Yearling Chinook Salmon Research Articles

Impact of the Potholes Reservoir Caspian Tern Breeding Colony on Out‐Migrating Juvenile Salmonids in the Mid‐Columbia River

AbstractWe examined the foraging behavior and diet of Caspian terns Hydroprogne caspia breeding at Potholes Reservoir, Washington, in 2003, 2005, and 2006, and we developed a bioenergetics model to estimate impacts on juvenile salmonids Oncorhynchus spp. from Columbia River stocks. Potholes Reservoir Caspian terns mostly foraged on local fish (68–97% of tern bill loads) rather than traveling to the Columbia River. Our model suggested that only 8,913–94,139 juvenile salmonids were consumed, representing 0.02–0.38% of the salmonids available to Caspian terns. Local foraging is probably explained by higher net profitability of Potholes Reservoir fish prey. Columbia River steelhead O. mykiss were the only juvenile salmonids that were energetically comparable with local Potholes Reservoir fish, mostly due to their high energy density and relatively large size. Passive integrated transponder tag analyses showed that Potholes Reservoir Caspian terns preferred steelhead (predation rates = 0.42–1.06%) to all other salmonid stocks (coho salmon O. kisutch = 0.09–0.36%; subyearling Chinook salmon O. tshawytscha = 0.009–0.040%; yearling Chinook salmon = 0.05–0.17%). Given the proposed reduction in nesting habitat at East Sand Island (ESI; where the current Caspian tern population consumes 3.6–5.3 million juvenile salmonids annually), we estimated the impact on salmonid stocks that would occur if ESI Caspian terns relocated to Potholes Reservoir. Depending on diet scenario, 100% relocation could result in juvenile salmonid consumption between 2.2 and 6.6 million fish, with lower values being much more likely, making Potholes Reservoir the colony location of least likely impact among all sites within the Columbia River drainage. We suggest that selection of sites for ESI relocation should be based on scientific evidence combining a quantitative approach, such as bioenergetics modeling linked to prey population growth rate.

The Juvenile Salmon Acoustic Telemetry System: A New Tool

AbstractLimitations of biotelemetry technology available in 2001 prompted the U.S. Army Corps of Engineers Portland District to develop a new acoustic telemetry system to monitor survival of juvenile salmonids through the Columbia River to the Pacific Ocean. Eight years later, the Juvenile Salmon Acoustic Telemetry System (JSATS) consists of microacoustic transmitters (12 mm long, 0.43 g weight in air), autonomous and cabled receiving systems, and data management and processing applications. Transmitter pulse rate can be user‐defined and as configured for this case study was set at 5 seconds, with an estimated tag life of 30 days and detection range of 300 m. Before JSATS development, no technology existed to study movement and survival of fish smaller than 10 g migrating long distances from freshwater and into saltwater. In a 2008 study comparing detection probabilities, travel times, and survival of 4,140 JSATS‐tagged and 48,433 passive integrated transponder (PIT)‐tagged yearling Chinook salmon (Oncorhynchus tshawytscha; mean fork length 133.9 and 135.3 mm, for JSATS and PIT‐tagged fish, respectively) migrating the Snake and Columbia rivers to the Pacific, the JSATS provided survival estimates at more locations with greater precision, using less than one‐tenth as many tagged fish as the traditional PIT‐tag system. While designed to be optimized for juvenile salmonid survival assessment in the Columbia River basin, JSATS technology may be used in a variety of environments. Information regarding different acoustic telemetry systems from various vendors is presented and discussed relative to the nonproprietary JSATS.

Species-Specific Spatial and Temporal Distribution Patterns of Emigrating Juvenile Salmonids in the Pacific Northwest

The vertical and horizontal distribution of juvenile salmonid migrants on approach to the dams influences bypass success in rivers. Accordingly, fish distributions have been studied for nearly three decades. These studies, however, have not been integrated and summarized in a single body of work to determine overall patterns in the spatial distribution of emigrants. We reviewed peer-reviewed and gray literature to summarize species-specific trends in the horizontal and vertical distributions of emigrating salmonids as measured by several different methods. We found that there were no species-specific differences in horizontal distributions and that fish were often oriented with the river thalweg. There were weak differences between species in vertical distributions, e.g., juvenile yearling steelhead were shallower during the day than yearling Chinook salmon. For sockeye, coho, and subyearling Chinook salmon, the data were limited or conflicting. Studies were purposefully designed to measure distributions at certain dams under particular environmental conditions for specific, local purposes. The non-standard sampling design has hampered the development of testable hypothesis on fish distributions in the Snake and Columbia rivers. Recent advances in individual-based models are offering the potential to forecast fish distributions near dams and facilitate improved bypass system design.

Ontogenetic Shifts in Diets of Juvenile and Subadult Coho and Chinook Salmon in Coastal Marine Waters: Important for Marine Survival?

AbstractSuccessfully shifting to a more piscivorous diet may be an important factor in the growth and survival of juvenile coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha during their first summer in the northern California Current. Nonmetric multidimensional scaling and cluster analysis of diets by size showed several distinct groupings as the salmon grew during their first marine summer. These size‐based diet differences were clearly driven by increased rates of piscivory for both species. Fish prey composition, feeding intensity, and fish prey–predator length ratios all significantly increased for coho salmon at approximately 240 mm fork length when they changed from diets dominated by juvenile rockfishes Sebastes spp., the larvae of crabs Cancer spp., and adult euphausiids to one of predominantly juvenile forage fish. As Chinook salmon grew, they gradually increased the proportional contribution (by weight) of fish prey in their diets—from 55% in the smallest length‐class examined (80–100 mm) to 95% in the largest one (>375 mm). Chinook salmon fed in the same marine environments as coho salmon and consistently ate more and longer fish prey at a given size than coho salmon but had lower overall feeding intensity, perhaps owing to a higher level of prey selection. Relating subsequent interannual adult salmon returns to juvenile diets showed mixed results. During lower‐survival years, coho salmon ate fewer and smaller fish prey, while subyearling Chinook salmon had less total food and more empty stomachs. We did not find consistent trophic patterns for yearling Chinook salmon in relation to their ultimate survival.

Spatial distribution of ocean habitat of yearling Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon off Washington and Oregon, USA

AbstractWe determined the habitat usage and habitat connectivity of juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon in continental shelf waters off Washington and Oregon, based on samples collected every June for 9 yr (1998–2006). Habitat usage and connectivity were evaluated using SeaWiFS satellite‐derived chlorophyll a data and water depth. Logistic regression models were developed for both species, and habitats were first classified using a threshold value estimated from a receiver operating characteristic curve. A Bernoulli random process using catch probabilities from observed data, i.e. the frequency of occurrence of a fish divided by the number of times a station was surveyed, was applied to reclassify stations. Zero‐catch probabilities of yearling Chinook and yearling coho salmon decreased with increases in chlorophyll a concentration, and with decreases in water depth. From 1998 to 2006, ∼ 47% of stations surveyed were classified as unfavorable habitat for yearling Chinook salmon and ∼ 53% for yearling coho salmon. Potentially favorable habitat varied among years and ranged from 9 856 to 15 120 km2 (Chinook) and from 14 800 to 16 736 km2 (coho). For both species, the smallest habitat area occurred in 1998, an El Niño year. Favorable habitats for yearling Chinook salmon were more isolated in 1998 and 2005 than in other years. Both species had larger and more continuous favorable habitat areas along the Washington coast than along the Oregon coast. The favorable habitats were also larger and more continuous nearshore than offshore for both species. Further investigations on large‐scale transport, mesoscale physical features, and prey and predator availability in the study area are necessary to explain the spatial arrangement of juvenile salmon habitats in continental shelf waters.

Performance of a prototype surface collector for juvenile salmonids at Bonneville Dam's first powerhouse on the Columbia River, Oregon

AbstractDuring April–July 2000, we radio‐tagged and released juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) to evaluate a prototype surface flow bypass at Bonneville Dam on the Columbia River. The mock bypass, called a prototype surface collector (PSC), had six vertical slot entrances that were each 6 m wide and 12 m deep. The PSC was retrofitted to the upstream face of Bonneville Dam's First Powerhouse. Our objectives were to: (1) assess species‐specific differences in movement patterns and behaviour of fish within 6 m of the face of the PSC, (2) estimate the efficiency and effectiveness of the PSC and (3) evaluate factors affecting the performance of the PSC. We found that 60–72% of the fish, depending on species, detected within 6 m of the PSC entered it. Of the fish that passed the First Powerhouse at turbines 1–6, 79–83% entered the PSC. Diel period was a significant contributor to PSC performance for all species, and day of year was a significant contributor to PSC performance for subyearling Chinook salmon. The PSC was twice as effective (%fish/%flow) as the spillway, passing 2.5:1 steelhead and subyearling Chinook salmon and 2.4:1 yearling Chinook salmon per unit of water. If fully implemented, the PSC would increase the percentage of fish that pass the First Powerhouse through non‐turbine routes from 65–77% (without the PSC) to 76–85% (with the PSC), depending on species. Published in 2008 by John Wiley & Sons, Ltd.

Migration Depths of Juvenile Chinook Salmon and Steelhead Relative to Total Dissolved Gas Supersaturation in a Columbia River Reservoir

AbstractThe in situ depths of juvenile salmonids Oncorhynchus spp. were studied to determine whether hydrostatic compensation was sufficient to protect them from gas bubble disease (GBD) during exposure to total dissolved gas (TDG) supersaturation from a regional program of spill at dams meant to improve salmonid passage survival. Yearling Chinook salmon O. tshawytscha and juvenile steelhead O. mykiss implanted with pressure‐sensing radio transmitters were monitored from boats while they were migrating between the tailrace of Ice Harbor Dam on the Snake River and the forebay of McNary Dam on the Columbia River during 1997–1999. The TDG generally decreased with distance from the tailrace of the dam and was within levels known to cause GBD signs and mortality in laboratory bioassays. Results of repeated‐measures analysis of variance indicated that the mean depths of juvenile steelhead were similar throughout the study area, ranging from 2.0 m in the Snake River to 2.3 m near the McNary Dam forebay. The mean depths of yearling Chinook salmon generally increased with distance from Ice Harbor Dam, ranging from 1.5 m in the Snake River to 3.2 m near the forebay. Juvenile steelhead were deeper at night than during the day, and yearling Chinook salmon were deeper during the day than at night. The TDG level was a significant covariate in models of the migration depth and rates of each species, but no effect of fish size was detected. Hydrostatic compensation, along with short exposure times in the area of greatest TDG, reduced the effects of TDG exposure below those generally shown to elicit GBD signs or mortality. Based on these factors, our results indicate that the TDG limits of the regional spill program were safe for these juvenile salmonids.

Evidence of Delayed Mortality on Juvenile Pacific Salmon Passing through Turbines at Columbia River Dams

AbstractWe evaluated the survival of juvenile salmon through turbines in Columbia River dams and found no differences between two operations but strong evidence of delayed mortality from turbine passage. After tagging with a passive integrated transponder (PIT) tag and a radio tag, yearling Chinook salmon Oncorhynchus tshawytscha were released at McNary Dam on the Columbia River through a turbine operating both within 1% of peak efficiency (a discharge rate of 317 m3/s) and outside the 1% range at the maximum blade angle (464 m3/s). Estimated relative survival to a detection array 15 km downstream was 0.871 at 317 m3/s and 0.856 at 464 m3/s and 0.858 and 0.814, respectively, to an array 46 km downstream. The highest point estimates of survival occurred under the lower discharge, suggesting that operating turbines within 1% of peak efficiency is a useful guideline for fish protection at McNary Dam. In a concurrent evaluation using balloon tags, estimated mean direct survival ranged from 0.930 to 0.946. Radio tag estimates were significantly lower than balloon tag estimates under both operations. Based on these differences, we estimated that delayed mortality comprised from 46% to 70% of total estimated mortality. We reviewed the literature and concluded that delayed mortality was caused by sublethal impacts to fish sensory systems, which increased vulnerability to predation in the tailrace. We recommend that future research to improve turbine designs and operations for fish passage focus on this major component of mortality.

Upstream Migration of Minijack (Age‐2) Chinook Salmon in the Columbia River: Behavior, Abundance, Distribution, and Origin

AbstractIt has recently been demonstrated that a large percentage of yearling Chinook salmon Oncorhynchus tshawytscha smolts released from a production‐scale hatchery on the Yakima River display an underappreciated life history strategy. Instead of migrating to the ocean for long‐term rearing and growth, males may instead undertake a short‐term migration downstream, turn around, and migrate back upstream where they reproductively mature at age 2. Following local hatchery traditions, these fish are referred to as “minijacks.” We used information produced from (1) large‐scale passive integrated transponder (PIT)‐tagging programs at hatcheries in the Columbia and Snake River basins and (2) the installation of PIT tag detectors in the fish passage ladders built into dams on these rivers to investigate the occurrence, behavior, distribution, and origin of minijacks. A minijack was operationally defined as a fish detected in a ladder after 1 June in the same year it was released. Minijacks were found in every hatchery release group of more than 7,500 PIT‐tagged Chinook salmon smolts reported (2002, 13 groups; 2003, 15 groups). Minijack population migration upstream past Bonneville Dam peaked in late June and July. This lagged migrations of age‐4 adults (from the same populations) by approximately 2 months. However, minijacks also displayed population‐specific variation in timing of upstream migrations past Bonneville Dam; minijacks from spring Chinook salmon populations appeared before fall Chinook salmon populations. Detection rates of minijacks at all dams ranged from 0.02% to 0.33% of the total smolts released for different hatchery groups. Expansion of this rate, based on the relation between minijack estimates at Cle Elum Hatchery (before release) and detections at Bonneville Dam (after release), suggests that minijack abundance in the Columbia and Snake River basins exceed hundreds of thousands of fish.

Caspian Tern Predation on Juvenile Salmonids in the Mid‐Columbia River

AbstractWe used a bioenergetics approach to determine the magnitude of predation by Caspian terns Sterna caspia on juvenile salmonids Oncorhynchus spp. in the mid‐Columbia River during 2000 and 2001. Caspian terns nesting on Crescent Island, Washington, located below the confluence of the Snake and Columbia rivers, consumed several hundred thousand juvenile salmonids each year of the study. Tern consumption of smolts was higher in 2001 (679,000 smolts; 95% confidence interval (CI): 533,000–825,000 smolts) than in 2000 (465,000 smolts; 95% CI: 382,000–547,000 smolts) as a result of an increase in tern breeding pairs, fledging success, and percentage of salmonids in the diet. On‐colony detection rates of passive integrated transponder tags from in‐river migrating smolts were also higher in 2001 (0.90–12.40%) than in 2000 (0.03–1.60%); the higher predation rates in 2001 were probably caused by extreme drought conditions that resulted in reduced spill from hydroelectric dams, lower river flows, and increased travel times for in‐river migrating smolts. Tern predation rates on juvenile steelhead O. mykiss were higher than those on yearling Chinook salmon O. tshawytscha in both years. The impacts of tern predation on steelhead smolts and yearling Chinook salmon from the Snake River were slight after accounting for the high proportion of smolts collected for transportation above Crescent Island. Survival of steelhead smolts from the upper Columbia River that are not transported above Crescent Island may be significantly affected by tern predation, particularly in low‐flow years. Appreciably higher predation rates on salmonids by Crescent Island terns than those observed in 2001 are unlikely considering the constraints on tern colony expansion, limited capacity for increased per capita smolt consumption by terns, and current high transportation rates for Snake River smolts.

Fine‐Scale Behavioral Responses of Pacific Salmonid Smolts as They Encounter Divergence and Acceleration of Flow

AbstractWe assessed fine‐scale behavioral responses of the smolts of four Pacific salmonid species to open and constricted channels in a flume. Natural migrants encountered two geometrically similar parallel channels with different hydraulic conditions representing constricted and open treatments. Observation of route selection under alternate discharge scenarios provided evidence of behavioral choice by smolts. As expected, the majority of smolts passed through the open channel in a ratio consistent with flow. After controlling for the influence of flow, both initial channel selection and subsequent channel rejection was higher for the constricted channel; rejection was probably due to fish detecting an area of rapidly accelerating flow. The majority of smolts traveled downstream headfirst and faster than the mean midcolumn water velocity. Those that faced the flow passed at a slower rate and tended to select the open treatment. The few yearling Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch smolts that did not pass through the treatment channels, but held position within the flume, were larger than their conspecifics that passed downstream. Large steelhead (anadromous rainbow trout O. mykiss) smolts and subyearling Chinook salmon were more likely to pass the constricted channel than smaller fish. These results suggest that efforts to effectively guide fish with diversion structures will require understanding how the structures alter the local hydraulic environment and, thus, influence fish behavior.

Diel differences in surface trawl fish catches off Oregon and Washington

Abstract Surface rope trawls have recently been used to investigate pelagic fish communities off the west coast of North America. We examined surface rope trawl catches from locations off the Washington and Oregon coast to determine whether they differed day and night. We paired day and night samples from the same location taken within 7 days of each other. Fifty-one sample pairs fit our criteria with 33 of these controlled for tidal state. Samples were taken at 11 different stations during the months of May, June, and September from 1998 to 2002. We used the sign test to compare median densities for nine of the most abundant and commonly occurring fish species: two juvenile salmonids—coho salmon ( Oncorhynchus kisutch ) and yearling Chinook salmon ( O. tshawytscha ); four small pelagics—northern anchovy ( Engraulis mordax ), Pacific herring ( Clupea pallasi ), Pacific sardine ( Sardinops sagax ), and whitebait smelt ( Allosmerus elongatus ); and three larger predatory fishes—Pacific hake ( Merluccius productus ), chub mackerel ( Scomber japonicus ), and jack mackerel ( Trachurus symmetricus ). Both species of salmon were caught at higher densities during the day. The small pelagic and predatory species were caught in higher densities at night. The differences were significant for both salmonids, Pacific hake, chub mackerel, and all small pelagic species. No consistent pattern of correlation existed between the catch differences and differences in temperature or salinity between day and night samples. We believe diel patterns of fish vertical distribution and behavior coupled with the actual depths the net samples are primarily responsible for catch differences.

The vertical distribution of juvenile salmon (Oncorhynchus spp.) and associated fishes in the Columbia River plume

AbstractSimultaneous trawling at surface and at depth at one location off the Columbia River, Oregon, in June 2000 identified the depth distribution of juvenile salmonids and associated fishes. Juvenile salmon off the Columbia River were distributed primarily near the surface, within the upper 12 m. Highest densities of subyearling chinook salmon (Oncorhynchus tshawytscha) off the Columbia River were associated with high surface currents and decreasing tidal levels, with time of day possibly a co‐factor. Densities of yearling chinook salmon increased with higher turbidity. Pacific herring (Clupea pallasi) was the most abundant and commonly caught forage fish, with density increasing at night, probably related to diel vertical migration. Catches of juvenile salmonids were not associated with catches of forage fishes. Daytime surface trawling appears to be an appropriate method for assessing the distribution and abundance of juvenile salmonids in marine habitats.

Smolt-to-adult return rates of juvenile chinook salmon transported through the Snake-Columbia River hydropower system, USA, in relation to densities of co-transported juvenile steelhead

To reduce mortality associated with passage of migrating juvenile salmonids through the Snake-Columbia River Federal power system, a large percentage of smolts migrating from the Snake River basin are currently transported downstream through the hydropower system in fish-transport barges. It has recently been suggested that transportation-associated stressors may reduce the fitness of juvenile chinook salmon Oncorhynchus tshawytscha and increase mortality after seawater entry. Because the major stressor for transported juvenile chinook salmon is believed to be co-transportation with larger and more aggressive juvenile steelhead O. mykiss, we tested the hypothesis that smolt-to-adult return rates (SARs) of transported yearling chinook salmon were negatively correlated with densities of co-transported steelhead. Our analysis, using SARs and barge loading data for groups of chinook salmon transported on a daily basis in 1995, 1998, and 1999, failed to confirm a relationship between chinook salmon survival and steelhead density. These results do not preclude the possibility of an undetected inverse relationship between post-release survival of transported chinook salmon and densities of co-transported steelhead, but do suggest that if such an effect exists it is less important than other factors, such as seasonal changes in estuarine and marine productivity or predator abundance.

Pseudobranch and gill Na +, K +-ATPase activity in juvenile chinook salmon, Oncorhynchus tshawytscha: developmental changes and effects of growth hormone, cortisol and seawater transfer

The teleost pseudobranch is a gill-like structure often fused to the anterior of the opercular cavity. Pseudobranch cells are mitochondria rich and have high levels of Na +, K +-ATPase activity. In this study, pseudobranch Na +, K +-ATPase activity in juvenile chinook salmon ( Oncorhynchus tshawytscha) was compared to gill Na +, K +-ATPase activity, a known marker of parr–smolt transformation, in three experiments. In two stocks of New Zealand chinook salmon, pseudobranch Na +, K +-ATPase activity was found to significantly increase during development. At these times gill Na +, K +-ATPase activity was also elevated. Pseudobranch Na +, K +-ATPase activity did not increase 10 days after transfer from fresh water to 34 ppt seawater, a treatment that resulted in a twofold increase in gill Na +, K +-ATPase activity. Cortisol (50 μg/g) and ovine growth hormone (5 μg/g) implants had no effect on pseudobranch Na +, K +-ATPase activity in underyearling chinook salmon, while gill Na +, K +-ATPase activity was stimulated by each hormone. In yearling chinook salmon, only cortisol stimulated pseudobranch Na +, K +-ATPase activity 14 days post-implantation. It was concluded that the pseudobranch differs from the gill in terms of the regulation of Na +, K +-ATPase activity and a role during adaptation to seawater is likely to be limited.

Comparison of Migration Rate and Survival between Radio-Tagged and PIT-Tagged Migrant Yearling Chinook Salmon in the Snake and Columbia Rivers

Abstract A study was conducted to compare the travel times, detection probabilities, and survival of migrant hatchery-reared yearling chinook salmon Oncorhynchus tshawytscha tagged with either gastrically or surgically implanted sham radio tags (with an imbedded passive integrated transponder (PIT) tag) with those of their cohorts tagged only with PIT tags in the Snake and Columbia rivers. Juvenile chinook salmon with gastrically implanted radio tags migrated significantly faster than either surgically radio-tagged or PIT-tagged fish, while migration rates were similar among surgically radio-tagged and PIT-tagged fish. The probabilities of PIT tag detection at downstream dams varied by less than 5% and were not significantly different among the three groups. Survival was similar among treatments for median travel times of less than approximately 6 d (migration distance of 106 km). However, for both gastrically and surgically radio-tagged fish, survival was significantly less than for PIT-tagged fish, for ...

Relative Vulnerability to Avian Predation of Juvenile Salmonids Tagged with Passive Integrated Transponders in the Columbia River Estuary, 1998–2000

Abstract Caspian terns Sterna caspia and double-crested cormorants Phalacrocorax auritus that colonize dredge-spoil islands in the Columbia River estuary prey upon millions of juvenile Pacific salmonids annually. We estimated the relative vulnerability of various salmonid stocks to these predators by using data from passive integrated transponder (PIT) tags detected on these colonies; 96,382 tags were detected from the 1998–2000 migration years. On tern colonies, detection rates were highest for tags from steelhead Oncorhynchus mykiss and lowest for tags from yearling chinook salmon O. tshawytscha. However, detection rates on cormorant colonies were similar for tags from steelhead and coho salmon O. kisutch but lower for tags from yearling chinook salmon. Analyses based on migration history showed tags of transported fish were frequently detected in lower proportions than those of their counterparts that migrated in-river, the pattern being most pronounced in steelhead. Analyses based on origin (hatchery ...

Plasma insulin-like growth factor-I concentrations in yearling chinook salmon (Oncorhynchus tshawytscha) migrating from the Snake River Basin, USA

During the parr-to-smolt transformation (smoltification) of juvenile salmonids, preadaptive changes in osmoregulatory and ionoregulatory ability are regulated in part by the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. If food intake is sufficient, plasma IGF-I increases during smoltification. On the other hand, plasma IGF-I typically decreases in fasting fish and other vertebrate animals. Because food availability is limited for juvenile salmonids undertaking an extended 6- to 12-week springmigration to and through the Snake-Columbia River hydropower system (northwestern USA), IGF-I concentrations might be expected to decrease, potentially compromising seawater tolerance. To address this possibility,yearling chinook salmon Oncorhynchus tshawytscha reared in three Snake River Basin hatcheries were sampled before release and at two downstream dams. Dry masses ofmigrating fish either did not increase during themigration (in 2000, an average-flow year), or decreased significantly (in 2001, a low-flow year). In both years, plasma IGF-I levels were significantly higher (1.6-fold in 2000, 3.7-fold in 2001) for fish sampled at the last dam on the lower Columbia River than for fish sampled prior to release. Plasma IGF-I concentrations inmigrating fish may, nonetheless, have been nutritionally down-regulated to some degree, because plasma IGF-I concentrations in juvenile chinook salmon captured at a Snake River dam and transported to the laboratory increased in fed groups, but decreased in unfed groups. The ability ofmigrating smolts to maintain relatively elevated IGF-I levels despiteRestricted food intake and loss of body mass is likely related to smoltification-associated changes in hormonal balance.

Estimating route-specific passage and survival probabilities at a hydroelectric project from smolt radiotelemetry studies

A tag–release study is illustrated using radio-tagged chinook (Oncorhynchus tshawytscha) smolts to concurrently estimate passage rates and survival probabilities through the spillway and turbines of a hydroelectric project. The radio antennas at the forebays of the dam were arranged in double arrays allowing the estimation of route-specific detection probabilities and converting smolt detections to estimates of absolute passage. A maximum likelihood model is presented using the downstream detection histories to jointly estimate the route-specific passage and survival probabilities. In turn, these estimates were combined to estimate smolt survival through the dam, pool, and the entire hydroelectric project. The detailed migration information derived by these techniques can be used to evaluate mitigation programs focused on improving downstream passage of migrating salmonid smolts. At a mid-Columbia River hydroproject, the average spillbay survival calculated across replicate releases of hatchery and run-of-river yearling chinook salmon smolts was 1.000 ( estimated standard error, [Formula: see text] = 0.0144). Average survivals through the two different powerhouses at the hydroproject were estimated to be 0.9409 ([Formula: see text] = 0.0294) and 0.9841 ([Formula: see text] = 0.0119). Project survival after combining the route-specific survival and passage probabilities was estimated across stocks to be 0.9461 ([Formula: see text] = 0.0016).

Estimation of smolt-to-adult return percentages for Snake River Basin anadromous salmonids, 1990–1997

From numbers of juvenile salmonids (smolts) tagged between 1990 and 1997 with passive-integrated-transponder (PIT) tags and detections at downstream hydropower projects on the lower Snake and Columbia Rivers, we applied and adapted stratified tagrecapture methods to estimate the number of PIT-tagged smolts that experienced each possible detection history through the dams. Using adult detection recordsupon, return after 1–3 years of ocean residence, we estimated smolt-to-adult return (SAR) percentages for fish in detection-history categories that included downstream barge transport, migration in-river following detection, and migration in-river with no detection. We used bootstrap methods to estimate 95% confidence intervals for estimated SARs and ratios of SARs for selected detection-history categories. In general, though small numbers of returning adults and statistical uncertainty at various stages of the estimation procedure led to fairly imprecise SAR estimates, some general trends were evident. Adult return percentages for spring/summer yearling chinook salmon and steelhead were highest for fish transported from Lower Granite and Little Goose Dams but only slightly higher than for nondetected fish. Passage routes of nondetected fish (through spill and turbines) may represent optimal passage conditions. Once a juvenile fish is entrained in a bypass system ata “collectordam,” transporting the fish maximizes the probability of its eventual return as an adult.