Before they end up filleted and sautéed on your dinner plate, salmon lead some pretty extraordinary, globe-trotting lives.
After being born in a freshwater stream, salmon hatchlings run for the ocean. They stay there for years and swim thousands of miles before deciding it’s time to settle down and lay eggs in the stream where they were born.
According to one theory, its all about magnetism. The idea is that when salmon are young, they leave their mark on the Earth’s magnetic field at the mouth of the river where they come from. Years later, when the salmon head back home to spawn, they home in on that pattern. In a study released Thursday in Current Biology, the scientists who came up with that theory now say they have proof that’s exactly how the fish are finding their way.
Nathan Putman, the study’s lead author and a postdoctoral researcher at Oregon State University in Corvallis, says that magnetic detection is “one of their tools for being really good navigators.” The fish also use their sense of smell to help them locate the exact stream of their birth.
Fishery managers may be able to use the result to guess where their fish will be and how their populations may change because of climate change and fishing, says Putman.
Many salmon stocks around the world are going down, and scientists want to know why strange things happen, like why millions of wild sockeye salmon didn’t come back to Canada’s Fraser River in 2009. Its possible a glitch in the salmons navigational abilities played a role.
An even bigger concern is whether being raised in hatcheries somehow alters salmons “internal GPS. After being born in tanks, these salmon are let out into streams and rivers. They make up a big part of the “wild” salmon that swim in the ocean and end up on your plate.
Putnam worries that something about their hatchery upbringing could throw off how these salmon perceive magnetic fields. The Earth’s magnetic field isn’t very strong, and man-made objects can weaken it. This means that even something as simple as the iron supports in the fish tanks or the nearby power lines could mess up the salmon’s magnetic imprint.
“Then they might not be very good at navigating, and that could cause problems,” he says.
If hatchery-born salmon get lost on their way back home, they might end up in the wrong stream and breed with wild salmon. That’s a problem because studies show that hatchery-raised salmon don’t do as well as their wild counterparts when it comes to surviving in the wild. When they mate, the wild stock becomes genetically weaker.
Salmon have one of the most incredible migration stories in the animal kingdom Born in freshwater streams and rivers, they make their way hundreds or even thousands of miles out to sea as juveniles before returning to their exact place of birth to spawn and die But how on earth do salmon navigate back to the very same river where they were born, often years later? Recent research has uncovered some fascinating details about the salmon’s navigational skills.
Developing a Mental Map
A salmon’s journey starts right after they hatch. They initially use their sense of smell to establish a mental map of their home stream. As young salmon, called smolts, prepare to migrate out to the ocean, they use cues like the chemical composition of the water, the strength of the earth’s magnetic field, and landmarks to imprint the location of their home river
Studies have shown that salmon have specialized cells called magnetoreceptors that help them detect the intensity and inclination of the Earth’s magnetic field. Like a natural GPS, this allows them to get their exact bearing as they start their ocean-bound migration. Their sensitive sense of smell also allows them to build a mental map of the unique scent of their home river as they swim downstream.
Orienting With the Magnetic Field
When salmon are out in the open ocean, they use the magnetic field to find their way. By feeling the strength and tilt of the field, they can find their latitude and longitude and get oriented. Researchers have found that the magnetic information is stored in the brain stem, which is one of the oldest and most primitive parts of a salmon’s brain.
Interestingly, slight natural drift in the magnetic field lines near the ocean causes corresponding drift in the migration routes the salmon take. In one study, researchers found that the migration route of salmon changed over 27 years in line with shifts in the magnetic field over the same time period. Their internal magnetic compass is so sensitive that even subtle changes alter their bearings.
Homing In With Smell
As salmon near the coast after a year or more at sea, their sense of smell takes over from the magnetic field as the primary homing mechanism. Having memorized the scent of their home stream as smolts, adults rely on their keen sense of smell to identify it among hundreds of other rivers.
Even the slightest differences in mineral content, vegetation, and soil composition give each river a unique olfactory signature. Salmon have an incredible ability to recall and match these scents to navigate back to their natal stream with pinpoint accuracy after years away.
Local Adaptations
Different salmon species and populations have developed ways of returning home that work with the way they migrate. Because they only have a few nursery lakes to use, sockeye salmon, for example, have to be very good at finding their way. Chinook salmon can travel longer or shorter distances to get to their spawning grounds upstream, so they aren’t as good at finding their way home.
In one study comparing two populations of chinook in the Yukon River, the population that migrated further inland had superior magnetic orientation skills, illustrating local adaptations. The salmon’s navigational toolkit has evolved to equip each population with the precision they require.
Threats to Navigation
While salmon are exceptionally equipped to navigate far distances, their migration patterns are being disrupted by human activities. Dams interfere with their ability to detect chemical cues and access spawning grounds. Climate change and river acidification are altering the sensory signals salmon rely on. Pollution and artificial noise can overwhelm their senses.
There is still much to learn about how salmon perform their iconic migrations with such precision. But new threats are highlighting the need to protect the environmental conditions and cues salmon require to navigate using their specialized magnetic, visual, and olfactory senses. Their navigational toolkit is intricate and delicate, and critical to the continuation of wild salmon runs.
How Do Salmon Find Their Way?
FAQ
How do salmon remember where to go?
Do salmon always return to the same place?
How do salmon detect magnetic fields?
Why do salmon have to go upstream?
How do salmon know where they come from?
We think they can tell directions in the ocean by the earth’s magnetic field acting like a compass. When they find the river they came from they start using smell to find their way back to their home stream. They build their “smell memory-bank” when they start migrating to the ocean as young fish. What do salmon eat?
How do salmon navigate?
Scientists believe that salmon navigate by using the earth’s magnetic field like a compass. When they find the river they came from, they start using smell to find their way back to their home stream. They build their ‘smell memory-bank’ when they start migrating to the ocean as young fish.
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.
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.