The Lifecycle of Salmon
Enhanced Video Resource

This video segment from Nature: “Salmon: Running the Gauntlet” explores the lifecycle of wild salmon in the Pacific Northwest. This resource describes how they live most of their lives in the North Pacific Ocean and highlights their journey home, to spawn in the freshwater streams where they were born. The segment describes the habitats of different species of wild salmon in the Northwestern United States, as well as their spawning process and subsequent death.

Discussion Questions:

  • What draws Pacific Northwest salmon back to freshwater sources to spawn?
  • Describe the different habitats of Pacific Northwest salmon.
  • How did Redfish Lake get its name? Which species of salmon calls this lake home?
  • Briefly describe the life, spawning process and death of Pacific Northwest salmon.

Background Essay:

Most salmon are anadromous, meaning they are born in freshwater, migrate to the sea where they live for most of their lives, and then return to freshwater streams to spawn. Adult salmon stop feeding when they enter fresh water and survive on stored body fat.  Salmon return to the streams where they were born for the spawning process, with some species, such as Sockeye and Chinook salmon, travelling up to 1,000 miles to spawn. Researchers believe salmon use their sense of smell to help locate their home streams.

To begin the spawning process, the female salmon lays her eggs in a redd (nest), up to 18 inches deep, which she digs in the gravel stream beds with her tail. After a male fertilizes the eggs, the female covers the hole and digs a new one, where she deposits more eggs. This process continues until she has laid all her eggs. Females can lay up to 8000 eggs and deposit their eggs in up to 7 different holes. After spawning, all male and female Pacific salmon die within a few weeks.

The number of wild salmon in the Pacific Northwest has decreased dramatically over the past 200 years due to a combination of natural and human-related factors. Many species of salmon in the Pacific Northwest are listed as threatened or endangered on the Endangered Species List. In the Colorado River, the salmon population is approximately 3% of what it was in the early 1800s. Some factors posing threats to salmon are rising stream and river temperatures, due to climate change; natural predators; pollution; overharvesting (through commercial fishing, etc.); and dams on rivers, which obstruct passage to spawning areas.

In order to increase the number of wild salmon, scientists have created fish hatcheries in the Pacific Northwest, to produce and raise millions of salmon each year, which are then released into the wild. The hatcheries take adult salmon from spawning grounds, remove eggs from the female salmon, fertilize them with milt (white liquid containing sperm), and incubate the eggs in plastic bags and PVC pipes. After about a year or more, they release the salmon into the wild. After these salmon are released, they are considered part of the wild salmon population.

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National Science Education Standards:

Grades 9-12:

Content Standard C: Life Science
Fundamental concepts and principles that underlie this standard include:
  • The Behavior Of Organisms
    • Multicellular animals have nervous systems that generate behavior. Nervous systems are formed from specialized cells that conduct signals rapidly through the long cell extensions that make up nerves. The nerve cells communicate with each other by secreting specific excitatory and inhibitory molecules. In sense organs, specialized cells detect light, sound, and specific chemicals and enable animals to monitor what is going on in the world around them.
    • Organisms have behavioral responses to internal changes and to external stimuli. Responses to external stimuli can result from interactions with the organism’s own species and others, as well as environmental changes; these responses either can be innate or learned. The broad patterns of behavior exhibited by animals have evolved to ensure reproductive success. Animals often live in unpredictable environments, and so their behavior must be flexible enough to deal with uncertainty and change. Plants also respond to stimuli.
    • Like other aspects of an organism’s biology, behaviors have evolved through natural selection. Behaviors often have an adaptive logic when viewed in terms of evolutionary principles.

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