Objective Standard sampling methods for fishes generally provide a reliable method for fish population assessments. However, they may not always be effective due to logistical, financial, or behavioral constraints. Channel Catfish Ictalurus punctatus are a nonnative species of interest in the Colorado River basin due to predation on native species. Electrofishing and hoop nets were used in a long-term monitoring program that was designed to assess the relative abundance and distribution of fishes within the Colorado River, Grand Canyon, USA, but have proven ineffective for Channel Catfish. Thus, our objective was to determine whether angling was an effective method to target Channel Catfish and whether it was useful as a supplemental sampling method for other fishes, such as Humpback Chub Gila Cypha.Methods Angling occurred within randomly selected segments of the Colorado River, Grand Canyon, USA, as part of a long-term fish monitoring project (2004-2025). Angling occurred each evening/night at camp using standardized methods for a minimum sample time of 1 h. We used generalized linear mixed-effects negative binomial models to assess whether angling catch data could detect changes in relative abundance and linear models to investigate changes in the distribution of Channel Catfish and Humpback Chub over time.Results Channel Catfish were the most abundant fish species that was captured by angling (n = 347), followed by the federally listed Humpback Chub (n = 214). Angling provided more Channel Catfish captures per sample size than hoop nets (n = 1) or electrofishing (n = 119) during our study period based on sample sizes of 566, 2,761, and 12,911 respectively. The modeled Channel Catfish relative abundance and distribution decreased substantially over time, whereas relative abundance and distribution of Humpback Chub increased substantially over time.Conclusions Using angling as a sampling method, we were able to detect changes in the relative abundance and distribution of Channel Catfish and Humpback Chub over time in the Colorado River, Grand Canyon. Multispecies monitoring programs are often limited by financial or logistical constraints. Therefore, assessing existing sampling methods to ensure that all species of interest can be effectively monitored is critical to successful adaptive management. Here, we provide a case study for the use of angling as a standardized monitoring method to determine relative abundance and distribution of Channel Catfish.

Objective Understanding how angler harvest behaviors change through time and in relation to different management regulations is essential for effective fisheries management. The factors that influence an angler's decision to harvest fish are likely complex and are currently poorly understood. This study used data collected from a long-term creel program to examine how angler harvest rates at a western tailwater trout fishery have changed through time and in relation to changing management regulations.Methods We analyzed over 40 years of creel survey data (1977-2024) from a tailwater Rainbow Trout Oncorhynchus mykiss fishery in the American Southwest to assess how angler harvest rates have changed over time and how gear choice and regulations may have influenced harvest decisions. We calculated daily harvest rates for groups of anglers and individual anglers when possible and used a Bayesian generalized linear model framework to look for differences in harvest rates under different management regulations and gear types.Results Angler harvest rates declined during the study. Significant differences in angler harvest rates were observed between angler groups using different gears. Anglers using fly-fishing gear were observed to have the lowest harvest rates, followed by anglers using spinning gear. Anglers using bait had the highest harvest rates over the course of the study. Additionally, differences in harvest rates were observed under different management regulations. Anglers harvested less fish when restrictive maximum length limits were in place for harvested fish. A less pronounced difference was observed in harvest rates related to the number of fish anglers were allowed to harvest, with anglers more likely to harvest their entire limit when the allowable harvest limit was higher. A significant shift in predominant gear type occurred in the fishery over the course of study, which suggests that some anglers may have been displaced by changing management regulations.Conclusion A declining harvest rate over time at Lees Ferry suggests angler's attitudes towards harvest have changed, but harvest behavior still appeared to be related to management regulations and angler gear choices. This change in harvest behavior was likely further increased by harvest-oriented anglers being displaced by restrictive harvest and gear regulations. Consideration of these factors may be beneficial for fisheries management decisions. Understanding factors that influence angler harvest behavior is crucial for informing fisheries management decisions. Restrictive harvest regulations may displace some anglers and alter the harvest behaviors of others. Recognizing how angler's attitudes change through time and in relation to management regulation will allow managers to provide angling opportunities to a diverse group of anglers within a fishery.

Understanding variation in life history traits, those traits that underlie rates of survival and reproduction, is important for assessing the long-term security and extinction risk of any population. Measuring life history traits is especially important for small, isolated populations exemplified by many desert fishes. We report life history variation within and among populations of the New Mexico state protected White Sands pupfish, Cyprinodon tularosa using life history data of somatic growth (length, wet weight, and dry weight) and reproductive allocation (gonadosomatic index, presence of eggs with yolks) from females (N = 775) collected during the summers of 2000 and 2001. C. tularosa occupies habitats that differ in water flow, salinity, and parasite communities and shows high inter-population variation in heritable body shape. We expected these ecologically divergent habitats and morphological differences may lead to similarly high inter-population variation in life history traits; however, contrary to our expectations, habitat and genetic ancestry were not strong predictors of life history trait variation. Redundancy analysis showed most life history variation occurred among individuals within habitats (> 70%). Multivariate analyses of life history traits suggested one of the most important patterns in life history trait variation was an apparent trade-off between lipid storage and reproductive allocation. Further, we found that digene parasites did not directly affect reproductive traits but may have important indirect impacts on life history trade-offs. Higher parasite density and higher reproductive investment were both associated with reduced lipid content. Overall, we conclude White Sands pupfish exhibited similar life history strategies across all four populations and sacrifice energy storage to maintain reproductive investment in the presence of parasites.

Objective Habitat fragmentation is common in riverine systems worldwide, and often thought of in a negative context. However, some barriers may create refugia for native species by excluding nonnative species. In the Colorado River, USA, recession of Lake Mead and subsequent river superimposition resulted in the formation of Pearce Ferry Rapid, a formidable hydraulic feature that may prevent nonnative fish from accessing native fish habitat in western Grand Canyon. Here, we analyzed fish communties above and below the rapid and used remote sending to determine species-specific movement above and below the rapid.Methods We compared fish communities above and below the rapid using nonmetric multidimensional scaling, and passive intergrated transponder antennas placed above and below the rapid to determine directional movement of native and nonnative species.Results The fish assemblage upstream of the rapid was dominated by native fishes, while nonnative fishes were more common downstream of the rapid. We documented limited upstream movement of native Razorback Sucker Xyrauchen texanus, Flannelmouth Sucker Catostomus latipinnis, and presumed Razorback Sucker x Flannelmouth Sucker hybrids. No upstream movement of native Humpback Chub Gila cypha or nonnative fishes occurred.Conclusions Pearce Ferry Rapid is likely a hindrance to upstream movement of native Razorback and Flannelmouth sucker and may be a barrier to upstream movement for nonnative fishes and native Humpback Chub. The rapid may prevent deleterious nonnative fishes from accessing native fish habitat. As reservoirs recede due to extreme drought, novel barriers such as Pearce Ferry Rapid are likely to emerge in riverine systems constricted by dams. Here, we provide a case study demonstrating the effects of a novel barrier on native fish. Understanding the effects of potential barriers in concert with environmental variables (e.g., flow) that facilitate or restrict movement can help inform management actions to benefit native fishes.

Two large dams on the Colorado River, Glen Canyon and Hoover Dam, have profoundly altered the river within Grand Canyon. Owing to widespread drought and increased water usage throughout the Southwest, water levels in Lake Mead declined by over 40 m since 2000, exposing over 80 km of newly emerged riverine habitat in the western Grand Canyon that experiences higher water temperatures and increased turbidity relative to upstream portions of the Colorado River within the Grand Canyon. Our objective was to investigate how the probability of fish occurrence has changed within the Colorado River in Grand Canyon as abiotic conditions have shifted in relation to these altered environmental conditions. We used 22 years of long-term fish monitoring data, from 2000 to 2022, on the mainstem of the Colorado River in the Grand Canyon to map the probability of occurrence based upon modeled water temperature for native and common nonnative salmonid species through space (river kilometer) and time in relation to declining water levels in Lake Mead. Our results suggest that native fish occurrence is strongly correlated with longitudinally increasing water temperature, while nonnative trout species were negatively correlated with increased water temperature downstream from the dam. Further, we found that nonnative trout species have experienced decreases in their probability of occurrence through time, while natives have experienced an increase in probability of occurrence. Information on distribution of fish prior to reservoir declines, and how the fish assemblage has shifted coincident with environmental changes, can help inform future management of native and nonnative fish in highly regulated river systems.

1. Habitat descriptions found in critical habitat designations and recovery plans are important for protecting endangered species. However, in order to protect critical habitat, it is necessary to update descriptions of habitat use when range shifts occur or new studies change the understanding of habitat use.2. This study examined the habitat use of a threatened desert fish to determine whether current habitat use matched the descriptions in recovery documents. Recovery documents describe humpback chub (Gila cypha) as being dependent on rocky, canyon-bound habitats during all life stages, but recent surveys found humpback chub in open, silt-laden habitats, suggesting this species may be able to occupy a wider range of habitats.3. Hoop net catch data from a long-term monitoring project in the Colorado River were used to compare catches of two size classes: juvenile/subadult (<200 mm total length [TL]) and adult humpback chub (>= 200 mm TL). Catch information was analysed on an individual net scale and on a geological segment scale using generalized linear mixed models.4. There was no difference in juvenile/subadult humpback chub catch between hoop nets set in rocky habitat compared with habitat with only fine sediment. Humpback chub catch for all life stages in a river segment characterized by silt banks exceeded or was not significantly different from catch in rocky segments.5. This case study demonstrates the importance of revisiting habitat descriptions, sampling in areas outside known or expected habitat and incorporating new data related to range expansion or habitat changes in recovery strategies to better describe and protect habitats that can support imperilled species.

Spawning phenology and associated migrations of fishes are often regulated by factors such as temperature and stream discharge, but flow regulation of mainstem rivers coupled with climate change might disrupt these cues and affect fitness. Flannelmouth sucker (Catostomus latipinnis) persisting in heavily modified river networks are known to spawn in tributaries that might provide better spawning habitat than neighboring mainstem rivers subject to habitat degradation (e.g., embedded sediments, altered thermal regimes, and disconnected floodplains). PIT tag data and radio telemetry were used to quantify the timing and duration of flannelmouth sucker tributary spawning migrations in relation to environmental cues in McElmo Creek, a tributary of the San Juan River in the American Southwest. We also tested the extent of the tributary migration and assessed mainstem movements prior to and after tributary migrations. Additionally, multiyear data sets of PIT detections from other tributaries in the Colorado River basin were used to quantify interannual and cross-site variation in the timing of flannelmouth sucker spawning migrations in relation to environmental cues. The arrival and residence times of fish spawning in McElmo Creek varied among years, with earlier migration and a 3-week increase in residence time in relatively wet years compared to drier years. Classification tree analysis suggested a combination of discharge- and temperature-determined arrival timing. Of fish PIT tagged in the fall, 56% tagged within 10 km of McElmo Creek spawned in the tributary the following spring, as did 60% of radio-tagged fish, with a decline in its use corresponding to increased distance of tagging location. A broader analysis of four tributaries in the Colorado River basin, including McElmo Creek, found photoperiod and temperature of tributary and mainstem rivers were the most important variables in determining migration timing, but tributary and mainstem discharge also aided in classification success. The largest tributary, the Little Colorado River, had more residential fish or fish that stayed for longer periods (median = 30 days), whereas McElmo Creek fish stayed an average of just 10 days in 2022. Our results generally suggest that higher discharge, across years or across sites, results in extended use of tributaries by flannelmouth suckers. Conservation actions that limit water extraction and maintain natural flow regimes in tributaries, while maintaining open connection with mainstem rivers, may benefit migratory species, including flannelmouth suckers.

One means of eradicating invasive molluscs is through dewatering or desiccation. Here, I show a practical approach for determining desiccation tolerance of molluscs. Laboratory studies of desiccation tolerance are usually conducted at constant humidity levels, with the amount of time to death, provided as an end point. However, in the natural environment humidity can vary hourly and time to death at a constant humidity is not relevant. A more practical method to determine desiccation tolerance is by measuring water loss. Additionally, knowing the length–weight relationship and desiccation tolerance one can calculate the predicted desiccated weight of a mollusc that would ensure 95

Hybridization between two sucker species, Razorback Sucker Xyrauchen texanus and Flannelmouth Sucker Catostomus latipinnis, historically has occurred but has been facilitated by anthropogenic habitat alteration. The ability to differentiate Razorback Suckers from Flannelmouth Suckers and hybrids is essential for the conservation and management of the endangered Razorback Sucker. The purpose of our study was to investigate allometry-that is, how shape changes with length-of Razorback Sucker, Flannelmouth Sucker, and their hybrids. Razorback Sucker and Flannelmouth Sucker were artificially spawned to produce four progenies: Razorback Sucker, Flannelmouth Sucker, female Razorback Sucker x male Flannelmouth Sucker and female Flannelmouth Sucker x male Razorback Sucker. We also used hatchery-reared Razorback Sucker and wild-captured Flannelmouth Sucker to fill the size-class gaps in our data. We conducted geometric morphometric analyses and used conditional inference trees to determine the length at which body shapes begin to differentiate among these four fish types. We used piecewise linear models to understand the allometry of each fish type and to evaluate the size at which body shape begins to differ from the juvenile form. Although we found statistical shape differences between the two hybrids, they would be difficult to detect with the naked eye. The results of our study showed that fish that are smaller than 140 mm total length (TL) are difficult to differentiate using shape alone. With the information provided in this study, field biologists should be cautious when identifying suckers smaller than 140 mm TL in the Colorado River basin.

The Colorado River in the Grand Canyon holds the largest remaining population of Humpback Chub Cila cypha, an endangered fish endemic to the Colorado River basin. Early surveys in the 1990s found that most Humpback Chub occupied the Little Colorado River and nearby areas in the mainstem Colorado River and were uncommon in the western Grand Canyon (below Kanab Creek, at river kilometer [rkm] 257.2). From 1939 to 2002, the Colorado River was typically inundated by Lake Mead to rkm 407 (at full pool). Since 2000, Lake Mead water levels have declined, and the current inflow is located almost 100 km downstream at rkm 503.1. Thus, the Arizona Game and Fish Department (AGFD) extended its system-wide monitoring downstream to Pearce Ferry rapid (rkm 478.6) in 2011. Electrofishing is relatively inefficient at capturing humpback Chub, but a small number of captures from 2011 to 2015 in the western Grand Canyon suggested that the Humpback Chub may have expanded its range downstream. Subsequently, hoop nets were added to AGFD system-wide monitoring in 2016 to better describe Humpback Chub distribution. The distribution of Humpback Chub observed in 2016 and 2017 differed from previous descriptions; we documented relatively large numbers of Humpback Chub, including age-0 fish, in the western Grand Canyon and observed the highest catches downstream of Diamond Creek (rkm 389.1). This suggests that a recent range expansion has occurred and that Humpback Chub in the western Grand Canyon do not utilize the Little Colorado River for reproduction and might therefore constitute a new subpopulation.

Razorback sucker (Xyrauchen texanus) and flannelmouth sucker (Catostomus latipinnis) live in sympatry in the Colorado River basin. Although morphological intermediates have been described since 1889, hybrids were seemingly rare. Rarity of hybrids was likely attributed to razorback suckers' ability to find conspecific mates throughout the basin. Dams have segmented the Colorado River, altering habitat and isolating native fish populations. As a result, razorback suckers became endangered. Razorback suckers are uncommon in the Colorado River and hybridization could increase because of limited conspecific mates. To understand the impacts of hybridization on recovery of the razorback sucker, information on hybrid viability is needed. We compared hatch success and larval survival of artificially spawned razorback sucker, flannelmouth sucker, and their hybrids. We were able to successfully spawn and rear all combinations, implying that there are limited pre- and postzygotic isolation mechanisms, and hybrids are likely to survive in the wild.

Global warming and deforestation can significantly increase stream temperatures. This study investigated how increased stream temperatures affected a tropical caddisfly (order Trichoptera: Hydropsychidae) from first order premontane streams in southern Costa Rica. Laboratory experiments were conducted to test the effects of increased temperature on mortality and behavior of a caddisfly (Leptonema sp.). Forested streams and a roadside stream had mean temperatures of 20.0 and 20.7 degrees C and standard deviations of 0.464 and 1.43 degrees C, respectively. At temperatures exceeding 22.3 degrees C caddisfly mortality increased and retreat building decreased, with near complete mortality at temperatures exceeding 25 degrees C. The roadside stream exceeded 22.3 degrees C, 11 % of the time during the three week study period. A laboratory study revealed that caddisfly larvae were able to survive in roadside stream water and only suffered mortalities at temperatures above similar to 22 degrees C, suggesting that increased water temperature restricts this species to cooler forested streams.

Glen Canyon Dam (GCD) on the Colorado River in northern Arizona provides water storage, flood control, and power system benefits to approximately 40 million people who rely on water and energy resources in the Colorado River basin. Downstream resources (e.g., angling, white water floating) in Glen Canyon National Recreation Area (GCNRA) and Grand Canyon National Park are impacted by the operation of GCD. The GCD Adaptive Management Program was established in 1997 to monitor and research the effects of dam operations on the downstream environment. We utilized secondary survey data and an individual observation travel cost model to estimate the net economic benefit of angling in GCNRA for each season and each type of angler. As expected, the demand for angling decreased with increasing travel cost; the annual value of angling at Lees Ferry totaled US$2.7 million at 2014 visitation levels. Demand for angling was also affected by season, with per-trip values of $210 in the summer, $237 in the spring, $261 in the fall, and $399 in the winter. This information provides insight into the ways in which anglers are potentially impacted by seasonal GCD operations and adaptive management experiments aimed at improving downstream resource conditions.

Summary Optimisation of control methods of invasive species using life‐history information may increase probability that techniques will be effective at reducing impacts of nuisance species. The northern crayfish, Orconectes virilis , has negatively affected native flora and fauna throughout the world in areas where it is non‐native. Yet, life history of invasive populations has rarely been studied. We investigated the life history of three introduced populations of O . virilis within Arizona streams using mark–recapture methods and a laboratory investigation of reproduction to identify times and techniques to maximise effects of mechanical control. We show the most effective time to implement crayfish control efforts is in autumn during their mating season, prior to onset of colder temperatures, at which time the majority of O. virilis become inactive. To improve crayfish survival, recapture and population density estimates, we suggest a mark–recapture programme using a robust sampling approach concentrated during spring and autumn. Identification of vulnerable points in the life history of nuisance species may aid in control efforts.

Melanoides tuberculata Muller, 1774 (Thiaridae), a freshwater prosobranch snail native to regions of Asia and Africa, was introduced into the U.S. in the 1960s and is now found in fifteen states. Melanoides tuberculata can affect native communities directly by displacing native snail species and indirectly by introducing foreign trematodes into novel environments. As the exact mechanisms of displacement of native snails by M. tuberculata are unknown, egg predation rates on native snails (Physella spp.) by two different size classes (>30 mm and 30 mm were found to consume Physella spp. and only 2.8% of M. tuberculata snails consumed egg masses. None of the M. tuberculata collected from Diamond Y Spring were found to be infected with C. formosanus.

Our objectives were to determine which habitat variables had the greatest influence on densities of the Three Forks springsnail (Pyrgulopsis trivialis) and pond snail (Physa gyrina), and to examine interactions between the two species. We measured density and several habitat variables in Three Forks Springs and Boneyard Bog Springs in east-central Arizona. Density of Three Forks springsnails was greatest (500/m(2)) in shallow water (< 5.6 cm), where density of pond snails was less (<4.6/m(2)), and closer to the springhead (< 0.8 m). Density of pond snails was greatest (66/m(2)) further away from the springhead (>= 32 m) and when temperatures were greater (>= 15.8 degrees C). Density of pond snails was low (1.1/m(2)) closer to the springhead (< 32 m) when pH was less (< 8.4). The two snails apparently partition habitat in response to competition for food or presence of predators.

Summary 1. Managing populations of predators and their prey to achieve conservation or resource management goals is usually technically challenging and frequently socially controversial. This is true even in the simplest ecosystems but can be made much worse when predator–prey relationships are influenced by complex interactions, such as biological invasions, population trends or animal movements. 2. Lough Neagh in Northern Ireland is a European stronghold for pollan Coregonus autumnalis, a coregonine fish and for river lamprey Lampetra fluviatilis, which feeds parasitically as an adult. Both species are of high conservation importance. Lampreys are known to consume pollan but detailed knowledge of their interactions is scant. While pollan is well known to be a landlocked species in Ireland, the life cycle of normally anadromous river lamprey in Lough Neagh has been unclear. The Lough is also a highly perturbed ecosystem, supporting several invasive, non‐native fish species that have the potential to influence lamprey–pollan interactions. 3. We applied stable isotope techniques to resolve both the movement patterns of lamprey and trophic interactions in this complex community. Recognizing that stable isotope studies are often hampered by high‐levels of variability and uncertainty in the systems of interest, we employed novel Bayesian mixing models, which incorporate variability and uncertainty. 4. Stable isotope analyses identified trout Salmo trutta and non‐native bream Abramis brama as the main items in lamprey diet. Pollan only represented a major food source for lamprey between May and July. 5. Stable isotope ratios of carbon in tissues from 71 adult lamprey showed no evidence of marine carbon sources, strongly suggesting that Lough Neagh is host to a highly unusual, nonanadromous freshwater population. This finding marks out the Lough’s lamprey population as of particular scientific interest and enhances the conservation significance of this feature of the Lough. 6. Synthesis and applications. Our Bayesian isotopic mixing models illustrate an unusual pattern of animal movement, enhancing conservation interest in an already threatened population. We have also revealed a complex relationship between lamprey and their food species that is suggestive of hyperpredation, whereby non‐native species may sustain high lamprey populations that may in turn be detrimental to native pollan. Long‐term conservation of lamprey and pollan in this system is likely to require management intervention, but in light of this exceptional complexity, no simple management options are currently supported. Conservation plans will require better characterization of population‐level interactions and simulation modelling of interventions. More generally, our study demonstrates the importance of considering a full range of possible trophic interactions, particularly in complex ecosystems, and highlights Bayesian isotopic mixing models as powerful tools in resolving trophic relationships.

The freshwater pearl mussel Margaritifera margaritifera is endangered throughout Europe. Historically, mussels were described on the basis of shell characteristics. In more recent years with the advent of molecular techniques many ‘species’ of molluscs have been found to be ecophenotypes. The pearl mussel is found in numerous rivers throughout Ireland and the UK with varying degrees of superficial differences. It is has been thought that the most divergent form is found in the Nore River, Ireland, Margaritifera m. durrovensis . The current investigation considers shell shape differences (using morphometrics — elliptic Fourier descriptors) in mussels from a variety of rivers in Ireland in relation to river pH. Results suggest that M. margaritifera has a fairly plastic phenotype, with a gradient of shape change in relation to water pH. Margaritifera m. durrovensis does not appear to be morphologically unique from other populations studied, instead occurring at one end of the shell shape gradient. Findings also suggest that shell shape may be characteristic to individual rivers. The existence of phenotypically distinct groups of Margaritifera margaritifera has particularly important implications for the future conservation of the species. Ex situ conservation and reintroduction efforts will need to consider both the genotypic and phenotypic suitability of mussels if translocation is to be used as a viable conservation tool in the future. Copyright © 2010 John Wiley & Sons, Ltd.

Habitat characteristics associated with lamprey ammocoetes (Lampetra spp.) were investigated at three different spatial scales: regional (Northern Ireland), catchment (Ballinderry River) and microhabitat. At the regional scale, ammocoetes were more abundant in rivers with a pH >= 8.2, while within a catchment, abundance was negatively related to the number of potential lamprey barriers and distance upstream. At the microhabitat scale, at sites where ammocoetes were present, ammocoetes were more abundant where median phi >= 1.94 (very coarse sand), where sediment depth >= 11.5 cm, and where kurtosis was >1.71. This study provides information on habitat associations of lamprey in the UK which may be of use in their conservation, in particular it highlights the negative association of migration barriers with lamprey abundance.

Populations of invasive fishes quickly reach extremely high biomass. Before control methods can be applied, however, an understanding of the contaminant loads of these invaders carry is needed. We investigated differences in concentrations of selected elements in two invasive carp species as a function of sampling site, fish species, length and trophic differences using stable isotopes (δ 15N, δ 13C). Fish were collected from three different sites, the Illinois River near Havana, Illinois, and two sites in the Mississippi River, upstream and downstream of the Illinois River confluence. Five bighead carp (Hypophthalmichthys nobilis) and five silver carp (Hypophthalmichthys molitrix) from each site were collected for muscle tissue analyses. Freshwater mussels (Amblema plicata) previously collected in the same areas were used as an isotopic baseline to standardize fish results among sites. Total fish length, trophic position, and corrected 13C, were significantly related to concentrations of metals in muscle. Fish length explained the most variation in metal concentrations, with most of that variation related to mercury levels. This result was not unexpected because larger fish are older, giving them a higher probability of exposure and accumulation of contaminants. There was a significant difference in stable isotope profiles between the two species. Bighead carp occupied a higher trophic position and had higher levels of corrected 13C than silver carp. Additionally bighead carp had significantly lower concentrations of arsenic and selenium than silver carp. Stable isotope ratios of nitrogen in Asian carp were at levels that are more commonly associated with higher-level predators, or from organisms in areas containing high loads of wastewater effluent.