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File application/x-troff-ms Evaluating the Trade-Offs between Invasion and Isolation for Native Brook Trout and Nonnative Brown Trout in Pennsylvania Streams
A popular conservation strategy for native trout species in western North America is to prevent invasions by nonnative trout by installing barriers that isolate native trout populations into headwater streams. In eastern North America, native Brook Trout Salvelinus fontinalis are frequently replaced in coolwater habitats by nonnative Brown Trout Salmo trutta and relegated to small headwater streams. In this study, we compared the effects of isolation and invasion by nonnative Brown Trout on the distribution and demographic structure of Brook Trout populations from 78 trout streams in northwestern Pennsylvania. The Brook Trout and Brown Trout distributions varied in predictable ways along the stream size gradient, with Brown Trout becoming dominant in larger streams. However, there was a prominent barrier effect, with streams 12 times more likely to have Brook Trout than Brown Trout when a downstream barrier was present between the sample site and the nearest Brown Trout stocking location. In comparison, 91% of the streams with Brown Trout had no downstream barrier, suggesting that barriers are important in creating refugia for Brook Trout. Brown Trout also appeared to have a negative impact on Brook Trout population demographics, as Brook Trout populations in sympatry with Brown Trout had fewer age-classes and lower population densities than allopatric Brook Trout populations. Isolating Brook Trout to small headwater streams with downstream barriers that prevent Brown Trout invasion could be a viable conservation strategy in regions where barriers would serve to reduce the negative impacts from Brown Trout. Since barriers could further fragment local Brook Trout populations, however, they would need to be strategically placed to allow for seasonal movements to maintain metapopulation structure and ensure population persistence.
Located in Resources / Brook Trout Related Publications
File Response of fish assemblages to declining acidic deposition in Adirondack Mountain lakes, 1984-2012
Adverse effects of acidic deposition on the chemistry and fish communities were evident in Adirondack Mountain lakes during the 1980s and 1990s. Fish assemblages and water chemistry in 43 Adirondack Long-Term Monitoring (ALTM) lakes were sampled by the Adirondack Lakes Survey Corporation and the New York State Department of Environmental Conservation during three periods (1984-87, 1994-2005, and 2008-12) to document regional impacts and potential biological recovery associated with the 1990 amendments to the 1963 Clean Air Act (CAA). We assessed standardized data from 43 lakes sampled during the three periods to quantify the response of fish-community richness, total fish abundance, and brook trout (Salvelinus fontinalis) abundance to declining acidity that resulted from changes in U.S. airquality management between 1984 and 2012. During the 28-year period, mean acid neutralizing capacity (ANC) increased significantly from 3 to 30 meq/L and mean inorganic monomeric Al concentrations decreased significantly from 2.22 to 0.66 mmol/L, yet mean species richness, all species or total catch per net night (CPNN), and brook trout CPNN did not change significantly in the 43 lakes. Regression analyses indicate that fishery metrics were not directly related to the degree of chemical recovery and that brook trout CPNN may actually have declined with increasing ANC. While the richness of fish communities increased with increasing ANC as anticipated in several Adirondack lakes, observed improvements in water quality associated with the CAA have generally failed to produce detectable shifts in fish assemblages within a large number of ALTM lakes. Additional time may simply be needed for biological recovery to progress, or else more proactive efforts may be necessary to restore natural fish assemblages in Adirondack lakes in which water chemistry is steadily recovering from acidification.
Located in Resources / Brook Trout Related Publications
File Sampling strategies for estimating brook trout effective population size
The influence of sampling strategy on estimates of effective population size (Ne) from single-sample genetic methods has not been rigorously examined, though these methods are increasingly used. For headwater salmonids, spatially close kin association among age-0 individuals suggests that sampling strategy (number of individuals and location from which they are collected) will influence estimates of Ne through family representation effects. We collected age-0 brook trout by completely sampling three headwater habitat patches, and used microsatellite data and empirically parameterized simulations to test the effects of different combinations of sample size (S = 25, 50, 75, 100, 150, or 200) and number of equally-spaced sample starting locations (SL = 1, 2, 3, 4, or random) on estimates of mean family size and effective number of breeders (Nb). Both S and SL had a strong influence on estimates of mean family size and ^ Nb; however the strength of the effects varied among habitat patches that varied in family spatial distributions. The sampling strategy that resulted in an optimal balance between precise estimates of Nb and sampling effort regardless of family structure occurred with S = 75 and SL = 3. This strategy limited bias by ensuring samples contained individuals from a high proportion of available families while providing a large enough sample size for precise estimates. Because this sampling effort performed well for populations that vary in family structure, it should provide a generally applicable approach for genetic monitoring of iteroparous headwater stream fishes that have overlapping generations.
Located in Resources / Brook Trout Related Publications / Stream Assessment and Monitoring
File Troff document Fall and Early Winter Movement and Habitat Use of Wild Brook Trout
Brook Trout Salvelinus fontinalis populations face a myriad of threats throughout the species’ native range in the eastern United States. Understanding wild Brook Trout movement patterns and habitat requirements is essential for conserving existing populations and for restoring habitats that no longer support self-sustaining populations. To address uncertainties related to wild Brook Trout movements and habitat use, we radio-tracked 36 fish in a headwater stream system in central Pennsylvania during the fall and early winter of 2010–2011.We used generalized additive mixed models and discrete choice models with random effects to evaluate seasonal movement and habitat use, respectively. There was variability among fish in movement patterns; however, most of the movement was associated with the onset of the spawning season and was positively correlated with fish size and stream flow. There was heterogeneity among fish in selection of intermediate (0.26–0.44 m deep) and deep (0.44–1.06 m deep) residual pools, while all Brook Trout showed similar selection for shallow (0.10–0.26 m) residual pools. There was selection for shallow residual pools during the spawning season, followed by selection for deep residual pools as winter approached. Brook Trout demonstrated a threshold effect for habitat selection with respect to pool length, and selection for pools increased as average pool length increased up to approximately 30 m, and then use declined rapidly for pool habitats greater than 30 m in length. The heterogeneity and nonlinear dynamics of movement and habitat use of wild Brook Trout observed in this study underscores two important points: (1) linear models may not always provide an accurate description of movement and habitat use, which can have implications for management, and (2) maintaining stream connectivity and habitat heterogeneity is important when managing self-sustaining Brook Trout populations.
Located in Resources / Brook Trout Related Publications
File Sensitivity and Vulnerability of Brook Trout Populations to Climate Change
Predicting future brook trout Salvelinus fontinalis distributions at the population scale under various climate scenarios is of interest to the Eastern Brook Trout Joint Venture. Previous larger scale models have been useful in highlighting the potential threat; however, the predicted air and water temperature errors associated with these models makes predictions of the persistence of individual brook trout populations problematic. We directly measured paired air and water temperatures in watersheds (N = 77) containing reproducing populations of brook trout in Virginia. We found that paired air and water temperature relationships are highly variable among patches but are a useful dataset to classify sensitivity and vulnerability of existing brook trout patches. We developed a classification system using sensitivity and vulnerability metrics that classified sampled brook trout habitats into four categories (High Sensitivity- High Vulnerability (51.9% ); High Sensitivity-Low Vulnerability (10.4 % ); Low Sensitivity-High Vulnerability (7.8 % ); Low Sensitivity-Low Vulnerability (29.9 % ). Our direct measurement approach identified potential refugia for brook trout at lower elevations and with higher air temperatures than previous larger scale modeling efforts. Our sensitivity and vulnerability groupings should be useful for managers making investment decisions in protecting and restoring brook trout.
Located in Resources / Brook Trout Related Publications / Brook Trout Related Climate Change Vulnerability Research
File Understanding environmental DNA detection probabilities: A case study using a stream-dwelling char Salvelinus fontinalis
Environmental DNA sampling (eDNA) has emerged as a powerful tool for detecting aquatic animals. Previous research suggests that eDNA methods are substantially more sensitive than traditional sampling. However, the factors influencing eDNA detection and the resulting sampling costs are still not well understood. Here we use multiple experiments to derive independent estimates of eDNA production rates and downstream persistence from brook trout (Salvelinus fontinalis) in streams. We use these estimates to parameterize models comparing the false negative detection rates of eDNA sampling and traditional backpack electrofishing. We find that using the protocols in this study eDNA had reasonable detection probabilities at extremely low animal densities (e.g., probability of detection 0.18 at densities of one fish per stream kilometer) and very high detection probabilities at population-level densities (e.g., probability of detection N0.99 at densities of ≥3 fish per 100 m). This is substantially more sensitive than traditional electrofishing for determining the presence of brook trout and may translate into important cost savings when animals are rare. Our findings are consistent with a growing body of literature showing that eDNA sampling is a powerful tool for the detection of aquatic species, particularly those that are rare and difficult to sample using traditional methods.
Located in Resources / Brook Trout Related Publications
File chemical/x-pdb Quantifying the effect of semi-natural riparian cover on stream temperatures: implications for salmonid habitat management
Previous studies examining the effects of riparian cover on stream temperatures have led to highly variable findings. In an attempt to reduce these uncertainties, this study examines the relationship between stream temperature variability and local climatic conditions over discrete 300-m sections of a watercourse. Seventeen stream sections were chosen within the Slaney catchment on the basis of riparian cover and size. Continuous monitoring over a 2-year period from May 2010 found that riparian cover had a measurable cooling effect on water temperatures at small spatial scales. The magnitude of this effect was dependent on stream size and local climactic conditions.
Located in Resources / Brook Trout Related Publications
File text/texmacs A Function-Based Framework for Stream Assessment & Restoration Projects
Stream restoration efforts have increased significantly in the US over the past few decades and are now recognized as a billion-dollar industry. These restoration efforts stem from centuries of abuse as humans continue to alter the riverine landscape for a variety of purposes, including farming, logging, mining and development on the floodplain, and the subsequent need for channelization and flood control. These activities have significantly diminished the natural functions of our stream corridors. Today stream corridor restoration efforts seek to improve or restore these lost functions. A variety of federal, state and local programs, along with efforts from non-profit organizations, provide funding for these programs. The goals are varied and range from simple streambank stabilization projects to watershed scale restoration. For these projects to be successful it is important to know why the project is being completed and what techniques are best suited to restore the lost functions. Knowing why a project is needed requires some form of functional assessment followed by clear project goals. To successfully restore stream functions, it is necessary to understand how these different functions work together and which restoration techniques influence a given function. It is also imperative to understand that stream functions are interrelated and build on each other in a specific order, a functional hierarchy. If this hierarchy is understood, it is easier to establish project goals. And with clearer goals, it is easier to evaluate project success.
Located in Resources / Brook Trout Related Publications / Stream Assessment and Monitoring
File Acid Mine Drainage and Effects on Fish Health and Ecology: A Review
Acid rock drainage (ARD) is produced by the oxidation of sulfide minerals, chiefly iron pyrite or iron disulfide (FeS2). This is a natural chemical reaction which can proceed when minerals are exposed to air and water. Acidic drainage is found around the world both as a result of naturally occurring processes and activities associated with land disturbances, such as highway construction and mining where acid-forming minerals are exposed at the surface of the earth. These acidic conditions can cause metals in geologic materials to dissolve, which can lead to impairment of water quality when acidic and used by terrestrial or aquatic organisms. metal laden discharges enter waters.
Located in Resources / Brook Trout Related Publications
File The Importance of Scale: Assessing and Predicting Brook Trout Status in its Southern Native Range
Occupancy models are of increasing interest to managers and natural resource decision makers. Assessment of status and trends, as well as the specific drivers influencing occupancy, both may change as a function of scale, and analyses conducted at multiple scales can help identify important mechanisms leading to changes in distributions. We analyzed extensive fine-scale occupancy data across the southern historic range of the brook trout, Salvelinus fontinalis to determine which landscape metrics and thresholds were useful in predicting brook trout presence across three relevant spatial scales and how brook trout occupancy varied by scale. Percentage occupancy declined markedly with increased spatial resolution, as 52% of watersheds (HUC10) but only 32% of subwatersheds (HUC12) and 14% of catchments (HUC14) were occupied. Across all three scales, habitats which were exclusively occupied by native brook trout (without non-native trout) were rare (<10%). CART models using GIS-derived landscape predictor variables were developed for three classification cases: Case 1:(brook trout; no brook trout), Case 2 (brook trout; non-native trout only; no trout), and Case 3 (brook trout only; brook and non-native trout; non-native trout only and no trout). Model results were sensitive to both scale and the number of classification categories with respect to classification accuracy, variable selection and variable threshold values. Classification accuracy tended to be lowest at the finest (catchment) scale potentially reflecting stochastic population processes and barriers to movement. Classification rates for the overall models were: Case 1: Watershed (80.19%); Subwatershed (85.06%); Catchment (71.13%); Case 2: Watershed (69.31%); Subwatershed (68.72%); Catchment (57.38%); Case 3: Watershed (58.91%); Subwatershed (59.83%); Catchment (47.59%). Our multiscale approach revealed soil permeability (positive) and atmospheric pollution (negative) to be important predictors. The predicted occupancy and observed status of brook trout appear to be influenced by the scale the data are collected and reported.
Located in Resources / Brook Trout Related Publications