Chinook Salmon

At this time of year, many species are migrating south to spend the winter months in warmer climates.  But, a few species are moving north including the Chinook salmon, Oncorhynchus tshawytscha.  The largest species of Pacific Ocean salmon, they are blue-green on the head and back and silver on the sides.  Their tails, backs, and upper fins have black spots, and the tooth gum line is black.  Salmon average three feet in length and weigh thirty pounds, but can grow past five feet and 110 pounds.

Chinook salmon, sometimes known as king salmon, are native to the northern Pacific Ocean and freshwater streams and rivers in the Pacific northwest.  They are born from eggs laid in autumn’s cool waters that hatch in springtime when those waters start to warm.  Young salmon feed on insects and small crustaceans in freshwater habitats until they become adults between one and two years of age.  An anadromous species, meaning they live in both freshwater and saltwater habitats, as adults, they travel downriver to the ocean, where they will spend the next one to five years following the warmer ocean currents, eating a diet of nutritionally-rich prey including herring, sandlance, and squid, allowing salmon to reach their large size.

Salmon are also known as semelparous, meaning they spawn once and then die.  As salmon reach maturity, they return in autumn to the rivers where they were born.  Females dig a nesting hole, called a redd, in which she deposits 3,000 to 14,000 eggs.  Males fight to be the one that pairs up with each female and fertilizes her egg nest.  A benefit to being big is that larger females lay more eggs and dig deeper redds.  A deep nest protects eggs better by not exposing them to faster, surface water.  Both parents guard the eggs for the first few weeks, but the parents will die before winter, months before the eggs hatch.

Returning salmon and their eggs offer a buffet for more than 125 species that depend on them as a food source just before winter.  Marine mammals including whales, orcas, sea lions, and harbor seals hunt large schools of salmon as they converge on the Pacific northwest coastal areas.  As salmon enter the river systems, they attract eagles, seagulls, herons, kingfishers, murres, and puffins.  A great variety of land mammals also make their way to the waterways including bears, wolves, minks, martens, weasels, and fox.  Shorebirds wade into deep water to snack on any eggs that may escape a redd.  Migrating birds on the Pacific flyway feast on salmon that are dying after spawning.  Insects feed on the decaying bodies, and in turn, are food for the smaller birds migrating south.

Chinook salmon populations have declined in recent decades and some populations of Chinook salmon are federally listed as endangered.  Loss of snowpack and shrinking glaciers have reduced the amount of water in streams and rivers.  Along with shallower waterways, warmer summers are raising stream temperatures leading to habitat where parasites and disease grow and attack more easily.  Severe storms and forest fires contribute to less undergrowth and more soil eroded into rivers causing siltation that constricts the passage of water and river inhabitants.  Supporting improvements in land use practices and saving habitat will greatly benefit Chinook salmon as well as the many other species they live with.