River Entry Research Articles

Coastal migration patterns of the four largest Barents Sea Atlantic salmon stocks inferred using genetic stock identification methods

Abstract Combining detailed temporal and spatial catch data, including catch per unit effort, with a high-resolution microsatellite genetic baseline facilitated the development of stock-specific coastal migration models for the four largest Atlantic salmon (Salmo salar) populations, Målselv, Alta, Tana and Kola rivers, contributing to the Barents Sea mixed-stock fishery. Målselv salmon displayed a restricted coastal movement with 85% of the fish captured within 20 km of their natal river. Kola salmon also demonstrated limited coastal movements in Norwegian waters, with most (> 90%) caught in eastern Finnmark. Multi-sea-winter (MSW) Alta salmon were caught west of Alta fjord across a broader stretch of coast while one-sea-winter (1SW) fish migrated more extensively along the coast prior to river entry. Tana salmon, however, were detected over a broad expanse (600 km) of the North-Norwegian coast. For all populations MSW salmon dominating catches earlier in the season (May–June) while 1SW fish were more common from July to August. This study provides an example of how traditional catch and effort information may be combined with genetic methods to obtain insights into spatial and temporal changes in Atlantic salmon catch composition and their associated migration patterns in a mixed-stock coastal fishery.

Earlier migration timing of salmonids: an adaptation to climate change or maladaptation to the fishery?

Recent studies reporting shifts in the timing of salmonid migrations have suggested global warming to be a cause. However, the specific mechanisms underlining the evolution of earlier migration timing in salmonid fishes are unknown. In this paper, I present a hypothesis by which fishery-induced selection works to advance the timing of salmonid migration, given that the timings of migration and breeding are genetically controlled heritable traits. Although late-spawning salmon brood lines enter rivers after early-spawning brood lines, there is evidence that all brood lines arrive in coastal fishing grounds at similar times. As such, late-spawning brood lines would be fished for longer periods of time, with their increased harvest rate imposing directional selection on earlier-spawning brood lines. Thus, fisheries-induced evolution could favor the earlier timing of river entry to escape coastal fisheries. Should earlier migration timing not be an adaptation to global warming — should it be a maladaptation to fisheries-induced selection instead — then it will have a negative impact on the sustainability of salmonid resources.

Transcriptome patterns and blood physiology associated with homing success of sockeye salmon during their final stage of marine migration

To better understand the mechanisms that lead to marine mortality of homing adult sockeye salmon (Oncorhynchus nerka), gill and blood biopsies were used in combination with biotelemetry to demonstrate how survival to freshwater entry is related to gene expression and physiological indices of stress. Microarray analysis of gene expression indicated multiple biological processes, including immune and stress responses, protein biosynthesis, and metabolism. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) analysis indicated fish with upregulation of genes related to stress and infection had higher marine survival compared with fish without this genomic signature. We proposed that higher marine survival of potentially stressed and immune compromised fish can be explained by stressed and infected fish being highly motivated to enter fresh water, leading to enhanced marine survival. However, once in a river, stressed and immune compromised fish could suffer higher mortality because of premature river entry. Overall, this study supports the idea that infection and stress are important biological processes influencing behaviour and fate of sockeye salmon during homing migrations.

Bioenergetic consequences of warming rivers to adult Atlantic salmon Salmo salar during their spawning migration

Abstract Climate change poses a challenge to wild fishes, yet little is known about the behavioural use and metabolic consequences of thermally heterogeneous water encountered by wild salmon during their energetically demanding upstream spawning migration. Temperature, body size and activity levels were modelled to predict energy depletion of salmon during their spawning migration in rivers. Archival temperature loggers revealed the thermal habitat of adult migrating Atlantic salmon (Salmo salar Salmonidae), which we used to apply bioenergetics models that estimated size‐dependent temperature‐driven metabolic expenditures as part of the costs of the migration. Between July 16 and August 19, the mean water temperature experienced by salmon (tFISH) ranged from 11.5 to 18.0°C (14.5 ± 1.2 SD °C) and closely followed the ambient surface water temperature (tRIVER) of the river (11.5–18.5°C; 14.8 ± 1.4°C) such that the regression equation tFISH = 3.24 + 0.76 (tRIVER) was highly correlated with observations (R2 = 0.94). Although temperature increases were predicted and confirmed to increase energetic costs, rates of energy depletion were more sensitive to changes in swimming speed and body size than to temperature increases in the range explored for this system. We conclude that warming could contribute to changing life history phenotypes of salmon in some rivers, for example, delayed river entry or reduced probability of iteroparity, with potentially more dire consequences for smaller individuals.

Timing is everything: Fishing-season placement may represent the most important angling-induced evolutionary pressure on Atlantic salmon populations.

Fisheries‐induced evolution can change the trajectory of wild fish populations by selectively targeting certain phenotypes. For important fish species like Atlantic salmon, this could have large implications for their conservation and management. Most salmon rivers are managed by specifying an angling season of predetermined length based on population demography, which is typically established from catch statistics. Given the circularity of using catch statistics to estimate demographic parameters, it may be difficult to quantify the selective nature of angling and its evolutionary impact. In the River Etne in Norway, a recently installed trap permits daily sampling of fish entering the river, some of which are subsequently captured by anglers upstream. Here, we used 31 microsatellites to establish an individual DNA profile for salmon entering the trap, and for many of those subsequently captured by anglers. These data permitted us to investigate time of rod capture relative to river entry, potential body size‐selective harvest, and environmental variables associated with river entry. Larger, older fish entered the river earlier than smaller, younger fish of both sexes, and larger, older females were more abundant than males and vice versa. There was good agreement between the sizes of fish harvested by angling, and the size distribution of the population sampled on the trap. These results demonstrate that at least in this river, and with the current timing of the season, the angling catch reflects the population's demographics and there is no evidence of size‐selective harvest. We also demonstrated that the probability of being caught by angling declines quickly after river entry. Collectively, these data indicate that that the timing of the fishing season, in relation to the upstream migration patterns of the different demographics of the population, likely represents the most significant directional evolutionary force imposed by angling.

Depositional canyon heads at the edge of narrow and tectonically steepened continental shelves: Comparing geomorphic elements, processes and facies in modern and outcrop examples

Marine geology data show that canyon heads can be the site of depositional processes and furnish the details of the geometry of their geomorphic elements. Canyon heads are usually floored by sediment with a prevailing coarse-grained nature and their sampling is very difficult thus preventing the characterization of the facies of their infill. Lithological and facies information is however available through outcrop studies. In this paper, we integrate modern seafloor and outcrop data to characterize the architecture of depositional canyon heads in tectonically active continental margins with a narrow shelf. The modern examples are located along the northeastern Sicilian margin (Milazzo and Niceto canyon-head systems), whereas the ancient one, Pliocene in age, is located onshore, along the Ligurian coast (Ventimiglia canyon-head system). The modern Milazzo canyon head is located at the coastline and has a steep slope. The flanking deposits are equivalent to the oldest Gilbert delta foresets of the Ventimiglia canyon head as the delta progrades directly into the upper slope. A deeply entrenched channel and a large chute mark the mostly erosional area directly facing the mouths of the rivers that enter the Milazzo canyon head. Laterally, the upper part of the foresets slope is characterized by a bulge with swales and ridges topography. These geomorphic elements are interpreted to be formed by debris flows and turbidity currents as suggested by the upper part of the Ventimiglia foresets, where chaotic, massive or graded deposits are observed. The swales and ridges topography gradually disapper downslope; this area is dominated by turbulent processes due to flow expansion from a confined to a more unconfined setting. An high turbulent flow environment is also confirmed by the formation of plunge pools, due to hydraulic jump, at the foresets-toesets transition. Similar features in the outcrop are infilled by bedsets facies with grain-size coarser than the eroded surroundings. The modern Niceto canyon head is connected landwards to a delta system that stretches across a 1 km wide shelf. Channelized delta distributaries are similar to the topset strata of the youngest deltas of the Ventimiglia canyon head. Channels are up to 200 m wide and 50 m deep and show axial bedform trains confirming that large scale trough cross beds are an important facies of channel infill. Wave reworking in the upper part of the topsets is also suggested by both the modern and outcrop data.Our work shows how the nature of the infill and the depositional processes at the canyon heads are dependent on the shelf width and can give hints on the degree of evolution of the canyon itself. In addition, our work shows how the location and character of river entry points is important in dictating lateral facies variations within canyon heads.

Day-night behavior in river entry of kutum and its relation to melatonin

Reproduction in most fish species is a scheduled phenomenon and spawning occurs at a precise time ensuring maximum survival of offspring. During the spawning season, reproductive activities of fish species and their daily entry to rivers are influenced by environment. Number of Rutilus frisii kutum entered a river discharging to Caspian Sea was analyzed to investigate the association between timing of river entry and day–night changes in environmental variables. Four thousand five hundred and sixty seven ascending adult kutum were collected in Khoshkrood River between March and May 2012. Physicochemical parameters were recorded and Melatonin levels were measured in a hundred migratory kutum over day and night during the spawning period. A significant effect of daytime on river entry was observed, as more fish entered the river at night. Melatonin levels decreased to the minimum level during peak days of migration, suggesting variations in melatonin levels can help to harmonize the daily rhythm in kutum migration.

Condition dependence in the marine exit timing of sockeye salmon (Oncorhynchus nerka) returning to Copper Creek, Haida Gwaii

We examined a small population of sockeye salmon (Oncorhynchus nerka) that enters their natal stream, to hold in their natal lake, months (>130 days) prior to spawning. This effectively decouples the influence of spawn timing requirements and behaviours from river entry (alternately referred to as “marine exit”) timing and is therefore a good model to study the migration strategies specifically associated with marine exit. We found individuals with early marine exit had higher growth rates in the months prior to river entry, had greater lipid density, were more likely male, more likely of the 2.2 versus 1.2 age class, had smaller gonads, and (if female) had more and smaller eggs. Body size at river entry did not vary seasonally. These patterns are explained using a life history model proposing that individual fish exit the sea when the marginal fitness benefits of further growth are outweighed by the marginal fitness cost of further marine residence. This point is reached at different times depending on body size, sex, lipid reserves, and the growth rate.

Environmental conditions and physiological state influence estuarine movements of homing sockeye salmon

The reproductive migration of anadromous salmonids through estuarine waters is one of the most challenging stages of their life cycle, yet little is known about the environmental and physiological conditions that influence migratory behaviour. We captured, sampled tissues, tagged and released 365 sockeye salmon (Oncorhynchus nerka) homing through inner coastal waters towards the Fraser River, British Columbia, Canada. Biotelemetry was used to assess the behaviour of individual sockeye salmon approaching estuarine waters and at river entry, which were related to both fish physiological condition at release and to prevailing environmental conditions. Sockeye salmon tended to stay close to the shore, migrated during the day, and movements were related to tide. Sockeye salmon migration rate was linked to wind-induced currents, salinity and an individual's physiological state, but these factors were specific to location and stock. We propose that wind-induced currents exposed sockeye salmon entering the estuary to stronger olfactory cues associated with Fraser River water, which in turn resulted in faster migration rates presumably due to either an increased ability for olfactory navigation and/or advanced reproductive schedule through a neuroendocrine response to olfactory cues. However, once the migration had progressed further into more concentrated freshwater of the river plume, sockeye salmon presumably used wind-induced currents to aid in movements towards the river, which may be associated with energy conservation. Results from this study improve our biological understanding of the movements of Fraser River sockeye salmon and are also broadly relevant to other anadromous salmonids homing in marine environments.

Integration of Random Forest with population-based outlier analyses provides insight on the genomic basis and evolution of run timing in Chinook salmon (Oncorhynchus tshawytscha).

Anadromous Chinook salmon populations vary in the period of river entry at the initiation of adult freshwater migration, facilitating optimal arrival at natal spawning. Run timing is a polygenic trait that shows evidence of rapid parallel evolution in some lineages, signifying a key role for this phenotype in the ecological divergence between populations. Studying the genetic basis of local adaptation in quantitative traits is often impractical in wild populations. Therefore, we used a novel approach, Random Forest, to detect markers linked to run timing across 14 populations from contrasting environments in the Columbia River and Puget Sound, USA. The approach permits detection of loci of small effect on the phenotype. Divergence between populations at these loci was then examined using both principle component analysis and FST outlier analyses, to determine whether shared genetic changes resulted in similar phenotypes across different lineages. Sequencing of 9107 RAD markers in 414 individuals identified 33 predictor loci explaining 79.2% of trait variance. Discriminant analysis of principal components of the predictors revealed both shared and unique evolutionary pathways in the trait across different lineages, characterized by minor allele frequency changes. However, genome mapping of predictor loci also identified positional overlap with two genomic outlier regions, consistent with selection on loci of large effect. Therefore, the results suggest selective sweeps on few loci and minor changes in loci that were detected by this study. Use of a polygenic framework has provided initial insight into how divergence in a trait has occurred in the wild.

Does Catch‐and‐Release Angling Alter the Behavior and Fate of Adult Atlantic Salmon During Upriver Migration?

AbstractTo reproduce, Atlantic Salmon Salmo salar return to freshwater rivers and migrate upriver to spawning areas. This migration is the basis for recreational fisheries, which for conservation reasons are increasingly characterized by catch‐and‐release angling. The effectiveness of catch and release for Atlantic Salmon conservation is contingent on the ability of individuals to recover from angling, resume migration, and reach spawning grounds at appropriate times. We monitored 27 caught and released Atlantic Salmon in River Gaula in 2013, a prominent and relatively pristine Norwegian river, by affixing external radio transmitters to them. Those fish were compared with a control group of 33 individuals caught and radio‐tagged at sea in bag nets before river entry. Whereas none of the control fish died during the study period, there were three mortalities among the caught‐and‐released fish (11%; significant difference). All mortalities were qualitatively associated with poor angler care, emphasizing the responsibility of anglers in practicing effective catch and release of Atlantic Salmon. Both control and caught and released Atlantic Salmon spent similar time resting below and in transiting a large natural barrier to migration, an 80‐m gorge. The angled and released Atlantic Salmon were distributed in similar locations throughout the river during the spawning season compared with control fish, but those caught and released later in the season appeared to migrate shorter total distances than control fish. Among the caught and released Atlantic Salmon, 17% were recaptured by anglers, which was similar to the rate of recapture of the control fish (21%). Ultimately, individual and population fitness was not likely to be significantly compromised as a result of catch and release because individuals were recorded in spawning areas at appropriate times. Catch and release can therefore be considered a tenable strategy for balancing the costs and benefits associated with the recreational fishery.Received September 26, 2014; accepted December 16, 2014

Hydrochemistry of Tigris River Water from its Iraqi‘s Territory Entry to Baghdad city

The present work deals with hydrochemistry of the major elements in Tigris River water, along the area stretching from the beginning of the river entry into Iraqi territory in the north, and to Baghdad city in the south. The results revealed an increase in the concentrations of the major elements in general, during the trajectory of the river to the south, as well as a relative increase in the concentrations of the elements during the winter, compared with their concentrations during the summer. The result also clarified that the composition of the river basin rocks plays the main control of the major elements hydrochemistry. The results indicated that the controlling rocks type of the Tigris main reservoirs are rang between carbonate and silicate compositions.

Migration behavior of maturing sockeye (Oncorhynchus nerka) and Chinook salmon (O. tshawytscha) in Cook Inlet, Alaska, and implications for management

Worsening recruitment of Alaskan Chinook salmon over the past decade has created major conservation problems. In Cook Inlet, lucrative Sockeye salmon fisheries are severely limited because of Chinook bycatch, restricting economic opportunity and creating political conflict between user groups. Although Chinook are thought to migrate at deeper depths than other salmon during the marine phase, an inability to quantify the depth difference has prevented regulatory changes to protect Chinook while allowing Sockeye fisheries to operate. Using a purpose-built acoustic telemetry array, we found that Chinook salmon repeatedly ‘patrolled’ back and forth in the nearshore fishing area for multiple weeks before river entry (a previously unrecognized behavior) while Sockeye salmon rapidly crossed the area to enter the river. Both species substantially increased migrations speeds at river entry. Migration speeds then progressively dropped, returning to baseline levels about 14 km upstream of the river mouth. Clear differences in the median depth of marine migration of Chinook (4.8 m) and Sockeye (1.8 m) were evident, enabling us to quantify the potential trade-off between reducing Sockeye harvest and increasing Chinook protection from using shallower gillnets in the commercial fishery. Based on the 16,608 depth measurements collected for Chinook and 3,389 measurements for Sockeye, reducing the vertical depth of surface-hung gillnets to one-half of current maximum depth would potentially reduce the Chinook interception rate by nearly two-thirds, while reducing Sockeye harvests by one-quarter. Alternatively, if commercial fishers were fully compensated for the reduced area of netting by allowing exactly compensatory increases in net length, Sockeye catches could potentially increase to 200% to 300% of current levels, but Chinook interceptions would remain similar to current levels despite reductions in net depth. Identifying an intermediate strategy between these two extremes could provide a ‘win-win’ solution rather than the current zero-sum game between deeply opposed stake-holders. Biotelemetry enabled rapid collection of very large numbers of depth measurements despite relatively few adults being tagged. The collected data have already been used to implement some of the first regulatory changes in the fishery in more than a decade and have identified a potential avenue for political accommodation between opposing user groups.

Coastal movements of migrating sea lamprey (Petromyzon marinus) in response to a partial pheromone added to river water: implications for management of invasive populations

How sea lampreys (Petromyzon marinus) search for and select reproductive habitat is poorly understood. Manual tracking of acoustically tagged migrants confirms the hypothesis that sea lampreys transition from extensive search to intensive search upon encounter with river water and return to extensive search upon leaving the plume. In addition, we document a previously unknown search tactic used to localize river mouths termed coastal rebounding. Increased intensive search in the river plume and subsequent approach to the river mouth is hypothesized to occur as a consequence of detection of a pheromone released by river resident larvae that indicate the presence of high-quality reproductive habitat. Application of two synthesized pheromone components caused migrants to increase time spent searching a plume by 57%; applications did not increase the likelihood of river entry. These findings suggest that partial pheromones constitute information that facilitates the search for river entrances, but prove insufficient to affect the decision to select a habitat. Proposed management tactics that rely on luring migrants into rivers with larval odor may prove ineffective without a complete blend of pheromone components.

Research on Water Ecological Protection and Restoration for Dangyang District of Juzhang River Area in Yichang City

In order to protect the aquatic ecological environment of Juzhang river, control the pollution, and protect the safety of drinking water quality, and make the water resourcesuse sustainably as well as promote the coordinated development of basin economic construction and environmental protection, its necessary to conduct the research of aquatic ecological environment protection and restoration of Dangyangdistrict of Juzhang River area in Yichangcity. The measurements of area water ecological protection and restoration were made for water pollution treatment, safety protection of domestic water resource and ecological restoration for the problems of Yichang river area water environment under the direction of Tai lake area treatment experience according to the principle of water environment protection and ecological restoration. The five measurements about the sum controlling for the river entry pollutants, the comprehensivetreatment for water environment, thefull precaution and full controllingfor industrial pollution, the construction of base facilities for water environment, the cooperation treatment for villages environ-ment. The four measurements of the ecological protective belt, man-made wet soil, biological mani-pulation and water plant ecological restoration were applied in the area water ecological restoration. The good effectiveness was obtained through the series of major projects.

Homing behaviour of Atlantic salmon (Salmo salar) during final phase of marine migration and river entry

Little is known about Atlantic salmon behaviour during the last phase of the marine homing migration and subsequent river entry. In this study, 56 adult Atlantic salmon in the Alta Fjord in northern Norway were equipped with acoustic transmitters. Salmon generally followed the coastline, but their horizontal distribution was also affected by wind-induced spreading of river water across the fjord. Mean swimming depth was shallow (2.5–0.5 m), but with dives down to 30 m depth. Timing of river entry was not affected by river flow, diel periodicity, or tidal cycles. Movements during the last part of the marine migration and river entry were unidirectional and relatively fast (mean 9.7 km·day−1). However, migratory speed slowed as salmon approached the estuary, with a significantly lower speed in the innermost part of the estuary than in the open fjord. Migration behaviour seemed not to be affected by handling and tagging, as there were no behavioural differences between newly tagged fish and those captured and tagged 1 year before their homing migration.

Environmental and lunar cues are predictive of the timing of river entry and spawning‐site arrival in lake sturgeon Acipenser fulvescens

The associations were quantified between daily and interannual variation in the timing of a closed population of lake sturgeon Acipenser fulvescens migration and arrival at spawning sites with stream environmental and lunar covariates. Spawning data were gathered from 1262 fish in Black Lake, Michigan 2001 to 2008 and by video monitoring 2000 to 2002. Sex-specific variation in responses to external cues was also tested. Results showed that a greater number of individuals initiated migration from lake to riverine habitats at dawn and dusk relative to other times of the day. Current and lagged effects of water temperature and river discharge, and periods in the lunar cycle were important variables in models quantifying movements into the river and timing of adult arrival at spawning sites. Different suites of covariates were predictive of A. fulverscens responses during different periods of the spawning season. The timing of initiation of migration and spawning, and the importance of covariates to the timing of these events, did not differ between sexes. Stream flow and temperature covaried with other variables including day length and the lunar cycle. Anthropogenic disruption of relationships among variables may mean that environmental cues may no longer reliably convey information for Acipenseriformes and other migratory fishes.

Factors influencing the behavior and duration of residence of adult Chinook salmon in a stratified estuary

The duration of residence, behavior, and thermal experience of adult Chinook salmon (Oncorhynchus tshawytscha) in a stratified lagoon- type estuary over a four-year period was determined using acoustic and radio biotelemetry transmitters and archival temperature tags. Results did not support the hypothesis that adult Chinook salmon would hold extensively and migrate slowly through the estuarine lagoon with return trips to the sea and use of the salt wedge for behavioral thermo-osmoregulation in re- sponse to high summer water temperatures. Passive tidal transport was not observed as predicted and entry from the sea to the estuarine lagoon occurred during all tidal phases suggesting that conserving energy was not a priority for fish during the estuarine phase of their migration. An unexpected finding was that the persistent pursuit pressure of pinnipeds, especially from California sea lions (Zalophus californianus), appeared to negate the suitability of estuarine lagoon as holding habitat. This finding led to the hypothesis that the risk of pinniped predation was primarily re- sponsible for the brief residence (<24 h on average) and rapid migration (mean 1.2 km/h, 0.42 body lengths/s) of adult Chinook salmon in the estuarine lagoon, especially given its relatively small size (7 km). This hypothesis will be difficult to test without exclusion of pinnipeds. Thermal records of fish that retreated back to the sea after tagging suggested that use of the marine river plume could be important for osmotic adaption to allow rapid migration through estuaries, which often contain concentrations of pred- ators anticipating the return of migrating salmon. Alternatively, use of the marine river plume could have occurred independent of predators. Fish retreat- ing back to the sea should be considered a tagging effect as downstream movement commonly occurs when adult salmonids are released after tagging. There was no evidence of any other tagging effects or biased behavior by fish tagged in this study. Regardless of the reasons, the successful migration of fish that held for weeks in the sea after tagging indicates that there could be considerable flexibility in the river entry timing of some salmon stocks. Tagging adult salmonids in the sea as they approach their natal rivers is ideal but the associated logistical challenges

River temperature and adult anadromous Atlantic salmon, Salmo salar, and brown trout, Salmo trutta

Abstract In terms of the spawning migration of adult salmon, Salmo salar L., water flow is often considered the primary factor controlling river entry and fluctuations in flow controlling when the fish subsequently migrate upstream. However, water temperature has also been suggested to modify the spawning migration of salmon, particularly their movements within estuaries and the timing of freshwater entry. Freshwater temperature is more likely to impact salmonid biology than flow, particularly in relation to temperature dependant metabolic costs, time of spawning and fecundity. Therefore, temperature may be more of a factor regulating salmonid populations in fresh water than flow itself. This study focuses on two aspects of the impact of temperature on salmonids in fresh water: first, how salmon may modify their behaviour to adapt to changes in temperature and second the potential relationship between temperature, environmental conditions (e.g. water quality) and physiology (e.g. maturation and olfaction) in regulating adult migration.

Osmoregulatory, metabolic, and nutritional condition of summer-run male Chinook salmon in relation to their fate and migratory behavior in a regulated river

We studied the migratory success of male summer-run Chinook salmon Oncorhynchus tshawytscha in the Puntledge River on Canada's Vancouver Island over a 3 yr period using bioteleme- try and non-lethal physiological biopsy. Principal component analysis was used to group co-varying physiological variables prior to comparing fish with different migratory behaviors (e.g. migration rate, holding times) and fate (migration and spawning success). Fish with low levels of endogenous energy stores (total protein, cholesterol, and triglycerides) and dietary minerals (calcium, magnesium, and phosphorus) at the time of sampling were found to subsequently ascend the most upstream natural barrier (Nib Falls) significantly faster than fish with higher levels. Fate was weakly associated with several physiological characteristics; successful migrants had significantly higher hematocrit values and significantly lower plasma K+ relative to failed migrants, suggesting that fish condition at river entry can influence subsequent behavior. Our results indicate that physiological and nutritional con- dition can influence adult migrating male summer-run Chinook salmon, but we did not find a physi- ological profile that could explain all behaviors and fates observed. This study represents one of the first to apply conservation physiology tools to study an imperiled river fish population.