World’s biggest ocean stingray tagged in the wild

Scientifically, researchers have tagged wild small-eye stingrays, the world’s largest and rarest sea urchin, in Mozambique.. These giant Pacific ocean fish, which can reach lengths of up to 10 feet, are rarely seen and are a critically endangered species.

After weeks of surveying the coast of the Basaruto Archipelago, National Geographic explorer and ray expert Andrea Marshall spotted a smalleye in shallow water. She dove in, lightly touched the animal with a six-foot pole, and took a small skin sample from its underside. The fish remained calm, which was a good sign: smallies have spines the length of human wrists. Any wrong move “would put us in mortal danger,” she says.

After the first successful experiment, Marshall and his colleagues spent months trying to find more small eyes that favored a particular part of the Mozambican coast. The scientists dove into dawn, the most likely time to see a smalleye, and focused on reefs where the fish had already been recorded. (Read how some stingrays can make noises.)

In total, the team was able to attach tags to 11 individual minnows, including acoustic and satellite, named for their small, raisin-sized eyes.

Marshall has experienced some close calls—for example, she discovered that a giant ray can lift itself up on its back like a scorpion and spin it around. But the fish cannot be blamed for defending themselves. When you can’t see well, “if something stabs you, you stab it back,” she says.

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Preliminary data so far reveal a very impressive animal that can dive to depths of more than 650 feet and swim hundreds of miles a day, says Marshall, who studies tiny eyes as a Mozambique-based founder. Marine Megafauna Foundation.

A day in the life of a little eye

All 11 rays were fitted with acoustic tags, and four received satellite tags, allowing scientists to track their long-distance journeys and subtle movements.

While the tagging program is in its relative infancy — it will take years to collect and analyze data — it offers a glimpse into the life of an enigmatic species, Marshall says.

For example, the findings reinforce previous research based on photography that suggests stingrays make long-distance journeys—the longest straight-line migration of any whiptail stingray, with at least 60 species in the family. The researchers hope the tagging data will reveal why small eyes invest so much energy to travel such distances.

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Although small stingrays can swim in shallow water, they regularly dive from 650 feet, which is impressive. One person in the study spent about two-thirds of it 100 feet below. This could explain their “ridiculously small eyes” and poor eyesight, Marshall says, since vision is not as critical in the dark depths. (See the giant stingray, which holds the record for the world’s largest freshwater fish.)

The tags also reveal that smalleyes move over reefs at night, especially between midnight and 6 a.m., when cleaner fish are typically less active. This means that smalleyes, like many other ray species, feed at dawn and dusk and sleep close to the rock at night.

Jonny Pini-Fitzsimmons, a biologist at Macquarie University in Australia, says he was fascinated by the team, which tagged 11 animals. “Since we know so little about this species, it’s all going to be exciting.”

“You can get a lot out of that data to understand what those movements mean in terms of their biology and ecology,” says Pini-Fitzsimmons, who was not involved in the tagging research. “What areas are they using? How many individuals make those movements and when?

For example, no one ever saw a small eye resting, so it was assumed that they never stopped swimming. But after being tagged, Marshall observed a ray deftly burying itself in the sand. Smalleyes may need to eat a large meal and then sit down to digest it, says Marshall.

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Pini-Fitzsimmons adds that he would be surprised if minnows rested frequently, but combined Marshall’s observation with photographic evidence showing sand stuck to their bodies, suggesting they bury themselves.

Race against the clock

Many questions remain. Why are small eyes so big? What do they do on the rocks at night? Do they give birth in the area?

The International Union for Conservation of Nature lists smalleye stingrays as data deficient, Marshall believes they are critically endangered. (See our beautiful photos of marine wildlife.)

Her goal is to collect as much information as possible for the IUCN to properly assess the species, which will lead to better conservation. If a species has such small numbers to begin with, threats such as water pollution, overfishing and the impact of climate change will affect it more.

“We’re racing against the clock,” she says, “to learn more and bring more attention to this incredible species that most people don’t know about.”


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