Submarine Cables in Olympic Coast National Marine Sanctuary: History, Impact, and Management Lessons

Two submarine cables were installed by plow burial in the seafloor through Olympic Coast National Marine Sanctuary for the Pacific Crossing fiber optic telecommunications system in 1999 and 2000. At the time, there were no published studies on impacts of submarine cable installation to seafloor habitats or biological communities. This made it challenging for resource management and permitting agencies to determine appropriate measures associated with these installations. A reasonable assumption was that the trenching required to bury the cables could disrupt benthic communities. As a result, the authorization to install the cable in Olympic Coast National Marine Sanctuary required post-installation field studies to monitor the impact of cable installation on benthic habitats and biological communities and the extent of recovery over time.

A cable inspection survey contracted by PCL in 2001 revealed that significant portions of each PC-1 cable in the sanctuary were not buried to 0.6 meter depth, and considerable lengths of cable were unburied or suspended above the seafloor. Protracted negotiations between PCL, Tyco, OCNMS, U.S. Army Corps of Engineers, and the Makah Tribe resulted in an agreement requiring cable re-installation throughout the sanctuary. Re- installation of the PC-1 cables was accomplished in 2006. Data analyzed in this report are from surveys completed between 2000 and 2004.

The monitoring program used a crewed submersible and remotely operated vehicle to collect video and still imagery of the seafloor. Benthic sediment grabs were collected across the affected area to characterize the seafloor and to verify habitat interpretation at locations where acoustic mapping data were available. Post-installation field studies conducted by sanctuary staff found recovery of seafloor habitats and biological communities to be relatively rapid, within months to a few years, particularly in areas of granular substrates. The longest lasting impacts may be changes to the physical structure of the seafloor along the trench. Investment in higher resolution data during the route planning phase can improve both cable burial and alignment of expectations between project proponents and marine area managers.

Sanctuary managers are responsible for balancing the needs of society, the ecological condition of natural resources, and consideration for existing uses of the area. The information presented in this report provides useful scientific information about the sanctuary's benthic habitats as well as management implications and monitoring recommendations for cable installations. Effective cable route planning can help identify areas susceptible to significant or persistent impacts that could be avoided during project construction. In areas where user conflicts are clearly identified, such as where bottom contact fisheries are conducted, post-installation surveys of submarine cables are recommended to identify where exposed cables put fishers at risk of snagging gear or damaging submarine cables.

Key Words

submarine cables, seafloor habitat, marine protected area, national marine sanctuary