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At least 415 records · Page 23Linked to original sources

USGS2004

The influence of diet, consumption and lipid use on recruitment of white bass

The abundance of white bass ( Morone chrysops ) in Lake Erie has declined in recent years, sparking interest in mechanisms influencing its recruitment. We evaluate two mechanisms affecting recruitment: diet and the potential for competition, and storage of lipid energy reserves and the relationship to overwinter survival. The fish in our study were characteristic of white bass in the northern portion of their range, feeding predominantly on zooplankton. Only the largest age-0 white bass ate fish as a significant portion of their diet. Over the summer sampling period, we found decreasing ration sizes, expressed as a percentage of maximum ration, as the summer progressed with a concomitant decrease in the relative amount of lipid storage. In laboratory experiments, age-0 white bass held at 5°C and given food ad libitum did feed, but at rates that were insufficient to maintain body weight. Loss in weight was accompanied with a loss in lipids at a rate of 2.8 mg of lipids per gram of body weight per day. Based on our data, we concluded that age-0 white bass in Lake Erie were food-limited. Food limitation resulted in reduced growth rates, presumably related to competition with other planktivorous fishes. Reduced growth results in increased mortality and, ultimately, low recruitment through increased risk of predation by larger piscivorous fishes, reduced ability for white bass to switch to more energetically profitable piscivory and the increased likelihood of higher overwinter mortality because of reduced lipid stores.

Michigan, New York, Ohio, Pennsylvania↗

USGS2009

Behavior of steelhead fry in a laboratory stream is affected by fish density but not rearing environment

We quantified the aggression, feeding, dominance, position choice, and territory size of naturally reared steelhead Oncorhynchus mykiss fry stocked with two types of hatchery-reared fry (from conventional and enriched rearing environments) at two densities in experimental flumes to determine how rearing environment and fish density affect the behavior of steelhead fry. We found that fry density had a significant effect on most response variables but that rearing treatment did not. The rates of threats and attacks were positively correlated with fry density, but the overall feeding rate was negatively correlated. Naturally reared fry were dominant more often at low densities, and hatchery-reared fry were dominant more often at high densities. There were no significant effects of hatchery rearing treatment on aggression, feeding, dominance, or territory size. The only significant effect of rearing treatment was on the position of naturally reared fry, which occupied more upstream positions when stocked with conventional than with enriched hatchery-reared fry. Overall, rearing environment had relatively little influence on the behavior of steelhead fry. Our results indicate that stocking hatchery-reared steelhead fry at low densities may have effects on similar-size wild fish comparable to an equivalent increase in the density of wild fish. We suggest that releasing hatchery-reared steelhead fry as a supplementation strategy may have few direct negative ecological effects on wild fry.

North American Journal of Fisheries Management↗

USGS1972

Some effects of aldrin-treated rice on Gulf Coast wildlife

Wildlife casualties from aldrin-dieldrin poisoning are associated with the planting of aldrin-treated rice seed along the Texas Gulf Coast. The fulvous tree duck ( Dendrocygna bicolor ), which depends on the rice field habitats and is highly susceptible to aldrin-dieldrin poisoning, is suffering a serious population decline in that area. Dead waterfowl, shorebirds, and passerines were collected on study areas in Wharton, Brazoria, and Chambers counties, Texas, from 1967 through 1971. Residues of aldrin or dieldrin were found in all samples of bird casualties and in all eggs, scavengers, predators, fish, frogs, invertebrates, and soils. Fulvous tree ducks appeared to be less resistant to aldrin than other ducks. Dieldrin residues in brains of dead fulvous tree ducks were low, but whole-body residues were as high as 16 ppm. Brains of other dead ducks and geese averaged 10 ppm dieldrin. Some dead birds were exposed by eating treated rice seed, but many dead birds with high dieldrin residues were species that feed largely on invertebrates. Although soil residues were low, snails and crayfish contained enough aldrin and dieldrin (average 9.5 ppm) to account for deaths in birds that fed heavily on these invertebrates over a period of time. When fulvous tree ducks were penned for 3 days in fields aerially planted with treated seed, 3 of 10 birds died with brain residues of 2.5, 2.9, and 6.8 ppm dieldrin, and others were intoxicated. None of eight died, and some gained weight, when penned in fields planted with untreated seed. This study adds further evidence for the suspected lethal effects of aldrin-treated rice seed on wild birds and other wildlife in rice field habitats.

Texas↗

USGS2025

Exploration of a piscicide delivery method for invasive Black Carp

A piscicide delivery method was designed to selectively target Black Carp Mylopharyngodon piceus, an invasive fish species in North America, which possesses pharyngeal teeth adapted for crushing mollusk prey. Many North American mollusks exist in small, fragmented populations susceptible to local extirpation. A Black Carp-selective toxic bait deployed properly could be used to protect those populations. Results represent initial efforts to construct an effective single-dose species-selective toxic bait. We prepared a bait by attaching a glass vial containing toxicant (antimycin A) to the exterior of a Corbicula fluminea clam valve. We designed the vial to break from the force of the fish’s pharyngeal teeth when attempting to crush and consume the clam. We tested suitable vial sizes for encapsulating piscicide and two attachment materials, an aquarium epoxy and ultraviolet light-cured attachment material. The aquarium epoxy was rigid and reinforced vials. The ultraviolet light-cured attachment material was softer, resulting in more vials broken at 3- and 24-h post feeding. In a second trial, toxic baits consisting of antimycin A piscicide were administered in pure ethanol and acetone carriers to Black Carp in assembled baits with vials attached to live clam valves at three concentrations (40.0 mg/mL in ethanol, 170.8 mg/mL and 341.5 mg/mL in acetone). We selected aquarium epoxy for assembled baits based on the bond between the epoxy and glass vial, which allowed a greater surface area to be exposed and broken. While Black Carp successfully broke vials containing piscicide, no treatment caused carp mortality. The delivery method was unsuccessful as a single dose antimycin A piscicide bait for Black Carp. Additional considerations for this approach are provided.

Journal of Fish and Wildlife Management↗

USGS2024

Visualizing wading bird optimal foraging decisions with aggregation behaviors using individual-based modeling

Foragers on patchy landscapes must efficiently balance time between searching for and consuming resources to meet their daily energetic requirements. Spatial aggregation foraging behaviors may improve foraging efficiency by sharing information on locations of resource hotspots. Wading birds are an example of patch foragers that form colonial aggregations during the breeding season to obtain sufficient prey energy to sustain themselves and their offspring each day. Here, we describe a spatially-explicit simulation model of wading bird optimal foraging that represents information sharing through visual cues. The overall purpose of the model is to describe how wading bird daily foraging and reproductive success may change with alternative water control management practices that determine spatial availability of prey for wading birds on the landscape, throughout their breeding seasons. Wading birds are simulated as individuals that operate independently, sampling and selecting among patches based on a prey density tolerance threshold, but also use information from other birds to inform their selection decisions. Foraging success is evaluated against the fundamental objectives of (a) fulfilling daily energetic demands and (b) minimizing predation exposure, by tracking individual daily energetic intake and time spent foraging. In this way, the model approximates population level dynamics of wading bird aggregations that emerge through collective decision making of birds simulated at the lower individual level. Key results of this study suggest that aggregation behaviors may improve population-level foraging success rates, and the optimal settling threshold may modulate when resources become more scarce or difficult to find. Thus, the model addresses ecological theory on the advantages of foraging in groups versus independently. This technique is appropriate for evaluating wading bird populations that forage on patchy landscapes, such as seasonally-pulsed wetlands, wherever sufficient information is available to describe (1) foraging behavior (e.g., feeding rate, flight speeds, patch selection decisions), (2) key landscape characteristics, (3) spatial distributions of prey densities among foraging patches, and (4) changes in prey densities through time. The model was designed to predict qualitative, testable spatial patterns of wading bird foraging movements which can be compared with empirical observations and empirically-derived habitat suitability models. These techniques can also be applied to other bird species, such as shorebirds, or more generally to any species that transits between discrete foraging patches.

Ecological Modelling↗

USGS2019

Associations between environmental pollutants and larval amphibians in wetlands contaminated by energy-related brines are potentially mediated by feeding traits

Energy production in the Williston Basin, located in the Prairie Pothole Region of central North America, has increased rapidly over the last several decades. Advances in recycling and disposal practices of saline wastewaters (brines) co-produced during energy production have reduced ecological risks, but spills still occur often and legacy practices of releasing brines into the environment caused persistent salinization in many areas. Aside from sodium and chloride, these brines contain elevated concentrations of metals and metalloids (lead, selenium, strontium, antimony and vanadium), ammonium, volatile organic compounds, hydrocarbons, and radionuclides. Amphibians are especially sensitive to chloride and some metals, increasing potential effects in wetlands contaminated by brines. We collected bed sediment and larval amphibians ( Ambystoma mavortium , Lithobates pipiens and Pseudacris maculata ) from wetlands in Montana and North Dakota representing a range of brine contamination history and severity to determine if contamination was associated with metal concentrations in sediments and if metal accumulation in tissues varied by species. In wetland sediments, brine contamination was positively associated with the concentrations of sodium and strontium, both known to occur in oil and gas wastewater, but negatively correlated with mercury. In amphibian tissues, selenium and vanadium were associated with brine contamination. Metal tissue concentrations were higher in tadpoles that graze compared to predatory salamanders; this suggests frequent contact with the sediments could lead to greater ingestion of metal-laden materials. Although many of these metals may not be directly linked with energy development, the potential additive or synergistic effects of exposure along with elevated chloride from brines could have important consequences for aquatic organisms. To effectively manage amphibian populations in wetlands contaminated by saline wastewaters we need a better understanding of how life history traits, species-specific susceptibilities and the physical-chemical properties of metals co-occurring in wetland sediments interact with other stressors like chloride and wetland drying.

Williston Basin↗

USGS2012

The interactive effects of excess reactive nitrogen and climate change on aquatic ecosystems and water resources of the United States

Nearly all freshwaters and coastal zones of the US are degraded from inputs of excess reactive nitrogen (Nr), sources of which are runoff, atmospheric N deposition, and imported food and feed. Some major adverse effects include harmful algal blooms, hypoxia of fresh and coastal waters, ocean acidification, long-term harm to human health, and increased emissions of greenhouse gases. Nitrogen fluxes to coastal areas and emissions of nitrous oxide from waters have increased in response to N inputs. Denitrification and sedimentation of organic N to sediments are important processes that divert N from downstream transport. Aquatic ecosystems are particularly important denitrification hotspots. Carbon storage in sediments is enhanced by Nr, but whether carbon is permanently buried is unknown. The effect of climate change on N transport and processing in fresh and coastal waters will be felt most strongly through changes to the hydrologic cycle, whereas N loading is mostly climate-independent. Alterations in precipitation amount and dynamics will alter runoff, thereby influencing both rates of Nr inputs to aquatic ecosystems and groundwater and the water residence times that affect Nr removal within aquatic systems. Both infrastructure and climate change alter the landscape connectivity and hydrologic residence time that are essential to denitrification. While Nr inputs to and removal rates from aquatic systems are influenced by climate and management, reduction of N inputs from their source will be the most effective means to prevent or to minimize environmental and economic impacts of excess Nr to the nation’s water resources.

Biogeochemistry↗

USGS2018

Intensive oyster aquaculture can reduce disease impacts on sympatric wild oysters

Risks associated with disease spread from fish and shellfish farming have plagued the growth and public perception of aquaculture worldwide. However, by processing nutrients and organic material from the water column, the culture of many suspension-feeding bivalves has been proposed as a novel solution toward mitigating problems facing coastal water quality, including the removal of disease-causing parasites. Here we developed and simulated an epidemiological model describing sympatric oyster Crassostrea virginica populations in aquaculture and the wild impacted by the protozoan parasite Perkinsus marinus . Our model captured the indirect interaction between wild and cultured populations that occurs through sharing water-borne P. marinus transmission stages, and we hypothesized that oyster aquaculture can enhance wild oyster populations through reduced parasitism as long as cultured oysters are harvested prior to spreading disease. We found that the density of oysters in aquaculture, which is commonly thought to lead to the spread of disease through farms and out to nearby populations in the wild, has only indirect effects on P. marinus transmission through its interaction with the rate of aquaculture harvests. Sufficient aquaculture harvest, which varies with the susceptibility of farmed oysters to P. marinus infection and their lifespan once infected, reduces disease by diluting parasites in the environment. Our modeling results offer new insights toward the broader epidemiological implications of oyster aquaculture and effective disease management.

Aquaculture Environment Interactions↗

USGS2015

Science foundation Chapter 5 Appendix 5.1: Case study dabbling ducks

Dabbling ducks are the most abundant group of waterfowl that overwinter in the shallow wetlands and ponds of San Francisco Bay (SFB). Species within this group are primarily omnivorous, feeding on both plant material and macroinvertebrate prey by “tipping” to access benthic foods in bottom sediments or by foraging in the water column. Although the majority of these ducks are migratory, smaller numbers also nest locally in the SFB. These species vary in body size, ranging from the large mallard ( Anas platyrhynchos ) to the small green-winged teal ( Anas crecca ). Other dabbling duck species present in the SFB include American wigeon ( Anas americana ), gadwall ( Anas strepera ), cinnamon teal ( Anas cyanoptera ), northern shoveler ( Anas clypeata ), northern pintail ( Anas acuta ), and wood duck ( Aix sponsa ). Most of these dabbling duck species are known to breed in the SFB with the exception of the American wigeon and green-winged teal. However, the majority of wintering ducks originate from breeding grounds in the Central Valley of California, Pacific Coast States, Alaska, and Intermountain States/provinces, prairie potholes, and boreal forest. Their wintering populations in SFB are greatest between October and January, and dabbling duck species are found in all SFB regions. However, most dabbling duck use is associated with former salt production ponds and in the north and south bays, and managed wetlands of the Suisun Marsh.

California↗

USGS2022

Spatial and temporal variability in lake trout diets in Lake Ontario as revealed by stomach contents and stable isotopes

Lake trout ( Salvelinus namaycush ) are an ecologically and economically important piscivore with reported differences in diet and feeding behaviour throughout its range. Eleven stomach content and stable isotope-based metrics were used to describe diets of 349 lake trout between two years (2013 and 2018) and among geographic zones (west, central, east, Kingston basin) in Lake Ontario. Using individual (e.g., volumetric, %V) and aggregate (e.g., index of relative importance, %IRI) diet metrics, we found an overwhelming dominance of alewife ( Alosa pseudoharengus ) in lake trout diets among some zones in 2013 (%V = 23.3 – 92.7; %IRI = 12.2 – 99.5) and all zones in 2018 (%V = 83.9 – 96.7; %IRI = 96.5 – 100). Round goby ( Neogobius melanostomus ) and rainbow smelt ( Osmerus mordax ) were secondary lake trout prey items with relative diet percentages only marginally reflected by spatial and temporal variation in prey abundance (round goby: %V = 1.0 – 33.3, %IRI = 0.1 – 13.2; rainbow smelt: %V = 2.5 – 54.0, %IRI = 0.1 – 54.0). Carbon (δ 13 C) and nitrogen (δ 15 N) isotopic niche areas and orientations were similar across all year-zone combinations reinforcing temporal and spatial consistency in lake trout diet. The findings of this study advance the time series in describing Lake Ontario lake trout diets and can be used to complement stock assessments and management decisions associated with carrying capacity for the diverse salmonid community.

Lake Ontario↗

USGS2020

Bidirectional connectivity via fish ladders in a large Neotropical river: Response to a comment

In a recent article, we described fitting electronic tags to the fish Prochilodus lineatus to document how a fishway connected aquatic habitats downstream and upstream of a major dam. Moreover, given that tagged fish remained upstream or downstream for periods extending months and years before returning to the fishway, and that observed patterns of passage were consistent with seasonal migratory cycles, and building on existing literature, we speculated that the fishway allows fish access to spawning habitats upstream and feeding habitats downstream. Our interpretation of the movement data resulted in several comments from Pelicice, Pompeu, and Agostinho (2020) and they outline various reasons by which, in their opinion, some of our conclusions may be mistaken. Their critique is threefold. First, they argue that the percentage of fish attracted into the fishway is too low to consider the fishway an effective link between the reservoir and the river downstream. We contend that without estimates of population size it is impossible to judge if 28% passage is “limited”; conceivably, the absolute number of fish passed may still be enough to maintain a viable population. Second, they assert that because receivers were located only in the fishway it is unknown if fish that used the fishway remained near the dam, or if they continued their migration. We counter with a brief literature review that documents P. lineatus migrating through reservoirs and spawning in tributaries. Third, they advocate for a broader conservation perspective and for additional research. We agree and, in the article, had already expressed this view that fishways are only a temporary fix and that we support their use only as an element of a broader environmental management package. We also agree with the need for more research but argue that procrastinating on conservation action may not be wise because we do not know if the research will be done, how long it will take, or what the cost may be of waiting.

Parana River↗

USGS2022

Ontogenetic development of pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus) from hatch through yolk absorption

Sturgeons have a complex free-embryo period extending from hatch to the initiation of exogenous feeding. Although available for some sturgeon species of the genus Acipenser , descriptions of the developmental stages of free embryos of the genus Scaphirhynchus are lacking. We characterised the ontogenetic development of pallid sturgeon ( Scaphirhynchus albus ) and shovelnose sturgeon ( S . platorynchus ) free embryos from hatch through melanin plug expulsion. The rate of development was similar between Scaphirhynchus species among free embryos from 4 pallid sturgeon and 7 shovelnose sturgeon crosses reared separately in the laboratory at a mean temperature of 17.8°C. Free embryos required a mean of 18.2 days postfertilisation (DPF; 323.5 cumulative thermal units; CTU) to reach melanin plug expulsion for pallid sturgeon and 17.9 DPF (318.3 CTU) for shovelnose sturgeon. Free embryos of both species showed overlap in lengths among developmental stages indicating that length of free embryos alone is insufficient to estimate age. Description of pallid sturgeon and shovelnose sturgeon free-embryo development provides a template to develop more sophisticated models incorporating length and stage to estimate the age of field-collected specimens. Improved estimates of free-embryo developmental stage and age may aid in the identification of timing and location of spawning and better inform flow manipulation and habitat management actions tailored to increase survival of early life-stage pallid sturgeon.

Ecology of Freshwater Fish↗

USGS2023

Red Knot stopover population size and migration ecology at Delaware Bay, USA, 2023

Red Knots ( Calidris canutus rufa ) stop at Delaware Bay on the mid-Atlantic coast of North America during northward migration to feed on eggs of horseshoe crabs ( Limulus polyphemus ). We conducted a mark-recapture-resight investigation to estimate the passage population of Red Knots at Delaware Bay in 2023. We used a Bayesian analysis of a Jolly-Seber model, which accounts for turnover in the population and the probability of detection during surveys. The 2023 passage population size was estimated at 39,361 (95% credible interval: 33,724–47,556). Although there is broad overlap in the credible intervals for population estimates from 2020–2023, the population estimate for 2023 was below 40,000 birds for only the second time since 2011. Horseshoe crabs have been harvested for use as bait in eel ( Anguilla rostrata ) and whelk ( Busycon ) fisheries since at least 1990. In the late 1990s and early 2000s, the number of Red Knots counted during aerial surveys at Delaware Bay declined from ~50,000 to ~13,000 and some avian conservation biologists hypothesized that horseshoe crab harvest levels in the 1990s prevented sufficient refueling for successful migration to the Arctic breeding grounds, reproduction, and survival for the remainder of the annual cycle. Since 2013, the harvest of horseshoe crabs in the Delaware Bay region has been managed using an Adaptive Resource Management (ARM) framework. The objective of the ARM framework is to manage sustainable harvest of Delaware Bay horseshoe crabs while maintaining ecosystem integrity and supporting Red Knot recovery with adequate stopover habitat for Red Knots and other migrating shorebirds. For annual harvest recommendations, the ARM framework requires annual estimates of horseshoe crab population size and the Red Knot stopover population size. The 2023 population size estimate will inform harvest recommendations in the next management cycle for decision making by the Atlantic States Marine Fisheries Commission.

Delaware, New Jersey↗

USGS2015

Annual variation in recruitment of freshwater mussels and its relationship with river discharge

Vital rates such as mortality, growth, and recruitment are important tools to evaluate the status of threatened populations and identify their vulnerabilities, leading to enhanced conservation strategies. Native freshwater mussels are a guild of largely sedentary, filter-feeding bivalves currently facing worldwide declines. Lack of recruitment has been identified as a major threat to mussel populations. A mussel bed in the Upper Mississippi River was sampled for 5 years (2008–2012). A trend analysis showed a significant decline in the percentage of species with juvenile representatives. Species were grouped into equilibrium and periodic life history strategies to assess past recruitment. Residuals from catch-curve regressions quantified past year-class strength of both strategists and Amblema plicata over a 13-year period (1994–2006), and identified strong and weak year-classes. Generalized linear regression models containing July maximum discharge and April minimum discharge explained 64% of the variation in recruitment strength of A. plicata . The best model for the equilibrium strategists explained 86% of the variation in recruitment and contained the same variables as A. plicata, but also incorporated the 7-day minimum discharge. For the periodic strategists, the model containing the number of low-flow pulses and the mean duration of high-flow pulses explained 56% of the variation in recruitment strength. Understanding variation in recruitment dynamics of native mussels and its relationship to river discharge will be useful in designing effective management strategies to enhance conservation of this imperilled fauna.

Minnesota↗

USGS2026

Whitefishes—Coregonus spp.

Coregonines represent a diverse group of fishes of the Salmonidae subfamily Coregoninae that have ecological, cultural, and economical importance throughout their range. They are prey for other commercially and recreationally important predatory fish and are harvested for human consumption (Cleland 1982). Coregonines are generally cool- and coldwater species distributed across the northern hemisphere. The Laurentian Great Lakes of North America experienced considerable loss of coregonine biodiversity due to overfishing, the effects of nonnative species, and habitat loss (Bunnell et al. 2023). This resulted in the extinction of several species (Deepwater Cisco, Longjaw Cisco, and Kiyi) and local extirpations of other species (Blackfin Cisco, Shortnose Cisco, Shortjaw Cisco, Bloater, and Cisco) across all lakes (Bunnell et al. 2023). Renewed interest in restoring coregonines as the native prey base in the Laurentian Great Lakes prompted the development of a multi-agency restoration framework (Bunnell et al. 2023, 2024), and stocking of hatchery-produced coregonines is one of the management tools being used in this large restoration effort. This chapter focuses on culture methods for Lake Whitefish, Cisco, and Bloater currently being propagated for restoration and reintroduction in the Great Lakes (Bunnell et al. 2023). The techniques used for these species can serve as a starting point for the culture of other cisco species, such as Kiyi, which fisheries managers may consider for restoration stocking. Lake Whitefish, Cisco, and Bloater (Figure 1) are similar in appearance but have distinctively different life histories. They are silvery-white-colored fish and possess an adipose fin. Lake Whitefish are distinguished from Cisco and Bloater by a snout that overhangs the lower jaw (subterminal), whereas Cisco and Bloater have a lower jaw that extends beyond the snout (terminal). Lake Whitefish can reach lengths up to 79 cm (Phillips et al. 1982). Cisco and Bloater are smaller, reaching lengths of 34 and 30 cm, respectively (Eshenroder et al. 2016; Bunnell et al. 2023). Cisco and Bloater are similar in appearance but can be differentiated by head profiles, number of gill rakers (47 for Cisco and 42 for Bloater; Bunnell et al. 2023), and body morphometry. Lake Whitefish spawn from September through January in water depths of 2–4 m (Phillips et al. 1982). Cisco spawn from November through December in water depths of 1–47 m (Paufve et al. 2022), whereas Bloater spawn later in winter (February through May) at depths of 37–92 m (Koelz 1929; Becker 1983; Eshenroder et al. 2016). After eggs of all three species hatch in the spring, larvae feed on zooplankton and then switch to larger invertebrate prey as they grow; some will begin to feed on other fish species as they reach maturity (Warren and Lehman 1988; Brown and Taylor 1992; Breaker et al. 2020; Gatch et al. 2021). All three species typically mature at ages 4–5, with some maturing beginning at age 2 (Beauchamp 2002; Gorman 2012; DeCosta 2016).

Book chapter↗

USGS2024

Feeding habits and ecological implications of the invasive Flathead Catfish in the Susquehanna River basin, Pennsylvania

Objective Flathead Catfish Pylodictis olivaris are a widespread aquatic invasive species within the United States and a recent invader in the Susquehanna River basin, Pennsylvania. Flathead Catfish are piscivores known to consume native and recreationally important fish species. In the mid-Atlantic United States, it is unknown how this invader is impacting food webs and which species may be at greatest predation risk. To address this knowledge gap, we DNA barcoded stomach contents collected from Flathead Catfish to identify prey species and elucidate potential predatory impacts of Flathead Catfish in the Susquehanna River. Methods We used a Bayesian hierarchical multivariate probit model to investigate if the probability of prey species occurrence in the diets of Flathead Catfish varied seasonally or was a function of Flathead Catfish length. Result A total of 576 Flathead Catfish were collected during 2020–2021, with 241 individuals having recoverable stomach contents. In all, we identified 47 different prey species. The most common prey species were rusty crayfish Faxonius rusticus , Margined Madtom Noturus insignis , and shiners Notropis spp . While frequency of occurrence of prey species differed across Flathead Catfish length classes (<300 mm, 301–600 mm, 601–900 mm TL), rusty crayfish were commonly found (33.7–44.0% of diets) in stomachs of all size-classes. Conclusion We found that Flathead Catfish length and seasonality did influence occurrence probability differentially for several prey species. For example, Channel Catfish Ictalurus punctatus were more likely to appear in shorter Flathead Catfish while Smallmouth Bass Micropterus dolomieu appeared in larger Flathead Catfish. We demonstrate significant variation in Flathead Catfish predation, increasing our understanding of predator–prey dynamics, which is necessary to better manage and identify future impacts to aquatic communities in the Susquehanna River basin.

Pennsylvania↗

USGS2014

Evaluation of analytical techniques to determine AQUI-S® 20E (eugenol) concentrations in water

There is a critical need in U.S. public aquaculture and fishery management programs for an immediate-release sedative, i.e. a compound that can be safely and effectively used to sedate fish and subsequently, allow for their immediate release. AQUI-S® 20E (10% active ingredient, eugenol; any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government) is being pursued for U.S. approval as an immediate-release sedative. As part of the approval process, data describing animal safety and efficacy are needed. Essential to conducting studies that generate those data, is a method to accurately and precisely determine AQUI-S® 20E concentrations in exposure baths. Spectrophotometric and solid phase extraction (SPE)–high pressure liquid chromatography (LC) methods were developed and evaluated as methods to determine AQUI-S® 20E (eugenol) concentrations in water, methods that could be applied to any situation where eugenol was being evaluated as a fish sedative. The spectrophotometric method was accurate and precise (accuracy, > 87%; precision, < 0.70 %CV) when determining eugenol concentrations in solutions of 50 to 1000 mg/L AQUI-S® 20E made with LC grade water and water with varying pH and hardness. The spectrophotometric method's accuracy was negatively affected when analyzing water containing fish feed. The SPE–LC method was also accurate and precise (accuracy > 86%; precision < 8.9 %CV) when determining eugenol concentrations in solutions of 50 to 1000 mg/L AQUI-S® 20E made with LC grade water and water with varying pH and hardness. The SPE–LC method was influenced to a lesser degree by the presence of fish feed indicating greater specificity for eugenol.

Aquaculture↗

USGS2015

Comparative demographics of a Hawaiian forest bird community

Estimates of demographic parameters such as survival and reproductive success are critical for guiding management efforts focused on species of conservation concern. Unfortunately, reliable demographic parameters are difficult to obtain for any species, but especially for rare or endangered species. Here we derived estimates of adult survival and recruitment in a community of Hawaiian forest birds, including eight native species (of which three are endangered) and two introduced species at Hakalau Forest National Wildlife Refuge, Hawaiʻi. Integrated population models (IPM) were used to link mark–recapture data (1994–1999) with long-term population surveys (1987–2008). To our knowledge, this is the first time that IPM have been used to characterize demographic parameters of a whole avian community, and provides important insights into the life history strategies of the community. The demographic data were used to test two hypotheses: 1) arthropod specialists, such as the ‘Akiapōlā‘au Hemignathus munroi , are ‘slower’ species characterized by a greater relative contribution of adult survival to population growth, i.e. lower fecundity and increased adult survival; and 2) a species’ susceptibility to environmental change, as reflected by its conservation status, can be predicted by its life history traits. We found that all species were characterized by a similar population growth rate around one, independently of conservation status, origin (native vs non-native), feeding guild, or life history strategy (as measured by ‘slowness’), which suggested that the community had reached an equilibrium. However, such stable dynamics were achieved differently across feeding guilds, as demonstrated by a significant increase of adult survival and a significant decrease of recruitment along a gradient of increased insectivory, in support of hypothesis 1. Supporting our second hypothesis, we found that slower species were more vulnerable species at the global scale than faster ones. The possible causes and conservation implications of these patterns are discussed.

Hawaii↗