Occurring in the North Pacific, Arctic oceans and associated freshwater systems, the sockeye salmon (Oncorhynchus nerka), often referred to as "red" or "blueback" salmon ranges south as far as the Klamath River in California and northern Hokkaido in Japan, to as far north as far as Bathurst Inlet in the Canadian Arctic and the Anadyr River in Siberia. Native people considered sockeye salmon to be an important food source, eating them fresh or drying them for winter use. One of the most important commercial fisheries on the Pacific coast of North America is supported by sockeye salmon. Sockeye are increasingly sought after in recreational fisheries, and remain an important mainstay of many subsistence users. The sockeye is historically Alaska's most valuable fish because of its high oil content and ability to retain its red color after canning.
Most sockeye are tinted a bluish silver, and are the slimmest and most streamlined of the five species of Alaskan salmon. One can distinguish sockeye salmon from Chinook, Coho, and pink salmon by their lack of large, black spots. They are different from chum salmon by the number and shape of gill rakers on the first gill arch. Sockeye salmon have twenty-eight to forty long, slender, rough or serrated closely set rakers on the first arch. Chum salmon have nineteen to twenty six short, stout, smooth rakers. Sockeye salmon which are immature, or which spawn prematurely, are elongate, fusiform, and somewhat laterally compressed. Their appearance is a striking metallic green blue back and head, iridescent silver sides, and a white or silvery belly. Some sockeye sport fine black speckling on the back, but large spots are absent. Young sockeye, while in fresh water, exhibit the same general coloration as immature sockeye salmon in the ocean, but they are less iridescent.
Juvenile sockeye have dark, oval parr marks on their sides. These parr marks are less than the diameter of the eye and rarely extend below the lateral line. Males which breed develop a humped back and elongated, hooked jaws filled with sharp caniniform teeth. Both sexes turn brilliant to dark red on the back and sides, pale to olive-green on the head and upper jaw, and white on the lower jaw. While in fresh water, juvenile sockeye salmon feed mainly upon zooplankton (such as ostracods, cladocerans, and copepods), benthic amphipods, and insects. In the ocean, sockeye salmon continue to feed upon zooplankton (such as copepods, euphausids, ostracods, and crustacean larvae), but also prey upon larval and small adult fishes (such as sand lance), and occasionally squid.
Sockeye salmon are anadromous, which means they live in the sea and enter freshwater systems to spawn. Juvenile sockeye salmon, after hatching, may spend up to four years in fresh water before migrating to sea as silvery a smolt. These smolt weigh only a few ounces. These young sockeye mature quickly in the open sea, and after only one to four years, can weigh as much as eight pounds. Mature sockeye salmon will travel thousands of miles to spawn in the same freshwater system where they were born. Not much is known about the navigational mechanisms or cues sockeye use on the high seas, although evidence suggests sockeye are somehow attuned to the earth's magnetic poles, and use them to orient themselves accordingly. Once near their natal freshwater system, sockeye salmon use their olfactory sense to guide them home. Like all Pacific salmon, sockeye salmon die within a few weeks after spawning.
Maturing sockeye salmon migrate from freshwater systems to the ocean during the summer months. There is little deviation in when the sockeye arrive at their destinations. Freshwater systems with lakes seem to produce the greatest number of sockeye. Sockeye spawning usually occurs in rivers, streams, and upwelling areas along lake beaches, and is carried out in the same fashion as other salmon. Some sockeye will stay close to freshwater, while others will migrate to the open sea. Sockeye salmon return to their natal stream to spawn after spending one to four years in the ocean. Those mature sockeye, which have spent only one year in the ocean, are called jacks and are, almost without exception, males. Sockeye grow quickly in open ocean. Returning adults usually weigh between four and eight pounds. Sockeye weighing in excess of fifteen pounds have been reported. Some sockeye populations elect to live in freshwater for the duration of their lives. This landlocked form of sockeye salmon, called "kokanee," reaches a much smaller maximum size than the anadromous form and rarely grows to be over 14 inches long.
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