MAPS: What's Beneath the Surface
of the Salish Sea?

Each map below represents one of these quadrants.

When you look down on the Salish Sea from the top of Mount Constitution on Orcas Island, the view before you is something special. But as beautiful as it may be, it only captures a fraction of what the Salish Sea has to offer. That’s because so much of the action is happening at the bottom. 

“Most people aren't aware of how much is going on below the surface,” said Joe Gaydos, Chief Scientist of the SeaDoc Society, which is a program of the Karen C. Drayer Wildlife Health Center at UC Davis. “It’s important to give people that information, because it's a crucial part of the ecosystem even if it's not seen by everybody.”

Below you’ll find four habitat maps that describe the seafloor in various parts of the Salish Sea. We asked Gaydos to help highlight some cool stuff in each map below.

To use the maps below, click and drag the line back and forth to compare the satellite maps to the corresponding seafloor maps.

The seafloor maps were produced by a large collaboration including Gary Greene and John Aschoff of SeaDoc Society's Tombolo mapping laboratory. Other collaborators include the Center for Habitat Studies at Moss Landing Marine Laboratories, Natural Resources Canada and the Canadian Hydrographic Service. The satellite images were provided by Kate Thomas using Esri World Imagery Layer.

This key applies to all maps on this page. 



There are two really cool things to point out on this map.

On the map below, pull the slider almost all the way over to the right. Along the shore of San Juan Island you will see a very narrow band of the maroon, rocky-type habitat, and then the sea floor just drops off into a very deep channel. Southern resident killer whales use this undersea “wall” to hunt salmon. They will actually use it as a barrier and will push schools of salmon up against it to make it easier to catch them. Pretty flipping cool.

It's actually the geology here that makes the west side of San Juan such a skookum spot to watch whales. The salmon come down the strait of Juan de Fuca and almost run into San Juan Island before turning north toward Canada or south toward Puget Sound. The whales are waiting there and they use the wall to help catch the salmon.

BONUS: Almost exactly between Vancouver Island on the west and San Juan on the east, there is a range of sea floor “mountains” coming up from the deep. If you look across the body of water on the surface you would assume it was just flat as a pancake. The maroon red represents the high, rocky habitat of these "seafloor mountains.” They are ideal for rockfish!  

— Joe Gaydos

before after


Pull the slider a bit to the right and check out the strip of brown. Geologists call this a “hummocky unconsolidated sediment” type of habitat. It is found at the bottom of the deep trough. The salmon actually make this turn heading northeast to return to the Fraser River. It is known locally as “turn point” off the northwest end of Stuart Island. The whales, of course, follow the salmon along that path.

This is basically the same channel and turn that oil tankers and cargo ships travel as they head to the city of Vancouver, BC.  — Joe Gaydos

before after


Take a look at the habitat surrounding Sucia Island.

The maroon color represents high-relief bedrock habitat. These are sedimentary-type rocks that have differentially eroded and provide a nice habitat for endangered rockfish and northern or pinto abalone. There is a lot of this kind of habitat around Sucia.

By comparison, if you look inside the curve of Sucia at Fossil Bay, you’ll see a blue area that represents a mud bottom habitat. There is no place for rockfish or abalone to hide here. You could look all day, but you wouldn’t find them. You’re more likely to find flatfish camouflaged on the surface of the mud seafloor in this embayment.  — Joe Gaydos

before after

Photo by NOAA


Let’s talk about the sand waves on this map.

If a person was to walk across the sea floor, he/she would hike up and down huge sand dune after huge sand dune, as if they were walking the beaches of the North Carolina coast. The water movement has created these massive sand-wave fields. Scientists have learned that a small forage fish called Pacific Sand Lance love to bury themselves into this sand to escape predators. The cool thing about Sand Lance is that they convert plankton into fat and they are important prey items for other fish (like salmon and lingcod), marine birds and marine mammals.  — Joe Gaydos

More from Volume 6: The Salish Sea

before after