Abstract
We estimated dry season survival of imperiled salmonids in an intermittent coastal stream in California across 4 years (2009–2012). Our study encompassed two dry and two wet winters, allowing us to explore patterns of survival across and within dry seasons with different antecedent precipitation. Apparent survival of age-0+ steelhead trout (Oncorhynchus mykiss) was higher following wet winters compared with dry winters. Moreover, antecedent precipitation was positively correlated with cumulative survival of age-0+ steelhead. Within years, apparent survival of steelhead varied among weeks with a tendency to decrease in the late summer, indicating that fish exhibited some resistance to seasonal drought. Additionally, we found a slight but significant survival advantage for age-0+ coho salmon (Oncorhynchus kisutch) compared with equal-aged steelhead. Our results emphasize the influence of antecedent precipitation in driving the survival of imperiled salmonids and highlight that these fishes are somewhat resistant to seasonal drought, at least to a point.
Highlights
Seasonal and multiyear drought events can result in loss of surface flow and extreme habitat contraction in lotic ecosystems (Stanley et al 1997; Hakala and Hartman 2004)
Previous studies have demonstrated that intermittent streams, which are common throughout the world (Larned et al 2010), can provide important breeding, rearing, and refuge habitats for stream fishes (e.g., Erman and Hawthorne 1976; Wigington et al 2006; Lake 2011)
Our results suggest that ecological responses to seasonal drought are conditional on drought severity, which varies among years
Summary
Seasonal and multiyear drought events can result in loss of surface flow and extreme habitat contraction in lotic ecosystems (Stanley et al 1997; Hakala and Hartman 2004). Other studies have demonstrated that intermittent streams can be harsh environments and sites of high mortality of resident fishes (Tramer 1977; Mundahl 1990) and other vertebrates (e.g., turtles; Leidy et al 2016). These contradictory results may reflect differences in drying severity, which can vary considerably through space and time. Interannual variability in drought severity results in dramatically different physical conditions from year to year within single streams (Acuña et al 2005; Boughton et al 2009; Hwan and Carlson 2016)
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