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Book review: Ecology of North American freshwater fishes

This book will be important in courses for upper undergraduates studying fish ecology or for graduate students. However, it will also be an excellent reference for the fishery manager who asks ‘Why does this fish do that?’. With the wealth of great information contained in Ross’ book, chances are an answer will be found. Review info: Ecology of North American freshwater fishes. Edited by Stephen T. Ross, 2013. ISBN: 978-0520249455, 408 pp.

Journal of Fish Biology

Biodiversity connections—‘ties that bind’

Connectivity is a foundational concept in ecology and conservation and was the organising theme for the 2022 Annual Meeting of the Southeastern Fishes Council, a professional organisation dedicated to the study and conservation of freshwater fishes native to the southeast region of the United States (US). We introduce a Special Contribution of six papers selected from presentations at that meeting that illustrate perspectives on connections created by fish migration and dispersal, evolved life histories and habitat affinities and interspecific facilitation. Although focused on streams of the southeast US, each of these topics is broadly relevant to freshwater fish conservation, particularly with respect to causes and consequences of migratory fish depletion, population fragmentation and species declines. Many other connections relevant to the ecology and conservation of freshwater fishes remain relatively unexplored but could substantively advance conservation. We highlight the potential that species evolutionary histories, that is connections through time, reconstructed using species distributions and phylogenies may improve predictions of species responses to environmental change. Identifying species interdependencies, including undiscovered interactions that support survival or reproduction, could provide insights into how species losses may cascade as aquatic communities unravel. Finally, efforts to elucidate diverse connections between people and freshwater biodiversity, particularly where fisheries are historic and streams mostly go unnoticed, may prove essential to building public support for conservation measures. A research agenda anchored on ‘biodiversity connections’ has the potential to advance ecological understanding and public engagement, elements essential to conserving freshwater fishes.

Ecology of Freshwater Fish

FishTraits: a database of ecological and life-history traits of freshwater fishes of the United States

The need for integrated and widely accessible sources of species traits data to facilitate studies of ecology, conservation, and management has motivated development of traits databases for various taxa. In spite of the increasing number of traits-based analyses of freshwater fishes in the United States, no consolidated database of traits of this group exists publicly, and much useful information on these species is documented only in obscure sources. The largely inaccessible and unconsolidated traits information makes large-scale analysis involving many fishes and/or traits particularly challenging. We have compiled a database of > 100 traits for 809 (731 native and 78 nonnative) fish species found in freshwaters of the conterminous United States, including 37 native families and 145 native genera. The database, named Fish Traits, contains information on four major categories of traits: (1) trophic ecology; (2) body size, reproductive ecology, and life history; (3) habitat preferences; and (4) salinity and temperature tolerances. Information on geographic distribution and conservation status was also compiled. The database enhances many opportunities for conducting research on fish species traits and constitutes the first step toward establishing a central repository for a continually expanding set of traits of North American fishes.

Fisheries

A moving target—incorporating knowledge of the spatial ecology of fish into the assessment and management of freshwater fish populations

Freshwater fish move vertically and horizontally through the aquatic landscape for a variety of reasons, such as to find and exploit patchy resources or to locate essential habitats (e.g., for spawning). Inherent challenges exist with the assessment of fish populations because they are moving targets. We submit that quantifying and describing the spatial ecology of fish and their habitat is an important component of freshwater fishery assessment and management. With a growing number of tools available for studying the spatial ecology of fishes (e.g., telemetry, population genetics, hydroacoustics, otolith microchemistry, stable isotope analysis), new knowledge can now be generated and incorporated into biological assessment and fishery management. For example, knowing when, where, and how to deploy assessment gears is essential to inform, refine, or calibrate assessment protocols. Such information is also useful for quantifying or avoiding bycatch of imperiled species. Knowledge of habitat connectivity and usage can identify critically important migration corridors and habitats and can be used to improve our understanding of variables that influence spatial structuring of fish populations. Similarly, demographic processes are partly driven by the behavior of fish and mediated by environmental drivers. Information on these processes is critical to the development and application of realistic population dynamics models. Collectively, biological assessment, when informed by knowledge of spatial ecology, can provide managers with the ability to understand how and when fish and their habitats may be exposed to different threats. Naturally, this knowledge helps to better evaluate or develop strategies to protect the long-term viability of fishery production. Failure to understand the spatial ecology of fishes and to incorporate spatiotemporal data can bias population assessments and forecasts and potentially lead to ineffective or counterproductive management actions.

Environmental Monitoring and Assessment

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.

southeastern United States

Generalist feeding strategies in Arctic freshwater fish: A mechanism for dealing with extreme environments

Generalist feeding strategies are favoured in stressful or variable environments where flexibility in ecological traits is beneficial. Species that feed across multiple habitat types and trophic levels may impart stability on food webs through the use of readily available, alternative energy pools. In lakes, generalist fish species may take advantage of spatially and temporally variable prey by consuming both benthic and pelagic prey to meet their energy demands. Using stomach content and stable isotope analyses, we examined the feeding habits of fish species in Alaska's Arctic Coastal Plain (ACP) lakes to determine the prevalence of generalist feeding strategies as a mechanism for persistence in extreme environments (e.g. low productivity, extreme cold and short growing season). Generalist and flexible feeding strategies were evident in five common fish species. Fish fed on benthic and pelagic (or nektonic) prey and across trophic levels. Three species were clearly omnivorous, feeding on fish and their shared invertebrate prey. Dietary differences based on stomach content analysis often exceeded 70%, and overlap in dietary niches based on shared isotopic space varied from zero to 40%. Metrics of community‐wide trophic structure varied with the number and identity of species involved and on the dietary overlap and niche size of individual fishes. Accumulation of energy from shared carbon sources by Arctic fishes creates redundancy in food webs, increasing likely resistance to perturbations or stochastic events. Therefore, the generalist and omnivorous feeding strategies employed by ACP fish may maintain energy flow and food web stability in extreme environments.

Ecology of Freshwater Fish

Mismatch between temperature and discharge disrupts spawning cues in a fluvial specialist, blue sucker Cycleptus elongatus

Seasonal movements cued by environmental variables are a critical component of riverine fish life history. Life-history events for species such as blue sucker Cycleptus elongatus are likely cued by discharge and temperature and may be disrupted if those life-history events and environmental regimes are mismatched. However, this effect may be dependent upon the habitat occupied when environmental cues are received by individuals. We tracked telemetered blue sucker in the Colorado River, Texas, USA, from 2015 to 2017 and modelled the relative effects of discharge, temperature and habitat structure on seasonal movement patterns. Tagged fish varied in their propensity to move, although most returned to their original tagging locations. Decreasing temperatures and increasing discharge resulted in increased seasonal movements. Temperature and discharge had the largest effect on movement behaviour, but the magnitude of movements was largely dependent on the year. Temperatures between 12 and 19°C and discharges between 10 and 240 m 3 s −1 resulted in greater probabilities of spawning movements. Spawning was most probable in 2015 and reduced or halted in 2016 and 2017. Future climate scenarios suggest North America will experience increased drought, warmer temperatures and more variable weather patterns. These future scenarios could negatively impact blue sucker by disrupting environmental cues and habitat availability for seasonal life-history events. Our results suggest temperature and discharge are critical cues for the species, but that their combined effect is largely dependent on the occupied habitat.

Texas

Resource partitioning across a trophic gradient between a freshwater fish and an intraguild exotic

The introduction of exotic species has the potential to cause resource competition with native species and may lead to competitive exclusion when resources are limiting. On the other hand, information is lacking to predict under what alternate trophic conditions coexistence may occur. Comparing diets of native yellow perch Perca flavescens and nonindigenous white perch Morone americana , we examined variation in resource partitioning and body condition across a prominent longitudinal nutrient gradient in Lake Erie (north‐eastern United States, Canada). As measured with Analysis of Similarity and Schoener's index, diet similarity declined monotonically from west to east tracking declines in nutrients, productivity and relative abundance of both species. Additionally, diet similarity increased from spring through fall, following seasonal development of stratification and hypolimnetic hypoxia—phenomena which tend to increase spatial overlap between these species. Finally, relative weights of both species peaked in the Central Basin (relative weights > 0.85), which, on average, had intermediate values of prey diversity, ecosystem trophic status and water clarity. Our results highlight that native yellow perch coexist with invasive white perch under a wide range of trophic conditions. Of importance to fishery managers, mesotrophy in the Central Basin correlated with the highest body conditions and intermediate prey resource partitioning, although the effect size was small and variable. While competitive exclusion appears unlikely, the goal of reducing nutrient inputs in Lake Erie could affect not only the distributions of both species but also stakeholder decisions about where to fish.

Lake Erie

A call for global action to conserve native trout in the 21st century and beyond

Trout and char (hereafter, trout ) represent some of the more culturally, economically and ecologically important taxa of freshwater fishes worldwide (Kershner, Williams, Gresswell, & Lobón‐Cerviá, 2019a ). Native to all continents in the Northern Hemisphere (as well as western Mediterranean Africa), trout belong to seven genera ( Oncorhynchus , Salvelinus, Salmo , Hucho, Parahucho, Brachymystax and Salvethymus ), which are distributed across more than 60 countries (Muhlfeld et al., 2019 ). Despite their broad importance as indicators of biodiversity in cold‐water ecosystems (Haak & Williams, 2013 ), as well as cultural icons for food and recreation, nearly half of the world's recognised trout species (IUCN, 2018 ) are imperilled or at risk of global extinction (Muhlfeld et al., 2018 , 2019 ). The root causes of their vulnerability include broad‐scale alteration of landscapes and watersheds, dams, overharvest, pollution, interactions with hatchery‐bred conspecifics and non‐native species. However, emerging threats such as climate change and related problems such as the spread of diseases and parasites pose significant challenges and uncertainties to native trout and their habitats (Kovach et al., 2016 ; Muhlfeld et al., 2018 ). Ultimately, conservation of native trout depends on understanding their diversity, a willingness to address threats at their root causes and implementing progressive conservation solutions that promote persistence of these iconic species in the face of growing human pressures.

Ecology of Freshwater Fish

Ecology of stream fish: Insights gained from an individual-based approach to juvenile Atlantic salmon

Using data from an ongoing study of juvenile Atlantic salmon growth and survival in tributaries of the Connecticut River, USA, we compare standard population-level approaches to those focusing on individuals. We highlight the potential benefits of resampling individually tagged stream fish as compared to standard approaches. Specifically we focus on growth, survival, movements and population estimation. The advantages of estimating sizes and growth rates from individual size trajectories include obtaining growth histories and the ability to perform retrospective analysis of the consequences of different life-history strategies. An example might be the patterns of growth leading to either early maturity or migration. Resampling known individuals is the only way we know to chart both short-term and long-term movements and to assign growth and mortality consequences to such movements. Finally, individual-level data permit robust estimation of survival and density/abundance using methods such as Cormack/Jolly-Seber. The results indicate that population estimates were about 10% lower using individual data than using population data, that survival from sample to sample was typically >90%, that the majority of recaptured fish did not move during the summer, that growth was rapid during spring and most fish lost mass during the summer and that growth trajectories for maturing and non-maturing fish showed substantially different patterns. An individual-based approach to stream fish ecology provides the opportunity to explore the mechanisms responsible for population-level patterns but comes at the cost of significant field effort. Tradeoffs between increased data resolution and the effort required to obtain the data must be considered before undertaking individual-based field studies of stream fishes.

Massachusetts

Identifying across‐system sources of variation in a generalist freshwater fish: Correlates of total and size‐specific abundance of yellow perch

Variation in fish abundance across systems presents a challenge to our understanding of fish populations because it limits our ability to predict and transfer basic ecological principles to applied problems. Yellow perch ( Perca flavescens ) is an ideal species for exploring environmental and biotic correlates across system because it is widely distributed and physiologically tolerant. In 16 small, adjacent systems that span a wide range of environmental and biotic conditions, yellow perch were sampled with a standard suite of gear. Water quality, morphometry, vegetation, invertebrates and fish communities were concurrently measured. Multimodel inference was used to prioritise regressors for the entire yellow perch sample and three size groups (35-80, 81-180, ≥181 mm TL). Across systems, pH and fish richness were identified as the key drivers of yellow perch abundance. At very low pH (<4.0), few fish species and few yellow perch individuals were found. At ponds with moderately low pH (4.0–4.8), numbers of yellow perch increased. Ponds with high pH (>4.8) had many other species and few yellow perch. Similar patterns for pH and fish community were observed for the two largest‐size classes. Negative interactions were observed between the medium‐ and large‐sized yellow perch and between the largest and smallest yellow perch, although interspecific interactions were weaker than expected. This examination of variability for an indicator species and its component‐size classes provides ecological understanding that can help frame the larger‐scale sampling programs needed for the conservation of freshwater fish.

Ecology of Freshwater Fish

Nowhere to hide: The importance of instream cover for stream‐living Coastal Cutthroat Trout during seasonal low flow

Through their multiple functions, refuges may be important for stream‐living fishes, particularly during stressful events such as seasonal low flow or drought. Coastal Cutthroat Trout Oncorhynchus clarkii clarkii is an ideal study organism to understand the importance of refuge. During seasonal low flow, lower water levels limit access to refuge and emigration, survival of fish is low, and predation risk is high. Under these conditions, we studied patterns of cover use from field observations and tested predictions from multiple hypotheses about cover use in a semi‐natural experiment. Boulders were the main cover selected by trout in natural streams. Trout disproportionately used cover near deeper water, and they selected larger‐sized cover in shallower water. Trout showed plasticity to switch among behaviours, concealing under cover and emigrating as first options, followed by grouping, and then habitat shifting. Lack of feeding and growth suggested that perceived threat of predation was a more important driver of behaviour than foraging. Emigration was also linked to cover, with higher levels of emigration associated with less cover availability, revealing a potential link between refuge and demography through emigration. Except for feeding, the intensity of alternative behaviours can increase or decrease depending on refuge availability. Collectively, findings of this work indicate that cover can be considered a critical limiting resource along with other fundamental resources of food and space for stream‐living fish.

Ecology of Freshwater Fish

Population-level effects of egg predation on a native planktivore in a large freshwater lake

Using a 37-year recruitment time series, we uncovered a field pattern revealing a strong, inverse relationship between bloater Coregonus hoyi recruitment success and slimy sculpin Cottus cognatus biomass in Lake Michigan (United States), one of the largest freshwater lakes of the world. Given that slimy sculpins (and deepwater sculpin Myoxocephalus thompsonii) are known egg predators that spatiotemporally overlap with incubating bloater eggs, we used recently published data on sculpin diets and daily ration to model annual bloater egg consumption by sculpins for the 1973&ndash;2010 year-classes. Although several strong year-classes were produced in the late 1980s when the proportion of eggs consumed by slimy sculpins was extremely low (i.e., <0.001) and several weak year-classes were produced when the proportion of bloater eggs consumed was at its highest (i.e., >0.10&ndash;1.0), egg predation failed to explain why recruitment was weak for the 1995&ndash;2005 year-classes when the proportion consumed was also low (i.e., <0.02). We concluded that egg predation by slimy and deepwater sculpins could have limited bloater recruitment in some years, but that some undetermined factor was more important in many other years. Given that slimy sculpin densities are influenced by piscivorous lake trout Salvelinus namaycush, the restoration of which in Lake Michigan has lagged behind those in lakes Superior and Huron, our study highlights the importance of an ecosystem perspective when considering population dynamics of fishes.

Lake Michigan

Catchment-scale determinants of nonindigenous minnow richness in the eastern United States

Understanding the drivers of biological invasions is critical for preserving aquatic biodiversity. Stream fishes make excellent model taxa for examining mechanisms driving species introduction success because their distributions are naturally limited by catchment boundaries. In this study, we compared the relative importance of catchment-scale abiotic and biotic predictors of native and nonindigenous minnow (Cyprinidae) richness in 170 catchments throughout the eastern United States. We compared historic and contemporary cyprinid distributional data to determine catchment-wise native/nonindigenous status for 152 species. Catchment-scale model predictor variables described natural (elevation, precipitation, flow accumulation) and anthropogenic (developed land cover, number of dams) abiotic features, as well as native congener richness. Native congener richness may represent either biotic resistance via interspecific competition, or trait preadaptation according to Darwin's naturalisation hypothesis. We used generalised linear mixed models to examine evidence supporting the relative roles of abiotic and biotic predictors of cyprinid introduction success. Native congener richness was positively correlated with nonindigenous cyprinid richness and was the most important variable predicting nonindigenous cyprinid richness. Mean elevation had a weak positive effect, and effects of other abiotic factors were insignificant and less important. Our results suggest that at this spatial scale, trait preadaptation may be more important than intrageneric competition for determining richness of nonindigenous fishes.

Ecology of Freshwater Fish

Historical changes in fish communities in urban streams of the southeastern U.S. and the relative importance of water-quality stressors

A total of 71 stream sites representing a gradient of urban land use was sampled across the Piedmont of the southeastern U.S. in 2014. Fish data collected (observed) at each site were compared to an expected community based on georeferenced historical (~1950 - ~1990) species occurrence records for stream segments (1:100,000 scale) containing the sampled stream sites. Loss of expected fish species (percent of fish species expected to occur but not observed) and homogenization (difference in Jaccard’s similarity of the fish community among sites observed and expected) were determined. On average, there was a 13.2% increase in the similarity of fish communities across sites, demonstrating evidence of community homogenization. Occurrence of Redbreast Sunfish (Lepomis auritus), Green Sunfish (L. cyanellus), and Bluegill (L. macrochirus) increased more than 50% over time (between observed and expected). Species loss increased significantly with urbanization whereas homogenization was not related to urbanization. Random forest analysis indicated that herbicides, insecticides, and centrarchid species richness were significant predictors of species loss. Of these, generalized additive model regression indicated that herbicides represented the most parsimonious model based on a single predictor. Stream base flow, elevation, and total nitrogen were significant predictors of homogenization. Generalized additive model regression indicated that decreased stream base flow was the single most important factor associated with increased homogenization. Chemical contaminants and associated ecosystem alteration and changes in stream flow may represent important regional influences on changes in fish communities in urban streams in the southeastern U.S.

Alabama, Georgia, North Carolina, South Carolina,

Potential population and assemblage influences of non-native trout on native nongame fish in Nebraska headwater streams

Non-native trout are currently stocked to support recreational fisheries in headwater streams throughout Nebraska. The influence of non-native trout introductions on native fish populations and their role in structuring fish assemblages in these systems is unknown. The objectives of this study were to determine (i) if the size structure or relative abundance of native fish differs in the presence and absence of non-native trout, (ii) if native fish-assemblage structure differs in the presence and absence of non-native trout and (iii) if native fish-assemblage structure differs across a gradient in abundances of non-native trout. Longnose dace Rhinichthys cataractae were larger in the presence of brown trout Salmo trutta and smaller in the presence of rainbow trout Oncorhynchus mykiss compared to sites without trout. There was also a greater proportion of larger white suckers Catostomus commersonii in the presence of brown trout. Creek chub Semotilus atromaculatus and fathead minnow Pimephales promelas size structures were similar in the presence and absence of trout. Relative abundances of longnose dace, white sucker, creek chub and fathead minnow were similar in the presence and absence of trout, but there was greater distinction in native fish-assemblage structure between sites with trout compared to sites without trout as trout abundances increased. These results suggest increased risk to native fish assemblages in sites with high abundances of trout. However, more research is needed to determine the role of non-native trout in structuring native fish assemblages in streams, and the mechanisms through which introduced trout may influence native fish populations.

Nebraska

Trophic pathways supporting Arctic grayling in a small stream on the Arctic Coastal Plain, Alaska

Beaded streams are prominent across the Arctic Coastal Plain (ACP) of Alaska, yet prey flow and food web dynamics supporting fish inhabiting these streams are poorly understood. Arctic grayling ( Thymallus arcticus ) are a widely distributed upper-level consumer on the ACP and migrate into beaded streams to forage during the short 3-month open-water season. We investigated energy pathways and key prey resources that support grayling in a representative beaded stream, Crea Creek. We measured terrestrial invertebrates entering the stream from predominant riparian vegetation types, prey types supporting a range of fish size classes, and how riparian plants and fish size influenced foraging habits. We found that riparian plants influenced the quantity of terrestrial invertebrates entering Crea Creek; however, these differences were not reflected in fish diets. Prey type and size ingested varied with grayling size and season. Small grayling (<15 cm fork length (FL)) consumed mostly aquatic invertebrates early in the summer, and terrestrial invertebrates later in summer, while larger fish (>15 cm FL) foraged most heavily on ninespine stickleback ( Pungitius pungitius ) throughout the summer, indicating that grayling can be insectivorous and piscivorous, depending on size. These findings underscore the potential importance of small streams in Arctic ecosystems as key summer foraging habitats for fish. Understanding trophic pathways supporting stream fishes in these systems will help interpret whether and how petroleum development and climate change may affect energy flow and stream productivity, terrestrial–aquatic linkages and fishes in Arctic ecosystems.

Alaska

Effects of stream intermittency on minnow (Leuciscidae) and darter (Percidae) trophic dynamics in an agricultural watershed

Stream intermittency is predicted to increase where water withdrawals and climate warming are increasing. In regions coupled with high fish diversity, understanding how intermittency influences fish trophic ecology is critical for informing ecosystem function. This study compared fish diets across seasons in perennial and intermittent streams to estimate the immediate and cumulative effects of stream drying on fish foraging patterns. We used gut content analysis to compare the diets of small-bodied, secondary consumer fishes, including two minnow and three darter species found in the lower Flint River Basin of southwestern Georgia, during both the summer (before stream dry-down) and fall (post flow resumption) seasons. Fish communities in perennial streams had greater diet richness compared to fishes in intermittent streams for both seasons. Darter diets were characterised by rheophilic aquatic insects in perennial streams and by benthic crustaceans (copepods, cladocerans and isopods) and predatory aquatic insects in intermittent streams. Minnow diets were typified by freshwater sponges, eggs and organic detritus in intermittent streams and by terrestrial insects and diatoms in perennial streams. Fishes in intermittent streams consumed significantly more benthic crustaceans in the fall (37% increase in proportional volume) compared to preflow cessation conditions in the summer, suggesting these organisms play an important, yet relatively unrecognised role in supporting fish communities in southeastern streams. Our findings enhance our understanding of how stream intermittency influences the trophic dynamics of secondary consumer fishes in an agricultural watershed increasingly affected by water scarcity.

Georgia