EVALUATION OF FISHWAY MODIFICATIONS TO IMPROVE PASSAGE OF ADULT CHINOOK SALMON AND STEELHEAD THROUGH THE TRANSITION POOL AT LOWER GRANITE DAM, 2008

Transcription

1 Technical Report EVALUATION OF FISHWAY MODIFICATIONS TO IMPROVE PASSAGE OF ADULT CHINOOK SALMON AND STEELHEAD THROUGH THE TRANSITION POOL AT LOWER GRANITE DAM, 2008 by T.S. Clabough, G.P. Naughton, M.A. Jepson, C.C. Caudill, and C.A. Peery 1 Department of Fish and Wildlife Resources University of Idaho, Moscow, Idaho And B.J. Burke National Marine Fisheries Service 2725 Montlake Blvd. East, Seattle, Washington for U.S. Army Corps of Engineers Walla Walla District 1 Present Address: Cramer Fish Sciences 121 W. Sweet Ave Moscow, ID

2 Technical Report EVALUATION OF FISHWAY MODIFICATIONS TO IMPROVE PASSAGE OF ADULT CHINOOK SALMON AND STEELHEAD THROUGH THE TRANSITION POOL AT LOWER GRANITE DAM, 2008 by T.S. Clabough, G.P. Naughton, M.A. Jepson, C.C. Caudill, and C.A. Peery 1 Department of Fish and Wildlife Resources University of Idaho, Moscow, Idaho And B.J. Burke National Marine Fisheries Service 2725 Montlake Blvd. East, Seattle, Washington for U.S. Army Corps of Engineers Walla Walla District 1 Present Address: Cramer Fish Sciences 121 W. Sweet Ave Moscow, ID

3 Table of Contents Table of Contents... ii Acknowledgements... ii Abstract... iii Introduction... 1 Methods... 1 Fishway modification... 1 Tagging and monitoring... 2 Passage times and fish behavior... 2 Statistical analysis... 4 Results... 4 Tailwater elevations... 4 Weir pool elevations and underwater orifice velocities... 5 Passage and behavior... 5 Temperature and overnighting Discussion Conclusions References Acknowledgements Many people provided their time and assistance during the course of this study T. Dick, D. Joosten, K. Johnson, and K. Tolotti installed and maintained radiotelemetry equipment. T. Dick, D. Joosten, S. Lee, and M. Donohue helped with field operations and data collection. K. Frick assisted with database management. Funding for this study was provided by the U.S. Army Corps of Engineers, Walla Walla District. We also thank F. Higginbotham and S. Milligan, U.S. Army Corps of Engineers, for their cooperation and assistance during all phases of this project. ii

4 Abstract Previous studies of Pacific salmon migration behaviors at Snake River dams indicated slow passage at transition pools in adult fishways. In 2001 and 2002, we conducted an experiment to evaluate if modified weirs affected adult salmon and steelhead passage times and route selection through the Lower Granite Dam transition pool. Attraction flows through weir orifices were experimentally manipulated using removable aluminum panels. Results from the studies indicated a greater percentage of radiotagged spring summer Chinook salmon passed straight through the transition pool and median transition pool passage times were significantly lower when the panels were deployed. Based on these results, the U.S. Army Corps of Engineers modified the fish ladder at Lower Granite Dam in 2006 prior to the migration season. Modifications included narrowing the transition pool and increasing the weir crest height of the lowest eleven weirs. To evaluate the effectiveness of the modifications, we radio-tagged and monitored adult spring-summer and fall Chinook salmon and steelhead as they passed Little Goose and Lower Granite dams and compared their performance to that measured during previous years without modifications in place. Transition pool passage times at Lower Granite Dam for spring-summer Chinook salmon were significantly faster in 2006 than in 2003 and 2004 (non-modified years). Spring-summer Chinook salmon passage times were also faster in 2008, though the results were not statistically different (P > 0.05) than in 2003 and The other runs exhibited similar, though not statistically different responses. The frequencies of downstream exits from the Lower Granite transition pool to the tailrace for spring Chinook salmon in 2006 and 2008 were lower than in 2003 and We also compared the difference in passage times by individual fish at Little Goose and Lower Granite dams in an effort to statistically control for interannual variation in river environment. Comparisons of interannual differences in passage times at the two dams indicated that passage times decreased for individual fish at Lower Granite Dam compared to Little Goose dam in modified years compared to the non-modified years. Passage times through the Lower Granite transition pool were also faster in 2006 and 2008 than in 2003 and However, the transition pool passage times were not as low as those achieved during the experimental weir modifications in 2001 and 2002 and passage behavior only improved for spring-summer Chinook salmon during 2008 with the permanent modification. This difference may have been caused by differences in river conditions among years, differences in fishway hydraulics between the experimental and permanent modifications, or both. iii

5 Introduction When tailwater elevations at Lower Granite Dam are high, the lowest weirs of the fish ladder (within the transition pool) become submerged. When submerged, water velocities through the underwater orifices of these weirs are decreased and this results in diminished attraction flows for adult salmon (Oncorhynchus spp.) and steelhead (O. mykiss) swimming upstream to spawn. In 2001 and 2002, experimental ladder modifications were tested at Lower Granite Dam to evaluate effects of increased underwater orifice velocities on fish passage times and behaviors. Results from these studies indicated that a greater percentage of radio-tagged spring and summer Chinook salmon (O. tshawytscha) passed straight through the transition pool and median transition pool passage times were significantly lower during the treatment condition (Naughton et al and 2007). In 2006, the Army Corps of Engineers structurally modified eleven weirs within the transition pool at Lower Granite Dam in an attempt to increase water velocities through the weirs and to facilitate the upstream passage of adult salmonids. In 2008, we monitored water elevations in the first two weir pools, and we radio-tagged adult Spring-summer Chinook salmon, steelhead and fall Chinook salmon at Ice Harbor dam and monitored passage at Lower Granite and Little Goose dams. We compared fish passage times and behaviors to those measured during previous years both with (2006) and without modifications in place (2003 and 2004). We additionally monitored the passage times and behaviors of these same fish at Little Goose Dam to account for interannual variation in passage conditions among study years. Fishway Modification Methods The Lower Granite modification consisted of narrowing the width of the transition pool from 38 ft to 20 ft near a 90-degree turn in the fishway just downstream from the transition pool (Figure 1). The eleven most downstream weirs were also modified with aluminum/steel plating to increase the height of weir crest by approximately 3.2 ft. This was designed to increase the depth of each weir pool, increase the hydraulic head, and thereby increase water velocities through the weir orifices. Increased orifice velocity is thought to facilitate attraction and entrance by adult salmonids. We used tailwater elevations at Lower Granite dam (obtained from to determine when and how many weirs were submerged before and after the 2006 weir modification. Transition pool water elevations were calculated by adding 1.5 ft to tailwater elevations (the 1.5 ft difference between the tailrace and fish ladder water elevation provides attraction flow for fish passage). In 2008, transition pool elevations below and above the first two downstream weirs in the fish ladder were measured with a water level meter to estimate weir head differences and underwater orifice velocities. Underwater orifice velocities were calculated using the following equation (Clay 1995): V = 2gh where h is the head and g is the acceleration of gravity. 1

6 Tagging and Monitoring We radio-tagged 360 spring summer Chinook salmon, 275 fall Chinook salmon, and 300 steelhead at Ice Harbor Dam from 15 April through 25 October 2008 using established methods. Three regurgitated tags were found (two at the release site and one in the Lower Granite Dam adult trap). For detailed descriptions of tagging methods see Mann and Peery (2005) and Naughton et al. (2006). A) B) Figure 1. A) Narrowing of the transition pool wall and B) aluminum/steel plating on lower eleven weirs in the fish ladder at Lower Granite Dam in We monitored movements of radio-tagged fish with fixed radio telemetry sites at Little Goose and Lower Granite dams (Figure 2). We used SRX/DSP receivers/processors (Lotek Wireless) connected to nine-element aerial Yagi and underwater antennas to determine when a fish first reached the tailrace, approached a fishway entrance, entered a fishway, moved within a fishway, and/or exited a fishway back into the tailrace. Seven underwater antennas at Lower Granite Dam and six underwater antennas at Little Goose Dam were used to detect when fish first entered the transition pool and exited the transition pool (moving upstream or downstream in the ladder). Telemetry data were downloaded from receivers every 1-2 weeks. Outages at Lower Granite transition pool receivers occurred on a total of 18 days (9 days in April, 5 days in May, and 4 days in June) in 2008 (totaling 8% of the total receiver-time). Passage Times and Fish Behaviors Passage time analyses included only first ascents, i.e., we excluded passage attempts after fallback events. However, we did calculate the fallback percentage (the number of unique fish with transmitters that fell back divided by the number of unique fish with transmitters known to have passed the dam) and the fallback rate (the number of fallback events divided by the number of unique fish known to have passed the dam) for both Little Goose and Lower Granite dams. Fall Chinook salmon that were diverted at the Lower Granite Dam fish trap and transported to hatcheries were not included in our analyses. 2

7 Lower Granite Dam Spillway Collection Channel North-shore opening North powerhouse opening Open orifice gates Flow South-shore openings Modified Transition Pool Yagi Antenna Underwater Antenna Little Goose Dam Spillway North-shore opening North powerhouse opening Collection Channel Closed orifice gates Flow South-shore opening Transition Pool Figure 2. Aerial view of radio antenna locations at Little Goose (lower panel) and Lower Granite dams (upper panel) during Tailrace aerial antennas were approximately 1 km downstream from the dams. We calculated six passage time metrics for radio-tagged salmon and steelhead at both Little Goose and Lower Granite dams. Specifically, we calculated the time fish used to swim from: (1) the first tailrace record to first approach at a dam fishway, (2) the first tailrace record to first entry at the dam, (3) first fishway approach to first fishway entry, (4) first fishway entry to first record in the transition pool (5) first record in transition pool to last record in transition pool, and (6) first tailrace record to last record at the top-of-ladder antenna. We also classified passage routes into one of three categories for each fish: (1) fish that swam straight through the transition pool, (2) fish that exited the transition pool into the collection channel or (3) fish that exited the transition pool into the tailrace. We evaluated transition pool passage times as they related to overnighting behavior. Specifically, we compared pool passage times for tagged fish that did or did not pass the transition pool on the same day as their first detection in the transition pool. Sample sizes of fall Chinook salmon and steelhead transition pool records were about one-third smaller at Little Goose Dam than Lower Granite during 2006 due to receiver outages. We matched the forebay and tailrace hourly temperatures to the time a fish first entered the transition pool (FP) to determine top-to-bottom temperature differences in the ladders in relation to overnighting behavior. 3

8 Statistical Analysis We used analysis of variance (ANOVA) to test whether transition pool passage times in 2006 and 2008 (modified weirs) were significantly different from 2003 and/or 2004 (non-modified). Transition pool passage times were natural log transformed to normalize the data. Tukey s multiple comparison tests (Zar 1999) were used to evaluate which years differed significantly from each other when overall ANOVA results were significant. We also used ANOVA to test if tailrace water temperatures encountered by adults were significantly different among study years for each run (based on the hourly tailrace temperature when a fish first entered the transition pool). Among those fish with complete migration histories at both dams, we calculated the difference in passage time at the two dams as (Transition Pool Passage Time Lower Granite ) i - (Transition Pool Passage Time LittleGoose )i for each individual fish i = 1-n where n was the total number of fish with complete passage records at both dams. We then used a Mann-Whitney U- test with Bonferroni correction to test whether there was a significant difference between the distributions of passage time differences among years. Specifically, we tested whether relatively fast fish at Little Goose were also fast at Lower Granite before and/or after the modification. Tailwater Elevations Results In 2008, average monthly transition pool water elevations in the first pool ranged from ft (above mean sea level) in August to ft in November (Figure 3). In May and the beginning of June 2008, fish ladder water elevations were relatively high compared to previous years (Figure 3). However, there were only four days in May when the most downstream weir (634 ft) was submerged and one of those four days when the second-most downstream weir (635 ft) was also submerged (Table 1). After the modification (2006, 2008) each of the eleven downstream weir crests were 3.2 ft higher than the pre-modification years ( ). Average monthly transition pool water elevations (ft) at Lower Granite Dam APR MAY JUN JUL AUG SEP OCT NOV Figure 3. Average monthly tailwater elevations (ft above sea level) at the most downstream weir (634 ft) in the fish ladder at Lower Granite Dam in , 2006, and

9 Table 1. Number of days in each month the two most downstream weirs (634 and 635 ft above sea level, respectively) were submerged at Lower Granite Dam in the study years , 2006, and Note: The elevation of weir submergence was estimated as the fish ladder elevation (1.5 ft higher than tailwater elevation) plus 2 ft in and tailrace plus 5.2 ft in 2006 and 2008 post-modification. Month Weir 1 April May June July August September October November Weir 2 April May June July August September October November Weir pool elevations and underwater orifice velocities Pool elevations below and above the two most downstream weirs in the fish ladder were measured weekly from April 16 through Dec 1, Target weir head differences (0.25 ft) and underwater orifice velocities (4.0 ft/sec) were met during low transition pool water elevations which occurred on average in April and August ( ft). However, when transition pool water elevations were above ft, weir head differences dropped below 0.25 ft, achieving estimated underwater orifice water velocities of less than 4.0 ft/sec (Figure 4). Based on transition pool passage dates, 75% of all radio-tagged fish in 2008 passed the dam when tailwater elevations were greater than 635 ft. Passage and behavior Of the 360 spring-summer Chinook radio-tagged at Ice Harbor Dam in 2006, 311 (86 %) were recorded at Little Goose Dam and 281 (78%) were recorded at Lower Granite Dam. Of the 275 radio-tagged fall Chinook salmon in 2008, 229 (83%) were recorded at Little Goose Dam and 220 (80%) were recorded at Lower Granite Dam. Of the 300 radio-tagged steelhead, 263 (88%) and 246 (82%) were recorded at Little Goose and Lower Granite dams in 2008, respectively. 5

10 Weir head difference (ft) A) Weir 1 Weir Under water orifice velocity (ft/sec) B) Transition Pool water elevation (ft) Figure 4. Weir head differences (A) and calculated under water orifice velocities (B) at the first and second-most downstream weirs in the fish ladder. Horizontal lines represent target weir head differences (A) and target underwater orifice velocities (B). 6

11 Fallback percentages ranged from % at both dams in In 2008, 5.7% of radiotagged spring-summer Chinook (7.8 % fallback rate), 6.3 % of fall Chinook and 2.0 % of steelhead fell back at Little Goose Dam. At Lower Granite Dam in 2008, 6.9% of radio-tagged spring-summer Chinook, 4.6 % of fall Chinook (5.2 % fallback rate) and 2.8 % (3.2% fallback rate) of steelhead fell back. Of the fish that fell back 85-88% and % at Lower Granite and Little Goose dams, respectively passed the dam a second or third time. Spring summer Chinook salmon had similar median passage times at Little Goose and Lower Granite dams in 2008 (Table 2). The largest median differences between dams for spring summer Chinook salmon were for first fishway entry to first transition pool time and total transition pool time (first pool to last pool). Median times from first entry to first pool and first pool to last for spring-summer Chinook salmon were almost an hour at Lower Granite Dam compared to less than a quarter of an hour at Little Goose Dam (Table 2). Table 2. Passage metrics Sample sizes and median time (hours) from first tailrace record to first fishway approach, first tailrace record to first fishway entry, first approach to first fishway entry, first entrance to first record in a transition pool (first pool), first pool to last record in the transition pool (last pool) prior to making last ascent of fishway, and total time to pass at Little Goose and Lower Granite dams for adult spring summer Chinook (SPSUCK) salmon, fall Chinook salmon (FACK), and steelhead(sthd) radio-tagged at Ice Harbor Dam in SPSUCK FACK STHD n Med. n Med. n Med. First tailrace to first approach Little Goose Lower Granite First tailrace to first entry Little Goose Lower Granite First approach to first entry Little Goose Lower Granite First entry to first pool Little Goose Lower Granite First pool to last pool Little Goose Lower Granite First tailrace to ladder top Little Goose Lower Granite

12 Median times from first fishway entry to first transition pool for fall Chinook salmon and steelhead ranged from minutes at Lower Granite Dam compared to less than two minutes for both species at Little Goose Dam (Table 2). Median transition pool passage times ranged from 3.5% to 25.8% of median dam passage times among runs at Lower Granite Dam. For spring summer Chinook salmon, transition pool passage times at Lower Granite Dam were statistically different among years (P < 0.001; Figure 5). In 2006 median transition pool passage times were significantly lower than in 2003 and Although passage times in 2008 were faster than in 2003 and 2004 they were not statistically different than the pre-modification years. For fall Chinook salmon and steelhead at Lower Granite Dam, we found no significant difference in pool passage times among years (P = for fall Chinook salmon and P = for steelhead; Figure 5). Median transition pool passage times were lower in 2006 and 2008 than in 2003 and 2004 for all runs but not as low as times reported during the prototype weir modification in 2001 and 2002 (Table 3). Comparison of the difference between passage times at Little Goose Dam and Lower Granite Dam revealed relatively faster passage at Lower Granite Dam in years after the modification. We found a significant difference among years in the paired difference in passage time for spring summer Chinook salmon (P <0.001), fall Chinook salmon (P = 0.027), and steelhead (P < 0.001). Median transition pool passage times differed between the two dams in 2006 compared to 2003 (P < 0.001) and 2004 (P = 0.004) and 2008 compared to 2003 (P < 0.001) for Chinook salmon (Figures 6-7). Fall Chinook salmon differences decreased in 2006 compared to 2004 (P = 0.004) and steelhead differences decreased in 2008 compared to 2003 and 2004 (P < 0.001). The percentage of fish that passed straight through the transition pool at Lower Granite Dam was variable, with the values observed in 2008 falling within the range observed in previous years (Table 5). A higher proportion of Chinook passed straight through the transition pool at Little Goose compared to Lower Granite; however, median transition pool passage times for fish that passed straight through at Lower Granite were similar to those at Little Goose Dam (Table 4). In contrast, a higher percentage of steelhead swam straight through the transition pool at Lower Granite Dam than at Little Goose Dam in Overall, a higher percent of springsummer Chinook salmon swam straight through the transition pool at Lower Granite Dam in the modified years (2006 & 2008) compared to the unmodified years ( ). A lower percent of fall Chinook salmon swam straight through the transition pool in the modified versus unmodified years, though sample sizes were low (n < 45) in the unmodified years. The percentage of steelhead that swam straight through the transition pool was similar between the modified and unmodified years (Table 5). 8

13 6 Spring/Summer Chinook 4 Log transformed FPLP (h) Fall Chinook 4 Log transformed FPLP (h) Steelhead 4 Log transformed FPLP (h) Up Down Up Down None None Mod Mod Figure 5. Means (crosses), medians (horizontal lines within boxes), quartiles (upper and lower bounds of boxes), 10th and 90th percentiles (ends of whiskers), and 5th and 95th percentiles (circles) of the natural log transformed transition pool passage times (FPLP) at Lower Granite Dam for spring summer Chinook salmon, fall Chinook salmon, and steelhead in , 2006 and Panels were up during control periods and down during treatments during the weir modification test in See Table 2 for sample sizes. 9

14 Table 3. Median time for radio-tagged adult spring summer Chinook salmon, fall Chinook salmon, and steelhead to swim through the transition pools (TP) at Little Goose and Lower Granite dams during , 2006, and Treatment Little Goose Lower Granite Species Year condition Median TP time (h) n Median TP time (h) n Spring-summer 2000 Control Chinook 2000 Treatment Control Treatment Control Treatment None None Modified Modified Fall Chinook 2000 Treatment Control Treatment Control Treatment None None Modified Modified Steelhead 1994 None None Treatment Control Treatment Control Treatment None None Modified Modified After initial weir modification structure was in place and weir panels were added at Lower Granite Dam. 2 Weirs in down position simulated modifications made to Lower Granite weirs for

15 6 Spring/Summer Chinook 4 Log transformed FPLP (h) n=306 n=306 n=179 n=179 n=224 n=224 n=159 n= Fall Chinook 4 Log transformed FPLP (h) n=26 n=26 n=37 n=37 n=124 n=124 n=171 n= Steelhead 4 Log transformed FPLP (h) n=188 n=188 n=131 n=131 n=140 n=140 n=173 n= LGO LGR LGO LGR LGO LGR LGO LGR Figure 6. Means (crosses within boxes), medians (horizontal lines within boxes), quartiles (upper and lower bounds of boxes), 10th and 90th percentiles (ends of whiskers), and 5th and 95th percentiles (circles) of the natural log transformed transition pool passage times of the same fish at Little Goose and Lower Granite dams for spring summer Chinook salmon, fall Chinook salmon, and steelhead in , 2006 and

16 Median transition pool time difference (hours) Spring/Summer Chinook Median transition pool time difference (hours) Median transition pool time difference (hours) Fall Chinook Steelhead Figure 7. Median transition pool passage time differences of individual fish at Little Goose and Lower Granite dams for spring summer Chinook salmon, fall Chinook salmon, and steelhead in , 2006 and Note y-axis scales are different. For sample sizes see Figure 6. 12

17 Table 4. Median time in hours (proportion) for radio-tagged adult spring summer Chinook salmon (SPSU CK), fall Chinook salmon (Fall CK), and steelhead (STHD) to swim through the transition pools at Little Goose (LGO) and Lower Granite (LGR) dams based on behaviors exhibited during The proportions of fish exhibiting each transition pool behavior are shown in parentheses. Exit pool Species Dam n Straight through but not ladder Exit ladder All behaviors SPSU CK LGR (0.27) 0.60 (0.39) (0.35) 0.85 (1.00) SPSU CK LGO (0.39) 0.26 (0.45) (0.16) 0.20 (1.00) Fall CK LGR (0.13) 0.72 (0.27) (0.59) 3.38 (1.00) Fall CK LGO (0.16) 0.57 (0.28) 9.18 (0.56) 1.92 (1.00) STHD LGR (0.31) 0.63 (0.21) 5.74 (0.48) 1.03 (1.00) STHD LGO (0.24) 0.45 (.017) (0.59) 3.12 (1.00) Overnighting and Temperature We used tailrace temperatures as surrogates for transition pool temperatures and found significantly higher temperatures experienced by radio-tagged spring summer Chinook salmon (P < 0.001) in 2006 than in and in 2008 than in 2003 (Figure 8). Radio-tagged fall Chinook salmon experienced significantly (P = 0.001) warmer tailrace temperatures in 2003 than in 2004, 2006, and Radio-tagged steelhead experienced (P < 0.001) warmer tailrace temperatures in 2003, 2004, and 2008 than in Differences in temperature between the top and bottom of fish ladders appear to slow migration at Snake River Dams (Caudill et al. 2006). Mean differences between hourly forebay and tailrace temperatures were slightly higher for all runs (except spring-summer Chinook in 2006 and 2008 and steelhead in 2008) of radio-tagged fish that overnighted at Lower Granite Dam compared to those that did not overnight, though mean temperature differences were smallest in 2006 and 2008 (Table 6). All radio-tagged fish that did not pass the dam on the same day as their initial detection at the dam had longer transition pool passage times. 13

18 Table 5. Percentage of radio-tagged Chinook salmon and steelhead passing straight through the transition pool, exiting the transition pool but not the dam and exiting the ladder into the tailrace at Lower Granite Dam in , 2006 and Sample sizes are in parentheses. Species Year Weirs n Straight through Exit pool but not ladder Exit ladder Spring-summer 2001 Control (21) 43.1 (90) 47.9 (98) Chinook 2001 Treatment (76) 29.3 (61) 34.1 (71) 2002 Control (42) 49.1 (56) 14.0 (16) 2002 Treatment (78) 37.0 (54) 9.6 (14) 2003 None (60) 31.4 (97) 49.2 (152) 2004 None (30) 34.2 (63) 49.5 (91) 2006 Modified (72) 38.8 (95) 31.8 (78) 2008 Modified (43) 38.9 (63) 34.6 (56) Fall Chinook 2001 Control (6) 55.6 (10) 11.1 (2) 2001 Treatment (14) 40.5 (15) 21.6 (8) 2002 Control (6) 14.3 (1) 2002 Treatment (6) 50.0 (12) 25.0 (6) 2003 None (7) 14.8 (4) 59.3 (16) 2004 None (15) 9.8 (5) 60.8 (31) 2006 Modified (23) 26.8 (55) 62.0 (127) 2008 Modified (24) 27.4 (49) 59.2 (106) Steelhead 2001 Control (39) 40.0 (32) 11.3 (9) 2001 Treatment (46) 39.8 (37) 10.8 (10) 2002 Control (55) 54.1 (92) 13.5 (23) 2002 Treatment (77) 46.0 (80) 9.8 (17) 2003 None (67) 25.6 (53) 42.0 (87) 2004 None (57) 17.9 (27) 44.4 (67) 2006 Modified (84) 22.4 (53) 42.2 (100) 2008 Modified (59) 21.1 (40) 47.9 (91) 14

19 17 Spring/Summer A) Chinook Tailrace temperature (C) A B C BC 9 Tailrace temperature (C) Fall B) Chinook A B B B 14 Tailrace temperature (C) C) Steelhead A A B A Figure 8. Least square means of tailrace temperatures (at the time of a fish s first pool) with standard error bars for spring summer Chinook, fall Chinook salmon, and steelhead in , 2006, and Note temperature scales are different. Letters above years denote significant differences. 15

20 Table 6. Number (percent) of radio-tagged Chinook salmon and steelhead overnighting at Lower Granite Dam, mean temperature difference between the forebay and tailrace temperature, and the median transition pool passage time (FPLP). Percent of fish overnighting is shown in parentheses. * Indicates that temperature data were not available for all fall Chinook and steelhead in 2006; therefore only fish with temperature data are shown. Steelhead* Yes 23 (20) No 91 (80) Note: negative values in the range of temperature difference indicate forebay temperatures were cooler than tailrace temperatures. 16 Mean temperature difference (C) Range of temperature difference (C) Year Species Overnight n 2003 Spring-summer Yes 92 (30) No 217 (70) Fall Yes 7 (26) No 20 (74) Steelhead Yes 52 (25) No 155 (75) Spring-summer Yes 40 (22) No 144 (78) Fall Yes 24 (47) No 27 (53) Steelhead Yes 42 (28) No 109 (72) Spring-summer Yes 47 (19) No 198 (81) Fall* Yes 33 (41) No 47 (59) Steelhead* Yes 8 (19) No 34 (81) Spring-summer Yes 38 (23) No 124 (77) Fall* Yes 48 (35) No 90 (65) Median FPLP (h)

21 Discussion We compared adult salmon and steelhead passage behavior in the Lower Granite Dam transition pool after weir modifications with pre-modification passage behaviors. Such analyses are clearly useful, though rigorous conclusions about the effects of the transition pool modifications on passage behavior are potentially confounded by interannual variability in other factors influencing passage behavior. Therefore, we also looked at the relative change in passage time between Little Goose Dam and Lower Granite Dam to account for interannual variability in environmental conditions insomuch as possible. Specifically, if the modification was successful, the times at Lower Granite Dam should have become relatively faster. This appeared to be the case, as comparisons of interannual differences in passage times at the two dams indicated that passage times decreased for individual fish at Lower Granite Dam compared to Little Goose dam in modified years compared to the non-modified years. Transition pool passage times at Lower Granite Dam for spring-summer Chinook were significantly faster in 2006 than in 2003 and 2004 and fall Chinook and steelhead exhibited similar, though not statistically faster passage in both modified years (Clabough et al. 2007). Faster transition pool passage times for spring summer Chinook salmon could be partly attributed to the higher temperatures in 2006 and 2008 than in 2003 and 2004 rather than the modifications per se. Keefer et al. (2004) observed radio-tagged fish migrating faster during warmer temperatures up to a threshold of approximately 20 ºC, above which fish slowed migration. At higher temperatures, warmer water at the tops of ladders compared to tailraces may induce fish to spend the night at the dam (overnight) and contribute to slower transition pool passage times (Caudill et al. 2006). The observed top-of-ladder versus tailrace temperature differences in 2006 and 2008 were lower than in previous years, despite warmer average temperatures. These patterns potentially confound interpretation of results. The percentage of fish that passed straight through the transition pool was lower for all runs in 2006 and 2008 compared to treatment periods during the experimental modification in 2001 and However, frequency of downstream exits from the transition pool to the tailrace was also lower for spring-summer Chinook salmon at Lower Granite Dam in 2006 and 2008 compared to 2003 and 2004; this pattern was not evident in the other two runs. The faster transition pool passage times and lower number of transition pool exits during the treatment periods in 2001 and 2002 were probably the result of increased flow at underwater weir orifices during treatment compared to control periods (Naughton et al. 2006). Measurements taken in 2008 indicated target underwater orifice velocities were only met during low tailwater conditions; a possible explanation for why transition pool passage times were not as low in 2008 as during the 2001 and 2002 treatment periods. Median transition pool passage times at Little Goose Dam were not lower in 2006 and 2008 compared to 2003 and 2004, further supporting the hypothesis that the ladder modification contributed to shorter passage times at Lower Granite Dam. Moreover, we also observed a decrease in the difference in transition pool passage times for individual fish between Lower Granite and Little Goose dams in 2006 and 2008 compared to 2003 and 2004, indicating that individual fish passing both dams passed Lower Granite Dam relatively quickly after the 17

22 modification. Conclusions Results from the 2006 and 2008 evaluation indicated that the modifications decreased transition pool passage times for all runs compared to the non-modified years ( ), though not all differences were statistically significant. A decrease in individual fish transition pool passage times was also observed between Little Goose and Lower Granites dams in the modified years compared to the non-modified years. A significant increase in the percent of fish passing straight through the transition pool was only observed for spring-summer Chinook salmon suggested that the modification increased the efficiency of passage for this run. Based on weir pool measurements taken in 2008, targeted underwater orifice velocities (4 ft/sec) that provide the best passage condition for adults were achieved only during low tailwater elevations ( ft in April, July, and August). In 2008, 75% of all radio-tagged fish passed Lower Granite Dam when under water orifice velocities were lower than the targeted (4 ft/sec). Median transition pool passage times in 2006 and 2008 may have not been as low as those achieved in the experiment because underwater orifice velocity targets were met only during low tailwater elevations when few tagged fish were passing the dam. 18

23 References Caudill, C. C., T. S. Clabough, G. P. Naughton, C. A. Peery, and B. J. Burke Water temperatures in adult fishways at mainstem dams of the Snake and Columbia rivers - biological effects. Technical Report U.S. Army Corps of Engineers, Walla Walla District, Walla Walla, WA. Clabough, T. S., G. P. Naughton, M. A. Jepson., C. C. Caudill, and C. A. Peery Evaluation of fishway modifications of adult Chinook salmon and steelhead through the transition pool at Lower Granite Dam, Technical Report U.S. Army Corps of Engineers, Portland District, Portland, OR and Walla Walla District, Walla Walla, WA. Clay, C. H Design of fishways and other fish facilities. Lewis Publishers, CRC Press, Boca Raton, FL. Keefer, M. L., C. A. Peery, T. C. Bjornn, M. A. Jepson, and L. C. Stuehrenberg Hydrosystem, dam and reservoir passage rates of adult Chinook salmon and steelhead in the Columbia and Snake Rivers. Transactions of the American Fisheries Society 133: Mann, R., and C. A. Peery Effects of water temperature exposure on spawning success and developing gametes of migrating anadromous fish, Progress Report, U.S. Army Corps of Engineers, Walla Walla District, Walla Walla, WA. Naughton, G. P., C. C. Caudill, C. A. Peery, T. S. Clabough, M. A. Jepson, T. C. Bjornn, and L. C. Stuehrenberg Experimental evaluation of fishway modifications on the passage behavior of adult Chinook salmon and steelhead at Lower Granite Dam, Snake River Technical Report U.S. Army Corps of Engineers, Walla Walla District, Walla Walla, WA. Naughton, G. P., C. C. Caudill, C. A. Peery, T. S. Clabough, M. A. Jepson, T. C. Bjornn, and L. C. Stuehrenberg Experimental evaluation of fishway modifications on the passage behaviour of adult Chinook salmon and steelhead at Lower Granite Dam, USA. River Research and Applications 23: Zar, J. H Biostatistical Analyses 4 th Ed. Upper Saddle River, New Jersey: Prentice Hall, Inc. 19