Fringe effects: detecting bull trout (Salvelinus confluentus) at distributional boundaries in a montane watershed

Robust assessment and monitoring programs are critical for effective conservation, yet for many taxa we fail to understand how trade-offs in sampling design affect power to detect population trends and describe spatial patterns. We tested an occupancy-based sampling approach to evaluate design considerations for detecting watershed-scale population trends associated with juvenile bull trout (Salvelinus confluentus) distributions. Electrofishing surveys were conducted across 275 stream sites from the Prairie Creek watershed, Northwest Territories, Canada. Site-level detectability of juvenile bull trout was not uniform, and imperfect detection affected modelled occupancy probabilities most in fringe habitats near distributional boundaries in steep reaches and large streams. We show that detecting a 30% change in watershed-level occupancy ≥78% of the time as conservation guidelines suggest, may require three repeat surveys (i.e., temporal replicates) and increased spatial sampling intensity of fringe habitats. Additional sampling effort in fringe sites could be offset by sampling fewer sites in core habitats to optimize designs for detecting demographic shifts in bull trout, while still minimizing risk of non-detection for this cryptic species.

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Genetic clustering methods reveal bull trout (Salvelinus confluentus) fine-scale population structure as a spatially nested hierarchy

Conservation Genetics ◽

10.1007/s10592-009-9969-y ◽

2009 ◽

Vol 11 (4) ◽

pp. 1421-1433 ◽

Cited By ~ 28

Author(s):

Will G. Warnock ◽

Joseph B. Rasmussen ◽

Eric B. Taylor

Keyword(s):

Population Structure ◽

Bull Trout ◽

Fine Scale ◽

Clustering Methods ◽

Salvelinus Confluentus ◽

Scale Population ◽

Nested Hierarchy ◽

Genetic Clustering

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Evaluating trade-offs in bull trout reintroduction strategies using structured decision making

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2016-0516 ◽

2018 ◽

Vol 75 (2) ◽

pp. 293-307 ◽

Cited By ~ 5

Author(s):

William R. Brignon ◽

James T. Peterson ◽

Jason B. Dunham ◽

Howard A. Schaller ◽

Carl B. Schreck

Keyword(s):

Decision Making ◽

Decision Model ◽

Sensitivity Analyses ◽

Bull Trout ◽

Salvelinus Confluentus ◽

Ecological Processes ◽

Structured Decision Making ◽

Management Actions ◽

Trade Offs ◽

Donor Population

Structured decision making allows reintroduction decisions to be made despite uncertainty by linking reintroduction goals with alternative management actions through predictive models of ecological processes. We developed a decision model to evaluate the trade-offs between six bull trout (Salvelinus confluentus) reintroduction decisions with the goal of maximizing the number of adults in the recipient population without reducing the donor population to an unacceptable level. Sensitivity analyses suggested that the decision identity and outcome were most influenced by survival parameters that result in increased adult abundance in the recipient population, increased juvenile survival in the donor and recipient populations, adult fecundity rates, and sex ratio. The decision was least sensitive to survival parameters associated with the captive-reared population, the effect of naivety on released individuals, and juvenile carrying capacity of the reintroduced population. The model and sensitivity analyses can serve as the foundation for formal adaptive management and improved effectiveness, efficiency, and transparency of bull trout reintroduction decisions.

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Detecting declines in the abundance of a bull trout (Salvelinus confluentus) population: understanding the accuracy, precision, and costs of our efforts

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f09-026 ◽

2009 ◽

Vol 66 (4) ◽

pp. 649-658 ◽

Cited By ~ 25

Author(s):

Robert Al-Chokhachy ◽

Phaedra Budy ◽

Mary Conner

Keyword(s):

Spatial Scales ◽

Sampling Effort ◽

Bull Trout ◽

Time Intervals ◽

Salvelinus Confluentus ◽

High Sampling ◽

Empirical Field ◽

Stage Class ◽

Considerable Resource ◽

Spatial Stratification

Using empirical field data for bull trout ( Salvelinus confluentus ), we evaluated the trade-off between power and sampling effort–cost using Monte Carlo simulations of commonly collected mark–recapture–resight and count data, and we estimated the power to detect changes in abundance across different time intervals. We also evaluated the effects of monitoring different components of a population and stratification methods on the precision of each method. Our results illustrate substantial variability in the relative precision, cost, and information gained from each approach. While grouping estimates by age or stage class substantially increased the precision of estimates, spatial stratification of sampling units resulted in limited increases in precision. Although mark–resight methods allowed for estimates of abundance versus indices of abundance, our results suggest snorkel surveys may be a more affordable monitoring approach across large spatial scales. Detecting a 25% decline in abundance after 5 years was not possible, regardless of technique (power = 0.80), without high sampling effort (48% of study site). Detecting a 25% decline was possible after 15 years, but still required high sampling efforts. Our results suggest detecting moderate changes in abundance of freshwater salmonids requires considerable resource and temporal commitments and highlight the difficulties of using abundance measures for monitoring bull trout populations.

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Geographic distribution, species displacement, and niche overlap for lake trout and bull trout in mountain lakes

Canadian Journal of Zoology ◽

10.1139/z93-034 ◽

1993 ◽

Vol 71 (2) ◽

pp. 238-247 ◽

Cited By ~ 57

Author(s):

David B. Donald ◽

David J. Alger

Keyword(s):

Trophic Structure ◽

Lake Trout ◽

Niche Overlap ◽

Mountain Lakes ◽

Bull Trout ◽

Salvelinus Confluentus ◽

East Central ◽

Allopatric Populations ◽

Trout Population ◽

The One

Indigenous lacustrine populations of bull trout (Salvelinus confluentus) and lake trout (S. namaycush) are spatially separated within the southern part of the zone of distributional overlap (northern Montana, southwestern Alberta, and east-central British Columbia). In this area, lake trout occurred primarily in mountain lakes of 1032–1500 m elevation, while bull trout were found primarily in lakes between 1500 and 2200 m. Introductions of lake trout in the twentieth century and data obtained from beyond the study area indicated that both fishes can establish significant allopatric populations (more than 5% of the catch) in large, deep lakes (>8 ha in area and >8 m deep) over a wide elevation range. We tested the hypothesis that lake trout displace or exclude bull trout from lakes by determining the outcome of introductions of lake trout into two lakes that supported indigenous bull trout. Lake trout were introduced into Bow Lake in 1964, and by 1992 the bull trout population was decimated there and in another lake (Hector) situated 15 km downstream. Thus, lake trout can displace bull trout and may prevent bull trout from becoming established in certain low-elevation lakes. Population age-structure analyses also suggest that lake trout adversely affected bull trout. Bull trout populations in sympatry with lake trout, including the one extirpated from Hector Lake, had few old fish (18% were more than 5 years old; N = 40 fish from three lakes) compared with allopatric populations (49% were more than 5 years old; N = 235 fish from seven lakes). Niche overlap and the potential for competition between the two char species were substantial. In lakes with trophic structure ranging from simple to complex, bull trout and lake trout fed on similar foods and had similar ecological efficiencies (growth rates). Predation by lake trout on bull trout was not documented during the study.

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