A simple encounter model was used to simulate the process of school formation at dawn for different densities of juvenile sockeye salmon. The results suggest that the process of school formation may be severely inhibited by a low encounter rate among juvenile sockeye at the lowest densities commonly observed in natural populations. Encounter rates of predators with schools are insensitive to density because under a given set of conditions, asymptotic school density is similar over a wide range of initial densities of prey individuals. Enhanced school formation may reduce predation risk at high sockeye density and provide a mechanism for the multiple equilibrium hypothesis of sockeye dominance cycles.
Parkinson, Eric A.. 1990. Impaired School Formation at Low Density: A Mechanism for Depensatory Mortality in Sockeye Salmon. Ministry of Environment. Fisheries Management Report. FMR99
Topic: Fish and Fish Habitats
Keywords: sockeye salmon, school formation, predation, density, juveniles
Scientific Name: Oncorhynchus nerka
English Name: Sockeye Salmon
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