George P. Naughton

Fallback by Adult Sockeye Salmon at Columbia River Dams

Abstract We implanted radio transmitters into sockeye salmon Oncorhynchus nerka in 1997 to determine the (1) fallback percentage and rate at eight Columbia River dams, (2) effect of fallback on adult counts at each dam, (3) relations between spillway discharge and fallback, (4) relations between injuries and fallback, and (5) relations of fallback and survival to spawning tributaries. The rate of fallback, that is, the total number of fallback events at a dam divided by the number of fish known to have passed the dam, ranged from 1.9% to 13.7% at the eight dams. The rate of fallback was highest at Bonneville Dam, the dam with the most complex fishway. Fallback produced overcounts of 2% to 7% at most dams. Fallback was weakly related to spill volume at Bonneville Dam. Significantly more sockeye salmon with head injuries fell back than fish without head injuries. About 40% of the sockeye salmon had injuries from marine mammals, but these injuries were not associated with the rate of fallback. The rate of su...

Predation on Juvenile Salmonids by Smallmouth Bass in the Lower Granite Reservoir System, Snake River

Abstract We estimated the consumption of juvenile salmon Oncorhynchus spp. and steelhead O. mykiss by smallmouth bass Micropterus dolomieu in the tailrace and forebay of the Lower Granite Dam and compared this consumption with that in the two major river arms of the upper Lower Granite Reservoir, Snake River, Idaho–Washington. We examined over 9,700 smallmouth bass stomachs from April through August during 1996 and 1997. Juvenile salmonids were not a major component of smallmouth bass diets by weight and number at any location in either 1996 or 1997. Of the approximately 8,600 stomach samples containing food items, only 67 had juvenile salmonid remains. Juvenile salmonids accounted for approximately 11% of smallmouth bass diets by weight in the forebay in 1996 and 5% in the Snake and Clearwater river arms in 1997, with smaller proportions at other locations. Crustaceans and nonsalmonid fishes were the dominant prey items by weight at all locations in 1996 and 1997 except for the Snake River arm in 1996, w...

Thermal exposure of adult Chinook salmon in the Willamette River basin.

Radiotelemetry and archival temperature loggers were used to reconstruct the thermal experience of adult spring Chinook salmon (Oncorhynchus tshawytscha) in the highly regulated Willamette River system in Oregon. The study population is threatened and recovery efforts have been hampered by episodically high prespawn mortality that is likely temperature mediated. Over three years, 310 salmon were released with thermal loggers and 68 were recovered in spawning tributaries, primarily at hatchery trapping facilities downstream from high-head dams. More than 190,000 internal body temperature records were collected (mean ~2800 per fish) and associated with 14 main stem and tributary reaches. Most salmon experienced a wide temperature range (minima ~8-10 °C; maxima ~13-22 °C) and 65% encountered potentially stressful conditions (≥18 °C). The warmest salmon temperatures were in lower Willamette River reaches, where some fish exhibited short-duration behavioral thermoregulation. Cumulative temperature exposure, measured by degree days (DD) above 0 °C, varied more than seven-fold among individuals (range=208-1498 DDs) and more than two-fold among sub-basin populations, on average. Overall, ~72% of DDs accrued in tributaries and ~28% were in the Willamette River main stem. DD differences among individuals and populations were related to migration distance, migration duration, and salmon trapping protocols (i.e., extended pre-collection holding in tributaries versus hatchery collection shortly after tributary entry). The combined data provide spatially- and temporally-referenced information on both short-duration stressful temperature exposure and the biologically important total exposure. Thermal exposure in this population complex proximately influences adult salmon physiology, maturation, and disease processes and ultimately affects prespawn mortality and fitness. The results should help managers develop more effective salmon recovery plans in basins with marginal thermal conditions.

Indirect effects of impoundment on migrating fish: temperature gradients in fish ladders slow dam passage by adult Chinook salmon and steelhead.

Thermal layering in reservoirs upstream from hydroelectric dams can create temperature gradients in fishways used by upstream migrating adults. In the Snake River, Washington, federally-protected adult salmonids (Oncorhynchus spp.) often encounter relatively cool water in dam tailraces and lower ladder sections and warmer water in the upstream portions of ladders. Using radiotelemetry, we examined relationships between fish passage behavior and the temperature difference between the top and bottom of ladders (∆T) at four dams over four years. Some spring Chinook salmon (O. tshawytscha) experienced ∆T ≥ 0.5 °C. Many summer and fall Chinook salmon and summer steelhead (O. mykiss) experienced ∆T ≥ 1.0 °C, and some individuals encountered ΔT > 4.0°C. As ΔT increased, migrants were consistently more likely to move down fish ladders and exit into dam tailraces, resulting in upstream passage delays that ranged from hours to days. Fish body temperatures equilibrated to ladder temperatures and often exceeded 20°C, indicating potential negative physiological and fitness effects. Collectively, the results suggest that gradients in fishway water temperatures present a migration obstacle to many anadromous migrants. Unfavorable temperature gradients may be common at reservoir-fed fish passage facilities, especially those with seasonal thermal layering or stratification. Understanding and managing thermal heterogeneity at such sites may be important for ensuring efficient upstream passage and minimizing stress for migratory, temperature-sensitive species.

Cool, Pathogen-Free Refuge Lowers Pathogen-Associated Prespawn Mortality of Willamette River Chinook Salmon

AbstractSpring Chinook Salmon Oncorhynchus tshawytscha are transported above dams in the Willamette River to provide access to blocked spawning habitat. However, 30–95% of these transplants may die before spawning in some years. To varying degrees, salmon in other tributaries—both blocked and unblocked—have similar prespawn mortality (PSM) rates. Our study determined whether holding fish in constant temperature, pathogen-free conditions prior to spawning increased survival through spawning in 2010 through 2012. In addition, we evaluated pathogens as a potential cause of PSM. To monitor survival we captured adult Chinook Salmon early and late in the season from the lower Willamette River and upper tributaries and held them until spawning in 13°C, pathogen-free water. Samples were collected at the time of transport, from moribund or dead fish throughout the summer, and after spawning in the autumn. Prespawn mortalities and postspawned fish from river surveys on holding and spawning reaches above traps were ...

Population Composition, Migration Timing, and Harvest of Columbia River Chinook Salmon in Late Summer and Fall

Abstract We used radiotelemetry to evaluate population composition, run timing, and reservoir harvest patterns for adult Columbia River fall-run Chinook salmon Oncorhynchus tshawytscha. Chinook salmon (n = 5,886) were collected at Bonneville Dam during August–October over 7 years. We selected for upriver bright (URB) populations en route to interior basin spawning sites because these groups are priority populations for both fisheries and conservation efforts. Run composition varied within and among years, but in all years a relatively large percentage of the earliest migrants returned to upper Columbia River sites and the majority of late-run fish returned to the Columbia River Hanford Reach. Deschutes, Yakima, and Snake River populations typically constituted small (≤17%) but relatively constant proportions of the run throughout each migration season. Population-specific migration timing distributions indicated modest but persistent timing differences among populations, particularly for Hanford Reach and...

Effects of Temporary Tributary Use on Escapement Estimates of Adult Fall Chinook Salmon in the Deschutes River, Oregon

Abstract International managers use escapement estimates of the Deschutes River, Oregon, population of fall Chinook salmon Oncorhynchus tshawytscha to forecast abundance and assess population health. Fish are externally marked in the Deschutes River, and a subsample of the marked fish is recovered on the spawning grounds to provide data for estimating escapement. Escapement would be overestimated if some of the marked fish exited the Deschutes River prior to spawning (i.e., used this tributary temporarily). We used mark–recapture and radiotelemetry techniques to calculate (1) the proportion of adult fall Chinook salmon that entered the Deschutes River and subsequently exited the river prior to spawning and (2) the effect of such temporary entrances on spawning ground escapement estimates. We used separate criteria to calculate maximum and minimum temporary tributary use rates, which were then used to adjust the escapement estimates made with external-tag data alone. Over the 3 years of study, the adjusted...

A Field Test of Eugenol-Based Anesthesia versus Fish Restraint in Migrating Adult Chinook Salmon and Steelhead

AbstractMany studies require the collection and handling of fish, which may have short- and long-term effects on their behavior and survival. We evaluated the effects of AQUI-S 20E, a eugenol-based anesthetic, on adult spring Chinook Salmon Oncorhynchus tshawytscha and winter steelhead O. mykiss in the Willamette River, Oregon. We experimentally compared the postrelease behaviors and movement into spawning tributaries of fish radio-tagged under anesthesia with those of fish radio-tagged while being manually held in a restraint device. Anesthetized Chinook Salmon were less likely than restrained Chinook Salmon to swim downstream (20% versus 47%), more likely to reascend the fishway at which they were collected (89% versus 60%), and more likely to escape to tributaries (82% versus 47%). The treatment effect persisted after statistically controlling for tag date, release time, and fish size. In contrast to Chinook Salmon, the percentages of anesthetized and restrained steelhead that moved downstream (17%), p...

Condition-Dependent En Route Migration Mortality of Adult Chinook Salmon in the Willamette River Main Stem

AbstractEpisodically high adult mortality during migration and near spawning sites has hindered the recovery of threatened spring-run Chinook Salmon Oncorhynchus tshawytscha in Oregon’s Willamette River basin. In 2011–2014, we assessed migration mortality for 762 radio-tagged adults along a ~260-km reach of the main stem of the Willamette River. Annual survival of salmon to spawning tributaries ranged from 0.791 (95% CI = 0.741–0.833) to 0.896 (0.856–0.926), confirming concerns about mortality in the migration corridor. In a series of general linear models, descaling, marine mammal injuries, and head injuries to adult Chinook Salmon were linked to reduced survival during migration to tributaries. Many injuries were minor (i.e., epidermal abrasions), which we hypothesize were unlikely to have caused direct mortality but may have increased salmon vulnerability to pathogens or other disease processes. Mortality in the main stem was not significantly associated with salmon body size, energetic status, sex, or...

Reservoir provides cool-water refuge for adult Chinook salmon in a trap-and-haul reintroduction program

Trap-and-haul is a mitigation strategy at many hydropower dams lacking upstream fish-passage facilities, and protocols are needed to maximise its effectiveness. We used biotelemetry to assess the potential benefits of releasing transported adult Chinook salmon (Oncorhynchus tshawytscha) into a cold-water reservoir v. a relatively warm-water tributary before spawning. Over 5 years, we released 160 salmon into Foster Reservoir (Oregon, USA) and another 102 into the South Santiam River near historical salmon spawning areas further upstream. In total, 70% of reservoir-released salmon entered an upriver tributary after spending a median of 3–95 days annually in the reservoir. Data recovered from 61 archival temperature loggers indicated that salmon were ~3–6°C cooler per day in the reservoir than in the river. We estimated that cumulative exposure of reservoir-released fish was reduced by 64 degree days, on average (range=–129 to 392), relative to river-released fish. Release into the reservoir was not risk free; 14% of all reservoir-released fish fell back downstream v. 1% of river-released fish. We conclude that reduced transport distance, reduced thermal exposure and potential survival benefits of releasing salmon into reservoirs should be weighed against risks of factors such as fallback and homing errors.