Oil spill assessment maps of the central Salish Sea – Marine seafloor & coastal habitats of concern – A tool for oil spill mitigation within the San Juan Archipelago, Washington State, USA

Publication Date


Document Type


Publication Title

Continental Shelf Research






The potential for oil spills within the San Juan Archipelago of the central Salish Sea of Washington State, USA, has been an increasing concern for some time. Within this region, the spectacular islands, coastline, and underwater environment has drawn tourists, fisher people, residents, and researchers from around the world to play, live, and study. The diverse biological resources of the region provide sustenance for many of the islanders and supports a valuable tourist industry for whale watching; salmon, crab, and shrimp fishing; and underwater diving – all of which can be adversely impacted by an oil spill.

The present plans to ship more hydrocarbon products, including diluted bitumen (dilbit), from transfer sites located along the coastline of mainland British Columbia, Canada, has the potential to increase tanker vessel traffic seven-fold through the San Juan Archipelago (Seattle Times, June 22, 2019). This, along with other types of marine traffic such as cruise ships, tug-and-tow barges, articulated tank barges, bulk carriers, freighters, and general cargo shipping will increase the risk of a collision, grounding, or other events that may lead to a significant oil spill. To date, the central Salish Sea region is only marginally prepared for an oil spill tracking, containment, and recovery action. Thus, a need exists to stage equipment for the mitigation of an oil spill event if critical marine habitats are to be protected. We focus on some of these critical benthic habitats such as for rockfish (Sebastes spp.), lingcod (Ophiodon elongatus), the forage fish Pacific sand lance (Ammodytes Personatus), eelgrass (Zostera marina) meadows that are recruitment habitat for herring (Clupus herengus), and kelp (Nerocystis luetkeana) forests.

To strategically locate or assemble any mitigation apparatus for a rapid response to an oil spill, a map showing critical marine habitats is a necessity. Such a map should highlight the most critical habitats along the marine transportation corridors (primarily Rosario Strait, Haro Strait, and Guemes Channel) as well as the relatively isolated sounds and bays including Padilla Bay, Samish Bay, and Fidalgo Bay that could act as depotcenters for oil accumulation. This study addresses that need and usefulness for such a map, as no longer can it be said that what lies beneath the sea's surface is “out-of-sight”, and thus “out-of-mind”. This means that this study is critical to the development of realistic Natural Resources Damage Assessment (NRDA) settlements and can be used to inform developments of future Geographic Response Plans (GRPs) of the State of Washington. The process described here is not unique to the central Salish Sea and can be used as a template elsewhere for NRDA's and other protective measures after being modified to account for specific habitats deemed critical to those areas.

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Funding Sponsor

U.S. Environmental Protection Agency


Diluted bitumen, Habitat mapping, Mitigation, Oil spills, Salish sea, Sub-tidal habitats


Moss Landing Marine Laboratories