Status of the Changing Lake Huron Ecosystem

The native offshore fish community in Lake Huron was disrupted by introductions of alewife and rainbow smelt and was dominated by invasive species by the 1950s.  More recently, introductions of dreissenid mussels, predatory zooplankters, and round gobies have further affected this community, which was in a state of collapse by 2006.  The offshore waters of Lake Huron have recently shown signs of increasing oligotrophy, including changes in the concentrations and seasonality of chlorophyll and shifts in zooplankton community size and community composition.  The estimated lakewide biomass of offshore prey fishes in Lake Huron remains at unprecedented low levels, and the offshore demersal fish community has collapsed and may currently be unstable.  Invasive alewife populations collapsed in 2003 and estimated biomass of this species has remained very low, but there are indications that rainbow smelt and bloater abundance are beginning to rebound.  Thiamine levels in lake trout eggs have increased in recent years, and there is evidence that natural reproduction of lake trout is occurring, although the abundance of wild lake trout remains relatively low.  Changes in fish habitat use and fish school characteristics suggest that large-scale changes may be occurring in the offshore benthic environment.  It is currently difficult to assess prey fish biomass estimates in the context of primary production and predator demand, as these are currently highly variable, poorly understood, and dependent on ongoing food web changes.