Diel vertical migrations by juvenile sockeye salmon and the antipredation window

Abstract

Diel migration between habitats containing different levels of food abundance may constitute a response to diel changes in the relationship between potential feeding rates and predation risks in the different habitats. For planktivores that locate their prey by sight (such as juvenile Oncorhynchus nerka) and that in turn are subject to predators that use sight to locate them, the diel time profiles of potential feeding rate and predation risk in near-surface waters may be determined largely by the relative densities of prey at the 2 trophic levels. A simple model of aquatic predation leads the authors to hypothesize the existence of brief "antipredation windows' for feeding at dawn and dusk. The optimal behavior for pelagic planktivores would be to migrate into surface waters to feed during these 2 daily windows and to migrate to deeper, less illuminated water during daylight hours. -from Authors