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Conflict between fisheries management and water quality
Professor Leif Hembre, Associate Professor of Biology, Hamline University
Conflict between fisheries management and water quality: Case studies of Minnesota Lakes stocked with rainbow trout
Lake eutrophication is often a ‘bottom-up’ process caused by increased nutrient (e.g., phosphorus, nitrogen) loading from the watershed as a result of land use changes (e.g., agriculture, urbanization). However, food web structure can also significantly affect the trophic state of a lake via ‘top-down’ effects. Many lakes in Minnesota and elsewhere are stocked with fish to provide recreational opportunities for anglers. Typically, the game fish stocked in lakes are piscivores (e.g., walleye, bass, muskie, etc) that primarily consume other fish, but in some cases zooplanktivorous species of fish such as rainbow trout are stocked. In these instances, the fisheries management of the lake can cause a lake to become more eutrophic via a ‘trophic cascade’ in which trout predation on herbivorous zooplankton (e.g., Daphnia) leads to increases phytoplankton biomass and lower levels of water clarity. This seminar will focus on the conflict between fisheries management and water quality through the exploration of data from case studies of two Minnesota lakes that have been regularly stocked with rainbow trout.