Q. How do salmon know where to spawn?

Pacific Northwest salmon live in many different habitats and travel long distances over the course of their lives. Adult salmon retrace these lifelong paths as they return to their natal streams to complete the final stage of life—spawning.

This journey takes all of the salmon’s energy and causes many people to wonder:

Q: How do salmon know where to spawn?

A: Unfortunately, the answer to this question is not as clear as the waters in which salmon prefer to spawn. This subject is still being studied; however, scientists are discovering that there are two key ways salmon find their spawning grounds: scent and magnetism. Which homing mechanism salmon use depends on the environment they are in at the time – either open ocean (where they live most of their lives) or freshwater habitats (where they are born and return to spawn).

Pacific salmon species

In the ocean, it is believed that salmon have sensors in their brains that function like a mapping system by detecting the earth’s magnetic field. Any given location on earth has its own unique magnetic makeup, like fingerprints for humans. Salmon use these sensors to find their home watershed’s “magnetic fingerprint.” Once they find that watershed, they can continue the freshwater portion of their spawning migration. Scientists are still learning about magnetic field detection mechanisms in salmon and other living organisms as well. Studies of sea turtles, migratory birds and other animals may help explain how salmon use and detect the earth’s magnetic field.

Once salmon have reached freshwater, they rely on unique scents to find their way back to their birth place. Studies have shown that after salmon are born, they imprint different scents picked up as they travel from their home streams to the open ocean. When adult salmon return to their natal watersheds to spawn, these scent memory banks help the salmon navigate waterways and find their hatching streams.

Although many salmon return to their home streams, there are some who spawn elsewhere. It may be unclear why some salmon spawn in different watersheds from which they hatched, but the result is genetic diversity and the re-population of some waterways that have been affected by geologic disasters.

To learn more about salmon and other Puget Sound fishes, click here.

The Burke Museum partners with the Seattle PI's Big Blog to answer commonly asked questions about the natural and cultural history of our region. This post originally appeared on the Big Blog on February 5. 

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Posted by: Andrea Barber