Coastal Services Center

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Protecting SAV during Ferry Terminal Expansion

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Submerged aquatic vegetation (SAV) is a federally protected resource that provides critical habitat to migrating juvenile salmon in the Pacific Northwest. In order to protect salmon, the Washington Department of Transportation is mapping all SAV that occurs near its existing ferry terminals with underwater videography in order to plan for expansion and renovation projects.

The Project: Protecting Critical Salmon Habitat while Expanding Puget Sound's Ferry System

Puget Sound's ferry system has been providing the public with essential transportation throughout the sound for over 50 years. In order to accommodate the transportation needs of a rapidly growing population, the state initiated an expansion project to utilize larger ferries and subsequently larger terminals.

As part of a larger project looking at the effect of the ferry terminals on migrating juvenile salmon, scientists from Battelle Marine Sciences Laboratory and the University of Washington are mapping eelgrass that occurs around all the terminals. The physical structure of the docks could limit the amount of light that reaches SAV beds, while wash from the ferry propellers could directly scour the beds and cause sediments to become suspended in the water, further reducing the amount of light available to the SAV. The maps are being used to help determine where to build with the least impact on SAV and to plan for SAV restoration and compensatory mitigation. Compensatory mitigation occurs when destruction to SAV is unavoidable, so developers create an equivalent SAV bed in a suitable location.

Mapping SAV requires that researchers are able to see the SAV that is growing on the seafloor. If environmental conditions permit, mapping can be accomplished from aerial photography. However, researchers can also use sensors that go beneath the water's surface, such as underwater videography or acoustics.

Mapping SAV Data with Underwater Videography

Researchers from Battelle are mapping SAV using underwater videography and a differential Global Positioning System (DGPS). With DGPS, the videos are recording spatial data that can be used in a geographic information system (GIS) to create thematic maps. They are mapping SAV that occurs within one-half of a kilometer on either side of the terminal with video. For areas under the docks, the researchers rely upon the observations of SCUBA divers.

The Result

The SAV maps are helping managers proactively protect and restore SAV in Puget Sound. For example, one docking terminal was built longer but not as wide as originally planned to avoid direct impact to the grass and to minimize the damage from the boat propeller wash. Later during the expansion project, a tugboat accidentally damaged a SAV meadow. Because they had a direct measure of the location and extent of seagrass before the damage, they were able to accurately plan and monitor restoration. All of these measures to protect and restore SAV are also helping to protect the juvenile salmon that depend on the resource as critical habitat.

For More Information

• Washington State Department of Transportation Washington State Ferries Eelgrass Protection Project
• Submerged Aquatic Vegetation: Data Development and Applied Uses CD-ROM
• Battelle Laboratories

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