Subyearling Fall Chinook Salmon Oncorhynchus Research Articles

No Evidence of Increased Survival or Decreased Straying from Acclimating Subyearling Fall Chinook Salmon to Release Locations in the Umatilla River of Oregon

AbstractSmolt‐to‐adult survival (SAS) and straying of subyearling fall Chinook Salmon Oncorhynchus tshawytscha that were acclimated in waters of their release site before river release was compared with those of fish that were transported to the river and released directly into the river. Results showed that there were no differences in average SAS, which was 0.08% for both acclimated and direct‐release groups, or straying, which averaged 33.8% and 35.3% for direct and acclimated release groups, respectively. We conclude that an acclimation period may not improve these metrics in subyearling‐released salmon.Received June 19, 2015; accepted October 31, 2015

Relative Vulnerability of PIT‐Tagged Subyearling Fall Chinook Salmon to Predation by Caspian Terns and Double‐Crested Cormorants in the Columbia River Estuary

AbstractWe quantified the percentage of PIT‐tagged subyearling fall Chinook Salmon Oncorhynchus tshawytscha that were consumed by Caspian terns Hydroprogne caspia and double‐crested cormorants Phalacrocorax auritus nesting on East Sand Island in the Columbia River estuary by electronically recovering PIT tags that were deposited on the bird colonies. We released 23 groups of PIT‐tagged subyearling fall Chinook Salmon from hatcheries in the lower Columbia River downstream of Bonneville Dam from 2002 to 2010. Vulnerability to avian predation was compared between PIT‐tagged subyearlings of two Columbia River basin stocks: tule and upriver bright (URB). Recoveries of PIT tags revealed that overall predation rates were significantly different between the tule stock (22%) and URB stock (3%); for fish that were detected as entering the lower Columbia River during the same week, predation rates also differed between stocks (tule: 21%; URB: 2%). Minimum predation rates on tule subyearlings originating from hatcheries downstream of Bonneville Dam were among the highest documented for any salmonid species in the Columbia River basin to date, occasionally exceeding 35% of the available fish. The ratio of URB fish consumed by the two avian predators indicated that the percentages were nearly equal (cormorant [%]: tern [%] = 51:49), whereas the ratio for tule‐stock fish consumed by the two avian species was not uniform (cormorant: tern = 81:19). Differences in predation rates between the tule stock and the URB stock may be attributable to migration behaviors exhibited in the estuary. We estimate that more than 8 million tule fall Chinook Salmon subyearlings released from hatcheries annually are consumed by double‐crested cormorants and Caspian terns nesting on East Sand Island; ongoing management actions by multiple federal, state, and tribal governments, if successful, will decrease predation on fall Chinook Salmon stocks.

Evidence for Parr Growth as a Factor Affecting Parr‐to‐Smolt Survival

AbstractData collected on juvenile anadromous salmonids implanted with passive integrated transponder (PIT) tags are used in mark–recapture analyses to understand the factors affecting survival of fish estimated between rearing in riverine habitat and dam passage. We estimated parr‐to‐smolt survival of PIT‐tagged naturally produced subyearling fall Chinook salmon Oncorhynchus tshawytscha to examine the previously unexplored influences of environmental and biological conditions measured prior to reservoir entry. Mean (±SE) parr‐to‐smolt survival of the early migrating cohorts was 45.4 ± 6.3% (n = 13) compared with 37.4 ± 4.7% (n = 13) for later migrating cohorts. Annual mean parr‐to‐smolt survival differed widely across years ranging from a low of 9.6 ± 0.5% (n = 2) in 2001 to a high of 81.7 ± 4.6% (n = 2) in 1999. Parr growth prior to reservoir entry and reservoir velocity provided the most information on variability in parr‐to‐smolt survival (N = 26, R2 = 0.75, corrected Akaike's information criterion [AICc] = −5.01). We suggest that parr growth and reservoir velocity were directly proportional to parr‐to‐smolt survival because fast growth and downstream movement reduces the time when fish are vulnerable to predators. The effect of reservoir velocity comports with previous published studies and supports management efforts to increase reservoir velocity. Few if any published studies explicitly relate parr growth measured on individual fish to survival estimated for their cohorts in freshwater. This study provides empirical evidence that upholds the long‐held belief that any anthropogenic activity that reduces growth of juvenile salmonids during freshwater rearing has the potential to reduce their survival.

Distinguishing between Natural and Hatchery Snake River Fall Chinook Salmon Subyearlings in the Field Using Body Morphology

AbstractWe used body morphology to distinguish between natural‐ and hatchery‐origin subyearling fall Chinook salmon Oncorhynchus tshawytscha in rearing areas of the Snake River and at a downstream dam during seaward migration. Using subjective eye and body shape characteristics, field personnel correctly classified 88.9–100% of natural subyearlings (N = 626) and 90.0–100% of hatchery subyearlings (N = 867) in rearing areas from 2001 to 2008. The morphological characteristics used by these personnel proved to have a quantitative basis, as was shown by digital photography and principal components analysis. Natural subyearlings had smaller eyes and pupils, smaller heads, deeper bodies, and shorter caudal peduncles than their hatchery counterparts during rearing and at the dam. A discriminant function fitted from this set of morphological characteristics classified the origin of fish during rearing and at the dam with over 97% accuracy. We hypothesize that these morphological differences were primarily due to environmental influences during incubation and rearing because it is highly probable that a large portion of the natural juveniles we studied were the offspring of hatchery × hatchery mating in the wild. The findings in this paper might provide guidance for others seeking to differentiate between natural and hatchery fish.

Water Velocity, Turbulence, and Migration Rate of Subyearling Fall Chinook Salmon in the Free‐Flowing and Impounded Snake River

AbstractWe studied the migratory behavior of subyearling fall Chinook salmon Oncorhynchus tshawytscha in free‐flowing and impounded reaches of the Snake River to evaluate the hypothesis that velocity and turbulence are the primary causal mechanisms of downstream migration. The hypothesis states that impoundment reduces velocity and turbulence and alters the migratory behavior of juvenile Chinook salmon as a result of their reduced perception of these cues. At a constant flow (m3/s), both velocity (km/d) and turbulence (the SD of velocity) decreased from riverine to impounded habitat as cross‐sectional areas increased. We found evidence for the hypothesis that subyearling Chinook salmon perceive velocity and turbulence cues and respond to these cues by varying their behavior. The percentage of the subyearlings that moved faster than the average current speed decreased as fish made the transition from riverine reaches with high velocities and turbulence to upper reservoir reaches with low velocities and turbulence but increased to riverine levels again as the fish moved further down in the reservoir, where velocity and turbulence remained low. The migration rate (km/d) decreased in accordance with longitudinal reductions in velocity and turbulence, as predicted by the hypothesis. The variation in migration rate was better explained by a repeated‐measures regression model containing velocity (Akaike's information criterion = 1,769.0) than a model containing flow (2,232.6). We conclude that subyearling fall Chinook salmon respond to changes in water velocity and turbulence, which work together to affect the migration rate.

Predicted Changes in Subyearling Fall Chinook Salmon Rearing and Migratory Habitat under Two Drawdown Scenarios for John Day Reservoir, Columbia River

AbstractWe evaluated the potential effects of two different drawdown scenarios on rearing and migration habitat of subyearling fall Chinook salmon Oncorhynchus tshawytscha in John Day Reservoir on the Columbia River. We compared habitats at normal operating pool elevation with habitats at drawdown to spillway crest elevation and drawdown to the historical natural river elevation for two flows (4,417 and 8,495 m3/s). Using two‐dimensional hydrodynamic modeling and a predictive habitat model, we determined the quantity and spatial distribution of rearing habitat and predicted water velocities. We predicted that the most habitat area would occur under normal pool elevation, but 93% of habitat was located in the upper third of the reservoir. Although less habitat area was predicted under drawdown to the spillway crest and the natural river, it was distributed more homogeneously throughout the study area. Habitat connectivity, patch size, and percent of suitable shoreline were greatest under drawdown to the natural river elevation. Mean cross‐sectional water velocity and the variation in velocity increased with increasing level of reservoir drawdown. Water velocities under drawdown to the natural river were about twice as high as those under drawdown to spillway crest and five times higher than those under normal pool. The variability in water velocity, which may provide cues to fish migration, was highest under drawdown to the natural river and lowest under normal pool elevation. The extent to which different drawdown scenarios would be effective in John Day Reservoir depends in part on restoring normative riverine processes.

Variables Influencing the Presence of Subyearling Fall Chinook Salmon in Shoreline Habitats of the Hanford Reach, Columbia River

AbstractLittle information currently exists on habitat use by subyearling fall Chinook salmon Oncorhynchus tshawytscha rearing in large, main‐stem habitats. We collected habitat use information on subyearlings in the Hanford Reach of the Columbia River during May 1994 and April–May 1995 using point abundance electrofishing. We analyzed measures of physical habitat using logistic regression to predict fish presence and absence in shoreline habitats. The difference between water temperature at the point of sampling and in the main river channel was the most important variable for predicting the presence and absence of subyearlings. Mean water velocities of 45 cm/s or less and habitats with low lateral bank slopes were also associated with a greater likelihood of subyearling presence. Intermediate‐sized gravel and cobble substrates were significant predictors of fish presence, but small (<32‐mm) and boulder‐sized (>256‐mm) substrates were not. Our rearing model was accurate at predicting fish presence and absence using jackknifing (80% correct) and classification of observations from an independent data set (76% correct). The habitat requirements of fall Chinook salmon in the Hanford Reach are similar to those reported for juvenile Chinook salmon in smaller systems but are met in functionally different ways in a large river.

Influence of River Conditions on Survival and Travel Time of Snake River Subyearling Fall Chinook Salmon

From 1995 to 2000, subyearling fall chinook salmon Oncorhynchus tshawytscha reared at Lyons Ferry Hatchery were PIT-tagged at the hatchery, trucked upstream, acclimated, and released into free-flowing sections of the Snake River weekly from early June to mid-July. We estimated survival probabilities and travel time through the lower Snake River and detection probabilities at dams for each weekly release group. The average median time between release and arrival at Lower Granite Dam was 43.5 d. For each group, we split this time into two nearly equal (on average) periods: one when most fish in the group were rearing and one when most fish had apparently begun active seaward migration. The estimated survival for hatchery fish from release to the tailrace of Lower Granite Dam decreased with release date each year. The estimated survival through this reach was significantly correlated with three environmental variables: survival decreased as discharge (“flow”) decreased, as water transparency increased, and as water temperature increased. Because the environmental variables were highly correlated among themselves, we were unable to determine whether any factors were more important than the others. All three factors have plausible biological consequences for rearing and actively migrating fish, and survival is probably influenced by all of them and possibly by interactions among them as well. Summer flow augmentation will increase discharge and decrease water temperature (provided the additional water is not too warm) and probably increase the speed of seaward migration of smolts, all of which are beneficial to the recovery of threatened Snake River fall chinook salmon.

Influence of Flow and Temperature on Survival of Wild Subyearling Fall Chinook Salmon in the Snake River

Summer flow augmentation to increase the survival of wild subyearling fall chinook salmon Oncorhynchus tshawytscha is implemented annually to mitigate for the development of the hydropower system in the Snake River basin, but the efficacy of this practice has been disputed. We studied some of the factors affecting survival of wild subyearling fall chinook salmon from capture, tagging, and release in the free-flowing Snake River to the tailrace of the first dam encountered by smolts en route to the sea. We then assessed the effects of summer flow augmentation on survival to the tailrace of this dam. We tagged and released 5,030 wild juvenile fall chinook salmon in the free-flowing Snake River from 1998 to 2000. We separated these tagged fish into four sequential within-year release groups termed cohorts (N = 12). Survival probability estimates (mean ± SE) to the tailrace of the dam for the 12 cohorts when summer flow augmentation was implemented ranged from 36% ± 4% to 88% ± 5%. We fit an ordinary least-squares multiple regression model from indices of flow and temperature that explained 92% (N = 12; P < 0.0001) of the observed variability in cohort survival. Survival generally increased with increasing flow and decreased with increasing temperature. We used the regression model to predict cohort survival for flow and temperature conditions observed when summer flow augmentation was implemented and for approximated flow and temperature conditions had the summer flow augmentation not been implemented. Survival of all cohorts was predicted to be higher when flow was augmented than when flow was not augmented because summer flow augmentation increased the flow levels and decreased the temperatures fish were exposed to as they moved seaward. We conclude that summer flow augmentation increases the survival of young fall chinook salmon.

Migrational Behavior and Seaward Movement of Wild Subyearling Fall Chinook Salmon in the Snake River

Abstract Flow augmentation increases flow and decreases temperature in reservoirs in the lower Snake River during the seaward migration of wild subyearling fall chinook salmon Oncorhynchus tshawytscha. A study of the migrational behavior and seaward movement of wild subyearling fall chinook salmon in the Snake River was necessary to help understand the efficacy of flow augmentation. We studied fall chinook salmon in the Snake River during 1992–2001. After analyzing mark–recapture data, we deduced that fall chinook salmon passed through at least four migrational phases, including (1) discontinuous downstream dispersal along the shorelines of the free-flowing river, (2) abrupt and mostly continuous downstream dispersal offshore in the free-flowing river, (3) passive, discontinuous downstream dispersal offshore in the first reservoir encountered en route to the sea, and (4) active and mostly continuous seaward migration. We used ordinary-least-squares multiple regression to test the effects of flow (m3/s), t...

Quantifying Flow-Dependent Changes in Subyearling Fall Chinook Salmon Rearing Habitat Using Two-Dimensional Spatially Explicit Modeling

Abstract We used an analysis based on a geographic information system (GIS) to determine the amount of rearing habitat and stranding area for subyearling fall chinook salmon Oncorhynchus tshawytscha in the Hanford Reach of the Columbia River at steady-state flows ranging from 1,416 to 11,328 m3/s. High-resolution river channel bathymetry was used in conjunction with a two-dimensional hydrodynamic model to estimate water velocities, depths, and lateral slopes throughout our 33-km study area. To relate the probability of fish presence in nearshore habitats to measures of physical habitat, we developed a logistic regression model from point electrofishing data. We only considered variables that were compatible with a GIS and therefore excluded other variables known to be important to juvenile salmonids. Water velocity and lateral slope were the only two variables included in our final model. The amount of available rearing habitat generally decreased as flow increased, with the greatest decreases occurring b...

Physiological Development and Migratory Behavior of Subyearling Fall Chinook Salmon in the Columbia River

Abstract We describe the migratory behavior and physiological development of subyearling fall chinook salmon Oncorhynchus tshawytscha migrating through John Day Reservoir on the Columbia River, Washington and Oregon. Fish were freeze-branded and coded-wire-tagged at McNary Dam, Oregon, from 1991 to 1994, to determine travel time to John Day Dam and subsequent adult contribution. Stepwise multiple regression showed that 47% of the variation in subyearling fall chinook salmon travel time was explained by the reciprocal of minimum flow and fish size. Smoltification, as measured by gill Na+-K+ adenosine triphosphatase (ATPase) activity, was not important in explaining variability in travel time of subyearling chinook salmon. Fish marked early in the out-migration generally traveled faster than middle and late migrants. Seawater challenges were used to describe physiological development and showed that osmoregulatory competence of premigrants in the Hanford Reach of the Columbia River increased with fish size ...