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USGS2022

Habitat associations of riverine fishes among rocky shoals

Understanding species' associations with physical habitat conditions is a fundamental goal of ecology. For organisms that occupy lotic ecosystems, relationships to streamflow are of particular importance, but these associations are unstudied for most species. We tested the predictability of fish–microhabitat relationships in river shoals (shallow, rocky areas with relatively swift water flow) using a large data set from the Conasauga River in Georgia, USA. Our objective was to assess the consistency of species-specific relationships with flow-dependent variables (depth, velocity, Reynolds number and Froude number) while accounting for other microhabitat variables (e.g. vegetation). We used data from 8285 seine-sets collected during late summer or autumn at 26 sites over 12 years to relate occurrence and counts of 22 fish species to habitat variables using generalised linear multiple regression models. Results showed that microhabitat models explained a substantial amount of the variation in counts for some species, although other species were poorly predicted. We classified 16 species as velocity specialists and nine species as depth specialists, with six species specialised for depth and velocity and three species classified as depth and velocity generalists. The variability in habitat associations that we observed suggests that species will be unevenly affected by anthropogenic activities that alter flows.

Georgia↗

USGS2011

Trophic relationships between a native and a nonnative predator in a system of natural lakes

Bull trout, a species of char listed as threatened under the US Endangered Species Act, have been displaced from portions of their historic range following the introduction of nonnative lake trout. It has been suggested that competitive exclusion as a result of trophic overlap between bull trout and lake trout may be the causal mechanism associated with displacement of bull trout. This study used stable isotope data to evaluate trophic relationships among native bull trout, nonnative lake trout and other fishes in seven lakes in Glacier National Park (GNP), Montana. Bull trout and lake trout had greater δ 15 N values relative to other fishes among lakes (δ 15 N ≥ 3.0‰). Lake trout had greater δ 15 N values relative to bull trout (δ 15 N = +1.0‰). Bull trout had greater δ 13 C values relative to lake trout in six of the seven lakes examined. Although both bull trout and lake trout had greater δ 15 N values relative to other fishes within lakes in GNP, differences in δ 15 N and δ 13 C between bull trout and lake trout suggest that they are consuming different prey species or similar prey species in different proportions. Therefore, displacement of bull trout as a direct result of complete overlap in food resource use is not anticipated unless diet shifts occur or food resources become limiting. Additionally, future studies should evaluate food habits to identify important prey species and sources of partial dietary overlap between bull trout and lake trout.

Montana↗

USGS2014

Predation on native sculpin by exotic brown trout exceeds that by native cutthroat trout within a mountain watershed (Logan, UT, USA)

We explored potential negative effects of exotic brown trout ( Salmo trutta ) on native sculpin ( Cottus sp.) on the Logan River, Utah, USA by (i) examining factors most strongly correlated with sculpin abundance (e.g., abiotic conditions or piscivory?), (ii) contrasting the extent of brown trout predation on sculpin with that by native cutthroat trout ( Oncorhynchus clarkii utah ) and (iii) estimating the number of sculpin consumed by brown trout along an elevational gradient using bioenergetics. Abundance of sculpin across reaches showed a strong ( r ≥ 0.40) and significant ( P < 0.05) correlation with physical variables describing width (positive) and gradient (negative), but not with abundance of piscivorous brown trout or cutthroat trout. In mainstem reaches containing sculpin, we found fish in 0% of age‐1, 10% of age‐2 and 33% of age‐3 and older brown trout diets. Approximately 81% of fish consumed by brown trout were sculpin. Despite a similar length–gape relationship for native cutthroat trout, we found only two fish (one sculpin and one unknown) in the diets of native cutthroat trout similar in size to age‐3 brown trout. Based on bioenergetics, we estimate that an average large (> 260 mm) brown trout consumes as many as 34 sculpin per year. Nevertheless, results suggest that sculpin abundance in this system is controlled by abiotic factors and not brown trout predation. Additional research is needed to better understand how piscivory influences brown trout invasion success, including in‐stream experiments exploring trophic dynamics and interactions between brown trout and native prey under different environmental conditions.

Utah↗

USGS2009

Influence of seasonal, diel, lunar, and other environmental factors on upstream fish passage in the igarapava fish ladder, Brazil

Upstream fish passage was evaluated during 12 months in the vertical-slot Igarapava Fish Ladder constructed around Igarapava Dam, in the heavily dammed Grande River, Southeast Brazil. A video monitoring system was used to observe 61,621 fish that passed the ladder, of which 93.5% were identified to 15 taxa. Among the migratory species, the most abundant were Pimelodus maculatus (33.6% of all fish), Leporinus octofasciatus (31.4%), Leporinus friderici (4.5%), and Prochilodus lineatus (3.1%). Seven taxa were classified as nonmigratory, and of these taxa, the small Bryconamericus stramineus was the most abundant (12.7%) of all fishes. Passage of the 'nonmigratory' taxa upstream in the ladder shows they are migratory in this system and have a strong behavioural drive to move to upstream habitat. Passage of most taxa had a strong seasonal pattern. While some species passed primarily during the day, others showed a distinct nocturnal pattern. Lunar phase and water temperature also strongly affected passage of some taxa. Rainfall and dam discharge had a small or null influence on most taxa; perhaps due to the fairly small catchment area of the reservoir and the highly regulated discharge at Igarapava Dam. ?? 2009 John Wiley & Sons A/S.

Ecology of Freshwater Fish↗

USGS2010

The effect of predation on stunted and nonstunted white perch

Predation is widely regarded as a means to prevent or minimise the establishment of a stunted (high density of slow growing individuals) population. We investigated the effect of predation on two different white perch Morone americana populations (stunted and nonstunted) by examining the stomach contents of piscivorous fishes. White perch and gizzard shad dominated piscivore diets in Branched Oak Lake, whereas white perch dominated piscivore diets in Pawnee Lake. White perch consumed in the stunted population (Branched Oak Lake) were larger and older than white perch consumed in the nonstunted population (Pawnee Lake). Many of the consumed white perch in the stunted population were sexually mature and had the opportunity to spawn at least once. In contrast, all of the consumed white perch in the nonstunted population were sexually immature. Predation may have reinforced the stunting of white perch in Branched Oak Lake through removal of the largest, oldest individuals. ?? 2010 John Wiley & Sons A/S.

Ecology of Freshwater Fish↗

USGS2018

Riparian defoliation by the invasive green alder sawfly influences terrestrial prey subsidies to salmon streams

Invasive species in riparian forests are unique as their effects can transcend ecosystem boundaries via stream‐riparian linkages. The green alder sawfly ( Monsoma pulveratum ) is an invasive wasp whose larvae are defoliating riparian thin‐leaf alder ( Alnus tenuifolia ) stands across southcentral Alaska. To test the hypothesis that riparian defoliation by this invasive sawfly negatively affects the flow of terrestrial prey resources to stream fishes, we sampled terrestrial invertebrates on riparian alder foliage, their subsidies to streams and their consumption by juvenile coho salmon ( Oncorhynchus kisutch ). Invasive sawflies altered the composition of terrestrial invertebrates on riparian alder foliage and as terrestrial prey subsidies to streams. Community analyses supported these findings revealing that invasive sawflies shifted the community structure of terrestrial invertebrates between seasons and levels of energy flow (riparian foliage, streams and fish). Invasive sawfly biomass peaked mid‐summer, altering the timing and magnitude of terrestrial prey subsidies to streams. Contrary to our hypothesis, invasive sawflies had no effect on the biomass of native taxa on riparian alder foliage, as terrestrial prey subsidies, or in juvenile coho salmon diets. Juvenile coho salmon consumed invasive sawflies when most abundant, but relied more on other prey types selecting against sawflies relative to their availability. Although we did not find effects of invasive sawflies extending to juvenile coho salmon in this study, these results could change as the distribution of invasive sawflies expands or as defoliation intensifies. Nevertheless, riparian defoliation by these invasive sawflies is likely having other ecological effects that merits further investigation.

Alaska↗

USGS2023

Smallmouth bass (Micropterus dolomieu) suppress Atlantic salmon (Salmo salar) feeding activity and increase aggressive behaviours at warmer temperatures

By 2050, mean temperature in the state of Maine, located in the Northeastern USA, is expected to increase nearly 1°C, which could directly affect native coldwater salmonid behaviour and increase competition with warmwater smallmouth bass. We conducted a microcosm experiment to examine the feeding and agonistic behaviour of endangered juvenile Atlantic Salmon ( Salmo salar ) at two temperatures (18 and 21°C) in the presence and absence of non-native Smallmouth Bass ( Micropterus dolomieu ). By visually reviewing footage of fish competition in our tanks, we quantified feeding and agonistic interactions. We predicted salmon would exhibit lower feeding activity than bass at 21°C and antagonistic interactions between the two species would increase with warming. We found salmon feeding activity was reduced by smallmouth bass presence and this effect was stronger at 21°C. We also found smallmouth bass aggression was strongest at 21°C when salmon were present. Lastly, feeding activity and aggression in both species changed with food availability. These findings illustrate the potential for invasive warmwater species to outcompete native salmonids for resources, especially under the warmer conditions predicted by climate change scenarios.

Maine↗

USGS2022

Lake trout (Salvelinus namaycush) otoliths indicate effects of climate and lake morphology on growth patterns in Arctic lakes

Climate change is occurring rapidly in the Arctic, and an improved understanding of the response of aquatic biota and ecosystems will be important for this data-limited region. Here, we applied biochronology techniques and mixed-effects modelling to assess relationships among growth increments found on lake trout ( Salvelinus namaycush ) otoliths ( N = 49) captured from 13 lakes on the Arctic Coastal Plain of northern Alaska, observed and modelled climate patterns, and individual-level fish and lake characteristics. We found that annual growth varied by year, fish growth slowed significantly as individuals aged, and females grew faster than males. Lake trout had higher growth in flow-through lakes relative to lakes that were perennially or seasonally connected. Annual growth was positively correlated with observed air temperature measurements from a local weather station for the period 1998–2014, but no clear warming trend was evident for this period. Modelled August air temperatures from 1978–2014 predicted lake trout annual growth (root mean squared error = 0.045 mm) and indicated increasing temperatures and annual lake trout growth over the period 1950–2014. This study demonstrated that biochronology techniques can reconstruct recent climate patterns and provide a better understanding of trends in Arctic lake ecosystems under a changing climate.

Alaska↗

USGS2002

Diet dynamics of the adult piscivorous fish community in Spirit Lake, Iowa, USA 1995-1997

Diets of adults of six important piscivorous fish species, black crappie Pomoxis nigromaculatus, largemouth bass Micropterus salmoides, northern pike Esox lucius, smallmouth bass Micropterus dolomieui, walleye Stizostedion vitreum, and yellow perch Perca flavescens were quantified in Spirit Lake, Iowa, USA from May to October in 1995-1997. Forty-one prey taxa were found in the diets of these species, including 19 species of fish. The most important prey taxa overall were yellow perch, amphipods and dipterans. Diets of northern pike and walleye were dominated by yellow perch. Largemouth bass diets included large percentages of both yellow perch and black bullhead Ameiurus melas. Smallmouth bass diets included large percentages of both yellow perch and crayfish. Black crappie and yellow perch diets were dominated by invertebrates, primarily amphipods and dipterans. There were pronounced differences in diets among species, among size classes within species and over time. Most of the dominant prey taxa we documented in the diets of piscivorous species were in accordance with previous studies, but a few deviated significantly from expectations. Many of the temporal diet changes were asynchronous among piscivorous species and size classes, suggesting different responses to common prey resources over time.

Ecology of Freshwater Fish↗

USGS1994

Habitat use by an endangered riverine fish and implications for species protection

We investigated habitat specificity of the amber darter (Percina antesella Williams & Etnier 1977), an imperiled fish from restricted portions of 2 rivers in the southeastern United States. Foraging amber darters occupied a narrow range of riffle habitat, consistently avoiding areas < 20 cm deep and with velocity < 10 cm. s-1 near the substrate, occupying areas with cobble or gravel substrate and average water-column velocity of 30 to 70 cm. s-1. During low to moderate flows, approximately 20% or more of the study areas contained suitable habitat for the species. Amber darters appeared rare, and the numbers of individuals were uncorrelated with the concurrent availability of suitable habitat. Protecting the amber darter may require more than maintaining adequate depths and velocities over gravel-cobble substrates. Until we understand the potential importance of migration and dispersal for maintaining small populations, suitable habitat should be maintained over the longest contiguous stream segments possible.

Ecology of Freshwater Fish↗

USGS2020

Hydrogeomorphological controls on reach‐scale distributions of cichlid nest sites in a small neotropical river

The Cichlidae are among the most diversified families of fish in the Neotropics and represent an important component of aquatic biodiversity. Understanding cichlid nest‐site selection is important for assemblages facing uncertain futures due to species invasions and environmental change. This information could be used to predict how inter‐ and intraspecific competition for reproductive space may affect populations with changing community dynamics or to identify areas as targets for conservation. We investigated which hydrogeomorphological factors correlated to preferred nest sites of four native cichlid species in the Bladen River, Belize. We recorded the locations of nest sites and collected habitat data through the study reach, including flow velocity, depth, sediment type, fish cover type richness and distance to the bank. Nest locations and physical habitat data were used to construct spatially explicit habitat models using boosted regression trees (BRTs). The models provided statistically significant evidence that physical habitat variables influence the distribution of the nest sites. We found that all species except Archocentrus spilurus were associated with substrate, specifically sand. Thorichthys meeki was also associated with lower water velocities, whereas Cichlasoma salvini was influenced by all five variables. Vieja maculicauda and Archocentrus spilurus were both influenced by flow velocity, distance to bank and depth, although A. spilurus preferred deeper, slightly faster locations about the same distance to the bank. This study suggests that the spatial distribution of nest sites within this cichlid community is significantly different than random and is at least partially governed by physical controls.

Monkey River Basin↗

USGS2022

Temporal segregation in spawning between native Yellowstone cutthroat trout and introduced rainbow trout

Hybridisation with introduced taxa poses a threat to native fish populations. Mechanisms of reproductive isolation can limit or prevent hybridisation between closely related species. Understanding how these mechanisms interact between the same species across geographically distinct occurrences of secondary contact, and how regional factors influence them, can inform our understanding of hybridisation as a threat and management actions to mitigate this threat. We used data collected on adult fish migration timing and approximate emergence timing of subsequent juvenile fish paired with genomic data to assess whether temporal isolation in the timing of spawning exists between Yellowstone cutthroat trout, rainbow trout and hybrids in the North Fork Shoshone River drainage in northwest Wyoming. We found evidence that Yellowstone cutthroat trout spawn, on average, two to four weeks later than rainbow trout and hybrids and two environmental covariates related to water temperature and discharge were associated with differences in spawning migration timing. Despite statistical support for Yellowstone cutthroat trout spawning later, disproportionately high numbers of rainbow trout and hybrids, paired with extended spawning seasons, lead to substantial overlap between all genotypes. Our results provide further evidence of temporal segregation in the timing of spawning as a mechanism of reproductive isolation between closely related species, but substantial spawning overlap suggests temporal segregation alone will not be enough to curtail hybridisation in conservation populations.

Wyoming↗

USGS2007

Movement patterns of armado, Pterodoras granulosus, in the Paraná River Basin

We studied the migratory behaviour of armado, Pterodoras granulosus , in the Paraná River Basin of Brazil, Paraguay and Argentina, during 1997–2005. This species invaded the Upper Paraná River after upstream dispersal was facilitated when Itaipu Reservoir inundated a natural barrier. Fish were tagged ( N = 8051) in the mainstems of the Yacyreta and Itaipu reservoirs, bays of major tributaries, the Paraná River floodplain above Itaipu Reservoir, and below dams. In all, 420 fish were recaptured of which 61% moved away from the release area. Fish moved a maximum of 215 km (mean 42), and at a maximum rate of 9.4 km·day −1 (mean 0.6). Of the 256 armados that moved away from the release site, 145 moved upstream towards unimpounded stretches of the Paraná River and 111 moved downstream into the reservoir and bays of its tributaries (maximum 150 km). Based on the observed migratory movements, we suspect that most of the reproductive output originates in tributaries to the reservoirs. The ability of this species to expand its range presents a conundrum by pitting fishery management interests against conservation needs. Maintenance of the important armado fisheries depends on the ability of the species to migrate freely to use spawning and nursery areas in reservoir tributaries and floodplains. However, its ability to migrate long distances can allow this non-native species the opportunity to invade most of the Upper Paraná River.

Parana River Basin↗

USGS2026

The effect of temperature, flow, density and disease on smallmouth bass (Micropterus dolomieu) early life growth rate

Individual growth rates of fish are influenced by gradually changing environmental conditions and rapid-onset events. However, there is a paucity of information on drivers of spatiotemporal variability in growth rates of fishes across large spatial extents. Using a 36-year dataset of smallmouth bass ( Micropterus dolomieu ) length-at-age data across 10 river reaches in Pennsylvania, USA ( n = 54,068 individuals), we estimated annual early life growth rates (mm year −1 ) and assessed the effects of relative abundance, summer temperature, summer streamflow rate and a disease outbreak on growth rate. We found that temperature had a positive effect on growth rate, varied spatially, and had a stronger effect in diseased reaches. There was also evidence for an impact of disease on early life growth through density-dependent mechanisms, with growth rates increasing from ∼85 to 101 mm·year −1 following disease-related decreases in abundance. This study adds to our understanding of the factors that shape early life growth, including rapid-onset events like disease which can have immediate and lasting effects on growth rate trajectory.

Pennsylvania↗

USGS2014

Diverse juvenile life-history behaviours contribute to the spawning stock of an anadromous fish population

Habitat quality often varies substantially across space and time, producing a shifting mosaic of growth and mortality trade-offs across watersheds. Traditional studies of juvenile habitat use have emphasised the evolution of single optimal strategies that maximise recruitment to adulthood and eventual fitness. However, linking the distribution of individual behaviours that contribute to recruitment at the population level has been elusive, particularly for highly fecund aquatic organisms. We examined juvenile habitat use within a population of sockeye salmon (Oncorhynchus nerka) that spawn in a watershed consisting of two interconnected lakes and a marine lagoon. Otolith microchemical analysis revealed that the productive headwater lake accounted for about half of juvenile growth for those individuals surviving to spawn in a single river in the upper watershed. However, 47% of adults had achieved more than half of their juvenile growth in the downstream less productive lake, and 3% of individuals migrated to the estuarine environment during their first summer and returned to freshwater to overwinter before migrating back to sea. These results describe a diversity of viable habitat-use strategies by juvenile sockeye salmon that may buffer the population against poor conditions in any single rearing environment, reduce density-dependent mortality and have implications for the designation of critical habitat for conservation purposes. A network of accessible alternative habitats providing trade-offs in growth and survival may be important for long-term viability of populations.

Alaska↗

USGS2016

Feeding ecology of the walleye (Percidae, Sander vitreus), a resurgent piscivore in Lake Huron (Laurentian Great Lakes) after shifts in the prey community

Recovering populations of piscivores can challenge understanding of ecosystem function due to impacts on prey and to potentially altered food webs supporting their production. Stocks of walleye (Percidae, Sander vitreus ), an apex predator in the Laurentian Great Lakes, crashed in the mid‐1900s. Management efforts led to recovery by 2009, but recovery coincided with environmental and fish community changes that also had implications for the feeding ecology of walleye. To evaluate potential changes in feeding ecology for this apex predator, we assessed diets in the main basin of Lake Huron and in Saginaw Bay, a large embayment of Lake Huron, during 2009–2011. Walleye switched their diets differently in the main basin and Saginaw Bay, with non‐native round goby (Gobiidae, Neogobius melanostomus ) and rainbow smelt (Osmeridae, Osmerus mordax ) more prevalent in diets in the main basin, and invertebrates, yellow perch (Percidae, Perca flavescens ) and gizzard shad (Clupeidae, Dorosoma cepedianum ) more prevalent in diets in the bay. Feeding strategy plots indicated that there was a high degree of individual specialisation by walleye in the bay and the main basin. Bioenergetic simulations indicated that walleye in Saginaw Bay need to consume 10%–18% more food than a walleye that spends part or all of the year in the main basin, respectively, in order to achieve the same growth rate. The differences in diets between the bay and main basin highlight the flexibility of this apex predator in the face of environmental changes, but changes in diet can alter energy pathways supporting piscivore production.

Ecology of Freshwater Fish↗

USGS2014

Incubation success and habitat selection of shore-spawning kokanee Onchorhynchus nerka: effects of water level regulation and habitat characteristics.

Changes to water-level regimes have been known to restructure fish assemblages and interfere with the population dynamics of both littoral and pelagic species. The effect of altered water-level regimes on shore-spawning kokanee Oncorhynchus nerka incubation success was evaluated using a comprehensive in situ study in Lake Pend Oreille, ID, USA. Survival was not related to substrate size composition or depth, indicating that shore-spawning kokanee do not currently receive a substrate-mediated survival benefit from higher winter water levels. Substrate composition also did not differ among isobaths in the nearshore area. On average, the odds of an egg surviving to the preemergent stage were more than three times greater for sites in downwelling areas than those lacking downwelling. This study revealed that shoreline spawning habitat is not as limited as previously thought. Downwelling areas appear to contribute substantially to shore-spawning kokanee recruitment. This research illustrates the value of rigorous in situ studies both for testing potential mechanisms underlying population trends and providing insight into spawning habitat selection.

Ecology of Freshwater Fish↗

USGS2016

Stable isotope evaluation of population- and individual-level diet variability in a large, oligotrophic lake with non-native lake trout

Non-native piscivores can alter food web dynamics; therefore, evaluating interspecific relationships is vital for conservation and management of ecosystems with introduced fishes. Priest Lake, Idaho, supports a number of introduced species, including lake trout Salvelinus namaycush , brook trout S. fontinalis and opossum shrimp Mysis diluviana . In this study, we used stable isotopes (δ 13 C and δ 15 N) to describe the food web structure of Priest Lake and to test hypotheses about apparent patterns in lake trout growth. We found that isotopic niches of species using pelagic-origin carbon did not overlap with those using more littoral-origin carbon. Species using more littoral-origin carbon, such as brook trout and westslope cutthroat trout Oncorhynchus clarki lewisi , exhibited a high degree of isotopic niche overlap and high intrapopulation variability in resource use. Although we hypothesised that lake trout would experience an ontogenetic diet shift, no such patterns were apparent in isotopic signatures. Lake trout growth rates were not associated with patterns in δ 15 N, indicating that variation in adult body composition may not be related to adult diet. Understanding trophic relationships at both the individual and species levels provides a more complete understanding of food webs altered by non-native species.

Idaho↗