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What do salmon do during the day vs. at night?

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In general, salmon—like all wildlife who aren’t at the top of the food chain—spend most of their time doing one of three things:

1. Hiding from predators;
2. Finding and eating food;
3. Trying to reproduce.

Which of the three activities takes precedence depends on life cycle factors and also on predator behaviours. Generally, if predators are nocturnal, salmon feed and move more during the day, whereas if predators are diurnal, salmon increase their nighttime activities. The situation is a little different for young alevins: they avoid light at all times, as they don’t yet have the protective colouring that would guard against ultraviolet rays and camouflage them from predators. So they feel safer at night. At night, all freshwater salmon are helped if the moon is full and the night well-lit (salmon find their food using visual cues).

When salmon feel the migratory impulse, they will move regardless of whether it’s day or night—the urge is so strong. Not surprisingly, the migration stage is also when salmon are most vulnerable to predators; they swim together in schools to minimize their risk. In the ocean, salmon are equally active in the day and at night.

When they return to freshwater streams as adults, the need to reproduce trumps the need to eat or hide from predators. In fact, spawning salmon have never been found with food in their bellies! Nighttime is the preferred spawning time. However, at the height of a spawning season, you can carefully stand on the banks of streams and watch them swimming past and spawning—in the day as well as at night. “Careful” is the operative word, since to salmon, you can look like a large predator and they can get spooked.

Fin,

Professor Salmon