‘Fossil’ Shark Beams Secrets Back Ashore

The megamouth shark caught earlier this week was alive and apparently well off the coast here Tuesday, captivating marine scientists with behavior that changes so distinctively from day to night that it’s as if the creature has an underwater alarm clock.

Don Nelson, a nationally known shark expert from Cal State Long Beach, has been at sea since Monday night tracking the rarely seen species that was tagged with two sonar tracking devices before its release Monday.

The transmitters show that the shark swims extremely slowly and relatively close to the surface from sunset to sunrise, then suddenly dives deep into the ocean and remains there until night, the researchers said.

It apparently is mimicking plankton, shrimp and other prey, which follow light and move closer to the surface when there is only weak moonlight.

“It’s using a different (feeding) technique than other big fishes,” said Bob Lavenberg, the Los Angeles ichthyologist who has been studying the creature since it was brought to shore Sunday. “We think it’s a vertical migrator. No other big fish like this does that.”

Other large fish such as basking sharks stay in a food-rich zone above an estimated 78 feet.

Nelson and his team of four marine biology students are aboard Nelson’s research vessel Discovery, staying within a mile of the shark all day and night.

But Nelson has teaching obligations and said he has to return to shore tonight. Lavenberg is hoping to find other researchers to take over, perhaps using a boat offered by Ethan Wayne--son of the late actor, John Wayne--a shark enthusiast who has been watching the activities since Monday.

The tracking devices that divers implanted in the shark’s back remain effective for three to six months. Lavenberg, who is fish curator at the Los Angeles County Museum of Natural History, hopes to trail the shark for at least a week.

“This new information is fascinating,” he said. “It is telling us a lot about his behavior.”

The megamouth turned out to be 16.1 feet long, which Lavenberg thinks is the longest of the five found in the world so far. Its girth is eight feet.

The shark is the first to be seen alive by scientists since the species was discovered in 1976. It is different from any other shark, looking less like most sharks than like a bronze-colored whale that has a big round head, black lips and hundreds of small teeth.

The shark, which probably weighs at least half a ton, was caught in a Dana Point fisherman’s gill net 7 miles offshore early Sunday. It was brought to Dana Point Harbor and tied to the boat by its tail for a day and a half before it was released at 5:30 p.m. Monday.

The shark has been described by researchers as a “living fossil,” a life form that has evolved little over millions of years. Such slow evolution is a sign that there has not been pressure on the creature to change and adapt, probably because it spends much of its time in depths where the environment hasn’t changed much.

Nelson said Tuesday morning from his boat that the megamouth was 10 to 12 miles offshore and headed farther out to sea. By 3 p.m., it was 15 miles offshore.

It moves about half a mile an hour, usually into the current, apparently so water and food can flow into its mouth.

The tracking data shows that the shark quickly dove about 140 feet to the ocean bottom when it was released about 2 miles off Dana Point.

It spent several minutes orienting itself, heading face first into the current. It then slowly ascended to about 45 feet from the surface, remaining in that general depth through the night.

At daybreak, its behavior changed abruptly. It dove to about 420 feet. By around 11 a.m., it was more than 500 feet below the surface and still moving at a speed of just half a mile an hour.

Marine experts said some organisms come to the surface during the night and move deeper during the day, so the shark is apparently assuming the same pattern as its prey.

“The megamouth goes where the food is,” Lavenberg said. “It’s just following along.”

The new information leads researchers to believe that the species may have escaped detection for so long because--unlike most large sharks--it remains deep during most of the day. Other large sharks move rapidly up and down in the ocean all day.

Also, only since 1979 have fishermen used gill nets that reach 100 feet below the surface.

Nelson said the shark appeared Tuesday to be in good condition despite the ordeal of being dragged to shore and tied to a boat in the harbor for a day and a half. He called the strong dive at sunrise an “encouraging sign.”

Nelson said the prognosis is good but cautioned that “we still don’t know if this animal is completely recovered yet.”

TRACKING THE MEGAMOUTH The megamouth shark apparently has very distinctive day and night behavior. It stays relatively near the surface at night, then at daybreak dives much deeper, to more than 500 feet down. The shark apparently is following its prey, which are shrimp and plankton that rise to the surface at night. 1. 5:30 p.m. The shark was tagged with two sonic pingers and released about 2 miles off Dana Point. Initially after release, the shark moved slowly to right itself near the surface, then veered sharply to the left and immediately plunged downward. 2. 5:30 p.m. to 5:45 p.m. The shark quickly descended to just above the bottom for a few minutes, apparently orienting nose-first into the current. After another few minutes, it slowly ascended toward the surface until it reached a depth of 45 feet. 3. 5:45 p.m. to daybreak The shark continued to swim seaward at a rate of about 1/2 m.p.h. into the current. The shark stayed consistently between depths of 39 and 46 feet. 4. Daybreak The shark abruptly stopped its slow swimming at dawn. It began a pronounced dive, descending to below 500 feet, where it continues to swim slowly. Late Tuesday afternoon, the shark was 15 miles seaward off Dana Point and heading farther out to sea. Source: Natural History Museum of Los Angeles County