Seasonal and Diel Patterns of Emergence from the Redd of Atlantic Salmon (Salmo salar) Fry

The emergence of Atlantic salmon (Salmo salar) fry from both artificial and wild redds was monitored on a daily basis for the duration of the emergence period by means of fry traps. On the nights of peak emergence, we made hourly checks. Emergence was largely restricted to three nights, during which most activity was confined to a 3-h period. We hypothesize that the sharp diel periodicity is due either to a stimulus–response or a clock-controlled mechanism and that synchronous nocturnal emergence is probably a predator avoidance tactic.