Watershed Level Response of Brook Trout Populations to Catastrophic Flooding of Tropical Storm Lee

In high-gradient systems, extreme flooding events act as cleansing mechanisms for stream organisms. In early September 2011, Tropical Storm Lee deposited over twelve inches of rain in the Loyalsock Creek watershed (north central Pennsylvania). A catastrophic flood occurred throughout the watershed on September 7 and 8, 2011 with peak flows (69,100 cfs) exceeding previous record flow (55,800 cfs). Throughout the watershed, the stream bed was scoured and new substrate materials were deposited, trees were uprooted from riparian areas, and stream biota was decimated.  As part of the PFBC Unassessed Waters Initiative, pre-flood brook trout populations were sampled in summer 2011 at 30 headwater stream study sites. Post flood samples were collected at each of these sites in 2012 and 2013. During 2012 sampling, we found very few brook trout in the 100-150mm size classes. Flooding essentially eliminated these size fish from these streams. Across study streams, some adult brook trout greater than 150mm were able to survive the flooding and were able to spawn in fall 2011. Results from 2012 indicate an extremely large age-0 year class, with recruitment of these fish into age-1 fish in 2013. Our results indicate recovery of these streams may take 5 or more years.