Female Building a Redd
Each species of salmon shows different preferences in terms of optimum spawning habitat. This ensures that available habitat is used efficiently with a minimum of competition.
The redd is the general location selected by a female for laying eggs. Within that site, she may dig several nests and deposit eggs in them over a period of several days. The female begins by “nosing,” an act in which she tests the gravel by probing, while cruising slowly over the bottom in the redd area. Having identified a suitable site, she turns on her side and begins flexing her body violently, slapping the gravel with her tail. This process dislodges gravel, which is lifted and carried slightly downstream by the current. After a series of digging motions, she swims to repeat the process. Sometimes the movements include tight circling or swimming over the nest in figure eights. Eventually, this produces a cone-shaped hollow varying in depth from just a few to as much as 15 inches (38 cm), depending on gravel composition and fish species.
The act of digging attracts males, who compete for the privilege of courtship. As a male manages to successfully ward off competitors, he joins the female in the nest in a series of movements that lead to egg and sperm release. The first of these movements is a “quiver,” in which the male moves alongside the female and his body undulates slightly. He may follow this by “crossing over” the female near the base of her tail. As the nest develops, the female begins “probing” the gravel with her tail. Gradually, the probing increases and the circling decreases. The female settles lower in the nest for longer periods. As this occurs, the male continues to quiver and frequently opens his mouth in a “gape.”
As the female nears egg deposition, she begins to “crouch,” a position much like the probe, but with mouth agape. By opening her mouth, she increases her resistance to the current, which forces her deeper into the nest cavity. When the female assumes the crouch, the male quickly moves alongside. Both rapidly vibrate their tails and the eggs and sperm are released. The eggs emerge from the female one or two at a time into water clouded by the sperm, or milt. As this occurs, other males stationed outside of the nest may rush in to try to fertilize the eggs themselves. If the dominant male makes chase, another male may try to occupy the nest.
From the “Adopt-A-Stream Foundation Field Guide to the Pacific Salmon,” by Robert Steelquist. We are grateful to Sasquatch Books for granting us permission to reproduce this description of salmon spawning.