2,551 research outputs found

    Rapid identification of European (Anguilla anguilla) and North American eel (Anguilla rostrata) by polymerase chain reaction.

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    A rapid and cost effective DNA test is described to identify European eel (Anguilla anguilla) and North American eel (Anguilla rostrata). By means of polymerase chain reaction (PCR) technique parts of the mitochondrial cytochrome b gene are amplified with species specific primers which are designed to produce PCR fragments of different characteristic sizes for European and American eel. The size differences can easily be made visible by agarose gel electrophoresi

    ASSESSING THE RELATIVE INFLUENCES OF ABIOTIC AND BIOTIC FACTORS ON A SPECIES’ DISTRIBUTION USING PSEUDO-ABSENCE AND FUNCTIONAL TRAIT DATA: A CASE STUDY WITH THE AMERICAN EEL (Anguilla rostrata)

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    Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi-species datasets. Here, we present a flexible method to compare abiotic and biotic influences at common scales. First, data representing abiotic and biotic factors are collected using a combination of geographic information system, remotely sensed, and species’ functional trait data. Next, the relative influences of each predictor variable on the occurrence of a focal species are compared. Specifically, ‘sample’ data from sites of known occurrence are compared with ‘background’ data (i.e. pseudo-absence data collected at sites where occurrence is unknown, combined with sample data). Predictor variables that may have the strongest influence on the focal species are identified as those where sample data are clearly distinct from the corresponding background distribution. To demonstrate the method, effects of hydrology, physical habitat, and co-occurring fish functional traits are assessed relative to the contemporary (1950 – 1990) distribution of the American Eel (Anguilla rostrata) in six Mid-Atlantic (USA) rivers. We find that Eel distribution has likely been influenced by the functional characteristics of co-occurring fishes and by local dam density, but not by other physical habitat or hydrologic factors

    Environmental determinism of year to year recruitment variability of European eel in a small coastal catchment, the Frémur river, north-west France

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    The influence of environmental factors (mainly the river flow) on the year-to-year variability of European eel Anguilla anguilla fluvial recruitment in a small coastal River (north-west France) was examined. A comprehensive survey of catches from fixed traps at two weirs located at 4·5 km (Pont es Omnes Dam) and 6·0 km (Bois Joli Dam) above the river mouth was carried out between 1997 and 2004. Young pigmented elvers (mean ± s.d. total length, 133·7 ± 29·6 mm) were recruited in eel-passes from February to October, but the main runs followed a modal curve from April to September with a peak centred in May to June. Catches varied greatly between years, from 381 to 26 765 elvers. For each trap, a positive linear relationship between monthly mean river flow that preceded the maximal intensity of captures and annual total catches was observed. These relationships explained 73·1% (P <0.01) and 89·0% (P <0.001) of the year-to-year variability of the recruitment observed in the Pont es Omnes and Bois Joli traps respectively. A significant increase in river flow at the beginning of the migration peak would thus trigger a greater proportion of A. anguilla settled in the estuary and in the downstream zone of the Fremur River to begin their freshwater colonization. The physicochemical roles of changes in river discharge in stimulating upstream migration are discussed. It is concluded that fluvial recruitment in the Fremur River is mainly determined by environmental factors

    Size, age composition, and upstream migration of American eels at the Millville Dam eel ladder, Shenandoah River, West Virginia

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    Abundances of American eel (Anguilla rostrata) are declining along the east coast of the United States and Canada, possibly due to habitat loss and barriers to migration. In Atlantic coast watersheds, dams detain upstream migration of juveniles, and little is known about age class composition, age-length relationships, or environmental cues to upstream migration of yellow-phase eels. An eel ladder was installed on the Millville hydroelectric dam, lower Shenandoah River, WV, to facilitate and monitor the upstream movement of yellow phase eels. Daily length measurements (TL cm) and weights (g) were taken on eels using the ladder during three sampling periods; spring/summer 2004 (May 14-July 23), fall 2004 (Sept 10-30), and spring/summer 2005 (June 1-July 31). Additionally, otolith-based ages were estimated from a subsample of eels. To examine environmental variables associated with upstream migration, candidate models were fit to daily count data and included combinations of four environmental covariates (barometric pressure, local precipitation, lunar illumination, and river flow) and a year effect. A total of 4,847 eels used the ladder during the three sampling periods. Eel sizes were similar among sampling periods (range 19-75 cm TL), and age estimates from 74 eels (21.4-55 cm TL) ranged from 3 to 10 years. Estimates of mean length at age of eels from Shenandoah River were low relative to published estimates from southern and northern latitudes. Peaks in eel counts coincided primarily with low levels of lunar illumination or with rise in river flow, and the data supported an additive model of lunar illumination and river flow. The data did not support single-variable or additive models with covariates of barometric pressure or local precipitation, or models with a year effect. Management strategies for American eels will benefit from short and long-term studies of eel ladders, including additional focus on eel counts, size and age composition, and upstream migration

    Seasonal movements of yellow-phase American eels ( Anguilla rostrata) in the Shenandoah River, West Virginia

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    American eels undergo extensive upstream migration in Atlantic coastal river systems. Few studies, however, have focused on movements of large yellow-phase American eels near dams in upper watersheds of Atlantic coastal rivers. We examined relationships between stream flow, water temperature, and lunar phase, and movements of radio-tagged yellow-phase American eels (518--810 mm TL) near Millville hydroelectric dam in the lower Shenandoah River, West. Movements of yellow-phase American eels differed among seasons. Water temperature and stream flow were associated with upstream migration during spring. Downstream movements during fall corresponded with decreasing water temperatures and darker nights near the new moon. Localized wandering (upstream and downstream movements) during summer occurred near dusk and dawn, and possibly reflected nocturnal foraging. In relation to hydroelectric facilities and eel passage within the Potomac River drainage, our data support a need for upstream passage during spring when water temperatures exceed 15°C

    Dietary plant soot supplementation improves the intestinal health status of farmed American eels (<em>Anguilla rostrata</em>)

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    The current study evaluated the effect of different dietary plant soot supplementation levels on the intestinal health status of American eels (Anguilla rostrata) cultured in concrete tanks. Nine concrete fish tanks were randomly divided into three groups and fed the diets with plant soot (PS) supplementation levels at 0, 3 g/kg, and 5 g/kg, respectively. After a feeding trial for 60 days, the intestinal tissues were sampled to measure health status parameters. The D-lactate level and DAO activity in the serum of the PS5 group were significantly lower than those of the PS0 group (P <0.05). Compared with the PS0 group, the villi length of the intestine in both PS3 group and PS5 group increased significantly (P<0.05). The muscular thickness of the intestine of the PS5 group was significantly higher than the PS0 group (P<0.05). The microvillus density of the intestine of the American eel was increased obviously in the PS5 group. The intestinal microbiota composition of plant soot groups was beneficially regulated with certain probiotics' higher relative abundances and some pathogenic bacteria' lower relative abundance. In conclusion, dietary 5 g/kg plant soot supplementation could benefit the intestinal health of farmed American eels

    Diel periodicity and chronology of upstream migration in yellowphase American Eels (Anguilla rostrata)

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    This thesis examined 24-h diel periodicity of upstream migration of yellow-phase American Eels (Anguilla rostrata), and the chronology of upstream movements within diel periods (day, night, and twilight). Further, relationships were examined for total lengths of upstream migrants and diel movements (vespertine, nocturnal, matutinal, and diurnal), as well as for total lengths and season of year. The thesis is comprised of two chapters: (1) an introduction and literature review on American Eel life history, migration and movement, and population concerns, and (2) a research study of diel periodicity and movement chronology of upstream migrant yellow-phase American Eels at an eel ladder. Study objectives were to (1) examine diel periodicity of upstream migrants using time-series spectral analysis, (2) describe the distribution of passage counts during diel periods (day, twilight, and night) among seasons (spring, summer, and fall), and (3) examine size of upstream migrants relative to diel and seasonal periods. Data were collected at the Millville Dam eel ladder on the lower Shenandoah River, West Virginia, from 2011--2014. Six multi-day passage events with a high number of passage counts were selected for analysis and categorized by season (spring, summer, late summer/early fall, fall) and diel periods of movement (vespertine, nocturnal, matutinal, and diurnal). To examine diel periodicity of movements, I graphically-depicted passage count data as time-series histograms (10-min bins) and used time-series spectral analysis (Fast Fourier Transformation, FFT) to identify cyclical patterns and periodicity of upstream migration. I also pooled histogram data into 14-h periods (18:00--08:00 hours) using 10-min bins for each multi-day passage event (representing vespertine, nocturnal, and matutinal movements). Using pooled 14-h histograms, I examined patterns of movements for each passage event and described multiple peaks of passage counts for vespertine, nocturnal, and matutinal movements by fitting a normal model and eight normal mixture models (2--9 mixtures). The Bayesian information criterion (BIC) was used to select the best approximating model. A mixed-model methodology was used to examine relationships among total length (TL), diel period, and season. Periodicity of movements closely followed a 24-h cycle of activity with most movement being nocturnal. Based on mixture model analysis, multimodal models were supported by the data, but distribution patterns and timing of upstream migration were complex and variable across the six passage events. An additive-effects model of diel period + season was selected as the best approximating model for the mixed-model analysis of TL. Also, the mean TL of individuals using the eel ladder decreased as the night progressed (i.e., from vespertine to diurnal periods of movement) and was the highest during fall (330.3 mm +/- 1.9 SE, n = 472) relative to similar mean values of TL for spring (304.1 mm +/- 1.0 SE, n = 1700), summer (301.2 mm +/- 1.1 SE, n = 1548) and late summer/early fall (303.4 mm +/- 0.87 SE, n = 2269). This study increased our understanding of upstream migration ecology of yellow-phase American Eels and dam passage at the Millville Dam eel ladder

    Ecological study of the tidal segment of the James River encompassing Hog Point : 1975 final technical report

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    Volume 1: Technical Reports Section 1: River Biota and Phytoplankton Entrainment Studies at the VEPCO Surry Nuclear Power Station Section 2: Zooplankton Entrainment at the Surry Nuclear Power Plant, James River, Virginia by G. C. Grant and B. B. Bryan Section 3: a. Plant Entrainment of Ichthyoplankton at the VEPCO Nuclear Power Station by J. V. Merriner and A. D. Estes b: Thermal Plume Entrainment of Ichthyoplankton at the· VEPCO Nuclear Power Station by J. V. Merriner and A. D. Este

    Estimating Relative Abundance of Young of Year American Eel, Anguilla rostrata, in the Virginia Tributaries of Chesapeake Bay. Final Report (2003 Reporting Year)

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    The Atlantic States Marine Fisheries Commission (ASMFC) adopted the Interstate Fishery Management Plan (hereafter referred to as FMP) for the American Eel in November 1999. The FMP focuses on increasing the state’s efforts to collect data on the resource and the fishery it supports through both fishery-dependent and fishery-independent studies. To this end, member jurisdictions (including Virginia) agreed to implement an annual abundance survey for young of year (YOY) American eels. The survey is intended to “…characterize trends in annual recruitment of the young of year eels over time [to produce a] qualitative appraisal of the annual recruitment of American eel to the U.S. Atlantic Coast (ASMFC, 2000). The development of these surveys began as pilot surveys in 2000 with full implementation by the 2001 season. Results from these surveys will provide necessary data on coastal recruitment success and further the understanding of American eel population dynamic
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