Early effects of an exotic salmonid removal project on native brook trout in a southern Lake Superior tributary

Exotic salmonids are valued elements of the Great Lakes fish community; however their effects on sympatric native species are undefined.  As part of a coaster brook trout (Salvelinus fontinalis) rehabilitation program, we are undertaking a physical removal program targeting Oncorhynchus mykiss and O. kisutch in a stream on the south shore of Lake Superior to evaluate their effect on resident and adfluvial brook trout.  Brook trout were monitored using electrofishing as well as PIT/RFID telemetry. During 2008-2009, we removed ~1800 fish (primarily age 0-1) per year from the 2.1 km study reach (62% O. mykiss, 38% O. kisutch).  Population estimates suggest a 24.7% increase in S. fontinalis in the removal stream with a 25.1% decrease in exotic salmonid population size (particularly O. kisutch); estimates from a nearby reference stream show an increase in non-native population abundances during the same period.  Of particular interest is an apparent increase in brook trout YOY during the second removal year.  We have also documented diet overlap between juvenile native brook trout and exotic salmonids that was both season and habitat specific. These preliminary effects suggest the removal protocol is sufficient to change population abundances and that native trout are responding positively to exotic removal.