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Fish passage systems (fishways) have become the most common mitigation tool for improving the connectivity of migratory fish populations in ecosystems with barriers to movement. Because fishways often have high-velocity and high-turbulence environments, fish should seek low-energy movement paths during passage. We tested this hypothesis by analyzing the swimming paths of 90 adult Pacific lamprey ( Entosphenus tridentatus ) in response to hydraulic conditions when passing a vertical-slot weir in an experimental fishway. Varying hydraulic conditions were achieved by manipulating three variables: water velocity (1.2, 1.8, 2.4 m/s), vertical-slot length (0.33 m, 0.66 m, 1.00 m), and presence or absence of a turbulence-inducing structure. Turbulence parameters, such as turbulent kinetic energy ( TKE ), were quantified using an Acoustic Doppler Velocimeter (ADV). Pacific lamprey exhibited context-dependent behaviors in response to turbulence whereby lamprey were more likely to move towards areas of lower turbulence along their swimming paths, but only as the surrounding turbulence within the vertical-slot increased. In contrast, when the surrounding turbulence within the vertical-slot was low, Pacific lamprey became more likely to move towards areas of higher turbulence. The ‘turbulence-avoidance’ behaviors likely allowed passage of the hydraulic obstacle by reducing energy expenditure or physiological stress, while the ‘turbulence-attraction’ behaviors may have resulted from lamprey using turbulence as a mechanism for upstream orientation. Overall, our results provide new insight into how fish may use turbulence as an important sensory modality for perceiving the aquatic environment. [ABSTRACT FROM AUTHOR]

• Warm stream temperatures increased female Chinook salmon prespawn mortality (i.e., mature salmon died prior to laying eggs). • Prespawn mortality was also higher for larger salmon and those of hatchery origin. • Higher stream temperatures by 2040 are likely to increase prespawn mortality. • However, some populations have low prespawn mortality under both current and future expected conditions. Conservation and restoration efforts for Pacific salmon Oncorhynchus spp. can be hampered by prespawn mortality, when adult fish reach reproductive sites but die before spawning. We examined annual estimates of female Chinook salmon O. tshawytscha prespawn mortality relative to individual fish traits (77,707 individual females) and reach-scale variables in 49 study reaches from 41 streams throughout the interior Columbia River Basin. Mean annual prespawn mortality estimates across 14 years ranged from 0 % to 65 %. For spring-run Chinook salmon, the probability of prespawn mortality decreased over the spawning period, was positively associated with mean August stream temperature and individual fish length, and was higher for hatchery-origin than natural-origin fish. Based on the basin-wide statistical model and future stream temperature predictions, average spring-run Chinook salmon prespawn mortality rates in 2040 were predicted to increase by 0–17 % for fish of natural origin and 1–17 % for fish of hatchery origin. Climate change is likely to exacerbate conditions that lead to prespawn mortality, particularly in low elevation stream reaches, for larger fish, and for those of hatchery origin. [ABSTRACT FROM AUTHOR]

Abstract River warming poses an existential threat to many Pacific salmon (Oncorhynchus spp) populations. However, temperature-mediated risks to salmon are often complex and addressing them requires species- and population-specific data collected over large spatial and temporal scales. In this study, we combined radiotelemetry with archival depth and temperature sensors to collect continuous thermal exposure histories of 21 adult spring- and summer-run Chinook salmon (O. tshawytscha) as they migrated hundreds of kilometers upstream in the Columbia River basin. Salmon thermal histories in impounded reaches of the Columbia and Snake rivers were characterized by low daily temperature variation but frequent and extensive vertical movements. Dives were associated with slightly cooler salmon body temperatures (~ 0.01 to 0.02 °C/m), but there was no evidence for use of cool-water thermal refuges deep in reservoirs or at tributary confluences along the migration route. In tributaries, salmon were constrained to relatively shallow water, and they experienced ~ 2–5 °C diel temperature fluctuations. Differences in migration timing and among route-specific thermal regimes resulted in substantial among-individual variation in migration temperature exposure. Bioenergetics models using the collected thermal histories and swim speeds ranging from 1.0 to 1.5 body-lengths/s predicted median energetic costs of ~ 24–40% (spring-run) and ~ 37–60% (summer-run) of initial reserves. Median declines in total mass were ~ 16–24% for spring-run salmon and ~ 19–29% for summer-run salmon. A simulated + 2 °C increase in water temperatures resulted in 4.0% (spring-run) and 6.3% (summer-run) more energy used per fish, on average. The biotelemetry data provided remarkable spatial and temporal resolution on thermal exposure. Nonetheless, substantial information gaps remain for the development of robust bioenergetics and climate effects models for adult Chinook salmon. Highlights • Adult Chinook salmon experienced low thermal variation in reservoirs. • Most salmon were cooler and experienced large diel fluctuations in tributaries. • There was no evidence for behavioral thermoregulation despite frequent salmon diving. • Energetic costs of migration were ~ 24–40% (spring-run) and ~ 37–60% (summer-run). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Timing data are difficult to analyze because conditions vary during the observation period. [•] We demonstrated methods to analyze “time-to-event” data under time-varying conditions. [•] We applied parametric models to the time for migrating salmonids to successfully pass a barrier. [•] The model captured pronounced diel behavior and the effects of time-varying covariates. [Copyright &y& Elsevier]

Abstract: In the multi-stock Columbia River system, managers estimate fall Chinook salmon, Oncorhynchus tshawytscha (Walbaum), escapements using various combinations of spawning ground surveys, harvest data and fish counts at dams and hatcheries. Our objectives were to improve upon the traditional methods, and to evaluate trade-offs among methods. Using data from radio-tagged (n =4421) and PIT-tagged (n =1950) adult salmon over eight years, we applied a mark-recapture method to estimate population-specific escapements, both aggregating data within year and stratifying them by week. Mark-recapture estimates differed between estimation techniques and from estimates generated using traditional methods. Stratifying data by week measured escapement estimate uncertainty more reasonably than aggregating data within year. Radiotelemetry provided better spatial resolution among populations for tributary spawners whereas PIT tags provided low-cost, easily replicated estimates using an existing detection system. Mark-recapture techniques had several advantages over current practices: quantifying uncertainty, transparent methods and reduced sensitivity to survey biases. [Copyright &y& Elsevier]