fishery. Despite some recent increases in returns, there is little disagreement on general long-term declining trends, which have resulted in many wild salmon species being listed as threatened or endangered under the Endangered Species Act. This report reviews the implications for salmon survival of a specific and relatively (compared to the magnitude of the Columbia River) small range of proposed water withdrawals that would further reduce river flows. Precise and credible forecasts of specific biological or ecological outcomes of these withdrawals (or almost any given range of specific proposed diversions) are beyond current scientific capabilities and knowledge. But as pointed out in Chapter 3, impacts of water withdrawals from the Columbia River on salmon survival rates vary according to seasonality of withdrawals. During periods of high base flows, and assuming that future seasonality of water withdrawals does not change, the upper end of the magnitude of water permit applications being considered in this report (1.3 million acre-feet) will have only minimal effects during periods of low water demand and low withdrawal rates. However, during the summer months of high water demand, the upper range of the prospective withdrawals considered in this report would decrease flows in the
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival Columbia River considerably, especially if these additional withdrawals were diverted during lower-than-average flows during July and August. Moreover, cumulative effects of individual withdrawals eventually result in important thresholds being crossed and with resulting deleterious effects on salmon. Trends such as likely future climate warming across the Columbia River basin; potential additional withdrawals from the Columbia Basin Project, upper basin states, provinces, and tribal reservations; degraded water quality, and periodic poor ocean conditions for salmon all point to additional risks in maintaining viable Columbia River salmon populations. The coincidence of more than one or all these unfavorable trends could have serious negative consequences for Columbia River salmonids. Given the current setting and likely future trends, additional withdrawals from the Columbia River during the summer months of high water demand and during low-flow years will pose substantial additional risks to salmon survival. These risks vary across salmon stocks, with stocks that inhabit the Columbia mainstem during low-flow periods exposed to greater risks. These greater risks to salmon survival should be carefully considered in decisions regarding potential future Columbia River withdrawals during low flows. Selecting the “best” model of salmon-environmental relationships was neither part of this study nor critical to its completion. Analyses and models presented by several expert scientists during open public meetings in the course of this study were used as background information for considering the degree to which additional water diversions, as well as changes to the river’s thermal regime, may pose increased risks to the survival of endangered fish species. This information, along with the large body of scientific evaluations of Columbia River salmon and their habitat, portrays a complex and only partially understood picture of the relative influences of many different environmental variables on salmon survival rates. Efforts to identify whether water velocity, temperature, or some other variable(s) are among the more important factors affecting juvenile salmon survival rates, or identifying critical thresholds associated with these variables, are therefore problematic. Within the body of scientific literature reviewed as part of this study, the relative importance of various environmental variables on smolt survival is not clearly established. When river flows become critically low or water temperatures excessively high, how-
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Managing the Columbia River: Instream Flows, Water Withdrawals, and Salmon Survival ever, pronounced changes in salmon migratory behavior and lower survival rates are expected. The issue of water use permitting decisions is controversial, as these decisions have important environmental, economic, and social implications. Instituting water use permit and extraction policies that vary according to season and river flows will require greater flexibility in these institutions than currently exists. This greater flexibility will be necessary, however, if risks to salmon survival are to be better managed and if salmon management is to move toward more adaptive regimes than used in the past. In addition to greater institutional flexibility, additional cooperation across the entire Columbia River basin appears necessary to better manage risks to salmon. For example, if the State of Washington and its water users exercise caution and restraint in considering the issue of additional water withdrawal permits for low-flow periods, the benefits of any measures will be decreased or negated if other entities in the basin do not adhere to similar practices. The following chapter reviews efforts at cooperation across the Columbia River basin and identifies some of the limits of and lessons from these efforts and what they bode for future cooperative regimes across the basin.
Representative terms from entire chapter: