A ‘Dead’ Volcano Off Canada Turned Out To Be Warm — And Covered In More Than 2 Million Skate Egg Cases

You may remember the 2023 headlines: an underwater volcano off British Columbia, assumed to be extinct and cold, turned out to be warm and covered in up to a million giant eggs. Canadian researchers have spent the years since measuring, counting and monitoring the site, and their reports change both halves of that story.

What Was Actually Found On The Summit?

A crowded skate nursery on warm, coral-covered rock, nearly a mile below the surface.

In 2023, the NorthEast Pacific Deep-sea Exploration Project, a partnership that includes Fisheries and Oceans Canada (DFO) and the Council of the Haida Nation, sent a remotely operated vehicle (ROV) to the Tuzo Wilson Seamount Complex, a pair of undersea volcanoes off British Columbia. Near the top of the southwestern seamount, now named Ts’íidaa (the Haida word for skate), the crew filmed a Pacific white skate laying an egg among thousands of others. The Pacific white skate is a pale, deep-sea relative of sharks and rays, and females can grow to about 6.5 feet long.

Live Science’s July 2023 account said the team had recorded the first footage of the species laying eggs. Cherisse Du Preez, the DFO deep-sea biologist who led the expedition, gave the outlet a rough guess of 100,000 to a million eggs on the summit.

Skate embryos develop inside tough collagen egg cases, nicknamed mermaid’s purses. The NorthEast Pacific Deep-sea Exploration Project says Pacific white skate cases start out golden and darken toward black as time passes and the embryo develops. A 2025 DFO technical report says the team has found dense egg cases, adult skates and egg laying, or likely egg-laying behavior, on the summit every year it has visited. That is the pattern of a nursery used year after year, not a single burst of spawning.

Was The Volcano Really Thought To Be Extinct?

By the explorers, yes. The scientific record was less certain.

Live Science reported that before the 2023 dives, the team believed the volcano was extinct and the surrounding water frigid. Formal reviews had not shown otherwise: according to the DFO technical report, earlier assessments of Canada’s offshore Pacific seamounts had not identified the complex as venting warm fluids.

Older research had hinted at a different picture. A 1977 paper in Nature called it a young submarine volcano, and a 1993 paper in the Journal of Geophysical Research described two composite volcanoes built from geologically recent lava. The DFO report adds that heat-flow measurements in nearby sediment in 1978 suggested warm fluids might be venting there, and a 1986 survey detected water-temperature anomalies consistent with venting that its cameras could not confirm.

Dives in 2021, 2023 and 2024 settled the question. Cameras found yellow mineral staining and bacterial mats around openings that released shimmering water. Temperature probes showed that vent water averaged about 1°C warmer, and up to about 2°C warmer, than the 2.24°C (36°F) background. In water that cold, the report treats that as a meaningful anomaly.

The heat source appears unusual. Rather than a typical vent field powered by magma, the report’s authors think the two seamounts work as a linked pair. Cold seawater seeps into one, picks up heat as it moves through the crust beneath a blanket of sediment, and flows out of the other, pushed along by pressure differences between the cold and warm columns of water. They say this kind of system has been documented at only three other places, all in the Pacific. The 2025 expedition report describes continuing work, including an instrument mooring left on Ts’íidaa’s summit to track water conditions for a year.

Could The Warm Water Help The Eggs Develop?

Possibly, but the evidence so far comes from watching nurseries, not testing them.

The best-known comparison comes from the Galápagos. In a 2018 study in Scientific Reports, researchers described a 2015 ROV dive at a vent field north of the islands, where they counted 157 Pacific white skate egg cases. About 58 percent lay within roughly 66 feet of black smoker chimneys, vents that pour out hot, mineral-darkened water. More than 89 percent were recorded while the vehicle’s sensor read warmer than the 2.76°C (about 37°F) background. That sensor rode on the vehicle, on average about 11 feet above the seafloor, so it measured the water over the eggs rather than at the eggs themselves.

The Galápagos team proposed that skates use the heat to speed up development, because deep-sea skate eggs are among the slowest to develop of any animal’s. A related species, the Alaska skate, needs about 1,290 days at 4.4°C (40°F), and the authors estimated that, if Pacific white skates develop at a similar rate, their embryos would need more than 1,500 days at Galápagos background temperatures. They presented the heat idea as a hypothesis. The study did not experimentally warm eggs or compare development rates to test it.

At Tuzo Wilson, development appears to be even slower. DFO’s preliminary data suggest Pacific white skate embryos there take roughly five to nine years to fully develop, and the project’s nursery page notes that even modest warming could shorten that wait. Whether it does at this site is still under study.

The heat is also patchy. During the 2025 expedition, two probe readings near yellow-stained rock crevices on Ts’íidaa ran only 0.1 and 0.5°C above background, according to the expedition report. DFO also found that most egg cases sit on bare, current-swept rock, packed most densely along the summit and ridge among bamboo coral, while few or none turned up on a heavily sedimented slope. The technical report’s authors suggest strong water flow and plentiful food may help the skates in several ways, with warm venting as one possible factor that could shorten incubation directly or help indirectly.

What Does The Evidence Actually Support?

A large, reused nursery on a warm volcano, with the reasons skates choose it still open.

DFO later replaced the 2023 guess with a count. Researchers tallied 5,566 egg cases in 489 overhead seafloor photos covering about 53,000 square feet. In the main nursery, above about 5,460 feet deep, the photos averaged roughly one case for every 4 square feet. Scaling that density across this top 250 vertical feet or so of the summit, an area of about a third of a square mile, produced an estimate of more than 2.1 million cases. The team says the true number is almost certainly higher, because cases pile up and tuck into crevices. The report adds that no other published skate nursery has a higher recorded density.

That total counts egg cases, not confirmed living embryos, and it covers two species. Of all cases photographed, 20 percent were identified as Arctic skate and 16 percent as Pacific white skate; the remaining cases, more than 60 percent, could not be identified in the images.

The nursery is also refilled. At one long-term monitoring site checked in 2023 and 2024, researchers found about one new, yellow case (under a year old) for every 108 square feet. Extrapolated across the main nursery, DFO estimates that skates lay more than 78,000 Pacific white skate cases there each year, a preliminary figure drawn from a single site.

Because this evidence comes from video, photos, probes and repeat visits rather than experiments, picture the summit less as a dead volcano that came back to life and more as a long-used nursery on warm volcanic rock, where heat, currents, coral and scarce sediment all remain candidates for why the skates keep coming back.