Latin name

Oncorhynchus kisutch

Other names

Silver salmon, silversides, hookbill, hooknose, sea trout, blueback; French: saumon coho; Japanese: gin-zake.

Identification

Head thick, forehead broad. The tail stem is high. In the sea and when entering rivers, the scales are silvery, shiny. The body is elongated and somewhat compressed, and the head is a tapered shape. This species has a dark metallic blue or blue-green color for most of its life, which turns silvery on its flanks and belly. There are small black spots on the back and on the upper paddle of the tail fin. It can be distinguished from chinook salmon by the absence of black spots on the lower tail blade and white or gray gums at the base of the teeth. Chinook salmon have small black spots on both tail blades and black gums. Spawning adults of both sexes have a darker back and head and maroon or reddish flanks. Males turn dusky green above and on the head, bright red on the sides, and blackish underneath. In females, flanks become pinkish-red. Males develop a prominent snout with two hooks, called a kype, with large teeth that make it impossible to close the mouth. Juveniles 4 to 19 cm long have transverse dark stripes on their bodies, descending below the lateral line, with an oval or triangular dark spot between these stripes (usually above the lateral line).

Distribution

It is endemic to the North Pacific Ocean and the rivers flowing into it. In North America it occurs from Point Hope, Alaska, in the Chukchi Sea south to Monterey Bay, California. It has occasionally been reported in the sea as far south as Baja California, Mexico. Most are found along the coast and in spawning rivers. Occasional specimens are found in the Shantar Islands, Sakhalin, and Hokkaido. Acclimatized and successfully bred in Chilean rivers of the Pacific coast.

Habitat

A migratory fish, it enters rivers to spawn. After spawning, like other Pacific salmon, it dies. In the relic Lake Sarannoye in Kamchatka, it forms a living dwarf form. It is the most heat-loving of the Pacific salmon: it winters at 5.5-9 °C, south of the pink salmon.

Size

Coho do not reach the size of their larger chinook counterparts and are caught between 4 and 8 pounds in most places. The world record for all tackle is 33 pounds and 4 ounces caught in the Great Lakes. Fish up to 31 pounds have been caught in Alaska, where the average catch ranges from 8 to 12 pounds and 24 to 30 inches in length. Coho are up to 88 cm long and weigh up to 6.5 kg. The average length of commercial coho salmon in Alaska is 71 cm and weighs about 4 kg. When entering the rivers of Kamchatka, the average length is about 60 cm and the average weight is 3.4-3.5 kg. Males are usually somewhat larger than females. In their first summer in the rivers, juvenile coho grows up to 4-7 cm in length; yearlings in Kamchatka rivers grow up to 5-13 cm in length; two-year old coho grow up to 10-17 cm. A sharp acceleration of growth comes after a sting in the sea. Two-year old juveniles that had rolled out of the river in the summer have a length of 28-30 cm by December. Fish that have rolled down to the sea as yearlings reach sexual maturity in the third year, and those that have rolled down as two-yearlings - in the fourth year of life. In both cases, the duration of the marine phase of coho salmon life is the same.

Life history and Behavior

Like all Pacific salmon species, coho salmon are anadromous. They hatch in freshwater streams, spend part of their lives in the ocean, and then spawn in freshwater. Adult males usually enter streams at age 2-3, but adult females do not return to spawn until age 3. All, whether males or females, spend their first year in the stream or river in which they hatched. The timing of coho salmon entering tributaries also varies. For example, coho salmon in Alaska enter spawning streams from July through November, typically during periods of high flow. In California, the entry occurs from September through March, with most of the spawning occurring from November through January. In some streams with barrier falls, adults arrive in July, when the water is low and the falls are passable. In larger rivers, adults must arrive earlier because it takes several weeks or months for them to reach the spawning grounds in the upper reaches of the rivers. The timing of spawning is also governed by water temperature in spawning areas. Where temperatures are low and eggs develop slowly, spawners have developed early spawning times to compensate, and conversely, where temperatures are warm, adults spawn late. Little is known about oceanic migrations. Apparently, there are more coho salmon in the eastern Pacific and along the coast of North America than in the western Pacific. Offshore tagging indicates that mature southeast Alaska coho salmon move northward during the spring and concentrate in the central Gulf of Alaska in June. Later, they disperse toward the coast and migrate along the shoreline until they reach their creek. Most coho salmon do not appear to migrate long distances, tagged individuals have been found up to 1,200 miles from the tagging site.

Food and feeding habits

In the ocean, coho salmon grow rapidly, feeding on a variety of organisms including herring, sawfish, sand lance, squid, and crustaceans. Like all Pacific salmon, coho salmon do not feed when they enter freshwater to spawn. Juvenile coho salmon in freshwater feed on chironomid larvae, and in summer, they feed primarily on adult insects that enter the water. They often swallow the eggs and juvenile salmon. In the sea, the silver salmon feeds on fish (capelin, herring, etc.).

Reproduction

It spawns at water temperatures of 1-8°С from August to January, and in the upper reaches of the Kamchatka River - until half of March. The eastern coast of Kamchatka distinguishes between summer (spawning in September-October) and fall (spawning in November and later) coho salmon by spawning time. Spawning grounds are found all along Kamchatka rivers from the tidal influence zone to the headwaters of rivers. It spawns in rivulets, river channels and river beds with clear cold water and gravel substrate, but it never spawns in lakes. Often, spawning takes place in the same places where chum or sockeye had previously spawned. Most of the silver salmon, however, spawn in places with faster currents than chum and sockeye, laying eggs in and in springs in the upper reaches of rivers while a rule chum, sockeye, and pink salmon never reach. The silver salmon lays eggs in nests excavated by females at depths of 10-30 cm. Fertility varies from 1.2 to 6.3 thousand, on average 4.9 thousand eggs. In the basin of the Paratunka River (southeastern coast of Kamchatka), the hatching of fry from eggs occurs from mid-January until June, while juveniles leave the ground from the beginning of March until the end of July. In fresh waters, juvenile coho salmon occur in springs, channels, lakes, and in main channels from upstream to the mouth. The majority of juvenile coho salmon migrate to the sea in the second year after hatching, with a smaller portion migrating in the third year. The juvenile coho salmon rolls into the sea from Kamchatka rivers from early June to the end of August.