The salmonfly (Pteronarcys californica) is a large stonefly species that is ecologically important and recreationally significant to anglers in coldwater river systems throughout the western United States. Salmonflies are sensitive to disturbance and pollution and are considered an indicator of quality coldwater stream habitat. They are declining in range and abundance in some river systems and their extirpation from several western rivers has led to restoration attempts including habitat improvement projects and direct reintroductions. These efforts could be improved with a clear understanding of the causes of these declines, a quantitative description of the species' preferred habitat, and practical management recommendations for the restoration of habitat where it has been lost. The objective of this study was to measure variables that describe the physical habitat of sites supporting varying densities of salmonflies in Colorado. Width to depth ratio, bed slope, D50 sediment size, percent fine sediment, and embeddedness were measured at 18 riffle sites and compared to an index of salmonfly density estimated over 3 years. Correlation analysis and multiple linear regression with model selection were used to identify important variables. Salmonfly density was highest at sites with low amounts of fine sediment, low cobble embeddedness, and large cobble size. Fine sediment (particles < 2 mm) was the single best predictor of salmonfly density and ranged from 0–6% at sites with high salmonfly densities. As habitat characteristics influence the range and density of salmonflies in Colorado and elsewhere, results from this study can inform land use practices, flow management, and river restoration activities to benefit this important indicator species.

中文翻译：

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量化科罗拉多州的岩蝇Pteronarcys californica的栖息地偏好

鲑鱼（Pteronarcys californica）是一种大型的石蝇种类，对整个美国西部的冷水河流系统中的垂钓者而言，具有重要的生态意义和娱乐意义。鲑鱼对干扰和污染敏感，被认为是优质冷水流栖息地的指标。它们在一些河流系统中的范围和数量正在减少，它们从数条西部河流中的灭绝导致了恢复尝试，包括栖息地改善项目和直接再引入。可以通过清楚地了解造成这种下降的原因，定量描述该物种偏爱的栖息地以及为恢复失去的栖息地提供实用的管理建议来改善这些努力。这项研究的目的是测量变量，这些变量描述了支持科罗拉多州不同密度鲑鱼的地点的自然栖息地。在18个浅滩上测量宽宽比，河床坡度，D50沉积物尺寸，细沉积物百分比和嵌入度，并将其与3年内估计的鲑鱼密度指数进行比较。相关分析和多元线性回归与模型选择被用来识别重要变量。鲑鱼密度在细泥沙量少，卵石嵌入度低和卵石尺寸大的地方最高。细小沉积物（<2 mm的颗粒）是鲑鱼密度的唯一最佳预测指标，在鲑鱼密度高的地区，其范围为0–6％。由于栖息地的特征会影响科罗拉多州和其他地区鲑鱼的分布范围和密度，