The salmon that make it back to their home streams to spawn have beaten amazing odds. On average, out of every 1,000 eggs laid one survives to return and spawn.
Female Coho Salmon
Illustration courtesy of the U.S. Fish and Wildlife Service |
When the salmon reach the spawning grounds where they were born, males and females spawn together. The female digs out a shallow redd in the gravel on the river bottom using sweeping movements of her tail and letting the current wash away the silt and fine particles. While she is digging the redd, the dominate male keeps other males away.
When the female is ready to spawn, she lowers her anal fin into the redd. At this cue, the male swims alongside her and quivers. This quivering behavior stimulates the female to lay her eggs. The male then spreads his milt over the eggs to fertilize them.
The female immediately moves upstream and begins digging another redd. This digging automatically covers the previously laid eggs with a thin layer of gravel. The salmon continue to dig and spawn until the female is spent. A total of 5,000 eggs may be laid by a large female during the spawning time.
Decaying Salmon
Photo courtesy of the Bonneville Power Administration |
After their long journey upstream and their spawning act, the salmon are totally worn out. A few steelhead and sea-run cutthroat may survive after spawning and return to the ocean after a short time. However, all other Pacific salmon species are called kelts or spawned-out salmon at this stage. They may try to guard their redds or seek out the refuge of deep pools, but eventually their exhausted bodies will wash downstream. Their carcasses will feed scavenging animals and provide nutrients to the forests which grow near the rivers. The nutrients of their decaying bodies will also feed stream organisms, which will in turn feed young salmon.
The eggs need cool, clean, oxygenated water to survive. If all goes well, the eggs will hatch a few months later and the young salmon will start the life cycle all over again.
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