Ocean STEMulation: Salmon navigation

Focusing on science, technology, engineering, and math (STEM), as they pertain to the ocean.

The ocean looks, at least to us, largely devoid of landmark features. Of course, it’s not really – all sorts of geographical identifiers and other signals can be found beneath the surface – but it’s still amazing that animals can successfully navigate such a vast expanse. Have you ever wondered how they do it?

Research on sockeye salmon has now revealed new information about how these animals find their way from their nesting grounds, into the open ocean, and back.

When salmon are ready to reproduce, they return from the open ocean to the river where they were born. Photo by Ingrid Taylor via Flickr, Creative Commons License. 

Salmon are anadromous. This means that they are born in freshwater, but they grow up and mature in the ocean; they then return to rivers to reproduce. The amazing thing is that, after wandering great distances in the open ocean - they can spend up to five years and travel up to 8,000 miles - the salmon don’t just return to spawn in any river they can find. They return to the same river in which they were born.

How is this possible? It was known that salmon identify their home river using chemical signs once they were within a close range, but it wasn’t known how exactly they got to the correct area to begin with. Now, scientists have discovered that salmon find their spawning grounds by looking for their home river’s unique magnetic signature

Adult sockeye salmon during spawning season. Photo by Roger Tabor (USFWS) via Flickr, Creative Commons License. 

The earth has a magnetic field and when a salmon hatches it imprints on (essentially memorizes) the magnetic signature, which is unique, of the location of the river where it is born. It uses this then to find its way back.

In this study, scientists were able to deduce that because the earth’s magnetic poles change slightly over time (a process called geomagnetic field drift). Therefore, salmon’s migratory habits should change as well, in a corresponding way. The researchers looked at fisheries data that goes back 56 years in order to confirm their hypothesis. They noticed that for Fraser River sockeye salmon, the route to their home river is blocked by Vancouver Island. The salmon must detour north or south around the island to get to their spawning grounds. Sure enough, the data showed that, as the earth’s magnetic field changed over time, the way the salmon traveled to their home river also changed. 

While it was long suspected that animals use the earth’s magnetic field to find their way, this is the first study to demonstrate navigation by magnetic imprinting, or “learning” the magnetic field. 

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