PROGRAM INTRODUCTION

Salmon in the Pacific Northwest are well known for their remarkable migrations. To complete their complex life cycle, juvenile salmon make downriver migrations to grow in the food-rich north Pacific Ocean, and adults return to spawn their eggs in natal streams and tributaries. In the Columbia and Snake river basins, salmon still migrate more than 1,500 km to the ocean. Both the juveniles and adults are genetically programmed to interact with the complex environments they encounter during these long journeys. Their behavioral responses are adapted to enable them to survive in what we may perceive as a harsh environment.

Paths of juvenile chinook salmon showing their behavior as they approach Lower Granite Dam on the Snake River.

Juvenile salmon begin their journey to the ocean as they hitch a ride on rivers and streams swollen by rain or snow melt. However, hundreds of dams have been built over the last century to harness water for irrigation, flood control, and hydroelectric generation. Scientists at the Western Fisheries Research Center (WFRC) study juvenile salmon during migration in order to understand how they react to man-made structures such as large hydroelectric dams. To improve survival of juvenile salmon, operators of the dams (i.e., U.S. Army Corps of Engineers) on the main-stem Columbia and Snake rivers have built prototype passage devices to move them around dams. Since these devices are unfamiliar to juvenile salmon, USGS researchers are currently examining their behavioral responses.

Some of the most important cues for juvenile salmon migrating to the ocean are water velocity and flow patterns, which may provide fish a route to navigate complex rapids and the turbulence of large rivers. Similarly, water velocity patterns may provide juvenile salmon a road map to use in navigating the prototype fish passage structures being built at dams. Because their behavioral responses could make the difference in completion of a safe migration to the ocean, USGS researchers are conducting studies to examine juvenile salmon movements in relation to water velocity and flow patterns, particularly near fish passage structures.

Adult salmon after spawning below Bonneville Dam on the Columbia River.

Understanding adult salmon behavior is also key to understanding how they continue to cope with the many modifications that man has made to the riverine environments. Adult salmon still find locations to spawn in the main-stem Columbia River despite numerous dams. For example, chinook and chum salmon spawn in the tailrace below Bonneville dam where they have found suitable flows and gravels. USGS researchers are studying these spawning populations to understand how their behavior allows them to successfully reproduce in the shadow of a large hydroelectric dam.

Pacific lamprey passing Bonneville Dam on the Columbia River.

Migratory behavior is not unique to salmon. Migratory behavior and seasonal movements are known for many species of fish in the Northwest. Olfaction, the use of smell, is well known to guide salmon to their natal steams and may play some role in the upstream migration of Pacific lamprey to their spawning grounds. USGS scientists are conducting studies to identify how Pacific lamprey use their sensitivity to certain compounds to guide their behavior. Bull trout also make substantial seasonal movements in tributaries to the Columbia and Snake rivers, and USGS scientists are studying how their ability to swim may restrict behavior when meeting man-made structures such as culverts. In the upper Klamath River Basin, an area plagued by water quality issues, the Lost River and shortnose suckers make seasonal movements that can make them vulnerable to mortality due to poor water quality. Thus, USGS scientists are studying how the suckers behave in response to seasonal changes in water quality.

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