Seasonal temperature and precipitation regulate brook trout young‐of‐the‐year abundance and population dynamics

Abstract

Summary Abundance of the young‐of‐the‐year (YOY) fish can vary greatly among years and it may be driven by several key biological processes (i.e. adult spawning, egg survival and fry survival) that span several months. However, the relative influence of seasonal weather patterns on YOY abundance is poorly understood. We assessed the importance of seasonal air temperature (a surrogate for stream temperature) and precipitation (a surrogate for stream flow) on brook trout (Salvelinus fontinalis) YOY summer abundance using a 29‐year data set from 115 sites in Shenandoah National Park, Virginia, U.S.A. We used a Bayesian hierarchical model that allowed the effect of seasonal weather covariates to vary among sites and accounted for imperfect detection of individuals. Summer YOY abundance was affected by preceding seasonal air temperature and precipitation, and these regional‐scale drivers led to spatial synchrony in YOY abundance dynamics across the 170‐km‐long study area. Mean winter precipitation had the greatest effect on YOY abundance and the relationship was negative. Mean autumn precipitation, and winter and spring temperature had significantly positive effects on YOY abundance, and mean autumn temperature had a significant negative effect. In addition, the effect of summer precipitation differed along a latitudinal gradient, with YOY abundance at more northern sites being more responsive to inter‐annual variation in summer precipitation. Strong YOY years resulted in high abundance of adults (>age 1 + fish) in the subsequent year at more than half of sites. However, higher adult abundance did not result in higher YOY abundance in the subsequent year at any of the study sites (i.e. no positive stock–recruitment relationship). Our results indicate that YOY abundance is a key driver of brook trout population dynamics that is mediated by seasonal weather patterns. A reliable assessment of climate change impacts on brook trout needs to account for how alternations in seasonal weather patterns impact YOY abundance and how such relationships may differ across the range of brook trout distribution.

A geostatistical state‐space model of animal densities for stream networks

“…This is in stark contrast to the strongly negative effects of winter precipitation found in SNP (Kanno et al 2015(Kanno et al , 2016. This is in stark contrast to the strongly negative effects of winter precipitation found in SNP (Kanno et al 2015(Kanno et al , 2016.…”

“…This finding is similar to brook trout model results from a rangewide occupancy model . Similar results were also found for an Adirondack lake (Robinson et al 2010), streams in West Virginia (Huntsman and Petty 2014) and Michigan (Grossman et al 2012), and from demographic models for brook trout in Shenandoah National Park (SNP; Kanno et al 2015Kanno et al , 2016. Similar results were also found for an Adirondack lake (Robinson et al 2010), streams in West Virginia (Huntsman and Petty 2014) and Michigan (Grossman et al 2012), and from demographic models for brook trout in Shenandoah National Park (SNP; Kanno et al 2015Kanno et al , 2016.…”

Seasonal streamflow extremes are key drivers of Brook Trout young‐of‐the‐year abundance

“…For the southeastern United States, this method was found to predict streamflow at ungaged locations comparably to more complex methods (Farmer et al 2014). Based on the findings of previous studies (including Kanno et al 2016b: Table 2 Table 2. S2).…”

“…Predicted young-of-the-year abundance per 100 m compared to low fall streamflow and high winter streamflow. This finding is particularly concerning as YOY abundance has been found to be the main factor in driving Brook Trout populations in SNP as well as in Western Massachusetts (Bassar et al 2016, Kanno et al 2016b. Note that axes range from À2 to 4 standard deviations around the mean (represented by 0).…”

Native brook trout and invasive rainbow trout respond differently to seasonal weather variation: Spawning timing matters

“…Stock–recruitment relationships varied among sites in both species, although the frequency of positive stock–recruitment relationships was higher for BKT than RBT. Many stream salmonid populations do not show positive stock–recruitment relationships (Kanno et al., ; Milner et al., ), but positive relationships have been detected for BKT in both the Southern and Middle Appalachians and Michigan (Grossman et al., ; Petty, Lamothe, & Mazik, ; Zorn & Nuhfer, ).…”