The body of the chum salmon is deeper than most salmonid species. In common with other species found in the Pacific, the anal fin has 12 to 20 rays, compared with a maximum of 12 in European species. Chum have an ocean coloration of silvery blue green with some indistinct spotting in a darker shade, and a rather paler belly. When they move into fresh water the color changes to dark olive green and the belly color deepens. When adults are near spawning, they have purple blotchy streaks near the caudal peduncle, darker towards the tail. Spawning males typically grow an elongated snout or kype, their lower fins become tipped with white and they have enlarged teeth. Some researchers speculate these characteristics are used to compete for mates.
Spawning
Most chum salmon spawn in small streams and intertidal zones. Some chum travel more than up the Yukon River. Chum fry migrate out to sea from March through July, almost immediately after becoming free swimmers. They spend one to three years traveling very long distances in the ocean. These are the last salmon to spawn in some regions. In Alaska they are the first to spawn in June and August and are then followed by pink and coho salmon. They die about two weeks after they return to the freshwater to spawn. They utilize the lower tributaries of the watershed, tend to build nests called redds, really little more than protected depressions in the gravel, in shallow edges of the watercourse and at the tail end of deep pools. The female lays eggs in the redd, the male sprays milt on the eggs, and the female covers the eggs with gravel. The female can lay up to 4000 eggs.
Age
Chum live for an average of 3 to 5 years, and chum in Alaska mature at the age of 5 years.
Sizes
Adult chum usually weigh from with an average length of. The record for chum is and and was caught at Edie Pass in British Columbia.
Distribution
Chum salmon have the largest natural range of any Pacific salmon, and undergo the longest migrations within the genus Oncorhynchus, far up the Yukon River and deep into the Amur River basin in Asia. In lesser numbers they migrate thousands of kilometres up the Mackenzie River. Chum are found around the north Pacific, in the waters of Korea, Japan, and the Okhotsk and Bering seas, British Columbia in Canada, and from Alaska to California in the United States. In the Arctic Ocean they are found in limited numbers from the Laptev Sea to the Beaufort Sea. In North America chum salmon spawn from the Mackenzie River in the Arctic to as far south as Tillamook Bay, Oregon, although they were also reported in the San Lorenzo River near Santa Cruz, California in 1915 and the Sacramento River in northern California in the 1950s. In fall 2017 a half dozen chum salmon were counted in Lagunitas Creek about north of San Francisco, California. In the open ocean chum salmon stay fairly high on the water column, rarely diving below 50 meters. Their typical swimming depths are 13 meters from the surface during the day, and 5 meters during the night.
The registered total harvest of the chum salmon in the North Pacific in 2010 was some 313,000 tons, corresponding to 91 million fish. Half of the catch was from Japan, and about a quarter each from Russia and the United States. The chum salmon harvest was about 34% of the total harvest of all Pacific salmon species by weight. The chum salmon is the least commercially valuable salmon in North America. Despite being extremely plentiful in Alaska, commercial fishers often choose not to fish for them because of their low market value. Recent market developments have increased the demand for chum salmon. Markets developed for chum from 1984 to 1994 in Japan and northern Europe which increased demand. They are a traditional source of dried salmon.
