Steelhead Overshoot and Fallback Rates in the Columbia–Snake River Basin and the Inﬂuence of Hatchery and Hydrosystem Operations

ARTICLE

Shelby M. Richins and John R. Skalski* Columbia River Basin Research, School of Aquatic and Fishery Sciences, University of Washington, 1325 4th Avenue, Suite 1515, Seattle, Washington 98101, USA

Abstract Tributary overshoot occurs when adult salmonids homing to natal sites continue upstream past the mouth of their natal stream. Although overshooting is a common behavior by steelhead Oncorhynchus mykiss in the Columbia River basin, it has not been adequately quantiﬁed or explained. Using multistate release–recapture models, we examined the prevalence of overshooting and fallback to natal tributaries by 37,806 PIT-tagged steelhead from 14 tributaries of the Columbia River basin during 2005–2015. Eight populations had overshooting rates exceeding 50% in at least 1 year. Source of hatchery stock, rearing location, and release practices were found to have appreciable effects on overshoot rates. Overshooting was elevated in hatchery stocks reared upstream of release sites, but this effect may be lessened by utilizing endemic broodstocks and acclimating juveniles within the release basin. For one population of hatchery steelhead, acclimation within the release basin was found to decrease overshooting from 81% to 40%. Across both hatchery and wild populations, successful homing was found to decline 4 percentage points for every 5-percentage- point increase in overshoot rate. Average annual fallback probabilities ranged from 0.18 for Walla Walla River hatchery steelhead to 0.75 for Umatilla River wild steelhead. Fish stocks with the greatest fallback probabilities also had the greatest interannual variability in fallback rates. For John Day River wild steelhead and Tucannon River hatchery steelhead, the interannual range in fallback probabilities exceeded 0.50. We found evidence that spill at dams during March may enhance the fallback of overshooting steelhead and contribute to increased homing to natal tributaries. Therefore, additional attention should be paid to facilitating downstream dam passage of adult salmon.

Homing is a general pattern in many migratory animals Tributary overshoot occurs when adult ﬁsh homing to in which reproductive adults return to natal sites or the natal sites continue upstream past the mouth of their natal site of previous reproduction. Homing in rivers presents a stream (Ricker 1972). Subsequent return downstream is special challenge compared to lakes or marine environ- called “overshoot fallback” (Boggs et al. 2004; Naughton ments; decisions must be made at each branch of the river, et al. 2006). Overshooting has been documented in steel- and homeward migrations may include movement in head (Keefer et al. 2008a; Copeland et al. 2015), Chinook many compass directions. Paciﬁc salmon Oncorhynchus Salmon O. tshawytscha (Boggs et al. 2004; Keefer et al. spp. and steelhead O. mykiss are believed to imprint using 2008b; Gallinat and Ross 2009), Sockeye Salmon O. nerka multiple “landmarks” along their out-migration route as (Ricker and Robertson 1935), and Atlantic Salmon Salmo juveniles—a process called sequential imprinting (Ueda salar (Økland et al. 2001). Observed overshoot distances 2012; Bett and Hinch 2016). As adults, salmon and steel- range from less than 1 river kilometer (rkm; Ricker and head navigate complex river systems by identifying waters Robertson 1935) to 200 rkm or more (Boggs et al. 2004). that contain these memorized olfactory stimuli (Johnsen There is growing awareness that tributary overshoot is and Hasler 1980; Quinn 2005). a common behavior by steelhead in the Columbia River

*Corresponding author: [email protected] Received December 20, 2017; accepted July 27, 2018

1 2 RICHINS AND SKALSKI basin, with as many as half the fish in some populations Khan et al. 2013). Survival of postspawn steelhead mov- passing their natal river and ascending upstream dams ing through dams is lowest through turbines and juvenile (Bumgarner and Dedloff 2011; Copeland et al. 2015; Kee- bypass systems (Harnish et al. 2015). When available, fer et al. 2016). Unless steelhead successfully fall back at both prespawn steelhead (Khan et al. 2009) and steelhead dams to return downstream to natal sites, high levels of kelts (Wertheimer and Evans 2005; Wertheimer 2007; overshooting may significantly deplete naturally spawning Khan et al. 2013; Rayamajhi et al. 2013; Harnish et al. populations. Although tributaries may also receive over- 2015) exhibit a very strong preference for safer surface shooting steelhead from other rivers, large influxes of routes, such as spillways and sluiceways. The study by strays—particularly hatchery strays—can negatively Khan et al. (2009), who strongly recommended sluiceway impact population fitness (Chilcote 2003; Chilcote et al. operation during winter months to prevent turbine fall- 2011). back by adult steelhead at The Dalles Dam (rkm 309 on The act of homing may require exploration of multiple the Columbia River), supports the hypothesis that surface pathways to determine the correct route (Ricker 1972; flow at dams may benefit steelhead that overshoot their Keefer et al. 2008b). Therefore, it is unclear whether tribu- natal rivers. tary overshoot is part of the normal homing process or Many populations of salmon and steelhead in the whether it is exacerbated by human-induced changes to Columbia River basin are at risk of extinction (NMFS river systems and steelhead populations. Disruption of 2012); therefore, reliable estimates of overshoot and fall- memory development during imprinting or the decay back rates, as well as a greater understanding of the fac- of memories over time may inhibit the homing abilities of tors influencing these behaviors, are important for the salmonids and lead to higher rates of straying (reviewed management and conservation of steelhead in the Colum- by Keefer and Caudill 2014). Hatchery practices (Nish- bia River basin. Unfortunately, previous studies may have ioka et al. 1985; Pascual et al. 1995; Marchetti and Nevitt underreported overshooting rates because they used fish 2003), juvenile barging (Bugert and Mendel 1997; Keefer with unknown sources (Boggs et al. 2004; Keefer et al. et al. 2008c; Bond et al. 2017), temperature modification 2008a) or utilized a tally-based approach that ignored (Isaak et al. 2018), migration pathway obstruction (Khan detection efficiencies (Bumgarner and Dedloff 2011; Mur- et al. 2009), or extended ocean residency (Labelle 1992) doch et al. 2012; Keefer et al. 2016). To address these can have unexpected consequences for homing by adult knowledge gaps, our objectives were to (1) quantify over- salmonids and may also influence overshoot behavior. shooting and fallback to natal tributaries for multiple pop- In addition to correctly navigating to natal sites, many ulations of steelhead in the Columbia River basin using salmonids must also locate temporary holding areas that multistate release–recapture methods; (2) assess the extent are both thermally appropriate and energetically efficient. to which tributary overshoot and fallback are associated Interior Columbia River basin steelhead are stream matur- with hatchery rearing, juvenile barging, and ocean resi- ing, meaning that they (1) enter freshwater before they are dence time; and (3) investigate the effect of winter spill fully mature, (2) overwinter in rivers, and (3) spawn the and dam outflow on fallback to natal tributaries. following spring (Robards and Quinn 2002). A review by Quinn et al. (2016) found that this “premature migration” occurs in many anadromous fishes, potentially because of METHODS mortality risks at sea or physical factors in freshwater sys- This study used tagging and detection data from the tems (e.g., temperature or flow) that seasonally limit Columbia River basin PIT Tag Information System (PTA- access to spawning sites. The early return of adult steel- GIS), operated by the Pacific States Marine Fisheries head to freshwater may prompt overshooting to reach Commission (PSMFC 2015). Passive integrated transpon- suitable holding areas prior to their final movements to der tags are small, internal tags (10–14 mm long) with dis- spawning grounds. Overshooting by Chinook Salmon tinct identification codes that can be detected when a (Keefer et al. 2008b) and steelhead (Richins 2017) in the tagged fish passes through a magnetic field (McCutcheon Columbia River basin was found to increase as water tem- et al. 1994; Gibbons and Andrews 2004). Known-source peratures rose in late summer, indicating that the behavior steelhead from nine tributaries of the Columbia River and may serve thermoregulatory purposes. five tributaries of the Snake River were selected based on Overshooting within the Columbia River hydrosystem adequate sample sizes of PIT-tagged steelhead and the is of concern because downstream dam passage can be presence of instream detection sites in the natal tributaries hazardous for large adult fish (Ferguson et al. 2008) and from 2005 to 2015. All hatchery and wild populations can add significant migration delays (Wertheimer and included at least 250 tagged adults distributed across Evans 2005; Rayamajhi et al. 2013; Harnish et al. 2015). 8 years or more (Table 1). All steelhead were tagged as General options for downstream dam passage include tur- juveniles, and natal tributaries were determined based on bines, locks, spillways, and sluiceways (Wertheimer 2007; release location. Columbia River tributaries included STEELHEAD OVERSHOOT AND FALLBACK RATES 3

TABLE 1. Sample sizes of adult steelhead that were PIT-tagged as juveniles and subsequently detected at the Bonneville Dam adult fishway during run years 2005–2006 (05/06) to 2014–2015 (14/15). Run year was defined as June 1–May 31 of each year. Origin refers to the rearing history of the fish (hatchery or wild). Run year Tributary Origin 05/06 06/07 07/08 08/09 09/10 10/11 11/12 12/13 13/14 14/15 Total Lower Columbia River Hood River Hatchery 2 31 106 251 430 231 333 144 149 151 1,828 Wild 1 12 15 8 31 24 30 40 28 89 278 Fifteenmile Creek Wild 0 1 0 12 47 92 96 34 32 38 352 Deschutes River Wild 0 0 38 68 118 115 109 82 180 97 807 John Day River Wild 68 121 114 248 348 280 287 151 261 243 2,121 Umatilla River Hatchery 9 15 60 80 115 76 64 24 16 37 496 Wild 3 10 17 22 14 13 81 68 69 173 470 Walla Walla River Hatchery 33 36 25 300 416 223 261 120 111 167 1,692 Wild 11 11 10 8 61 95 115 92 57 75 535 Upper Columbia River Yakima River Wild 15 12 18 17 33 23 40 20 46 78 302 Wenatchee River Hatchery 408 404 338 468 819 526 422 384 188 190 4,147 Wild 0 0 2 8 69 75 53 33 31 39 310 Entiat River Wild 0 4 8 8 75 74 55 26 44 66 360 Snake River Tucannon River Hatchery 60 84 549 425 633 266 163 87 121 145 2,533 Wild 35 24 39 16 50 45 51 55 44 60 419 Clearwater River Hatchery 38 35 50 178 96 683 726 656 322 391 3,175 Wild 37 30 50 80 139 200 140 112 89 286 1,163 Grande Ronde River Hatchery 19 103 164 153 1,137 622 657 419 389 576 4,239 Wild 35 16 36 37 65 83 83 69 63 62 549 Salmon River Hatchery 37 21 68 83 1,656 1,237 1,471 968 973 1,147 7,661 Wild 17 22 19 49 158 104 126 70 118 148 831 Imnaha River Hatchery 32 36 33 33 734 442 392 163 340 408 2,613 Wild 38 14 36 124 151 124 143 71 94 130 925 Total 898 1,042 1,795 2,676 7,395 5,653 5,898 3,888 3,765 4,796 37,806

Fifteenmile Creek (located 309 rkm from the mouth of Quinn 2002), June 1 was used as the division between run the Columbia River) and the Hood River (rkm 273), years. To account for steelhead with additional detections Deschutes River (rkm 328), John Day River (rkm 351), beyond the defined run year, we manually examined the Umatilla River (rkm 465), Walla Walla River (rkm 509), individual detection histories of all fish that had observa- Yakima River (rkm 539), Wenatchee River (rkm 754), tions in consecutive run years, and we assigned fish to the and Entiat River (rkm 778) basins (Figure 1). Snake River proper run year. tributaries included the Tucannon River (located 100 rkm Tag records and detection histories were used to deter- from the Snake River’s confluence with the Columbia mine run timing, ocean age, stock, and barging history for River), Clearwater River (rkm 224), Grande Ronde River each fish. Adult run timing was represented by the day of (rkm 274), Salmon River (rkm 303), and Imnaha River the year that an individual steelhead was first seen at (1) (rkm 308) basins. The PIT tag detectors in the adult fish Bonneville Dam, (2) the closest dam with adult detectors ladders at McNary, Priest Rapids, Rock Island, Rocky downstream of the natal tributary, (3) the first dam with Reach, Wells, Ice Harbor, and Lower Granite dams were adult detectors upstream of the natal tributary, and (4) used to monitor overshooting (Figure 1). within the natal tributary after any overshoot movements. Adult migration performance was characterized by run Ocean age was calculated as the time between the last year. Because most populations of interior Columbia juvenile detection at a juvenile bypass system at a main- River basin steelhead begin their upstream migration in stream dam and the first detection of the adult migrant in summer and spawn the following spring (Robards and the Bonneville Dam adult fish ladders, rounded to the 4 RICHINS AND SKALSKI

FIGURE 1. Map of the Columbia River basin, with natal tributaries of PIT-tagged steelhead used in this study (BON = Bonneville Dam; TDA = The Dalles Dam; JDA = John Day Dam; MCN = McNary Dam; PRA = Priest Rapids Dam; WAN = Wanapum Dam; RIS = Rock Island Dam; RRE = Rocky Reach Dam; WEL = Wells Dam; ICH = Ice Harbor Dam; LMO = Lower Monumental Dam; LGO = Little Goose Dam; LGR = Lower Granite Dam; HEC = Hells Canyon Dam). nearest whole year. For each adult steelhead, information and 9–56 rkm upstream of the release river, respectively. on whether, as a juvenile, it out-migrated to the ocean in- In contrast, hatchery steelhead released in the Umatilla river or was barged as part of the juvenile transportation and Tucannon rivers were reared at hatcheries located a program was provided by Columbia River Data Access in short distance downstream (<5 rkm) of the release sites. Real Time (DART; CBR 2015). During the study period, the Wenatchee River hatchery Hatchery stocks were identified based on tag informa- program shifted from directly releasing juveniles to accli- tion in PTAGIS and additional information provided by mating all juveniles in the Wenatchee River basin over the Washington Department of Fish and Wildlife winter prior to release in the spring (Hillman et al. 2016). (WDFW; J. D. Bumgarner, WDFW, personal communi- Wenatchee River hatchery steelhead were designated as cation). For the Tucannon and Walla Walla River basin “acclimated” or “not acclimated” based on brood year populations, hatchery steelhead were further separated and text comments in mark files (Richins 2017). into endemic and nonendemic stocks based on mark file To investigate the influence of adult fishway location at names. Both the Tucannon and Walla Walla River basins dams on overshooting, we compared the behavior of fish received outplants of a nonendemic stock referred to as that passed through adult fish ladders on the same or the “Lyons Ferry” stock as well as endemic stocks derived opposite sides of the river in relation to the mouth of the from the wild steelhead in each basin. Hatchery steelhead natal tributary. Our working hypothesis was that migrants from the Tucannon, Walla Walla, Umatilla, and using the adult ladder on the same side of the dam as the Wenatchee River basins in this study were reared at cen- upstream tributary mouth would have lower overshoot tral hatcheries on the main-stem Columbia or Snake rivers rates. Adult fish ladder usage was determined for before transportation to release sites in tributaries. Hatch- Wenatchee River steelhead at Rock Island Dam, 24 rkm ery steelhead released in the Walla Walla and Wenatchee downstream of the natal river. For Walla Walla and River basins were reared at hatcheries located 108 rkm Yakima River steelhead, adult fish ladder usage was STEELHEAD OVERSHOOT AND FALLBACK RATES 5 determined at McNary Dam, 39 and 69 rkm downstream of the direct migration route to the natal tributary among of the natal tributaries, respectively. For the remaining the number of adults that passed Bonneville Dam. Finally, steelhead populations with average overshooting rates fallback to the natal tributary was defined as the condi- greater than 5%, the nearest downstream dam either tional probability of returning downstream to the natal lacked adult detectors during the study period or pos- tributary after overshooting and detection at an upstream sessed a ladder on only one shoreline. dam. We estimated fallback to the natal tributary instead Flow and spill data for the years 2005–2015 at dams of simply fallback at a dam because downstream path- upstream of each tributary were obtained from Columbia ways at dams had limited detection capabilities. The esti- River DART. We focused on conditions during late win- mation of natal tributary return probabilities was based ter and early spring when fallback was occurring but prior on the presence of instream arrays in the natal tributaries to spring spill operations, which were managed for juve- near the confluence with the Columbia River or Snake nile salmonid out-migration. For each dam, we calculated River. These arrays were located 1–76 rkm upstream of the average amount of outflow during winter months (i.e., the tributary mouth. Over time and across locations, the January, February, and March) in each year (2006–2015). size of the PIT tag used in the tag releases, hydrology, Spill was characterized as the proportion of days with any array location, and construction varied, resulting in differ- amount of flow through the spillway in January, Febru- ences in detection probability. However, within a release, ary, and March. This metric was chosen because Werthei- the tag type was almost always the same, and interannual mer (2007) found that even small amounts of surface flow variation in detection probabilities was accounted for in were effective for routing steelhead kelts away from tur- the multistate model. Comprehensive details about tribu- bines, indicating that the availability of surface passage tary arrays, detection efficiencies, and individual models options may be more important than the volume of flow. can be found in Richins (2017). It should be noted that there was limited variation in late- To determine whether overshooting steelhead entered winter spill patterns at many dams because of scheduled upstream spawning areas, the capture history of each spill operations within the 10-year period. overshooting fish was examined for subsequent observa- Estimation of migration parameters.— Multistate models tions at nonnatal tributary sites. Many overshooting steel- were used to study movement and survival of animals head were neither detected in an alternative spawning with multiple potential migration pathways (Schwarz and location nor estimated to have returned to the natal tribu- Arnason 2000; King and Brooks 2003). In addition to tary. This remaining proportion, or “undetermined loss,” modeling transitions between migration states, multistate represented an unknown combination of fish that, after models estimate and account for detection probabilities at overshooting, were harvested by fishermen, succumbed to detection sites. Annual movement rates were estimated for natural causes, strayed to areas without detectors, or each population by using multistate release–recapture failed to pass far enough into the natal tributary to reach models in Program Branch (Pope et al. 2016), as detailed instream detection arrays. by Richins (2017) and illustrated in Figure 2. Parameters Regression analyses.— To evaluate whether overshoot- and SEs were estimated using maximum likelihood. Prob- ing contributed to decreased return to the natal tributary, abilities of migration success, overshooting, and fallback we used weighted linear regression with rates estimated by to natal tributaries were joint probabilities of movement the multistate models. Total success and fallback probabil- and survival along each pathway. Migration success was ities were regressed against the probability of overshooting defined as the proportion of steelhead that successfully (after accounting for population and run year factors). To returned to the natal river, along any migration pathway, account for varying sampling precision, return frequencies after passing Bonneville Dam. Overshoot was defined as were weighted by the inverse of their variance. Weighted the proportion of steelhead that ascended a dam upstream linear regression was also used to analyze the influence of

FIGURE 2. Schematic of the multistate release–recapture model of steelhead direct homing, overshoot, and fallback pathways. 6 RICHINS AND SKALSKI

flow and spill on the probability of fallback to natal tribu- blocking factors for run year and run timing were taries. Stocks that were found to have different probabili- included in each base model (Snedecor and Cochran ties of fallback to natal tributaries based on tests of 1980:256); (2) rearing, barging, ocean age, and adult fish significance were modeled separately. ladder factors were tested for significance (P < 0.05) We used regression analysis to understand the influence within the regression model by using stepwise forward of developmental and hydrosystem factors. Because steel- selection (Draper and Smith 1998:336–338); and, finally, head located further than 120 rkm from the nearest (3) by the principle of marginality, higher-order covariate upstream dam with adult detectors overshot at negligible terms were added after main effects, and interaction terms rates (i.e., <5%), we only used regression analyses to eval- were only added after the main effects had been selected uate within-stock effects for steelhead from tributaries less (Fox 1997:148–149). When differences in behavior were than 120 rkm downstream of a dam where overshooting not significant, endemic and nonendemic hatchery stocks could be measured. These included steelhead from the were pooled. For overdispersed models, SEs were adjusted John Day, Umatilla, Walla Walla, Yakima, Wenatchee, by the scale parameter (McCullagh and Nelder 1989). Entiat, and Tucannon rivers. Instream temperatures were After fitting logistic models, we estimated the average available for only three steelhead runs. The Umatilla effects of ocean age, rearing, barging history, and adult River temperature data were obtained from the U.S. fishway location for steelhead from each tributary. Fitted Bureau of Reclamation (usbr.gov). Walla Walla and logit values were back-transformed to the binomial scale Tucannon River temperatures were obtained from the using the equation Washington State Department of Ecology (fortress. wa.gov/eap/flows). Mainstream water temperatures were ¼ 1 ; pi −β (2) available for all steelhead stocks examined by using data 1 þ e Xi from the nearest upstream dam above the natal tribu- fl taries. and the average percentage point in uence associated with Individual-based, binary, logit-link generalized linear each treatment factor was estimated after accounting for models (Hosmer and Lemeshow 2000) were also used to blocking factors. See Richins (2017) for a detailed descrip- examine the influence of hatchery rearing, juvenile barg- tion of the methods of analysis. ing, ocean residence time, and fishway location on adult Finally, we performed a meta-analysis of the effect of ’ migration behaviors. Models followed the general form each covariate across tributaries by using Fisher s combined-probability test (Fisher 1932). The P-values associated with covariates in individual stock models were ð pi Þ¼β′ ; loge Xi (1) fi 1 pi combined to provide an overall signi cance level by using the chi-square statistic, where β is a vector of regression coefficients; Xi is a vector χ2 ¼ ∑K ; of explanatory variables, including indicator variables and 2K 2 i¼1 loge Pi (3) covariates; and pi is the probability of success. Specifically, we modeled the probability of (1) early migration success, where K is the number of tributaries and Pi is the ith or moving from Bonneville Dam to the last dam with P-value. In all regression analyses, we checked for lever- adult detectors downstream of the natal tributary; (2) age points and outliers, examined multicollinearity moving from the last dam with adult detectors directly to among covariates, and verified assumptions of linearity. the natal tributary; (3) overshooting, or moving from the In addition, Richins (2017) used conditional inference last dam with adult detectors downstream of the natal trees to assess the robustness of the multiple regression tributary to the first dam with adult detectors upstream; results. (4) falling back and being detected in the natal tributary after overshooting; and (5) overall migration success, or the probability of moving from Bonneville Dam to the RESULTS natal tributary along any pathway. Because the data were In all populations, overshooting primarily occurred in binary and detection efficiencies were less than 100%, late summer and early fall (Figure 3). In contrast, move- logistic models estimated the joint probability of movement into natal tributaries after overshooting occurred ment and detection. When modeling overshoot behavior, most often in early spring of the following year (Figure 3). bias due to imperfect detection was minimal because Little movement over dams or into natal tributaries was main-stem dams had nearly 100% detection efficiency detected from late fall to midwinter. However, the range (Richins 2017). Model development followed three steps: in timing of natal tributary entry after overshooting was (1) to first account for annual and seasonal variation in large, and the distribution was bimodal in a few popula- detection efficiencies and environmental conditions, tions, including the Wenatchee River hatchery and John STEELHEAD OVERSHOOT AND FALLBACK RATES 7

FIGURE 3. Timing of overshoot and subsequent timing of first detection at the natal tributary for PIT-tagged Columbia River steelhead from tributaries located less than 120 rkm from the next upstream dam with adult detectors during migration years 2005–2006 to 2014–2015. Populations are presented in order of distance from Bonneville Dam, with Snake River populations listed last. Overshoot timing is the first detection date at an upstream dam. Box plots show median values (vertical line), first and third quartiles (outer box), and outliers (points) falling more than 1.5 times the interquartile range below the first quartile or above the third quartile.

Day River wild stocks (Richins 2017). In these popula- over Ice Harbor Dam than to continue in the Columbia tions, one peak in fallback to natal tributaries occurred in River over Priest Rapids Dam. For adult steelhead with October, followed by a second peak in late March. a Snake River origin, the average conditional rate of straying into the mid-Columbia River above Priest Overshoot and Fallback Rates Rapids Dam, given arrival at McNary Dam, was 1.7%. Overshooting occurred at high rates in multiple popula- All Columbia River populations from above the Snake tions. The highest annual overshooting estimate was River confluence had average conditional straying rates 70.8% (SE = 9.1%), which was observed for Umatilla into the Snake River above Ice Harbor Dam of less than River wild steelhead over McNary Dam in 2006–2007. 1.2%. Eight of the 23 wild and hatchery stocks examined had Many steelhead did not return to the home tributary overshooting rates exceeding 50% in at least 1 year (Fig- after overshooting; therefore, migration success rates ure 4). These estimates are the percentage out of the entire decreased with increasing overshoot rates (F = 41.5; run that passed Bonneville Dam. df = 1, 54; P < 0.0001). On average, for every 5-percen- Conditional overshooting rates, based on only those tage-point increase in the overshoot rate, there was an fish that ascended the closest downstream dam before the approximately 4-percentage-point decrease in the return natal tributary, were even higher (Richins 2017). For rate to the natal basin. Conditional on a fish overshooting, instance, in 2014–2015, 85.7% (SE = 3.1%) of Walla fallback rates to natal tributaries could be estimated in at Walla River hatchery steelhead that passed McNary Dam least 1 year for 11 of the populations (Figure 5); fallback went on to overshoot at Ice Harbor Dam, and 66.1% rates ranged from 7.7% (SE = 7.7%) for Tucannon River (SE = 6.6%) of Tucannon River wild steelhead that wild steelhead in 2006–2007 to 93.4% (SE = 6.3%) for passed Ice Harbor Dam went on to overshoot at Lower Entiat River wild steelhead in 2013–2014. Fallback rates Granite Dam. varied annually and were not related to overshooting rates Overshooting past upstream dams generally decreased (F = 0.30; df = 1, 33; P = 0.59). with increasing distance between the upstream dam and Some steelhead were detected in nonnatal tributaries the natal tributary mouth (Figure 4). Additionally, steel- where spawning could occur. Since many spawning loca- head from tributaries below the Snake River confluence tions did not possess instream arrays or traps, observa- were much more likely to overshoot into the Snake River tions at alternative sites are lower bound estimates of 8 RICHINS AND SKALSKI

FIGURE 4. Annual rates of overshoot (with 95% confidence intervals) by PIT-tagged steelhead over the nearest upstream dam with adult detectors for adult migration years 2005–2006 to 2014–2015 (i.e., 14/15; w = wild population; h = hatchery population). Natal tributaries are organized based on the distance between the tributary mouth and the upstream dam and are separated into those located less than 120 rkm and more than 120 rkm from the next upstream dam with adult detectors. actual straying. Additionally, due to wide variability in Factors Affecting Steelhead Overshoot and Fallback upstream array layouts and detection probabilities, com- Water temperature.— We found that as water tempera- parisons of alternative site observation rates between pop- tures in the main stem rose, adult steelhead were less ulations are of little value. However, it is notable that for likely to move directly to the natal tributary. A significant the Tucannon River wild population and Walla Walla effect was found for steelhead from six of the seven tribu- River hatchery population, more fish were detected in taries examined. For example, for natural-origin Walla upstream alternative tributaries than returned to the natal Walla River steelhead, the probability of moving directly river (Figure 5). Additionally, after overshooting at an to home decreased from over 90% to less than 25% as upstream dam, very few steelhead were detected at non- water temperatures increased from 10°Cto20°C. Statisti- natal tributary locations downstream of that dam. Unde- cally significant declines in movement directly to the natal termined losses were greater for hatchery populations than tributary in response to increasing temperature were also for wild populations (Figure 5), in part due to the lower found for steelhead from the Umatilla, Yakima, rates of fallback to natal tributaries for hatchery stocks, Wenatchee, Entiat, and Tucannon rivers. which were likely related to higher harvest rates of fin- Steelhead that experienced higher water temperatures clipped fish relative to unclipped wild fish. near their natal stream were also more likely to overshoot. STEELHEAD OVERSHOOT AND FALLBACK RATES 9

FIGURE 5. Average annual estimates of fallback to natal tributaries, straying, and loss of PIT-tagged steelhead that overshot their natal tributary and were detected at an upstream dam in the Columbia River basin during adult migration years 2005–2006 to 2014–2015 (w = wild population; h = hatchery population). Each bar is labeled with the number of years that were averaged for each population.

Regression results showed that higher water temperatures Tucannon River (F = 4.07; df = 1, 2,097; P = 0.044) near natal streams significantly (P < 0.05) increased over- and lower rates of overshooting at the next upstream shooting by steelhead from four of seven tributaries. The dam, Lower Monumental Dam (F = 9.224; df = 1, exceptions were steelhead from the John Day River 2,107; P = 0.002). For those fish that did overshoot, the (F = 2.73; df = 2, 2,033; P = 0.100), Umatilla fallback probabilities for fish with in-river or barged his- River (F = 2.08; df = 1, 823; P = 0.150), and Wenatchee tories were not different (F = 0.29; df = 1, 1,119; River (F = 2.73; df = 1, 2,074; P = 0.098). For the John P = 0.59). The net result was that Tucannon River steel- Day, Walla Walla, and Tucannon rivers, which had tribu- head that were barged as juveniles were less likely to tary temperature data, steep increases in overshooting return to their natal river than in-river migrants by an occurred when water temperatures averaged between 16°C average of 10 percentage points (SE = 3 percentage and 18°C. Because tributary and main-stem temperatures points). were often highly correlated, it was difficult to separate Hatchery rearing practices.— We examined the effects of the effects of temperature at the two locations. For exam- hatchery rearing at four tributaries where both wild and ple, for Tucannon River steelhead, main-stem tempera- hatchery stocks were present: the Umatilla, Walla Walla, tures appeared to have a larger estimated effect than natal Wenatchee, and Tucannon rivers (Figure 6). The meta-ana- tributary temperatures. Conversely, for the Walla Walla lysis found that hatchery rearing across these four tribu- River steelhead, natal tributary temperature had a greater taries impeded adult migration success in every stage, fl χ2 estimated in uence than main-stem temperature. including decreased early migration ( 6 = 17.5, P = 0.008), Juvenile barging effects.— Only the Tucannon River decreased movement directly to the natal tributary fi χ2 χ2 population had suf cient numbers of barged (n = 515) ( 8 = 46.8, P < 0.0001), increased overshooting ( 8 = 43.4, versus unbarged (n = 2,411) fish for analysis of barging P < 0.0001), decreased fallback to the natal tributary χ2 effects. Barging was associated with a 37-percentage- ( 8 = 55.3, P < 0.0001), and decreased overall migration χ2 point (SE = 3 percentage points) decrease in migration success ( 8 = 55.7, P < 0.0001) relative to wild steelhead. success between Bonneville Dam and Ice Harbor Dam However, overshooting was only elevated in stocks reared (F = 215.55; df = 1, 2,915; P < 0.0001). Median migra- at hatcheries upstream of release sites (Walla Walla and tion time through this 306-rkm stretch was on average Wenatchee rivers). Hatchery steelhead that were reared a 8 d for in-river fish compared with 49 d for barged fish. short distance downstream of the release basin (Umatilla However, above Ice Harbor Dam, the remaining barged and Tucannon rivers) were not significantly more likely to fish had higher rates of direct migration to the overshoot than wild steelhead (Figure 6). 10 RICHINS AND SKALSKI

FIGURE 6. Average effect of hatchery rearing during each stage of the adult migration by PIT-tagged steelhead reared at hatcheries upstream (9– 108 rkm) or a short distance downstream (<5 rkm) of release sites. “Effect” represents the average percentage point difference relative to wild steelhead as estimated by logistic regression. Hatchery stocks are subdivided by broodstock source (endemic or nonendemic) and release practice (directly released or acclimated), where relevant. STEELHEAD OVERSHOOT AND FALLBACK RATES 11

Broodstock and acclimation also affected overshoot to overshoot 18 percentage points more often (SE = 1 per- probability. For Walla Walla River steelhead, average centage point) than steelhead that passed in the western overshooting probabilities of the nonendemic Lyons Ferry ladder (n = 1,568) and 11 percentage points more often hatchery stock (n = 1,190) were 15 percentage points (SE = 1 percentage point) than steelhead that passed in higher (SE = 1 percentage point) than those of both the the middle ladder (n = 231). Adult fish ladder usage did wild stock (n = 535) and the endemic hatchery stock not exert as strong an influence (P > 0.10) on behavior (n = 474). Additionally, changing the overwinter acclima- for steelhead from the Walla Walla and Yakima rivers, tion of Wenatchee River hatchery steelhead from the located 39 and 69 rkm upstream, respectively, of McNary Columbia River to the Wenatchee River was associated Dam. with a tremendous decline in overshooting and an increase Hydroelectric facility operations.— Fallback was bimo- in successful homing. Hatchery steelhead that were dal in distribution, with peak occurrences in autumn and directly released as juveniles (n = 3,564) were 65 percent- again in late winter. Spill in late autumn is generally age points (SE = 1 percentage point; n = 310) more likely involuntary spill associated with flood control. Later-win- to overshoot than their wild counterparts, while steelhead ter spill at hydroelectric projects in the Columbia and that were acclimated in holding ponds before release as Snake rivers is generally low volume and infrequent until juveniles (n = 583) were only 25 percentage points the spring freshet or until mandatory spill begins for the (SE = 1 percentage point) more likely to overshoot (Fig- juvenile salmonid out-migration. We found mixed results ure 6). between the frequency of daily spill in autumn months In three of four tributaries, hatchery steelhead were less and estimated fallback probabilities. Two steelhead stocks likely to fall back than wild steelhead (Figure 5). Despite had positive associations between spill frequency and fall- the substantial benefits of acclimation for homing prior to back probabilities, whereas two other stocks exhibited sig- overshooting, we found no significant difference in the nificant negative associations (P < 0.05). probability of fallback to the natal tributary between accli- We also found that the number of days of spill during mated and directly released Wenatchee River steelhead March was positively associated with fallback rates to χ2 (F = 0.09; df = 1, 1,606; P = 0.76). natal tributaries for hatchery steelhead ( 8 = 16.83, Ocean age of returns.— Compared to barging and rear- P = 0.032). A similar relationship was suggested for wild fi χ2 ing practices, ocean residence time was associated with steelhead but was not signi cant ( 10 = 12.87, P = 0.231). smaller effects on migration success. Using meta-analysis, For many populations, statistical power to detect spill we found that increased ocean residence time was associ- effects was limited due to the small sample sizes of over- ated with reduced homing success during early migration shooting fish, a lack of tributary PIT tag detector arrays χ2 ( 10 = 21.7, P = 0.017), decreased movement directly to in some years, and the low variation in late-winter spill χ2 the natal tributary ( 14 = 43.8, P < 0.0001), increased patterns at some dams. The strongest effects were found χ2 overshooting ( 14 = 31.7, P = 0.005), and decreased over- for stocks with the highest annual fallback estimates, χ2 all success ( 14 = 24.3, P = 0.042). Spending 2 years including Tucannon River hatchery steelhead (F = 4.03; rather than 1 year in the ocean had estimated effects on df = 1, 6; P = 0.046) and Walla Walla River nonendemic overshooting ranging from a 4-percentage-point decrease (Lyons Ferry) hatchery steelhead (F = 7.19, df = 1, 5, (SE = 0.5 percentage point) for Wenatchee River steel- P = 0.022; Table 2). Though limited variation in spill and head to a 12-percentage-point increase (SE = 1 percentage the number of replicate years of observation resulted in point) for Entiat River steelhead. Increased ocean age did low statistical power, the slope of the regression line not significantly affect fallback to the natal tributary for between March spill and fallback to natal tributaries was χ2 any stock ( 14 = 14.4, P = 0.42). positive for 8 of 11 hatchery and wild stocks (one-tailed Adult fish ladder placement.— Three tributaries in this sign test: P = 0.113; Figure 7). In contrast, no relationship study were located directly upstream of a dam having two was found between fallback rates to natal tributaries and or more adult fish ladders with PIT arrays: the either (1) late-winter flow or (2) spill during January or Wenatchee, Walla Walla, and Yakima rivers. Passage in February. the adult fish ladder on the opposite shore of the natal tributary reduced direct homing (F = 28.47; df = 2, 1,594; P < 0.0001) and increased overshooting (F = 24.97; DISCUSSION df = 2, 2,075; P < 0.0001) by hatchery and wild Tributary overshoot is a pervasive behavior in many Wenatchee River steelhead. For this stock, ladder passage wild and hatchery Columbia River basin steelhead popula- orientation was determined at Rock Island Dam, located tions. We found annual steelhead overshooting rates 24 rkm downstream of the Wenatchee River mouth. Steel- exceeding 50% in 8 of 23 hatchery and wild populations. head that passed in the eastern ladder, on the opposite Such extreme overshooting rates are of concern because shore of the natal river mouth (n = 298), were estimated they may deplete small, native populations or may lead to 12 RICHINS AND SKALSKI

TABLE 2. One-tailed P-values from tests of a positive association levels (reviewed by Bett and Hinch 2016), we hypothesized between estimated steelhead fallback rate and January, February, or that weaker imprinting strength could cause hatchery March spill at the nearest upstream dam with detectors in adult fishways. fi steelhead to overshoot more frequently than naturally Asterisks indicate a signi cant positive relationship (*P < 0.05) with fall- fi back rate to the natal tributary (N = number of years in which fallback reared sh. Instead, we determined that the effects of was estimated). Combined P-values were calculated using Fisher’s com- hatchery rearing on overshooting were better explained by bined probability test (equation 3). hatchery location relative to the next upstream dam, broodstock source, and acclimation practices. Month of spill Among the hatchery groups examined in this study, Stock N Jan Feb Mar overshooting was only elevated relative to naturally reared fish in hatchery stocks reared at hatcheries upstream of John Day River, wild 6 0.293 0.530 0.465 release areas, suggesting that overshooting steelhead were Walla Walla River, wild 6 0.931 0.309 0.380 homing to rearing sites. Havey et al. (2016) and Quinn Yakima River, wild 3 0.609 0.620 0.189 et al. (2016) found that imprinting begins during early Entiat River, wild 6 0.061 0.814 0.191 rearing stages; therefore, constructing hatcheries upstream Tucannon River, wild 8 0.132 0.571 0.253 of release areas may result in unanticipated upstream Walla Walla River, endemic 7 0.430 0.013 0.692 movement by returning adults. In this study, overshooting hatchery was reduced and movement directly to natal tributaries Walla Walla River, non- 7 0.264 0.774 0.022* was increased for hatchery stocks that were transplanted endemic (Lyons Ferry) downstream for release when using endemic rather than hatchery out-of-basin broodstock. Local adaptations (Candy and Wenatchee River, hatchery 4 0.849 0.530 0.320 Beacham 2000), including appropriate run timing (Pascual Tucannon River, hatchery 8 0.567 0.710 0.046* et al. 1995), may contribute to increased homing by ende- Combined wild 0.412 0.842 0.231 mic hatchery stocks. Combined hatchery 0.366 0.174 0.032* In addition to the use of endemic broodstock, juvenile acclimation over the winter substantially reduced overshooting by steelhead reared at upstream hatcheries. large influxes of hatchery strays into upstream areas. It is Remarkably, overwinter acclimation of Wenatchee River therefore important to develop an understanding of over- hatchery steelhead before release in spring was associated shooting behavior and its relationship to human activities. with a 41-percentage-point reduction in overshooting rela- Subsequent detections of overshooting steelhead indicated tive to direct release. Acclimation studies by Kenaston that overshooting involved a mixture of temporary and et al. (2001) and Clarke et al. (2016) did not produce simi- permanent straying, with some fish falling back to natal lar results; however, neither study utilized release groups rivers and others entering nonnatal spawning tributaries of steelhead that were reared upstream of release sites, upstream. and neither study acclimated juveniles for longer than 30 d. Developmental Influences We found little evidence to support the hypothesis that Hydrosystem Structure and Operations overshooting was linked to the strength of imprinted In addition to hatchery practices, we found evidence memories. Although older fish may be slightly more likely that overshoot and fallback rates are influenced by the to stray (Quinn and Fresh 1984; Quinn et al. 1991; hydrosystem, including adult fishway location and perhaps Labelle 1992; Pascual et al. 1995), longer ocean residency a lack of winter spill. When dams are located close to produced only small effects and did little to explain the natal tributaries, passage through ladders located on the high overshooting rates found in many Columbia River opposite shoreline relative to the natal tributary may con- basin steelhead populations. Because juvenile barging has tribute to a higher overshoot probability. In addition, wide been found to result in higher straying by adults (Bugert reservoir channels or high attraction flow at dams on the and Mendel 1997; Keefer et al. 2008c; Bond et al. 2017), opposite shoreline relative to the natal tributary may cause we hypothesized that it would also result in increased lateral olfactory clues to be missed (Keefer et al. 2006). overshooting. Instead, for Tucannon River steelhead, Steelhead native to the John Day River, located just while migration success to Ice Harbor Dam was reduced, 4 rkm upstream of John Day Dam, appear to have the further upstream overshoot behavior was lower for adults highest average overshoot rate of any population in this that were barged as juveniles than for those that migrated study. However, data were limited for John Day River in-river. Finally, because hatchery rearing is associated steelhead because PIT detection arrays were installed in with reduced brain development (Marchetti and Nevitt the two adult fish ladders at John Day Dam as recently as 2003), olfactory activity, and imprinting-related hormone 2017. Steelhead from the Tucannon River located 33 km STEELHEAD OVERSHOOT AND FALLBACK RATES 13

FIGURE 7. Regression (with 95% confidence intervals) of fallback rates to natal tributaries versus the number of spill days in March for the upstream dams at which overshooting steelhead were detected from hatchery (H) and wild Columbia River basin populations. Fallback rates to natal tributaries were adjusted by the detection efficiency in each natal tributary. above Lower Monumental Dam, with ladders located on tributaries in late winter and early spring indicates that both shores, also had higher-than-average overshoot rates. some may be choosing to overwinter in refugia upstream. Conversely, steelhead from the Entiat River had only Keefer et al. (2008a) also reported that some radio-tagged moderate overshoot rates; the Entiat River is located steelhead from the John Day, Umatilla, and Walla Walla 15 km above Rocky Reach Dam, which had a single lad- rivers overwintered in Snake River reservoirs, several der on the same side of the Columbia River as the tribu- dams above their natal streams. Because upstream areas tary mouth. may be used by many adult steelhead as holding areas, After overshooting, few factors were found to be asso- attention should be paid to facilitating downstream dam ciated with fallback rates to natal tributaries. Differences passage during late winter and early spring, when spill at in fallback between hatchery and wild steelhead were dams is currently infrequent. found; however, we believe that the differences may be Unfortunately, fallback to natal tributaries after over- largely due to selective harvest of hatchery fish in shooting may be dangerous for adult steelhead because upstream areas. The fallback of steelhead to natal passage options from fall through late winter can be 14 RICHINS AND SKALSKI limited to turbine passage, at least until spring spill opera- overshooting by hatchery steelhead, such as rearing fish tions begin for juvenile downstream fish passage. Based near the release basin, using endemic broodstock, and on studies of downstream passage by steelhead kelts acclimating juveniles over winter before release. (Wertheimer and Evans 2005; Wertheimer 2007; Norman- Changes to river systems resulting from human activi- deau Associates 2011, 2014; Khan et al. 2013; Rayamajhi ties may have intensified overshooting and limited the et al. 2013; Harnish et al. 2015), we hypothesized that ability of steelhead to fall back to natal tributaries. In the late-winter spill may also aid in the fallback of prespawn construction of new dam projects, the location of adults. Despite limited inferential power, we identified upstream spawning tributaries should be taken into con- March spill as being positively associated with fallback sideration when determining the placement of adult fish rates to natal tributaries for hatchery steelhead and, to a ladders. Location of hatchery facilities should also lesser extent, for wild steelhead. This analysis examined account for overshoot behavior. Additionally, because conventional spillway operations; however, surface flow upstream areas are often used by adult steelhead for over- through spillway weirs may also benefit downstream wintering, greater attention should be paid to facilitating migrants (Khan et al. 2009). downstream dam passage during late winter and early Experimental studies during late winter and early spring. Allocating even small amounts of surface flow for spring would provide the additional management informa- prespawn steelhead may enhance fallback to natal tribu- tion needed to adjust spill programs to increase overshoot taries and contribute to the recovery of wild steelhead fallback rates and reduce prespawn mortality. The benefit populations. of using sluiceways to promote adult steelhead fallback Adult steelhead are facing increased summer water tem- should concurrently be examined. Improvement could be peratures and decreased overall flow in the Columbia measured either by increases in overall migration success River (Quinn and Adams 1996; Quinn et al. 1997). Quinn to natal tributaries or by higher proportions of overshoot- et al. (1997) found that river warming began 30 d earlier ing steelhead that successfully return to home. The John in 1993 than in 1937; furthermore, between 1949 and Day River steelhead stock would be an ideal subject for 1993, annual maximum temperatures rose by 1.8°C. such a study, as their average overshoot rates at McNary Numerous investigators have reported blockage of adult Dam exceeded 50% and their annual probabilities of fall- steelhead migration when water temperatures exceed 19°C back ranged from 25% to 75%. (Stabler 1981; McCullough 1999; Richter and Kolmes A technological advance currently under development 2006). Neilson et al. (1994) reported that water tempera- in the Columbia River basin—spillway PIT tag detectors tures exceeding 22°C resulted in avoidance behavior in —would benefit such studies. Randomized block experi- adult steelhead. Fish and Hanavan (1948) noted that steel- ments could be used to evaluate whether the frequency of head gathered in coolwater refugia when water tempera- fallbacks is associated with alternative spill operations. tures exceeded 21.7°C. Overshooting will likely increase as Because of the multiple-year lag time between the PIT tag- water temperatures continue to increase, prompting steel- ging of juveniles and the return of adults, a proactive head to seek upstream temperature refugia. Because approach would be required. In-season acoustic or radio upstream areas will increasingly be used as adult steelhead tag studies of downstream-migrating adults constitute holding areas, greater attention will need to be focused on another alternative, but sample sizes might be small. Both facilitating downstream dam passage for fallback as cli- the near-field and migration-level evaluations could guide mate change continues. spill practices that would ultimately improve adult migration success rates. ACKNOWLEDGMENTS Management Implications This project was funded by the Bonneville Power Tributary overshoot merits more attention as man- Administration (BPA) under Contract Number 74892, agers work to recover threatened and endangered popu- Project Number 1991-051-00, as part of BPA’s program lations of steelhead in the Columbia River basin. to protect, mitigate, and enhance fish and wildlife affected Overshooting not only occurred at high levels in multi- by the development and operation of hydroelectric facili- ple populations but also was associated with lower ties on the Columbia River and its tributaries. We appre- migration success rates. In addition to providing the first ciate Thomas Quinn and Timothy Essington for sharing robust estimates of overshooting and fallback to natal their knowledge and suggestions. Additionally, we thank tributaries for steelhead in the Columbia River basin, Joseph Bumgarner (WDFW) for providing input and our study highlights several important management information about hatchery stocks, and we are grateful to implications. First, to reduce influxes of hatchery strays the members of the Columbia River Basin Research team into wild populations upstream, managers should adopt for determining the juvenile transportation status of our hatchery practices that do not further heighten study fish. Finally, this work would not have been possible STEELHEAD OVERSHOOT AND FALLBACK RATES 15 without the data contributed by many fishery agencies and Gallinat, M. P., and L. A. Ross. 2009. Tucannon River spring Chinook organizations to PTAGIS. There is no conflict of interest Salmon hatchery evaluation program: 2008 annual report. Report to declared in this article. the U.S. Fish and Wildlife Service, Project 1411-08-J011, Olympia, Washington. Gibbons, J. W., and K. M. 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