'Record' number of fish found in the undersea abyss

Three kilometres beneath the ocean's surface, life finds a way – in abundance.

When scientists announce they've found something in the deeper depths of the ocean, it's natural to brace yourself – it's still 2020, after all.

However, what oceanographers in the U.S. and U.K. found when they sent a probe 3,000 metres beneath the waves wasn't the Kraken or C'thulu, but a throng of ordinary eels. In fact, the scientists, from the University of Hawaii, the Monterey Bay Aquarium Research Institute, and the U.K.'s National Oceanography Centre are calling it a 'record' number of fish observed at that depth.

That should be a relief, and even an exciting find, and in many ways it is, given how little nourishment there is on the sunless ocean floor compared to areas nearer the coasts.

“Our observations truly surprised us,” lead author Astrid Leitner said in a release from the School of Ocean and Earth Science and Technology at the University of Hawaii. “We had never seen reports of such high numbers of fishes in the sparsely-populated, food-limited deep-sea.”

Undersea eels Drazen Lab/UH Mānoa; Deep CCZ Exp

Cutthroat eels on seamount summit in CCZ; almost 3,000 metres deep. (Photo credit: Drazen Lab/UH Mānoa; Deep CCZ Exp)

The researchers observed the fish in the Clarion Clipperton Zone, a large region stretching most of the way from Hawaii to Mexico. Their expedition focussed on three previously unexplored abyssal seamounts, underwater mountains whose summits go no higher than 3,000 metres below the sea's surface.

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At the site depicted in the photograph above, they counted some 115 cutthroat eels, a species not very well known to science. It's the most-ever amount of fish observed at that depth, and it suggests abyssal seamounts are even more able to support life than previously thought, compared to the deeper abyssal plains that surround them.

That has some implications for the exploitation of undersea resources, and the impact on surrounding wildlife. The CCZ where the seamounts are located is currently being explored for copper, cobalt, zinc and manganese.

“Our findings highlight how much there is still left to discover in the deep sea, and how much we all might lose if we do not manage mining appropriately," Leitner said.

The findings were published in the journal Deep Sea Research.