Towards Rebuilding the Yellow Perch Stocks in the Fluvial Lake Saint-Pierre (St. Lawrence River, Canada) By Mitigating the Impacts of Agricultural Practices

Following two decades of dramatic decline of yellow perch landings in Lake Saint-Pierre (St.Lawrence River, Canada), fisheries were recently closed. While the fishing pressure was a determining factor in adult mortality, year class strength index pointed out important recruitment failures since the 1990’s. Lake Saint-Pierre is a large and shallow fluvial lake, (400km2; average depth is 3 m) listed as a biosphere reserve by the UNESCO in 2000. Despite its acknowledged socio-economic value (fishing, hunting, ecotourism, etc.), corn and soy crops were grown over large expanses in the floodplain. Using a spatially explicit modeling approach combined with land use analyses, we highlighted that current agricultural practices resulted in a net loss of the best potential spawning habitats for yellow perch. This is especially true for the shallowest portion of the spawning habitat in the floodplain, located just under the two-years flooding recurrence. Our 2D model was validated using 7-years of extensive larval sampling (2005-2011) conducted early in spring just after hatching. We concluded that it is mandatory to restore the best spawning habitats in order to regain a higher level of recruitment. In order to assist the restoration efforts, we identified the most valuable areas for spawning around Lake Saint-Pierre.