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At least 289 records · Page 16Linked to original sources
USGS1989

Magnification of secondary production by kelp detritus in coastal marine ecosystems

Kelps are highly productive seaweeds found along most temperate latitude coastlines, but the fate and importance of kelp production to nearshore ecosystems are largely unknown. The trophic role of kelp-derived carbon in a wide range of marine organisms was assessed by a natural experiment. Growth rates of benthic suspension feeders were greatly increased in the presence of organic detritus (particulate and dissolved) originating from large benthic seaweeds (kelps). Stable carbon isotope analysis confirmed that kelp-derived carbon is found throughout the nearshore food web.

Science↗
USGS1965

Automatic feeder for small fish held in tanks

The Northville (Michigan) Biological Station has been a center for study of the developmental morphology of coregonid fishes. This work requires the production of numerous individual series of lake herring, lake whitefish, and several species of chubs from parent fish of positively known identity. The offspring of individual pairs or groups of fish must be held in individual tanks from the time they hatch until they reach maturity. One of the important problems in this project has been the poor growth of most fish. Though some have grown well, their growth has been less than that of the same species in nature, and a few fish from each hatch have grown very slowly. Irregularity of feeding may contribute to the slow growth of laboratory fish. The hatchery caretaker feeds them several times during his 8-hour workday, but they must go without food during the remaining 16 hours. The high metabolic rate of small fish, however, appears to make them strongly inclined toward almost continual feeding. Belief that greater, more regular food consumption would result from a mechanical feeder providing a continuous supply of food over a longer period of the day led to development of the equipment described in this paper.

Progressive Fish-Culturist↗
USGS1995

Predator-prey relations and competition for food between age-0 lake trout and slimy sculpins in the Apostle Island region of Lake Superior

Slimy sculpins ( Cottus cognatus ) are an important component of the fish community on reefs and adjacent nursery areas of the Great Lakes and overlap spatially with age-0 lake trout ( Salvelinus namaycush ). Important interactions between these fishes are possible during the lake trout's first year of life, which could include predation on each other's eggs and larvae, and competition for food resources. We investigated the diets of age-0 lake trout and slimy sculpins on a lake trout spawning reef (Gull Island Shoal) and adjacent nursery area (near Michigan Island) in the Apostle Island region of western Lake Superior during June through September from 1988 through 1991. Organisms in stomachs of 511 lake trout and 562 sculpins were identified and counted. Of the 11 major food types found in age-0 lake trout stomachs from both areas, Mysis was the dominant food item (mean volume in stomachs = 68%) and occurred in about 3/4 of the fish analyzed. Copepods, cladocerans, chironomid pupae, fish, and Bythotrephes were also common in the diet (frequency of occurrence > 4%). Diets of lake trout were more diverse on the reef than on the nursery area where Mysis dominated the diet. Slimy sculpins were only found in lake trout greater than 50 mm. Mysis was an important food item of slimy sculpins over the reef but not over the nursery area, where Diporeia was by far the most important taxon. A variety ofben-thic invertebrates (Asellus, chironomids, benthic copepods, and snails) comprised the bulk of the sculpin diet over the reef. Sculpins also ate lake trout eggs in November. Based on cluster analysis, diets were most similar over the reef where both consumed Mysis , calanoid copepods and chironomid pupae. Diets diverged over the nursery areas where sculpins were strictly benthic feeders and lake trout maintained their planktonic diet. In Lake Superior, where lake trout recruitment through natural reproduction has become well established, the coexistence of the two species appears amicable. However, in other Great Lakes with higher sculpin to lake trout ratios on a reef, the coexistence of the two species may be a bottleneck for age-0 lake trout survival beginning with egg deposition and ending when age-0 lake trout move off the reef and the two species no longer compete for a common food resource.

Journal of Great Lakes Research↗
USGS2020

Compilation of mercury data and associated risk to human and ecosystem health, Bad River Band of Lake Superior Chippewa, Wisconsin

Mercury is an environmentally ubiquitous neurotoxin, and its methylated form presents health risks to humans and other biota, primarily through dietary intake. Because methylmercury bioaccumulates and biomagnifies in living tissue, concentrations progressively increase at higher trophic positions in ecosystem food webs. Therefore, the greatest health risks are for organisms at the highest trophic positions and for humans who consume organisms such as fish from these high trophic positions. Data on environmental mercury concentrations in various media and biota provide a basis for comparison among sites and regions and for evaluating ecosystem health risks. The U.S. Geological Survey, in cooperation with the Natural Resources Department, Bad River Band of Lake Superior Chippewa, have compiled a dataset from analyses of mercury concentrations in surface water, bed sediment, fish tissue, Rana clamitans (green frog) tissue, Haliaeetus leucocephalus (bald eagle) feathers, Lontra canadensis (North American river otter) hair, Zizania palustris (northern wild rice), and litterfall from samples collected in the Bad River watershed, Wisconsin during 2004–18. These data originated from either the Natural Resources Department or another agency based on samples collected within or near to Bad River Tribal lands before transfer to the U.S. Geological Survey for compilation and analysis at the onset of the project. This report describes the compiled mercury dataset, provides comparisons to similar measurements in the region and elsewhere, and evaluates health risks to humans and to the sampled biota. Except for litterfall, data were not collected on a consistent, regular basis over a sufficient period to evaluate temporal patterns. The reported mercury concentrations are generally similar to those reported elsewhere in the upper Great Lakes region. Reported values are consistent with atmospheric deposition as the principal source and reflect a favorable environment for mercury methylation. Fish mercury concentrations increased at higher food web positions and generally increased with length in most species measured. Sander vitreus (walleye) present the greatest risk to humans among fishes considered here because of their high trophic position and associated elevated mercury concentrations in combination with relatively high walleye consumption rates by the Native American community. Methylmercury concentrations in wild rice are generally low and likely pose little health risk. Despite reports of declining atmospheric mercury deposition across eastern North America during the past decade, a downward trend in litterfall mercury deposition was not evident in samples collected during 2012–18. Limitations in this data compilation and analysis were noted due to missing information such as collection dates and site locations for some samples. Regular monitoring of mercury in litterfall and surface waters along with periodic collection of fish would enable evaluation of temporal change in the mercury cycle that might affect future risk to humans and aquatic ecosystem inhabitants.

Wisconsin↗
USGS2012

Ground water and climate change

As the world's largest distributed store of fresh water, ground water plays a central part in sustaining ecosystems and enabling human adaptation to climate variability and change. The strategic importance of ground water for global water and food security will probably intensify under climate change as more frequent and intense climate extremes (droughts and floods) increase variability in precipitation, soil moisture and surface water. Here we critically review recent research assessing the impacts of climate on ground water through natural and human-induced processes as well as through groundwater-driven feedbacks on the climate system. Furthermore, we examine the possible opportunities and challenges of using and sustaining groundwater resources in climate adaptation strategies, and highlight the lack of groundwater observations, which, at present, limits our understanding of the dynamic relationship between ground water and climate.

Nature Climate Change↗
USGS2023

Dietary comparison of age-0 sturgeon (Scaphirhynchus sp.) between upper and lower Missouri River basins

Understanding potential limiting factors affecting population growth of the endangered pallid sturgeon, Scaphirhynchus albus, is important in the upper (UMOR) and lower Missouri River (LMOR) basins. The UMOR is upstream of several reservoirs and generally has more natural habitat features, whereas the LMOR is downstream of these reservoirs and has been channelized to support navigation. In both sections, pallid sturgeon recruitment to age-1 is a concern, but hypothesized for different reasons. One hypothesis in the LMOR centers on food limitation for age-0 fish, which is not considered an issue in the UMOR, but evaluating this hypothesis is challenging given the rarity of age-0 pallid sturgeon. As a result, the related, more abundant shovelnose sturgeon ( S. platorhynchus ) has been considered as a potential surrogate to assess food-related hypotheses. Thus, the purpose of our study was to compare diets of age-0 sturgeon captured in 2016 from three reaches in the LMOR (Copeland, Langdon, and Lexington) with individuals captured from a reach in the UMOR (Williston) during the same year to provide additional context regarding potential food limitation in the LMOR. Consumption percentage (prey weight in the gut as a percentage of body weight) was similar among all reaches, but diet composition was different for the most downstream reach in the LMOR. Age-0 sturgeon in the UMOR reach as well as the two upstream LMOR reaches primarily consumed Diptera larvae along with Ephemeroptera nymphs. In contrast, age-0 sturgeon in the most downstream LMOR reach (Lexington) almost exclusively consumed Diptera larvae. These results may provide information on relative differences in prey availability between Lexington and the other upstream reaches but the similarity in consumption percentage values across all reaches provide further evidence that age-0 sturgeon are not food limited in the LMOR.

Upper and lower Missouri River basins↗
USGS1957

Physical and ecologic features of the Sagadahoc Bay Tidal Flat, Georgetown, Maine

Sagadahoc Bay is open to the ocean at the south and has no significant fresh-water stream entering it. The intertidal zone is roughly a mile long by half a mile wide; most of it is made up of medium to fine sand, but organic-rich mud characterizes the head of the flat and the protected coves. Refraction-seismograph surveys showed that the bedrock surface lies 30 to 200 feet below the surface of the tidal flat and that it is irregular and fluted longitudinally. Repeated surveys indicate that the intertidal flat builds up and cuts down but is apparently in equilibrium with the present sea level. The sediment that fills the bay came from the sea. Waves and tidal currents tend to move it landward; storms accelerate this, or reverse the direction of movement, depending on the characteristics of the storm. Tidal- and wave-generated currents 0.1 foot above the bottom range in velocity from 0.35 to 0.82 foot per second on incoming tides and from 0.20 to 0.58 foot per second on ebbing tides. Incoming tides float large quantities of sand landward; ebbing tides never carry floating sand. Two distinctive and extensive Mya shell-pavement layers were found at depths of roughly 2 and 3 feet below the present surface of the tidal flat. The lower layer is approximately 1,000 years old according to a radiocarbon age determination of its Mya shells. It is suggested that these shell layers formed by sluicing away of a layer of sand about 2 feet thick, which had been thrown into loose packing by an earthquake at high tide. The earth shock induced a submarine slide of the sand in the outer part of the bay, which oversteepened the profile of the sand headward nearly to the head of the bay. Mya and other shells settled through the layer of quicksand while the sand was running out seaward. Living in the intertidal zone is the usual assemblage of clams, gastropods, crustaceans, worms, and seaweeds found on most northern New England tidal flats. The Mya arenaria population is decreasing, but in general myas are more numerous in the muddy areas than in the sandy areas. They grow more rapidly in the sand, though in the past decade there has been no significant renewal of the Mya population in the sandy part of the flat. Macoma balthica inhabits the muddy areas, whereas Ensis, Spisula, and Arctica are restricted to the low-tide zone and the shallow water below. Gemma gemma grows in great abundance in the sandy part of the flat but is rare in the muddy parts. Small shrimp and green crabs are common. The calcareous shells of these animals are all potential fossils, but the shrimp and crab exoskeletons are not, for their tests are rapidly decomposed in this environment. Other potential fossils are wood and bark, acorn caps, conifer cones, leaves of deciduous trees, seeds, and occasionally even grass stems and pieces of eel grass. All these are reasonably well preserved in the constant reducing environment that prevails an inch or two below the surface. An inverse relationship exists between the abundances of Mya arenaria and Gemma gemma. Cores and test pits show that gemmas are more numerous on the Sagadahoc flat now than they have been in the recent past (estimated 10–100 years). Gemmas are the dominant mollusk in the sandy part of the flat now that the myas are so extremely rare. The speculation is that gemmas became dominant largely because the Mya population was greatly reduced by intensive digging during and just after the last war and through depredations by green crabs. Possibly the warming climate has favored the gemmas selectively. The writer infers that the gemmas are a serious competitor of the myas and that the gemmas now starve out Mya spat, which is known to be carried into the bay each spring and fall. Two recommendations are made: (1) determining under controlled laboratory conditions the food requirements of Gemma and the density of Gemma population that will permit survival of Mya larvae from set through a stage that will assure maturation; and (2) killing off a large percentage of the Gemma population and observing whether or not a natural set of Mya occurs. Gemmas can be killed quickly under a flame shield such as is used to soften asphalt-sand mixtures in street paving. Inasmuch as gemmas are ovoviviparous they should not repopulate the flat rapidly.

Maine↗
USGS2006

Cadmium risks to freshwater life: derivation and validation of low-effect criteria values using laboratory and field studies

In 2001, the U.S. Environmental Protection Agency (EPA) released updated aquatic life criteria for cadmium. Since then, additional data on the effects of cadmium to aquatic life have become available from studies supported by the EPA, Idaho Department of Environmental Quality (IDEQ), and the U.S. Geological Survey, among other sources. Updated data on the effects of cadmium to aquatic life were compiled and reviewed and low-effect concentrations were estimated. Low-effect values were calculated using EPA's guidelines for deriving numerical national water-quality criteria for the protection of aquatic organisms and their uses. Data on the short-term (acute) effects of cadmium on North American freshwater species that were suitable for criteria derivation were located for 69 species representing 57 genera and 33 families. For longer-term (chronic) effects of cadmium on North American freshwater species, suitable data were located for 28 species representing 21 genera and 17 families. Both the acute and chronic toxicity of cadmium were dependent on the hardness of the test water. Hardness-toxicity regressions were developed for both acute and chronic datasets so that effects data from different tests could be adjusted to a common water hardness. Hardness-adjusted effects values were pooled to obtain species and genus mean acute and chronic values, which then were ranked by their sensitivity to cadmium. The four most sensitive genera to acute exposures were, in order of increasing cadmium resistance, Oncorhynchus (Pacific trout and salmon), Salvelinus ('char' trout), Salmo (Atlantic trout and salmon), and Cottus (sculpin). The four most sensitive genera to chronic exposures were Hyalella (amphipod), Cottus, Gammarus (amphipod), and Salvelinus. Using the updated datasets, hardness dependent criteria equations were calculated for acute and chronic exposures to cadmium. At a hardness of 50 mg/L as calcium carbonate, the criterion maximum concentration (CMC, or 'acute' criterion) was calculated as 0.75 mug/L cadmium using the hardness-dependent equation CMC = e(0.8403 ? ln(hardness)-3.572) where the 'ln hardness' is the natural logarithm of the water hardness. Likewise, the criterion continuous concentration (CCC, or 'chronic' criterion) was calculated as 0.37 mug/L cadmium using the hardness-dependent equation CCC = (e(0.6247 ? ln(hardness)-3.384)) ? (1.101672 - ((ln hardness) ? 0.041838))). Using data that were independent of those used to derive the criteria, the criteria concentrations were evaluated to estimate whether adverse effects were expected to the biological integrity of natural waters or to selected species listed as threatened or endangered. One species was identified that would not be fully protected by the derived CCC, the amphipod Hyalella azteca. Exposure to CCC conditions likely would lead to population decreases in Hyalella azteca, the food web consequences of which probably would be slight if macroinvertebrate communities were otherwise diverse. Some data also suggested adverse behavioral changes are possible in fish following long-term exposures to low levels of cadmium, particularly in char (genus Salvelinus). Although ambiguous, these data indicate a need to periodically review the literature on behavioral changes in fish following metals exposure as more information becomes available. Most data reviewed indicated that criteria conditions were unlikely to contribute to overt adverse effects to either biological integrity or listed species. If elevated cadmium concentrations that approach the chronic criterion values occur in ambient waters, careful biological monitoring of invertebrate and fish assemblages would be prudent to validate the prediction that the assemblages would not be adversely affected by cadmium at criterion concentrations.

Scientific Investigations Report↗
USGS2022

Floodplains and climate change

Floodplains are landscape features that are periodically inundated by water from adjacent rivers (Opperman et al. 2010). Ecologically, functional floodplains are characterized by three primary elements: connectivity, flow regime, and spatial scale. Water quantity flowing over floodplains can vary greatly. Based on a flood’s effects on the floodplain, three flood categories have been defined: floodplain-activation floods, floodplain-maintenance floods, and floodplainresetting floods (Box 1). Several physical parameters determine the types of ecosystems on floodplains and the species they will support; these include temperature, water depth, water velocity, and hydrologic connectivity (Opperman et al. 2010). Natural ecosystems commonly found on floodplains include annual vegetation, forests, seasonal wetlands, and permanent ponds or wetlands (Whipple et al. 2012). Floodplains provide many valuable ecosystem services: attenuation of flood flows which reduces flood risk, filtration of surface water, recreation, fisheries, agriculture, biodiversity, food availability, and groundwater recharge, which contributes to more-sustained and cooler dry-season flows (Opperman et al. 2010). -------------------------------------------------------------------------------------------------------------- Box 1 Floodplain-activation flood A small magnitude flood that occurs relatively frequently and produces characteristic ecological benefits such as food-web productivity and habitat creation for native fish spawning and rearing. Floodplain-maintenance flood A higher magnitude flood that, in addition to providing ecological benefits, results in geomorphic changes including bank erosion and deposition on the floodplain. Floodplain-resetting flood A very high-magnitude flood that occurs rarely and results in extensive geomorphic changes, such as the scouring of floodplain surfaces and changes in channel location due to avulsion. ----------------------------------------------------------------------------

California↗
USGS2002

Interactions of an insecticide with competition and pond drying in amphibian communities

Amphibian populations are often imbedded in agricultural landscapes. Therefore the potential for contamination of their habitat is considerable. Our study examined the effects of an insecticide (carbaryl, a neurotoxin), on larval amphibian communities experiencing natural stresses of competition for resources, predation, and pond drying. In a set of experimental ponds, tadpoles of three anuran species (southern leopard frog [ Rana sphenocephala ], plains leopard frog [ R. blairi ], and the Woodhouse's toad [ Bufo woodhousii ]) were added to 1000-L ponds containing leaf litter, plankton, two newts ( Notophthalmus viridescens ), and four overwintered green frog ( R. clamitans ) tadpoles. We manipulated the overall tadpole density (low or high), pond hydroperiod (constant or drying), and chemical exposure (0, 3.5, 5.0, or 7.0 mg/L carbaryl) of the ponds. We measured mass, time, and survival to metamorphosis to determine treatment effects. Carbaryl positively affected Woodhouse's toad survival, although it had a negligible effect on both leopard frog species. Tadpole density interacted with the chemical treatment: Proportionately more Woodhouse's toads survived to metamorphosis in high-density environments than in low-density or control environments. Greater survival may be an indirect effect of increased algal food resources from carbaryl exposure. Most newts lost mass over the course of the experiment, although ponds with drying hydroperiods and high anuran density were the least favorable environments. Overwintered green frogs exposed to carbaryl had longer larval periods on average than did green frogs in control ponds. Our study demonstrated that even sublethal, short-lived contaminants can alter natural communities in ways that cannot be predicted from simple, one-factor studies.

Missouri↗
USGS1981

Mercury in the muscle tissue of fish from three northern Maine lakes

There is evidence that fish in Canadian wilderness areas exhibit elevated mercury levels because of the oligotrophic nature of the lakes they inhabit (BROUZES et al. 1977). D'ITRI et al. (1971) reported higher levels of mercury in trout from oligotrophic waters than in trout from eutrophic waters in unpolluted areas. They attributed part of the difference to differences in the food of the fish in the two types of waters. Position on the trophic scale is an important factor determining the degree of bioaccumulation of mercury by aquatic organisms, especially fish. Elevated mercury levels have been reported in fish from three wilderness lakes in northern Maine (NORMANDEAU ASSOCIATES 1978). Concentrations exceeding 0.50 ~g/g were detected in the muscle tissue of many of the fish. We report the levels of mercury in the muscle tissue of brook trout (Salvelinus fontinalis) and lake trout (S. namaycush) from three northern Maine lakes. Mercury levels in fish from two wilderness lakes in the same drainage basin were compared with each other, and in turn with those in fish from a lake in a separate drainage basin. The fish species composition in one of the wilderness lakes, Cliff Lake, is different from that in the other two lakes, enabling us to analyze the effects of trophic structure on mercury concentration in top carnivores. It is unlikely that mercury from agricultural, geological, or local industrial sources occurs in these lakes.

Bulletin of Environmental Contamination and Toxico↗
USGS2011

Mercury on the move during snowmelt in Vermont

Although mercury (Hg) emissions peaked in the United States over the last 20 to 40 years and are now declining, they remain well above natural background levels in soils and sediments. Only a small fraction of the Hg deposited from the atmosphere to the terrestrial landscape runs off in streamflow. However, some of this Hg is methylated in the environment and can potentially bioaccumulate to the top of food webs, posing a hazard to people who eat fish, especially children and pregnant women. What factors determine the amount of Hg that runs off in streams? During the 2000 snowmelt at Sleepers River in Vermont, strong correlations were found between dissolved and particulate mercury and the respective dissolved and particulate organic carbon fractions, even when data were pooled from 10 streams of diverse watershed size and land cover. Episodic export of particulate Hg during the highest flows appears to be the dominant mechanism of Hg movement.

Vermont↗
USGS2005

Perchlorate isotope forensics

Perchlorate has been detected recently in a variety of soils, waters, plants, and food products at levels that may be detrimental to human health. These discoveries have generated considerable interest in perchlorate source identification. In this study, comprehensive stable isotope analyses ( 37 Cl/ 35 Cl and 18 O/ 17 O/ 16 O) of perchlorate from known synthetic and natural sources reveal systematic differences in isotopic characteristics that are related to the formation mechanisms. In addition, isotopic analyses of perchlorate extracted from groundwater and surface water demonstrate the feasibility of identifying perchlorate sources in contaminated environments on the basis of this technique. Both natural and synthetic sources of perchlorate have been identified in water samples from some perchlorate occurrences in the United States by the isotopic method.

Analytical Chemistry↗
USGS2023

DNA metabarcoding-based evaluation of the diet of Big Brown Bats (Eptesicus fuscus) in the Mid-Atlantic region

High-throughput DNA sequencing can generate large genetic datasets in a cost-effective manner. Although the diet of Eptesicus fuscus (Big Brown Bat) has been studied widely in natural and rural systems using visual identification of prey items in feces, our aim was to more completely assess diet using a metabarcoding approach across a wide urban–natural landscape gradient in the mid-Atlantic region. Concordant with our expectations and previous Big Brown Bat diet studies from visual identification, we observed a high abundance of Coleoptera (beetles) relative to other insect orders. Although a possible improvement over visual techniques for studying food habits, we suggest caution in interpreting metabarcoding results in diet studies. We noted observations of environmental or contaminant taxa within these data, and designed a stringent filtering method that we used to eliminate these taxa, but that also removed previously documented prey taxa from our dataset.

Maryland, Pennsylvania, Virginia, West Virginia↗
USGS1995

Accumulation and loss of arsenic and boron, alone and in combination, in mallard ducks

Arsenic and boron are common in the environment, and wildlife can be exposed to toxic concentrations through both natural and human-influenced processes. We exposed adult male mallard ducks to dietary concentrations of 300 ppm arsenic as sodium arsenate, 1,600 ppm boron as boric acid, or both and estimated the tissue accumulation and loss rates when the ducks were returned to uncontaminated food. Both elements were accumulated rapidly; equilibrium levels were reached for arsenic in 10 to 30 d and for boron in 2 to 15 d. Accumulation of each element was slowed by the presence of the other in the diet. Boron was eliminated by mallards very rapidly, with few detectable residues ≥ 1 d after removal of boron from the diet; arsenic was also rapidly lost with half-lives of 1 to 3 d (half-lives were not constant throughout the loss period). Arsenic loss rate was not affected by the presence of boron. Arsenic accumulated to the highest level in liver tissue, with blood and brain levels lower; concentrations in the liver and blood were proportional but affected by the presence of boron. Boron concentrations were highest in the blood, followed by the brain and liver; concentrations in the blood and liver were proportional.

Environmental Toxicology and Chemistry↗
USGS2021

Understanding the effects of climate change via disturbance on pristine arctic lakes — Multitrophic level response and recovery to a 12-yr, low-level fertilization experiment

Effects of climate change-driven disturbance on lake ecosystems can be subtle; indirect effects include increased nutrient loading that could impact ecosystem function. We designed a low-level fertilization experiment to mimic persistent, climate change-driven disturbances (deeper thaw, greater weathering, or thermokarst failure) delivering nutrients to arctic lakes. We measured responses of pelagic trophic levels over 12 yr in a fertilized deep lake with fish and a shallow fishless lake, compared to paired reference lakes, and monitored recovery for 6 yr. Relative to prefertilization in the deep lake, we observed a maximum pelagic response in chl a (+201%), dissolved oxygen (DO, −43%), and zooplankton biomass (+88%) during the fertilization period (2001–2012). Other responses to fertilization, such as water transparency and fish relative abundance, were delayed, but both ultimately declined. Phyto- and zooplankton biomass and community composition shifted with fertilization. The effects of fertilization were less pronounced in the paired shallow lakes, because of a natural thermokarst failure likely impacting the reference lake. In the deep lake there was (a) moderate resistance to change in ecosystem functions at all trophic levels, (b) eventual responses were often nonlinear, and (c) postfertilization recovery (return) times were most rapid at the base of the food web (2–4 yr) while higher trophic levels failed to recover after 6 yr. The timing and magnitude of responses to fertilization in these arctic lakes were similar to responses in other lakes, suggesting indirect effects of climate change that modify nutrient inputs may affect many lakes in the future.

Alaska↗
USGS2020

Effects of density reduction on age-specific growth of stream-dwelling Brown Trout

Density-dependent growth has been well documented among stream-dwelling Brown Trout Salmo trutta populations. In Spearfish Creek, South Dakota, biomass of adult Brown Trout (>200 mm) is about three times greater than that reported for similar Black Hills streams, whereas the mean length of adult fish is about 30% less. Here, we evaluate density reduction as a management tool for improving the growth rate of stream-dwelling Brown Trout. We compared age-specific growth of wild Brown Trout in stream sections receiving 50% reductions in fish abundance (removal sections) to that of fish in sections containing natural densities (control sections). Annual growth in length and weight of older Brown Trout (age > 2) was greater in removal sections compared to control sections, particularly among fish between 230 and 280 mm TL (ages 3–4). We attribute the growth response to constraints imposed by food availability and the strong feeding hierarchies, characteristic of larger (older) Brown Trout. Data collected from PIT-tagged fish that were recaptured 2 years after fish removal efforts revealed that growth responses owing to density reduction likely did not extend beyond 1 year. Nonetheless, among cohorts that showed improved growth after the first year, we found that their growth advantage was sustained into the second year. At removal sections, age-3 and older Brown Trout that experienced greater growth after 1 year were larger than fish from control sections 2 years later at age 5 and older. Identification of cohort(s) for which density-dependent growth is most pronounced could help to focus efforts on targeted reduction of specific fish sizes/ages that minimize the cost–benefit ratio of fish removal efforts.

South Dakota↗
USGS2026

Effects of prey and tissue type on δ13C and δ15N discrimination and turnover rates of rainbow trout

Stable isotope analysis is used often in ecological studies to examine dietary patterns of consumers and food web structure, yet we still know little regarding some underlying assumptions, including for well-studied species like rainbow trout Oncorhynchus mykiss . We assessed δ 13 C and δ 15 N discrimination (∆) and turnover rates in blood, liver and white muscle of rainbow trout fed natural prey items (sculpin and chironomids). Liver had the fastest turnover rates for both δ 15 N and δ 13 C (4–6 months), followed by blood (4–7 months) and white muscle (7–9 months). Metabolism accounted for more isotopic turnover (82–93%) than growth, with the exception of δ13C in the blood of rainbow trout fed chironomids (33% of isotopic turnover was metabolic). Discrimination factors differed by tissue and diet, with ∆δ 15 N showing highest enrichment in white muscle (3.8‰; 95% CI 3.3–4.3), followed by blood (2.9‰; 95% CI 2.4–3.4) and liver (2.5‰; 95% CI 1.9–3.1) compared to the hatchery diet. The ∆δ 13 C of liver showed higher enrichment (1.9‰; 95% CI 1.7–2.1) than white muscle (1.7‰; 95% CI 1.4–2.0) and blood (1.5‰; 95% CI 1.3–1.7). It is crucial that future models incorporate species-specific tissue turnover and discrimination factors to enable drawing strong inferences and improve accuracy of model predictions.

Hydrobiologia↗