Changes in the Status of Native Brook Trout on Laurel Hill, Southwestern Pennsylvania

To evaluate the status of native Salvelinus fontinalis (Brook Trout) on Pennsylvania's Laurel Hill, we sampled fish, assessed habitat, and documented water quality from 20 non-randomly selected headwater streams of northwest- and southeast-facing slopes. In late spring and early summer of 2011 and 2014–2016, we sampled fish communities and measured specific conductance (μS/cm), total alkalinity (mg/l as CaCO3), pH, and total dissolved aluminum (2011 and 2016). In addition, in 2015 we determined land-use patterns, riparian canopy, and substrate composition. Mean pH values among the streams recently assessed were significantly higher than historic values; however, all other water-quality parameters were similar. Native Brook Trout were present in all streams, and annual natural reproduction was evident in 90% of streams. Even though fish were present, we observed marked declines in total catch in both 0-age and adult trout; the overall reduction approached 60% when compared with those documented in 1983. We discuss possible causes for the observed declines, including acid deposition, introduction of nonnative/invasive species, water withdrawal, habitat fragmentation/alteration, predation, and climate change.