Long-term trends in habitat use of offshore demersal fishes in western Lake Huron suggest large-scale changes in the benthic environment

We estimated mean depths of capture for offshore demersal fish species, grouped into three habitat-based guilds (shallow benthic, pelagic, and deep benthic), using fall bottom trawl data from the western main basin of Lake Huron from 1976-2007.  The mean depth of capture of the shallow and deep benthic guilds initially exhibited a trend toward capture in shallower water, switched to a trend toward capture in deeper water in 1991, and changed back to a trend toward capture in shallower water in 2001-2002.  The pelagic guild showed a similar pattern, but the initial change point occurred in 1981.  All guilds and all pelagic and deep benthic species exhibited a change to a trend to capture in shallower water during 1999-2002.  These trends suggest that large-scale factors are affecting the habitat use of offshore demersal fish species in Lake Huron.  The depth distributions of the three guilds have converged in recent years, indicating that habitat for offshore demersal fishes may be limiting.  Our results suggest that the benthic ecology of the western main basin of Lake Huron is undergoing profound changes across a large spatial scale, and we suggest that these changes may be related to recent invasions of exotic species.