Salmon Spawn

By Bill Hauser

Salmon deposit eggs during summer that incubate until mid-winter when the fish hatch as alevins and, in spring, become free swimming fry. After some development and growth, they become juveniles called parr or fry until they become smolts that migrate to the ocean. In the ocean, they grow and mature until they migrate back to freshwater to spawn. After salmon return to their stream of origin, they spawn and die.

This sounds easy enough but the details are often more murky.

During summer, salmon enter freshwater and return to their home stream to spawn. And during this time, they do not ingest food. Usually, males approach the spawning grounds first and begin to establish territories. Chasing and nipping is fair game and there is lots of splashing and dashing. Eventually, females arrive and the games intensify as males vie to attract and keep females. A female selects a mate based on size (bigger is better), color (brighter is usually better), body shape (taller is usually better), and kype (lower jaw) development.

When the salmon are nearly mature, the female begins to dig the nest, or redd, in earnest. She turns on her side and flexes her body. She displaces materials during both the down slap and, through suction, the body flex and the rise of the tail. Fine particles are put into suspension and carried downstream. Larger gravel settle and water will percolate more freely through the cleaned gravel. After a modest depression is completed, the male and female simultaneously spawn with a burst of eggs and sperm. The female moves forward and begins to dig again. Displaced gravel covers the first batch of fertilized eggs and a new pit is created. The pair spawns again and repeats the process of digging and spawning until all the eggs have been deposited. (The actual redd is the mound of gravel, not the pit.) Note that this means: a) not all eggs are spawned at one time; and, b) each group of eggs is deposited in a different part of the redd – so if there is damage to one part of the redd (e.g., freezing or fungus), not all of the eggs will be affected.

So far, so good but we have five species of salmon spawning in our waters. As usual, each species has slightly different needs. And remember, these “rules” are not hard and fast. There are always exceptions.

Larger-sized fish are stronger and they can move larger gravel and spawn in faster water. Their redds are usually deeper. So Chinook salmon often spawn in deeper, faster water with larger gravel size.

Usually, Sockeye salmon migrate into lakes where they typically pause and spend about a month or so to mature before they move to spawning grounds.

Pink salmon often spawn soon after they enter freshwater with a short migration. Some populations spawn in intertidal reaches, but in some drainages, they migrate much farther upriver to spawn.

Chum salmon prefer to spawn in upwelling river reaches. Upwelling water is typically warmer in winter than surface water so spawning is often later and egg development is faster.

Coho salmon prefer to spawn in headwaters reaches often above beaver dams. They often pause in the lower reaches of a drainage and wait until fall rains raise the water level and make bever dams easier to navigate.

And then they die.

Egg development varies with water temperature but takes about six months. This all happens through the winter and under the ice.