The sockeye salmon, scientifically known as Oncorhynchus nerka, is the third-most common Pacific salmon species, following pink and chum salmon. The genus name "Oncorhynchus" is derived from the Greek words "onkos" meaning "barb" and "rhynchos" meaning "snout." The species name "nerka" is the Russian term for the anadromous form of the fish. The name "sockeye" originates from the Halkomelem language, spoken by the indigenous people along the Fraser River in British Columbia. In Halkomelem, the term "sθə́qəy̓" means "red fish," which aptly describes the distinctive coloration of the species.
The sockeye salmon, also known as red or blueback salmon, exhibits a remarkable color transformation throughout its life cycle. While residing in the ocean, sockeye salmon have a bluish-silver hue. However, upon returning to their spawning grounds, their bodies turn a vibrant shade of red, while their heads adopt a greenish color. Sockeye salmon typically measure between 60 to 84 cm (2 ft 0 in – 2 ft 9 in) in length and weigh anywhere from 2.3 to 7 kg (5–15 lb). Two notable characteristics of the species are their long, serrated gill rakers, numbering between 30 and 40, and the absence of spots on their tails or backs.
Sockeye salmon can be found in various regions, spanning both the eastern and western Pacific. In the eastern Pacific, their range extends as far south as the Columbia River, with occasional sightings as far south as the 10 Mile River on the Mendocino Coast of California. In the western Pacific, sockeye salmon are known to inhabit northern Hokkaidō Island in Japan. The species' distribution also includes the farthest reaches of the Bathurst Inlet in the Canadian Arctic and the Anadyr River in Siberia. Notably, sockeye salmon display an incredible inland migration capability, with the farthest recorded journey being to Redfish Lake, Idaho. This migration involves traveling over 1,400 km (900 mi) by river from the ocean and ascending to an elevation of 2,000 m (6,500 ft).
Sockeye salmon exhibit a diverse diet, showcasing patterns of limnetic feeding behavior. They display vertical movement within the water column, engage in schooling, follow a diel feeding chronology, and selectively prey upon zooplankton. The ability to adapt their feeding strategies allows them to minimize the risk of predation while ensuring sufficient intake of food for survival. Unlike other Pacific salmon species, sockeye salmon extensively feed on zooplankton throughout their life stages, both in freshwater and saltwater environments. Additionally, they demonstrate a preference for small aquatic organisms such as shrimp and incorporate insects into their diet during the juvenile stage.
Sockeye salmon exhibit a diverse range of life histories, with the majority adopting anadromous behavior. This life history involves juvenile salmon migrating from freshwater lakes and streams to the ocean before returning as adults to their natal freshwater environments for spawning. However, it's worth noting that some sockeye, known as kokanee, forgo the oceanic migration and spend their entire lives in freshwater lakes. The typical life cycle of sockeye salmon involves spending one to two years in the lake as juveniles before migrating to the ocean. After two to three years in the ocean, adult sockeye salmon return to freshwater to spawn. Females usually spawn in 3–5 redds over a span of several days. The eggs typically hatch within six to nine weeks, and the fry then rear in lakes before embarking on their journey to the ocean.
The reproductive behavior of sockeye salmon involves various tactics employed by males, including competition, sneaking, and hierarchical and non-hierarchical groupings around receptive females. Males' reproductive success is more variable compared to females and is influenced by factors such as size and shape. Female reproductive success, on the other hand, is determined by the number of eggs laid, body size, and the survival of the eggs, which is influenced by the quality of the nest environment. Males do not engage in parental care and move between females after depositing sperm. Females, however, are solely responsible for nest selection, preparation, and defense until their death or displacement.
Sockeye salmon exhibit both aggressive and competitive behaviors during their reproductive processes. Dominant males primarily direct their aggression towards intruding dominant males, while subordinate males may also experience aggression. Spawning females display aggression towards intruding females or other spawning females in close proximity. Acts of aggression play a crucial role in reproductive success, influencing nest site quality and access to males. Competition for resources, such as food and space, can occur during the lake residence period of sockeye salmon. Interspecific competition may also arise, leading to interactive segregation as species emphasize differences in diet and habitat to avoid competition.