Welcome to our Fish Factors Mini-Series! Each quarter we will share important stories on factors impacting Upper Columbia salmon and trout!
*Written by Tracy Bowerman
Female Pacific salmon and steelhead dig a depression in the gravel where they deposit their eggs and then dig a second depression upstream to cover the eggs with coarse gravel. The resulting nest, called a redd, creates a hydraulic feature that helps oxygenated water flow over the eggs as they develop in the gravel. During the development period, egg mortality can occur because of fine sediment infiltrating the gravel, physical disturbance to the redd, and dewatering. Thus, salmon egg-to-hatch survival can benefit from watershed restoration actions that reduce erosion to limit fine sediments inputs into spawning streams, such as ensuring that streams have healthy riparian buffers and decommissioning or repairing unconsolidated dirt roads.
Recently hatched juvenile salmon are called alevins, which typically remain in the gravel until they have fully absorbed their yolk sacs, at which time they swim out of the gravel as fry. These tiny fish are preyed upon by many types of animals, including birds, snakes, and larger fish. As these vulnerable fry grow, they develop parr marks, or dark vertical bands on their sides, which help camouflage them from predators. During this crucial life stage, fry and parr need complex habitats, including woody debris, overhanging banks and riparian vegetation, pools, and slow-moving side channels, where they can hide from predators and find aquatic invertebrates to eat.