Salmon | Nature Adventure

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Biology

Salmon are large fish that hatch in freshwater streams before migrating out to the ocean, where they live until it's time to reproduce. Then, during the period of time called "spawning", they come back to the same rivers they hatched at in order to mate and lay their eggs. This back and forth migratory behavior may not seem like a big change to us, but going from freshwater to saltwater is extremely difficult on the fish's morphology! Their entire body chemistry changes to adapt to a saltwater or freshwater environment.

Along with these chemical changes, salmon also experience physical changes during the spawning season. Different salmon change in different ways, but males typically grow a humped back, turn a vibrant red and green, and may even develop fangs or hooked jaws. To return to their spawning place, they have to travel upstream, even jumping over short waterfalls! This is where many salmon are caught by predators like bears, eagles, and wolves, who will wait at the top of the stream to catch fish mid-jump. People have called this season the "salmon run".

After spawning, most salmon will die. The journey from the sea to the river takes so much energy from them that their bodies simply cannot survive the return trip, and are thus programmed to die soon after their mission is complete. Mass die-offs of salmon are common right after breeding season, which provides ample food for scavengers both on land and in the water.

Ecological Importance

During the salmon run - the time when salmon return to freshwater rivers to spawn - they provide incredibly important nutrition to bears and other animals waiting along the river. Not only does this help the bears through the winter by bulking them up for hibernation, bears actually leave about half of the salmon they catch on the forest floor!

You might think this seems like a waste, but the nitrogen produced by salmon as they decompose is vital to maintaining the health of the entire forest. Trees and other plants need nitrogen to grow big and healthy; it's one of the most important fertilizers for plants, and as the salmon bodies break down, all the nutrients and nitrogen in their system goes directly into the soil. This then feeds the plants, insects, and scavengers of the forest, making the entire ecosystem reliant on the annual salmon run.

Did you know?

Salmon typically spend their juvenile years in freshwater ponds, just like those created by beavers!

Healthy beaver populations not only change the entire ecosystem to create more sources of water, but help to nurture young salmon in the safety of their lakes. Short beaver dams allow high tide water to come in, and block off larger channels when the low tide comes. This means that young salmon can easily enter and exit these pools of water to avoid predation by larger fish, who can't get over the walls at high tide.

These salmon then go on to be killed by bears and many are left along the banks of the river to decompose. This, in turn, feeds the trees that the beaver eats and builds their dams out of, protecting the next generation of salmon so that the cycle may start all over again.

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