Why Dozens of Octopuses Marched Out of the Sea

November 2, 2017

When Brett Stones and his dolphin-watching tour group SeaMor finished their evening excursion last Friday in Wales, it was already dark out. In the distance, they spotted something with an indiscernible yet familiar shape.

“It looked like a bit of a blob,” said Stones. When the group approached, they saw that it was a curled octopus, a species commonly found off the beaches of Ceredigion.

Roughly a foot long, the animal was crawling about 30 feet inland. And it wasn’t alone. As they walked through the area, they found 20 to 30 more octopuses seemingly crawling on land, in a space about half as big as a soccer field.

“It sort of brings out this mothering instinct. You just want to save them,” said Stones. “It’s quite emotional to see them flailing.”

He and several others who were nearby inspected the octopuses for signs of injury and found no visible evidence of harm. Stones has lived in the area all his life, but he says he’s never seen anything like it.

Using plastic containers, Stones and the others at the beach scooped up the octopuses and carried them to deeper water, where they plopped them back into the ocean.

Over the next couple of nights, Stones said he returned to the same beach in the morning and found several of the same species dead.

Octopuses are nocturnal, meaning more may have crawled onto land while the local people slept.

Even more baffling to Stones is how energetic the octopuses seemed when they were moved back to sea.

“Every one we found was quite alive. Their tentacles were coming around and grabbing hold [of our hands], but in the morning, we found more dead. No bites or damage,” said Stones. Just inexplicably dead.

Unknown Cause of Death

Without a physical examination of the octopuses, it’s difficult for scientists to speculate exactly what may have prompted the rarely seen behavior.

Octopuses are some of the world’s most curious invertebrates, and it’s not the first time they’ve emerged from the water on their own volition. In 2015, video caught an octopus hopping out of a tidal pool to attack a crab and drag it back down into the water.

“When I was a student, one jumped out of a tank and traveled down the hallway,” said Jenny Hofmeister, who’s now a postdoctoral scholar at the Scripps Institution of Oceanography in San Diego. In 2016, an octopus named Inky became a legend when it slipped out of its tank, slithered down a pipe, and escaped into the ocean.

Hofmeister speculates that overcrowding from booming populations could have prompted the octopuses out of the water en masse. One study published in Current Biology in 2016 found that, as fishermen take more and more of the large animals that feed on octopuses, their populations have boomed. This means the invertebrates would have to travel farther to find food, and perhaps equally important to an octopus, shelter. And that drive could have pushed them toward land, Hofmeister speculated.

“I would need to know the sex ratio of the octopuses that are doing this,” said James Wood, owner of the Coral Sea Aquarium and editor of the site Cephalopod Page. Without having examined the octopuses or knowing specifics of the environment in which they died, Woods says he can only speculate as to why they all suddenly walked onto land.

End of Life?

“It could be that they’re undergoing senescence,” said Wood, who wrote a paper on the topic in 2002. The term refers to the end stages of an octopus’s life when it begins to feed less, exhibit less coordination, and wonder around without direction.

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