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"Emerging Explorer" Hooked on Mysterious Leviathan

Stefan Lovgren
for National Geographic News
January 26, 2004
 
Every fall, scores of leviathans fill Monterey Bay in California, an
army of parasite-ridden ocean dwellers with truncated bodies that make
them look like swimming heads.

But these are no bloodthirsty sea monsters. They're Mola mola, or giant ocean sunfish, gentle creatures named for their habit of lying at the ocean surface, appearing to sunbathe. The largest bony fish in the world, the molas can grow to be over 10 feet (3 meters) long and weigh up to 5,000 pounds (2,250 kilograms).


Yet despite their appearance, little is known about them.

Tierney Thys is changing all that. For the past three years, the Monterey-based marine biologist and her colleagues have plunged into the world's oceans, using satellite tagging and DNA analysis to uncover the secrets of one of the most peculiar inhabitants of the sea.

Her study, which is partly funded by the National Geographic Society Committee for Research and Exploration, is revealing new insights into how the molas live, how they reach such gargantuan proportions, and how they tie into the vast web of open ocean life.

"Contrary to popular belief that the mola is simply a lazy lollygagging sunbather, it is in fact quite an industrious creature, plumbing the cold dark depths of the ocean repeatedly over the course of a day," said Thys.

"In today's ocean, highly impacted by human actions through climate change, overfishing, and pollution, some experts predict that only low energy forms like jellyfish will prosper," added Thys. "The mola, which subsists primarily on a jellyfish diet, could end up being the fish of the future."

Goofy Design

Thys, a California native, became fascinated with the mola after seeing a picture of it on her advisor's wall at Duke University in Durham, North Carolina, where she earned a doctorate degree in zoology, specializing in biomechanics, in 1998.

"I thought, 'That's got to be the most unlikely fish in the sea,'" recalled Thys, whose dissertation investigated the mechanics of swimming muscles in fish. "What in the world is that animal's story?"

After swimming with the molas in the wild, she was hooked. "They may look goofy, but they are spectacular underwater, incredibly graceful, like a slow flapping bird gliding on the ocean currents," Thys said.

Silver-colored, the molas have a rounded hind end and gritty sandpapery skin that is covered with copious amounts of mucus. They're infamous for their impressive parasite load. Some 40 different types of parasites have been recorded on these fish. A female may carry more than 300 million eggs in her single ovary.

The molas are found in all tropical and temperate oceans, often being mistaken for sharks with their dorsal fins flapping out of the water.

"The mola really pushes the boundaries of fish form," said Thys. "It seems a somewhat counter-intuitive design for plying the waters of the open seas. Yet the more I learn about it, the more respect and admiration I have for it. It's just radically different from the standard fish design."

Tagging the Mola

Thys's team has so far tagged 22 molas off the coasts of California, South Africa, Japan, Taiwan, and Australia to learn more about interactions between regional populations, where the molas spawn, how they locate their jellyfish prey, and if there are more sunfish species yet to be discovered.

Over several months, each animal's tag records in two-minute intervals the location, temperature, and depth of the water it's traveling through. At a predetermined time, the tags detach, rise to the surface and upload the accumulated data via satellite directly to the team's computer in California.

Preliminary results show that molas, unlike other large marine vertebrates, are mostly home bodies and unlikely to make large-scale migrations. The movement patterns of Japanese molas indicate that they are not passively drifting with the current, but swimming to adjust their positions.

"While they do not appear to make basin-scale migrations, mola are active, making repeated dives below the thermocline"—the boundary between the warmer, oxygen-rich surface layer of the ocean its colder, oxygen-poor depths—"throughout the day," said Thys. "Their surface behavior supports the claim that they're basking in order to thermally recharge after deep dives."

Meanwhile, DNA evidence shows that mola populations appear clearly divided between the Atlantic and Pacific Oceans, while intra-oceanic differences between Northern and Southern Hemispheres appear nominal.

"We've located several significantly genetically divergent individuals from Australia and South Africa, and these likely represent two brand new ocean sunfish species," said Thys. "We need more samples to be certain."

The molas are eaten throughout Asia—in Taiwan, the gut is served as "Dragon Intestines"—and some experts have warned that populations in the western Pacific are declining.

While the molas are unpopular in Europe and the United States, they are the most common bycatch of the drift net fishery, comprising over 25 percent of the California bycatch, and as much as 90 percent of the drift net swordfish fishery bycatch in Spain.

"We hope our long-term tracking work will shed insight into diurnal behaviors as well as seasonal movement patterns," said Thys. "With this knowledge, fishermen and managers may be able to reduce the amount of mola bycatch."

Census of Marine Life

Thys's research is part of the Census of Marine Life, a billion-dollar (U.S.) study involving 300 scientists from 53 countries, which hopes to gain a better understanding of the life in all oceans—past, present and future.

According to a recent interim report, the census is discovering three new fish species per week. By the time they're done in 2010, scientists say they may find more than two million different species of marine life.

Thys believes there's never been a more vital or exciting time to explore the world's oceans.

"We think we know this planet, but we've barely scratched the surface," she said. "We're just now discovering places in the ocean that you could call 'the Serengetis of the Seas,' hot spots where large ocean predators converge to hunt migrating schools of prey."

In addition to publishing research and compiling a book on molas, Thys is the science editor at Sea Studios Foundation, a documentary film company. She is currently working on a series about Earth system science and global environmental change, scheduled to air on U.S. public television in 2005.

"I hope my work can help to raise awareness of the oceans, not only of the life within this fantastic boundary-less blue, but also of the vital role the oceans play in our climate by transporting heat, sequestering carbon dioxide, and providing the reservoir for our water supplies," Thys said.
 

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