‘Thrilled’ Scientists Give Up Tracking of Shark : Marine biology: Expert describes the megamouth specimen as ‘a very amazing animal, a very great scientific oddity.’ A National Geographic crew filmed the tracking as part of a future special.

Scientists said goodby Wednesday night to the megamouth shark they had tracked for two days, and returned to shore to analyze the data collected from the creature they describe as healthy, hardy and utterly fascinating.

“I have a feeling this may be the very first megamouth tracking and the very last one,” Don Nelson, a shark expert who led the tracking expedition, said via his ship radio before heading back.

Nelson and his team of four marine biologists from Cal State Long Beach and UC Santa Barbara stopped tracking the 16-foot fish about 8 p.m. Wednesday off Oceanside. Their research vessel was expected to pull ashore in Huntington Harbour around 4 a.m. today.

The crew abandoned the fish because their boat has limited food and fuel, and Nelson needs to return home because of teaching commitments at Cal State Long Beach. Although the shark carries two sonar transmitters, there is little chance that the scientists will be able to re-establish contact.

“We’d like more (data), we’d like six months worth,” Nelson said. “There’s never a point that you think you have enough data. But we’re thrilled with what we have. It’s much more than we ever expected.”

The shark is only the fifth megamouth to be brought to shore in the world, and the first one to be seen alive by scientists. Nelson said an underwater videotape of the shark and his two days at sea with the fish revealed it to be unique in many ways.

“It’s a very amazing animal, a very great scientific oddity,” Nelson said. “It is so different from the rest. There’s nothing close to it.”

Scientists were most amazed that the shark was able to breathe in shallow water while it was tied by its tail to a boat in Dana Point Harbor. It apparently had the ability to pump water over its gills so it can breathe. Other large shark species would have died because they need to keep moving to breath.

The shark was accidentally snared in a gill net off Dana Point early Sunday. It was released outside Dana Point Harbor 39 hours later, after scientists implanted the transmitters in its back.

By Wednesday evening, the fish had swum about 25 miles at an estimated rate of half a mile an hour. It was headed offshore and to the south, reaching 20 miles offshore Oceanside by Wednesday evening.

Scientists were especially delighted by the fish’s pattern of movement synchronized to dawn and dusk.

The shark spent the nights at depths of 40 to 65 feet, moving slowly up and down. Then, about 6:30 a.m., a little after daybreak, it made pronounced dives to about 450 feet. Around dusk, beginning about 5:20 p.m., it moved back up, staying again at the 40-to-65-foot depth overnight.

“It’s just like clockwork,” Nelson said. “It’s amazing how precise the animal appears to be in its dawn and dusk transitions.”

The fish apparently imitates its prey--plankton, shrimp and other organisms that follow light. They move to the surface during the night when the light is weak, and move deeper when light is stronger during the day.

The megamouth is a filter feeder, moving slowly so water and can flow into its yard-wide jaws. Unlike some other more aggressive and fast-moving sharks, it poses no threat to people.

Nelson, who has been studying sharks for years, described his days at sea with the megamouth as “one of the best trackings with any shark I’ve ever had,” he said. “It’s very good data and we should be able to plot it when we get back.”

A National Geographic crew producing a documentary on sharks filmed Nelson and his crew at sea Wednesday. The filmmakers, who have been studying sharks and other large fish for two years, videotaped the animal for scientists at the Los Angeles County Museum of Natural Science on Monday.

Nelson said he was surprised by the public’s interest and affection for the animal.

“It’s amazing that there are so many people hoping the shark lives,” he said. “It wasn’t very long ago people would have wanted it dead. But there’s more awareness now.”