IntroductionLarge rivers exhibit spatiotemporal heterogeneity, where habitat structure affects spatial and temporal overlap between zooplankton and planktivores. In the central United States, the non-native, planktivorous silver carp (Hypophthalmichthys molitrix) dominates fish communities in complex riverscapes. Understanding how silver carp and native planktivores interact with zooplankton through space and time is essential for anticipating changes to trophic stability and energy pathways and can inform silver carp management. The objectives of this study were to assess spatiotemporal patterns in zooplankton and planktivorous fish densities, including investigating evidence of zooplankton diel vertical migration and whether planktivores display diel patterns in main channel and off channel habitat use.MethodsThe vertical distributions of three zooplankton taxa and the spatial distributions of silver carp and native planktivores were quantified over a 24-h period in main channel and off channel habitats of three locations in the Illinois River, USA during October 2018.ResultsPlanktivorous fishes > 30 cm total length were dominated by silver carp and were consistently denser in off channel habitats during the day and night. At some sites, densities of cladocerans, copepods, and rotifers differed between the main channel and off channel habitats. Cladoceran, copepod, and rotifer taxa did not exhibit daily changes in vertical distribution. Cladoceran taxa were denser in off channel habitats at night than during the day, while copepod densities were consistently higher near the bottom of the off channel habitat.DiscussionDeclining densities of off channel cladocerans during the day may have been due to movement from nearshore areas or the sediment, planktivory by diurnally feeding fishes, or drift. Unchanging diel rotifer densities support other research showing that these small-bodied taxa with short life cycles persist in the face of high planktivory. Increases in cladocerans during the night in off channel habitats may have been due to a combination of sediment use, decreased nighttime planktivore foraging rates, drift from upstream sources, water flow, and movement from lateral areas. Zooplankton subsidies from the off channel areas of the riverscape support high densities of invasive silver carp and native planktivores.

Some fishes with close phylogenetic relationships and similar ecological requirements exhibit a very different status in the wild and in responses to human-induced disturbance. This is the case with the US federally endangered pallid sturgeon Scaphirhynchus albus (Acipenseridae) and the more common shovelnose sturgeon S. platorynchus . We review the literature among the life stages for pallid sturgeon and shovelnose sturgeon to assess the degree of ecological overlap and discuss the implications of drawing inference from shovelnose sturgeon when considering potential management actions for pallid sturgeon. While shovelnose sturgeon have overlapping ecological requirements with pallid sturgeon at multiple life stages, differences between these species limit the utility of shovelnose sturgeon to inform conservation and management actions within specific life stages. For instance, the species have different free embryo drift distance requirements, but likely similar habitat requirements as juveniles and adult spawners. This example demonstrates the importance of understanding ecological differences when considering potential management actions from a surrogate species. Although the 2 congeners often exhibit ecological overlap, we encourage careful consideration when using surrogate data from shovelnose sturgeon to inform pallid sturgeon recovery efforts.

Large free-flowing rivers are rare but important ecosystems. Environmental conditions in these systems vary through space and time, resulting in dynamic patterns of habitat quality for aquatic species. Such variability could influence invasive species success by altering habitat quality, thereby supporting native species adapted to these conditions. Our study examined spatial and temporal trends in energetic habitat quality between native gizzard shad (Dorosoma cepedianum) and invasive silver carp (Hypophthalmichthys molitrix) in the free-flowing Wabash River, USA. Environmental conditions (water temperature, velocity, prey type and density) were sampled throughout the river and used as input data to a spatially explicit bioenergetics model to predict fish growth rate potential as an index of habitat quality. Seasonal energetic habitat quality varied considerably for both species. Spring habitat quality was poor for both species throughout the river, and only small portions of the river were suitable during summer, mainly in off-channel habitats. More of the river was suitable for gizzard shad, especially during autumn. During all seasons, spatial overlap in high-quality habitat was high between species, especially in the highly suitable off-channel and main-channel border habitats. Promoting habitats in unregulated rivers that provide combinations of flow, food availability, and temperature unique to native species may be important for supporting native species and deterring invasive species. Dam removals that allow access to diverse off-channel habitats may promote biodiversity and protect against invasions in riverscapes.

The Ohio River of North America drains from the forested catchments of the western Appalachian foothills to the floodplains of the Mississippi River Basin. Invasive planktivorous silver carp (Hypophthalmichthys molitrix) are absent upstream but are established and increasingly more abundant downstream. The invasion gradient of silver carp within tributaries along the Ohio River may modify food webs in different ways from low productivity upstream to high productivity downstream. Based on patterns in other productive, invaded Great Rivers of North America, silver carp, which feed on phytoplankton and zooplankton, were predicted to reduce the trophic position of top predators and alter the trophic niches of native planktivores in established downstream tributaries even though these systems have high, agriculturally driven productivity. Body condition and stable isotopes (delta 15N and delta 13C) of native fish species and zebra mussels (Dreissena polymorpha) were quantified in tributaries along the entire Ohio River in 2020 to compare trophic niche and fish condition as a function of the presence and absence of invasive silver carp and river productivity. The isotopic niches of native planktivorous gizzard shad (Dorosoma cepedianum) and piscivorous largemouth bass (Micropterus nigricans) were broader and more depleted in the lower Ohio River where tributaries were agriculturally dominated, highly productive and silver carp were abundant and reproducing. Additionally, gizzard shad and largemouth bass were in poorer condition in the lower reaches of the Ohio River despite the high productivity there, suggesting that silver carp disrupt food webs from their middle-out trophic position. Silver carp populations are likely subsidized by high sources of production in the lower Ohio River, allowing them to become densely populated and dominate food webs, perhaps explaining why the species has not rapidly invaded and established in the upper Ohio River where productivity is lower. Invasive species in rivers worldwide may be facilitated by catchment-level processes such as farming, urban use and forestation, allowing them to rapidly establish, persist, reach high densities and ultimately drive native food web interactions. Because silver carp are among the most farmed fish in the world, the risk to rivers worldwide is going to increase as their use as an economical protein source rises to meet food security needs, especially in highly productive river tributaries as this study suggests.

Species interactions among multiple invasive species can present hidden challenges for management and eradication efforts. Bighead and Silver carp (Hypophthalmichthys nobilis and H. molitrix, respectively) are closely related species that have co-invaded the Mississippi River and many of its tributaries, including the Illinois River. We used a combination of causal inference and dynamic models to test for interspecific interactions in a 10-year data set of hydroacoustic density data from the Illinois River. The results suggest that Bighead and Silver carp are exploiting different ecological strategies; where Bighead carp shows fast initial growth but low equilibrium density and Silver carp had a lower low-density growth rate but larger equilibrium population density. Further, we found evidence for a positive interspecific effect of Silver carp on Bighead carp. The mechanism leading to the observed positive interactions is unknown, but could be an effect of ecological facilitation, differential responses to harvest of both species, or hybridization and introgression. Finally, while these results provide valuable information in the ecological strategies and relationships between these species, simulations of the resulting models suggest that the magnitude of the positive interaction is likely too small to be exploited for innovative multispecies management interventions.

Few effective methods for controlling invasive species exist. Within invaded fish assemblages, commercial harvest is a management option. Silver carp (Hypophthalmichthys molitrix) populations are dense throughout much of the Mississippi River basin and are harvested for control and commercial use. Quantifying mortality rates of silver carp and comparing them to other studies will guide expanding removal efforts throughout the watershed. Silver carp total annual mortality was compared between the Illinois River which is heavily harvested and the Wabash River which is not. The contribution of fishing mortality to total mortality should be apparent in the Illinois River if it exceeds natural mortality. Detection and survival probabilities were determined using a longitudinal Cormack-Jolly-Seber model of acoustically tagged adult silver carp during 2011 through 2018 in both rivers, which is a unique approach only possible with long-term data from individual fishes. Proportion detection probability of individuals was consistently > 0.8 among years in both rivers. Survivorship analysis translated to total annual mortality (mean +/- 95% confidence interval) for the tagged silver carp in the Wabash River being 0.03 +/- 0.02 across all years. This estimate was considerably lower than in the Illinois River where total mortality ranged from 0.23 +/- 0.07 in 2017 to 0.78 +/- 0.14 in 2014. Despite the high total annual mortality of silver carp in the Illinois River, densities of these fish remain high there, likely due to high reproduction of survivors and immigration from the connected Mississippi River basin. This study serves as a method for evaluating the impacts of large-scale removal efforts. But the relative impact of density-dependent intraspecific feedbacks such as improved reproduction and reduced intraspecific competition of survivors in heavily invaded ecosystems needs to be understood.

The susceptibility of ecosystems to range expansions of invasive species must be predicted. Silver carps (Hypophthalmichthys molitrix) threaten the uninvaded Great Lakes and other aquatic ecosystems throughout North America. Invasive common carps (Cyprinus carpio) already occur throughout the continent in rivers and lakes where silver carps may invade. Movement and habitat use of common carps may inform predictions about how silver carps use new environments. Acoustic telemetry combined with stationary receivers and active tracking were used to simultaneously compare movement probability, movement rate, and extent of movement including dam passages of both species in the upper Illinois River during summer 2019 through fall 2021. Common carps had larger core ranges, whereas silver carps moved longer distances. Environmental cues affecting the timing of spring movement were similar between the fishes. Habitat selection during summer was similar between the species only during one year. Both fish species passed through lock and dam complexes at similar times, although common carps used lock chambers and silver carps moved through gates. Because silver carps are likely to spread much farther and faster than common carps due to their greater seasonal movement, a more migratory species should be explored to determine whether the movements of such fishes inform future long-distance silver carp dispersal. Management for control of common carp and silver carp requires different tactics for targeting habitat for harvest control and perhaps design and use of barriers.

Stream and river ecosystems present fluvial fishes with a dynamic energy landscape because moving water generates heterogeneous flow fields that are rarely static in space and time. Fish movement behavior should be consistent with conserving energy in these dynamic flowing environments, but little evidence supporting this hypothesis exists. Here, we tested experimentally whether three general movement behaviors-against the current, with the current, or holding position (i.e., staying in one position and location)-were performed in a way consistent with minimizing the cost of swimming in a heterogeneous flow field. We tested the effects of water velocity on movement behavior across three age classes (0, 1, and 5 years) of two different fluvial specialist fishes, the pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus). Individuals from the three age classes were exposed to a continuous and dynamic velocity field ranging from 0.02 to 0.53 m s-1, which represented natural benthic flow regimes occupied by these species in rivers. Both sturgeon species exhibited the same pattern with regard to their tendency to hold position, move upstream, or move downstream. Moving downstream was positively associated with velocity for all age groups. Moving upstream was inversely related to velocity for young fish, but as the fish aged, moving upstream was not related to water velocity. The oldest fish (age 5) moved upstream more frequently compared to the younger age classes. Holding position within a water current was the most frequent behavior and occurred with similar probability across the range of experimental velocity for youngest fish (age 0), but was inversely related to velocity in older fish. Our experiment across age classes suggests that the suite of swimming behaviors exhibited by fluvial specialists might have evolved to mitigate the energetic costs of complex energy landscapes generated by moving water to ultimately maximize net energy gain.

A group of loosely related, large-bodied fishes collectively called carps have had a complex relationship with North Americans. Despite lessons learned about invasive Common Carp Cyprinus carpio in the early 1900s, Bighead Carp Hypophthalmichthys nobilis, Black Carp Mylopharyngodon piceus, Grass Carp Ctenopharyngodon idella, and Silver Carp H. molitrix were introduced to the United States more than 50 years ago and are expanding throughout the Mississippi River basin. Increased economic value in the North American seafood market could aid management. Complete eradication through harvest is unlikely, but controlling densities and containing dispersal may be possible. Improving perceptions of nutrition, palatability, and safety of wild-caught carps should increase consumer demand. A branding and marketing effort launched in June 2022 renamed the foodstuff produced from the four species as the trademarked brand Copi. The "Choose Copi: Eat Well. Do Good." campaign allows consumers to know that these fishes are an environmentally sound and responsible alternative to other seafood choices. The Copi brand has gained interest nationwide, with food processors and distributors engaged, although the contribution of Copi to harvest removal from rivers and resulting population dynamics is yet to be quantified. Developing a regional fishing industry for Copi, while also aiding fisheries and aquaculture for native species, remains an economic and logistical challenge within the vast river network.

Marine food chains are highly stressed by aggressive fishing practices and environmental damage. Aquaculture has increasingly become a source of seafood which spares the deleterious impact on wild fisheries. However, continually monitoring water quality to successfully grow and harvest fish is labor intensive. The Hybrid Aerial Underwater Robotic System (HAUCS) is an Internet of Things (IoT) framework for aquaculture farms to relieve the farm operators of one of the most labor-intensive and time-consuming farm operations: water quality monitoring. To this end, HAUCS employs a swarm of unmanned aerial vehicles (UAVs) or drones integrated with underwater measurement devices to collect the in situ water quality data from aquaculture ponds. A critical aspect in HAUCS is to develop an effective path planning algorithm to be able to sample all the ponds on the farm with minimal resources (i.e., the number of UAVs and the power consumption of each UAV). Three methods of path planning for the UAVs are tested, a Graph Attention Model (GAM), the Google Linear Optimization Package (GLOP) and our proposed solution, the HAUCS Path Planning Algorithm (HPP). The designs of these path planning algorithms are discussed, and a simulator is developed to evaluate these methods’ performance. The algorithms are also experimentally validated at Southern Illinois University’s Aquaculture Research Center to demonstrate the feasibility of HAUCS. Based on the simulations and experimental studies, HPP is particularly suited for large farms, while GLOP or GAM is more suited to small or medium-sized farms.

Abstract Invasive species and climate change are accelerating changes in biodiversity. Predicting these changes is difficult, especially in large rivers which are hotspots of freshwater biodiversity and important dispersal corridors for aquatic organisms. The lower Illinois River is a major dispersal corridor between the Mississippi River watershed and the North American Great Lakes. The mainstem of this river is highly modified for navigation and may serve as a refuge for invasive species. We compared native and invasive fishes within trophic groups at the scale of an entire river to determine how invaders have risen to dominance. During fall 2012-2017, mainstem river fishes were sampled using standard gears and side-aspect, split-beam echosounding. Biomass and individual body sizes of fishes were used to estimate consumption. Whole-assemblage biomass and consumptive demand of herbivores, insectivores, planktivores, and piscivores were extrapolated from river segments to the entire 315-km main channel. The consumptive demand of native and invasive planktivores was simulated as a function of increasing river temperature and declining food quality. Across the entire fish assemblage, invaders dominated biomass but not species richness each year. Invasive and native fishes reached a fall-season maximum of 6,370 thousand tons and 2,942 thousand tons within the mainstem river, respectively. The total biomass of all but the piscivore trophic group was dominated by invasive fishes. Regardless of total assemblage biomass, invasive fishes had lower energy demand than natives, likely providing them a competitive advantage. Invasive planktivores required less energy than natives to compensate for both increased temperature and declining food quality. Assemblages of invasive species with large bodies and efficient energy consumption allow them to dominate trophic levels and spread into novel ecosystems.

Rivers and their flooded alluvial plains integrate physical, biological, and human processes at the scale of continents. Despite their ecological and economic values, these complex ecosystems are poorly understood and highly modified by humans. A primary problem is that most research in fluvial ecosystems has been conducted in small streams and then scaled up to rivers. Furthermore, the point where a stream transitions into a river is not well understood. Although many conceptual models exist, the role that large river–floodplain complexes play within these frameworks is lacking. These models focus on flooding as a temporary reset to river ecosystems, but floodplains and rivers may continue to interact long after floodwaters recede. We revisit the concept of the riverscape, a unique mosaic of perennially interacting wetland and channel habitats that have unique ecological properties during both non-flood and flooding periods relative to the small tributary streams within the riverscape network. This strong bidirectional interaction within low-lying alluvial plains may define large rivers. To determine whether a riverscape is indeed a useful unit of study for river ecology, conservation, and restoration, baseline conditions with measurable, comparable metrics, such as primary and secondary production need to be established. Responses of these metrics to multiple stressors and restoration such as levee setbacks, wetland mitigation, and dam removals will inform both basic models of riverscape function and future management actions. Because humans currently affect nearly all aspects of the environmental structure and function of riverscapes, human perceptions of riverscape value and threat need to be considered as a fundamental component of riverscape ecology.

1. Invasive species management can benefit from predictive models that incorporate spatially explicit demographics and dispersal to guide resource allocation decisions.2. We used invasive bigheaded carps (Hypophthalmichthys spp.) in the Illinois River, USA as a case study to create a spatially explicit model to evaluate the allocation of future management efforts. Specifically, we compared additional harvest (e.g. near the invasion front vs. source populations) and enhanced movement deter- rents to meet the management goal of reducing abundance at the invasion front.3. We found additional harvest in lower river pools (i.e. targeting source populations) more effectively limited population sizes upriver at the invasion front compared to al- locating the same harvest levels near the invasion front. Likewise, decreasing passage (i.e. lock and dam structures) at the farthest, feasible downriver location limited invasion front population size more than placing movement deterrents farther upriver.4. Synthesis and applications. Our work highlights the benefits of adopting a multi- pronged approach for invasive species management, combining suppression of source populations with disrupting movement between source and sink populations thereby producing compounding benefits for control. Our results also demonstrate the importance of considering metapopulation dynamics for invasive species control programs when achieving long- term management goals.

Invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix have infested and caused largescale ecological and economic damage to the Illinois, Mississippi, and Ohio rivers. We compiled demographic data from 42,995 fish from 23 pools in the Illinois, Mississippi, and Ohio rivers, which universities and management agencies previously collected as part of management, monitoring, and research activities. We used this data set to test whether demographic rates (length–weight relations including body condition, mortality, growth curves, and female maturity curves) varied among subpopulations across a gradient of invasion status. We found that length–weight relations and growth curves varied among subpopulations, whereas maturity curves did not. Our findings demonstrated spatial variability in demographic rates for Bighead and Silver carp across a broad geographic area in relation to invasion status and river conditions. Herein, we provide general subpopulation management options and present different hypotheses to explain the observed spatial variability in demographic rates.

Invasive bigheaded carps, genus Hypophthalmichthys, are spreading throughout the Mississippi River basin. To explore the efficacy of a consumer-based market (i.e., invasivorism) to manage them, we developed a conceptual model and evaluated three harvest approaches-direct contracted removal, volume-based incentives ("fisher-side" control), and set-quota harvest ("market-side" control). We quantified the efficacy of these approaches and potential population impact in the Illinois River. Contracted removal was effective for suppressing small populations at the edge of the range but cannot support a market. "Fisher-side" removals totaled 225,372 kg in one year. However, participation was low, perhaps due to reporting requirements for fishers. The "market-side", set-quota approach removed >1.3 million kg of bigheaded carp in less than 6 months. Larger, older fish were disproportionately harvested, which may hinder the ability to suppress population growth. Total density declined in one river reach, and harvest may reduce upstream movement toward the invasion fronts. With sufficient market demand, harvest may control bigheaded carp. However, lack of processing infrastructure and supply chain bottlenecks could constrain harvest, particularly at low commodity prices. Given the geographical scale of this invasion and complicated harvest logistics, concerns about economic dependence on invasivorism that encourage stock enhancement are likely unmerited.

Introgressive hybridisation between two invasive species has the potential to contribute to their invasion success and provide genetic resiliency to rapidly adapt to new environments. Additionally, differences in the behaviour of hybrids may lead to deleterious ecosystem effects that compound any negative impacts of the invading parental species. Invasive silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) provide an opportunity to evaluate how hybridisation may influence the behaviour, dispersal, and spread of an invasive species introgressive complex. In order to investigate the role hybrids may have in the invasion ecology of bigheaded carps, we examined the distribution, movements, and environmental cues for movement of two invasive fishes and their hybrids in the Illinois River (U.S.A.). Early generation hybrids (e.g. F-1,F-2, and first-generation backcross individuals) composed a greater proportion of the population at the invasion front where abundances of bigheaded carp were low. A greater proportion of early hybrids passed through dams upstream towards the invasion front than did other hybrids and parental species. The movements and environmental cues for movement of late-generation backcrosses (more genetically similar to parental genotype) were not different from the parental species with which they shared the most alleles. Although the direction of the relationship between movement and environment was sometimes different for the parental species and associated advanced generation hybrids, these results indicate that management for parental species will also affect most hybrids. Although early generation hybrids are rare, our results indicate they may disperse towards low-density population zones (i.e. invasion fronts) or are produced at greater frequency in low-density areas. These rare hybrids have the potential to produce a variety of unique genetic combinations that could result in more rapid adaptation of a non-native population to their invaded range potentially facilitating the establishment of invasive species.

Offspring survival, cohort performance, and ultimately population dynamics are strongly influenced by maternal characteristics (e.g., fecundity), whereas paternal contribution is often considered limited to genetic-driven fitness of males through sexual selection. However, male contribution to reproductive success can be particularly influential in species exhibiting paternal offspring care. Polychlorinated biphenyls (PCBs) are widespread, persistent contaminants that can disrupt maternal reproductive processes and negatively affect offspring. In contrast, how PCBs affect paternal reproductive success is largely unknown, but could ultimately affect population dynamics. We examined the effects of lifelong PCB exposure on the reproductive processes of male fathead minnows (Pimephales promelas), a species exhibiting sole paternal offspring care, by examining endocrine-associated gene expression, testes histology, secondary sexual characteristics, courtship ability, offspring care, and offspring survival. PCBs minimized male secondary sexual characteristics, but did not affect gonadal end points or inhibit ability to court females. Fathers exposed to high concentrations of dioxin-like PCBs had changes in gene expression, reduced offspring care behavior, and higher embryo mortality, possibly due to fathers spending less time within nests and less frequently tending to embryos. Through complex interactions among gene expression, physical characteristics, and behavior, PCBs inhibit paternal reproductive success and have the potential to suppress population size.

Invasive bigheaded carp species (Hypophthalmichthys spp.) from Asia have experienced rapid range expansion and population explosions in rivers of the United States resulting in ecosystem damage currently being witnessed and documented by fishery biologists. In addition, silver carp (H. molitrix) present a danger of injury and death to unsuspecting boaters, water skiers or recreational fishers due to their propensity to jump in response to boat motor noise. Fishing-down bigheaded carp populations for human consumption will reduce environmental damage and potential human injury and mortality until other control measures become available. The name "carp" conveys an extremely negative brand name for purposes of product marketing. We suggest that the silver carp be renamed by the professional scientific community to silverfin (a trademarked name currently used in culinary circles) and the bighead carp (H. nobilis) to bighead. The suggested common names changes represent a simple, albeit small step to reducing bigheaded carp population numbers based on sound product naming strategies developed and used in marketing science.

Paddlefish Polyodon spathula and three sturgeon species are present in the upper Mississippi River; of these four species, two are commercially and recreationally important (Paddlefish and Shovelnose Sturgeon Scaphirhynchus platorynchus), and two are protected under federal or state endangered species laws (Pallid Sturgeon S. albus and Lake Sturgeon Acipenser fulvescens). Before management strategies can be implemented, quantification of movement patterns is necessary to determine the appropriate spatial scale for management. To increase the available relevant information, we investigated broad-scale movement patterns of the above species in the upper Mississippi River by using telemetry. All four species were capable of long-range (>300-km) movements, and these movements were cued by the changing river stages and water temperature. Ultimately, our data suggest that sturgeon and Paddlefish movement patterns are highly variable, with fish moving freely among rivers (e.g., the Mississippi, Missouri, Illinois, Ohio, and Des Moines rivers) across many political boundaries and encompassing multiple regulatory agencies. This migratory nature can lead to portions of the population being subject to harvest in multiple management units, affecting population dynamics, biology, harvest, and management/recovery in both the natal area and in the harvest areas. To effectively manage or recover these highly mobile fish populations, interjurisdictional collaboration will be necessary.

Although environmental DNA (eDNA) is increasingly being used to survey for the presence of rare and/or invasive fishes in aquatic systems, the utility of this technique has been limited by a poor understanding of whether and how eDNA concentrations relate to fish density, especially in rivers. We conducted a field study to systematically test whether the eDNA released by a model invasive fish, Silver Carp (Hypophthalmichthys molitrix), was related to the density of this species in a large river. We quantified fish density throughout the 460 km long Illinois River using hydroacoustic surveys at 23 sites while concurrently collecting 192 surface water samples for eDNA analysis. We found that Silver Carp numerical density and biomass density were positively and non-linearly related to eDNA concentration and detection rate. Both eDNA concentration (copy number) and detection rate increased rapidly as Silver Carp density increased but plateaued at moderate densities. These relationships could prove useful for estimating Silver Carp relative abundance in newly invaded locations where population numbers are low to moderate. Future studies should explore the causes of this nonlinear relationship as it would ultimately benefit aquatic species monitoring and management programs.