Salmon Facts

Salmon ['sa-mən]

A type of fish that starts its life in fresh water, grows up in the ocean, and returns to its home river to spawn.


Salmon belong to the genus, Onchorhynchus. Steelhead also belong to this genus but are not considered true salmon.

Salmon are fish. But what is a fish? It's a cold-blooded vertebrate with gills, fins, and a body that is usually covered with scales and lives in water. Salmon breathe with their gills, which are covered by opercula. They can sense their environment in a variety of ways. Along what is called the lateral line, fish can sense motion, vibration, and sound. Salmon also have an excellent sense of smell. It comes from using two comma-shaped holes on either side of their heads, called olfactory receptors, that enable them to understand information in their environment.

Most fish live in either salt water or fresh water. But some fish are diadromous (dye-AD-ruh-mus) — meaning they can live in fresh and salt water, at different times in their lives. Catadromous fish are born in salt water, move to freshwater to feed, and return to saltwater to spawn (lay their eggs). Anadromous (ah-NAD-ruh-mus) fish begin their lives in freshwater, move to saltwater to feed, and return to freshwater to spawn.


Salmon, and their relatives the steelhead, are anadromous fish. This means that they begin their lives as eggs in the cold mountain streams, such as those of central Idaho. When it is time for them to do so, they swim downstream all the way to the Pacific Ocean where they grow to become adults. Later in their lives they swim back up those same streams and return to their birth streams to spawn.

The Salmon Life Cycle


Image courtesy of U.S. Fish and Wildlife Service Northeast Region

The life cycle of a salmon is very interesting and complex. It starts with the young salmon, called alevin (or sac-fry), who begin their lives by hatching from eggs. These inch-long fish still carry a yolk sac which is twice their size. Alevin remain in the gravel for several more weeks, absorbing their nutritious yolk and beginning to feed on bits of food that float through the gravel.

One night, the alevins swim out of the gravel and begin feeding on microscopic water animals called zooplankton. They are now known as salmon fry. Salmon fry develop some skin marks — vertical black bars called parr marks. For tiny fish living among underwater vegetation, parr marks are great camouflage. They help the tiny fish blend in with stream-bottom vegetation instead of catching the eye of predators.


Image courtesy of U.S. Geological Survey

About the time that salmon fry have grown to be as long as your hand, they begin to lose their stripes and take on a sleeker appearance. They are becoming smolts, the teenagers of the salmon world. Teenage salmon have a strong urge to leave home and begin traveling. The smolts head into the current and begin their long journey to the ocean. Smolts are definitely going through some major changes, called smoltification, while on this journey. Their bodies are changing so that they can live in salt water. During their trip, they will eat insects that land on the water, worms, small shrimp, and tadpoles.

Once in the ocean, smolts will live in schools for a while, for safety. But when they become adults, salmon head out into the deeper sea, where they live, eat, and swim all alone. They dine on herring, crustaceans, krill, and young fish.


Adult salmon

When adult salmon feel the urge to spawn, they know it is time to come home. They are usually about 2 to 6 years old at this time. Some, like Idaho's salmon, must swim as much as 900 miles to reach their spawning sites. How do salmon know their way home? This is a mystery, even to scientists, but it has to do with homing. When they leave their birth stream as smolts, they store information about the scents of the stream, and they continue storing such information as they swim all the way to the ocean. In this way, young salmon create a scent trail to follow in the future.


During their migration home, salmon stop feeding. They travel upstream from the ocean back to their place of first hatching. This requires traveling against the currents, jumping over waterfalls, traversing shallow streams, and continuing even when they are exhausted from their long journey and lack of food. As salmon migrate, their bodies change. Males, for example, develop a hooked snout and a hump on their back. The color of their bodies changes too, depending upon the species.

After spawning

Once salmon arrive home again, they begin one of the most impressive displays of energy known as spawning. The female salmon hovers above a bed of gravel, facing into the current while a male hovers above her. She rolls onto her side so that her tail is flat against the gravel. With powerful flexes of her body, she turns her tail into a shovel and digs at the gravel, tossing it downstream and creating a depression in the stream bed for her eggs. The female then swims upstream a few feet, digs another depression, and deposits her eggs. Every time she tosses the gravel downstream, she covers the previous nest with rocks. With each new nest she makes, she will cover the prior one, protecting the eggs from predators. One female will dig a number of nests and deposit hundreds of eggs in each one. Each individual egg is about the size of a pea. Collectively, the nests are called a redd.

After spawning, the male leaves to find another mate, but the female stays by her nest for a short time to protect it. When both the male and female have finished spawning they will die. The fish eggs will hatch in 30 to 90 days. And the cycle begins again for a new batch of salmon.

Salmon eggs

Salmon Are Challenged

Grand Coulee Dam

When the rivers in the Columbia River Basin were running free, smolts from high in Idaho's Sawtooth Mountains could reach the sea in about eight days. Today, the Idaho smolts must travel through water slowed by eight huge dams, and they must get through or around those dams somehow. Their fast-water float downstream now requires several months.

This creates many health challenges for fish whose bodies are preparing to be in salt water but have been delayed and are still swimming in fresh water. Smoltification can begin to reverse if smolts are delayed in their migration for too long. This reversal often dooms the fish. Even if smoltification stays on schedule, smolts face increased predation from fish that thrive in the warm, slow waters of reservoirs.

Salmon going up river

Getting around the dams is also a physical challenge. Engineers and biologists knew that salmon would need help getting around dams, but they didn't anticipate some of the other problems that would occur. Smolts that survive the slow-motion journey and predators can be killed by a dam's turbines or bashed about in a complex array of pipes and screens designed to save them from the turbines.

Scientists have created fish ladders and fish bypasses which they believe would help the salmon get around the dams going both to and from the ocean.

Fish ladder

But not all dams have these tools to help the fish. The fish ladders are long, watery staircases that the salmon must leap up, step by step, to reach a reservoir. Many fish can climb fish ladders and continue on their journey, but they use up precious energy and suffer extra stress. Salmon returning to Idaho must climb many fish ladders at multiple dams. Biologists, fishery managers, and engineers continue to focus on finding ways to help young salmon. Many salmon die before they have completed their full life cycle.

Fisheries, biologists, and engineers have tried many methods to help salmon, but the salmon population is still decreasing. Salmon, though, remain an important symbol for everyone living in the Pacific Northwest. Salmon have provided food and heritage for many Americans — Native American tribes, non-Indian fishing communities, generations of sports anglers, and the general public of the Northwest who have adopted salmon as a symbol. Biologists and educators hope that if more people understand these amazing fish and the reasons behind their decline, more people will understand why some new methods are being considered to help salmon!

Other obstacles that salmon face in migration are:

  • Sediment — excess amounts of dirt and other particles entering the water can smother salmon eggs and trap or block salmon.
  • Loss of Cover — without cover, salmon have no protection or shade relief.
  • Pollution — such as stormwater or agricultural runoff affects water quality, and thus, affects salmon.
  • Drought — shallow streams are difficult for the adult salmon to swim.
  • Predators — bears, eagles, and other hunters can get to the tired salmon easily.
  • Water Sports — activities in spawning streams and rivers during migration can disrupt salmon or even kill them.

Where Are All The Salmon?

Salmon going up stream

“The salmon are one of our best teachers. We learn from them that we have to do certain things by the seasons. We watch the salmon as smolts going to the ocean and observe them returning home. We see the many obstacles that they have to overcome. We see them fulfill the circle of life, just as we must do. If the salmon aren't here, the circle becomes broken and we all suffer.”

— Leroy Seth, Nez Perce

Fish Hatcheries

Freshwater hatchery
Freshwater hatchery

At first, fish hatcheries seemed to be a great way to protect salmon species from extinction. In protected and controlled environments, millions of salmon eggs hatch, and millions of salmon fry grow to smolt-hood without risk of predation. And all these millions of protected smolts can then be released into the rivers and the ocean to grow into salmon adults that will find their way home. That's the theory.

In the 1800s, hatcheries were built with the idea that they could increase the number of salmon for use by commercial and sport fishermen. The thinking was . . . more salmon = higher catch rates = boon for the economy. In the 1900s, the thinking shifted as dams began destroying huge numbers of salmon. Fish managers thought they could produce enough salmon in hatcheries to replace the salmon being killed or blocked by dams.

Hatchery salmon face the same problems as wild fish, having to dodge predators, navigate past dams, and find their way back home again to spawn. Unfortunately, because they are from a hatchery, these salmon never find their spawning grounds and they have weaker genetics than their wild relatives. If hatchery salmon spawn with wild salmon, they contribute their weakened genetics to wild salmon, which then can weaken the survival of the wild fish.

Saltwater salmon farm
Saltwater fish farm

Hatchery salmon threaten wild salmon restoration in another indirect way — they confuse people's understanding of salmon populations. It's difficult to argue that salmon are in danger of extinction when someone hauls in thousands of pounds of salmon from the ocean, or another person stands on a bridge admiring spawning salmon. They don't see the empty rivers, streams, and lakes of Idaho, which were once the source of millions of wild salmon. They see lots of salmon and they want the right to catch even more.

Hatcheries can play an important role in salmon recovery if they focus on protecting genetic diversity.

Salmon For The Future

Lots of salmon migrating

No matter how hopeless the plight of the salmon might seem, scientists remain confident that salmon can be restored. Here's why:

High-elevation streams, like those in Idaho's mountains, are in good condition and offer excellent salmon habitat because they are usually in protected areas that are likely to remain healthy. Most of the people living in the Pacific Northwest want salmon restored and are willing to help achieve this goal. Biologists, politicians, tribes, and land managers are working together to address salmon restoration at the regional level.

Three Action Options

Here are three specific actions scientists are already taking, or are actively investigating, to ensure that salmon survive well into the future.


Far fewer salmon are returning now to their spawning grounds in Idaho than have come back in the past. In an attempt to increase return rates, fisheries managers have been working to make sure more salmon survive their first journey down the Snake and Columbia rivers. They have been collecting smolts from reservoirs and piping them into barges, which then carry them downriver past the last dam on the Columbia. Unfortunately, less than one percent of the transported fish return later as spawning adults. The return rate before the eight dams was much higher. Still, some people argue that barging should remain part of the recovery plan because ninety percent of the smolts are released alive.

Fish barge
Image courtesy of Idaho Fish and Game

In-River Migration

Federal officials believe they can improve salmon recovery by increasing the speed of water as it flows through reservoirs. Dams could be operated to release large amounts of water during the weeks that smolts migrate to sea. With increased speed, the migration rate could improve.

This might help salmon in some parts of the Columbia Basin, but it won't help the salmon migrating from Idaho. The reservoirs on the Lower Snake River are maintained at a full level; additional water would not move any faster through those reservoirs.

Another proposal calls for dam draw-downs — reducing the amount of water behind dams to concentrate and accelerate the flow. This would also speed up the journey downstream. But it poses different problems. Draw-down reduces the efficiency of turbines and increases their ability to injure fish; it would also disable bypass operations and fish ladders. And, it is very expensive.

Fish transportation
Image courtesy of Idaho Fish and Game

Dam Removal

No one proposes removing all of the dams in the Columbia River system, but people are talking seriously about altering the four dams in the lower Snake River. They are proposing that the river be allowed to flow around the concrete portions of these dams.

These four dams were among the last built in the basin. Before the dams were completed, Idaho's salmon population had remained stable, even though salmon had to migrate past several dams on the Columbia. After the dams on the lower Snake were completed, however, salmon numbers dropped. Today, all of Idaho's wild salmon populations are listed under the Endangered Species Act.

Pond lily dam removal
Image courtesy of U. S. Fish and Wildlife Service

You Can Help

Here are some things we all can do to help salmon enjoy cool, clean, free-flowing water.

  • Conserve energy — if we use less, we won't need to depend as much on the electricity made by dams.
  • Recycle aluminum — recycled aluminum needs only 5% of the electricity that primary aluminum uses when making new metal.
  • Conserve water.
  • Dispose of household liquid wastes properly.
  • If you fish, know the difference between trout and salmon at all life stages.
  • If you canoe or kayak, avoid spawning streams during spawning times.
  • Let your community and elected representatives know that you support salmon restoration.

Fascinating Fact

  • There are six species of salmon that swim the rivers that empty into the northern Pacific Ocean.
  • In their journeys from their home to the ocean, some Idaho salmon will swim as far as Alaska!
  • Salmon spend one to three years as adults in the ocean.
  • Worldwide, more salmon are available now than in the last fifty years, because the collapse of salmon in the Pacific Northwest coincided with huge production through fishing in Alaska and British Columbia. During the same time, salmon farms in Norway and Chile produced one billion pounds of fish per year.
  • There is only one species of salmon in the Atlantic Ocean.
  • Captain Meriwether Lewis, of the Lewis and Clark expedition, encountered salmon immediately after crossing the continental divide and entering the Lemhi River watershed. Lewis and his companions were out of food. The Shoshone offered the men salmon, along with other food.
  • People from Japan to Russia value salmon and include them in various ceremonies.

Top 10 Questions

October 2013

Thanks to Jeff Heindel, Fish Hatcheries Supervisor, Idaho Department of Fish and Game; and Adare Evans, Wildlife Educator, Idaho Department of Fish and Game for the answers.

  1. How many types of salmon are there?

    In Idaho we have two types. We have chinook and sockeye salmon. There are five species in the eastern side of the Pacific Ocean: chinook, sockeye, coho, pink, and rainbow trout (which is technically trout). (From Naomi at Owyhee Harbor Elementary in Boise)

  2. Why do salmon swim upriver to their birthplace?

    They go back to their birthplace because they remember it. Salmon will hatch out of their nest and they stay in that stream for a while. When it's time for them to go to the ocean, they swim backwards, smelling the water the entire way. Water has smells to it based on the minerals in the water. Salmon smell the water in the stream where they were born, and they remember it. They follow that smell all the way back to their birthplace so they know where to lay their eggs. It seems to be an internal drive for them to go back to that particular spot. (From Alexander at Riverside Elementary School in Boise)

  3. Why are salmon pink?

    During their maturation phase, salmon will undergo a coloration change. The color change is more accentuated in the males because the coloration change helps them compete for the females. Diet is a factor in coloration too. A more natural diet of foods that contain a lot of pigment can color the flesh of the fish giving it a pink or red color. (From Lauren at Cynthia Mann Elementary School in Boise)

  4. What do salmon eat?

    They eat different things depending on their age. When they hatch, they have a built-in food supply consisting of a yolk on their belly. When that goes away and they are in the Idaho streams, they eat something called zooplankton. These are tiny organisms that we cannot see without a microscope. Once in the ocean, they switch from eating plankton and insects to eating fish or other things in the ocean, depending on the type of salmon. (From Jackson at Owyhee Harbor Elementary School in Boise)

  5. How far can salmon swim?

    They can swim a long distance. They swim several miles in a day. Their journey to the ocean and back is 600 to 900 miles each way. When they are in the ocean, they swim thousands of miles. (From Josie at Cynthia Mann Elementary School in Boise)

  6. How fast does a salmon's heart pump?

    How fast a fish's heart will pump depends on a lot of things. Is the fish excited? Is it being chased by a predator, or is it in a resting phase? Water temperature will also have a role in this. In cooler water, the salmon's heart slows down. The heart does not have to beat as fast to move blood around the body. (From Jameson at Riverside Elementary School in Boise)

  7. Do fish have nostrils like people?

    The two comma-shaped holes on each side of a salmon's head are its nostrils. These receptors absorb molecules from water and tell the fish what's going on in its environment. (From Maddy at Owyhee Harbor Elementary School in Boise)

  8. What would happen if salmon went extinct?

    Ecologically, it would be very, very detrimental. Salmon are important to the health of Idaho. When they go to the ocean, they eat and eat and eat, filling their bodies up with important nutrients. When they come back to Idaho and die, those nutrients act like fertilizer and help our streams and our plants. Also, their dead bodies feed so many other animals. They are a keystone species, meaning that they're at the top of an arch, supporting so many other things. If they went extinct, it would be detrimental to the plants and animals of Idaho. (From Braden at Cynthia Mann Elementary School in Boise)

  9. How long can a salmon live?

    In Idaho, the sockeye and chinook live about three to five years. If we go to the colder climates on the coast where growth is slower in fresh water, salmon can live up to eight years. (From Parker at Riverside Elementary School in Boise)

  10. How much do salmon eat compared to their weight?

    Salmon eat a fair amount. In the wild, they will consume large quantities of food. In general, much of that food - bugs and invertebrates - have a lot of water. The wild salmon take in a lot of food organisms to try to gain weight. In a hatchery, salmon will eat between three and six percent of their body weight a day. That's why salmon need a hatchery environment to maintain their base metabolism and to also have enough food to give them a bit of growth. (From Ethan at Cynthia Mann Elementary School in Boise)