The sockeye salmon (Oncorhynchus nerka) is a cold water fish that has adapted to life in both fresh and salt water habitats. Adult salmon spend up to four years in the salt water of the ocean before they return to fresh water rivers and streams to lay eggs or spawn. The sockeye salmon is different from other species of salmon in that the juveniles spend a portion of their lives in a lake associated with the river used for spawning.
Cold water ocean habitats for the sockeye salmon range along the Pacific coast of North America from Washington State to Alaska. They are also found in the Bering Sea from Alaska across to Siberia and south to Japan. These salmon are abundant in fresh water rivers and streams of Washington State, Alaska, and British Columbia.
Mature sockeye salmon living in the ocean are silver in color with a slight blue tint. Also referred to as blueback salmon, their silver coloring allows them to avoid predators. Upon entering fresh water in order to spawn, the sockeye salmon changes to a bright red color in order to attract a mate.
Female red salmon spawn or lay eggs in the gravel of a fresh water riverbed. The eggs are laid in nests known as redds and are fertilized soon after by the male salmon. After fertilization, the female sweeps her tail across the gravel to cover the eggs. She then moves on and lays another batch. Female sockeye salmon can lay more than 2,000 eggs during spawning.
Salmon eggs take from two to four months to hatch, during which time the young salmon survives on the yolk within the egg. After hatching, the young salmon enter the stage of its life cycle known as the alevin. Alevins look like tiny fish with the balloon-shaped yolk sac still attached to their bodies. They remain in the nest for several more weeks and survive on the food in the yolk sac.
It is when it is in the alevin stage that the salmon learns the smell of the water, plants, and rocks of the area. The smell is what gives the adult salmon the ability to return to the same fresh water habitat for spawning. Taken together, the smells are unique enough that the salmon will travel thousands of miles to return to the river or stream of its own birth.
After the alevin stage, a young sockeye salmon absorbs the yolk sac and develops into a fry. As a fry, the salmon is about an inch long and is able to finally leave the nest in search of food. At several months of age, the fry acquires vertical stripes and becomes known as a parr. After one to two years, the parr develops into a smolt.
The smolt heads toward the ocean and its body begins to change so that it can survive in salt water. Groups of smolts will gather at the mouth of the river and wait until their kidneys and gills are developed enough to adapt to the ocean. Adult salmon live in the ocean for about four years before traveling back to the river or stream for spawning.