Bottom-dwelling Species Research Articles

A Preliminary Study of the Age and Growth Patterns of a Sea Toad, Chaunax abei Le Danois, 1978, in Suruga Bay, Japan

Chaunax abei Le Danois, 1978, is a bottom-dwelling species caught by bottom trawls in Suruga Bay. In the present study, we assessed the age and growth pattern of C. abei from Suruga Bay during the period of 2021–2022 for the first time. The total length (TL) of the population ranged from 37.4–268.8 mm (mean ± SD: 124.7 ± 3.64 mm), and the fish weight (W) between 1.11–491.75 g (mean ± SD: 58.40 ± 7.25 g). The length-weight relationship was estimated as 𝑊𝑊=(2.07 × 10−5)𝑇𝑇𝑇𝑇2.996 (r2 = 0.937). Age determination was based on annual growth ring counts of transverse sections of the sagittal otoliths and age ranged from 1 to 12 years, with the majority of fish aged 4 (32.79 %) years old. The von Bertalanffy growth function was used to model the growth, and the parameters were found as: TL∞ = 468.1 mm, K = 0.056 year-1, t0 = -0.402 year. This research provides the first results on the growth of C. abei and enriches the regional fisheries biology database. Furthermore, it presents the primary population data on the growth patterns of one of the chaunacid species.

A dataset of thermal preferences for Mediterranean demersal and benthic macrofauna

Climate change is swiftly reshaping marine ecosystems, affecting different biological levels. Changes in thermal conditions profoundly influence ectotherms’ growth, behaviour, and functions, making knowledge of species’ thermal preferences (TP) crucial for understanding their responses to ongoing warming. However, obtaining this data is challenging due to limited studies, especially for deep-sea demersal and bottom-dwelling species. Here, we present the MedFaunaTP dataset, a collection of survey-based TPs for 939 Mediterranean species of fish, crustaceans, molluscs, echinoderms, cnidarians, and tunicates calculated using species abundance data obtained from the international bottom-trawl survey in the Mediterranean (MEDITS) and bottom temperature data derived from the Copernicus Monitoring Environment Marine Service. MEDITS estimates are based on species biomass indices from 27587 sampling stations, collected from 1994 to 2020, covering the northern Mediterranean Sea and spanning depths from 10 to 800 m. The MedFaunaTP dataset may serves as a valuable resource for understanding and addressing marine ecosystem ecological, conservation, and management challenges in the context of climate change and associated global warming.

Water quality profits by the submerged macrophyte community consisting of multi-functional species-rich groups

The re-establishment of submerged macrophytes facilitates the formation of a clear-water state in shallow eutrophic lakes. But most restorations of submerged macrophytes are often unstable and cannot maintain a stable clear-water state, probably because the species and functional diversity have not been fully taken into account. In this study, we try to explore submerged macrophyte communities and water quality changes under different submerged macrophyte combinations through mesocosm experiments. We hypothesized that communities with high species and functional diversity would be more conducive to improving water quality. The results showed that the mean community biomass of single-species and 8-species were higher than 5-species. And the stability and mean relative growth rate of the 8-species community were higher than the 5-species community. With the same configuration of three functional groups, the 8-species community was more stable and had better water quality than the 5-species community. The path analysis revealed that different functional groups of submerged macrophytes play different roles. The erect and canopy-producing submerged macrophytes were conducive to reducing total suspended solids (TSS) concentrations in the water column during community construction. In contrast, bottom-dwelling submerged macrophytes were conducive to reducing total nitrogen, total phosphorus, and TSS concentrations during the stage of disturbances. Our results also suggested that canopy-producing groups may have a competitive advantage for light over bottom-dwelling species. Based on the above results and biodiversity insurance hypothesis, we conclude that the community consisting of multi-functional species-rich groups is conducive to building stable submerged macrophyte communities and obtaining a stable clear-water state. Our findings will improve water quality management and pollution control for eutrophic shallow lakes.

Comparison of Behavior and Space Use of the European Bullhead Cottus gobio and the Round Goby Neogobius melanostomus in a Simulated Natural Habitat.

Simple SummaryInvasive round goby and native European bullhead are bottom-dwelling species that occupy a similar niche and are expected to compete for similar resources. Knowledge of how species behave in novel conditions without competition has implications for how they will interact. Our objective was to investigate the space use, flow velocity preferences and tolerance, shelter use, feeding behavior, and activity patterns of specimens of both species to better understand their basic behavior characteristics. Space in a habitat simulator system was divided for purposes of analysis into seven zones among which fish could move freely. We observed individual fish during acclimatization periods and normal behavior periods of darkness and light. The results showed few differences between species. Round goby showed a preference for areas with slow running water, whereas the bullhead gravitated to higher velocity waters. The species exhibited similar patterns in time spent in zones in a given period, spending most of the time in the shelter and the mid-stream zone. Despite the low differences observed, we can conclude that the fish needed a long acclimatization period for behavior stabilization, which should be considered in future studies.The round goby is an invasive fish in Europe and North America that threatens native species by predation and competition. Its habitat preferences are similar to those of the European bullhead, which it displaces from shelters and out-competes for available resources. We assessed the microhabitat preferences, shelter use, and activity of the round goby and European bullhead in single-species experiments in habitat simulator systems to investigate their behavior in a novel environment. Fish were video-recorded for 28 h in the presence of shelter and feed with water velocity ranging from 0.00 to 0.96 m s−1. The two species showed similar behavior under given conditions. A primary difference was in stress-induced behavior in the initial phases of observation. The round goby spent more time in movement when outside the shelter and a longer time in the escape zone in the exploration period during light. Our results confirmed a significant preference of round goby for low velocity areas and a preference for higher velocities in the European bullhead. Both species were able to cope with velocities > 0.7 m s−1. Therefore, the reported invasion success of round goby is probably not driven by space use or activity patterns, but rather by higher adaptability.

Free-Living Aquatic Turtles as Sentinels of Salmonella spp. for Water Bodies.

Reptile-associated human salmonellosis cases have increased recently in the United States. It is not uncommon to find healthy chelonians shedding Salmonella enterica. The rate and frequency of bacterial shedding are not fully understood, and most studies have focused on captive vs. free-living chelonians and often in relation to an outbreak. Their ecology and significance as sentinels are important to understanding Salmonella transmission. In 2012–2013, Salmonella prevalence was determined for free-living aquatic turtles in man-made ponds in Clarke and Oconee Counties, in northern Georgia (USA) and the correlation between species, basking ecology, demographics (age/sex), season, or landcover with prevalence was assessed. The genetic relatedness between turtle and archived, human isolates, as well as, other archived animal and water isolates reported from this study area was examined. Salmonella was isolated from 45 of 194 turtles (23.2%, range 14–100%) across six species. Prevalence was higher in juveniles (36%) than adults (20%), higher in females (33%) than males (18%), and higher in bottom-dwelling species (31%; common and loggerhead musk turtles, common snapping turtles) than basking species (15%; sliders, painted turtles). Salmonella prevalence decreased as forest cover, canopy cover, and distance from roads increased. Prevalence was also higher in low-density, residential areas that have 20–49% impervious surface. A total of 9 different serovars of two subspecies were isolated including 3 S. enterica subsp. arizonae and 44 S. enterica subsp. enterica (two turtles had two serotypes isolated from each). Among the S. enterica serovars, Montevideo (n = 13) and Rubislaw (n = 11) were predominant. Salmonella serovars Muenchen, Newport, Mississippi, Inverness, Brazil, and Paratyphi B. var L(+) tartrate positive (Java) were also isolated. Importantly, 85% of the turtle isolates matched pulsed-field gel electrophoresis patterns of human isolates, including those reported from Georgia. Collectively, these results suggest that turtles accumulate Salmonella present in water bodies, and they may be effective sentinels of environmental contamination. Ultimately, the Salmonella prevalence rates in wild aquatic turtles, especially those strains shared with humans, highlight a significant public health concern.

Round goby versus marbled crayfish: alien invasive predators and competitors

Aquatic biodiversity is threatened by spread of invasive alien species. Round goby Neogobius melanostomus is an invasive fish in large European rivers as well as in coastal waters near their mouths and marbled crayfish Procambarus virginalis is a highly invasive crustacean. Both are small, bottom-dwelling species occupying similar habitat and shelters and utilizing similar food sources. We hypothesized that goby presents a threat to both native and non-native astacofauna in invaded ecosystems. We tested this through laboratory experiments designed to determine aggressiveness and competitiveness of goby against marbled crayfish as a model for other North American cambarid crayfish, assessing goby prey size selection and competition with marbled crayfish for space and shelter. Gobies showed high aggressiveness and dominance over the crayfish. Goby predation on juvenile crayfish was limited by mouth gape size. In goby/crayfish pairs of similar weight, gobies were more aggressive, although each affected the behavior of the other.

Sensing the structural characteristics of surfaces: texture encoding by a bottom-dwelling fish.

The texture of contacted surfaces influences our perception of the physical environment and modulates behavior. Texture perception and its neural encoding mechanisms have traditionally been studied in the primate hand, yet animals of all types live in richly textured environments and regularly interact with textured surfaces. Here we explore texture sensation in a different type of vertebrate limb by investigating touch and potential texture encoding mechanisms in the pectoral fins of fishes, the forelimb homologs. We investigated the pectoral fins of the round goby (Neogobius melanostomus), a bottom-dwelling species that lives on substrate types of varying roughness and whose fins frequently contact the bottom. Analysis shows that the receptive field sizes of fin ray afferents are small and afferents exhibit response properties to tactile motion that are consistent with those of primates and other animals studied previously. In response to a periodic stimulus (coarse gratings), afferents phase lock to the stimulus temporal frequency and thus can provide information about surface texture. These data demonstrate that fish can have the capability to sense the tactile features of their near range physical environment with fins.

Ontogenic change in the vertical swimming of East Asian common octopus Octopus sinensis paralarvae under different water flow conditions

The East Asian common octopus Octopus sinensis is a bottom-dwelling species, but goes through a planktonic phase as ‘paralarvae’ during the first several weeks of life. As the swimming performance of the paralarvae is relatively poor, their dispersion relies primarily on ocean currents; however, vertical swimming may play an important role in their horizontal dispersion by controlling their buoyancy in the current. Within this context, ontogenic changes in vertical swimming in relation to the ambient water flow are key to understanding the dispersion properties of the paralarvae and the subsequent onset of settlement, yet this information remains largely unknown. Here, we investigated the effects of different water flows (downward × 4 velocities, stagnant and upward × 5 velocities) on the vertical swimming position in test columns using laboratory-raised O. sinensis paralarvae aged 0, 5, 10 and 15 days during the day and at night. Paralarvae younger than 10 days ( 5 mg) commenced short clinging behaviour, and their swimming positions dispersed downwards during daytime regardless of the water flow, indicating the onset of the transition to settlement. In contrast, their position shifted to near the upper limit at night by swimming upwards, even under downward water flows. Our results suggest that O. sinensis exhibits characteristic behaviour that alternates between diurnal descent dispersion with clinging (hyperbenthic trait) and nocturnal upward swimming (planktonic trait) during the transition to permanent benthic life.

Potential Hazard of Lanthanides and Lanthanide-Based Nanoparticles to Aquatic Ecosystems: Data Gaps, Challenges and Future Research Needs Derived from Bibliometric Analysis.

Lanthanides (Ln), applied mostly in the form of nanoparticles (NPs), are critical to emerging high-tech and green energy industries due to their distinct physicochemical properties. The resulting anthropogenic input of Ln and Ln-based NPs into aquatic environment might create a problem of emerging contaminants. Thus, information on the biological effects of Ln and Ln-based NPs is urgently needed for relevant environmental risk assessment. In this mini-review, we made a bibliometric survey on existing scientific literature with the main aim of identifying the most important data gaps on Ln and Ln-based nanoparticles’ toxicity to aquatic biota. We report that the most studied Ln for ecotoxicity are Ce and Ln, whereas practically no information was found for Nd, Tb, Tm, and Yb. We also discuss the challenges of the research on Ln ecotoxicity, such as relevance of nominal versus bioavailable concentrations of Ln, and point out future research needs (long-term toxicity to aquatic biota and toxic effects of Ln to bottom-dwelling species).

The pupillary light responses of animals; a review of their distribution, dynamics, mechanisms and functions.

The timecourse and extent of changes in pupil area in response to light are reviewed in all classes of vertebrate and cephalopods. Although the speed and extent of these responses vary, most species, except the majority of teleost fish, show extensive changes in pupil area related to light exposure. The neuromuscular pathways underlying light-evoked pupil constriction are described and found to be relatively conserved, although the precise autonomic mechanisms differ somewhat between species. In mammals, illumination of only one eye is known to cause constriction in the unilluminated pupil. Such consensual responses occur widely in other animals too, and their function and relation to decussation of the visual pathway is considered. Intrinsic photosensitivity of the iris muscles has long been known in amphibia, but is in fact widespread in other animals. The functions of changes in pupil area are considered. In the majority of species, changes in pupil area serve to balance the conflicting demands of high spatial acuity and increased sensitivity in different light levels. In the few teleosts in which pupil movements occur they do not serve a visual function but play a role in camouflaging the eye of bottom-dwelling species. The occurrence and functions of the light-independent changes in pupil size displayed by many animals are also considered. Finally, the significance of the variations in pupil shape, ranging from circular to various orientations of slits, ovals, and other shapes, is discussed.

Neural network modeling of monthly salinity variations in oyster reef in Apalachicola Bay in response to freshwater inflow and winds

Estuarine organisms have varying tolerances and respond differently to salinity. Bottom-dwelling species such as oysters tolerate some change in salinity, but salinity outside an acceptable range will negatively affect their abundance as well as their survival within this sensitive ecosystem. Salinity in the Apalachicola Bay is heavily influenced by freshwater inflow discharged from the Apalachicola River. In this study, artificial neural network (ANN) was applied to correlate the monthly salinity variations at an oyster reef in Apalachicola Bay to the river inflow and wind. Parameters in the ANN were trained until the simulated salinity data correlated well with the observations from 2005 to 2007. Once the model is trained and optimized, the ANN structure is verified comparing the simulated data to the second dataset from 2008–2010. Four neural network training algorithms, including gradient decent, scaled conjugate gradient, quasi-Newton, and Levenberg–Marquardt, have been evaluated. The scaled conjugate gradient algorithm was selected for this study because it provides the best correlation with the value of 0.85. The verified ANN model was applied to investigate the potential impacts of freshwater reductions from upstream river on the salinity in the oyster reef. By comparing the resulting salinity from ANN model simulations to the optimal salinity range for oyster growth, the impacts of freshwater reduction scenarios on oyster growth can be examined.

Turbulent oyster larvae at risk of starvation

The numbers are staggering: for every oyster that makes it onto a dinner plate, 10 million siblings perished as larvae, and the factors that lead to such shocking statistics fascinate Heidi Fuchs from Rutgers, The State University of New Jersey, USA. Having realised early in her career that water turbulence can determine where the larvae of bottom-dwelling species settle, Fuchs discovered recently that oyster larvae swim harder – propelled by microscopic hairs (cilia) covering two fleshy oval wings that protrude out of the larva's shell – when they are tumbling in strong currents: ‘[which] made me wonder about the energetic cost to the larvae and how much they would have to eat to make up for it’, says Fuchs. Could agitated larvae consume enough in choppy conditions to sustain their turbulent lifestyle?Despite their minute size, Fuchs reckons that oyster larvae (Crassostrea virginica) are some of the easiest plankton to work with; ‘We get them delivered overnight from a hatchery’, she explains. However, measuring the oxygen consumption of the minute 2-week-old molluscs and observing their swimming manoeuvres as they swirled around in water simulating eddies in a gentle stream through to smashing storm breakers was technically challenging. ‘Fortunately, Adam Christman perfected some techniques in advance and my graduate student, Jackie Specht, was able to assist’, says Fuchs, recalling how Specht took charge of the oxygen measurements that would tell them how much energy the larvae consumed, while she monitored the larvae's swimming movements. The duo also added microscopic algae (Isochrysis galbana) to the swishing water during some of the trials, to investigate how much the turbulence affected the larvae's ability to feed.Monitoring the larvae, the team could see that although the tiny youngsters spent more time swimming downward in the roughest conditions, on the occasions when they swam upward, their energy consumption doubled, even though their energy use became more efficient – thanks to the turbulence counteracting the effects of gravity. And the larvae that were provided with an algae diet used more energy than the unfed larvae as they beat their propulsive cilia to produce a feeding current, in addition to propelling themselves through the water.However, Fuchs and Diane Adams were most surprised at the impact that the churning water had on the larvae's ability to feed. Although the young oysters bumped into more algae in the choppiest conditions, they grasped hold of less food. ‘Our interpretation is that the water motion… made it more difficult for the cilia to handle or retain food particles. We suspect that the larvae can increase their ciliary activity for either swimming or feeding, but they cannot do both at full capacity at the same time, so in strong turbulence they focus most efforts on swimming’, says Fuchs.In fact, the larvae were so seriously impaired that they were unable to consume enough food to survive in the most turbulent waters, no matter how many algae were available. Fuchs says, ‘Our observations suggest that many of these larvae could be lost to turbulence-induced starvation’, admitting that she is surprised by how badly the young oysters are affected. However, she suspects that smaller (younger) larvae may be at less risk of starvation, as they have not developed their sense of balance and should conserve more energy by spending less time swimming against the turbulent conditions.

Levels of 1-hydroxypyrene in urine of people living in an oil producing region of the Andean Amazon (Ecuador and Peru).

Polycyclic aromatic hydrocarbons (PAHs) are contaminants with carcinogenic effects but little is known about their presence in environments surrounding oil drilling operations and spills or exposure levels in nearby communities. The objective of this study was to characterize PAH levels in people living near oil drilling operations in relation to fish consumption, occupation, source of water and other socio-demographic characteristics. This pilot study examined PAH exposure by measuring 1-hydroxypyrene (1-OHP) in urine samples using high-performance liquid chromatography and fluorescence detection from 75 women and men in the Ecuadorian and Peruvian Amazon living near oil drilling operations and who answered a questionnaire collecting socio-demographic, occupational and dietary information. Data were analyzed using multiple linear regression models. The mean value of 1-OHP was 0.40μmol/mol creatinine, 95% CI 0.32-0.46μmol/mol creatinine. Women who used water from a surface source (for washing clothes or bathing) had almost twice the amount of 1-OHP in their urine (mean 1-OHP=0.41μmol/mol creatinine, 95% CI 0.28-0.54μmol/mol creatinine, n=23) as women who used water from either a well, a spring or rain (mean 1-OHP=0.22μmol/mol creatinine, 95% CI 0.11-0.34μmol/mol creatinine, n=6). Men who reported eating a bottom-dwelling species as their most commonly consumed fish (mean 1-OHP=0.50μmol/mol creatinine, 95% CI 0.36-0.64μmol/mol creatinine, n=31) had twice as much 1-OHP in their urine as men who reported a pelagic fish (mean 1-OHP=0.25μmol/mol creatinine, 95% CI 0.15-0.35μmol/mol creatinine, n=15), signaling either oral (fish consumption) or dermal (while standing in water fishing benthic species) exposure. More contact with surface water and benthic fish may result in higher levels of 1-OHP in human urine among the study population. Reducing the amount of oil and wastes entering the waterways in Andean Amazonia would be one way to reduce exposure.

Determination of the toxic variability of lipophilic biotoxins in marine bivalve and gastropod tissues treated with an industrial canning process

ABSTRACTContamination of shellfish with lipophilic marine biotoxins (LMB), pectenotoxins (PTXs), yessotoxins (YTXs) and okadaic acid (OA) toxin groups in southern Chile is a constant challenge for the development of miticulture considering the high incidence of toxic episodes that tend to occur. This research is focused on using methodologies for assessing the decrease in toxins of natural resources in Chile with high value, without altering the organoleptic properties of the shellfish. The species were processed through steaming (1 min at 121°C) and subsequent canning (5 min at 121°C). Changes in the profiles of toxins and total toxicity levels of LMB in endemic bivalves and gastropods were determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The total reduction of toxicity (≈ 15%) was not related to the destruction of the toxin, but rather to the loss of LMB on removing the shells and packing media of canned products (***p < 0.001). Industrial processing of shellfish reduces LMB contents by up to 15% of the total initial contents, concomitant only with the interconversion of PTX-group toxins into PTX-2sa. In soft bottom-dwelling species with toxicities beyond the standard for safe human consumption (≥ 160 μg OA-eq kg–1), toxicity can be reduced to safe levels through industrial preparation procedures.

The Dragon as a Fisherman: China’s Distant Water Fishing Fleet and the Export of Environmental Insecurity

China has been a coastal fishing nation known for targeting “trash fish,” which are smaller, less valuable coastal and bottom-dwelling species. Over the last thirty years, the country’s fishing activities have evolved considerably as China has grown increasingly reliant on a growing Distant Water Fishing (DWF) fleet to provide for the steadily rising domestic demand for wild-caught fish. The goal of this study is to explore the possible environmental security implications of China’s large and growing DWF fleet.

Larval dispersal modeling of pearl oyster Pinctada margaritifera following realistic environmental and biological forcing in Ahe atoll lagoon.

Studying the larval dispersal of bottom-dwelling species is necessary to understand their population dynamics and optimize their management. The black-lip pearl oyster (Pinctada margaritifera) is cultured extensively to produce black pearls, especially in French Polynesia's atoll lagoons. This aquaculture relies on spat collection, a process that can be optimized by understanding which factors influence larval dispersal. Here, we investigate the sensitivity of P. margaritifera larval dispersal kernel to both physical and biological factors in the lagoon of Ahe atoll. Specifically, using a validated 3D larval dispersal model, the variability of lagoon-scale connectivity is investigated against wind forcing, depth and location of larval release, destination location, vertical swimming behavior and pelagic larval duration (PLD) factors. The potential connectivity was spatially weighted according to both the natural and cultivated broodstock densities to provide a realistic view of connectivity. We found that the mean pattern of potential connectivity was driven by the southwest and northeast main barotropic circulation structures, with high retention levels in both. Destination locations, spawning sites and PLD were the main drivers of potential connectivity, explaining respectively 26%, 59% and 5% of the variance. Differences between potential and realistic connectivity showed the significant contribution of the pearl oyster broodstock location to its own dynamics. Realistic connectivity showed larger larval supply in the western destination locations, which are preferentially used by farmers for spat collection. In addition, larval supply in the same sectors was enhanced during summer wind conditions. These results provide new cues to understanding the dynamics of bottom-dwelling populations in atoll lagoons, and show how to take advantage of numerical models for pearl oyster management.

Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification

Following the Chicxulub impact, many foraminifera in near-surface waters perished, but bottom-dwelling species survived. Impact experiments suggest that sulphate in Chicxulubs target rocks was released as predominantly sulphur trioxide, which would have been converted to sulphuric acid in the atmosphere and swept down swiftly by larger particles, acidifying the ocean surface.

HYDROLOGIC CORRELATES OF BULL TROUT (Salvelinus confluentus) SWIMMING ACTIVITY IN A HYDROPEAKING RIVER

There is a growing need to develop quantitative relationships between specific components of river flow and the behavioural responses of fishes. Given this, we tested for an effect of hydrologic parameters on axial swimming muscle electromyograms of bull trout (Salvelinus confluentus) in a large hydropeaking river (river discharge ranging from 0 to 1790 m3/s) while controlling for other exogenous factors such as temperature and light intensity. Hourly mean discharge had a significant positive effect (R2 = 0.13–0.31; depending on the distance from the dam) on swimming muscle activity. Within-hour changes in river flow from 0 to 1045 m3/s did not elicit a hyperactive response in bull trout. When a subset of electromyogram transmitters were calibrated to swimming speed, we found there were periods, across a range of river discharges, when bull trout were not actively beating their tails—a behaviour documented in some bottom-dwelling species associated with moving water. Not including these periods of rest, bull trout swam at median hourly speeds of 0.53 body lengths per second. Understanding fish behaviour in the context of their physical environment may help explain population-level responses to hydrologic change. Copyright © 2013 John Wiley & Sons, Ltd.

Fish Prey Selection by the Common KingfisherAlcedo atthisin Northern Iberia

The Common Kingfisher Alcedo atthis is a fish-eating predatory bird that is reported to prey mainly on pelag- ic, benthic, or both types of fish prey. It still remains unclear whether the species has the capacity to prey indistinctly on all types of fish, regardless of their position within the water column. The aim of our study was to test if kingfishers are able to select particular fish prey or if, by contrast, they feed on the most abundant and accessible fish. We identi- fied the fish prey consumed by kingfishers at 14 nests in total, and also sampled, using electrofishing surveys, fish prey availability on the river stretches where the nests were located. We used Savage's index in order to check whether there was prey selection. Overall, kingfishers preyed upon eight fish species: Bermejuela Acondrostoma arcasii, Bleak Alburnus alburnus, Pyrenean Stone Loach Barbatula quignardi, Ebro Barbel Luciobarbus graellsii, Pyrenean Gudgeon Gobio lozanoi, Ebro Nase Parachondrostoma miegii, Pyrenean Minnow Phoxinus bigerri, and Brown Trout Salmo trutta. The most con- sumed prey were pelagic species (Pyrenean Minnow and Brown Trout). These results suggest that the Kingfisher preys on pelagic species because of their accessibility and avoids bottom-dwelling species, which may remain hidden from this predator. kingfishers preyed mostly on fish of 50 to 60 mm in length, but mean size values varied prey-specifically, possibly because of the vertical specific distribution in relation to the fish age and species and, finally, prey availability.

Mercury and Selenium Concentrations in Biofilm, Macroinvertebrates, and Fish Collected in the Yankee Fork of the Salmon River, Idaho, USA, and Their Potential Effects on Fish Health

The Yankee Fork is a large tributary of the Salmon River located in central Idaho, USA, with an extensive history of placer and dredge-mining activities. Concentrations of selenium (Se) and mercury (Hg) in various aquatic trophic levels were measured in the Yankee Fork during 2001 and 2002. Various measurements of fish health were also performed. Sites included four on the mainstem of the Yankee Fork and two off-channel sites in partially reclaimed dredge pools used as rearing habitat for cultured salmonid eggs and fry. Hg concentrations in whole mountain whitefish and shorthead sculpin ranged from 0.28 to 0.56 μg/g dry weight (dw), concentrations that are generally less than those reported to have significant impacts on fish. Biofilm and invertebrates ranged from 0.05 to 0.43 μg Hg/g dw. Se concentrations measured in biota samples from the Yankee Fork were greater than many representative samples collected in the Snake and Columbia watersheds and often exceeded literature-based toxic thresholds. Biofilm and invertebrates ranged from 0.58 to 4.66 μg Se/g dw. Whole fish ranged from 3.92 to 7.10 μg Se/g dw, and gonads ranged from 6.91 to 31.84 μg Se/g dw. Whole-body Se concentrations exceeded reported toxicological thresholds at three of four sites and concentrations in liver samples were mostly greater than concentrations shown to have negative impacts on fish health. Histological examinations performed during this study noted liver abnormalities, especially in shorthead sculpin, a bottom-dwelling species.