A Fall run, male Coho Salmon (Oncorhynchus kisutch), has arrived at its natal stream and is making its way to its gravel spawning ground on Eagle Creek, in Oregon’s Columbia Gorge. After having spent between one and three years at sea, these anadromous fish begin their return to clean-flowing freshwater streams to begin their spawning cycle.
While at sea, Coho have a classic Pelagic camouflage pattern, with white belly, silver sides and a blue-black back. This pattern of coloring affords them enhanced concealment from all directions. The dark back hides them from above, against the darkness of the deeps. A white belly against the bright background of the sky above; and highly reflective sides which dazzle when viewed from either side.
Upon entering the freshwater environment, their bodies begin a radical transformation that is initiated by the change of salinity within the brackish waters of a freshwater streams discharge plume at sea. Increasingly as the Coho begins its migration up-stream, their jaw becomes hooked, and the teeth more pronounced. Their skin reddens and the head turns an olive green, with the females often becoming darker in color than males. A mature specimen can reach lengths of 28 inches, and will weigh between 7 and 11 pound; in some instances can reach up to 36 pounds.
Shortly after spawning, Coho salmon will die, and in turn release an abundance of ocean sequestered nutrients into the freshwater and surrounding forest environments. In no small part, the nutrients released by the parents death, will fertilize and strengthen the steams’ ecology; and thus increase the rate of survival for the offspring who will spend the next one to two years within the freshwater habitat.