June, 1998

Three factors are responsible for the decline of Puget Sound's once robust chinook salmon runs:

• Freshwater degradation
• Excessive harvests
• Ocean conditions

In more detail, here is how each of the factors has caused the rapid decline of Puget Sound chinook:

Freshwater degradation
The degradation and manipulation of rivers and streams flowing into Puget Sound may be the most important cause of the decline of the region's chinook runs. That is because chinook spawn in the main channels and large tributaries of the state's large rivers. These are the places heavily degraded by floods as well as dams, levies and other flood control devices.

Floods can destroy chinook eggs in several ways:

Natural causes
Chinook eggs incubate in river bed gravel for several months. Strong flood waters sweeping over the nests can bury, suffocate with sediment or wash away the eggs.

Man-made causes
While flooding is natural, its effects have been made worse by human developments on the rivers. Those developments include dikes, riprap on banks and bridge crossings which constrict rivers' natural flows. These constrictions prevent rivers from expanding over their natural flood plains. The constrictions force the flooding rivers' energy downward into the gravel. The straightening of rivers also makes flood waters more powerful. The powerful downward pressure of the water scours the salmon nests.

Stream bank trees and bushes play an important role in flood control. The vegetation stabilizes stream banks, prevents erosion, filters debris and helps control and energy of floods. Riprapping banks or constructing levies removes this important vegetation.

The loss of forests along rivers and streams and some logging practices can make flooding worse. For example, logging roads cut on steep slopes or on flood plains can release debris that fills nearby rivers with sediment and gravel. Dams and withdrawals of water from rivers for agricultural, industrial or municipal uses can change their natural flows, creating mounds of gravel which worsen the effects of floods by raising the level of the stream bed.

After hatching, young chinook face other potentially deadly hazards in rivers for up to a year before going to sea. They include: loss of wetlands, pollution, high water temperatures, low water levels, altered flows due to dam operations and loss of estuaries.

Adult chinook returning from the sea face many of the same hazards, especially since the salmon generally migrate inland when river are flowing at their lowest levels of the year. Dams also can block adult salmon from prime spawning areas in state rivers.

Logging practices that remove trees from river banks affect adult and young chinook. Chinook rely on logs and branches to form pools that provide protection from predators.

The overall loss of freshwater habitat in the Puget Sound region is significant, cumulative and widespread. It cannot be restored easily, quickly or cheaply. More land will be urbanized as the state's population grows, causing the pressures on chinook and other salmon and wildlife species to increase.

Ocean survival
Chinook are not thriving in the saltwater stage of their lives. It may be because of unusually warm water, lack of food or other factors. Improvement in ocean conditions alone is not likely to improve the health of these chinook stocks.

Overharvest
Past chinook harvest rates have been too high. Reduced harvest rates in recent years have failed to return more wild chinook to the spawning gravel.

The chinook stocks in the worst shape are from the Nooksack (north and south forks), Dungeness and Stillaguamish (south fork) rivers. Other runs failing to meet spawning goals for several consecutive years are from the Skagit (spring), Skagit (summer/fall), Stillaguamish (north fork), Snohomish, White, Elwha and Hood Canal rivers plus Lake Washington chinook.

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