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Large Mouth Shark Population Declining

Basking sharks are the second-largest shark (and fish), after the whale shark.
Basking sharks are the second-largest shark (and fish), after the whale shark.
Scientists Are Using High-Tech Tags to Find out More

Some unwitting humans are bobbing in the water off the coast of California. A gigantic shark, 30 feet long, rises from the depths of the dark ocean. The shark slowly approaches them with it's mouth ominously agape. And then it hones in on lunch: plankton. Introducing the basking shark, the world's second-largest shark.

We don't know much about basking sharks except that they have been systematically hunted and inadvertently killed to a point near extinction, and now they're getting some attention from local scientists, governments and fishermen.

Steven G. Wilson of Stanford University's Hopkins Marine Station led the effort to secure a grant to tag and follow three basking sharks off the coast of California with state-of-the-art satellite tracking.

Researchers have long been tagging sharks with low-tech, brightly colored ID tags. These "spaghetti tags" look like bits of neon seaweed stuck on the sharks' backs.

The new satellite tags are similarly attached but they are loaded with high-tech equipment, which costs up to $5,000 apiece. The research project will be one of the first to use this kind of technology with basking sharks on the West Coast.

Sean van Sommeran of the Pelagic Shark Research Foundation in Santa Cruz will do the tagging for researchers at Stanford. He inserts a barbed pin--a surgical harpoon--into the shark's flesh near the base of the dorsal fin.

"You need to get it right in the stable part of the animal [so] it's out of its way," explains Van Sommeran, who has been tagging sharks since 1988. "The dart fastens right in the hide. These animals make great platforms for this type of research. Like most sharks, they are resistant to infections, and the wound heals right up without problems."

The satellite tags have internal computers that will take measurements of pressure, light, depth, and global position, archive the information, and after 350 days, eject from the shark and float to the surface. There, they will transmit the data via satellite to the researchers' computers.

The North Pacific population of basking sharks has been in sharp decline. Van Sommeran first saw a basking shark when he was 15 years old. "Basking sharks were once so abundant they were considered a nuisance, a hazard to navigation," he says.

But those days of abundance are gone. "I haven't laid eyes on one since 2002," Van Sommeran adds.

According to the IUCN Red List, the international authority on conservation status, the basking shark is "vulnerable" worldwide. Worse, the North Pacific stock is marked "endangered."

Basking sharks have a few marine predators, including the orca, but their primary threat comes from humans. Basking sharks get their name from their habit of feeding on zooplankton close to the ocean's surface. They appear to bask as they sieve food through their gills, but this habit makes them easy targets for fishing.

It's large, oily liver helps it float and it can account for one-quarter of the total body weight. And it also makes it valuable to humans. Shark-liver oil, or "squalene," has been used as a nutritional supplement, lamp fuel, industrial lubricant, and folk remedy. Hakarl, an obscure Icelandic delicacy made from sticking a shark in the sand and letting it ferment, is often made from basking sharks. Here in Monterey Bay, the sharks were killed for their hides, meat, and fins.

Van Sommeran and his team are waiting for a sighting of a basking shark to begin the task of tagging. He says Monterey Bay is a hot spot for finding one. "There's a network of fishing and whale-watching boats that will help spot one," he says.

If they don't turn up the hoped-for shark by this fall, Van Sommeran's team will range as far as San Diego using aircraft for spotting.

But the researchers must be selective in their tagging. With only three tags, they can afford to lose one. The researchers fasten the tags using a long pole as they lean out from a small skiff in open water.

"You have to go out at first light," says van Sommeran. "The wind picks up sometime between 11 and 2, the waves swell, and there are white caps. You don't want to be doing this in a bouncy boat."

Van Sommeran hopes this research will help basking sharks. "So far, our only data we have for them is when we're killing them," he says. And that happens only at the surface. He's curious where the sharks spend most of their time, how fast and how far they travel.

"This is a perfect opportunity to know them better," van Sommeran said. "Perhaps some day we will be able to reflect back on the history and be glad we didn't lose them."

Learn more about the Hopkins Marine Lab at www-marine.stanford.edu, and more about Sean van Sommeran's work at pelagic.org.

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