Basking Sharks’ Disappearance Worries Experts : Environment: World’s second-largest fish is in drastic decline. In the ‘50s, hundreds lived in Monterey Bay alone. The last bay survey found only one.

Basking sharks, the three-ton gentle giants of the ocean, seem to have disappeared from many coastal areas around the world, and researchers want to know why.

The plankton-eating animals, named for their tendency to float on the surface, grow to 30 feet or more in length. They are the world’s second-largest fish, after the whale shark.

Little is known about the basking shark’s biology, habits and population. But what is known is worrisome, according to Sean Van Sommeran, executive director of the Pelagic Shark Research Foundation in Santa Cruz.

“We have aerial photos of the California coast from the 1940s and ‘50s showing thousands of basking sharks, with hundreds in Monterey Bay alone,” he said. “But in our last survey of the bay, we found only one.”

The basking shark is generally brownish gray, often mottled, and distinguished by a large, floppy dorsal fin, a cavernous mouth, small eyes and large gills near the head that stretch almost completely around the thick, cylindrical body.

As recently as 1990-91, the foundation had spotted 300 sharks in Monterey Bay and tagged 81 of them. Similar decreases have been reported in Ireland, Norway, Korea and Japan, he said.

The foundation, part of the Earth Island Institute, has just received $5,000 from the World Wildlife Fund to set up a network of shark-watchers--often charter and commercial fishing boat captains--to track the fish population and find out why it’s dwindling.

One likely culprit is man.

Until the 1940s, the basking shark was hunted around the world for oils and its liver, causing a collapse of the population in many areas.

But synthetic oils eventually replaced shark products almost everywhere, and there is no known commercial fishing of the animal on the West Coast, said Leeanne Laughlin, a state Fish and Game biologist in Long Beach.

But man still takes his toll on the basking giants.

In British Columbia, specially equipped boats once deliberately rammed the sharks and killed them because fishermen considered the floating giants a danger to navigation.

Last year, a pair of harpooned basking sharks with their fins cut off was found off Santa Barbara. Shark fin soup is a popular delicacy, especially in Asian countries, and has been blamed for similar attacks on other shark species.

The slow-moving basking sharks make an easy target, and there are no legal restrictions on hunting the animals. Van Sommeran says the sharks are also targeted by some boaters and jet skiers.

“It is technically legal to go out and just harass them or commercially fish them,” he said. “We’ve found basking sharks with arrows shot into them.”

While Van Sommeran would like the basking sharks protected, as white sharks were recently, he said scientists must produce more authoritative data--especially in today’s anti-regulatory climate.

Direct attacks may explain some decreases, but there are even more disturbing possibilities, including pollution and climate changes, said John McCosker, a leading shark researcher with the California Academy of Sciences.

“A creature as large as it is, is like a canary in an oceanic coal mine,” he said. “As their numbers decrease, it’s a sign that if we’re not causing direct reduction, we’re probably causing indirect reduction because of water quality.”

Not all researchers are certain the population is in decline.

Greg Calliet of the Moss Landing Marine Laboratories says accurate counts of the sharks are so few that it’s impossible to know whether they have vanished, moved on or simply show cyclical population changes.

“I frankly don’t think there is enough observation on basking sharks to tell us anything,” he said. “There’s no way you can target basking sharks--they move around too much.”

The sharks may migrate far out to sea or remain under water at certain times, some researchers say. Van Sommeran contends that the decline is too steep to be explained by natural cycles.

He notes that sharks procreate more like mammals than fish, giving birth to only a few young, thus making their population more vulnerable.

“There are basking sharks that reach up to 40 feet, and we believe it takes them 100 years to get that big,” he said. “So if you kill even one, it takes a long time to replace.”