Mass Redistribution of Pelagic Lake Fish Under High Winds: A Freshwater Equivalent of Ocean Fronts

Ocean fronts are often associated with upwellings, eddies and enhanced vertical circulation which concentrate zooplankton abundances and attract pelagic fish as well as avian and mammalian predators. At a smaller scale, recent research in lakes has found that strong winds can form a re-circulating epilimnion which concentrates zooplankton along the thermocline. This study explores whether cisco (a schooling pelagic lake fish) respond to high winds in similar ways to the response of marine pelagic fish to ocean fronts and redistribute to areas of higher prey abundance. A field program was conducted in 2010 on Lake Opeongo (Ontario, Canada) using hydroacoustic surveys, netting programs and lake-water physical parameters collections. Results suggest that 1) strong winds that concentrate zooplankton abundance occur frequently over the growing season, 2) the redistribution of pelagic fish occurs in clear steps depending on wind intensity, and 3) under high winds pelagic fish congregate at remarkably high numbers directly underneath the thermocline at the downwind end of the fetch. Last we present a hypothesis of how the deep pelagic schools in the hypolimnion can sense high surface winds, and demonstrate that the benefits from windy conditions may contribute to larger pelagic fish across Ontario's landscape. The significance of these events is discussed in terms of fisheries surveys, and the spatial and foraging ecology of aquatic organisms.