Mark Hudy

Dispersal and Within-Stream Spatial Population Structure of Brook Trout Revealed by Pedigree Reconstruction Analysis

Abstract Spatial patterns of spawning and early dispersal have important implications for the population dynamics of stream-dwelling salmonids, but the limitations of marking technology have made it difficult to measure these processes in wild populations. We used microsatellite DNA markers and sibship and parentage analyses to follow the dispersal, spatial distribution, and distribution of reproductive success in a small, isolated western Virginia population of brook trout Salvelinus fontinalis at 4, 16, and 28 months after fry emergence. For the 2004 year-class (high-recruitment cohort), we identified 180 full-sibling families representing individual spawning events. Offspring were unevenly distributed across families, with 16% of the families accounting for 50% of the offspring and 53% of the families being represented by fewer than three individuals. However, a large proportion of adults had some successful reproduction. Spatial and family size distributions at 4 months after emergence were similar be...

Rainbow Trout and Brook Trout Mortality from High Voltage AC Electrofishing in a Controlled Environment

Abstract Twelve groups of 250 hatchery rainbow trout (Salmo gairdneri) and brook trout (Salvelinus fontinalis) were electroshocked in hatchery raceways and monitored for 15 days. The mean immediate, delayed, and total mortality was less than 2% at all alternating current voltages tested (350, 700, and 760 volts). Radiographs of surviving trout showed that only a small percentage (<3%) had dislocated or fractured vertebrae. Excessive delayed mortality from the use of high-voltage alternating current to sample trout populations in waters with low conductivity should be of little concern for most management activities.

Successful restoration of an acidified native brook trout stream through mitigation with limestone sand.

Abstract Limestone sand was added by helicopter directly to the headwaters of Fridley Run (Mountain Run), a first-order stream in the George Washington National Forest, Virginia, in August 1993. This was done to mitigate the effects of anthropogenic, atmospherically derived acid deposition and to enable restoration of a reproducing population of brook trout Salvelinus fontinalis. Brook trout, which had been historically present in this stream, had been absent for at least the last 20 years. Water quality improved immediately following liming, and the effects of the direct application have lasted 44 months to date. The mean monthly water chemistry difference between the acidic control and upper sampling sites (1.1 km below the liming site) was an increase in pH (+1.14 units), acid neutralizing capacity (ANC; +49 μeq/L), Ca2+ (+73 μeq/L), and Ca: H ratio (+382) and a decrease in total Al (−279 μgm/L). The mean monthly difference between the acidic control and the lower sampling sites (1.8 km below the limin...

Movement and Recolonization of Potomac Sculpin in a Virginia Stream

Abstract Movement patterns of benthic fishes have not been widely studied, but an understanding of those movement patterns may be necessary in assessing the full effects of habitat fragmentation and the need to restore connectivity in fragmented watersheds. We evaluated nonspawning movement of 3,353 marked Potomac sculpin Cottus girardi over a 1-year period on a 3.14-km segment of a third-order stream. In addition, we conducted a fish removal experiment at the pool–riffle sequence scale (90 m) to evaluate the effects of fish density on movement and recolonization rates. The majority of recaptured Potomac sculpin stayed within 30 m of their original capture location throughout the study (81% at 30 d; 64% at 75 d; 53% at 363 d). Upstream (US) movement was greater than downstream (DS) movement at 30 d (US 17%; DS 3%), 75 d (US 30%, DS 6%) and 363 d (US 32%, DS 15%). After 75 d, 10% of the fish that moved upstream moved more than 250 m (21% after 363 d). The maximum distance moved was 1,711 m in 75 d. There w...

Effective number of breeders provides a link between interannual variation in stream flow and individual reproductive contribution in a stream salmonid

The effective number of breeders that give rise to a cohort (Nb) is a promising metric for genetic monitoring of species with overlapping generations; however, more work is needed to understand factors that contribute to variation in this measure in natural populations. We tested hypotheses related to interannual variation in Nb in two long‐term studies of brook trout populations. We found no supporting evidence for our initial hypothesis that N^b reflects N^c (defined as the number of adults in a population at the time of reproduction). N^b was stable relative to N^C and did not follow trends in abundance (one stream negative, the other positive). We used stream flow estimates to test the alternative hypothesis that environmental factors constrain Nb. We observed an intermediate optimum autumn stream flow for both N^b (R2 = 0.73, P = 0.02) and full‐sibling family evenness (R2 = 0.77, P = 0.01) in one population and a negative correlation between autumn stream flow and full‐sib family evenness in the other population (r = −0.95, P = 0.02). Evidence for greater reproductive skew at the lowest and highest autumn flow was consistent with suboptimal conditions at flow extremes. A series of additional tests provided no supporting evidence for a related hypothesis that density‐dependent reproductive success was responsible for the lack of relationship between Nb and NC (so‐called genetic compensation). This work provides evidence that Nb is a useful metric of population‐specific individual reproductive contribution for genetic monitoring across populations and the link we provide between stream flow and Nb could be used to help predict population resilience to environmental change.

Flood Effects on Road–Stream Crossing Infrastructure: Economic and Ecological Benefits of Stream Simulation Designs

ABSTRACTStream simulation design is a geomorphic, engineering, and ecologically based approach to designing road–stream crossings that creates a natural and dynamic channel through the crossing structure similar in dimensions and characteristics to the adjacent natural channel, allowing for unimpeded passage of aquatic organisms, debris, and water during various flow conditions, including floods. A retrospective case study of the survival and failure of road–stream crossings was conducted in the upper White River watershed and the Green Mountain National Forest in Vermont following record flooding from Tropical Storm Irene in August 2011. Damage was largely avoided at two road–stream crossings where stream simulation design was implemented and extensive at multiple road–stream crossings constructed using traditional undersized hydraulic designs. Cost analyses suggest that relatively modest increases in initial investment to implement stream simulation designs yield substantial societal and economic benefi...

Experimental test of genetic rescue in isolated populations of brook trout

Genetic rescue is an increasingly considered conservation measure to address genetic erosion associated with habitat loss and fragmentation. The resulting gene flow from facilitating migration may improve fitness and adaptive potential, but is not without risks (e.g., outbreeding depression). Here, we conducted a test of genetic rescue by translocating ten (five of each sex) brook trout (Salvelinus fontinalis) from a single source to four nearby and isolated stream populations. To control for the demographic contribution of translocated individuals, ten resident individuals (five of each sex) were removed from each recipient population. Prior to the introduction of translocated individuals, the two smallest above‐barrier populations had substantially lower genetic diversity, and all populations had reduced effective number of breeders relative to adjacent below‐barrier populations. In the first reproductive bout following translocation, 31 of 40 (78%) translocated individuals reproduced successfully. Translocated individuals contributed to more families than expected under random mating and generally produced larger full‐sibling families. We observed relatively high (>20%) introgression in three of the four recipient populations. The translocations increased genetic diversity of recipient populations by 45% in allelic richness and 25% in expected heterozygosity. Additionally, strong evidence of hybrid vigour was observed through significantly larger body sizes of hybrid offspring relative to resident offspring in all recipient populations. Continued monitoring of these populations will test for negative fitness effects beyond the first generation. However, these results provide much‐needed experimental data to inform the potential effectiveness of genetic rescue‐motivated translocations.

Model-Based Clustering in a Brook Trout Classification Study within the Eastern United States

Abstract Data collected on the population status (extirpated or present) of brook trout Salvelinus fontinalis at the landscape level across the eastern United States is useful for identifying important stressors and predicting brook trout status at the watershed level. However, when dealing with data compiled over a large region, a single model may not adequately describe relationships between variables. To find models with better classification performance, we used a Monte Carlo model-based clustering method with logistic regression models to obtain subregions with good predictive performance. To subdivide the eastern United States into subregions, we used Voronoi tessellations with randomly selected centers. The average fraction correctly classified for fit was the criterion used when searching for optimal models within clusters. Logistic regression models were chosen by stepwise selection based on five explanatory variables: Elevation, percentage of forested land, percentage of agricultural land, road ...