Brook and Brown Trout Thermal Habitat Use During the Summer

Elaine Langone Center, Forum

We measured the thermal regimes of key trout (Salvelinus fontinalis and Salmo trutta) habitats during summer 2016 (from June to August) in three different tributaries of Loyalsock Creek: Little Bear Creek, Dry Run and Ogdonia Creek. Within each stream, five eaches were selected for electrofishing surveys conducted in mi-June and end of August to evaluate: 1) the number of fish by age class and 2) their use of the thermal habitat. The habitat position of each fish sampled was noted during each survey. The results howed that Little Bear Creek is significantly colder than Ogdonia Creek and Dry Run (p < 1.78E-06). Ogdonia Creek presents the warmest temperature regime of the three studied streams (p= 0.00296), with maximum daily values up to 22.03 and 24.90oC from upstream to downstream; reaching the critical thermal tolerance value for brook trout. Brook trout juvenile abundance is statistically different across the three streams (p < 0.003), with Dry Run having the highest abundance. At the beginning of the summer, there were less adult and juvenile brook trout in Ogdonia Creek. While in August, Ogdonia had the higher brook trout juvenile abundance, especially in the upper stream sites (p < 0.05). Brown trout abundances were different for Little Bear and Dry Run at the beginning of the summer (p < 0.05), with Little Bear Creek having the lower values. By August, only Ogdonia Creek showed a higher abundance of young of the year brown trout. Young of the year brown trout almost always occupy the top part of the riffles when both species are present and show higher weight values then brook trout. By August, more young of the year brook trout are observed at the edges of cooler pools, leaving the warmer riffles. From the position recorded and the abundances per sites at the beginning and the end of the summer, the brook trout seem to display more movements toward the cooler pool and upstream reaches. Those results are important to understand the dynamics between both species. Brook trout seem to move toward the cooler upstream reaches throughout the summer, which are known to have less aquatic macroinvertebrate abundance. This adds to the extra energetic expenditures from moving upstream, therefore potentially affecting the growth of brook trout compared to brown trout, which seem to be able to exploit the same thermal habitat throughout the summer.