Digging the Nest Salmon nests are called redds. They are dug feverishly in the stream and riverbeds by the female, who, having established her territory, faces upstream, turns on her side and begins scooping out gravel using sweeping movements of her tail. Redds can be up to 60 centimetres long and up to 15 centimetres deep, depending on the size of the species. Many salmon dig multiple nests. While the female digs, male partners keep intruders at bay, though nest-building females can be similarly ferocious. Gravel size and quality is a key factor in determining egg survival.

Spawning With mouths agape, both male and female salmon position themselves vertically above the redd. Males compete aggressively with one another for spawning privileges, with larger males dominating. Simultaneously, the female releases her eggs (up to 15,000 for the largest species), the male releases his sperm or milt and fertilization takes place. In some cases, two or three males join one female in the release. Females then cover the nest with gravel, which protects the eggs but allows circulation of water. Most salmon, battered and weakened by the upstream run, lacking in food energy, and experiencing rapid glandular aging, die within days of spawning (semelparity). A few species (Atlantic salmon, steelhead trout, cutthroat trout) survive to repeat the spawning cycle at least once. Spawn survivors are known as kelts.