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At least 253 records · Page 14Linked to original sources

USGS2025

Off-channel habitat use by silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) in the upper Mississippi River

The spread of invasive carp in the Mississippi River Basin of the U.S. has caused substantial ecological and economic problems. Although there are a variety of strategies to manage invasive carp, removal remains a central part of many efforts. To be most effective, large-scale removal of invasive carp should target fish when they are densely aggregated in locations with favorable conditions for deploying fishing gear. We used acoustic telemetry to track off-channel habitat use by silver carp Hypophthalmichthys molitrix and bighead carp H. nobilis in backwaters and impounded areas across three navigation pools of the upper Mississippi River to identify factors associated with high densities. Backwater areas generally had high use when temperatures were warm and river discharge was high, and impounded areas generally had high use when temperatures were cooler and discharge was lower. Models of habitat use suggest silver carp and bighead carp show predictable habitat relationships in off-channel areas that could improve removal efficiency.

Illinois, Iowa, Missouri↗

USGS2025

Evaluation of juvenile salmon behavior to inform downstream fish passage development at a high head dam

F ish passage development is a priority at Tieton Dam, on the Tieton River in Washington state, because passage options were not included when the dam was constructed nearly 100 years ago. To inform downstream passage design, we conducted a study to evaluate migration and near-dam behavior of juvenile salmon. The primary goal of the study was to determine how fish approached the dam and to identify areas where they congregated. In its current configuration, water is passed through a deep intake located approximately 548 m upstream of the dam, so there was interest in determining if juvenile salmon spent more time near the intake or at the dam. We found that tagged fish primarily entered the dam forebay offshore and arrived at the dam near the spillway on the left bank of the reservoir. Tagged fish had extended residence times in the forebay and moved repeatedly between the intake and the dam. Using thermal profile data, we inferred that juvenile salmon likely occupied the upper 5 m of the water column during May and June before moving to deeper portions of the water column (10–27 m) during July–September when the reservoir became thermally stratified. We found that a small percentage of tagged fish passed the dam when the reservoir was rapidly drawn down during August–October, but additional research may be needed to fully assess entrainment risk through the intake. These findings suggest that downstream fish passage could be developed at Tieton Dam with a high probability of success, given that most fish survived reservoir passage and spent considerable time near the dam where they would be available to discover and utilize new passage routes.

Washington↗

USGS2025

Water residence time and water depth influence on nutrient conditions, eutrophication endpoints and habitat quality in backwater lakes of a large floodplain river

Many eutrophication studies focus on the external supply of critical nutrients like nitrogen and phosphorus, but hydrology and geomorphology can enhance or dampen the effects of excessive nutrient supply. We studied six backwater lakes in the Upper Mississippi River that varied in water residence time and water depth. Eutrophication in these systems is responsible for negative impacts such as cyanobacterial blooms and toxicity, and floating plant and algal mats that disrupt recreational water uses. Increasing backwater residence time was associated with more nitrate removal and a greater likelihood of nitrogen limitation, as well as greater accumulations of duckweed. Backwaters with greater depth and lower nitrogen concentration had less likelihood of filamentous algal accumulations. The median water residence time of backwaters with low duckweed (11.7 days) and no filamentous algae (16.9 days) approached the 12-day target to maintain overwintering conditions in backwaters for fisheries survival, supporting that water residence times in this range would likely improve both winter and summer water quality. Mean depth in backwaters with low duckweed and no filamentous algae was ~1.3 m, while shallower backwaters were more likely to produce duckweed and filamentous algae mats. This indicates that deeper backwaters might reduce the likelihood of eutrophication impacts. Natural resource management at the local level may not always be able to answer global and regional threats, but habitat restoration of hydrology and geomorphology can possibly alleviate or reduce large-scale threats at the local level.

Minnesota, Wisconsin↗

USGS2025

Long‐term effects of low‐drop grade control structures on channel evolution in the Yazoo River Basin

Channel incision is a widespread problem, especially in river basins that have an extensive history of channel alterations. Because channel incision causes large ecological and economic consequences, the prevention of continued migration of headcuts, defined as a steep change in stream gradient over a short reach, has been the focus of many stream engineering projects. Low-drop grade control structures (GCS) are a type of structure installed to halt the upstream movement of a headcut and were widely installed in the rivers and streams of the Yazoo River Basin in northern Mississippi. The goal of this study was to evaluate the long-term effects of these structures 30+ years post installation. To assess GCS effects on channel morphology, stream cross-section surveys were used to calculate Bank Height Ratio, Width-to-Depth Ratio, and Entrenchment Ratio, while point estimates made along each transect were used to calculate the average sediment size distribution for each of 30 sites. Analyses revealed that the GCS were successful in checking channel incision moving headward in the streams: sites upstream of the GCS were less incised and had greater accumulations of fine substrates compared to sites downstream and sites on streams lacking erosion control structures. Given the widespread use of GCS, these results can inform efforts aimed at managing channel incision.

Mississippi↗

USGS2025

Big River bluegill: Combining vital rates and long-term monitoring to understand population dynamics in large rivers

Long-term monitoring indicates bluegill catch rates are relatively stable in some reaches of the Upper Mississippi River and highly variable in others, whereas in the Illinois River, catch rates have decreased. A lack of age structure information precludes understanding population processes responsible for patterns in catch rates. To build a better understanding of why catch rates have changed over time, we integrated short-term age structure information with long-term monitoring data to quantify and assess spatial patterns in bluegill population dynamics across six study reaches of these two rivers. Specifically, we estimated and compared age and size structure, growth, maturity, mortality, and recruitment. We used quantile regressions to apply age estimates to long-term data for investigating trends in age-based catch rates reflective of recruitment (age-1 catch rates), mortality (using age-1 and age-2+ catch rates), and spawning stock (age-2+). Our findings indicate trends in bluegill age-2+ catch rates increased and then stabilized across upstream study reaches, but dynamic rates, size structure, and age at maturity varied among reaches. Bluegill populations in downstream study reaches had low maximum size, early maturation, low mean age, low proportional stock density, declining recruitment, and declining age-2+ catch rates. An insufficient number of bluegills were collected from the study reach furthest downstream to adequately quantify dynamic rates. Our results support life history theory in that bluegill respond to unstable environmental conditions through life history adaptations. These findings show how integrating periodic age structure information with long-term monitoring can enhance population assessments.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗

USGS2026

A tool for prioritizing gravel augmentation reaches for sediment starved rivers

Gravel augmentation is a widely used restoration technique used to improve habitat below dams, including salmonids spawning habitat. However, gravel augmentation can be cost-prohibitive, and it is often unclear which stream segments have the highest potential to benefit spawning salmonids. A tool to help prioritize reaches for gravel restoration could aid managers in making good decisions. To address this need, we convened a group of fishery managers to create Intrinsic Potential (IP) habitat models. We used stream attributes related to salmonid spawning habitat: elevation, width, and gradient from the synthetic stream channel dataset NetMap. We then used the IP models to develop an easy-to-use and flexible tool for identifying high spring-run Chinook Salmon ( Oncorhynchus tshawytscha ) IP along ~100 m reaches based on a conceptual model developed by the fishery managers. The tool allows for the inclusion of winter steelhead ( O. mykiss ) IP spawning habitat and allows users to incorporate mean August stream temperature maxima under recent conditions and projected under future climate change, land ownership (public or private or both), reach access distance, distance to and type of gravel sources, and relative gravel movement potential. We explore the prioritization tool with three demonstration strategies for the Upper Rogue River basin, Oregon, USA: (1) Spring Chinook Salmon Strategy, (2) Co-occurrence with winter steelhead Strategy, and (3) Climate Change Strategy. Our analysis demonstrates that altering management priorities directly influences which stream reaches are identified for gravel augmentation. In the three strategies we compared, a small number of current conservation reaches located downstream of spring Chinook Salmon spawning were identified using the tool. In addition, we identified a small number of reaches with no conservation strategy for winter steelhead spawning that meet prioritization criteria. Furthermore, under a climate change scenario, we highlight how new gravel source permitting could expand the set of viable augmentation reaches. The tool is publicly available on GitHub.

Oregon↗

USGS2026

Development and assessment of fluorescent-dyed, preserved invasive grass carp (Ctenopharyngodon idella) eggs as surrogates for live eggs in transport and dispersal control experiments

Invasive species such as grass carp ( Ctenopharyngodon idella ) pose substantial ecological threats to North American freshwater ecosystems. Understanding their early life stage behavior is critical for management efforts. From spawning to hatching, invasive carp eggs must remain suspended in the water column while drifting downstream for the best chance of survival. This highly vulnerable life stage is a potential target for population control to reduce recruitment. However, studying egg transport and potential dispersal control techniques is challenging, because the availability of live eggs and time period for experimentation are extremely limited. Additionally, accurately replicating the physical characteristics and transport mechanisms of fish eggs using surrogates in laboratory and field studies is not trivial. This study presents a novel method to create fluorescein-dyed, preserved grass carp eggs as surrogates for live eggs in transport and dispersal control experiments. This technique enables year-round studies of grass carp egg transport, offering managers a reliable tool for developing and testing dispersal control and passive sampling methods for invasive carp eggs. In this study, we rehydrate and dye preserved grass carp eggs in varying concentrations of aqueous fluorescein for a range of rehydration times, evaluate dye retention and egg visibility under ultraviolet light (UV-A), and measure diameters and settling velocities for comparison with live eggs. Eggs rehydrated in 0.100 g per liter fluorescein for 30 min maintain adequate brightness for up to 40 min in mixed conditions and exhibit mean settling velocities and densities similar to live eggs, making them ideal for laboratory experiments using quantitative imaging techniques.

River Research and Applications↗

USGS2026

Population dynamics of Northern Pearl Dace Margariscus nachtriebi in anthropogenically altered headwater streams of the Nebraska Sandhills Ecoregion

Empirical evidence of population demographic responses to environmental perturbations is a major knowledge gap for aquatic vertebrate populations. Extensive habitat alteration including channelization of headwater streams influences the habitat template on which small-bodied fish are dependent to carry out distinct life stages and maintain or increase population growth. The objectives of this study were to (1) determine differences in geomorphic characteristics, and instream habitat (i.e., mesohabitat availability, water depth, and macrophyte coverage) in channelized and unchannelized stream sites, and (2) estimate survival of Northern Pearl Dace Margariscus nachtriebi in channelized and unchannelized stream sites. A capture-mark-recapture robust design study was conducted where a total of 1994 Northern Pearl Dace were double tagged and 853 were recaptured over the 374-day field study. Geomorphic characteristics and instream habitat in channelized and unchannelized stream sites differed (Pillai's Trace = 0.950, F (8, 6) = 14.228, p = 0.002). Specifically, mean sinuosity index ( F (1, 13) = 20.723, p = 0.0005) and the percentage of pool mesohabitat ( F (1, 13) = 4.929, p = 0.045) were both reduced in channelized versus unchannelized stream sites. Northern Pearl Dace seasonal survival was lower in channelized sites (Ŝ Spring to Summer = 0.34; SE = 0.06) compared to unchannelized sites (Ŝ Spring to Summer = 0.93; SE = 0.03) during spring to summer. Annual survival differed between channelized sites (Ŝ = 0.001; SE = 0.009) and unchannelized sites (Ŝ = 0.047; SE = 0.024). Channelization in headwater streams influenced population demographic parameters of stream fish. Northern Pearl Dace exhibited reduced survival in channelized sections of headwater streams flowing through the largest intact grassland ecosystem in North America. Mitigating channelization in streams may benefit persistence of native prairie fishes by increasing survival and subsequently aid in the restoration of headwater streams that flow through grassland ecosystems in North America.

Nebraska↗

USGS2026

Non-physical barrier design and environmental conditions alter routing and survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento-San Joaquin River Delta

Pacific salmon face substantial challenges when migrating through anthropogenically modified river systems, such as the Sacramento-San Joaquin River Delta (the Delta). Non-physical behavioral barriers, such as the bioacoustic fish fence (BAFF), are one potential solution for guiding fish away from hazards without obstructing water flow. However, the effectiveness of these technologies depends on abiotic and biotic conditions. In the Delta, a BAFF was deployed at Georgiana Slough in 2011, 2012, and 2024 to deter juvenile Chinook salmon ( Oncorhynchus tshawytscha ) from migrating into the interior Delta, a region associated with lower survival than the mainstem Sacramento River. We leveraged nine years of acoustic telemetry data to evaluate BAFF performance across flow conditions and two BAFF designs (2011/2012 vs. 2024), and to assess the BAFF's contribution to improving through-Delta survival. The BAFF reduced routing into Georgiana Slough from 26.5% without a barrier to 8.9% in 2011/2012 and 15.9% in 2024. In general, routing into Georgiana Slough increased with the proportion of flow entering the channel during periods without a BAFF and during the 2024 deployment but remained constant during the 2011/2012 deployment. Additionally, BAFF effectiveness declined with increasing input flow. Ultimately, reduced routing into Georgiana Slough during the 2024 BAFF deployment resulted in an increase in estimated through-Delta survival between 0.2 and 1.6 percentage points depending on release group. Our results provide valuable insights into the role of non-physical barriers in complex river systems and inform future management strategies for protecting migrating juvenile Chinook salmon in the Sacramento-San Joaquin River Delta.

California↗

USGS2026

How tough a passage? Nonnative fish entrainment survivability at a major dam in the western USA

The Colorado River downstream of Glen Canyon Dam (GCD) in the southwest USA demonstrates anthropogenic modification including altered flow and temperature regimes and established nonnative species in upstream reservoirs. Water overallocation and megadrought are contributing to new potential invasion pathways for nonnative fishes through dam releases. In this study, we quantified factors that influence survival of fish entrained at GCD, a pathway for nonnative fishes to leave Lake Powell and enter the Grand Canyon as reservoir levels remain near historic lows since the reservoir initially filled. We measured conditions of entrainment through GCD using a mechanical Sensor Fish device and evaluated potential barotrauma by comparing our results to previous studies. Under measured conditions, a fish's gas bladder would expand by a factor of 2.7 due to entrainment, potentially resulting in injury from barotrauma. We estimated members of Centrarchidae may survive entrainment at problematically high rates across all water levels where entrainment is expected. Minimizing nonnative fish entrainment through GCD is best achieved through maintenance of water levels higher than those in recent years, potentially decreasing both entrainment likelihood and survival.

Arizona↗

USGS2004

Modelling effects of discharge on habitat quality and dispersal of juvenile humpback chub (Gila cypha) in the Colorado River, Grand Canyon

A two-dimensional hydrodynamic model was applied to seven study reaches in the Colorado River within Grand Canyon to examine how operation of Glen Canyon Dam has affected availability of suitable shoreline habitat and dispersal of juvenile humpback chub (Gila cypha). Suitable shoreline habitat typically declined with increasing discharges above 226-425 m3/s, although the response varied among modelled reaches and was strongly dependent on local morphology. The area of suitable shoreline habitat over cover types that are preferred by juvenile humpback chub, however, stayed constant, and in some reaches, actually increased with discharge. In general, changes in discharge caused by impoundment tended to decrease availability of suitable shoreline habitat from September to February, but increased habitat availability in spring (May-June). Hourly variation in discharge from Glen Canyon Dam substantially reduced the amount of persistent shoreline habitat at all reaches. Changes in suitable shoreline habitat with discharge were shown to potentially bias historical catch per unit effort indices of native fish abundance up to fourfold. Physical retention of randomly placed particles simulating the movement of juvenile humpback chub in the study reaches tended to decline with increasing discharge, but the pattern varied considerably due to differences in the local morphology among reaches and the type of swimming behaviour modelled. Implications of these results to current hypotheses about the effects of Glen Canyon Dam on juvenile humpback chub survival in the mainstern Colorado River are discussed. ?? 2004 John Wiley and Sons, Ltd.

River Research and Applications↗

USGS2004

Challenging the assumption of habitat limitation: An example from centrarchid fishes over an intermediate spatial scale

Habitat rehabilitation efforts are predicated on the frequently untested assumption that habitat is limiting to populations. These efforts are typically costly and will be ineffective if habitat is not limiting. Therefore it is important to assess, rather than assume, habitat limitation wherever habitat rehabilitation projects are considered. Catch-count data from a standardized probability-based stratified-random monitoring programme were examined for indirect evidence of backwater habitat limitation by centrarchid fishes in the Upper Mississippi River System. The monitoring design enabled fitting statistical models of the association between mean catch at the spatial scale of tens of river kilometres and the percentage of contiguous aquatic area in backwater at least 1 m deep by maximizing a stratum-area weighted negative binomial log-likelihood function. Statistical models containing effects for backwater limitation failed to account for substantial variation in the data. However, 95% confidence intervals on the backwater parameter estimates excluded zero, indicating that population abundance may be limited by backwater prevalence where backwaters are extremely scarce. The combined results indicate, at most, a weak signal of backwater limitation where backwaters are extremely scarce in the lower reaches, but not elsewhere in the Upper Mississippi River System. This suggests that habitat restoration projects designed to increase the area of backwaters suitable for winter survival of centrarchids are unlikely to produce measurable benefits over intermediate spatial scales in much of the Upper Mississippi River System, and indicates the importance of correct identification of limiting processes. Published in 2004 by John Wiley and Sons, Ltd.

River Research and Applications↗

USGS2005

Flow regime alterations under changing climate in two river basins: Implications for freshwater ecosystems

We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee-Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river-floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee-Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee-Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability of the river to assimilate wastewater treatment plant effluent. Our study illustrates the types of changes that river ecosystems might experience under future climates. Copyright ?? 2005 John Wiley & Sons, Ltd.

River Research and Applications↗

USGS2005

Effects of stream flow intermittency on riparian vegetation of a semiarid region river (San Pedro River, Arizona)

The San Pedro River in the southwestern United States retains a natural flood regime and has several reaches with perennial stream flow and shallow ground water. However, much of the river flows intermittently. Urbanization-linked declines in regional ground-water levels have raised concerns over the future status of the riverine ecosystem in some parts of the river, while restoration-linked decreases in agricultural ground-water pumping are expected to increase stream flows in other parts. This study describes the response of the streamside herbaceous vegetation to changes in stream flow permanence. During the early summer dry season, streamside herbaceous cover and species richness declined continuously across spatial gradients of flow permanence, and composition shifted from hydric to mesic species at sites with more intermittent flow. Hydrologic threshold values were evident for one plant functional group: Schoenoplectus acutus, Juncus torreyi, and other hydric riparian plants declined sharply in cover with loss of perennial stream flow. In contrast, cover of mesic riparian perennials (including Cynodon dactylon, an introduced species) increased at sites with intermittent flow. Patterns of hydric and mesic riparian annuals varied by season: in the early summer dry season their cover declined continuously as flow became more intermittent, while in the late summer wet season their cover increased as the flow became more intermittent. Periodic drought at the intermittent sites may increase opportunities for establishment of these annuals during the monsoonal flood season. During the late summer flood season, stream flow was present at most sites, and fewer vegetation traits were correlated with flow permanence; cover and richness were correlated with other environmental factors including site elevation and substrate nitrate level and particle size. Although perennial-flow and intermittent-flow sites support different streamside plant communities, all of the plant functional groups are abundant at perennial-flow sites when viewing the ecosystem at broader spatial and temporal scales: mesic riparian perennials are common in the floodplain zone adjacent to the river channel and late-summer hydric and mesic annuals are periodically abundant after large floods. Copyright ?? 2005 John Wiley & Sons, Ltd.

River Research and Applications↗

USGS2006

Restoration and colonization of freshwater mussels and fish in a southeastern United States tailwater

The French Broad River originates in North Carolina, flows west into Tennessee and at its confluence with the Holston River forms the Tennessee River. Douglas Dam, located on the French Broad River 52 km above its mouth, is operated primarily for peaking hydroelectric power and flood control. Prior to completion of the dam in 1943, the lower French Broad River contained about 53 species of freshwater mussels and 100 species of fish. By 1977, the fauna in the 52-km-long tailwater was reduced to 12 species of mussels and 42 native species of fish. Improvements in tailwater conditions occurred following initiation of minimum flows in 1987, and consistent reaeration of discharge in 1993. From 1988 to 2002, we sampled three sites (4, 28, and 39 km downstream of the dam) to monitor the fish assemblage. Each year since 1988, we have collected one or more additional species, indicating continued immigration. We collected 82 native and 9 exotic species of fish overall, but the maximum of 67 species in 1 year suggests that some species reside in the tailwater at low densities or all immigrants may not successfully colonize the tailwater. There is limited potential for most extirpated species of mussels to naturally recolonize the tailwater because source populations are isolated. Consequently, 19 754 adult mussels of 19 species were introduced between 1997 and 2000. Survival of translocated mussels has been high, and successful reproduction of at least one translocated species has occurred. Additionally, four mussel species are naturally colonizing the tailwater. Colonization and recruitment of additional mussel species is expected as populations of their host fishes increase. We believe that the improved conditions of the tailwater may allow for the re-establishment of sustaining populations of 30 mussel species of historic occurrence, but the continued operation of Douglas Dam as a peaking hydroelectric project will reduce the probability of successfully reintroducing some species.

River Research and Applications↗

USGS2006

Nitrogen dynamics in sediment during water level manipulation on the Upper Mississippi River

Nitrogen (N) has been linked to increasing eutrophication in the Gulf of Mexico and as a result there is increased interest in managing and improving water quality in the Mississippi River system. Water level reductions, or 'drawdowns', are being used more frequently in large river impoundments to improve vegetation growth and sediment compaction. We selected two areas of the Upper Mississippi River system (Navigation Pool 8 and Swan Lake) to examine the effects of water level drawdown on N dynamics. Navigation Pool 8 experienced summer drawdowns in 2001 and 2002. Certain areas of Swan Lake have been drawn down annually since the early 1970s where as other areas have remained inundated. In the 2002 Pool 8 study we determined the effects of sediment drying and rewetting resulting from water level drawdown on (1) patterns of sediment nitrification and denitrification and (2) concentrations of sediment and surface water total N (TN), nitrate, and ammonium (NH 4 + ). In 2001, we only examined sediment NH 4 + and TN. In the Swan Lake study, we determined the long-term effects of water level drawdowns on concentrations of sediment NH 4 + and TN in sediments that dried annually and those that remained inundated. Sediment NH 4 + decreased significantly in the Pool 8 studies during periods of desiccation, although there were no consistent trends in nitrification and denitrification or a reduction in total sediment N. Ammonium in sediments that have dried annually in Swan Lake appeared lower but was not significantly different from sediments that remain wet. The reduction in sediment NH 4 + in parts of Pool 8 was likely a result of increased plant growth and N assimilation, which is then redeposited back to the sediment surface upon plant senescence. Similarly, the Swan Lake study suggested that drawdowns do not result in long term reduction in sediment N. Water level drawdowns may actually reduce water retention time and river-floodplain connectivity, while promoting significant accumulation of organic N. These results indicate that water level drawdowns are probably not an effective means of removing N from the Upper Mississippi River system.

Upper Mississippi River↗

USGS2006

Ecology of an estuarine mysid shrimp in the Columbia River (USA)

The estuarine mysid, Neomysis mercedis, has colonized John Day and other run-of-the-river Reservoirs of the Columbia River, over 400 km from the estuary. In John Day Reservoir N. mercedis numbers peaked (2 m-3) in August in areas near the dam in association with lower water velocity and softer bottom than at the upstream sampling sites. Neomysis broods were primarily released in late spring and early fall. Gut content analysis showed that Neomysis feeds mostly on cladoceran zooplankton and rotifers in John Day Reservoir. Diel vertical migration was documented, with daytime distribution restricted to the bottom and preferentially to the soft-textured sediments in the deepest areas. Common pelagic fishes in the reservoir, especially juvenile American shad (Alosa sapidissima) and chinook salmon (Oncorhynchus tshawytscha), are daytime zooplankton feeders that cannot prey on Neomysis owing to mysid diel vertical migration. Thus, Neomysis has become an important food web component in John Day Reservoir. We also collected N. mercedis further upstream in Lower Granite Reservoir, where another estuarine crustacean, Corophium salmonis, also is reported, underscoring the need to better understand the role of these estuarine invertebrates in the trophic ecology of the Columbia River. Copyright ?? 2006 John Wiley & Sons, Ltd.

Oregon, Washington↗

USGS2006

Evaluation of energy expenditure in adult spring Chinook salmon migrating upstream in the Columbia River Basin: an assessment based on sequential proximate analysis

The upstream migration of adult anadromous salmonids in the Columbia River Basin (CRB) has been dramatically altered and fish may be experiencing energetically costly delays at dams. To explore this notion, we estimated the energetic costs of migration and reproduction of Yakima River-bound spring Chinook salmon Oncorhynchus tshawytscha using a sequential analysis of their proximate composition (i.e., percent water, fat, protein, and ash). Tissues (muscle, viscera, and gonad) were sampled from fish near the start of their migration (Bonneville Dam), at a mid point (Roza Dam, 510 km upstream from Bonneville Dam) and from fresh carcasses on the spawning grounds (about 100 km above Roza Dam). At Bonneville Dam, the energy reserves of these fish were remarkably high, primarily due to the high percentage of fat in the muscle (18-20%; energy content over 11 kJ g-1). The median travel time for fish from Bonneville to Roza Dam was 27 d and ranged from 18 to 42 d. Fish lost from 6 to 17% of their energy density in muscle, depending on travel time. On average, fish taking a relatively long time for migration between dams used from 5 to 8% more energy from the muscle than faster fish. From the time they passed Bonneville Dam to death, these fish, depending on gender, used 95-99% of their muscle and 73-86% of their viscera lipid stores. Also, both sexes used about 32% of their muscular and very little of their visceral protein stores. However, we were unable to relate energy use and reproductive success to migration history. Our results suggest a possible influence of the CRB hydroelectric system on adult salmonid energetics.

Oregon, Washginton↗