Impact of fertilization and stocking on trophic interactions and growth of juvenile sockeye salmon (Oncorhynchus nerka)

Using 16 years of data on nutrients, plankton, and sockeye fry and smolts from Packers Lake, Alaska, we test the impact of nutrients and fry stocking on the growth and productivity of juvenile sockeye salmon (Oncorhynchus nerka). To enhance sockeye production, this lake was fertilized (1983–1996) and stocked annually (1987–1996) with sockeye fry. Before fertilization, the density of sockeye fry was low (1 mm) Daphnia were significantly reduced in density under heavy predation by sockeye fry, the growth of juvenile sockeye declined, even under continued fertilization. We show that fry density and associated food web structure are major determinants of juvenile sockeye responses to fertilization and stocking. This study probably provides the first long-term experimental results linking limnological and nutrient – food web concepts to trophodynamics and productivity of juvenile sockeye salmon.