He studies the ecology and conservation of freshwater fishes worldwide, with special interest in large lakes and rivers of Africa and North America. Major research themes include fish migrations, climate warming, inland fisheries, and stressor assessments, all of which are pursued in partnership with NGOs and management agencies. His team addresses these questions using intensive field work, environmental chemistry, GIS mapping, and statistical synthesis with the aim of understanding large-scale ecological patterns to aid in prioritizing conservation efforts.