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File Broad-Scale Patterns of Brook Trout Responses to Introduced Brown Trout in New York
Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta are valuable sport fish that coexist in many parts of the world due to stocking introductions. Causes for the decline of Brook Trout within their native range are not clear but include competition with Brown Trout, habitat alteration, and repetitive stocking practices. New York State contains a large portion of the Brook Trout’s native range, where both species are maintained by stocking and other management actions.We used artificial neural network models, regression, principal components analysis, and simulation to evaluate the effects of Brown Trout, environmental conditions, and stocking on the distribution of Brook Trout in the center of their native range. We found evidence for the decline of Brook Trout in the presence of Brown Trout across many watersheds; 22% of sampled reaches where both species were expected to occur contained only Brown Trout. However, a model of the direct relationship between Brook Trout and Brown Trout abundance explained less than 1% of data variation. Ordination showed extensive overlap of Brook Trout and Brown Trout habitat conditions, with only small components of the hypervolume (multidimensional space) being distinctive. Subsequent analysis indicated higher abundances of Brook Trout in highly forested areas, while Brown Trout were more abundant in areas with relatively high proportions of agriculture. Simulation results indicated that direct interactions and habitat conditions were relatively minor factors compared with the effects of repeated stocking of Brown Trout into Brook Trout habitat. Intensive annual stocking of Brown Trout could eliminate resident Brook Trout in less than a decade. Ecological differences, harvest behavior, and other habitat changes can exacerbate Brook Trout losses. Custom stocking scenarios with Brown Trout introductions at relatively low proportions of resident Brook Trout populations may be able to sustain healthy populations of both species within their present range.
Located in Science and Data / Brook Trout Related Publications
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 Science and Data / Brook Trout Related Publications
File Impacts of Exotic Rainbow Trout on Habitat Use by Native Juvenile Salmonid Species at an Early Invasive Stage
The detrimental impact of introduced Rainbow Trout Oncorhynchus mykiss on native communities has been well documented around the world. Previous studies have focused on streams where the invasion has been successful and the species is fully established. In eastern Quebec, the invasion of Rainbow Trout is an ongoing process and, for now, there are few established populations. The presence of two native salmonids in these rivers, Atlantic Salmon Salmo salar and Brook Trout Salvelinus fontinalis, implies a risk of competition for habitat, despite the relatively low density of the Rainbow Trout populations, as all three species are known to use similar resources. In order to evaluate the strength of the interaction between the invading fish and the native species, we sampled nine rivers (five with Rainbow Trout and four free of Rainbow Trout) and characterized the habitat used by the three salmonids at the juvenile stage. River-scale analysis revealed that in invaded rivers, Rainbow Trout were associated with habitats characterized by closer proximity to the shoreline and by increasing shoreline cover. Estimates of habitat niche overlap integrating depth, water velocity, and substrate size revealed that niche overlap between Brook Trout and Atlantic Salmon significantly increased in the presence of Rainbow Trout. Furthermore, the two indigenous species preferred full cover in the absence of Rainbow Trout but in the presence of Rainbow Trout, which also preferred full cover, the indigenous species moved to more open habitats. Rainbow Trout showed a high growth rate, despite a size disadvantage at the beginning of the growing season, as compared with Atlantic Salmon and Brook Trout. It thus appears that even at an early stage of invasion, when its density is still low, Rainbow Trout significantly impact native salmonids.
Located in Science and Data / Brook Trout Related Publications
File Conservation Genetics of Remnant Coastal Brook Trout Populations at the Southern Limit of Their Distribution: Population Structure and Effects of Stocking
We examined genetic variation within and among a group of remnant coastal brook trout Salvelinus fontinalis populations along the coast of the northeastern United States. These populations occur at the southern limits of anadromy for this species and could form the foundation of a restored anadromous metapopulation. We also tested for genetic introgression between these populations and the hatchery source that has been used to stock these sites. The overall FST for the natural populations at 12 microsatellite loci was 0.145 (95% confidence interval, 0.108–0.183), and D was 0.225 (0.208–0.243). On average, 94.6% of individuals were correctly assigned to the population where they were collected. Our results suggest that there is little gene flow even between geographically proximate populations. We found little evidence that repeated historic stocking from a known hatchery source has led to genetic introgression into these wild coastal brook trout populations. One hybrid individual appeared to be a backcross between an F1 and a hatchery individual. Another hybrid individual could not be classified. Our results suggest that nonintrogressed and potentially locally adapted populations of brook trout persist in several small coastal New England streams. These populations should be the focus of future efforts to restore anadromous brook trout in this region.
Located in Science and Data / Brook Trout Related Publications
File The influence of land cover composition and groundwater on thermal habitat availability for brook trout populations
Brook charr (Salvelinus fontinalis) is a sentinel fish species that requires clean, cold water habitats generally resulting from landscapes that allow for surface water flows devoid of sediment and contaminants and high groundwater discharge of cold water. As such, brook charr are impacted by land cover changes that alter stream temperature regimes. We evaluated brook charr populations across their eastern and midwestern range in the United States with reference to thermal habitat availability in relationship to land cover and percent baseflow. We found that while forest cover does protect brook charr thermal habitat, high levels of groundwater discharge can allow for increased levels of agriculture within a watershed by keeping the water cold in spite of warm ambient summer temperatures. Our study concludes that with enhanced communication among land, water and fisheries managers, society can provide for sustainable stream salmonid populations despite increased threats on cold water resources.
Located in Science and Data / Brook Trout Related Publications
File Octet Stream Individual behaviour and resource use of thermally stressed brook trout Salvelinus fontinalis portend the conservation potential of thermal refugia
Individual aggression and thermal refuge use were monitored in brook trout Salvelinus fontinalis in a controlled laboratory to determine how fish size and personality influence time spent in forage and thermal habitat patches during periods of thermal stress. On average, larger and more exploratory fish initiated more aggressive interactions and across all fish there was decreased aggression at warmer temperatures. Individual personality did not explain changes in aggression or habitat use with increased temperature; however, larger individuals initiated comparatively fewer aggressive interactions at warmer temperatures. Occupancy of forage patches generally declined as ambient stream temperatures approached critical maximum and fish increased thermal refuge use, with a steeper decline in forage patch occupancy observed in larger fish. These findings suggest that larger individuals may be more vulnerable to stream temperature rise. Importantly, even at thermally stressful temperatures, all fish periodically left the thermal refuge to forage. This indicates that the success of refugia at increasing population survival during periods of stream temperature rise may depend on the location of thermal refugia relative to forage locations within the larger habitat mosaic. These results provide insights into the potential for thermal refugia to improve population survival and can be used to inform predictions of population vulnerability to climate change.
Located in Science and Data / Brook Trout Related Publications
File Linking movement and reproductive history of brook trout to assess habitat connectivity in a heterogeneous stream network
1. Defining functional connectivity between habitats in spatially heterogeneous landscapes is a particular challenge for small-bodied aquatic species. Traditional approaches (e.g. mark–recapture studies) preclude an assessment of animal movement over the life cycle (birth to reproduction), and movement of individuals may not represent the degree of gene movement for fecund species. 2. We investigated the degree of habitat connectivity (defined as the exchange of individuals and genes between mainstem and tributary habitats) in a stream brook trout (Salvelinus fontinalis) population using mark–recapture [passive integrated transponder (PIT) tags], stationary PIT-tag antennae and genetic pedigree data collected over 4 years (3425 marked individuals). We hypothesised that: (i) a combination of these data would reveal higher estimates of animal movement over the life cycle (within a generation), relative to more temporally confined approaches, and (ii) movement estimates of individuals within a generation would differ from between-generation movement of genes because of spatial variation in reproductive success associated with high fecundity of this species. 3. Over half of PIT-tagged fish (juveniles and adults) were recaptured within 20 m during periodic sampling, indicating restricted movement. However, continuous monitoring with stationary PIT-tag antennae revealed distinct peaks in trout movements in June and October–November, and sibship data inferred post-emergence movements of young-of-year trout that were too small to be tagged physically. A combination of these methods showed that a moderate portion of individuals (28–33%) moved between mainstem and tributary habitats over their life cycle. 4. Patterns of reproductive success varied spatially and temporally. The importance of tributaries as spawning habitat was discovered by accounting for reproductive history. When individuals born in the mainstem reproduced successfully, over 50% of their surviving offspring were inferred to have been born in tributaries. This high rate of gene movement to tributaries was cryptic, and it would have been missed by estimates based only on movement of individuals. 5. This study highlighted the importance of characterising animal movement over the life cycle for inferring habitat connectivity accurately. Such movements of individuals can contribute to substantial gene movements in a fecund species characterised by high variation in reproductive success.
Located in Science and Data / Brook Trout Related Publications
File Brook Trout Movement in Response to Temperature, Flow, and Thermal Refugia within a Complex Appalachian Riverscape
We quantified movements of brook trout Salvelinus fontinalis and brown trout Salmo trutta in a complex riverscape characterized by a large, open-canopy main stem and a small, closed-canopy tributary in easternWest Virginia, USA. Our objectives were to quantify the overall rate of trout movement and relate movement behaviors to variation in streamflow, water temperature, and access to coldwater refugia. The study area experienced extremely high seasonal, yearly, and among-stream variability in water temperature and flow. The relative mobility of brook trout within the upper Shavers Fork watershed varied significantly depending on whether individuals resided within the larger main stem or the smaller tributary. The movement rate of trout inhabiting the main stem during summer months (50 m/d) was an order of magnitude higher than that of tributary fish (2 m/d). Movement rates of main-stem-resident brook trout during summer were correlated with the maximum water temperature experienced by the fish and with the fish’s initial distance from a known coldwater source. For main-stem trout, use of microhabitats closer to cover was higher during extremely warm periods than during cooler periods; use of microhabitats closer to cover during warm periods was also greater for main-stem trout than for tributary inhabitants. Main-stem-resident trout were never observed in water exceeding 19.5◦C. Our study provides some of the first data on brook trout movements in a large Appalachian river system and underscores the importance of managing trout fisheries in a riverscape context. Brook trout conservation in this region will depend on restoration and protection of coldwater refugia in larger river main stems as well as removal of barriers to trout movement near tributary and main-stem confluences.
Located in Science and Data / Brook Trout Related Publications
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 Science and Data / Brook Trout Related Publications
File The temperature–productivity squeeze: constraints on brook trout growth along an Appalachian river continuum
We tested the hypothesis that brook trout growth rates are controlled by a complex interaction of food availability, water temperature, and competitor density. We quantified trout diet, growth, and consumption in small headwater tributaries characterized as cold with low food and high trout density, larger tributaries characterized as cold with moderate food and moderate trout density, and large main stems characterized as warm with high food and low trout density. Brook trout consumption was highest in the main stem where diets shifted from insects in headwaters to fishes and crayfish in larger streams. Despite highwater temperatures, trout growth rates also were consistently highest in the main stem, likely due to competitively dominant trout monopolizing thermal refugia. Temporal changes in trout density had a direct negative effect on brook trout growth rates. Our results suggest that competition for food constrains brook trout growth in small streams, but access to thermal refugia in productive main stem habitats enables dominant trout to supplement growth at a watershed scale. Brook trout conservation in this region should seek to relieve the ‘‘temperature–productivity squeeze,’’ whereby brook trout productivity is constrained by access to habitats that provide both suitable water temperature and sufficient prey.
Located in Science and Data / Brook Trout Related Publications
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