AN EVALUATION OF THE RELATIVE QUALITY OF DIKE POOLS FOR BENTHIC MACROINVERTEBRATES IN THE LOWER MISSOURI RIVER,USA

A habitat‐based aquatic macroinvertebrate study was initiated in the Lower Missouri River to evaluate relative quality and biological condition of dike pool habitats. Water‐quality and sediment‐quality parameters and macroinvertebrate assemblage structure were measured from depositional substrates at 18 sites. Sediment porewater was analysed for ammonia, sulphide, pH and oxidation–reduction potential. Whole sediments were analysed for particle‐size distribution, organic carbon and contaminants. Field water‐quality parameters were measured at subsurface and at the sediment–water interface. Pool area adjacent and downstream from each dike was estimated from aerial photography. Macroinvertebrate biotic condition scores were determined by integrating the following indicator response metrics: % of Ephemeroptera (mayflies), % of Oligochaeta worms, Shannon Diversity Index and total taxa richness. Regression models were developed for predicting macroinvertebrate scores based on individual water‐quality and sediment‐quality variables and a water/sediment‐quality score that integrated all variables. Macroinvertebrate scores generated significant determination coefficients with dike pool area (R² = 0.56), oxidation–reduction potential (R² = 0.81) and water/sediment‐quality score (R² = 0.71). Dissolved oxygen saturation, oxidation–reduction potential and total ammonia in sediment porewater were most important in explaining variation in macroinvertebrate scores. The best two‐variable regression models included dike pool size + the water/sediment‐quality score (R² = 0.84) and dike pool size + oxidation–reduction potential (R² = 0.93). Results indicate that dike pool size and chemistry of sediments and overlying water can be used to evaluate dike pool quality and identify environmental conditions necessary for optimizing diversity and productivity of important aquatic macroinvertebrates. A combination of these variables could be utilized for measuring the success of habitat enhancement activities currently being implemented in this system. Published in 2011 by John Wiley & Sons, Ltd.     

FISH ASSEMBLAGES AT ENGINEERED AND NATURAL CHANNEL STRUCTURES IN THE LOWER MISSOURI RIVER: IMPLICATIONS FOR MODIFIED DIKE STRUCTURES

Large rivers throughout the world have been modified by using dike structures to divert water flows to deepwater habitats to maintain navigation channels. These modifications have been implicated in the decline in habitat diversity and native fishes. However, dike structures have been modified in the Missouri River USA to increase habitat diversity to aid in the recovery of native fishes. We compared species occupancy and fish community composition at natural sandbars and at notched and un‐notched rock dikes along the lower Missouri River to determine if notching dikes increases species diversity or occupancy of native fishes. Fish were collected using gill nets, trammel nets, otter trawls, and mini fyke nets throughout the lower 1212 river km of the Missouri River USA from 2003 to 2006. Few differences in species richness and diversity were evident among engineered dike structures and natural sandbars. Notching a dike structure had no effect on proportional abundance of fluvial dependents, fluvial specialists, and macrohabitat generalists. Occupancy at notched dikes increased for two species but did not differ for 17 other species (81%). Our results suggest that dike structures may provide suitable habitats for fluvial species compared with channel sand bars, but dike notching did not increase abundance or occupancy of most Missouri River fishes. Published in 2011 by John Wiley & Sons, Ltd.     

DISTRIBUTION AND HABITAT USE OF THE MISSOURI RIVER AND LOWER YELLOWSTONE RIVER BENTHIC FISHES FROM 1996 TO 1998: A BASELINE FOR FISH COMMUNITY RECOVERY

Past and present Missouri River management practices have resulted in native fishes being identified as in jeopardy. In 1995, the Missouri River Benthic Fishes Study was initiated to provide improved information on Missouri River fish populations and how alterations might affect them. The study produced a baseline against which to evaluate future changes in Missouri River operating criteria. The objective was to evaluate population structure and habitat use of benthic fishes along the entire mainstem Missouri River, exclusive of reservoirs. Here we use the data from this study to provide a recent‐past baseline for on‐going Missouri River fish population monitoring programmes along with a more powerful method for analysing data containing large percentages of zero values. This is carried out by describing the distribution and habitat use of 21 species of Missouri River benthic fishes based on catch‐per‐unit area data from multiple gears. We employ a Bayesian zero‐inflated Poisson model expanded to include continuous measures of habitat quality (i.e. substrate composition, depth, velocity, temperature, turbidity and conductivity). Along with presenting the method, we provide a relatively complete picture of the Missouri River benthic fish community and the relationship between their relative population numbers and habitat conditions. We demonstrate that our single model provides all the information that is often obtained by a myriad of analytical techniques. An important advantage of the present approach is reliable inference for patterns of relative abundance using multiple gears without using gear efficiencies. Copyright © 2011 John Wiley & Sons, Ltd.     

赣江中游洪水防御对策与措施

综合分析了赣江中游的防洪现状和存在的主要问题,提出了赣江中游洪水的防御对策和措施．     

LONG‐TERM COTTONWOOD FOREST DYNAMICS ALONG THE UPPER MISSOURI RIVER,USA

The upper Missouri River bottomland in north‐central Montana, USA, retains much of the physical character it had when traversed by Lewis and Clark around 1805. We used geospatial data to quantify long‐term changes in the distribution of bottomland vegetation, land use patterns and channel planform for a 257‐rkm segment of the Missouri River above Fort Peck Reservoir. This segment is less ecologically altered than downstream segments, but two dams completed in the mid‐1950s have decreased the frequency and magnitude of floods. The area of forest is sparse because of geomorphic setting but, contrary to public perception, has remained relatively constant during the past century. However, the stability of forest area obscures its spatial and temporal dynamics. We used state and transition models to quantify fates and sources of forest during two periods: 1890s–1950s and 1950s–2006. Total forest area was 6% greater in 2006 than it was in the 1890s, largely due to reduced forest loss to erosional processes and gains related to progressive channel narrowing. Channel narrowing resulted in part from human‐caused peak flow attenuation. A modified transition matrix, used to examine future steady‐state conditions, projected little change in forest area; however, these projections are likely an overestimate. The extent to which 2006 forest area represents a transient adjustment to a new flow regime versus a dynamic, quasi–steady state will be determined by the long‐term interplay among hydrologic factors, channel processes, water management and land use practices. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

EMERGENT SANDBAR CONSTRUCTION FOR LEAST TERNS ON THE MISSOURI RIVER: EFFECTS ON FORAGE FISHES IN SHALLOW‐WATER HABITATS

Emergent sandbars on the Missouri River are actively managed for two listed bird species, piping plovers and interior least terns. As a plunge‐diving piscivore, endangered least terns rely on ready access to appropriately sized slender‐bodied fish: <52 mm total length for adults and <34 mm total length for young chicks. As part of a multi‐agency recovery programme, aimed at enhancing nesting habitat for plovers and terns, the U.S. Army Corps of Engineers mechanically created several emergent sandbars on the Missouri River. However, it was unknown whether sandbar construction is a benefit or a detriment to forage abundance for least terns. Therefore, we studied the shallow‐water (<1.5 m) fish community near river and mechanically created emergent sandbars during three nesting seasons (2006–2008). We sampled every 2 weeks each year from late May to July within 15–16 areas to document the relative abundance, species richness and size classes of fish. Fish relative abundance was negatively related to depth. Catches were dominated by schooling species, including emerald shiner, sand shiner, spotfin shiner and bigmouth buffalo. Significant inter‐annual differences in relative abundance were observed, with generally increasing trends in intra‐seasonal relative abundance of shiners and the smallest size classes of fish (<34 mm). Significant differences in the fish communities between the sandbar types were not detected in this study. Results suggest that mechanical sandbar habitats host comparable fish communities at similar levels of relative abundance. Further analyses are required to evaluate if the levels of fish relative abundance are adequate to support least tern foraging and reproduction. Published in 2011 by John Wiley & Sons, Ltd.     

SIZE‐FRACTIONATED PHYTOPLANKTON GROWTH AND MICROZOOPLANKTON GRAZING RATES IN THE UPPER ST. LAWRENCE RIVER

Chlorophyll‐a‐specific growth and grazing rates of phytoplankton in three size fractions (0.2 to 2 µm, 2 to 20 µm, and 20 to 153 µm) were determined using dilution assays (n = 38) that were conducted from May to December 2009 in the St. Lawrence River (discharge approx. 7135 m³ s^?1) from its headwaters at Lake Ontario to 180 km downstream. There was no discernible difference in phytoplankton growth or grazing rates as a function of river reach sampled. At water temperatures below 20°C specific rates of growth and grazing were closely matched (0.43 day^?1), suggesting tight coupling of phytoplankton grazing in the water column. However, specific phytoplankton growth rates exceeded specific grazing rates by 0.29 day^?1 when river water temperature exceeded 20°C. Nevertheless, the greater specific growth rate did not manifest in greater phytoplankton biomass with transit downstream suggesting the importance of grazer organisms on benthic surfaces that graze phytoplankton in this reach of a large river. Copyright © 2011 John Wiley & Sons, Ltd.     

WATER QUALITY DURING TWO HIGH‐FLOW YEARS ON THE LOWER MISSOURI RIVER: THE EFFECTS OF RESERVOIR AND TRIBUTARY CONTRIBUTIONS

Complex socioeconomic and ecological issues, ranging from impaired streams to Gulf of Mexico hypoxia, have made nutrient management an increasingly important issue across the USA. High flows during 2010 and 2011 provided a unique opportunity to investigate trends in discharge, total nitrogen, nitrate/nitrite, total phosphorus, ortho‐phosphorus, suspended sediment and total suspended solids during two distinct high‐flow years on the Missouri River. We compared collections taken during 2010 and 2011 at 12 lower Missouri River locations (river kilometers 1212 to 71) and 22 Missouri River tributary locations. During 2011, average concentrations for all sampled parameters were significantly lower, despite significantly higher total discharge, than 2010 concentrations. Differences in water chemistry between years are likely attributed to the primary source of water. Tributary inflow created high flows during 2010, whereas record releases from Gavins Point Dam created high flows during 2011. Analysis of flow estimated the contribution of these releases at each site and revealed strong positive relationships between the percentage of estimated tributary flow at each site and the concentrations of total nitrogen, total phosphorus and total suspended solids. These monitoring efforts underline the contrasting impacts that tributary streams and reservoir releases have on nutrient export of the Missouri River during high‐flow events and reveal a larger trend of increased nutrient concentrations as the proportion of Missouri River tributary flow increased. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. River Research and Applications published by John Wiley & Sons, Ltd.     

EROSION OF RIVER SANDBARS BY DIURNAL STAGE FLUCTUATIONS IN THE COLORADO RIVER IN THE MARBLE AND GRAND CANYONS: FULL‐SCALE LABORATORY EXPERIMENTS

This research examines the mass failure and seepage erosion of sandbars due to rapid fluctuations in river stage using a full‐scale laboratory model. Hydroelectric dams operated to provide electricity at peak demand produce rapid river stage fluctuations. During decreasing river stage, the groundwater table becomes higher than the river stage, increasing pore water pressures and exfiltrating groundwater. This can cause seepage erosion and mass failures in the banks and bars. In the Colorado River in the Marble and Grand Canyons, maximal downramp and upramp rates have been imposed on the Glen Canyon Dam operations. Our experiments research the efficacy of these discharge ramp rate restrictions to reduce sandbar erosion. The laboratory model consists of a two‐dimensional sandbar face (8 m long, 2.5 m high and 0.5 m wide). Multiple experiments were conducted in a range of slopes, varying from 12° to 26°. An analysis of historical and current ramp rates at 47 locations along the river provided the basis of laboratory downramp rates in the range from 0.1 to 0.6 m h^?1. Results show that bank stability is reached at a slope of approximately 14°. The erosion of intermediate slopes (18° – 22°) is controlled by seepage erosion, whereas the erosion of steep slopes (26°) is governed by mass failures. Erosion rates per diurnal cycle do not depend on ramp rates, but they increase with sandbar steepness. Therefore, steep sandbar faces would rapidly erode by mass failure and seepage erosion to shallower stable slopes in the absence of other erosion processes, regardless of dam discharge ramp rates. Our experiments only address seepage erosion and mass failure; increasing the daily magnitude and/or duration of peak discharge may increase the erosion of bars by turbulent sediment transport. Copyright © 2012 John Wiley & Sons, Ltd.     

EFFECTS OF FLOW DYNAMICS ON THE AQUATIC‐TERRESTRIAL TRANSITION ZONE (ATTZ) OF LOWER MISSOURI RIVER SANDBARS WITH IMPLICATIONS FOR SELECTED BIOTA

Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar‐specific models of discharge‐area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing‐dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota. Published in 2011 by John Wiley & Sons, Ltd.     

HISTORIC CHANGES (1941–2008) IN SIDE CHANNEL AND BACKWATER HABITATS ON AN UNCHANNELIZED REACH OF THE MISSOURI RIVER

Flow regulation has had pervasive effects on aquatic ecosystems within the world's large rivers. While channelization on the lower Missouri River has led to major changes in the river and its floodplain, including the loss of shallow water habitats, effects of upstream dams on unchannelized reaches on the Missouri have not been formally assessed. We quantified changes in the number and size of off‐channel habitats, specifically backwaters and side channels, on the 95‐km unchannelized reach of the Missouri below Gavins Point Dam (Yankton, South Dakota) using historical (1941, 1983–1985, 2008) aerial imagery. Total and mean areas of side channels declined by 77% and 37% and total and mean length decreased by 79% and 42% from 1941 to 2008. Total area of backwaters increased by 40% from 1941 to 2008, whereas mean area decreased by 36%. Our findings suggest that sharp declines in the area and length of side channels have occurred on this unchannelized remnant reach of the Missouri River, with likely significant impacts on aquatic ecosystem processes. Copyright © 2011 John Wiley & Sons, Ltd.     

PATTERNS OF ICHTHYOFAUNAL DISTRIBUTION AND CONNECTIVITY IN NAVIGABLE AND FREE‐FLOWING REACHES OF A MAJOR RIVER SYSTEM: THE ALLEGHENY RIVER IN PENNSYLVANIA

Connectivity throughout large riverine networks is often compromised by lock and dam (L/D) structures designed to facilitate year‐round navigation. The resultant interruption of flow inhibits free passage of aquatic biota potentially isolating mainstem and tributary communities. Our objectives were (i) to evaluate the impact of a series of navigational L/D structures on two targeted fish assemblages (TFAs): large‐bodied (>250 mm total length) pelagic and benthic (darter) communities and (ii) to examine patterns of tributary and mainstem connectivity. We systematically captured fishes utilizing gillnets, benthic trawls and backpack electrofishers from an impounded and a free‐flowing reach extending over 203 km of the Allegheny River in Pennsylvania. Species richness among the large‐bodied targeted fish assemblage was distributed somewhat evenly throughout each pool, peaking near dams and in an undredged pool. Depauperate darter assemblages of low species richness characterized most of the navigable reach with diversity and abundance concentrated in L/D tailrace areas. By contrast, darter communities inhabiting the free‐flowing reach were more diverse, abundant and evenly distributed, indicating the influence of uninterrupted connectivity. Community similarity at mainstem/tributary junctions increased with increasing tributary size with 50% of the mainstem species complement also inhabiting the largest tributary. This study underscores the importance of dams as barriers to ichthyofaunal connectivity, particularly to those benthic fishes which are relatively immobile and habitat specific, and the importance of mainstem/tributary junctions as avenues of riverine connectivity. Copyright © 2013 John Wiley & Sons, Ltd.     

DYNAMICS OF IN‐STREAM WOOD AND ITS IMPORTANCE AS FISH HABITAT IN A LARGE TROPICAL FLOODPLAIN RIVER

The recruitment of wood from the riparian zone to rivers and streams provides a complex habitat for aquatic organisms and can influence both aquatic biodiversity and ecosystem function. The Daly River in the wet–dry tropics of northern Australia is a highly seasonal, perennially flowing sand‐bed river where surveys of river wood aggregations at the reach scale (~2 km) in 2008 and 2009 recorded densities of 37–78 km^?1 and identified distinct types of river wood aggregations: key pieces, standing trees, fallen trees, wrack and single pieces. After larger than average flows in the 2008/2009 wet season, between 46% and 51% of the surveyed river wood had moved. The distribution of wood age classes indicated continual recruitment and slow turnover of wood within the river. Surveys of fish and habitat characteristics at the mesohabitat scale (~100 m) showed fish species richness; diversity and fish abundance were not correlated to the proportion of wood present. Fish assemblage structure was associated with wood cover as well as other environmental variables such as stream width and depth. The importance of in‐stream wood also varied for different species and age classes of fish. This study documents the dynamic nature of river wood aggregations and their complex and variable distribution and suggests their importance as fish habitat in this tropical river. Copyright © 2012 John Wiley & Sons, Ltd.     

HIGH‐HEAD DAMS AFFECT DOWNSTREAM FISH PASSAGE TIMING AND SURVIVAL IN THE MIDDLE FORK WILLAMETTE RIVER

Many high‐head dams in Oregon's Willamette River basin were constructed without fish passage facilities for downstream migrants. Instead, fish pass dams via hydroelectric turbines, surface spillways or deep‐water regulating outlets. The availability of these routes varies seasonally with dam operations and reservoir depth, which can fluctuate by tens of meters. To assess how dam and reservoir operations affect fish movement timing and survival, we used rotary screw traps below three Willamette basin dams and at two riverine sites above reservoirs. Traps were operated 2950 days over 8 years, and >195 000 fish were collected. Samples above reservoirs were primarily native salmonids (Oncorhynchus spp.), daces (Rhinichthys spp.) and sculpins (Cottus spp.), while those below dams were often dominated by non‐native Centrarchidae. Capture rates at riverine sites were highest from late winter to early summer, coincident with juvenile Chinook salmon emigration. Conversely, collection below dams was largely restricted to late fall and winter when reservoirs were drawn down to annual lows and discharge was high. We hypothesize that winter operations facilitated fish access to dam turbines and regulating outlets, whereas spring–summer operations entrapped fish in reservoirs and restricted volitional downstream passage. Total fish mortality was ≤2% at riverine sites and was 36–69% below dams. Estimates were highest for non‐native species and juvenile Chinook salmon. Fatal injuries were consistent with traumas related to pressure, shear and contact and there were size‐related and morphology‐related risk differences. Mitigation opportunities include fish bypass system development, retrofits for existing routes and seasonally appropriate reservoir draw down to allow fish passage. Copyright © 2012 John Wiley & Sons, Ltd.     

NUMERICAL SIMULATION OF SUMMER CIRCULATION IN THE EAST CHINA SEA AND ITS APPLICATION IN ESTIMATING THE SOURCES OF RED TIDES IN THE YANGTZE RIVER ESTUARY AND ADJACENT SEA AREAS

Based on the COHERENS (a Coupled Hydrodynamical Ecological model for Regional Shelf seas), a three-dimensional baroclinic model for the summer of East China Sea (ECS) was established with the sigma-coordinate in the vertical direction and spherical coordinate in the horizontal direction. The circulation patterns of the Kuroshio Current, the Taiwan Warm Current (TWC), the Tsushima Current and the Yangtze Diluted Water (YDW) were successfully simulated with this model. The calculated results are fairly consistent with previous observations and studies. Based on this baroclinic current field, the Lagranian particles tracking was simulated to estimate the possible origins of the red tides frequently occurring in the Yangtze River estuary and its adjacent sea areas. If there are “seeds” (cysts) of the red tide algae at the seabed of the Taiwan Strait, the offshore of Fujian and Zhejiang Provinces and the northeast Taiwan Island, those are extremely possible sources of the red tides in the Yangtze River estuary and its adjacent sea areas. Field data are needed to confirm it. Numerical simulation to estimate the source of the red tides is a new application of the Lagrangian transport in the marine ecology.     

THE RELATIONSHIP BETWEEN THERMAL REGIME ALTERATION AND SPAWNING DELAY OF THE FOUR MAJOR CHINESE CARPS IN THE YANGTZE RIVER BELOW THE THREE GORGES DAM

Large dams often alter flow and thermal regimes downstream, resulting in fish spawning delays and larval abundance declines. Accurate prediction of the delayed spawning period under changed thermal regime is critical for selecting a correct timing to modify dam operation and to release the environmental flow needed to enhance fish spawning. We used correlation analysis to investigate the relationship between thermal regime alteration and spawning delay of the four major Chinese carps (FMCC) below the Three Gorges Dam in the Yangtze River, China, using a 13‐year ecological data series (1997–2009). Eighteen variables were defined to quantify thermal regime and related to two variables representing spawning timing. Our results demonstrate that the start of FMCC spawning has been delayed from early May to middle June since the Three Gorges Dam initiated operation in 2003. Water temperature declines of 2 °C–4 °C in March, April and May (a critical period for gonad development) were the principal reason for the observed spawning delay. The variable most associated with spawning timing was the arrival date of the cumulative temperature needed for gonad development from stages IV to V (D_DegDayIV–V), which describes the long‐term impacts of the timing, magnitude and duration of thermal regime upon gonad development. Only the cumulative temperature for gonad development and the minimum temperature for FMCC spawning (18 °C) are both satisfied, the occurrence of suitable flow conditions, that is, flow increase or flash flood, would produce a successful spawning event. Consequently, we suggest that the experimental flow increase process of the Three Gorges Reservoir aimed at enhancing FMCC spawning should initiate after 15 June when the requisite thermal regime can be met. Copyright © 2013 John Wiley & Sons, Ltd.     

SPATIAL,SEASONAL AND INTER‐ANNUAL VARIABILITY IN ENVIRONMENTAL CHARACTERISTICS AND PHYTOPLANKTON STANDING STOCK OF THE TEMPERATE,LOWLAND RIDEAU RIVER,ONTARIO, CANADA

Chlorophyll‐a, biomass and living unit concentrations were monitored across the Rideau River over a three‐year period. The results show that a continuum of changing physical, biological and chemical conditions altered the phytoplankton standing stock of the Rideau River. From year to year, weather conditions and anthropogenic impacts like discharge control had a clear effect on the phytoplankton community. The year 2000, with poorer growing conditions and higher flow regime, had a significantly lower phytoplankton standing stock across all the stations. Based on hydrological characteristics, the Rideau River was divided into four distinct reaches, and ANOVAs show a clear reach effect on phytoplankton standing stock. The invasive zebra mussel consistently reduced the phytoplankton standing stock downstream from the main invasion zone over the three years, although there were differences between years. The non‐native zebra mussel further altered the phosphorus–phytoplankton standing stock relationship. Nutrients, ions and metals were not clearly correlated to standing stock in this three‐year study, although the significant effect of the four reaches suggested that environmental characteristics other than hydrological conditions may have an influence. Phytoplankton development downstream followed a polynomial model. However, unlike the stages of development characterizing many river continuum models, the pattern observed in the present study was affected by zebra mussels followed by anthropogenic impacts of discharge control and eutrophication. This and other studies on the Rideau River highlight the significance of scale (spatial and temporal) and metrics selected when evaluating environmental impacts and developing watershed models. Copyright © 2011 John Wiley & Sons, Ltd.     

POPULATION STRUCTURE IN THREE SPECIES OF CO‐DISTRIBUTED SALMONID FISHES IN THE PEACE RIVER AND TRIBUTARIES NEAR A MAJOR PROPOSED HYDROELECTRIC DEVELOPMENT IN NORTHEASTERN BRITISH COLUMBIA,CANADA

Dam construction and reservoir formation represent profound anthropogenic alterations to natural riverscapes, especially in terms of connectivity in migratory fishes. The Peace River in northeastern British Columbia (BC), Canada, is the largest river system in BC, home to 39 native fishes and currently has two major hydroelectric projects, and a third one (‘Site C’) is proposed. Three co‐distributed and migratory fishes, the bull trout (Salvelinus confluentus), Arctic grayling (Thymallus arcticus) and the mountain whitefish (Prosopium williamsoni) are key species in the Peace River ecologically and in terms of recreational fisheries. We examined microsatellite DNA variation in these species to assess genetic diversity, levels of population subdivision and connectivity to better understand potential impacts and to provide baseline information for subsequent monitoring. Expected heterozygosity and number of alleles averaged 0.65 and 7.7, 0.73 and 11.9, and 0.72 and 10.8 for bull trout (nine loci), Arctic grayling (10 loci) and mountain whitefish (10 loci), respectively. Estimates of the effective number of breeders (N_b) ranged from 35 to 255 for bull trout to over 3700 for Arctic grayling. Population subdivision (F_ST, θ) was 0.040, 0.063 and 0.023 in bull trout, Arctic grayling and mountain whitefish, respectively (all p < 0.001). Temporal differences within localities for all species accounted for <1% of total variation in allele frequencies. An estimated 6.2% (mountain whitefish), 4.6% (bull trout) and 8.8% (Arctic grayling) of fish samples were inferred (p < 0.05) to be immigrants to one locality from another locality. Our results suggest that connectivity amongst localities is important to successful completion of the life history of each species, the potential disruption of which will be a critical aspect of post‐development monitoring. Copyright © 2013 John Wiley & Sons, Ltd.