Tuesday, September 27, 2005

Great white shark mission...incomplete

For most of a year, Greg Skomal has been thinking and talking about a girl he met last September.
A great white shark circles in a lagoon on Naushon Island off Woods Hole on Sept. 24, 2004. The 14-foot, 1,700-pound fish stayed two weeks before a team of biologists and commercial fishermen drove the fish from the lagoon.

He refers to her as ''the white shark'' or ''the Naushon shark.''

You may remember her as Gretel, the 14-foot, 1,700-pound great white that swam into a shallow lagoon off Woods Hole last Sept. 21 and stayed for two weeks, apparently trapped.

A local fisherman discovered the fish at the lagoon, a popular Naushon Island swimming hole. Skomal, a shark biologist with the Massachusetts Division of Marine Fisheries, planted a data-retrieval tag in the shark's dorsal fin two days later, hoping it would eventually reveal details of the fish's lifestyle in the open sea. Nobody had ever put such a data tag on a great white in the Northeastern Atlantic.

But it was two full weeks before a team of biologists and commercial fishermen could drive the fish from the lagoon. The shark made no obvious effort to depart on its own. And the day she left - driven through a series of strategically placed nets by powerful water hoses - the data tag popped off, dashing Skomal's hopes for a scientific coup.

''It's really a kick in the stomach for a lot of people,'' he told the Times that day.

Next to nothing is known about the Atlantic Ocean habits of the great white shark, the sea's most fearsome predator. More is known about the species in the Pacific, where an abundance of specimens feed on seals off the Northern California coast.

Skomal had hoped the tag would reveal the depths at which the fish spent most of its time, the extent of its travels, and the routes it followed, for example.

In the year since the Naushon shark returned to sea, on Oct. 4, tracked by a news helicopter, Skomal has given about 50 public presentations about the fish. Unable to advance the scientific understanding of the great white because of the loss of the data tag, he has at least settled on the details of the natural phenomenon that drew worldwide attention to Woods Hole.

By comparing first-hand observations with video footage and numerous photographs, Skomal determined the shark to be 14 feet in total length and to weigh 1,726 pounds. Growth charts indicate the fish would have been between 10 and 14 years old at the time.

And by settling on the shark's size and age, he thinks he has debunked a common belief about its purpose for entering the lagoon and reluctance to leave, namely, that she was pregnant. The Naushon shark probably hadn't reached sexual maturity yet, Skomal said. This typically coincides with a minimum ''fork length'' - nose to nook of the tail fins - of 16 feet.
''It discounts that theory that she's in there to give birth,'' he said.

Whereabouts unknown

The battle to drive the fish from the long and narrow lagoon between Naushon and a smaller neighboring island was epic. State wildlife officials were determined to evacuate it alive and unharmed. They speculated it entered the shallow lagoon - its maximum depth is 20 feet - on a storm tide and became trapped when the tide receded. So they hoped it would leave on the next high tide. It didn't.

Rescuers tried luring it out with bait, including a whole seal carcass tethered to a moving boat, but the typically voracious shark never bit. They muddied the water with lime, electrified it, churned it into a lather, but nothing seemed to compel the shark seaward.

Eventually the team set up a maze of nets that guided the shark most of the way to Martha's Vineyard Sound. They finally drove it away with high-pressure water hoses.

Had this failed, there were only two options left on the table, Skomal said last week: dragging it out with tailor-made tail lasso, and drugging it.

Skomal was opposed to the last option. ''I have sedated sharks before,'' he said. ''And it's killed them.''

The state never considered killing the shark.

As for Gretel's current whereabouts and for whether she'll ever come back, nobody knows.

Skomal hasn't laid eyes on a great white in Cape Cod waters since she left, he said. Which isn't to say they're not there, somewhere.

In July he visited Chatham's Monomoy Island to observe a gray seal with a deep, crescent gouge in its side. The teeth marks were characteristic of those of a great white. Just a month earlier, biologists with the National Oceanic and Atmospheric Administration photographed a large great white swimming near the carcass of a minke whale floating 20 miles southeast of Martha's Vineyard. Undoubtedly, Skomal said, ''There is evidence of great white shark predation.''
On the hunt

Still smarting from the disappointment of the lost data tag, Skomal is actively looking for the great whites.

With a $16,000 grant from the Massachusetts Environmental Trust, he has undertaken to plant a tag on another great white. To assist in his quest, he's hired two Chatham commercial fishermen to be his scouts.

''We have a strong interest in pursuing what we started with the white shark,'' Skomal said. ''Now I just need to find the animals.''

Chatham is a good place to look because of the large and growing seal population of Monomoy Island. Once great whites reach a certain size, about 1,000 pounds, they give up their fish diet and start hunting for seals and whale carcasses. It stands to reason that the sharks might follow the seals.

''That's kind of the take-home message,'' Skomal said.

This is not to say the local population of great whites will itself boom. The great white sits at the top of its food chain, and apex predators are necessarily scarce. There's only so much room at the top. But the whites already living but generally unseen might appear more often, Skomal said.

This does not seem to be the case so far. Indeed, he said, the incidence of great whites, which are known to have attacked humans in Massachusetts just three times, remains so small, that he was shocked to learn of a scientist who claimed their numbers in the northeast were declining.
''It's like saying the number of Big Foots in the Northeast is declining,'' he said.


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