Effects of Climate‐Related Stream Factors on Patterns of Individual Summer Growth of Cutthroat Trout

Abstract

Coldwater fishes are sensitive to abiotic and biotic stream factors, which can be influenced by climate. Distributions of inland salmonids in North America have declined significantly, with many of the current strongholds located in small headwater systems that may serve as important refugia as climate change progresses. We investigated the effects of discharge, stream temperature, trout biomass, and food availability on summer growth of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri, a species of concern with significant ecological value. Individual size, stream discharge, sample section biomass, and temperature were all associated with growth, but had differing effects on energy allocation. Stream discharge had a positive relationship with growth rates in length and mass; greater rates of prey delivery at higher discharges probably enabled trout to accumulate reserve tissues in addition to structural growth. Temperature effects were positive but not significant, and support in growth models was limited, likely due to the cold thermal regimes of the study area. The strength of the discharge effect on growth suggests that climate adaptation strategies for coldwater fishes that focus solely on thermal characteristics may be misleading and highlights the importance of considering multiple factors, including hydrologic regimes, in conservation planning.

Interacting Effects of Density‐Dependent and Density‐Independent Factors on Growth Rates in Southwestern Cutthroat Trout Populations

“…The second DI effect that was hypothesized to affect RGCT growth and was included within the candidate set of models was mean stream discharge (m 3 /s). We hypothesized that low flows negatively affect salmonid demography and individual growth due to reduced available habitat, reduced delivery of drift forage, and increased crowding effects (Jenkins et al 1999;Nislow et al 2004;Letcher et al 2015;Bassar et al 2016;Kovach et al 2016;Uthe et al 2019). We calculated mean discharge between the initial day of capture and the day of recapture.…”

Population Dynamics and Temporal Trends of Bull Trout in the East Fork Salmon River, Idaho

“…Discharge in the East Fork Salmon River was not available, and Bull Trout that spawn in the East Fork Salmon River spend the majority of the year in other locations such as the main stem of the Salmon River or other tributaries (Schoby and Keeley 2011); thus, the discharge in the upper Salmon River was used as an index of years with higher or lower streamflow. Discharge (termed Avgflow ) was included as a predictor variable because streamflow has previously been documented to influence growth (Harvey et al 2006; Jensen and Johnsen 1999; Letcher et al 2015; Teichert et al 2010; Uthe et al 2019) and survival in salmonids (Al‐Chokhachy and Budy 2008; Howell et al 2016; Letcher et al 2015; McCormick and High 2020; Richard et al 2015). Low streamflow also has the potential to limit salmonid populations by reducing habitat quantity and quality (e.g., Magoulick and Kobza 2003), which may impact population survival.…”

“…Water temperature was included as a predictor variable because the severity of both summer and winter water temperatures can affect salmonid growth (Armstrong and Nislow 2012; Letcher et al 2015; Richard et al 2015; Selong et al 2001; Uthe et al 2019) and survival (Jakober et al 1998; Letcher et al 2015; Meyer et al 2014; Selong et al 2001). Average summer (June–August; termed SummerTemp ) and winter (December–February; termed WinterTemp ) water temperature was sporadically available for the East Fork Salmon River during this study, but as mentioned above, adult Bull Trout are only in the East Fork Salmon River for a portion of the year.…”

Fisheries Volume 45 Number 2 February 2020

“…During 2015, the date at which the majority of YOY emigrated (90th percentile) occurred 41 days earlier than 2016, and no LCT were captured in the screw trap after June 1, 2015 in contrast with July 8, 2016. Emigrating YOY were also considerably smaller in 2015 than 2016, and the warm stream temperatures in combination with low discharge likely limited forage and growth opportunities (Uthe et al 2019 ). Excessive warming may also have driven the earlier migration patterns as average daily temperatures exceeded 22°C by the end of May with daily maximum temperatures in excess of 25°C (Dickerson and Vinyard 1999 ).…”