Oncorhynchus keta (Walbaum, 1792): chum salmon

Biological Description

The lack of distinct black spots on the back and caudal fin distinguished adult chum and sockeye salmon from the other species. The 19 or 20 short, stout gill rakers on the first arch of the chum salmon distinguish it from sockeye, which have 28 to 40 long, slender gill rakers. Spawning adult chum salmon have greenish to dusky mottling on the sides, and the males have reddish-purple vertical markings.

Life History

In Washington, chum salmon spawn principally from October to December. Females are highly territorial and under high spawning densities may not spawn completely before death because of their aggressive behavior toward other females. The female digs a nest in medium or fine gravel in the stream riffles. Usually the areas used are not far from salt water. The spawning act is similar to that of other salmon. The average size of chum salmon redds is 2.7 square yards in the Columbia River. The average egg production is about 3,000, but large females produce up to 4,000. The large eggs hatch in 2 weeks to 4.5 months, depending on water temperature. Most of the high mortality from the fertilized egg to early fry stage (70 percent to over 90 percent) occurs during the embryonic stage. Most of this mortality is caused by poor environment where silt settles in the lower sections of the rivers, preventing sufficient dissolved oxygen from reaching the eggs. The newly hatched fry absorb their yolk sac in 30 to 50 days, again depending on water temperature. The young fry (1.1 to 1.4 inches long) usually are in fresh water for only a few days after emerging from the gravel. They migrate downstream at night from April through June.

Juveniles migrate to the ocean between March and June, when they are 1.2 to 2.6 inches long. They grow rapidly in the marine environment and have been reported to reach 4.7 to 9.8 inches by late July or early August. Mature chum salmon spend six months to four years at sea, where they reach an average length of 25 inches (range, 17-38) and an average weight of 9 pounds (range, 3-45).

Geographic Distribution

Chum salmon ascend rivers along the Pacific coast from the Sacramento River in California north to the Bering Strait, and east to the MacKenzie River. Chum salmon are also found in Asia from Korea and Japan north along the Asian coast to the Arctic Ocean.

Habits and Habitats

Adult chum salmon are usually ripe and dark in color when they enter fresh water. They spawn soon afterward and may die, all within one week. Often spawning may occur just at the head of tidewater. Upon emergence from the stream gravel, chum salmon fry begin to migrate to the ocean. For a while it was believed that chum salmon fry did not feed in fresh water, but Sparrow (1968) has reported extensive feeding in the Cowichan River, British Columbia.

Diet

While in fresh water, juvenile chum salmon feed on Diptera larvae, diatoms, and cyclops. In salt water, juveniles remain near the shore until late July or August and feed on various species of zooplankton (copepods, euphausids, and tunicates are main foods). The food of adults consists of polychaetes, pteropods, squid, crustacean larvae, copepods, amphipods, euphausids, and fish. The fish include at least five families: Clupeidae, Myctophidae, Gadidae, Scorpaenidae, and Hexagrammidae. Fish, mostly juveniles, made up 10 to 19 percent of the food volume in one study. In other studies up to 50 percent of the stomach contents by weight were composed of fish.

Idaho Conservation Status

Idaho Native or Import

The chum salmon is not present in Idaho.

Comments

The chum salmon is third in abundance among the five Pacific species. It is primarily a commercial fish and accounts for about 13 percent of the catch. The average annual harvent of chum salmon in Washingtonis about 300,000 fish. Recent success with hatcheries for chum salmon suggests that it has the potential to become more abundant.

This species has always been important to Native Americans for food and, in the north, as food for sled dogs. This species is not readily caught by anglers either in the ocean or in fresh water.

Credits

Sparrow 1968.Wydoski and Whitney 1979. Image Copyright Joseph Tomelleri. Used by permission.

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