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At least 1,153 records · Page 64Linked to original sources
USGS2026

Putting weight to work: A review and examples of weight-based indicators in freshwater fish stock assessment

Despite being a direct measure of biomass and central to fisheries management, weight-based metrics remain underutilized in freshwater fish stock assessment. Here, we present a concise review of the application of weight in evaluating freshwater fish populations. We examine the historical use of weighing, assess how weight is applied across subdisciplines of freshwater fish science, contrast weight- and length-based approaches, and identify biases in their application. We then synthesize weight-based metrics, indices, and models within four broad categories—population and community weight structure; condition, growth, and efficiency; reproductive potential and production; and yield and exploitation dynamics—highlighting approaches that inform fish ecology, population and community dynamics, and vital rates. We conclude by identifying key opportunities and methodological innovations needed to expand the effective use of weight-based metrics in freshwater fish conservation and management.

North American Journal of Fisheries Management↗
USGS2025

Decadal stability in stream fish communities and contemporary ecological drivers of species occupancy in two Appalachian U.S. National Parks

Objective Although conserving fish biodiversity in lotic systems is challenging, protected areas can provide refuge from certain environmental stressors. In the Appalachian region, USA, the National Park Service manages Delaware Water Gap National Recreation Area (DEWA) and New River Gorge National Park & Preserve (NERI), which contain abundant and diverse freshwater resources. To assess the effectiveness of these protected areas in conserving stream fishes, we evaluated decadal changes and ecological drivers of species occupancy and detection. Methods Using fish assemblage data from backpack electrofishing surveys conducted in both parks during 2013–2014 and 2022–2023, we quantified temporal differences in species occupancy and detection probabilities using a Bayesian hierarchical multispecies occupancy modeling approach. For the 2022–2023 survey, we included habitat variables as predictors of occupancy and detection. Results Community composition and occupancy probabilities for species in both parks remained similar through time, with the most recent occupancy estimates ranging from 0.07 (90% CI = 0.02, 0.14) for Variegate Darter Etheostoma variatum and Rainbow Darter E. ­caeruleum to 0.73 (90% credible interval = 0.59, 0.85) for Blacknose Dace Rhinichthys atratulus . Changes in occupancy were more prominent at Delaware Water Gap National Recreation Area than New River Gorge National Park & Preserve, with Yellow Perch Perca flavescens having a posterior mean difference of −0.17 [90% credible interval = −0.35, −0.01] and American Eel Anguilla rostrata having a high posterior probability (>80%) of occupancy increasing by at least 1%. Habitat variables were related to community structure, but effects varied in significance, magnitude, and direction among species and parks. Conversely, species-specific detection probabilities were comparatively less affected by environmental and sampling effort predictors. Conclusions Between 2013 and 2023, occupancy estimates for 44 fish species across two protected, ecologically diverse landscapes remained relatively stable. Furthermore, we highlight the efficacy of national parks in maintaining freshwater fish biodiversity amidst rapid global change.

New Jersey, Pennsylvania, West Virginia↗
USGS2020

Wait and snap: eastern snapping turtles (Chelydra serpentina) prey on migratory fish at road-stream crossing culverts

There is growing evidence that culverts at road-stream crossings can increase fish density by reducing stream width and fish movement rates, making these passageways ideal predator ambush locations. In this study, we used a combination of videography and δ 13 C stable isotope analyses to investigate predator–prey interactions at a road-stream crossing culvert. Eastern snapping turtles ( Chelydra serpentina ) were found to regularly reside within the culvert to ambush migratory river herring ( Alosa spp.). Resident fish species displayed avoidance of the snapping turtles, resulting in zero attempted attacks on these fish. In contrast, river herring did not display avoidance and were attacked by a snapping turtle on 79% of approaches with a 15% capture rate. Stable isotope analyses identified an apparent shift in turtle diet to consumption of river herring in turtles from culvert sites that was not observed in individuals from non-culvert sites. These findings suggest that anthropogenic barriers like culverts that are designed to allow passage may create predation opportunities by serving as a bottleneck to resident and migrant fish movement.

Biology Letters↗
USGS2016

Fishing diseased abalone to promote yield and conservation

Past theoretical models suggest fishing disease-impacted stocks can reduce parasite transmission, but this is a good management strategy only when the exploitation required to reduce transmission does not overfish the stock. We applied this concept to a red abalone fishery so impacted by an infectious disease (withering syndrome) that stock densities plummeted and managers closed the fishery. In addition to the non-selective fishing strategy considered by past disease-fishing models, we modelled targeting (culling) infected individuals, which is plausible in red abalone because modern diagnostic tools can determine infection without harming landed abalone and the diagnostic cost is minor relative to the catch value. The non-selective abalone fishing required to eradicate parasites exceeded thresholds for abalone sustainability, but targeting infected abalone allowed the fishery to generate yield and reduce parasite prevalence while maintaining stock densities at or above the densities attainable if the population was closed to fishing. The effect was strong enough that stock and yield increased even when the catch was one-third uninfected abalone. These results could apply to other fisheries as the diagnostic costs decline relative to catch value.

Philosophical Transactions of the Royal Society B:↗
USGS2015

Aquatic pollution increases use of terrestrial prey subsidies by stream fish

Stream food webs are connected with their riparian zones through cross-ecosystem movements of energy and nutrients. The use and impact of terrestrial subsidies on aquatic consumers is determined in part by in situ biomass of aquatic prey. Thus, stressors such as aquatic pollutants that greatly reduce aquatic secondary production could increase the need for and reliance of stream consumers on terrestrial resource subsidies. To test this hypothesis, we surveyed stream fish, their diets and resource availability in 16 subalpine streams over a regional gradient of trace metals known to strongly impact aquatic insect communities (i.e. fish prey) in the Colorado Rocky Mountains, USA. Fish increased their reliance on terrestrial insect prey as stream metals increased. Relative biomass of terrestrial insects in stomach contents of Brook and Brown Trout increased with respect to aquatic insect biomass and total stomach contents. Drifting insect biomass showed a declining trend for aquatic, but not terrestrial insects, over the metal gradient. Trout densities were unrelated to metal concentrations in streams where we found fish. Synthesis and applications . Our results indicate that diets of aquatic consumers can become more terrestrial as aquatic stressors that limit in situ food production increase and that these subsidies may compensate for loss of aquatic resources. This work implies an important connection between preserving aquatic–terrestrial linkages and management of fish populations in stressed watersheds. Specifically, intact riparian zones and aquatic–terrestrial linkages are likely to be important for maintaining trout production in streams with moderate metal contamination.

Colorado↗
USGS2019

Anthropogenic land‐use change intensifies the effect of low flows on stream fishes

As ecosystems experience simultaneous disturbances, it is critical to understand how multiple stressors interact to affect ecological change. Land‐use change and extreme flow events are two important stressors that could interact to affect fish populations. We evaluated the individual and interactive effects of discharge and land‐use change associated with oil and natural gas development on populations of two stream fishes over a 7‐year period. We used repeated‐state (i.e. abundance trends) and rate (i.e. colonization and persistence) responses to advance our understanding of flow‐ecology relationships in a multiple‐stressor framework. Overall, fish abundance, colonization and persistence declined as discharge decreased. The effect of land‐use change associated with oil and natural gas development differed between species, with the abundance of Mottled Sculpin declining and Mountain Sucker increasing as land‐use change increased. We found both synergistic and antagonistic interactions between discharge and land‐use change. Land‐use change intensified the effect of low flows for Mottled Sculpin and lead to greater variability in responses to flow for Mountain Sucker. These differences between species' responses are likely due to differences in their physiological tolerances and behavioural adaptations to disturbance. Synthesis and applications . Our research provides empirical evidence for the complex interactions that can arise between discharge and anthropogenic land‐use change. Management efforts to reduce inputs of sediments and chemical contaminants associated with land‐use change (e.g. silt fences, vegetative buffers) and promote quality refuge habitats (i.e. in‐stream habitat restoration) could help mitigate the negative effects of low‐flow extremes on stream fishes. Further development of flow‐ecology relationships in a multiple‐stressor framework will help guide management of stream fishes, and provide a better understanding of the mechanisms underlying responses of different species.

Wyoming↗
USGS2025

Unobserved individual and population level impacts of fishing gear entanglements on North Atlantic right whales

Fishing gear entanglements can compromise health and lower survival and reproductive output of wildlife, which can slow population growth or cause population declines. However, entanglements may go unobserved, making it difficult to quantify their effects on individuals' vital rates and a population's trajectory. Fishing gear entanglements are a leading cause of death for North Atlantic right whales, Eubalaena glacialis , an endangered species whose population has declined substantially over the last decade. Key sources of observation error have not been addressed when quantifying the effects of entanglement on this species. We formulated a hidden Markov model that integrated 28 years of photo identification records, visual health assessments, entanglement assessments, and hormone assays to estimate body condition dynamics, and entanglement, survival, and reproductive rates of female North Atlantic right whales. The model also accounted for observation errors, including entanglements and reproductive events that were unobserved. Whales entangled in fishing gear were drastically more likely to experience declines in body condition and had lower survival rates than whales that were not entangled. Additionally, only whales in good body condition became pregnant. Between 1994 and 2021 entanglements reduced the expected number of calves born by 12.9% (95% credible interval: 8.2%–19.6%) and the expected number of females alive at the end of 2021 by 18.5% (95% credible interval: 8.6%–29.4%). Fishing gear entanglements have reduced the North Atlantic right whale population's capacity to recover and have increased the importance of the health and survival of the remaining living whales. Therefore, reducing the risk of fishing gear entanglements is likely necessary for the population to recover.

Animal Conservation↗
USGS2022

Reducing uncertainty in climate change responses of inland fishes: A decision-path approach

Climate change will continue to be an important consideration for conservation practitioners. However, uncertainty in identifying appropriate management strategies, particularly for understudied species and regions, constrains the implementation of science-based solutions and adaptation strategies. Here, we share a decision-path approach to reduce uncertainty in climate change responses of inland fishes to inform conservation and adaptation planning. With the Fish and Climate Change database (FiCli), a comprehensive, online, public database of peer-reviewed literature on documented and projected climate impacts to inland fishes, users can identify relevant studies and associated management recommendations via geographic regions, response types (i.e., fish assemblage dynamics, demographic, distributional, evolutionary, phenological), fish taxa, and traits (e.g., thermal guilds, feeding type, parental care, habitat type) and use a suite of summary tools to make more informed decisions. For both data-rich and data-poor scenarios, we demonstrate that this approach can reduce uncertainty in understanding climate change responses. Using thermal sensitivity as an example, we also establish the utility of FiCli database to address other user-defined, management-relevant questions via supplementary analyses. This decision-path approach can be applied to rapid assessments, management decisions, and policy development and may serve as a model for other conservation decision-making processes.

Conservation Science and Practice↗
USGS2017

Seventy years of stream‐fish collections reveal invasions and native range contractions in an Appalachian (USA) watershed

Aim Knowledge of expanding and contracting ranges is critical for monitoring invasions and assessing conservation status, yet reliable data on distributional trends are lacking for most freshwater species. We developed a quantitative technique to detect the sign (expansion or contraction) and functional form of range‐size changes for freshwater species based on collections data, while accounting for possible biases due to variable collection effort. We applied this technique to quantify stream‐fish range expansions and contractions in a highly invaded river system. Location Upper and middle New River (UMNR) basin, Appalachian Mountains, USA. Methods We compiled a 77‐year stream‐fish collections dataset partitioned into ten time periods. To account for variable collection effort among time periods, we aggregated the collections into 100 watersheds and expressed a species’ range size as detections per watershed (HUC) sampled (DPHS). We regressed DPHS against time by species and used an information‐theoretic approach to compare linear and nonlinear functional forms fitted to the data points and to classify each species as spreader, stable or decliner. Results We analysed changes in range size for 74 UMNR fishes, including 35 native and 39 established introduced species. We classified the majority (51%) of introduced species as spreaders, compared to 31% of natives. An exponential functional form fits best for 84% of spreaders. Three natives were among the most rapid spreaders. All four decliners were New River natives. Main conclusions Our DPHS‐based approach facilitated quantitative analyses of distributional trends for stream fishes based on collections data. Partitioning the dataset into multiple time periods allowed us to distinguish long‐term trends from population fluctuations and to examine nonlinear forms of spread. Our framework sets the stage for further study of drivers of stream‐fish invasions and declines in the UMNR and is widely transferable to other freshwater taxa and geographic regions.

North Carolina, Virginia↗
USGS2021

A new composite abundance metric detects stream fish declines and community homogenization during six decades of invasions

Aim We developed a new technique, utilizing species-specific counts of individuals from historical fish community samples, to examine landscape-level, spatio-temporal trends in relative abundance distributions. Abundance-based historical distribution analyses are often plagued by data comparability issues, but provide critical information about community composition trends inaccessible to those using analyses based only on species presence–absence. We established trends in native and non-native fish abundance and community homogenization, uniqueness and diversity to help local conservation managers prioritize targets and motivate similar studies globally to support fish conservation. Location Upper and middle New River (UMNR) basin, Appalachian Mountains, USA. Methods We compiled catch data from 61 years of fish community surveys (1958–2019) and tested for community homogenization by comparing data from repeatedly sampled sites (1900s versus 2000s samples) using dispersion analyses. We measured community uniqueness (site contributions to beta diversity) and species diversity (Shannon index) at sampled streams to identify potential conservation hotspots. We then used regression analyses and Wilcoxon signed-rank tests to examine species-specific basin-wide and local abundance trends and identify species of potential conservation concern. Results Dispersion of sites in species abundance space was significantly greater in the 1900s compared with the 2000s, indicating homogenization had occurred. Of 36 native species analysed, 44.4% (16) showed basin-wide declines. Non-native species exhibited mixed patterns; site-level abundance increased in 2 of 15 species analysed (13%). Main conclusions Our results indicate basin-wide community homogenization has occurred within the UMNR, but many unique and diverse communities persist. If conserved, these could help maintain regional fish diversity. We found basin-wide declines in four endemic species, as well as spread patterns of non-native and native species that were not detected by a presence–absence analysis applied within the same study area. This finding illustrates the importance of considering both species’ abundance and occurrence patterns as separate dimensions of biodiversity to inform conservation planning.

North Carolina, Virginia, West Virginia↗
USGS2022

Resource selection and species interactions between native and non-native fishes in a simulated stream system

Effective fishery management necessitates understanding of resource partitioning by fishes that inhabit complex systems composed of biotic and abiotic features. Evaluations of non-native species introductions have continually demonstrated adverse effects associated with abundance and distribution of native fishes. Therefore, understanding resource selection and interactions between native and non-native species is important for recovery efforts. Habitat use by two native fish species (largescale sucker Catostomus macrocheilus [Girard] and mountain whitefish Prosopium williamsoni [Girard]) and one non-native fish species (pumpkinseed Lepomis gibbosus [Linnaeus]) of the Kootenai River, Idaho, were evaluated in a laboratory stream system. Trials were conducted in allopatry and in sympatry with and without the presence of wood to describe habitat selection in the context of on-going habitat rehabilitation efforts. Interactions were evident between native largescale sucker and non-native pumpkinseed concerning use of a woody structure and current velocity. Mountain whitefish used low-velocity habitats and selected locations that were further from wood when in sympatry with pumpkinseed. Our research suggests that habitat use of native, large-river fishes may be influenced by the presence of a non-native species, and that considering such interactions is critical when designing and implementing habitat rehabilitation efforts in river ecosystems.

Fisheries Management and Ecology↗
USGS2018

The spatial scale of biotic change in Chihuahuan Desert fish assemblages

1. We examined riverine desert fish assemblages in the Chihuahuan Desert, USA at multiple spatial scales of similarity to assess long-term changes to assemblage distinctiveness, identify individual species responsible for changes, and determine the importance of geographic context and species resolution in interpreting patterns of change. 2. We used a well-documented historical data set on fish distribution and abundance, and recent collections of fishes that provided a paired analytical design across 36 localities spanning nearly three decades of time. Patterns of faunal homogenization and differentiation were assessed at basin-wide, sub-basin and river-reach scales with species occurrence and relative abundance data. Individual species responses were examined to identify the drivers of assemblage change across time. 3. Patterns of similarity varied across spatial scales and produced seemingly incongruous trends in assemblage similarity across time. Patterns of assemblage distinctiveness depended on the spatial extent of the analyses, the geographical structuring of the fish assemblages, and whether occurrence or relative abundance data were used. These dependencies led to interesting and conflicting patterns of homogenization and differentiation. The Rio Grande sub-basin showed strong homogenization with convergence between upstream and downstream reaches that corresponded to declining water quality and quantity from the Rio Conchos in Mexico. In contrast, the Pecos River sub-basin showed strong differentiation between upstream and downstream reaches that corresponded to the successful colonization and spread of the non-native gulf killifish (Fundulus grandis) in the highly degraded upper reach. Spatial variability in fish assemblages and their degree of change from historical conditions were largely dependent on anthropogenic modifications to the flow regime and variability in the success of invasive gulf killifish in the basin. 4. The use of species occurrence or abundance data, and the spatial scale of analysis are crucial choices in studies of faunal homogenization and differentiation, and we have demonstrated how these choices lead to variable results for our study system. Our multi-scale approach and examination of individual species responses identified the ultimate drivers of these differences and illustrated the importance of scale-dependent effects and geographical context on patterns of assemblage distinctiveness, especially with regard to species invasion, species loss and abundance shifts.

Texas↗
USGS2020

Forecasting the combined effects of anticipated climate change and agricultural conservation practices on fish recruitment dynamics in Lake Erie

Many aquatic ecosystems are experiencing multiple anthropogenic stressors that threaten their ability to support ecologically and economically important fish species. Two of the most ubiquitous stressors are climate change and non‐point source nutrient pollution. Agricultural conservation practices (ACPs, i.e. farming practices that reduce runoff, prevent erosion, and curb excessive nutrient loading) offer a potential means to mitigate the negative effects of non‐point source pollution on fish populations. However, our understanding of how ACP implementation amidst a changing climate will affect fish production in large ecosystems that receive substantial upstream sediment and nutrient inputs remains incomplete. Towards this end, we explored how anticipated climate change and the implementation of realistic ACPs might alter the recruitment dynamics of three fish populations (native walleye Sander vitreus and yellow perch Perca flavescens and invasive white perch Morone americana ) in the highly productive, dynamic west basin of Lake Erie. We projected future (2020–2065) recruitment under different combinations of anticipated climate change ( n = 2 levels) and ACP implementation ( n = 4 levels) in the western Lake Erie catchment using predictive biological models driven by forecasted winter severity, spring warming rate, and Maumee River total phosphorus loads that were generated from linked climate, catchment‐hydrology, and agricultural‐practice‐simulation models. In general, our models projected reduced walleye and yellow perch recruitment whereas invasive white perch recruitment was projected to remain stable or increase relative to the recent past. Our modelling also suggests the potential for trade‐offs, as ACP implementation was projected to reduce yellow perch recruitment with anticipated climate change. Overall, our study presents a useful modelling framework to forecast fish recruitment in Lake Erie and elsewhere, as well as offering projections and new avenues of research that could help resource management agencies and policy‐makers develop adaptive and resilient management strategies in the face of anticipated climate and land‐management change.

Michigan, Ohio, Indiana↗
USGS2023

Fish functional gradients along a reservoir cascade

1.The transformations of fish assemblages caused by reservoir cascades can be severe at the reach scale, but basin-scale effects are less clear. However, prevailing river concepts provide a framework for predicting basin-scale effects. 2. To determine if predictions made by the River Continuum Concept relative to the function of fish assemblages are sustained in a temperate river transformed into a reservoir cascade, we examined longitudinal trends in the distribution of fish functional traits over 23 reservoirs of the Tennessee River, USA. 3. In all, 115 species were recorded representing 62 traits, with trait richness increasing longitudinally in a downstream direction. Trophic, reproductive, and habitat traits showed various increasing and decreasing patterns up and down the reservoir cascade. The observed gradients in trait richness and trait distributions were generally consistent with those expected in unregulated rivers, with few unexpected results. 4. The transformation of lotic systems into lentic ones has changed habitats and sources of food and encouraged the proliferation of certain feeding (e.g., detritivores, planktivores, invertivores, piscivores), reproduction (e.g., nest spawners polyphils, broadcast spawners phytolithophils), and habitat (slow current, lacustrine, large river) traits. In essence, reservoirs have expanded downstream habitats in an upstream direction, and thus allowed upstream expansion of species and traits that would have normally not been well represented in upper reaches of the Tennessee River basin. Nevertheless, the impounded Tennessee River has maintained much of its functional integrity, despite extensive alterations to the riverscape. 5. We suggest that while reservoirs have been shown to have major local-scale effects on riverine fish assemblages, with access to riverine habitats, and with proactive conservation strategies, fish functional richness can remain remarkably high at the basin scale.

Alabama, Georgia, Kentucky, North Carolina, South ↗
USGS2024

Fish assemblage and functional trait responses to small-dam removal

Dams are one of the greatest threats to freshwater biodiversity and efforts to remove dams to restore riverine systems are increasing. However, dam-removal studies have primarily focused on taxonomic responses to large dam removals with little work on the functional trait responses of fish to small-dam removals; such a focus limits the application of results in regions with different taxonomic compositions. We explored taxonomic and functional trait responses of fish assemblages to two small-dam removals over 10 years using a Multiple Before After Control Impact design at a dammed and an undammed river. Eight life-history traits were used to calculate functional diversity (RaoQ) and determine the position of each fish species within a multivariate life-history space relative to three life-history strategy endpoints: opportunistic, periodic, and equilibrium. The distance of each species relative to these endpoints was used to calculate community weighted means (CWM), allowing us to examine the shift in life-history strategy of a given assemblage after dam removal. Based on life-history theory, we predicted a decrease in the CWM of equilibrium strategists and an increase in the CWM opportunistic strategists after dam removal. For the dammed river, we observed changes in assemblage structure at both the control and impact sites driven primarily by shifts from a lentic to lotic assemblage, with the most apparent change occurring in the formerly impounded sites. These changes tended to occur within 1 year, suggesting rapid colonization by lotic species after habitat change. By contrast, no change in assemblage structure was found for the undammed river, suggesting that dam removal was the primary driver of the shifts in assemblage structure observed in the dammed river. We found no change in the CWM of periodic strategists or RaoQ of all life-history traits at any site after dam removal. Based on CWM, life-history strategies shifted in response to dam removal at impounded sites where equilibrium strategists decreased and opportunistic strategists tended to increase after the impounded sites changed from a stable lentic environment to an unstable lotic environment, supporting predictions made by life-history theory. Our results suggest that small-dam removal may provide ecological benefits by restoring fish assemblages to a more natural riverine state and reversing the negative effects of dam construction on the ecosystem. We demonstrate that combining both trait-based and taxonomic approaches can improve our ecological understanding of the impacts of dam removal on fish assemblages and provide relevant data for local management.

South Carolina↗
USGS2025

How accurately does eDNA reflect the spatial distribution of cold-water fish? Field validation from a temperate lake

Applications of environmental DNA (eDNA) based detection technology to evaluate the distribution of aquatic organisms are increasing; yet field validations of eDNA are important to measure accuracy in study systems. To successfully apply this technology to species conservation, it is critical to understand how both species biology and environmental conditions affect the accuracy of inference from eDNA detection data. We implemented a field assessment of the accuracy and spatial resolution of eDNA-based species distributions for a native cold-water, schooling fish, cisco Coregonus artedi , that has been reintroduced to a deep temperate lake. We leveraged a combination of acoustic telemetry, providing known spatial locations of tagged fish, and lake-wide eDNA sampling to infer their distribution in Keuka Lake, New York, USA. Sub-surface (12 m and 18 m depths) eDNA samples were collected to accommodate the diel vertical migration behaviour of this fish species. The results of this study validated the accuracy of positive eDNA detections with the distribution of tagged fish to coarse spatial scales. Yet, several fine-scale locations revealed a mismatch between eDNA and acoustic telemetry detections; consistent with rapid transport of genetic material via lake currents. Empirical measurements of lake currents using drifters found cisco eDNA detections could deviate from specimens' source locations by as much as 3.3 km at 12 m depth or 1.5 km at 18 m depth over a 24 h transport period. Our study indicates that accurate species distributions estimated from eDNA sampling in lakes may require further understanding of transport mechanisms and persistence of environmental genetic material to relate point detections to source animal locations. Integrating eDNA sampling with additional data collection of species biology and environmental conditions will increase the spatial resolution of fish distribution assessments.

New York↗
USGS2010

Seasonal and interannual effects of hypoxia on fish habitat quality in central Lake Erie

1. Hypoxia occurs seasonally in many stratified coastal marine and freshwater ecosystems when bottom dissolved oxygen (DO) concentrations are depleted below 2–3 mg O 2 L -1 . 2. We evaluated the effects of hypoxia on fish habitat quality in the central basin of Lake Erie from 1987 to 2005, using bioenergetic growth rate potential (GRP) as a proxy for habitat quality. We compared the effect of hypoxia on habitat quality of (i) rainbow smelt, Osmerus mordax mordax Mitchill (young-of-year, YOY, and adult), a cold-water planktivore, (ii) emerald shiner, Notropis atherinoides Rafinesque (adult), a warm-water planktivore, (iii) yellow perch, Perca flavescens Mitchill (YOY and adult), a cool-water benthopelagic omnivore and (iv) round goby Neogobius melanostomus Pallas (adult) a eurythermal benthivore. Annual thermal and DO profiles were generated from 1D thermal and DO hydrodynamics models developed for Lake Erie’s central basin. 3. Hypoxia occurred annually, typically from mid-July to mid-October, which spatially and temporally overlaps with otherwise high benthic habitat quality. Hypoxia reduced the habitat quality across fish species and life stages, but the magnitude of the reduction varied both among and within species because of the differences in tolerance to low DO levels and warm-water temperatures. 4. Across years, trends in habitat quality mirrored trends in phosphorus concentration and water column oxygen demand in central Lake Erie. The per cent reduction in habitat quality owing to hypoxia was greatest for adult rainbow smelt and round goby (mean: -35%), followed by adult emerald shiner (mean: -12%), YOY rainbow smelt (mean: -10%) and YOY and adult yellow perch (mean: -8.5%). 5. Our results highlight the importance of differential spatiotemporally interactive effects of DO and temperature on relative fish habitat quality and quantity. These effects have the potential to influence the performance of individual fish species as well as population dynamics, trophic interactions and fish community structure.

Lake Erie↗
USGS2010

Do larval fishes exhibit diel drift patterns in a large, turbid river?

Previous research suggested larval fishes do not exhibit a diel drift cycle in turbid rivers (transparency <30 cm). We evaluated this hypothesis in the turbid, lower Missouri River, Missouri. We also reviewed diel patterns of larval drift over a range of transparencies in rivers worldwide. Larval fishes were collected from the Missouri River primary channel every 4 h per 24-h period during spring-summer 2002. Water transparency was measured during this period and summarized for previous years. Diel drift patterns were analyzed at the assemblage level and lower taxonomic levels for abundant groups. Day and night larval fish catch-per-unit-effort (CPUE) was compared for the entire May through August sampling period and spring (May - June) and summer (July - August) seasons separately. There were no significant differences between day and night CPUE at the assemblage level for the entire sampling period or for the spring and summer seasons. However, Hiodon alosoides, Carpiodes/Ictiobus spp. and Macrhybopsis spp. exhibited a diel cycle of abundance within the drift. This pattern was evident although mean Secchi depth (transparency) ranged from 4 to 25 cm during the study and was <30 cm from May through August over the previous nine years. Larval diel drift studies from 48 rivers excluding the Missouri River indicated the primary drift period for larval fishes was at night in 38 rivers and during the day for five, with the remaining rivers showing no pattern. Water transparency was reported for 10 rivers with six being <30 cm or 'low'. Two of these six turbid rivers exhibited significant diel drift patterns. The effect of water transparency on diel drift of larval fishes appears taxa-specific and patterns of abundant taxa could mask patterns of rare taxa when analyzed only at the assemblage level. ?? 2010 Blackwell Verlag, Berlin.

Journal of Applied Ichthyology↗