Salmon and other fish swim upstream because it is part of their reproductive life cycle. Rivers with fresh water are where salmon are born. They spend most of their lives in the ocean, but they return to the river where they were born to lay their own eggs. Salmon swim upstream to get from one place to another and to make sure their young live long enough to hatch and become adults. The trip is hard, but it leads to healthy salmon populations that people and other animals rely on for food.
The main reason salmon swim upstream is to ensure the survival of their offspring. This fish spawning habit is what leads to the salmon passing down their genes successfully. That’s right, salmon are anadromous, which means they are born in fresh water, spend most of their adult lives in salt water, and then spawn in fresh water.
As young salmon hatch in their home stream, they learn the smell of it. As they migrate downstream and into the ocean they may even memorize certain scents along the way. Even after being away for a long time, these salmon will use the smells to “test the waters” and find their home stream when they return as adults. The smell will fade if they swim up the wrong river, so they’ll go back down to try another stream.
To prepare for spawning, the female salmon will create a depression in the riverbed using her tail. The depression is called a redd. It’s where she lays her eggs, and the male puts milt, or sperm, on them to make them fertile. The female salmon then covers the redd with gravel before moving on to create a new one. A single female salmon can lay between 2,500 and 7,000 eggs and create up to seven redds.
Though salmon species live anywhere from two to eight years, most die within days or weeks of reproducing. These fish are good for the ecosystem because they provide food and nutrients, and they can even help plants grow. After bears or birds feed on salmon in the forest in Alaska, their carcasses are left behind. They release nutrients into the soil that nourish the Sitka spruce and hemlock trees.
Some studies have shown that salmon use the Earths magnetic field to guide their migration. This helps them travel long distances and understand where they are going. The intensity and the inclination of the Earths magnetic field helps the salmon orient themselves. Salmon have this trait built into their genes, so they don’t have to learn it from other fish. Some salmon come from as far away as Japan, but most of the salmon that spawn in Seattle come from Alaska. Some Atlantic salmon may even swim 200 miles up the river to find their preferred places to spawn.
Salmon are amazing fish that can swim upstream against fierce currents to return to the exact spot where they were born to spawn and die. This incredible journey is known as the salmon run.
The Life of a Salmon
Salmon start their lives hatching in freshwater streams and rivers. After 1-5 years, they undergo an incredible transformation that allows them to survive in the ocean and head downstream to mature. After spending 1-4 years roaming the ocean and growing considerably in size, the salmon undergo another amazing transformation to prepare for the journey back upstream. Their coloring changes, sexual organs mature, and their physiology adapts for the transition from salt to freshwater. Using their acute sense of smell and inborn knowledge of their birthplace, the salmon unerringly swim back upstream sometimes over incredible distances, leaping up waterfalls and battling fierce currents along the way.
How Do Salmon Swim Upstream?
Salmon are built for the heroic upstream journey:
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Salmon have a streamlined, hydrodynamic body shape to reduce drag in water.
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Powerful caudal (tail) fins propel them upstream
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Salmon alter between red slow-twitch and white fast-twitch muscle fibers for sustained and burst swimming.
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Scales become thicker to protect against bruising and injury.
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Accurate sense of smell detects the characteristic scent of their home river.
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Responsive vision guides them when leaping up rapids and waterfalls.
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Salmon likely use the earth’s magnetic field as a guide, like a compass, to maintain the correct ocean migration route.
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Once the salmon are in the river system, the chemical cues from their home stream always lead them upstream.
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Heart fitness improves so that muscles can get energy from the blood during the hard journey.
The Spawning Salmon Run
Using their powerful sense of smell, athletic prowess, and internal navigation, the salmon return to the exact site of their birth after years roaming the ocean. Upon arriving at the spawning ground, female salmon build nests called redds to lay their eggs, while males fertilize them. Most salmon species die soon after spawning, having expended the last of their energy to complete the life cycle. However, a small percentage of Atlantic salmon can survive to make the journey again.
The salmon run represents an incredible natural journey that enables the salmon life cycle to continue. Scientists remain in awe of how these determined fish can home so accurately and battle such obstacles to reach their spawning grounds. Their heroic efforts upstream provide nourishment for surrounding ecosystems through the dispersal of nutrients from the oceans. Truly, salmon are superfish!
How Salmon Swim Upstream
FAQ
What makes salmon swim upstream?
How do salmon swim up waterfalls?
How do salmon know where to travel upstream?
Why do fish swim against the current?
Why do salmon swim upstream?
Salmon swimming upstream is both a form of migration and a way to ensure that their young survive long enough to hatch and grow into adults. The journey is challenging but leads to the successful salmon populations that animals and humans depend on for food. The main reason salmon swim upstream is to ensure the survival of their offspring.
How do salmon find their home stream?
As young salmon hatch in their home stream, they learn the smell of it. As they migrate downstream and into the ocean they may even memorize certain scents along the way. Even after being away for many years, when these salmon return to their birthplace as adults, they will use those smells to “test the waters” and find their home stream.
Can you catch salmon if you swim upstream?
While not being in much of a feeding mood, it is possible to catch salmon while they swim upstream in rivers. Many salmon are caught on dry and streamer flies during their journey up the rivers. As the flies usually just pass them by fairly quickly, due to the fast current, I don’t believe they take them because they are hungry.
Why do salmon swim high up rivers?
The migrating salmon need cool and well-oxygenated water simply to be able to make the entire journey upstream and once the eggs are laid (usually in gravel beds), their continued survival heavily depends on the presence of oxygen in the water. Yet another reason for the salmon to swim high up the rivers is security.