Dr. Stephen Riley

Photo of Dr. Stephen Riley Speaker at 2013 Changing Lakes Forum

Dr. Stephen Riley

Stephen Riley is a fisheries biologist working for the U. S. Geological Survey in Ann Arbor, Michigan. He received his B.Sc. and M.Sc. from the University of Waterloo and a Ph.D. from Colorado State University. Stephen has 30 years of experience working on fish populations throughout North America.

Stephen is currently a member of the Great Lakes Fishery Commission’s Board of Technical Experts and the editor of the North American Journal of Fisheries Management. His work is currently focused on deepwater fish ecology in the Great Lakes, with emphasis on lake trout.

Professional Affiliation

USGS Great Lakes Science Center
Ann Arbor, MI, USA

2013 Changing Lakes Topic

Status of the Changing Lake Huron Ecosystem

The native offshore fish community in Lake Huron was disrupted by introductions of sea lamprey, 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. The offshore waters of Lake Huron have recently shown signs of increasing oligotrophy, including reductions in phosphorus levels, changes in the concentration and seasonality of chlorophyll, and shifts in zooplankton abundance and community structure. The estimated lakewide biomass of offshore prey fishes in Lake Huron reached unprecedented low levels, and the offshore demersal fish community had collapsed by 2006. Invasive alewife populations crashed in 2003 and estimated biomass of this species has remained very low, while native bloater abundance is beginning to rebound. Thiamine levels in lake trout eggs have increased in recent years, and natural reproduction and recruitment of lake trout is occurring lakewide. Changes in offshore fish habitat use 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. Data on nearshore fish species are sparse, but many species appear to be stable and some are increasing in abundance. The recent increased occurrence of Cladophora events and botulism outbreaks may also be related to recent foodweb changes. It has been suggested that Lake Huron may be undergoing a regime shift, and the consequences for future ecosystem services from the lake are uncertain.

 

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