Does Fish Passage Reduce Salmon Migration Barriers?

Reducing Barriers with Fish Ladders

Fish ladders, also known as fish passes, are structures designed to facilitate the migration of fish through barriers such as dams. Effective fish ladders typically feature a series of pools or steps that allow fish to swim upstream. For example, the Bonneville Dam, a major obstacle on the Columbia River, features a fish ladder with 16 pools, each 4 feet deep, that provides a smooth and gradual ascent for salmon and other fish species.

Designing Efficient Fish Passes

Efficient fish passes are designed with the specific needs of the target species in mind. For instance, salmon require a specific temperature range and water velocity to successfully navigate through a fish pass. A well-designed fish pass might include features such as aeration systems to maintain optimal water conditions, and a series of pools with varying depths and velocities to accommodate different species and size classes. The success of a fish pass is often measured by its ability to pass a certain percentage of the target species, with some studies indicating that well-designed fish passes can pass up to 90% of migrating fish.

Case Study: The Elwha Dam Removal

The removal of the Elwha Dam on the Elwha River in Washington state is a notable example of how fish passage can be used to reduce barriers to salmon migration. The dam, which was removed between 2011 and 2014, was a major obstacle to the migration of chinook and coho salmon. As a result of the dam removal, the river has experienced a significant increase in salmon populations, with counts reaching over 1,000 fish per day. The success of the Elwha Dam removal highlights the importance of fish passage in restoring healthy salmon populations and promoting ecosystem balance.