A guide to Pacific Salmon

By John Krist,
Senior reporter

Five species of Pacific salmon (chinook, coho, chum, pink and sockeye) and two species of seagoing trout (steelhead and coastal cutthroat) are found in North America. All seven species are members of the genus Oncorhynchus, from the Greek words onkos (hook), rynchos (nose), referring to the prominent hooked jaw that develops in males during mating. All are anadromous, a Greek word meaning "running upriver," which refers to their migration between freshwater streams and the ocean.

Adult salmon fight their way upstream to spawn in the same streams in which they were born, leaping waterfalls, evading predators, climbing around dams on long fish ladders. Females that survive the long journey lay eggs in shallow nests, or redds, which they scoop out of the gravel of the stream bottom using powerful flicks of their tails. Males fertilize the eggs by releasing sperm into the water. The female then covers each redd with gravel. Each pair may excavate several redds, and all adult salmon die after spawning (steelhead and coastal cutthroat are exceptions, able to migrate more than once).

Incubation time ranges from five to 10 weeks. The fertilized eggs hatch into fry, tiny fish with their yolk sacks still attached. Once the yolk sacks have been absorbed, the fry emerge from the gravel and begin feeding in open water. When they grow to fingerling size and prepare to migrate downstream, a process that takes only a few weeks in some species but may last as long as two years in others, they are known as smolts.

During their downstream migration, smolts undergo profound physiological changes as their bodies prepare to make the transition from freshwater to saltwater. Their coloration changes from olive and brown, which helps them hide in streams, to silver, better suited to life in the open ocean. They begin producing a different type of hemoglobin to cope with the lower oxygen content of seawater. And the salt pumps in their gill membranes reverse operation. In streams, the pumps act to prevent loss of salt from body cells into the surrounding fresh water; in the ocean, they must make it possible for the fish to excrete excess salt absorbed from the surrounding seawater.

After reaching the sea, the fish disperse. The length of their stay in the open ocean varies by species, from as little as six months to as long as eight years. Once they have reached sexual maturity, they seek out their natal streams to repeat the reproductive process. Once they re-enter freshwater, they stop feeding, relying on reserves of stored fat to survive the arduous journey. They change color again, the males adopting bright hues. Males of some species also develop large hooked jaws. Fighting the current, and being battered against rocks and other obstacles, takes its toll; many of the adult fish are visibly decaying by the time they reach their spawning gravels. Death comes within a few days or weeks.

The following profiles highlight some of the differences among salmon species.

CHINOOK
Scientific name: Oncorhynchus tshawytscha
Also known as: King, tyee, spring salmon
Description: The largest of any salmon, chinook may be up to 58 inches in length and weigh up to 129 pounds, although they are more commonly up to 36 inches in length and weigh up to 30 pounds. Spawning in streams that are larger and deeper than other salmon use, chinook spawn from late summer to late fall, depending on the run. Fry and smolts usually stay in freshwater from one to 18 months before travelling downstream to estuaries, where they remain up to six months. Chinook salmon spend one to eight years at sea before returning to spawn.

COHO
Scientific name: Oncorhynchus kisutch
Also known as: Silver salmon
Description: Smaller and slimmer than the chinook salmon, coho salmon reach up to 38 inches in length and weigh up to 31 pounds, although they more commonly weigh between 6 and 12 pounds. Spawning occurs from November to January, with the eggs hatching the following spring. Coho fry remain in streams for over a year. Most return to spawn when they are three years old.

CHUM

Chum

Scientific name: Oncorhynchus keta
Also known as: Dog, calico, chub, keta salmon
Description: Averaging 23 to 32 inches in length and 3 to 18 pounds, chum may grow as large as 40 inches and 45 pounds. Chum fry usually migrate to estuaries immediately after emerging from the redd, and then spend several months there before heading out to sea. Chum usually spawn in their third, fourth or fifth year, in the lowermost reaches of rivers, rarely traveling more than 100 miles upstream. They are the last of the Pacific salmon to return to their natal streams each year.

PINK
Scientific name: Oncorhynchus gorbuscha.
Also known as: Humpy, humpback salmon
Description: Up to 30 inches in length and weighing up to 12 pounds, pink salmon more commonly weigh 3 to 5 pounds and average 17 to 24 inches in length. Pink salmon begin migrating downstream almost immediately upon emergence from the gravel and move rapidly into near-shore nursery areas and shallow marine waters. Pinks return to spawn after about 18 months at sea.

SOCKEYE
Scientific name: Oncorhynchus nerka
Also known as: Red salmon, blueback, silver trout and kokanee (landlocked form)
Description: Sockeye are unique among Pacific salmon in that juveniles rear for at least a year or two in lakes before migrating to saltwater. They range in size up to 33 inches and 15 pounds. Once they begin migrating downstream, sockeye salmon progress steadily toward the ocean. After one to two years offshore, they return and spend one to eight months in the lake before spawning.

COASTAL CUTTHROAT TROUT
Scientific name: Oncorhynchus clarki clarki (clarki refers to William Clark of the Lewis and Clark expedition)
Also known as: Sea trout, sea-run cutthroat, red-throat trout, harvest trout
Description: Adult cutthroat average 1 to 4 pounds and can reach 20 inches in length. The coastal cutthroat trout is unlike most salmon species because it may spawn more than once. Adults commonly enter streams during the fall and feed on the eggs from other salmons' spawn. Young cutthroat can spend as long as nine years in fresh water before they migrate to the estuaries and ocean in the spring, most commonly three years from emergence. Coastal cutthroat trout usually spend less than one year in salt water before returning to spawn.

STEELHEAD

Steelhead

Scientific name: Oncorhynchus mykiss (previously known as Salmo gairdneri)
Also known as: Coastal rainbow trout, silvertrout, steelie, hardhead, ironhead
Description: Spawning in streams and rivers, steelhead rear in freshwater for one to four years before migrating downstream through estuaries to the open ocean. Unlike salmon, steelhead migrate individually rather than in schools. Steelhead spend one to five years at sea before returning to natal streams or rivers. Steelhead do not always die after spawning. They can reach 45 inches in length and 40 pounds in weight, although they usually weigh less than 10 pounds.