Chum Salmon (Oncorhynchus keta)
Chum Salmon (Oncorhynchus keta) – a commercial anadromous fish, the second most populous of the Oncorhynchus genus, the Salmonidae family. It occurs widely all over the northern Pacific Ocean, along the American coast – from San Francisco to the north as far as the Mackenzie River Basin (the Arctic Ocean). Along the Asian coast, the C.S. is found from the Korean Peninsula to the north as high as Providence Bay. Single species can go up the Lena, Yana, Indigirka, and Kolyma rivers. C.S. is first mentioned in the work “Kamchatka” by the explorer S.P. Krasheninnikov (1756).
The chum can grow to 1 m in length and to 10 kg in weight. Males are larger than females. C.S. enters the rivers for spawning, traveling up sometimes as far as 1,000 km. Chum comes for spawning mostly within the age of 4–6 years. By and large, the species of 3–10 years old participate in reproduction. Two types represent C.S. almost in all areas of its habitat: summer (average body length is up to 60 cm) and autumn (body length is up to 75 cm). The autumn C.S. is bigger in size and weight, more fertile, and has a higher growth rate.
The summer chum prevails in the northern regions and the autumn one – in the southern. Both types occur in the Amur River and the rivers of Sakhalin and Ayan-Okhotsk District. The summer C.S. matures at the age of 3–5 years. It migrates to rivers from the beginning of July to the end of August and, in mid-August, spawns in the mountain affluents of the large rivers, at the orifice of the ground waters, and in the gravel and fast water. The female can lay up to 3,000 eggs. Eggs are orange, as large as 7 mm in diameter. The egg stage is 103–120 days. Chum fry run to sea when they are 4–5 cm long. The autumn C.S. matures at the age of 4 years and enters the rivers end August–early September, advancing much farther than the summer chum. It spawns later, often under ice. It can lay eggs at the outlet of ground waters, producing about 4,000 eggs on the average. The autumn chum grows faster than the summer one.