Rare Shark Is Filmed, Released : Marine study: The 15-foot megamouth caught off Dana Point early Sunday was also tagged so that scientists can track its movements.

After 1 1/2 days in captivity, a mysterious species of shark described as an alien appearing out of the depths was allowed to slip back into the sea Monday after elated researchers videotaped it underwater and implanted two radio transmitters to track its movements.

The 15-foot megamouth shark is the first to survive after being brought to shore and the only one in the world ever to be filmed and studied alive. Caught accidentally in a fisherman’s gill net off Dana Point early Sunday, the bronze-colored fish with cavernous, yard-wide jaws and a bulbous head seemed healthy and strong when it was released a mile out from the harbor Monday evening.

“I feel a bit sad to see him go, but I’m really elated,” said Bob Lavenberg, an ichthyologist and curator of fishes at the Los Angeles County Museum of Natural History who was the first one to identify the fish, and who coordinated the research.

“This was an opportunity to get knowledge about a really rare fish and an opportunity to be environmentally sensitive at the same time by putting the fish back where he belongs,” Lavenberg said. “It’s the best of both worlds. He couldn’t be better, and now we can get some real science done.”

One of the largest sharks in the world, the megamouth--with its large, round head and whale-like appearance--is intriguing to scientists because its appearance is so different from that of other sharks and because extremely little is known about it. The male shark caught Sunday, dubbed Mega, is only the fifth megamouth ever to be caught or found since the species was first discovered off Hawaii 14 years ago.

Relieved that the fish survived but happy that they detained it long enough to get their work done, shark researchers now believe they can glean piles of information from their videotapes and trackers to better understand the megamouth, known scientifically as Megachasma pelagios.

“Knowing life forms will help us tell the story of life on Earth,” Lavenberg said.

Underwater photographers working with the Los Angeles County Museum of Natural History and National Geographic were awed by what they saw, surfacing with vivid descriptions of the creature.

“When you swim right up to it, you know you’re seeing something different. It has gigantic eyes and big rubbery black lips,” said Michael de Gruy, who has been filming a documentary on sharks for National Geographic for two years. “It’s massive, with big, lumbering movements.”

The fish, which apparently eats plankton, not meat, seems to be a docile species, letting divers touch it, even its mouth.

“He would sort of flinch when people touched him, and his eyes would shift. When I swam to his side, he turned and looked at me,” said Mark Dell’ Aquila, an underwater photographer hired by the museum.

The ocean off Dana Point Harbor was turned into an open-air zoo as curious people and the news media in boats and yachts encircled the shark, which was tied by its tail to the Moonshiner, the boat from which it was caught. Several people dove into the water to get a closer look at the shark, while a noisy TV helicopter hovered above and jet skis roared in close. There were so many people diving that it made the water murky, angering the museum’s video teams.

“What a circus!” Lavenberg said. “Only in California can they turn this into a happening.”

Otto Elliott, a commercial fisherman and skipper of the 38-foot Moonshiner, said he caught the megamouth in his gill net about 7 miles offshore about 2:30 a.m. Sunday while fishing for swordfish. He had to slice open his $5,000 net to keep the shark alive, but he said he did so because he knew he had accidentally caught a rare, bizarre treasure.

Lavenberg called colleagues around the nation and in Japan but couldn’t find an aquarium that could take the fish, since it is so big.

A diver with a dart gun implanted two transmitters into the fish that will tell scientists how deep and how far offshore it lives. Don Nelson, a nationally known shark expert from Cal State Long Beach, plans to track the fish at sea for at least two days.

A 1-inch square of muscle was cut out of the megamouth’s hide near its dorsal fin so that scientists can compare it with tissue from well-known sharks to see how the species are related.

Lavenberg described the shark as a “living fossil,” a life form that has evolved slowly deep in the ocean.

“This species is at least 10 million years old, and it has changed very little,” he said. “It shows evolutionary stability over time.”

Leighton Taylor, a San Francisco aquarium consultant, is one of a handful of shark experts in the nation to become increasingly excited about the megamouth since it was captured Sunday.

“We call ourselves the shark Mafia, and we’ve been calling each other daily about this,” he said, adding that there will be “tremendous” new information from the videotapes and trackers.

“Man has been a student of fish for 500 years, and he has intensively studied them for the last 100 years,” Taylor said, “but there’s this monstrous fish that’s eluded us for all these years, except for the last 15 years or so.”

To unknowingly help in the quest for knowledge, the shark endured discomfort and some minor bruises, since it was tied to the Moonshiner by a rope around its tail for 39 hours.

“That’s like someone interrogating you for two days,” Dell’ Aquila said. “It was good to see him go after all he’s been put through.”

Hundreds of people stood on the shore, some yelling “Let it go, let it go,” and a Redondo Beach-based conservation group called the Sea Shepherd Conservation Society demanded the shark’s immediate release.

For a few tense hours at sea while the crew waited for the radio transmitters to arrive from Long Beach, the shark looked weak and stressed, rolling over to show its white underbelly. Worried, Lavenberg and the crew were prepared to release it so that it wouldn’t die, but the shark started to perk up and the devices arrived in time.

“I had a lump in my throat thinking he was going to die,” Lavenberg said.

When its tail was untied about 5:30 p.m., the shark righted itself, pointed down and swam away strong and fast, “like it was saying ‘I’m outta here!’ ” de Gruy said. “Considering what he’s been through, he swam off incredibly strong. What a feeling it was to see that.”

Elliott, his wife, Catherine, and his first mate and stepson, Rob Worrell, were probably more relieved than anyone else that the fish survived captivity.

“If they can’t keep it, we want to let it go. We don’t want it to die,” Catherine Elliott said earlier in the day. “This is something that will go down in history.”

The divers were fascinated with the megamouth’s black lips and two large brown eyes covered with a thin milky membrane. Lavenberg also said it was clear that the shark had spawned recently because of the condition of its reproductive organs.

The copper coloring, the same as most middle-ocean fish, leads Lavenberg to the new belief that the shark may thrive in shallower waters than the 700 to several thousand feet previously thought. Scientists had believed that the megamouth escaped detection for so long because it lived in inaccessible depths, but now they wonder if there is some other reason.

“Now we can track him,” Lavenberg said. “Maybe we’ll find out it just goes offshore and hangs out in just 100 meters of water or so. This is exciting new information.”

The National Geographic documentary on sharks and related fish will be aired in 1992.

“We’re trying to present a picture that contradicts the notion of sharks as predators eating little old ladies,” said Mimi de Gruy, who has been working on the film with her husband. “If we can learn a little more about it and gain greater understanding and sympathy, that’s wonderful.”

Times staff writer David Reyes contributed to this report.

MEGAMOUTH SHARK * Megachasma pelagios, commonly referred to as the megamouth shark, averages about 15 feet in length and weighs about a ton. The megamouth shark gets its name from its wide mouth. It has 236 rows of needle-sharp teeth, and its jaws are nearly 4 feet wide. * The huge, round mouth filters crustaceans from the sea, similar to the feeding technique of some whales. But much like the great white shark, the megamouth appears to be able to jut its jaws forward, pulling in as many planktonic creatures as possible. * Despite the shark’s fearsome maw, scientists assume from its soft skeleton and flabby muscles that the megamouth is a slow-swimming plankton feeder that poses no threat to humans. * Before the megamouth was discovered in 1976, the only other known plankton-eating sharks were the basking shark and the whale shark. Both feed by straining minute organisms from surface waters. It is unknown whether the megamouth is also a surface feeder. No other shark has the megamouth’s bulbous snout, jaw-structure, gill rakers (fine sleve-like structures that filter tiny deep-sea shrimp out of huge swallows of water) and deep fin grooves. Source: Sea Frontiers magazine and Oceans magazine.