Thermal sensitivity reveals different susceptibility to climate warming for Brook Trout (Salvelinus fontinalis) streams in close proximity.

Abstract

A warming climate has been widely recognized as an existential threat to populations of Eastern Brook Trout (Salvelinus fontinalis) inhabiting headwater streams spanning the Appalachian Mountains. However, little information is available on the status of individual streams at fine-scale geographic levels. To address this issue, we evaluated air and in-stream temperature time-series over a seven-year period among 10 streams on Laurel Hill in southwestern Pennsylvania. Thermal sensitivity (E, the slope of the air-instream temperature relationship) was calculated for each stream during the Brook Trout growth seasons (April-September) to determine potential effects on resident fish. Values of E varied interannually within and among streams in terms of annual maximum growth season temperatures, days of Brook Trout thermal stress (>18 °C), and estimated number of days to hatch. A value of E approximating 0.42 served as an inflection point above which periods of thermal stress rose sharply. E was also positively related to estimated days to hatch. Overall, the data from this study document differing responses to warming from streams as close as 2 km apart, suggesting a need for conservation measures at a local level. The use of paired in-stream and riparian temperature data loggers provides an inexpensive way to identify and to monitor streams that may be particularly vulnerable to warming. Data from this study indicated that warming has detrimental implications for resident eastern Brook Trout and, without consideration of groundwater and riparian canopy protection, along with revised stocking paradigms, continuing existential impacts can be expected. Identifying which streams are most susceptible to warming impacts on Brook Trout using a simple metric, such as thermal sensitivity, will allow for more targeted conservation efforts by fishery/watershed managers to protect this at-risk native species.