World’s biggest ocean stingray tagged in the wild

For the first time in science, researchers have tagged wild small-eyed stingrays, the world’s largest and rarest sea stingray, in Mozambique. These monster fish from the Pacific Ocean, which can reach 10 feet in length, are so rare that they are likely a critically endangered species.

After weeks of exploring the coast off the Bazaruto Archipelago, a National Geographic explorer and ray expert Andrea Marshall finally spotted a small eye in shallow water. She dove down and with a six-foot pole gently touched the animal, taking a small sample of skin from its underside. The fish remained calm, which was a good sign: the tiny eyes have a stinging spike the length of a human forearm. Any wrong move “would put us in mortal danger,” she says.

After this first successful experiment, Marshall and his colleagues spent months searching for more smalleyes that prefer a particular stretch of the Mozambique coast. The scientists dived at dawn, the most likely time to see smalleye, and focused on reefs where there were already documented sightings of the fish. (Read how some stingrays can make a sound.)

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

Marshall experienced some close calls – for example, she discovered that the huge ray could lift its stinger above its back and spin it around like a scorpion. But the fish can’t be blamed for defending itself. When you can’t see well, “if something stings you, you push it back,” she says.

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

A day in the life of a tiny eye

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

Although the tagging program is in its relative infancy—collecting and analyzing the data could take years—it promises a tantalizing glimpse into the life of a mysterious species, Marshall says.

For example, the findings support previous photography-based research that suggests smalleyes make long-distance trips — the longest known straight-line migration of any whip ray, a family of at least 60 species. The researchers hope the tagging data will reveal why the tiny eyes invest so much energy to travel so far.

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While smalleye stingrays can swim in shallow water, they regularly dive below 650 feet, an impressive depth. One person in the study spent two-thirds of his time below a hundred feet. This may explain their “ridiculously small eyes” and poor vision, Marshall says, since vision is not as important in the dark depths. (See the huge stingray that set the record for the world’s largest freshwater fish.)

The tags also reveal that smalleyes roam the reefs at night, especially between midnight and 6 a.m., when the cleaner fish aren’t usually active. This may mean that smalleyes feed at dawn and dusk and sleep near the reef at night, as do several other stingray species.

Jonny Pinney-Fitzsimmons, a biologist at Australia’s Macquarie University, said she was impressed by the team that tagged 11 animals. “Because we know so little about the species, it’s all going to be exciting.”

“There’s so much you can get from these data to understand what these movements mean in terms of their biology and ecology,” says Pinney-Fitzsimmons, who was not involved in the tagging research. “What zones are they using? How many individuals make these movements and when?’

For example, no one has ever seen a small eye at rest, so it is assumed that it never stopped swimming. But Marshall spotted one ray that deftly burrowed into the sand after being tagged. It’s possible for small eyes to eat heavily and then need to sit down and digest, Marshall says.

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Pinney-Fitzsimmons adds that she would be surprised if the little eyes rested often, but Marshall’s observation, combined with photos of evidence showing sand clinging to their bodies, could suggest they buried themselves.

A race against the clock

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

The International Union for Conservation of Nature lists small-eyed stingrays as data deficient, and Marshall believes they are likely critically endangered. (See our beautiful photos of ocean wildlife.)

Its aim is to collect enough information for the IUCN to properly assess the species, which would lead to better protection. When a species has such low numbers to begin with, it is hit even harder by threats such as water pollution, overfishing and the effects of climate change.

“We’re racing against time,” she says, “to learn more and bring more attention to this amazing species that most people don’t even know exists.”



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