Hydrosystem, Dam, and Reservoir Passage Rates of Adult Chinook Salmon and Steelhead in the Columbia and Snake Rivers

Transcription

1 Transactions of the American Fisheries Society 133: , 2004 Copyright by the American Fisheries Society 2004 Hydrosystem, Dam, and Reservoir Passage Rates of Adult Chinook Salmon and in the Columbia and Snake Rivers MATTHEW L. KEEFER,* CHRISTOPHER A. PEERY, THEODORE C. BJORNN, 1 AND MICHAEL A. JEPSON Idaho Cooperative Fish and Wildlife Research Unit, Biological Resources Division, U.S. Geological Survey, University of Idaho, Moscow, Idaho , USA LOWELL C. STUEHRENBERG 2 Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, Washington 1-20, USA Abstract. We assessed upstream migration rates of more than,000 radio-tagged adult Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss past a series of dams and reservoirs on the Columbia and Snake rivers. Most fish passed each dam in less than 2 d. Migration behavior in reservoirs and through multiple dam reservoir reaches varied within and between years and between species. Within years, spring summer Chinook salmon migrated more rapidly as water temperature and date of migration increased; between years, spring summer Chinook salmon migrated fastest in low-discharge years. migrations slowed dramatically when summer water temperatures peaked within each year, then increased as rivers cooled in fall. Mean summer temperatures explained more between-year variation in steelhead passage rates than did differences in discharge. Fall Chinook salmon migration rates also slowed during periods of warm water. Protracted passage times within the hydrosystem were most likely for fish from all runs that fell back over and reascended dams and for steelhead that sought thermal refugia by straying temporarily into coldwater tributaries. Development of river systems has significantly altered migration conditions for anadromous salmonids and potentially hampered the ability of fish to reach spawning areas and successfully reproduce. Salmon and steelhead that migrate far upriver to spawn may be especially vulnerable because of the increased likelihood of anthropogenic effects. Most anadromous adult salmonids migrating upstream in the Columbia River and its major tributary, the Snake River, migrate in an environment altered by main-stem hydropower dams and water diversions. Where upstream salmon stocks previously encountered occasional rapids and falls, they now must pass a series of hydroelectric dams and associated river-run reservoirs en route to natal spawning grounds (Figure 1). From Bonneville Dam (river kilometer [rkm] 235) to Chief Joseph Dam (rkm ) on the Columbia River are nine hydroelectric projects and approximately 550 km of impoundments. Fish that migrate to spawning areas in the Snake River must * Corresponding author: mkeefer@uidaho.edu 1 Deceased. 2 Retired. Received December 1, 2003; accepted May 4, 2004 pass eight dams and impoundments from Bonneville Dam to the upstream extent of Lower Granite Reservoir near Asotin, Washington (rkm 55). Upstream passage is no longer possible past Chief Joseph Dam on the Columbia River nor past Hell s Canyon Dam (rkm 1) on the Snake River. Construction and management of the Columbia Snake hydropower system have been implicated, along with habitat degradation, hatchery management practices, and other issues in basinwide declines of wild anadromous salmonids (Raymond 1; National Research Council ). Twelve Columbia basin stocks are currently listed under the Endangered Species Act (ESA), three as endangered (NMFS ). Columbia basin stream-type (Healey ) spring summer Chinook salmon Oncorhynchus tshawytscha spawn in the Snake River basin and lower Columbia River tributaries (mostly spring run) or in upper Columbia River tributaries upstream from Rock Island Dam. Ocean-type fall Chinook salmon mostly spawn in main-stem reaches, the majority of the upriver run returning to the Hanford Reach of the Columbia River and smaller numbers to the Deschutes and Snake rivers (Dauble and Watson ). Upper Columbia River summer-run Chinook salmon are also considered 1413

2 1414 KEEFER ET AL. FIGURE 1. Map of the Columbia River basin showing receiver sites and major dams: BO Bonneville, TD The Dalles, JD John Day, MN McNary, PR Priest Rapids, WP Wanapum, RI Rock Island, RR Rocky Reach, WL Wells, CJ Chief Joseph, GC Grand Coulee, IH Ice Harbor, LM Lower Monumental, GO Little Goose, GR Lower Granite, and HC Hell s Canyon. as ocean-type (Myers et al. 1). Based on life history characteristics, Snake River Chinook salmon are treated as spring summer and fall groups, whereas upper Columbia runs are considered as spring and summer fall stocks (West Coast Chinook Salmon Biological Review Team ). The upriver run of steelhead O. mykiss is mostly from the Snake River basin; additional populations spawn in the upper Columbia, Klickitat, Deschutes, John Day, and Yakima rivers (Raymond 1; ODFW and WDFW 2002). Management concerns for adult migrants in the Columbia River basin include delays and reduced reproductive fitness associated with dam and reservoir passage (Dauble and Mueller 13; Geist et al. ). Direct and delayed mortality from fallback over dam spillways or through turbines and reduced survival rates due to hydrosystem operations and changes in river environment may also negatively affect adult migrants (Quinn et al. ; Dauble and Mueller ). No studies of upstream migration rates in the Columbia and Snake rivers preceded dam construction, but some estimates have been made since dams were built (Burck and Jones 13; French and Wahle 1; Gray and Haynes 1; Haynes and Gray ; Liscom et al. 15). However, interpretations from Columbia and Snake river tagging studies were limited because of small numbers of tagged fish or limited geographical areas (reviewed in Bjornn and Peery ). Large-scale radio-tagging of adult salmonids began in the early s (Bjornn et al. 1, 2002), when several thousand adult spring summer Chinook salmon and steelhead were radio-tagged from to 14 to study passage through the lower Snake River. Concurrently, Blankenship and Mendel (14) studied radio-tagged adult fall Chinook salmon passage through the lower Snake River, and Stuehrenberg et al. (15) studied adult Chinook salmon behavior at selected upper Columbia River dams. These and other studies identified passage problems and established baseline information on adult migration through portions of the basin. However, comprehensive multiyear research on passage through the hydrosystem and on full adult migration histories has been lacking. Advances in radiotelemetry have facilitated increasingly large-scale monitoring of individual adult fish. In, we began radio-tagging adult

3 ADULT SALMONID PASSAGE RATES 1415 TABLE 1. Numbers of adult Chinook salmon and steelhead tagged with radio transmitters at Bonneville Dam (Columbia River basin) from to. Species and run 1 Total Chinook salmon Spring Summer Fall Total , , 2 1, , , 1, 3, ,151 3,20 3,1 1,32 3,142 4,051,2 salmonids at Bonneville Dam, the most downstream Columbia River site, where large numbers of adult fish can be efficiently collected. Over 5 years we tagged and released,2 adult salmon and steelhead near the dam and monitored them as they migrated upstream through the hydrosystem and into major tributaries. The research had multiple objectives, including monitoring finescale movements at dams (Reischel and Bjornn 2003; Boggs et al. 2004), harvest and survival rates (Bjornn et al. ), and distribution to tributaries and hatcheries (Keefer et al., in press b). Our objectives for this paper were to describe fish passage at individual Columbia and Snake River dams and reservoirs and through longer hydrosystem reaches that included multiple dams and reservoirs. We provide here separate summaries of adult passage at dams, through reservoirs, and through hydrosystem reaches, and we evaluate how migration timing, river discharge, and water temperature were related to migration behaviors. Methods Fish trapping and tagging. Adult salmon and steelhead were trapped in the Bonneville Dam adult fish facility (AFF) adjacent to the Washington-shore ladder as they migrated upstream. In 5 years (, excluding 1), radio transmitters were placed in,2 fish: 3,1 spring, 1,32 summer, and 3,142 fall Chinook salmon and 4,051 steelhead (Table 1). Spring Chinook salmon were tagged in all years in April and May, summer Chinook salmon in June through mid to late July, and fall Chinook salmon from early August (, ) or September (1) through October. were tagged from early to mid-june through October (,,, ). We used dates established by the U.S. Army Corps of Engineers (USACE) to separate between spring, summer, and fall-run Chinook salmon at Bonneville Dam (USA- CE ). For our purposes, radio-tagged fish kept their run designation regardless of date of passage at upstream sites. Spring and summer Chinook salmon were combined for some analyses, which is common in Columbia basin research. Each day fish were tagged, a weir was lowered in the Washington-shore ladder to divert fish into the AFF via a short section of ladder. Adult fish entered the laboratory into a large tank and were either diverted into anesthetic tanks for tagging or returned via a chute to the main ladder. We did not tag smaller jack (precocious) salmon or steelhead with fork length less than 50 cm. We radiotagged nearly random samples of adult fish in,, and 1. Selections were not truly random because only fish passing via the Washington-shore ladder were sampled, the proportion sampled each day varied, and no fish were sampled at night; some small steelhead were excluded when we had deployed all of the smaller transmitters on a given tagging day. Of the fall Chinook salmon, we selected those that spawn mostly in the Hanford Reach, Snake, or Deschutes rivers (referred to as upriver brights ) and excluded sexually mature fish (referred to as Tules ) returning to Bonneville Reservoir hatcheries. However, differentiation between the two groups was based on coloration, an imperfect but useful measure (Myers et al. 1). The length of daily trapping periods depended on the number of fish to be outfitted with transmitters and the number moving up the ladder. In and, we followed the same tagging protocols as in earlier years but also selected fish with passive integrated transponder (PIT) tags that identified where fish were tagged as juveniles. We used an automated PIT-tag detection system (Mc- Cutcheon et al. 14) to identify PIT-tagged fish before they were diverted into the anesthetic tank. We attempted to tag fish in proportion to their abundance based on long-term averages of runs at Bonneville Dam. However, run timing varied each year, causing some deviations that could not be wholly compensated for by in-season adjustments in the tagging schedule. We tagged fish throughout each run, and therefore tended to undersample during migration peaks and oversample during pas-

4 141 KEEFER ET AL. sage nadirs. The largest departures from representative sampling occurred from gaps in tagging: no summer Chinook salmon were tagged in July or the second half of July in and 1, and elevated water temperatures precluded tagging fall Chinook salmon in August of 1. We intentionally radio-tagged more late-migrating (B-group) than early-migrating (A-group) steelhead to increase samples of Snake River fish. Overall, however, radio-tagged fish were representative of the runs each year. On average, radio-tagged samples made up 0.% of spring summer Chinook, 0.40% of fall Chinook, and 0.2% of steelhead counted passing Bonneville Dam each year (USACE ). We followed the anesthesia and intragastric tagging methods described in Keefer et al. (2004). Standard transmitters used were 3-V and -V radio tags (Lotek Wireless, Inc., Newmarket, Ont.) that transmitted a digitally coded signal every 5 s on a set frequency. Some combination radio data-storage transmitters (RDST tags) and combination acoustic and radio transmitters (CART tags) were also used in and. Three-volt tags weighed g in air ( cm), -V tags were 2 g (.3 1. cm), RDST tags were 34 g ( cm), and CART tags were 2 g (.0 1. cm). Code sets allowed us to monitor up to 2 fish/frequency. All transmitters were cylindrical with 43 4 cm antennas and were powered by lithium batteries. After tagging, fish were moved to a 2,25-L oxygenated recovery and transport tank where they were held until released (usually h). All fish radio-tagged from to 1 fish were released about.5 km downstream from Bonneville Dam at sites on both sides of the river. In and, 5 1% of each run were released at the downstream sites. The remaining fish were released in the Bonneville Dam forebay as part of a separate evaluation (sample sizes in Table 1). Fish released in the forebay were not used in Bonneville Dam or reservoir passage time analyses but were included in upstream summaries. Study area and telemetry monitoring. The study area included four main-stem dams and reservoirs in the lower Columbia River (Bonneville, The Dalles, John Day, McNary), four lower Snake River dams and reservoirs (Ice Harbor, Lower Monumental, Little Goose, Lower Granite), and two upper Columbia River dams (Priest Rapids, Wanapum; Figure 1). Monitoring occurred throughout each migration at the four lower Columbia River dams, Ice Harbor, and Lower Granite dams in all years, at Lower Monumental and Little Goose dams in all years except, at Priest Rapids Dam from to 1, and at Wanapum Dam in. We assessed movements and passage rates of radio-tagged fish with fixed radiotelemetry receivers. Aerial Yagi antennas were placed on shorelines adjacent to tailrace areas at dams (Figure 1) and tributary mouths, and underwater antennas made of coaxial cable were used to monitor ladder exits at dams. Configurations were similar between locations. On average, tailrace receivers operated 1% to more than % of the time at lower Columbia and Snake River dams. Top-of-ladder receivers operated more than 5% of the time (except for one damaged at McNary Dam). Receivers at Priest Rapids and Wanapum dams operated more than 5% of the time. Outages occurred primarily because of power loss, receiver malfunction, vandalism, or full memory banks. Passage time calculations and statistical analysis. All passage times (d) and rates (km/d) were calculated from telemetry records at the fixed receivers. Dam passage times were calculated from the first record at a tailrace receiver ( km downstream from dams) to the last record at a receiver at the top of the ladder (see Bjornn et al. for additional details on receiver locations). Dam passage times included time fish spent migrating downstream out of a tailrace, a behavior we believe was related to route searching or a reaction to unfavorable passage conditions at dams. Some fish from all stocks fell back over dams and reascended ladders one or more times; only first passage times are reported here. Reservoir passage rates (km/d) were calculated from the last top-ofladder record at the downstream dam to the first tailrace record at the upstream dam. When fish fell back and reascended the downstream dam before migrating upstream, the reservoir start time began after the last passage at the downstream dam. Reservoir passage rates were calculated in the lower Columbia and Snake rivers but not in the upper Columbia River where monitoring was limited. Passage times and rates were also calculated for longer hydrosystem reaches that integrated multiple dam and reservoir passages and the time fish spent falling back over and reascending dams. Hydrosystem passage times were calculated from the Bonneville tailrace past McNary (four dams, three reservoirs, 23 km), Priest Rapids (five dams, four reservoirs and Hanford Reach, 40 km), and Lower Granite (eight dams, seven reservoirs, 42 km) dams, and from the Ice Harbor tailrace past Lower Granite Dam (four dams, three reservoirs, 15

5 ADULT SALMONID PASSAGE RATES 141 FIGURE 2. Mean daily discharge (flow) at Bonneville Dam on the lower Columbia River, April September. km). Hydrosystem passage times for fish that fell back at one or more dams were compared to times for fish that did not fall back using Kruskal Wallis chi-square tests of medians. We did not differentiate between periods of active upstream migration, diel rhythms, temporary holding, downstream movements related to route searching, or prespawn staging. Most migration segments were downstream from known spawning areas, but prespawning behavior may have occurred for some Clearwater River stocks in Lower Granite reservoir and some fall Chinook salmon downstream from Hanford Reach spawning grounds. The small number of steelhead that overwintered within the study reaches were excluded from passage rate calculations. We noted when behavior by spring-migrating steelhead differed from that of fall migrants. Time steelhead strayed temporarily into downstream tributaries during summer and fall were included in calculations because the behavior was widespread and an integral part of the migration (e.g., more than 50% of tagged fish strayed temporarily; Bjornn et al. ; High 2002). Distributions of passage times were rightskewed because some fish took several days or weeks to pass each dam or reservoir; therefore, medians and quartiles were used to describe passage times and rates. We obtained mean daily discharge and water temperature data (Figure 2) at dams on the Columbia and lower Snake rivers from the U.S. Army Corps of Engineers and Grant County Public Utility District (compiled by the University of Washington at html). Temperature data collection ended in September or October at many dams, so temperature was not used in some steelhead and fall Chinook analyses. Individual radio-tagged fish and fish from different portions of each run could encounter a wide and complex range of discharge and temperature conditions during their upstream migration. As a result, individual fish passage times and rates were widely variable and were poorly correlated (r 2 mostly 0.) with most available environmental variables. To reduce variability in passage measures within years, we grouped fish with similar passage dates (day of the year) at each location (using semimonthly blocks of 15 or 1 d) and used median times or rates for each block as the dependent variable. Median times or rates for the full migration were used in between-year comparisons. Two environmental variables were considered: river discharge and water temperature. These were selected because data were of fairly good quality and were available at most dams for most of each year. Other measures, such as river velocity, may have been better predictors of fish behavior, but such data were unavailable. Within years, mean discharge and temperature for each semimonthly

6 141 KEEFER ET AL. TABLE 2. Median passage times (d) and rates (km/d) and number (N) of radio-tagged salmonids recorded from the Bonneville Dam (BO) tailrace to past McNary (MN), Priest Rapids (PR), and Lower Granite (GR) dams and from the Ice Harbor (IH) tailrace to past Lower Granite Dam for each year studied. that wintered over within a reach were not included when the behavior affected passage times. BO MN (23 km) BO PR (40 km) BO GR (42 km) IH GR (13 km) Year N Time Rate N Time Rate N Time Rate N Time Rate Spring Chinook salmon Summer Chinook salmon Fall Chinook salmon block were used as predictors. Mean daily values over the date range when 0% of radio-tagged fish passed a site or means over longer periods (e.g., April July, June August) were used to evaluate between-year differences in fish behavior. Exposure to elevated temperatures can lead to prespawn mortality (Gilhousen ; McCullough 1), so the number of days when main-stem temperatures exceeded 21 C (the incipient lethal temperature identified in Coutant 1 and McCullough et al. ) was also used as an independent variable in between-year comparisons. Migration timing (the semimonthly block when each fish arrived at a dam or reservoir) was used as a third independent variable. Timing, which integrates environmental conditions and the maturation changes occurring for adult migrants, can be a good predictor of fish activity (Økland et al. ; Hodgson and Quinn 2002). Semimonthly blocks were numbered sequentially starting with the earliest arrivals from each run in block 1 (e.g., April 1 15 block 1 for spring summer Chinook salmon and August 1 15 block 1 for fall Chinook salmon). The effects of seasonal migration timing, water temperature, and river discharge on migration times were examined with weighted linear and quadratic regression models (SAS Institute ) for semimonthly blocks within each year. Weighting was by the number of fish per block. Although linear models were adequate for most analyses, environmental variables, such as temperature during the steelhead and fall Chinook migrations, were parabolic, and quadratic regressions were more appropriate. Regression results were considered significant at P 5. We were more interested in general behavior patterns than in producing predictive passage models for individual dams or reservoirs. Therefore, we report specific regression results for selected migration sites but also include qualitative summaries. Results Chinook Salmon Hydrosystem Passage Rates Among radio-tagged Chinook salmon, spring fish migrated most slowly through the Columbia River hydrosystem and summer fish migrated fastest. Median passage rates in the Columbia River were km/d for spring fish, 24 3 km/d for summer fish, and km/d for fall fish (Table 2). The fastest migrants from each run migrated from Bonneville Dam to past McNary Dam (four dams, three reservoirs) in about d, and most migrated through that reach in less than 20 d (Fig-

7 ADULT SALMONID PASSAGE RATES 141 FIGURE 3. Medians (horizontal lines in boxes), quartiles (lower and upper bounds of boxes), 5th and 5th percentiles (solid circles), and th and 0th percentiles (dash ends of vertical lines) of passage times for adult salmonids in the Columbia River basin from the Bonneville tailrace past McNary (MN), Priest Rapids (PR), and Lower Granite (GR) dams and from the Ice Harbor (IH) tailrace past Lower Granite Dam (all years combined). Salmonids (Sp spring, Su summer, and Fa fall Chinook salmon; and Sh steelhead) were monitored via radiotelemetry. ure 3). Most Chinook salmon migrated from Bonneville Dam to past Priest Rapids Dam (five dams, four reservoirs, and the Hanford Reach) or past Lower Granite Dam (eight dams, seven reservoirs) in d. Chinook salmon typically passed through the lower Snake River at slightly lower rates than through the Columbia River (Table 2). Seasonal migration timing. Hydrosystem passage rates for spring summer (combined) Chinook salmon increased within each year as migration date at Bonneville Dam progressed. Semimonthly median passage rates increased significantly (P 5) through time in of 15 weighted linear regression models from the Bonneville Dam tailrace past McNary, Priest Rapids, and Lower Granite dams (Appendix Table A.1). On average, rates increased 2 5 km/d every 2 weeks in all years. The pattern of increasing rates over time was less prevalent in the lower Snake River (Ice Harbor to Lower Granite dams), passage rates increasing significantly through time only in (Table A.1). Most radio-tagged fall Chinook salmon returned to lower Columbia River tributaries or the Hanford Reach, and relatively few migrated up the Snake or upper Columbia rivers (Table 2). In, semimonthly median migration rates from Bonneville Dam to McNary Dam decreased significantly (P 05) from August (33 km/d) to October (1 km/d; Appendix 1). Semimonthly medians ranged from 1 km/d in 1 to 32 km/d in ; no trends through time were statistically evident. River discharge and temperature. Mean daily Columbia River discharge at Bonneville Dam from April through July (this period includes annual snowmelt and passage of almost all spring summer Chinook salmon) ranged from 51% of the 30- year mean in to 13% of average in ( mean,00 m 3 /s; Table 3). Peak discharge at Bonneville Dam occurred in late May or early June in 1, in late April in, and in mid-may in (Figure 2). Between-year differences in Snake River discharge at Ice Harbor Dam were proportionately similar to those for the lower Columbia River. Main-stem water temperatures in the Columbia and Snake rivers ranged from about C during early April to C in late August and early September. Mean water temperatures during spring summer Chinook salmon migrations at Bonneville Dam were coolest in and and warmest in 1 and (Table 3). August temperature means and maxima tended to be highest in 1 and. Within years, river discharge was generally not correlated with spring summer Chinook salmon migration rates through the three hydrosystem reaches that started at Bonneville Dam (Table A.1). Thirteen of 15 regression models using semimonthly Columbia River discharge and median passage times were nonsignificant (P 5). The TABLE 3. Mean April July discharge and water temperature and mean and maximum August temperatures at Bonneville (BO) and Ice Harbor (IH) dams, Columbia River basin,. Year 1 Discharge (m 3 /s) BO,300,000,200,00 3,500 April July means IH 3,0 3,00 2,00 2,0 1,200 Temperature ( C) BO IH Mean ( C) BO August temperatures IH Maximum ( C) BO IH

8 1420 KEEFER ET AL. two exceptions were in, when rates increased as discharge increased through the Bonneville Lower Granite reach, and in when rates decreased as discharge increased through the Bonneville McNary reach. Discharge was not correlated with spring summer Chinook rates in the lower Snake River, except in 1 when rates decreased as discharge increased. Water temperature was strongly positively correlated with migration date (day of the year) for the spring summer Chinook migrations, and regression results were similar to the models for migration timing (Table A.1). Fall Chinook salmon migrations were characterized by low discharge, especially in. Migration rates from Bonneville Dam to McNary Dam decreased significantly in, but not significantly in, as discharge increased (Table A.1). Fall Chinook migrated significantly faster as temperatures decreased in. The relationship was parabolic in ; passage rates were lowest when water temperatures were warmest and, again, late in the migration when temperatures were low. Much of the between-year variability in median hydrosystem passage times for spring summer Chinook salmon was explained by Columbia River discharge. Spring Chinook passed fastest in low discharge years and slowest in high discharge years (0. r 2 0.0, 1 P 53, weighted linear regression) from Bonneville Dam past McNary, Priest Rapids, and Lower Granite dams (Figure 4). Passage times for the three reaches were approximately twice as long in (mean April May discharge, m 3 /s) as in (3,43 m 3 /s). Mean discharge and water temperature were negatively correlated, so migration rates were highest in warm (low discharge) years. Water temperature rate models had lower r 2 values than discharge rate models. Summer Chinook salmon passage was slower in years with high June July discharge, but models were less significant than for spring fish, at least partially because no summer Chinook salmon were tagged in July. With data included, no regressions were significant (P 5). Without data, Bonneville McNary summer Chinook passage times were strongly correlated with mean June July discharge (r 2 0., P 0). Bonneville Lower Granite and Bonneville Priest Rapids models (r 2, P ) were not significant. Passage rates in the Snake River were negatively correlated with discharge at Ice Harbor Dam for spring (May June discharge, r 2 0.1, P 1) and summer (15 June 15 July discharge, r 2 0.5, FIGURE 4. Median annual spring Chinook salmon passage times from the Bonneville (BO) tailrace past McNary (MN), Priest Rapids (PR), Ice Harbor (IH), and Lower Granite (GR) dams versus mean daily Columbia River discharge from April to May,. Linear regressions weighted by the number of fish/year produced r 2 values of 0. (P 23) for the BO MN reach, 0. (P 53) for the BO PR reach, 0. (P 1) for the BO IH reach, and 0.0 (P 14) for the BO GR reach. P 05) Chinook salmon. Between-year differences in all hydrosystem passage rates were proportionately smaller in summer than in spring, and inclusion of summer Chinook salmon data did not substantially change results. Fall fish hydrosystem passage rates varied little between years (Table 2). Fallback. For all years combined, 1% of spring, % of summer, and 3% of fall Chinook salmon fell back over and reascended a dam at least once before passing McNary Dam (Table 4). Annual median Bonneville McNary passage times for spring fish that fell back before passing McNary Dam were 3 d longer than for fish that did not fall back (P 01, Kruskal Wallis 2 tests). Median times were 1 3 d longer for summer fish that fell back, and time differences were significant (P 2) in 2 of 5 years. Medians were 15 d longer for fall fish that fell back (P 05, all years). Higher proportions of each run fell back before passing Lower Granite Dam than before passing McNary Dam (Table 4). Median Bonneville Lower Granite times for fallback fish were longer (5 14 d for spring, 0 d for summer, and 2 d for fall fish) than for fish that avoided fallback. Differences were significant (P 5) in all 5 years for spring fish, in 1 of 2 years for fall fish (none fell back in 1), and in no years for summer fish.

9 ADULT SALMONID PASSAGE RATES 1421 TABLE 4. Percent of radio-tagged salmonids that fell back and reascended at a Columbia River basin dam before they passed McNary and Lower Granite dams by year,. Sample sizes are the same as those in Table 2. Year Fallback before passing McNary Dam (%) Chinook salmon Spring Summer Fall Fallback before passing Lower Granite Dam (%) Chinook salmon Spring Summer Fall Total Hydrosystem Passage Rates Seasonal migration timing. Median steelhead migration rates through multiple dam reservoir hydrosystem reaches were slower and more variable than for Chinook salmon (Figure 3). Rates in each year tended to be slowest through the Bonneville McNary reach and fastest through the lower Snake River reach (Table 2). Semimonthly median times for the Bonneville McNary reach were about d (24 km/d) in June and early July, increased rapidly to 30 0 d (4 km/d) in August, then decreased through September to nearly d again in late October. Median Bonneville Lower Granite passage times were about 25 d (1 km/d) for steelhead arriving in early June, increased in all years to more than 0 d ( km/d) for late June or July arrivals, and then steadily decreased to nearly 20 d (23 km/d) in late October. Weighted quadratic regression models fit the median passage rate data well for the Bonneville McNary and Bonneville Lower Granite reaches in each year (Table A.1). Patterns were similar for the Bonneville Priest Rapids reach, but models were nonsignificant (P 5) in the first 3 years when samples of upper Columbia River steelhead were small. Passage times varied least through the lower Snake River reach, where most semimonthly medians were 15 d ( 20 km/d). with the longest Ice Harbor Lower Granite passage times mostly entered the reach in August. River discharge and temperature. Within years, semimonthly discharge at Bonneville Dam was poorly correlated with steelhead migration rates from Bonneville Dam to McNary Dam (Table A.1). Water temperature was a better predictor of Bonneville McNary migration rates; rates in all years were lowest when temperatures at Bonneville Dam were high. Using semimonthly blocks within years, passage rates for Bonneville Priest Rapids, Bonneville Lower Granite, and Ice Harbor Lower Granite were mostly not correlated with either discharge or available temperature data (1 of 24 regressions nonsignificant at P 5; Table A.1). Correlating annual steelhead hydrosystem passage rates with annual discharge and temperature data was difficult because migrations were so protracted. Most steelhead migrated during the decreasing hydrograph in all years, and discharge differences did not explain much between-year variation. Broad measures of main-stem water temperatures were better predictors of steelhead behavior. Migration rates were lowest in years when main-stem water temperatures were highest and warm water periods were prolonged. Median Bonneville-McNary passage times for steelhead were nearly twice as long in warm years (, ) than during cooler years (; Table 2). Weighted linear regressions for the 4 years were significant for both mean summer temperature (r 2 0.1, P 4) and total days over 21 C (r 2 0., P 22). Median Bonneville Lower Granite passage time was positively correlated with mean summer temperatures in the Columbia (r 2 0.1, P ) and Snake (r 2 0., P ) rivers. Bonneville Priest Rapids passage times increased with lower and upper Columbia River water temperatures, but no models were significant (P 5). Median steelhead travel times through the lower Snake River varied by less than 1 d between years (Table 2), and no environmental metrics were significant. Fallback. For all years combined, % of radiotagged steelhead fell back at least once before passing McNary Dam, and 15% fell back at least once before passing Lower Granite Dam (Table 4). that fell back took 2 d longer to pass through the Bonneville McNary reach than those that did not fall back (P 53, all years, Kruskal Wallis 2 tests). Fallback fish took 1

10 1422 KEEFER ET AL. TABLE 5. Median passage times (d) and, in parentheses, the number of radio-tagged spring, summer, and fall Chinook salmon and steelhead recorded passing lower Columbia and Snake River dams for each year studied. Dam Year Bonneville The Dalles John Day McNary Spring Chinook salmon (2) 1.4 (15) 0. (01) 1.3 () 1.4 (4) 1.1 (25) 2. (351) 1.2 (35) 1.1 (413) 1.0 (5) Summer Chinook salmon 1.1 (22) 2.1 (354) 1.5 (342) 1.0 (30) 1.0 (50) 1.3 () 0. (24) 1.1 (255) 1.0 (30) 0. (45) 1 0. (2) 0. (2) 0. (245) 0. (21) 0. (205) 0. (4) 0. (204) 0. (155) 0. (142) 0. (242) Fall Chinook salmon 2.4 (0) 1.1 (13) 1.0 (13) 1.3 (14) 1.4 () 0. (2) 0.5 (1) 0. (1) 0.5 (15) 0. (141) 1 0. (0) 0. (543) 0. (44) 0. (21) 0. (300) 0. (4) 1.0 (2) 1.3 (20) 0. (23) 0.4 (23) 0. (1) 0. (22) 0. () 0. (44) 0. (4) 0. (3) 0. (3) 0. (302) 0. (5) 0. (20) 0. (33) 0. (43) 0. (5) 0. (505) 0.4 (20) 0.4 (2) 0.4 (3) 0.4 (421) d longer to pass from Bonneville Dam to Lower Granite Dam, which in 2 of 4 years was significantly longer (P 2) than for fish that avoided fallback. Chinook Salmon Dam Passage Times Most of the radio-tagged adult Chinook salmon passed each lower Columbia River or Snake River dam, as determined primarily by fishway ladder and occasionally by navigation lock detections. Tagged fish passed dams almost exclusively during daylight hours, and the few that ascended ladders during evening exited at night. Most passed dams less than 3 h after passing tailrace receivers (Table 5). When fish from the same run were combined across years, median dam passage times ranged from 0.52 to 1.25 d at lower Columbia River dams (Figure 5) and from 0.4 to 1.03 d at lower Snake River dams (Figure ). Long passage times were most frequent for all Chinook salmon at John Day Dam, where 14% of each run took more than 5 d to pass (Table ). Median passage times at Priest Rapids Dam in,, and part of 1 were 2. d for 1 spring fish and 1.40 d for 15 summer fish. At Wanapum Dam, medians in were 0. d for 3 spring fish and 0.1 d for 13 summer fish. Seasonal migration timing. In 4 of 5 years at Bonneville and Dalles dams and in 2 of 5 years at McNary Dam, dam passage times for spring summer (runs combined) Chinook salmon steadily decreased (P 5) as migrations progressed (Table A.2). No relationship between migration date and passage time was observed at John Day Dam. Patterns were inconsistent and mostly nonsignificant at Snake River dams (Table A.2). For fall fish, passage times at lower Columbia River dams tended to increase slightly as migrations progressed. No patterns in passage times for fall fish were evident at lower Snake River dams, where sample sizes were small. River discharge and temperature. As for hydrosystem reaches, water temperature and date were positively correlated for spring summer Chinook salmon at individual dams within each year. Regression results using temperature were similar to those described above using migration timing. In almost all years, river discharge was not correlated with passage times for spring summer fish at either lower Columbia or lower Snake River dams (Table A.2). Water temperatures during fall Chinook migrations rose from August to early September, and then decreased steadily. Most radio-tagged fish passed dams during the cooling phase. No linear or quadratic regression models with semimonthly temperature and median passage times for fall fish were significant (P 5) at Bonneville or

11 ADULT SALMONID PASSAGE RATES 1423 TABLE 5. Extended. Dam Year Ice Harbor Lower Monumental Little Goose Lower Granite Spring Chinook salmon 1 0. (2) 0. (22) 1.5 () 0. (204) 0.5 (41) 1.1 (245) 0. (15) 0.5 (1) 0.5 (24) Summer Chinook Salmon 1.0 (230) 0. () 0. () 0. (35) 1. (55) 1.1 (233) 1.1 (135) 0. (155) 0.4 (33) (14) 0. (4) 0. (43) 0. (3) 0.3 () 0.5 (44) 0.5 (2) 0. (30) 0. (0) Fall Chinook salmon 0.5 (33) 0.4 (33) 0.4 (2) 0.5 (4) 1. (55) 1.2 (233) 1.3 (135) 0. (155) 0.5 (33) (25) 0.3 (2) 0.3 () 0.4 (1) 1.0 (14) 0.5 (52) 0.4 (1) 0.5 (1) 0. (43) 0. () 2.3 () 0. (22) 0. (234) 0. (34) 0.3 (415) 0.3 (3) 0.4 (2) 0.5 (3) 0.4 (21) 0.4 () 0.4 (2) 0.4 (23) 1.1 (151) 0. (205) 0. (223) 0. (20) McNary dams (the only two dams with temperature data available for the full migrations). Models using discharge at the four lower Columbia River dams were almost all nonsignificant (Appendix 2). Differences in discharge and temperature explained some between-year variability in median dam passage times for spring Chinook salmon: slower passage in years with higher mean discharge and faster passage in warm years. However, weighted regression models using the date ranges when most spring fish had passed each dam were almost all nonsignificant (P 0.) for both tem- FIGURE 5. Medians (horizontal lines in boxes), quartiles (lower and upper bounds of boxes), 5th and 5th percentiles (solid circles), and th and 0th percentiles (dash ends of vertical lines) of times for radio-tagged salmonids to pass (traverse) Columbia River dams (all years combined). Abbreviations are as follows: BO Bonneville, TD The Dalles, JD John Day, and MN McNary. FIGURE. Medians (horizontal lines in boxes), quartiles (lower and upper bounds of boxes), 5th and 5th percentiles (solid circles), and th and 0th percentiles (dash ends of vertical lines) of times for radio-tagged salmonids to pass (traverse) Snake River dams (Columbia River basin; all years combined). Abbreviations are as follows: IH Ice Harbor, LM Lower Monumental, GO Little Goose, and GR Lower Granite.

12 1424 KEEFER ET AL. TABLE. Percent of radio-tagged salmonids (all years combined) that took more than 5 d to pass Columbia River basin dams and reservoirs. Sample sizes are the same as those in Tables 5 and ; SH steelhead. Dam Bonneville The Dalles John Day McNary a McNary b Ice Harbor Lower Monumental Little Goose Lower Granite c Lower Granite d Dam passage (%) Chinook salmon Spring Summer Fall SH a McNary to Ice Harbor. b McNary to lower Hanford receiver. c Lower Granite to Snake River receiver. d Lower Granite to Clearwater River receiver Reservoir passage (%) Chinook salmon Spring Summer Fall SH perature and discharge. Likewise, no models were significant for between-year comparisons of summer Chinook salmon dam passage times. Dam Passage Times Similar to Chinook salmon, radio-tagged steelhead passed dams primarily during daylight hours, and most passed each dam, as verified by detections. passed dams faster than Chinook salmon (Figure ), median times being d at lower Columbia River dams and d at lower Snake dams (Table 5). In the upper Columbia, 41 steelhead passed Priest Rapids Dam in and (median 0. d) and 23 passed Wanapum dam in (0.4 d). Few steelhead (all years combined) took more than 5 d to pass individual dams, except at John Day Dam (Table ). Seasonal migration timing. Nonoverwintering steelhead passed dams from late May through December. passage times were typically fastest in late September and October and for some of the earliest June migrants. Passage was slowest when water temperatures peaked in August and again in November and early December before the onset of overwintering. Regression models using semimonthly blocks were mostly nonsignificant (P 5) at lower Columbia River dams, except passage times decreased through time in at Dalles and John Day dams (P 5, weighted linear regression; Table A.2). In the Snake River, quadratic models were significant (P 5) in and at Ice Harbor Dam, and in at Lower Monumental and Little Goose dams: in all cases steelhead passage times were relatively high in late summer and late fall and were lowest in September and early October. River discharge and temperature. Temperature data were unavailable at most dams during the second half of the steelhead migrations each year and analyses were not performed on the partial datasets. Discharge was low through most of each steelhead migration, and regression models were generally not predictive (Table A.2). Chinook Salmon Reservoir Passage Rates Median migration rates through the eight lower Columbia and lower Snake River reservoirs (all but Lower Granite reservoir, all years combined) ranged from 4 to 0 km/d for spring Chinook salmon (Figures, ), 1 to km/d for summer fish, and 51 to 5 km/d for fall fish (Table ). In the lower Columbia River, spring and summer fish consistently migrated more rapidly through John Day and McNary reservoirs than through the Bonneville and Dalles reservoirs. Fall fish also migrated fastest through John Day reservoir. In McNary reservoir, fall fish that returned to Hanford Reach migrated quickly, whereas those that returned to the Snake River migrated more slowly, (rates similar to those through the Bonneville and Dalles reservoirs). In the three lower Snake River reservoirs, summer fish migrated fastest and spring fish migrated slowest. Migration rates were slower through Lower Granite reservoir, especially for fish that returned to Clearwater River. Few spring summer or fall Chinook salmon took more than 5 d to pass through any reservoirs, except Lower Granite reservoir (Table ).

13 ADULT SALMONID PASSAGE RATES 1425 FIGURE. Medians (horizontal lines in boxes), quartiles (lower and upper bounds of boxes), 5th and 5th percentiles (solid circles), and th and 0th percentiles (dash ends of vertical lines) of migration rates for radiotagged salmonids through Columbia River reservoirs (all years combined). Abbreviations are as follows: BO Bonneville, TD The Dalles, JD John Day, and MN McNary. Medians rates for the McNary reservoir are designated s for fish that entered the Snake River and h for those that entered the Hanford Reach of the Columbia River. FIGURE. Medians (horizontal lines in boxes), quartiles (lower and upper bounds of boxes), 5th and 5th percentiles (solid circles), and th and 0th percentiles (dash ends of vertical lines) of migration rates for radiotagged salmonids through Snake River (Columbia River basin) reservoirs (all years combined). Abbreviations are as follows: IH Ice Harbor, LM Lower Monumental, GO Little Goose, and GR Lower Granite. Median rates for the Lower Granite reservoir are designated c for fish that entered the Clearwater River and s for those that continued up the Snake River. Seasonal migration timing. Reservoir migration rates for spring summer Chinook salmon increased with reservoir entry date within each year (runs combined; Table A.3). Median rates for fish grouped by semimonthly blocks increased significantly (P 5) through time in 1 of 20 weighted linear regression models for lower Columbia reservoirs (e.g., Figure ). Models were not significant (P 5) for Bonneville (1), John Day (), and McNary (, ) reservoirs. Rates increased about 4 km/d (range, km/ d) every 2 weeks in the significant models. In the three lower Snake River reservoirs, rates increased with entry date in all years, and 5 of 13 weighted linear models were significant (P 5), including 1 year (1) for Ice Harbor reservoir and 2 years (, ) for Lower Monumental and Little Goose reservoirs. As for downstream reservoirs, migration rates through Lower Granite reservoir to the Clearwater and Snake River receivers increased with Lower Granite reservoir entry date in all years, although statistical models were constricted by sample sizes. Within years, semimonthly migration rates for fall Chinook salmon in Bonneville and the Dalles reservoirs were relatively constant. In contrast, fall fish migration rates through the John Day and McNary Hanford reservoirs were highest in August and again in early November, rate nadirs occurring in October. River discharge and temperature. Within years, river discharge was not correlated with spring summer or fall Chinook salmon reservoir passage rates in lower Columbia River reservoirs, with one exception: in, spring summer fish rates decreased significantly as discharge increased through the Dalles, John Day, and McNary reservoirs (Table A.3). Spring summer fish mi- FIGURE. Semimonthly median migration rates for spring summer Chinook salmon passing through the Dalles reservoir (Columbia River basin), based on the semimonthly block when fish entered this reach,.

14 142 KEEFER ET AL. TABLE. Median passage rates (km/d) and, in parentheses, the number of radio-tagged spring, summer, and fall Chinook salmon and steelhead recorded passing through lower Columbia and Snake River reservoirs by year, where IH Ice Harbor Dam, GR Lower Granite Dam, HAN Hanford receiver, SNR Snake River receiver, and CWR Clearwater River receiver. Kilometer values are the distances between the downstream dams and the receivers at the upstream ends of reservoirs. Site Year Bonneville (0 km) The Dalles (3 km) John Day (0 km) McNary IH ( km) McNary HAN (3 km) Spring Chinook salmon 1 3 (34) 3 (405) 51 (404) 4 (40) (43) 41 (21) 43 (35) 50 (32) 52 (344) 2 (52) 1 () 3 (330) (303) (30) 0 (450) 55 () 5 () 0 (1) (202) 4 (43) 5 (35) 2 (5) 4 (2) 0 (1) Summer Chinook salmon 1 54 () 5 (214) (15) () (200) 51 () 5 (14) 0 (1) 3 (2) () 1 () (1) 3 (1) (153) 3 (15) 4 (1) 0 (25) 4 (32) (3) 0 () 2 (3) (1) (154) 3 (2) Fall Chinook salmon 1 4 (24) 54 (235) 5 (32) 4 (32) 5 (24) 55 (30) 4 (2) 3 (1) (30) 4 (32) 53 (2) 50 () (2) 55 (23) 1 (322) 24 (31) 1 (2) 25 (5) 30 (00) 30 (421) 30 (51) 31 (541) 3 (552) 43 (244) 40 (3) 41 (30) 4 (45) 35 (1) 31 (2) 2 (422) 31 (35) 35 (2) 33 (3) 4 (20) grated through lower Snake River reservoirs more quickly when discharge was low, but only models for passage through Lower Monumental and Little Goose reservoirs in and were significant (Table A.3). Discharge peaked early in, and most spring summer fish migrated during the decreasing hydrograph. Significant models for discharge may have reflected underlying influences of migration timing and water temperature. Between-year differences in reservoir migration rates for spring summer Chinook salmon were strongly related to mean discharge over the date range when 0% of each run entered a reservoir. Fish migrated fastest through Bonneville, Dalles, and John Day reservoirs in years with low mean discharge for both spring (0. r 2 0.5, linear regression) and summer ( r 2 0.4) fish. Rates also increased as annual seasonal discharge decreased in McNary reservoir for fish that entered the Snake (r spring fish, 0.3 summer fish; 5 years) or upper Columbia rivers (r spring fish, 0.4 summer fish; 4 years). Spring (0.4 r 2 0.) and summer (0. r 2 ) fish migrated faster through all four Snake River reservoirs in low discharge years. Substituting mean discharge for the full migration period (April July) produced similar regression coefficients. Fall fish migrated through lower Columbia reservoirs (including McNary Hanford) faster in (low discharge) than in (near-average discharge) in almost all semimonthly pairs, but differences were small. Reservoir Passage Rates migrated through lower Columbia and lower Snake River reservoirs much more slowly than Chinook salmon, median rates for all years combined being km/d (Figures, ). Compared with Chinook salmon, relatively large proportions ( 4%) of steelhead took more than 5 d to pass through lower Columbia River reservoirs and Lower Granite Reservoir (Table ), and 34% took more than d to pass through Bonneville, the Dalles, McNary-Ice Harbor, and Lower Granite reservoirs. Telemetry records at fixed receivers in tributaries indicated that many steelhead strayed temporarily into coldwater refugia during reservoir passage, particularly during the warmest periods, and the behavior was strongly associated with the long migration times.