Every fourth year the Adams River in Canada's British Columbia turns red from thousands or sometimes millions of migrating Sockeye Salmon (Sockeye translated from Salish word for red fish) to fulfill their final task - spawning! Once they leave the Pacific Ocean drawn by an instinct to find their possible birth place they turn their color into vivid olive heads and bright red backs. Also the body shuts down the metabolism and this means they suffer hunger and energy needed to swim upriver for more than 500 km through the Fraser River drainage into the Salmon River, Shuswap Lake and their final stretch - Adams River.
There they face another obstacle; swift current, competing salmon, bears and shallow warm river.
Along this tiring journey they have to fight off competitor males and females over spawning nests and best locations. Once a couple have found their nesting spot (mostly shallow gravel bottom with little current) the female 'digs' a redd (spawning nest) with its caudal (rear) fin by laying on its side and flipping the caudal fin vigorously until the fine sand and gravel are washed out and a 10-20 cm deep nesting bowl has formed.
The couple might still wait for hours or even days before they're ready to release the eggs and semen.
When the moment comes the female signals the male by an intense shiver of its body and releasing the sticky eggs which immediately are fertilized my the male before they drop into the redd and cling to gravel and rocks to hatch. The adults die from exhaustion and become nutrients for the river system, predators (bear, wolverine, eagles, gulls, etc) .
Since the spawning happens in the midst of the autumn the hatching of the future offspring is crucial. Sudden river run off or over freezing river arms can destroy the eggs and the entire effort to come that far was for nothing. Well, not quite; since each dead salmon will contribute with its decomposing body to the growth of the surrounding forest, becoming a quick and easy meal for predators which fatten up for winter and add nutrient to the river and ocean.
Once the Aelvins (tiny salmon feeding from its egg sack) hatch they turn into fry (small salmon in its first year) and later migrate down the river into the Pacific Ocean where they continue their 3-4 years cycle in large shoals throughout the Pacific. Where they go and what triggers the spawning urge is little known about. Mother Nature still have a few tricks and secrets up her sleeves. Text: Beat J Korner