Effects of Increased Discharge on Nonnative Brook Trout in a Small Mountain Stream

Boulder Creek in Boulder, Utah is a small mountain stream that supports a reproducing population of nonnative brook trout.  Historically, water withdrawals resulted in complete dewatering with minimal flow provided by small seeps and/or springs.  Recent mitigation agreements led to the maintenance of a constant flow of 2 cubic feet/second (cfs) that began in 2010.  In order to examine the effect of flow maintenance on the brook trout population, population estimates, biomass, and condition factors were determined for three years prior (2008, 2009, 2010) to and two years after (2011, 2012) the increase in discharge.  Brook trout abundance, biomass and condition increased beginning in 2010, less than 8 months after discharge was increased.  Findings suggest that even small increases in sustained discharge may be highly beneficial to salmonid species in small mountain streams.