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Harrisburg, PA, United States

Wagner T.,U.S. Geological Survey | Deweber J.T.,Pennsylvania State University | Detar J.,Pennsylvania Fish and Boat Commission | Sweka J.A.,U.S. Fish and Wildlife Service
Transactions of the American Fisheries Society | Year: 2013

Predicting the distribution of native stream fishes is fundamental to the management and conservation of many species. Modeling species distributions often consists of quantifying relationships between species occurrence and abundance data at known locations with environmental data at those locations. However, it is well documented that native stream fish distributions can be altered as a result of asymmetric interactions between dominant exotic and subordinate native species. For example, the naturalized exotic Brown Trout Salmo trutta has been identified as a threat to native Brook Trout Salvelinus fontinalis in the eastern United States. To evaluate large-scale patterns of co-occurrence and to quantify the potential effects of Brown Trout presence on Brook Trout occupancy, we used data from 624 stream sites to fit two-species occupancy models. These models assumed that asymmetric interactions occurred between the two species. In addition, we examined natural and anthropogenic landscape characteristics we hypothesized would be important predictors of occurrence of both species. Estimated occupancy for Brook Trout, from a co-occurrence model with no landscape covariates, at sites with Brown Trout present was substantially lower than sites where Brown Trout were absent. We also observed opposing patterns for Brook and Brown Trout occurrence in relation to percentage forest, impervious surface, and agriculture within the network catchment. Our results are consistent with other studies and suggest that alterations to the landscape, and specifically the transition from a forested catchment to one that contains impervious surface or agriculture, reduces the occurrence probability of wild Brook Trout. Our results, however, also suggest that the presence of Brown Trout results in lower occurrence probability of Brook Trout over a range of anthropogenic landscape characteristics, compared with streams where Brown Trout were absent.Received June 20, 2012; accepted September 25, 2012. © 2013 Copyright Taylor and Francis Group, LLC.

Sweka J.A.,U.S. Fish and Wildlife Service | Wagner T.,U.S. Geological Survey | Detar J.,Pennsylvania Fish and Boat Commission | Kristine D.,Pennsylvania Fish and Boat Commission
Journal of Fish and Wildlife Management | Year: 2012

Fisheries biologists often use backpack electrofishing to sample stream fish. A common goal of sampling is to estimate density and/or biomass to make inferences about the status and trends of fish populations. One challenge when estimating population size is determining an appropriate site or reach length to sample. In this study, we empirically determined the required length of stream that needs to be sampled, assuming the study design is one site per stream, in order to achieve a desired level of accuracy for brook trout density and biomass estimates in Pennsylvania headwater streams. Long sample reaches (600 m) were chosen on seven first to third order streams and these sites were broken into twelve 50-m subreaches. Each subreach was sampled by removal electrofishing techniques until either five electrofishing passes were completed or no brook trout were captured. The total density and biomass of brook trout over all 50-m subreaches was considered the "true" density and biomass for the entire reach. We then performed computer simulations in which various numbers of 50-m subreaches were randomly selected and catches from each subreach were summed within the first three electrofishing passes to simulate removal sampling of site lengths ranging from 50 to 550 m. Population estimates were made using a removal estimator and density and biomass were calculated using various stratification schemes based on fish age and size. Estimates of density and biomass were then compared to the true values to assess the possible range in bias of estimates for a given reach length. Results from our simulations suggest a 200-to 250-m-long or a 400-to 450-m-long stream reach or site is needed to estimate brook trout density and biomass within 50% and 25%, respectively, of the true density and biomass. This information and our methodology will be valuable to fisheries managers in developing standardized protocols for assessing trout populations in small streams.

Wagner T.,U.S. Geological Survey | Deweber J.T.,Pennsylvania State University | Detar J.,Pennsylvania Fish and Boat Commission | Kristine D.,Pennsylvania Fish and Boat Commission | Sweka J.A.,U.S. Fish and Wildlife Service
North American Journal of Fisheries Management | Year: 2014

Many potential stressors to aquatic environments operate over large spatial scales, prompting the need to assess and monitor both site-specific and regional dynamics of fish populations. We used hierarchical Bayesian models to evaluate the spatial and temporal variability in density and capture probability of age-1 and older Brook Trout Salvelinus fontinalis from three-pass removal data collected at 291 sites over a 37-year time period (1975-2011) in Pennsylvania streams. There was high between-year variability in density, with annual posterior means ranging from 2.1 to 10.2 fish/100 m2; however, there was no significant long-term linear trend. Brook Trout density was positively correlated with elevation and negatively correlated with percent developed land use in the network catchment. Probability of capture did not vary substantially across sites or years but was negatively correlated with mean stream width. Because of the low spatiotemporal variation in capture probability and a strong correlation between first-pass CPUE (catch/min) and three-pass removal density estimates, the use of an abundance index based on first-pass CPUE could represent a cost-effective alternative to conducting multiple-pass removal sampling for some Brook Trout monitoring and assessment objectives. Single-pass indices may be particularly relevant for monitoring objectives that do not require precise site-specific estimates, such as regional monitoring programs that are designed to detect long-term linear trends in density.Received April 22, 2013; accepted September 18, 2013. © 2014 Copyright © Taylor & Francis Group, LLC.

Rutherford E.S.,National Oceanic and Atmospheric Administration | Allison J.,Pennsylvania Fish and Boat Commission | Ruetz C.R.,Grand Valley State University | Elliott J.R.,National Oceanic and Atmospheric Administration | And 5 more authors.
Transactions of the American Fisheries Society | Year: 2016

Abstract: The Walleye Sander vitreus is an important sport fish that has experienced low reproductive success in some Great Lakes tributaries since severe population declines began in the late 1940s. In the Muskegon River, a Lake Michigan tributary, natural reproduction of Walleyes remains low and is largely supplemented by stocking. We evaluated the influence of abiotic factors on Walleye reproductive success in the Muskegon River during April and May 2009 and 2010 by (1) estimating Walleye egg density and survival; (2) estimating the size, density, abundance, and survival of Walleye larvae; and (3) relating our estimates to physical habitat conditions. Egg densities were 70-fold higher in 2009 than in 2010, but eggs experienced colder water temperatures, higher river discharge rates, and lower survival in 2009 relative to 2010. Egg survival in incubators was positively related to temperature and negatively related to flow at most sites. In both years, Walleye larvae that hatched during periods of cooler temperature were smaller than larvae that hatched later during periods of warmer temperature. Walleye larval densities were highest near spawning grounds and decreased downstream. Bayesian estimates of variability in larval densities indicated that temporal variability was twice as high as spatial variability in the Muskegon River. Larval survival was much lower in 2009 than in 2010, resulting in an approximately sevenfold higher production of larvae in 2010 than in 2009. Survival was highest for smaller larvae that hatched early in April 2010, when temperatures were warm and discharges were low and stable; in contrast, survival was much lower for larger larvae hatching later in 2010 or for large and small larvae in 2009, when water temperatures were colder and discharges were higher and more variable. Our results suggest that abiotic factors, primarily temperature and river flow, likely control the early survival of Walleyes in the Muskegon River. Received February 9, 2015; accepted January 11, 2016 Published online April 19, 2016 © 2016, © American Fisheries Society 2016.

Blazer V.S.,U.S. Geological Survey | Iwanowicz D.D.,U.S. Geological Survey | Walsh H.L.,U.S. Geological Survey | Sperry A.J.,U.S. Geological Survey | And 6 more authors.
Environmental Monitoring and Assessment | Year: 2014

Fishes were collected at 16 sites within the three major river drainages (Delaware, Susquehanna, and Ohio) of Pennsylvania. Three species were evaluated for biomarkers of estrogenic/antiandrogenic exposure, including plasma vitellogenin and testicular oocytes in male fishes. Smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, and redhorse sucker Moxostoma species were collected in the summer, a period of low flow and low reproductive activity. Smallmouth bass were the only species in which testicular oocytes were observed; however, measurable concentrations of plasma vitellogenin were found in male bass and white sucker. The percentage of male bass with testicular oocytes ranged from 10 to 100 %, with the highest prevalence and severity in bass collected in the Susquehanna drainage. The percentage of males with plasma vitellogenin ranged from 0 to 100 % in both bass and sucker. Biological findings were compared with chemical analyses of discrete water samples collected at the time of fish collections. Estrone concentrations correlated with testicular oocytes prevalence and severity and with the percentage of male bass with vitellogenin. No correlations were noted with the percentage of male sucker with vitellogenin and water chemical concentrations. The prevalence and severity of testicular oocytes in bass also correlated with the percent of agricultural land use in the watershed above a site. Two sites within the Susquehanna drainage and one in the Delaware were immediately downstream of wastewater treatment plants to compare results with upstream fish. The percentage of male bass with testicular oocytes was not consistently higher downstream; however, severity did tend to increase downstream. © 2014 The Author(s).

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