EVALUATION AND APPLICATION OF POPULATION SIZE ESTIMATORS TO ASSESS BROOK TROUT (SALVELINUS FONTINALIS) RESPONSE TO A NON-NATIVE SALMONID REMOVAL IN A SMALL MICHIGAN COLDWATER STREAM

Non-native salmonids have been stocked into the Great Lakes since the 1870s and now naturalized populations use tributary environments to reproduce and for their juvenile life stage. Historically, brook trout were the only salmonid to inhabit the tributary environment and numerous studies suggest that exotic salmonids negatively affect brook trout by competing for limited resources. Other studies have been successful at removing non-native salmonids and the native populations increased. During this project 5,320 exotic salmonids were removed from a tributary of Lake Superior from 2008 to 2010 significantly reducing their density and young-of-year brook trout density increased by 260% the year after the study suggesting interspecific competition may be occurring. In order to monitor the salmonid populations closely, three techniques were used to assess population size of this small brook trout population. Mark-recapture estimates had large confidence intervals, so changes in population size could not be detected. Depletion estimates were hampered by sample size constraints and likely underestimated the population size. Relative abundance seemed to be the least likely to be biased because sampling was done on a frequent basis, which helped identify apparent changes in capture probability making it the best option to monitor changes in population size