In a scientific first, researchers in Mozambique have tagged wild minnows, the world’s largest and rarest marine fish.. These Pacific monster fish, which can grow up to 10 feet long, are so rarely seen that they are possibly an endangered species.
After weeks of exploring the beaches of the Bazaruto Archipelago, National Geographic explorer and radiation expert Andrea Marshall finally saw a small eye in the shallow water. He went in, and with a six-foot pole, gently touched the animal and removed a small sample of skin from underneath. The fish remained calm, which was a good sign: small fish have stinging spines the length of human forearms. “Every wrong move puts us in mortal danger,” he says.
After the first successful experiment, Marshall and his colleagues spent months finding more minnows that favor a particular part of the Mozambican coast. The scientists dove in at dawn, the most likely time to see a small eye, and focused on reefs that already had documented sightings of the fish. (Read how some thorns can make sounds.)
In total, the team managed to attach tags including acoustic and satellite to 11 individual tiny eyes, named for their tiny, raisin-sized eyes.
Marshall experienced some close calls—for example, he noticed that a giant ray could lift its stinger from its back and swing it around like a scorpion. But you can’t blame the fish for defending itself. When you can’t see well, “if something pushes you, you push it back,” he says.
So far, preliminary data show a very impressive animal, one that can dive to depths of more than 650 feet and swim hundreds of miles a day, says Marshall, who is the founder of the Mozambican study on minnows. . Maritime Megaphone Foundation
A day in the life of a little eye
All 11 rays had acoustic tags, and four also had satellite tags, allowing scientists to track their long journeys and fine-scale movements.
While the tagging program is in its relative infancy — data collection and analysis could take years — it promises a glimpse into the life of an enigmatic species, Marshall says.
For example, the findings reinforce previous photography-based research showing that littleeyes make long-distance journeys — the longest known straight-line migration of any wagtail species, a family of at least 60 species. The researchers hope the tagging data will reveal why the tiny eyes invest so much energy into long-distance travel.
While minnows can swim in shallow water, they regularly dive below 650 feet, which is an impressive depth. One subject in the study spent two-thirds of his time below a hundred feet. This could explain their “funny little eyes” and poor vision, Marshall says, since vision isn’t as important in the dark depths. (See the giant poppy fish that holds the record for the world’s largest freshwater fish.)
The tags also show that smalleyes are moving over the reefs at night, especially between midnight and 6 a.m., when the cleaner fish aren’t usually active. This could mean that smalleyes feed at dawn and dusk and sleep near the reef at night, as do several other ray species.
Jonny Pinney Fitzsimmons, a biologist at Australia’s Macquarie University, says the team that tagged the 11 animals was impressed. “Since we know so little about this species, things will be exciting.”
“There’s a lot you can glean from this data to understand what these movements mean in terms of their biology and ecology,” says Pini-Fitzsimmons, who was not involved in the tagging research. “What kind of areas are they using? How many people do these movements and when?”
For example, no one had ever seen a minnow at rest, so it was assumed that they never stopped swimming. But Marshall spotted a ray that had cleverly buried itself in the sand. Small eyes may eat a large meal and then have to sit and digest, says Marshall.
Pinney-Fitzsimmons adds that he would be surprised if minnows rest often, but Marshall’s observation, along with photographic evidence of sand clinging to their bodies, could indicate that they bury themselves.
Race against the clock
Many questions remain. Why are small eyes so big? What do they do on the rock at night? Do they give birth in the area?
The International Union for Conservation of Nature lists the minnows as data deficient, And Marshall believes they are likely to be severely endangered. (See our beautiful photos of ocean wildlife.)
His goal is to gather enough information so that the IUCN can properly assess the species, leading to better conservation. When a species has very few numbers to begin with, threats such as water pollution, overfishing, and the effects of climate change are severely damaged.
“We’re racing against the clock to learn more and bring more attention to this incredible species that most people don’t even know about,” he says.