One of nature’s most incredible migrations is that of the salmon After spending years roaming the ocean, salmon are able to return from thousands of miles away back to the exact river or stream where they were born to spawn How on earth do salmon accomplish this amazing navigational feat? In this article, I’ll explore the mystery of salmon homing and the sensory tools that guide them home.
Imprinting on Their Birthplace
A key factor in how salmon navigate is that they imprint on their surroundings at birth As juvenile salmon, also called smolts, prepare to migrate from their freshwater habitat to the ocean, they use their senses to memorize unique identifying cues about their home river or stream
Some key things salmon imprint on:
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The precise chemical signature of the water. Salmon have a great sense of smell and can pick up on the unique mix of smells, minerals, and sediments.
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The magnetic field and geomagnetic cues. Salmon are sensitive to the subtle differences in the magnetic field between locations.
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Landmarks like mountains, outcroppings and vegetation. Salmon may use vision to imprint on physical landmarks around their natal waters.
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Celestial cues from the sun and stars. Some research indicates salmon orient themselves based on the location of the sun.
Salmon absorb all of this sensory information during their “smoltification” phase to lock in the environmental fingerprints of their birthplace.
Retracing Their Steps Through Smell
Smell and detecting chemical cues play an outsized role in how salmon navigate back to their natal river. Scientists believe adult salmon primarily rely on their keen sense of smell to pick out where they were born once they return from the ocean to coastal waters.
By imprinting on the scent profile of their home stream as smolts, adult salmon can pick out that unique odor fingerprint amid all the other river and coastal smells. Even after years away, salmon are able to pinpoint chemical traces of “home.”
Researchers have tested this by blocking the sense of smell of returning salmon. These fish struggle to locate their home river and often will stray into the wrong waters. Clearly, smell is a key part of their navigational toolkit.
Following the Earth’s Magnetic Field
In addition to smell, salmon also rely heavily on magnetic field cues embedded in their brains to determine their location.
As juvenile salmon prepare to migrate to the ocean, they not only imprint on the scent of their home waters, but on its precise magnetic signature as well. Scientists have discovered that the iron oxide crystals in a salmon’s brain are magnetically imprinted with the field strength, inclination angle and other factors unique to their natal location.
Research shows that messing with the magnetic field around salmon causes them to become disoriented and lose their direction. The earth’s magnetic field provides an important compass that guides salmon’s amazing journeys thousands of miles back home.
Backup Tools: Vision, Tides and Celestial Cues
Salmon have a few other backup sensory tools to aid their navigation:
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Visual cues – While not their primary method, salmon may use landmark memories and visual cues near home waters. Their vision sharpens as they transition from salt to fresh water.
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Tidal patterns – Salmon appear to use predictable tidal movements and currents to help steer them towards home once they near coastal waters.
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Celestial cues – Salmon may orient themselves using the location of the sun. Low-light sensitivity helps them navigate when solar cues are limited.
These secondary sensory tools provide redundancy in the salmon’s navigational system. If one sense is blocked or impaired, others can fill in to keep them on track.
An Inherited Map and Clock
Two final fascinating pieces to the salmon migration mystery are their inherited map and clock:
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Homing instinct – Salmon inherit a genetically imprinted “map” locking in the location of their home waters, allowing offspring to retrace the same journey.
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Spawning clock – Salmon have an internal “clock” set to their home stream’s spawn time, so they know when to return from the ocean to freshwater.
These innate tools passed down through generations contribute to salmon’s legendary homing migration.
An Exceptional Navigational System
Together with backup senses, inherited homing and timing, salmon have evolved a truly impressive and robust navigation system guiding their iconic journey. Their persistence in returning home sustains entire ecosystems and wildlife that depends on them, and provides opportunities for new generations of salmon to repeat the miracle.
Millions of Salmon Return Home | National Geographic
How do salmon know where their home is when they return?
How do salmon know where their home is when they return from the ocean? Salmon come back to the stream where they were ‘born’ because they ‘know’ it is a good place to spawn; they won’t waste time looking for a stream with good habitat and other salmon. Scientists believe that salmon navigate by using the earth’s magnetic field like a compass.
Why do salmon spawn back to spawn?
Years later, when the salmon head back home to spawn, they home in on that pattern. In a study published Thursday in Current Biology, the scientists behind that theory now say they have evidence that’s exactly how the fish are navigating.
How do salmon find their way back to their home River?
After hatching in a freshwater stream, young salmon make a break for the ocean, where they hang out for years, covering thousands of miles before deciding its time to settle down and lay eggs in their natal stream. So how do these fish find their way back to their home river? According to one theory, it’s all about magnetism.
When do salmon spawn?
Once they have completed their migration to the ocean, the salmon grow rapidly and mature into adults. Adult salmon spend several years in the ocean, feeding on small fish and other marine organisms, before returning to their natal stream or river to spawn. When the adult salmon return to their natal stream or river, they are called spawners.