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Why Does Salmon Swim Upstream? The Ultimate Guide on Salmon Spawning and What Drives This Behavior in Salmon

Why Does Salmon Swim Upstream? The Ultimate Guide on Salmon Spawning and What Drives This Behavior in Salmon

The autumn months are the start of colder weather for many. The leaves begin to change, the jackets and sweaters come out, and pumpkin-flavored snacks seem to take over our stores. To fishermen, birds, and bears, autumn means salmon runs, when the salmon swim back upstream to the rivers they came from. Which begs the question: Why do salmon swim upstream?

Salmon are anadromous. This means they are born in fresh waters and migrate to saltwater oceans, only to return back home to “spawn” or reproduce. After which, most salmon die naturally due to the rigors of the salmon run and the toll it takes on their bodies.

There is a lot to unpack in that statement, so we’ve put together this guide to teach you about what spawning is, why salmon do it, and how in the world they can find their birthplaces after years of being away and without a GPS on their smartphone! 

We cover the following items in this post:

Why Does Salmon Swim Upstream?

Salmon swimming in a river.

Salmon swim upstream to reproduce in the same river they were born in, and to enable their offspring to thrive. This is part of the salmon run, in which salmon spawn.

Spawning is when aquatic animals release their eggs and sperm into the water in order to reproduce. Salmon do so in gravel beds, known as redds. Not all aquatic animals spawn, but many do.

This spawning process helps them successfully pass down their genes. As we mentioned above, salmon are anadromous, meaning they are born in fresh water and migrate to the saltwater oceans for most of their lives. They return to the freshwater rivers they were born in to reproduce, after years of being away.

Smells and Magnetic Fields

Salmon use two resources to help them find their way home while swimming upstream:

  1. The earth’s magnetic field helps them locate the river they came from.
  2. Their sense of smell helps them find their home stream within that river.

As they migrate downstream toward the ocean, young salmon learn the smell of the streams and rivers they pass through. After being away for many years in the ocean, salmon remember the scents of their birthplace and will return to the same rivers they were born in. They use the earth’s magnetic field as a compass on the journey.

This salmon migration is part of the normal anadromous salmon life cycle.

How Do Salmon Swim Upstream?

Salmon jumping out of the water, headed upstream. Why does salmon swim upstream?

Salmon spend years in the ocean, swimming and developing their strength. When the salmon return home to spawn, they use that strength and development to battle the conditions. They swim and jump, when necessary, against the currents, rapids, and smaller waterfalls they need to get past.

In order to leap, salmon use a burst of speed to jump out of the water to clear vertical obstacles and waterfalls. Some salmon can jump as high as 12 feet!

The conditions are as bad or worse than you can imagine. Hundreds or thousands of miles of swimming against the current, upstream, and avoiding the aforementioned obstacles, as well as hunters and predators like bears, otters, and even bald eagles — especially in Alaska.

Rocks and debris can create calm areas behind them, and the salmon use these calm areas in addition to areas of turbulence where the water may flow back upstream to navigate up the rivers. 

The swim upstream is very tiring and by the time they reach their spawning grounds they are almost completely out of energy. 

However, there are some man-made mechanisms to assist the salmon in their journey. Fish ladders and other bypasses enable salmon to get past barriers like dams. They allow the salmon to swim up smaller steps around the barrier to get to the water on the other side and continue their journey.

What Happens When Salmon Swim Upstream? 

A river with salmon in it.

Salmon swim upstream to find the river they were hatched in to reach their spawning grounds. Here, they spawn (or reproduce) and then most of them die. Specifically, all Pacific Ocean salmon die, and many Atlantic Ocean salmon do as well.

When the female salmon reach their home rivers, they will create a depression in the riverbed with their tails called redds. After forming the redd she will lay her eggs in them, and the male salmon will deposit their sperm, or milt, on them to fertilize them.

What Is The Lifespan of a Salmon?

The average salmon lifespan is 4 – 5 years, but the timeline can vary depending on several factors. Most salmon die shortly after the reproduction process. Let’s take a look at the lifespan of some species of salmon:

  • Atlantic salmon: 13 years
  • Chinook salmon: 9 years
  • Sockeye salmon: 8 years
  • Chum (Keta) salmon: 7 years
  • Pink salmon: 3 years
  • Coho salmon: 5 years
  • Masu salmon: 3 years

Their bodies become a source of food, attracting bears and birds to feed on them after they die from the spawning process. Also, nutrients from salmon carcasses are released into the water and are then transferred from the ocean to wildlife.

How Many Salmon Make It Upstream?

Bears hunt salmon while they jump out of the water. Why does salmon swim upstream?

Some estimate that roughly 90% of salmon, that haven’t been caught or died already, make it home to spawn. However, there is no efficient way to measure this due to a lack of sophisticated salmon tracking in the wild.

Unfortunately, not all salmon make it to their destination. Those that die on the way home are categorized as “en route mortality.”

How Long Does a Salmon Run Last?

It can depend on the type of salmon, the location of the salmon, and the terrain they have to swim in and against. However, we’d say the average run is roughly between 1 to 3 months, often taking place in the late spring through the early fall.

Spawning then begins once the salmon make it home safely.

What Triggers Salmon to Spawn?

The triggers for spawning can vary by fish, and it is believed that environmental cues tell the salmon when it’s time to spawn.

Examples of these environmental cues are:

  • Changes in water temperature
  • Changes in the availability of food
  • Changes to the salt levels of the water

Are Salmon The Only Fish That Swim Upstream? 

A bell trout swimming.

No, they’re not.

Bull trout and steelhead trout are also anadromous. The steelhead spawn more than once in their lifetime. Some bull trout migrate to the ocean and return to spawn in the rivers, while some remain in the rivers their entire lives and never journey to the oceans.

Final Thoughts: Why Do Salmon Swim Upstream

Salmon are anadromous and are born in fresh water and migrate to the open ocean. They return to the stream they were born at to spawn and reproduce. Some Atlantic salmon populations can make the trip multiple times while Pacific salmon populations die within days of completing the trip. 

The running of the salmon is an important part of its lifecycle and reproduction. It also has a major impact on the environment surrounding the lakes and rivers they are swimming against, as the dead salmon provide nutrition to the surrounding ecosystem after they pass.

You shouldn’t fish for or eat spawning salmon though. These fish are of far less quality than ocean-caught salmon as they have depleted their bodies to make it home.

Frequently Asked Questions (FAQs)

Why Do Salmon Swim Back to Their Birthplace? 

Adult salmon are believed to return to the stream they were born in because they view it as a safe place to spawn.

If salmon can’t find the correct stream, most will continue until they use all their energy to find it. Others will simply find other salmon to reproduce with. 

Why Do Fish Swim Against The Current?

Fish swim against the current for multiple reasons including:

  • Migrating back to where they were hatched
  • Searching for food
  • Increasing the water flowing through their gills and giving them more oxygen

How Far Can a Salmon Swim In One Day?

Salmon can swim around 40 to 45 miles in a single day depending on water conditions and the current flow that day.

Coho, sockeye, and chinook salmon are the strongest swimmers and will be able to swim the most in a single day depending on environmental conditions. Chum, or keta salmon, are also very strong swimmers.

What Time Of Year Do Salmon Swim Upstream?

Pacific salmon migrate back to their birthplace from spring through fall.

Most Atlantic Salmon also migrate to the stream they were hatched on the same schedule. Autumn is the peak season when most salmon are migrating back to the stream of their birth.