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Joint Canada-US Deep-Sea Coral Seamount Survey Post #4

October 06, 2022

On September 6th, an international team of researchers assembled to survey deep-sea coral and sponge habitats on seamounts 300 miles offshore of the U.S.-Canada border in the Northeast Pacific Ocean. Follow this blog to learn what they discover.

Group of 9 common dolphins swimming rapidly in blue water. Rare sighting this far north of common short-beaked dolphins bow-riding the Canadian Coast Guard Vessel John P Tully. Credit: NOAA Fisheries/Paul Hillman.

Cobb Seamount: Guided by Dolphins

During our transit from Corn to Cobb Seamount, we got quite the treat. A pod of a dozen or so dolphins approached the vessel and spent the next half hour bow-riding. Bow-riding is a common behavior by dolphins and porpoises during which they position themselves to be lifted up and pushed forward by pressure waves created off the bow (or front) of a large vessel. (Source = Encyclopedia of Marine Mammals).

That was pretty cool, but even cooler was finding out that seeing these dolphins here was a big surprise. At first glance, they looked like Pacific white-sided dolphins. But something didn’t seem right to Caroline Fox, the seabird and marine mammal observer on this survey from Environment and Climate Change Canada. Fortunately, I captured a full-body image of one leaping with my video camera. Caroline was able to send the images and the related video to her colleagues that specialize in marine mammals, and they confirmed that these are actually common dolphins. While common dolphins are some of the most abundant and familiar dolphins in the world, that’s not the case this far north. The last sighting in Washington State was in 2017. They hadn’t been seen in British Columbia since 2015. 

Common dolphins are, however, often associated with underwater geologic features where upwelling occurs, such as seamounts. So, it’s exciting to see this information confirmed here—on the relatively unexplored Cobb-Eickelberg Seamount chain.

Woman with binocular looks out over a blue ocean.
Seabird and marine mammal observer Caroline Fox perched on “monkey island,” which is the highest platform on the ship. She’s conducting observations to gather information on what species may be associated with these seamounts. Credit: NOAA Fisheries/Paul Hillman.

Seamounts Explained, and the Cobb Hotspot

In the last blog, I promised to explain how these seamounts formed. I mean, why would there be these groupings of underwater mountains out this far in the ocean? The answer is because of the Cobb hotspot.

The Cobb hotspot is a marine volcanic hotspot, which means that magma rising from the Earth’s mantle cools as it hits ocean water and creates underwater volcanoes. Over millions of years and because of plate tectonics, the volcanoes rising from the Cobb hotspot have moved to the northwest, forming an underwater mountain range called the Cobb-Eickelberg Seamount chain. So, seamounts are basically underwater mountains.

Map of Northeast Pacific Ocean showing bathymetry. Two boxes surround two seamount chain, and two circles illustrate the location of the Cobb and Bowie hotspots.
Google Earth image showing the locations of the Cobb and Bowie hotspot and the underwater mountain ranges they have created as the Pacific plate has moved to the northwest. Credit: Google Earth. Graphics by NOAA Fisheries/Paul Hillman.

Though the Cobb hotspot is relatively close to the west coast of the U.S., this seamount chain extends over 1,000 miles to the Aleutian Trench in Alaska. And this hotspot is not alone. You can also see the Bowie hotspot on the map above, which has created its own underwater mountain range. The Kodiak-Bowie Seamount chain could be a target for future surveys of deep-sea coral and sponge habitat. 

These geologic connections from the Aleutian Islands to the Pacific Northwest are one of the reasons these seamount chains have been targeted for exploration. Seamounts provide structure on what might otherwise be a monotonous seafloor. And variability of the seafloor provides variability in habitat, which in turn increases biodiversity. These seamount chains may also form distribution pathways for deep-sea corals, sponges, and other organisms. 

Cobb Seamount Revisited – Refining Our Understanding

This research expedition is funded in part by a national NOAA program, the Deep-Sea Coral Research and Technology Program. For management purposes, NOAA Fisheries is split into five regions: Greater Atlantic, Southeast, West Coast, Alaska, and the Pacific Islands. And each region is funded on a rotational basis to conduct deep-sea coral research, which fuels the national database. This one-stop-shop for deep-sea coral information in the U.S. helps us understand where deep-sea corals occur and how they might be important as habitat for other species. All this information also helps scientists develop predictive models to speculate about unexplored areas, and for regional fisheries management councils to make more informed decisions to manage our nation’s fisheries sustainably.

The Deep-Sea Coral Research and Technology Program was established back in 2007. Alaska’s first rotation was 2012 to 2014 and focused on the Gulf of Alaska, Aleutian Islands, and the Bering Sea. The second rotation started in 2020 and will extend into 2023, and added this international partnership to study the Cobb-Eickelberg Seamount chain. Back in 2012, Fisheries and Oceans Canada was the first to explore Cobb Seamount in partnership with NOAA Fisheries’ Northwest and Southwest Fisheries Science Centers. They did so with a remotely operated vehicle (ROV) and an autonomous underwater vehicle (AUV). They found the seamount to be rich with deep-sea coral.

Rocky surface with several species of corals, hydrocorals and cup corals rising from the substrate.
Diverse corals encountered on Cobb Seamount during the 2012 survey. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Hard bottom covered in white, branching hydrocoral. with brittle stars mixed in. A couple rosethorn rockfish swim above the hydrocoral.
Dense coverage of Stylaster hydrocoral seen during the 2012 survey. Credit: Fisheries and Oceans Canada/NOAA Fisheries.

However, that 2012 expedition targeted specific sites on Cobb Seamount where scientists expected there to be coral. Our current effort is exploring the seamount using a random sample design. On this 2022 expedition, we were super fortunate to be joined by Dr. Janelle Curtis. She served as the chief scientist on that 2012 expedition, and she was quite surprised by what we found.

A rocky ledge covered in sand hovers over a sandy ocean floor. Rockfish hide under rocky ledges while brittle stars and sea stars occupy the sandy seafloor.
Harlequin and rosethorn rockfish find rocky habitat on otherwise sandy seafloor. Sea stars and brittle stars thrive on sandy bottoms, but corals and sponges have fewer footholds. Cobb Seamount, depth ~250 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Bathymetry map of Cobb Seamount overlaid with black lines and red dots. The black lines correspond to 2012 survey sites, while the red dots depict 2022 survey sites.
Bathymetry model of Cobb seamount showing 2012 survey sites (black lines) and 2022 sample stations (red dots). The lighter colors on the seafloor indicate shallower depths (~35 meters) vs. the dark colors are deeper (over 1000 meters). Credit: Fisheries and Oceans Canada.

After her experience on the 2012 survey, Janelle was astonished to see so much sand and relatively little coral on Cobb Seamount. This proved the point of why this sort of randomized survey is so valuable. While the past expedition showed that corals can be abundant on Cobb Seamount, they are not everywhere here, and the predictive models actually expected this too. 

But the models aren’t perfect. There were several sites where expectations did not match the observations. The best way to gain confidence in models is to ground truth them, which, again, is why this survey is so important. What we learn today will be incorporated into future models and help fine tune their accuracy. Visual observations also help us understand the true abundance of deep-sea corals and sponges on these seamounts, and perhaps add more value to those spots where we do find them.

A large trumped shaped white sponge rises from a rocky seafloor. Small cup corals dot the rock surface and a rockfish swims below the sponge. A single-stalked bamboo coral extends upward from the top of the rock.
Beautiful glass sponge with a rockfish swimming at its base. Cup corals and a bamboo coral live on the surrounding rock. Cobb Seamount, depth ~450 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Several large branching coral rise up from rocky seafloor. A rockfish swims among the coral.
Coral was less abundant on Cobb seamount than the others, which could make sites like this even more worthy of protection. Cobb Seamount, depth ~500 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.

Another notable observation on Cobb Seamount was seeing lots and lots of blackspotted rockfish. Typically, this particular species lives at depths of 350 to 500 meters. However, they were consistently much shallower on Cobb Seamount (in the 150 to 300 meter range). Another species was also particularly abundant—rosethorn rockfish. At one point, Chief Scientist Chris Rooper, estimated that at least 75 percent of the rockfish we were seeing were rosethorns.

Two blackspotted rockfish swim low over the bottom in between two black rocks. White coral rubble lies beneath them. Crinoids extend up from the seafloor with feathery arms.
Blackspotted rockfish swimming over broken Stylaster hydrocoral and several crinoids, which are relatives of sea stars. Cobb Seamount, depth ~200 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
An old fishing line runs through a sandy patch between large boulders. Rockfish hover over the rocky substrate.
Rosethorn rockfish among some rocks where a line of derelict fishing gear lies along the bottom. Notice a lack of coral on these rocks. Derelict fishing gear can rub along the rocks, which may remove and prevent any corals from growing there. Cobb Seamount, depth ~175 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.

With Cobb Seamount having the most surface area of the seamounts we’re surveying and rising closest to the surface, it’s also the seamount that experiences the most fishing effort. So, it was no surprise to see impacts of fishing gear, including some derelict gear that snags or breaks and ends up on the bottom.

Across our country, Regional Fisheries Management Councils are constantly evaluating our marine resources. The information and models that come out of surveys like this help management decide on future approaches, such as what areas might need some protection and what areas don’t.

A single rosethorn rockfish swims over a sandy bottom littered with hydrocoral rubble. Crinoids extend their feathery arms up from the bottom.
Rosethorn rockfish swimming over more Stylaster hydrocoral rubble and crinoids. The broken hydrocoral may be a sign of fishing impact. Cobb Seamount, depth ~200 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.

In our fifth and final blog, we will wrap up with what we find on Brown Bear Seamount. Like Eickelberg and Corn Seamount, it has never been explored with cameras before. For now, feast your eyes on some more captivating photos from Cobb Seamount.

A white branching coral rises up from a rock pinnacle covered in orange and white cup corals.
Corals, cup corals, and hydrocorals sprout up from a rocky outcrop. Cobb Seamount, depth ~350 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
A yellow branching bamboo coral extends up from the bottom like fingers.
A delicate and graceful bamboo coral extends up from the bottom. Cobb Seamount, depth ~450 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Rockfish swim between two large boulders covered in white hydrocoral and a couple snails. Broken pieces of hydrocoral cover the seafloor between the rocks.
Rockfish living among the rocks, which are populated by hydrocorals, snails, and more. Cobb Seamount, depth ~180 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Ledges of bedroom with sand filling in lower spots. Hundreds of clams lie on the sandy bottom. Rockfish hide in rocky crevices.
Clams! This was the only place we saw clams among the rocks, and lot of them too. Cobb Seamount, depth ~250 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
A single sea whip rises from a sandy seafloor with brittle stars wrapped about it. The sandy is covered in dozens of scallops.
This image is notable for the brittle stars living on a sea whip (another species of coral), but look at the seafloor. More shellfish! These are scallops. Both the clams and scallops were found shallower than 250 meters, which is why we likely didn’t see them at other seamounts. Cobb Seamount, depth ~230 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
Bedrock covered in life with branching corals, cup corals, seastars, brittle stars, snails, and rockfish swimming around.
A diversity of life lives around this coral stalk, including rockfish, sea stars, brittle starts, cup corals, hydrocoral, and more. Cobb Seamount, depth ~300 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
A long eel-shaped fish swimming in black water.
Unidentified species of eelpout. Cobb Seamount, depth ~480 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.
An orange siphonophore with tentacles hanging below and branched polyps drifts above the seafloor.
siphonophore floating above the bottom. Siphonophores are actually colonial organisms, meaning they’re made up of specialized individuals called zooids. The zooids cooperate to accomplish different functions necessary for life, including digestion, reproduction, and movement. Cobb Seamount, depth ~700 meters. Credit: Fisheries and Oceans Canada/NOAA Fisheries.


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Last updated by Alaska Fisheries Science Center on February 15, 2023