Latin name

Oncorhynchus nerka

Other names

Sockeye, red salmon, blueback salmon, big redfish; French: saumon nerka; Japanese: beni-zake, himemasu. The landlocked form is called kokanee salmon, Kennerly’s salmon, kokanee, landlocked sockeye, kickininee, little redfish, silver trout; French: kokani.

Identification

The slimmest and most streamlined of the Pacific salmon, which are elongated and somewhat compressed from the sides. The head is small. The caudal fin notch is deeper than that of coho salmon. The back and top of the head is metallic green-blue, the sides are iridescent silvery, and the belly is white or silvery. Small black speckles may occur on the back, but there are no large spots. In breeding males, the back is hunched, and the jaws are elongated, hooked, with sharp, enlarged teeth. The back and sides of both sexes turn shiny to dark red, the head and upper jaws pale to olive green, and the lower jaws white. The completely red body distinguishes the sockeye from the otherwise similar chum salmon, and the lack of large, distinct spots distinguishes it from the other three Pacific salmon of North America.

Distribution

Salmon are native to the North Pacific Ocean and its tributaries. In North America, it is found from the Sacramento River, California, to Point Hope, Alaska. It is distributed off the Asian Pacific coast, the Bering Sea, and the Sea of Okhotsk. Populations of the Kamchatka River on the eastern shore of the peninsula and the Ozernaya River are the most abundant. The next largest populations are spawning sockeyes in the basins of the Palana and Bolshaya rivers on the west coast of Kamchatka and in the Okhota River basin. It also spawns in the rivers of the Kamchatka Peninsula on the Okhotsk coast, the Kuril Islands and Bering Island. Nurka winters in the Pacific Ocean and partly in the Bering Sea, in areas restricted in winter by isotherms +1 - +6°С.

Habitat

Passage fish. Salmon are an anadromous species; they live in the sea and enter fresh water to spawn. They mostly enter rivers and streams that have lakes at their headwaters. Young fish can live in lakes for up to 4 years before returning to the ocean. Some lakes have a dwarf form. These are predominantly males, maturing without a stingray in the sea. Dwarf seals are found in Lake Dalneye on the Kamchatka Peninsula, and dwarf females are found here, but in very low quantities. Dwarf male seals are also found in the lake in the Okhota River basin. Lakes Kronotskoye on Kamchatka and Sopochnoye on Iturup Island are home to a live form of seal, which also, like the dwarf seal, never leaves the sea, but differs from the latter in that it can reproduce independently of the migrating seal.

Size

An adult sockeye usually weighs 4 to 8 pounds. The world record for all-tackle fishing is held by an Alaskan fish that weighed 15 pounds, 3 ounces. The average length and weight of sexually mature sockeye varies considerably among populations, with an average length of 50-65 cm and a weight of 2-3.5 kg. Some individuals are up to 80 cm long and weigh 5 kg. Males are generally significantly larger than females. Young seals grow slowly in fresh waters and in different lakes very differently: yearlings may have a length of 4.5-13 cm and a weight of 5-20 g. Two-year-olds are 7-20 cm long and have a weight of 10-50 g. The sharp acceleration of growth begins after the stinging to the sea, where the seal lives 2-3, less often 4 years, and returns to spawn in the fourth, fifth or sixth, much more rarely in the seventh year of life.

Life history and Behavior

Salmon return to their home stream to spawn after spending 1 to 4 years in the ocean. They enter freshwater systems from the ocean during the summer months or in the fall, traveling thousands of miles. In most populations, the timing of arrival to spawning grounds varies little from year to year.

Food and feeding habits

Plankton-eating fish. Young fish feed in lakes on zooplankton, in streams and rivers on benthos, mainly chironomid larvae and, in summer, on adult insects that fall into the water. In the sea, the salmon feeds mainly on macroplankton - euphausiids and hyperiids. They may also eat juvenile fish. Fish that migrate to spawn stop eating in fresh water. In the ocean, salmon feed on plankton as well as crustacean larvae, and small adult fish and sometimes squid.

Reproduction

The seal enters lakes about a month before spawning and acquires mating attire as it matures. At the river spawning grounds, they usually arrive shortly before spawning in their mating attire. Spawning of spring seals occurs in July-August, summer seals in September-October and in Kurilskoye Lake it lasts until February. The female digs a hole of about 0.5 to 0.7 m2, 20-45 cm deep, into the ground. On the bottom, where larger stones remain, she lays eggs in 3 to 5 separate nest holes. The size and depth of the hole depend on the size of the fish. Around one female, there are several males. After the eggs are expelled and fertilized, the female buries the nests. The female guards the nest for 10-15 days before her death. As a result, the ground with the previously laid eggs is torn up few times, which leads to the mass death of the eggs of the previously spawned fish. The fecundity of the seal is 1.2-6.5 thousand eggs. 0.5-5.0% of the eggs remain unmet. The fecundity of the seal spawning in lakes is much lower than that of those spawning in rivers. The lake form of the seal has a fecundity of 400-800 eggs, and the dwarf seal has 400-600 eggs. The eggs are 4.5-4.7 mm in diameter in migrating seals and about 3 mm in dwarf seals. The larvae emerge from the eggs in 140-180 days after fertilization, depending on the conditions of incubation. The mortality of eggs during the incubation period varies greatly, averaging about 35% in Kuril Lake and 50-60% in Dalneye Lake. It depends mainly on the flow rate at the spawning grounds and the degree of nest digging. The yolk sac dissolves within 30-50 days, after which the larvae emerge from the ground and begin to actively feed, they are about 3 cm long at this time. The fry from the key spawning grounds soon roll into the main river channel; from the lake spawning grounds they migrate to the open part of the lake. Juvenile sockeye born in the rivers usually roll off to the sea as yearlings, less often as yearlings. In lakes, young fish live for one, two or three years before migrating to the sea. The quantity of fry that migrate to the sea from the Dalneye Lake is 0,05-1,13% of all the eggs laid by the previous generation females. From Kamchatka rivers, juvenile fish migrate from June to August and normally begin immediately after the ice melts in the lakes. The migrations take place mainly in the evening and at night.