Background Information

The Salmon and Steelhead Life Cycle
Species of Salmon and Steelhead Found in California
What Salmon and Steelhead Need in Their Creek Habitat
A Healthy Salmon and Steelhead Run = A Healthy Watershed
Threats to Salmon and Steelhead
How to Help Salmon and Steelhead

Pacific salmon and steelhead trout have existed for at least two millions years in the Pacific coastal areas of North America - from Baja California through Alaska. In the past 150 years, many salmon and steelhead populations have declined in abundance and biological diversity in California and in other parts of their range.

The decline of salmon and steelhead is relevant for all Californians living in our state, even if you aren’t a fisherman and even if you don’t like fish. That’s because it can be seen as the proverbial canary in a coalmine - a signal of declining watershed health.

While there are some natural causes contributing to the decline of salmon and steelhead in California, human activities have played a significant role. Municipal water supplies, dams, farming, livestock, logging, and development all contribute to the loss and degradation of aquatic habitats.

The Salmon and Steelhead Life Cycle
The salmon and steelhead life cycle begins and ends when the spawning salmon lay their eggs in cool, clean rivers and streams, covering them with gravel for protection. When they first hatch, the baby salmon and steelhead (called alevin) are attached to a yolk sac, which nourishes them for a time. These tiny alevin stay hidden within the gravel of the streambed.

Egg and Alevin stage

When the yolk sac is used up, the young salmon and steelhead must leave the gravel bed to look for food, which consists of tiny aquatic plants and animals. Called fry at this stage, the young salmon and steelhead are striped for camouflage. They are prey to predators like ducks, great blue herons, and larger fish. Some fry stay in fresh water only a few months, while others wait a few years before migrating to the ocean.

When they are ready to migrate, the young salmon and steelhead begin the dangerous trip to the ocean, encountering predators, dams, and other obstacles along the way. For protection, they swim at night and hide during the day.

For several weeks or months, the young salmon and steelhead stay in saltwater estuaries and bays where the river meets the ocean. They undergo a special process called smolting (and are called smolts), in which their bodies change in many ways to tolerate living in salt water. Salt is very dehydrating, so their bodies must become able to drink the saltwater and get rid of the excess salts through special salt cells in the gills and mouth lining, and through changes in the kidney.

Finally, the salmon and steelhead swim into the vast ocean. Within the ocean, many salmon and steelhead travel with ocean currents in circular routes. Some may wander up to 2,000 miles from their home stream, while others stay closer to home. Eating a rich seafood diet, including herring and anchovies, the salmon and steelhead mature into adult fish. In the ocean, they must avoid predators like tuna, seals, dolphins, whales, and human fishers.

After two to four years, depending on the species, salmon and steelhead are ready to reproduce, or spawn. At first, they use ocean currents, stars, and the earth's magnetic forces to find their way to their home stream. As they get closer, they use their sense of smell to find the exact place where they were hatched. Their journey upstream is difficult; the salmon and steelhead must jump up waterfalls, find their way around dams, and avoid predators.

Once salmon and steelhead reach their spawning grounds, the female digs a nest, or redd, by turning on her side and flapping her tail to make a depression. She then deposits a few hundred pink or red eggs into the depression. A male swims next to her and fertilizes the eggs with a stream of liquid called milt, which is full of sperm.

The female covers the eggs when she digs the next nest just a foot or so upstream, throwing gravel onto the first nest. This process continues until an average of 3,000 eggs are laid. Pacific salmon die after spawning, usually within two weeks, but steelhead can live to spawn again. The eggs stay in the nest all winter and hatch in the spring, when the cycle will continue as before.

Fish that move from freshwater to saltwater and then back again are called anadromous fish. The benefit of an anadromous life style is that salmon and steelhead have access to a better food supply in the ocean, and yet their eggs and young are safer in the fresh water creek or stream.

While the anadromous life cycle has advantages, it also has two distinct disadvantages. It exposes salmon and steelhead to all sorts of hazards in the creek or stream, in the estuary, and then in the ocean. It also takes a lot of energy, not only for the long distances the salmon and steelhead have to travel, but also because their bodies must transform to live in very different salt water and freshwater environments.

Because of their migrating lifestyle and their sensitivity to water temperature and quality, salmon and steelhead are particularly vulnerable to changes in the waterway and beyond.

Species of Salmon and Steelhead Found in California
Steelhead trout and five species of Pacific salmon are all native to California. (The salmon family includes the Pacific salmon and steelhead trout, on which this unit focuses, but also includes other trout and chars.) Today, Chinook and coho salmon are the two most common species in California, along with steelhead. The other three -- pink, chum, and sockeye -- are extinct or rare here.

Chinook, coho, and steelhead have very similar life cycles, but they also have distinct differences that help to reduce competition among them.

  • Chinook Salmon
    Chinook Salmon. Illustration from U.S. Forest Service
    Chinook salmon are found in California from the Oregon border to as far south as the San Joaquin River. They are the largest of the Pacific salmon species. In California, they may weigh as much as 80 pounds and be over 4 feet long, but they are more commonly 15 to 30 pounds. Chinook are called “king salmon,” probably because of their large size.

Young Chinook salmon spend from 2 months to a year in fresh water, and then may stay several months in the estuary before moving to the ocean. In the ocean, California Chinook usually head north and may reach as far as Washington State. Chinook return to spawn when they are anywhere from 2 to 7 years old. Most Chinook will enter freshwater in the fall (fall-run Chinook), but a few will enter in the spring (spring-run Chinook).

  • Coho Salmon
    Coho Salmon. Illustration from U.S. Forest Service
    Coho salmon are found in California from the Oregon border south to the Big Sur River. They are much smaller than Chinook salmon; they are typically 16-32 inches long and weigh 7-12 pounds, but may get up to 20 pounds. They are also called “silver salmon.”

Young coho spend about a year in freshwater before moving to the estuary. In the ocean, coho usually travel shorter distances than Chinook, but may swim as far south as Baja California or as far north as Oregon. After spending two years in the ocean, most coho enter fresh water from November to January (winter-run coho). Coho often spawn in smaller streams than do Chinook.

  • Steelhead Trout
    Steelhead Trout. Illustration from U.S. Forest Service
    Steelhead trout are related to Pacific salmon, but they are actually the same species as rainbow trout. Steelhead trout and rainbow trout are two names that reflect two distinct life history patterns. Steelhead trout migrate to the ocean like salmon, while rainbow trout spend their entire life in the stream. Ocean-going forms of the trout can convert to resident forms during droughts or when a dam blocks access to the ocean.

Steelhead live in streams and rivers all along the California coast. They also live in tributaries in the Sacramento River and in Northern Baja California. Steelhead trout grow much bigger than rainbow trout, which stay in streams. They average 15-20 pounds, but may get as big as 28 pounds and be over 3 feet long.

They may spend one to four years in fresh water, then one to four years in the ocean. They usually migrate back to fresh water after two years in the ocean, returning to their spawning ground in either summer or winter. In either case, they wait until winter to spawn. Unlike salmon, steelhead do not necessarily die after they spawn. They will often go back to the ocean, and then return to fresh water to spawn again.

What Salmon and Steelhead Need in Their Creek Habitat
A habitat is the place where an organism lives; it may be a wetland, estuary, forest, grassland, river, stream, or ocean. An animal cannot survive without a habitat that provides the food, water, shelter, and reproductive conditions it needs.

For critical parts of their life cycle, salmon and steelhead depend on a freshwater creek or stream habitat. A suitable freshwater habitat contains the following elements.

  • Cool, Clean, Oxygen-Rich Water
    Salmon and steelhead need cool water. The optimum temperature depends on the species and the life stage. In general, however, if the water temperature is higher than 640 F (180 C), salmon and steelhead may become sluggish and more susceptible to disease and predators. While temperatures in the 740-780 F (230-260 C) range may be lethal, steelhead in California can sometimes tolerate these higher temperatures for short periods of time. Their ability to do so depends partly on the age of the fish, the temperature to which it is already acclimatized, and how much food is available.

The water also needs to be rich in oxygen. Water becomes more oxygenated as it bubbles over rocks and boulders, and is able to hold the oxygen better at lower temperatures.

Salmon and steelhead also need water that is free of pollution. Heavy metals and organic contaminants, found in stormwater runoff, sewage, and industrial wastewater, are harmful to them. While nitrogen and phosphorus are important nutrients when present in low concentrations, high levels can cause excess algae to grow in the water; when the algae die, the decomposition process depletes the dissolved oxygen in the water, robbing salmon and steelhead of the oxygen they need.

  • Gravel
    A healthy salmon and steelhead creek habitat consists of three different sizes of rocks. Salmon and steelhead need gravel beds for spawning and for the incubation of their eggs. The preferred gravel size depends on the species, but is generally from the size of a pea to the size of a lemon (2 mm to 64 mm). To be suitable for egg incubation, the gravel must be free of silt (very fine particles of soil) and other sediments. If the spaces between the gravel are plugged with fine sediments, the eggs will suffocate and die.

Larger rocks, called cobble, are necessary to stabilize the creek bed. Cobble is generally from the size of a lemon to the size of a basketball (64 mm to 256 mm). Salmon and steelhead also need even larger rocks, called boulders, to provide shelter for young fry and spawners. (Boulders are anything larger than about a basketball, or over 256 mm.)

  • Cover
    Salmon and steelhead need creeks that have lots of trees and shrubs growing along their edges. These plants shade the creek and help keep the water cool. By holding the soil with their roots, these plants also prevent erosion and help keep the water clean. Fallen logs and broken tree branches in the creek channel provide cover for salmon and steelhead protection from predators. Plants along the bank also help to provide food, as insects and spiders living on the plants fall into the water. This is especially important in small streams where plants may hang well out toward the middle of the stream.
  • Riffles and Pools
    The salmon and steelhead creek habitat must contain areas with both riffles and pools. A riffle is a shallow area where water flows rapidly over a rocky or gravelly streambed. Riffles are important because they oxygenate the water and they provide habitat for insects and other invertebrates, which are food for young salmon and steelhead. Riffles are also where salmon and steelhead build their nests or redds.

A pool is a deep area where the water flows more slowly. Here the water tends to be cooler than in the open areas. Salmon and steelhead need pools for resting and for hiding from predators. In many streams, fallen logs help create pool habitat by controlling water flow and the transport of gravel and cobble.

  • Food
    Young salmon and steelhead depend on insects for food. Insects, like stoneflies, live in gravel creek beds, while other may fall into the water from the creek-side trees and shrubs. The insects need plant material and algae to eat, and are affected by pollutants, silt, and changes in water temperature and flow.
  • Passage Along the Creek to the Ocean
    The different segments of the creek must be connected to one another, at least during critical times of the year. Salmon and steelhead need to be able to move up and down the creek to search for food and suitable water conditions (for example, the lower reaches of the creek may get too warm in summer, while the upstream areas are cool enough). Dams, bridges, and road and railway culverts may block fish movement within the creek, and may also impede the movement of fish to and from the ocean.

A Healthy Salmon and Steelhead Run = A Healthy Watershed
Some people think that what they do on land cannot affect salmon and steelhead. In fact, how people behave on land is critical to the survival of salmon and steelhead. One reason is that water runs off the land and drains into creeks and rivers. Another is that much of the water Californians use in their homes, businesses, and agriculture is taken from rivers and streams, reducing available salmon and steelhead habitat.

A watershed is the area of land that drains into a particular body of water. Disturbances such as erosion, chemicals, and human structures all affect the flow of water and the content of that water. A healthy watershed is one in which:

  • Rainfall is absorbed, and then released slowly.
  • Plants and their roots help to hold the soil in place.
  • Streams run clear and cool, and summer flows are not restricted.
  • Water quality is high. This means that water has little suspended sediment, a high level of oxygen, cool temperatures, and lacks pollutants.
  • Native fish and wildlife populations are healthy, productive, and diverse.
  • Stream channels are stable and are not undergoing long-term adjustment to a major human disturbance (for example, erosion of gravel from the stream bed directly downstream from a dam).
  • Natural disturbances like floods or landslides occur but the stream is able to recover and return to its more typical, stable condition. This is called dynamic equilibrium.
  • Natural stream processes are allowed to take place (for example, the stream is free to meander and change course over time).
  • There is adequate woody debris or large boulders to promote the formation of pools.
  • Flood plains slow the velocity of occasional floods because the stream is free to flood over its banks.

As the characteristics of a healthy watershed overlap with salmon and steelhead needs, the presence or absence of salmon within a watershed is an indication of that watershed’s healthiness.

Threats to Salmon and Steelhead
Many things that people do in the watershed harm salmon and steelhead.

  • We use water for domestic, agricultural, and industrial uses. In doing so, we reduce both the quantity and quality of salmon and steelhead habitat. In California, there are over a thousand dams for the purpose of storing and distributing water. These dams not only pose a physical barrier to migrating salmon and steelhead and dry up salmon and steelhead habitat, but they also change the natural flow and temperature of water and the natural transport of sediment.
  • We use chemicals that pollute water. The herbicides, pesticides, and fertilizers we use on farms or in our gardens often eventually end up in a stream or creek. Oil and grease from cars can also pollute streams.
  • We build new houses, buildings, and roads. When development is near the creek itself, salmon and steelhead may be directly impacted. Many forms of development increase soil erosion, and the eroded soil winds up in the creek bed. There, the eroded soil can clog up the spaces between the gravel, smothering eggs, alevin, and aquatic insect larvae. Also, a watershed with many roads, parking lots, homes, businesses, and non-porous surfaces can cause more runoff, increasing the likelihood of flooding.
  • We log trees. Poor logging practices can be harmful to creek habitats. It removes trees that help keep hillsides stable, and can cause soil and rocks to slip down the hill and into the creek bed. In other areas of the watershed, removing trees can cause water to run too quickly over the land. This can lead to increased erosion and to rapid increases in stream flows during rain or snowmelt.
  • We raise livestock. Livestock can trample creek banks and cause them to erode. They can also eat creek-side vegetation that stabilizes the banks, and remove the shade that keeps water temperatures cool. Cattle can also compact soil, causing more rapid runoff.
  • We fish. People enjoy eating salmon and steelhead, and obtain them through both commercial and sport fishing. There are regulations determining the number that people can catch based on an estimate of how many salmon and steelhead are in the ocean; if that estimate is too high, people may catch too many salmon and steelhead and not enough will return to spawn.

These actions themselves are not necessarily wrong, and many are necessary for human survival. However, the way we conduct these and other activities in the watershed can have a huge impact on salmon and steelhead. By managing these activities carefully, we can allow vital populations of both people, and salmon and steelhead in the watershed.

How to Help Salmon and Steelhead
When salmon and steelhead habitat becomes polluted, flooded by dams, drained, or paved over, they have nowhere else to go. In California, restoring and protecting salmon and steelhead habitat can be a complex problem that does not lend itself to a quick fix.

The activities in this unit will help students explore some of the complexities of this issue as they see that salmon and steelhead and the people in their community are interconnected. Working with a salmon and steelhead resource professional in your area, they will investigate ways to restore salmon and steelhead habitat in your local creek (See Activity 12: Planning a Restoration Project ). In addition, some actions that everyone can take to help salmon and steelhead include:

  • Using less water
  • Reducing electricity use
  • Reducing lawn area to decrease the need for watering
  • Landscaping with native plants
  • Gardening with organic compost
  • Fixing oil leaks in cars
  • Using less toxic household cleaners
  • Keeping oil, soap, and other substances out of storm drains
  • Keeping vehicles, livestock, and pets out of streams and lakes.
  • Supporting organic farmers, who use fewer herbicides and pesticides when growing food.


  1. California’s Salmon and Steelhead Teacher’s Guide and Student Activities, by Dianne Higgins.
  2. Napa County Resource Conservation District. “Steelhead Trout.” Accessed 12/19/06.
  3. “Anadromous Fishes of California” by Donald Frey, Jr. California Department of Fish and Game, 1979. Accessed 12/19/06.
  4. Salmon Protection and Watershed Network Reports. Accessed 12/19/06.
  5. SalmonSmart; A Guide to Help People Help Salmon. Accessed 12/19/06.
  6. “The Life Cycle of Salmon.” U.S. Forest Service. Accessed 12/19/06.