Oncorhynchus gorbuscha, commonly known as the Pink Salmon or Humpback Salmon, is a widespread species of Pacific salmon. This fish is native to the Pacific and Indian Oceans, extending into adjacent Arctic Ocean waters. Pink Salmon are notable for their distinct characteristics, making them easily identifiable.
Distinctive Physical Traits
Pink Salmon are smaller than other Pacific salmon species, measuring between 20 to 25 inches in length and weighing 3 to 5 pounds. In the ocean, these fish exhibit a bright, silvery coloration on their sides and belly, with a steel blue to blue-green back. They are also characterized by large, oval-shaped black spots on their back, adipose fin, and tail fin.
As Pink Salmon migrate to freshwater for spawning, their appearance undergoes a significant transformation. Their bright oceanic colors fade to a dull grey or brownish-green on the back, with a yellowish-white belly. During this period, males develop a prominent, muscular hump on their back, which is the origin of their “humpback salmon” nickname. This hump, along with an enlarged head and hooked jaws, serves a role in competitive interactions among males during spawning.
Its Unique Life Cycle
Pink Salmon are characterized by a strict two-year life cycle, which is the shortest among all Pacific salmon species. Every individual matures, spawns, and dies at exactly two years of age. This leads to genetically distinct “odd-year” and “even-year” populations that typically do not interbreed, creating predictable patterns where some rivers may have larger returns in specific years.
The life cycle begins with eggs laid in freshwater redds, or nests, typically in gravel beds. These eggs hatch from December to February, depending on water temperature, and the young, known as alevins, remain under the gravel, absorbing nutrients from their yolk sacs. In March or April, the juveniles emerge from the gravel as fry and quickly migrate downstream to estuaries and then to the ocean.
Pink Salmon spend approximately 18 months in the saltwater environment, feeding on zooplankton, crustaceans like shrimp and krill, and small fish to accumulate energy for their spawning migration. Once they reach sexual maturity at two years old, they undertake a final journey back to their natal freshwater streams or rivers to spawn. After depositing their eggs and fertilizing them, both males and females die, having expended all their energy reserves in reproduction.
Habitat and Ecological Role
Pink Salmon inhabit the temperate to polar latitudes of the North Pacific Ocean, with their distribution extending from California north to Alaska and across to Asia, including regions from North Korea to Arctic Russia. As an anadromous species, they live primarily in saltwater but migrate to freshwater rivers and streams for spawning. These spawning grounds are often found closer to tidewater than those of other Pacific salmon, typically within 30 miles of a river mouth.
In their marine environment, Pink Salmon are active predators, feeding on pelagic invertebrates, small fish, and cephalopods. Their diet of crustaceans contributes to the pink hue of their flesh. Throughout their life cycle, Pink Salmon serve as a food source for a wide array of predators, including larger fish, marine mammals, seabirds, bears, and wolves.
After spawning, the carcasses of dead Pink Salmon become an important source of nutrients for the river ecosystem. The decaying bodies release marine-derived nutrients into the freshwater environment, supporting aquatic invertebrates, other fish species, and even riparian vegetation. This transfer of nutrients highlights their role in connecting marine and freshwater food webs, contributing to the health and productivity of both environments.