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At least 289 records · Page 16Linked to original sources
USGS2023

Density-dependent processes and population dynamics of native sculpin in a mountain river

Understanding the processes governing population dynamics is important for effective conservation and environmental management. Disentangling the relative role of density-dependent versus density-independent processes on population dynamics is often made difficult by the inability to control for abiotic or biotic factors, but long-term datasets are invaluable in this pursuit. We used a 14-year dataset from the Logan River, Utah, to assess long-term trends in abundance and evidence of density-dependent and density-independent effects on population dynamics of Paiute sculpin ( Cottus beldingii ) across six sites. Additionally, we evaluated the feeding ecology of sculpin over 4 years. Sculpin densities generally increased from upstream to downstream, and the annual per capita rate of increase was negatively and significantly correlated with sculpin density at four of six sites. We observed a negative relationship between total gut content and sculpin density but did not observe a negative relationship between relative condition and density. Sculpin displayed a generalist feeding strategy, and interannual differences in diet composition appeared to be influenced by interannual differences in flow, particularly years with higher magnitude flow. The observed spatial patterns in sculpin abundance throughout the watershed matched those of invasive brown trout ( Salmo trutta ), the top piscivore in the Logan River, and likely represent affinities for the suite of ecological conditions associated with downstream sections of the Logan River. Our results suggest that sculpin populations are regulated largely by density-dependent processes and match those from other studies on sculpin population dynamics including a range of species and habitats that differ vastly in abiotic conditions.

Ecology of Freshwater Fish↗
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↗
USGS2023

Larval cisco and lake whitefish exhibit high distributional overlap within nursery areas

Coregonine fishes, including lake whitefish ( Coregonus clupeaformis ) and cisco ( C. artedi ), are socioecologically important in the Laurentian Great Lakes and of conservation concern, but the processes driving recruitment variability are unclear. In Lake Ontario, cisco and lake whitefish exhibit similar spawning behaviours and early life histories, but population trajectories are diverging. One hypothesis is that sympatric cisco and lake whitefish larvae occupy distinct habitats and experience dissimilar local environmental conditions, despite co-occurrence within nursery areas. We described the spatiotemporal distributions of larval cisco and lake whitefish among multiple Lake Ontario embayment nursery areas, characterised physical habitat features associated with their distributions, determined the degree of spatial habitat partitioning between species and evaluated how habitat niche divergence occurred along an ontogenetic progression. Both species were widely distributed across larval nursery areas, though lake whitefish were less abundant and more narrowly distributed than cisco. Within the yolk sac stage, lake whitefish occupied more nearshore, shallower and colder waters than cisco, indicating potential habitat niche partitioning between congeners. However, distributional differences were subtle and likely driven by differential hatch timing and staggered ontogenetic habitat shifts. Combined, our results illustrate similar habitat use between cisco and lake whitefish through the larval stage and demonstrate that ontogeny and species-specific phenology influence habitat use for these species. This study provides additional evidence that the early life histories of cisco and lake whitefish are highly similar and does not support the hypothesis that larval habitat use differences are a major driver of differential recruitment success for these species.

New York↗
USGS2023

Seasonal shifts in diel vertical migrations by lake-dwelling coastal cutthroat trout, Oncorhynchus clarkii clarkii, reflect thermal regimes and prey distributions

Lakes provide important habitat for salmonids that may use them as a primary feeding area between periods of reproduction. The seasonal changes in vertical thermal structure in lakes can affect the distribution of salmonids on seasonal and diel time scales as they search for, consume, and digest prey that also exploits the water column's distribution of food, temperature and light. Our goal was to analyse the vertical distribution of wild, native coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) in Lake Washington on daily and seasonal time scales. This lake is stratified in the summer and isothermal in winter, allowing us to compare vertical movements between periods with and without thermal structure in water 50 m deep. We predicted that trout would be deeper in the water column during stratified months and shallower during isothermal months, and shallower at night than in the day. Overall, the trout showed these patterns in the depths and temperatures they occupied, tending to be within or below the thermocline in the summer but not in the coolest water available, and closer to the surface when the lake was isothermal. The trout were also closer to the surface at night and deeper during the day. The vertical range of these diel movements shifted with the seasons–deepest in October, as the thermocline deepened and weakened, and shallowest in January when the lake was isothermal. These seasonal and diel vertical distribution patterns by the trout optimise metabolism for growth, and facilitate feeding on planktivorous fishes that also show seasonal and diel vertical distribution changes.

Washington↗
USGS2023

Food web changes reflected in age-0 piscivore diets and growth

Lake Erie walleye ( Stizostedion vitreum ) recruitment fluctuates annually and depends partially on their diet and growth during their first year of life. In recent decades, age-0 walleye diet and growth may be responding to food web changes in western Lake Erie. To determine how age-0 walleye have responded to changes in prey species and abundance, we compared diet between 2019, 2014 and 1994–1999. Larval walleye ate predominantly cyclopoids in 2019, compared to 1994–1999 when calanoids were the most consumed copepod. Juvenile walleye ate predominantly large cladocerans and benthic invertebrates in 2019, compared to 2014 and 1994 when fish was the most consumed prey. Additionally, in 2019 and 2014, age-0 walleye ate two of the current aquatic invasive species (AIS), Bythotrephes longimanu s and Neogobius melanostomus , and the historical AIS, Osmerus mordax . Age-0 walleye were smaller in 2019 than in 2014 and switched to consuming more AIS and less fish suggesting that more energetically favourable prey were not available. While age-0 walleye showed adaptation to new prey and conditions, they had a lower quality diet because they consumed less fish, but also because the invasive fish they now consume have a lower energy density than native species. However, lower quality diet and size may not result in reduced survival, if adequate alternative prey is available. Continued monitoring of age-0 walleye diet could provide confirmation that lower diet quality during the first year decreased walleye growth and aid to identify any effects changes in age-0 diets has on recruitment to the adult population.

Michigan, Ohio↗
USGS2023

Native fish abundance and habitat selection changes in the presence of nonnative piscivores

We compared abundance patterns and developed resource selection models for imperilled native southwestern (USA) fishes in the presence and absence of Black Bass ( Micropterus spp.) to evaluate how fishes alter their selection for habitats when sympatric with a nonnative piscivore. We collected data using snorkel surveys and in-stream habitat sampling in Fossil Creek (AZ), upstream (native fish only) and downstream (native and nonnative fish) of a fish barrier. The abundance of all Roundtail Chub ( Gila robusta ), small (≤127 mm total length [TL]; vulnerable to predation) Sonora Sucker ( Catostomus insignis ) and Speckled Dace ( Rhinichthys osculus ) was significantly reduced, but the abundance of both small and large (>127 mm TL; invulnerable to predation) Desert Sucker ( Catostomus clarkii ) was similar in sampling reaches with and without Black Bass. When sympatric with Black Bass, small Roundtail Chub increased their selection for riffles by 2.57 times and small Desert Sucker reduce their selection for pools by 6.90 times while also selecting for faster flow velocity and finer substrates in lotic mesohabitats. Large native fishes altered selection least, notwithstanding an increased selection for canopy cover in sampling reaches with Black Bass. Observed shifts in resource selection are consistent with predator avoidance strategies. Our study highlights the behavioural consequences of nonnative piscivores on native fish communities and stresses the importance of maintaining lotic mesohabitats as potential refugia for vulnerable native fishes when nonnative piscivores are present.

Arizona↗
USGS2024

Deposited sediment influences occurrence of functional traits of stream fishes

To better understand stream-fish sensitivity to fine sediment, we documented assemblage-wide responses by selected traits along a sedimentation gradient. We then discuss the management implications of these ‘dose–response’ relations in the contexts of biotic assessments and conservation of sediment-sensitive species. We identified a spatial gradient in sediment deposition among streams within the upper Piedmont of the Roanoke River basin in North Carolina and Virginia. We assessed fine-sediment sensitivity of 81 species based on eight species traits stratified by four attributes: food preference, feeding location, spawning substrate and spawning behaviour. We then ranked each trait and scored each species with respect to its sediment sensitivity. Using data from electrofishing surveys during 2018–2019, we calculated proportional abundances of traits observed at 30 sites throughout the study area and grouped species by their aggregate sensitivity scores. We assessed relations between embeddedness and silt cover and occurrences of species and traits using a combination of regression and ordination approaches. All traits tested responded to embeddedness or silt cover, or both. Feeding traits exhibited the strongest responses to embeddedness, while reproductive traits exhibited the strongest responses to silt cover. Our findings indicate that negative responses of the probability of presence for high-sensitivity traits to embeddedness and silt cover were linear, with no apparent thresholds. Additionally, proportional abundances of species with multiple high-sensitivity traits were inversely related to embeddedness and silt cover. Overall, our findings regarding population-level responses to sedimentation were consistent with our findings for trait-specific responses. Our analysis of species sensitivity to fine sediment corroborated the patterns we saw in our trait-specific analyses, indicating that population responses to sedimentation can be predicted from combinations of species traits. The ‘dose–response’ relations we documented may be applicable to managing sediment impacts on fishes, especially in the contexts of biotic assessments and conservation of sediment-sensitive species.

North Carolina, Virginia↗
USGS2024

Shift in piscivory by salmonids following invasion of a minnow in an oligotrophic reservoir

Predation can play an important role in structuring ecological communities, and predator–prey dynamics can be altered following the introduction of new species. An unauthorized introduction of redside shiner ( Richardsonius balteatus ) into reservoirs in the Upper Skagit River, Washington, USA created concern that a consequent shift in predator–prey dynamics in the reservoirs could reduce recruitment and production of native salmonids in the basin. We estimated predation mortality in Ross Lake on nonnative redside shiner and juvenile native salmonids to evaluate the potential role of predation in regulating these populations and limiting survival of native species of concern. We used bioenergetics modelling and stable isotope analysis combined with directed field measurements of growth, seasonal diet and thermal experience of piscivorous salmonids to quantify their consumption demand on prey fishes to evaluate the relative magnitude of predation mortality on invasive redside shiners and native salmonids. While redside shiner are the dominant prey fish species in Ross Lake, the modest biomass of native salmonids consumed could translate into substantial mortality, the magnitude of which depended on the timing and size at which prey fishes were eaten. This information provides important context for how nonnative species may indirectly impact native species through shared predation (apparent competition) and can inform conservation decisions surrounding nonnative species control, sustainability of native salmonids and introductions of anadromous fishes.

Ecology of Freshwater Fish↗
USGS2024

Thermal transfer rate is slower in bigger fish: How does body size affect response time of small, implantable temperature recording tags?

The recent miniaturisation of implantable temperature recording tags has made measuring the water temperatures fish experience in the wild possible, but there may be a body size-dependent delay in implanted tag response time to changes in external temperature. To determine whether fish body size affects the response rate of implanted temperature tags, we implanted 20 Salvelinus fontinalis (127–228 mm fork length (FL), 15.1–120.4 g) with temperature recording tags and subjected them to rapid temperature changes (±8°C in less than 2 seconds) in the laboratory. We found that thermal transfer rates, and the lag in temperature tag response rate, was positively correlated with fish size, but the direction of temperature change (colder or warmer) had no significant effect. In fish exposed to a slower rate of temperature change (2°C h −1 ) implanted tags did not show a response lag. Understanding the limitations of this important technology is crucial to determining the utility of the data it produces and its ability to accurately measure fish thermal experience in the wild.

Ecology of Freshwater Fish↗
USGS2025

Niche partitioning among three apex piscivorous fishes: Evidence of limited intraguild predation

This study aimed to understand the ecological relationship among burbot Lota lota , brown trout Salmo trutta and lake trout Salvelinus namaycush , with a focus on burbot, a species of greatest conservation need in Wyoming. While we hypothesised a reciprocal intraguild predation dynamic, where competition and predation occur between predators based on size or age structure, our findings provided limited support for this hypothesis. Both dietary overlap and trophic position were minimal among burbot, brown trout and lake trout. Instances of reciprocal predation were rare; no predation between burbot and lake trout was observed; and brown trout was the only species consumed by all predators (burbot 0.02 mean proportion by weight; lake trout 0.09 mean proportion by weight). Predation by brown trout on burbot was negligible, contributing only 0.01 to the mean proportion by weight and frequency of occurrence. Additionally, both burbot and brown trout were less piscivorous than expected, with fish comprising 0.36 and 0.17 of their mean proportion by weight in their overall diets, respectively. Overall, our findings suggest that these predators coexist with limited competitive or predatory interactions, likely due to differences in prey selection.

Wyoming↗
USGS2025

Predicted fish vulnerability to stream drying in the western U.S.A.

The frequency, magnitude and extent of stream drying is increasing due to climate change and human water demand. Fish vulnerability to increased stream drying is a combination of sensitivity (innate tolerance to low streamflow) and exposure to stream drying. To understand fish tolerance to low flow and susceptibility to decline under changing streamflow conditions, we estimated species-specific measures of sensitivity to low streamflow, determined relationships to species traits and evaluated vulnerability to future reductions in streamflow for 60 species. We found that sensitivity varied across species, and some variation was explained by life history strategy, spawning strategy and body size. Periodic life history strategy, pelagic spawning and larger size corresponded to an increased sensitivity to stream drying. Under future projections of August streamflow, 90% of sites were predicted to decrease in flow magnitude. Vulnerability to changes in streamflow, the combination of sensitivity and exposure, varied slightly across the study species, with the percent of inhospitable sites under future climate scenarios increasing for 87% of the species. Despite being relatively insensitive to low streamflow, vulnerability was high for multiple species dominant in mountainous areas, driven by high levels of exposure to stream drying. Our results illustrate the potential for species traits to predict sensitivity to low streamflow and demonstrate that exposure may play a large role when defining species vulnerability to stream drying. The ability to predict species tolerances and susceptibility to decline will become increasingly important in prioritising conservation efforts under changing environmental conditions.

Idaho, Montana, Nebraska, North Dakota, South Dako↗
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↗
USGS2006

Patterns of foraging and distribution of bluegill sunfish in a Mississippi River backwater: Influence of macrophytes and predation

We studied the trophic interactions and spatial distributions of bluegills Lepomis macrochirus and largemouth bass Micropterus salmoides in a macrophyte bed in Lake Onalaska, a backwater lake in the upper Mississippi River. The diets of adult and age-0 bluegills were similar and changed seasonally probably in response to changes in life stages of macroinvertebrates (i. e. emergence of winged adults). Diets and diel patterns of abundance of bluegill suggest that age-O and adults were feeding in the vegetated, littoral zone. Predation by age-O largemouth bass appears to influence use of vegetated habitat by age-0 bluegills. In summer, when most age-O bluegills were vulnerable to predation by age-O largemouth bass, bluegill abundance was strongly correlated with vegetation biomass. In October and November, piscivory by age-O largemouth bass was limited by gape. Consequently, the relationship between the abundance of age-O bluegills and vegetation biomass was weakened because predation risk by age-O largemouth bass was reduced.

Wisconsin↗
USGS2006

Efficacy of a vacuum benthos sampler for collecting demersal fish eggs from gravel substratum

We used two densities of eggs (low=900 eggs/m 2 ; high=5100 eggs/m 2 ) in laboratory experiments to estimate the recovery efficiency of the Brown benthos sampler for collecting fish eggs from gravel substrate and to determine if differences (e. g., 5-fold) in egg density in the substratum could be detected with the sampler. The mean egg recovery efficiency of the sampler in the low and high density treatments was 30% (SE=8.7) and 35% (SE=3.8), respectively. The difference between the treatment means was not significant. Therefore, data from the two treatments were pooled and used to estimate the recovery efficiency of the sampler (32.7%, SE=4.4). However, we were able to detect a 5× difference in the number of eggs collected with the sampler between the two treatments. Our estimate of the recovery efficiency of the sampler for collecting fish eggs was less than those reported for the sampler's efficiency for collecting benthic macroinvertebrates. The low recovery efficiency of the sampler for collecting fish eggs does not lessen the utility of the device. Rather, ecologists planning to use the sampler must estimate the recovery efficiency of target fauna, especially if density estimates are to be calculated, because recovery efficiency probably is less than 100%.

Ecology of Freshwater Fish↗
USGS2006

Bioenergetic relations in submerged aquatic vegetation: An experimental test of prey use by juvenile bluegills

We experimentally tested the hypotheses that bluegills in vegetated habitats grow more rapidly than in nonvegetated habitats because (1) vegetated habitats contain a greater caloric density and (2) are less susceptible to energetic depletion. The 10-week experiment was conducted in enclosures containing factorial combinations of the presence or absence of Vallisneria americana and juvenile bluegills Lepomis macrochirus. After 6 weeks, Vallisneria-only treatments contained a mean of 1048 cal/m2 in the benthos, whereas treatments with both Vallisneria and bluegills contained 610 cal/m2. Hyalella azteca, a preferred prey of bluegill, were nearly depleted in nonvegetated enclosures, whereas Hyalella densities in enclosures with Vallisneria were much less effected by fish. Bluegill growth was significantly greater with Vallisneria than without but declining water temperatures after week 6 resulted in slower growth despite abundant prey. Ultimately, growth of bluegill resulted from an interaction between availability and ingestion of prey, and water temperature. ?? Munksgaard, 1998.

Ecology of Freshwater Fish↗
USGS2006

Seasonal variation in habitat use by marsh fishes

We used I-m 2 throw traps to examine habitat use by smallsized fishes within a mosaic of wet prairies and sloughs in the headwaters of the St. Johns River, Florida between August 1992 and November 1995. Estimates of total fish density and biomass varied temporally, but did not differ significantly between habitats. Patterns of habitat use, however, differed among the five numerically dominant species. Bluefin killifish, mosquitofish, and golden topminnows were more abundant in sloughs than in wet prairies. In contrast, Everglades pygmy sunfish were more abundant in wet prairies than in sloughs. Finally, the abundance of least killifish did not differ between habitats. Fish densities were positively correlated with plant biomass (i. e., habitat complexity) and negatively correlated with water depth (i. e., hydrology). Species richness and composition were similar among habitats. However, consistent differences in the relative abundance of numerically dominant species between habitats indicated some degree of habitat-specific assemblage structure. Most species were concentrated into deeper sloughs during drying events. This assemblage of small-sized fishes appears to respond relatively rapidly to changes in habitat structure and hydrologic conditions. We therefore recommend that resource managers consider using fishes as indicator taxa to evaluate the efficacy of ongoing restoration and management efforts in wetland systems.

Florida↗
USGS2003

Diel distribution of age-0 largemouth bass, Micropterus salmoides, in B. E. Jordan Lake, North Carolina (USA) and its relation to cover

We used prepositioned area electrofishers (PAEs, 10×1.5 m) to assess diel differences in distribution of age-0 largemouth bass, Micropterus salmoides , in August 1992–1993 in a paired sampling design. PAEs were placed parallel to shore in an embayment of an unvegetated reservoir (B. E. Jordan Lake, North Carolina, USA). The catch per unit effort (CPUE=fish/PAE) was significantly higher at night than during the day in both years, indicating that age-0 largemouth bass exhibit nocturnal inshore movements. Age-0 largemouth bass captured inshore during day were smaller than those captured at night, indicating that movement patterns may change ontogenetically. Inshore-offshore movements of age-0 largemouth bass were significantly reduced in the presence of cover, suggesting that diel movements were influenced by specific habitat components. Diel movements likely were related to foraging, resting and predator avoidance behavior and could affect population dynamics and introduce bias in assessment programs.

North Carolina↗
USGS2004

Assessing the potential for fish predation to impact zebra mussels (Dreissena polymorpha): Insight from bioenergetics models

Rates of annual food consumption and biomass were modeled for several fish species across representative rivers and lakes in eastern North America. Results were combined to assess the relative potential of fish predation to impact zebra mussels (Dreissena polymorpha). Predicted annual food consumption by fishes in southern waters was over 100% greater than that in northern systems because of warmer annual water temperatures and presumed increases in metabolic demand. Although generally increasing with latitude, biomasses of several key zebra mussel fish predators did not change significantly across latitudes. Biomasses of some less abundant fish predators did increase significantly with latitude, but increases were not of the magnitude to offset predicted decreases in food consumption. Our results generally support the premise that fishes in rivers and lakes of the southern United States (U.S.) have inherently greater potential to impact zebra mussels by predation. Our simulations may provide a partial explanation of why zebra mussel invasions have not been as rapid and widespread in southern U.S. waters compared to the Great Lakes region. ?? Blackwell Munksgaard, 2004.

Ecology of Freshwater Fish↗