LA PAZ, Mexico — We were suited up and about to make our first dive of the trip in the Sea of Cortez, but it wasn't the thrilling moment we'd imagined. The water was murky and rough, and the chance of seeing what we'd traveled to the southern tip of Baja to see was fading with the afternoon sun.
Just then a crew member saw our quarry. Half a dozen fins sliced through the choppy surface in lazy jerks, moving steadily toward us. There was no mistaking what they were: sharks. Hammerhead sharks.
Suddenly the prospect of scuba diving amid a school of prehistoric-looking creatures with a fearsome reputation was less than attractive.
No one would admit to being afraid, of course, but the race to be first one in had slowed noticeably.
"It's kind of a love-hate thing," said Shelton (Doc) White, who owns the charter boat Mirage from which we were diving. "(Passengers) want to see the sharks, but at the same time they're scared to death it might really happen."
Once we worked up the courage to join the hammerheads, though, we found that they wanted nothing to do with us. Just as White had predicted, the school disappeared within seconds of our entering the water, and only a couple of us were able to glimpse their dim silhouettes.
Visibility in the Sea of Cortez is notoriously unpredictable, ranging from Caribbean-clear to swamp-like. A periodic condition known as a plankton bloom clouded the water during the first days of our visit. But visibility improved to about 60 feet by the end of the week, allowing all of us to see schooling sharks in the distance.
White, a 40-year-old former Navy pilot who combines a charter dive business in San Diego with underwater photography sales, has been in the water with half a dozen types of sharks, including great whites, makos and black tips. He ran into his first school of hammerheads six years ago in Mexico's Sea of Cortez.
"It was like a freight train," he recalled. "Ten sharks wide, 10 sharks deep and as far as the eye could see. I'd say there were at least 500 of them."
Rather than back up to his boat, as a more sensible person might have done, he tried to move in closer with his underwater camera. The eight-foot sharks were strangely disinterested, until White exhaled. "The bubbles must have scared them," he said. "They all left, just like that."
Wait a minute. Hundreds of huge, potentially lethal fish afraid of a lone scuba diver? Well, they could be shy, or just unsociable. Not much is known about the hammerheads and their strange schooling behavior, which has been observed only in a few places, including the southern Sea of Cortez and near Ecuador's Galapagos Islands.
Peter Klimley, a researcher at Scripps Institution of Oceanography in La Jolla, has studied the hammerheads for eight years and still isn't sure why they form such large groups. It could be some sort of mating ritual, or a way of conserving energy, he said.
Some facts are clear. The sharks, which are scalloped hammerheads, can reach up to 12 feet, but are normally only about four to eight feet long. That's almost petite compared to the related great hammerhead, which can reach 20 feet and weigh up to 1,000 pounds.
In schooling, which can be from 20 to more than 100 individuals, the sharks lazily move about with no interest in food or aggression. They don't pay much attention to humans in the water, but the bubbles exhaled by scuba divers seem to bother them. Klimley and his associates have made most of their observations while skin diving--without the use of tanks.
During the day the sharks consistently stay near offshore islands and near a submerged extinct volcano known as the Sea Mount. But at night they scatter, heading off alone in different directions and traveling as far as 10 miles before returning at dawn.
There are no records of scalloped hammerhead attacks on humans, and Klimley said he's never seen the sharks exhibit serious threatening behavior. White said he worries more about strong currents and weather changes than shark attacks when he has divers in the water.
But those comforting facts are quickly forgotten when a few hammerheads sweep past. I spent most of one dive with my back to a wall of rock, looking into the blue emptiness for the return of a trio of them that came too close, while my diving partner (who hadn't seen them) blithely poked around some eel caves.
If you're around them long enough to get over the initial shock, however, you find that the hammerheads have a strange beauty all their own. Aside from the abrupt, fanlike head that looks as if it was attached by mistake, their bodies are sleek and smooth, and they glide through the water with no apparent effort.