Nature on Trail: Chinook Salmon

By Dennis Dauble

All salmon migrate from freshwater rivers to the ocean as juveniles before returning two to five years later as adults to spawn. I like to think of them as river travelers who grow up in the high seas.

Chinook salmon (Oncorhynchus tshawytscha) are the largest of the five species of Pacific salmon, hence the name “king salmon.” They average 15 to 30 pounds at maturity, with some reaching weights of over 60 pounds. Chinook salmon can be identified by a dark gum line and large spots on both lobes of their tail.

The center of abundance for Chinook salmon is the Columbia River where population size was as high as 10 million fish before over-fishing in the late 1800s. Human development activities further reduced runs to about two million fish today, most of which are of hatchery origin. This species is also distributed widely in rivers of the Puget Sound and Washington coast.

Chinook salmon are separated into runs based on time of adult entry into freshwater. Spring-run salmon prefer to spawn in the upper reaches of small streams, while most fall-run fish spawn in large rivers. Summer-run fish are intermediate in their migration timing and distribution.

Salmon return to their natal stream or from where they were hatched. This behavior is called homing. One theory proposes they “imprint” or become sensitized to an odor or substances present in the water during their early rearing period.  It’s this memory that helps guide salmon back upstream to spawning grounds.

A late summer hike along a streamside trail may lead to a chance encounter with Chinook salmon at work. Triggered by declining water temperature, female salmon select a site on a shallow gravel bar having suitable current. She digs a gravel nest, called a red, with her tail to deposit up to 5,000 eggs. The footprint of some redds is as large as a compact car.

Fisheries scientists count the number of redds present in a stream or river to get a rough measure of population size. These surveys are performed visually on foot along coastal streams or with the aid of low-flying aircraft in larger bodies of water such as the Hanford Reach of the Columbia River. A fall hike to the White Bluffs overlook provides a view of where several thousand salmon return to spawn in the Reach Monument.

Pacific salmon die after spawning. Their muscles deteriorate, fins fray, and patches of sores form to provide an almost clown-like appearance. In a weakened state, spawned-out salmon are easy prey for predators like bald eagles and black bear. Their carcasses slowly decompose to become part of the aquatic food chain needed to nourish the next generation of river travelers.

This article was originally published in the September+October 2010 issue of Washington Trails magazine.