Canadian Journal of Fisheries and Aquatic Sciences, Ahead of Print.
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 nondetection for this cryptic species.

中文翻译：

---

边缘效应：在山地流域的分布边界检测公牛鳟鱼（Salvelinus confluentus）

加拿大渔业和水产科学杂志，提前印刷。
稳健的评估和监测计划对于有效保护至关重要，但对于许多类群，我们无法理解采样设计中的权衡如何影响检测种群趋势和描述空间模式的能力。我们测试了一种基于占用率的抽样方法，以评估检测与幼年公牛鳟鱼 (Salvelinus confluentus) 分布相关的流域规模种群趋势的设计注意事项。电捕鱼调查是在加拿大西北地区草原溪流域的 275 个河流站点进行的。幼年公牛鳟鱼的站点级可检测性不均匀，并且在陡峭河段和大溪流中分布边界附近的边缘栖息地中，不完善的检测对建模的占用概率影响最大。我们表明，正如保护指南所建议的那样，在≥78% 的时间内检测到流域水平占用率的 30% 变化可能需要进行三次重复调查（即时间重复）并增加边缘栖息地的空间采样强度。边缘站点的额外采样工作可以通过在核心栖息地中采样更少的站点来抵消，以优化用于检测公牛鳟鱼人口变化的设计，同时仍然最大限度地减少这种神秘物种未被发现的风险。