Why do Chinook Salmon Need Green Shorelines?
Juvenile Chinook salmon in Lake Washington and Lake Sammamish use shallow, lakeshore habitat to avoid predators, find food, and grow before heading out to sea. Research has found that the smallest Chinook salmon enter Lake Washington between February and Mid-May, during which time they occupy shallow (from 4" to 4' deep), gradually sloping (<20% slope) lakeshore habitat (Tabor 2006). By June, when the salmon have grown to 4-5 inches long, they move into deeper waters to begin their migration out of the ship canal, toward Puget Sound and the Pacific Ocean.
Photo: Roger Tabor, US Fish & Wildlife | Photo: Roger Tabor, US Fish & Wildlife |
Protection from Predators
The tiny Chinook salmon that enter the lakes early in the spring rely on shallow lakeshore habitat to avoid larger predators.
Who are the potential predators?
- Cutthroat trout – Prefer deeper water.
- Large and small mouth bass – Once the water warms up in May or June, they move into shallow water, where they may eat juvenile Chinook salmon. Associated with structures like docks and rocks.
- Sculpin – Aggressive predator, hides in rocks and under docks.
- Yellow perch – Large population size means that they could eat many young salmon.
- Shorebirds (like heron, seagull, eagles, and cormorants) – Young Chinook are defenseless from these aerial predators without cover to hide under.
A multi-year study in Lake Washington found that during the period when juvenile Chinook salmon rely on shallow lakeshores, more juvenile Chinook salmon are found along unarmored lakeshores than shorelines with bulkheads and rip rap (Tabor 2006). Natural shorelines with gradual sloping beaches and natural habitat features (wood and overhanging vegetation) shelter juvenile Chinook salmon from predators. On the other hand, bulkheads create a steep shoreline, leaving small salmon vulnerable to predation.
Food
Downed wood and dense forests are natural components of lakeshore systems. During the daytime, when juvenile Chinook salmon are actively feeding, they tend to congregate around objects like large wood or overhanging vegetation (Tabor 2006). Together, downed wood and riparian vegetation provide organic debris to the lakeshore habitat, which in turn supports important insect prey for juvenile Chinook salmon. By incorporating large wood and overhanging vegetation, and creating shallow water habitat with Green Shoreline designs, lakeshore landowners may be able to create new foraging opportunities for juvenile Chinook salmon.