Researchers seek to shed light on behaviors

MOLOKINI ISLET » The blacktip reef shark glided lazily above the sandy bottom as our scuba party hovered a couple of dozen feet away.

The shark, maybe 6 feet long, paid us absolutely no mind, clearly intent on other business — finding fish — and soon faded from view.

Easily identified by the black tip of its dorsal fin, Carcharhinus melanopterus is one of the most common sharks in Hawaii waters. This one’s lack of interest in humans was at once reassuring and anticlimactic — and probably the most typical encounter that swimmers and divers have with these graceful beasts: They ignore us.

Unfortunately, that is not always the case, as evidenced by a spate of attacks this year and last.

The most recent happened Wednesday off Wailea, Maui, where California visitor Evonne Cashman was swimming in about 10 feet of water. She survived with various lacerations from head to hand.

"I’m very lucky," she said from her hospital bed.

Although the species was not identified, most attacks in Hawaii waters are by tiger sharks, Galeocerdo cuvier, which can be far more aggressive than their smaller reef-dwelling kin.

Even then, in many cases the shark takes a single bite and swims off, perhaps realizing its prey is not a monk seal or turtle.

There have been five such incidents so far this year, and in 2012 shark attacks here reached a record high.

There were 53 attacks in the United States last year, the most since 2000. Florida led the country with 26, followed by Hawaii at 10, according to the University of Florida’s International Shark Attack File report, released Feb. 11.

But fatalities here are few and far between.

The last fatal shark attack in Hawaii happened in April 2004, when Willis R. McInnis, 57, was attacked by a tiger shark while surfing off Pohaku Park, Maui, south of Napili. The Kahana man suffered a 14-inch bite wound in his right thigh and died of blood loss.

That was the first fatal attack here in more than 10 years.

The early 1990s, however, saw three deadly encounters. And sharks were strongly suspected in the disappearance of four other people during those years.

After attacks back then, the state would hire fishing crews to go out and hunt for the culprit, and many large tigers were caught and put on public display. But there was never any evidence that the guilty fish had been landed, and that controversial practice ultimately ended.

"The concept of ‘Let’s go out and kill them’ is an archaic approach to a shark attack problem, and its opportunities for success are generally slim to none," said George Burgess, who compiles the attack file for the Florida Museum of Natural History. "It’s mostly a feel-good revenge — like an ‘eye for an eye’ approach — when in fact you’re not likely to catch the shark that was involved in the situation. The shark that was involved in the situation also isn’t necessarily likely to do it again."

Yet the government of Australia sanctioned just such a culling hunt for endangered great whites last year, even though the nation had only an average year, with 14 attacks and two fatalities.

WITH TIGER SHARKS, moreover, research has shown they don’t necessarily hang around the same spot for long, although some will return to a favorite spot, researchers say. More typically, the sharks roam over vast distances.

"Tiger sharks are tremendously variable in their patterns of movements, and the mature females reproduce on a three-year cycle," University of Hawaii at Manoa shark researcher Carl Meyer said by email Friday. "These two factors have made it very challenging to figure out what is driving the movements of tiger sharks in our waters."

Meyer’s analysis of more than 10 years of tagging data, covering more than 100 tiger sharks, will be presented in an upcoming edition of the journal Ecology.

"This new analysis has really helped us to better understand factors driving the broad-scale and interisland movements of tiger sharks in Hawaii," he said.

Meanwhile, the state Department of Land and Natural Resources has awarded a two-year, $186,000 contract to Meyer and fellow marine biologist Kim Holland to study the spatial dynamics of tiger sharks around Maui.

Laura Stevens, education and outreach coordinator with the DLNR, said Maui is the focus because the island had a jump in the number of unprovoked shark incidents last year. The total was six.

Spear fishermen also are reporting "increasing boldness of large sharks encountered in Maui waters," Stevens said. "In order to select appropriate management responses to these events, we need to determine whether sharks around Maui show different behaviors than sharks around the other Hawaiian islands, or whether the reported incidents are simply due to chance. Specifically, it is necessary to determine whether large tiger sharks around Maui are more resident — more ‘site-attached’ — than they are around the other islands and also whether they exhibit greater use of inshore habitats than in other locations."

Meyer said he hopes to start tagging sharks around Maui in late September.

The study will use a combination of acoustic and satellite tagging to quantify the animals’ medium- to long-term movements.

Recently, Meyer teamed up with a researcher at the University of Tokyo to try a unique new kind of cutting-edge technology.

A device that has a camera, accelerometer and depth and temperature gauges is attached to the shark. That provides a huge amount of data that can be used to reconstruct a high-resolution, three-dimensional track of where the animal has been.

"It’s pretty neat," remarked UH-Manoa marine biology doctoral student Heather Ylitalo-Ward on her blog, "Tentacle Dreams."

She added, "I saw some of the video and it’s like you are riding on the back of a shark! It turns out that they often meet up with other shark pals and so there is great footage of them all together, even separate species mingling in the same area."

Great white sharks are spotted from time to time in Hawaii waters, but their appearances are rare.

After a 15-year-old boy named Billy Weaver was killed by a shark at the Mokulua islets near Lanikai in 1958, a culling hunt called the Billy Weaver Shark Research and Control Program brought in 697 sharks in 1959-60. Only two were great whites.

A similar effort in 1967-69 brought in 1,727 sharks, none of them great whites.

That’s because great whites, Carcharodon carcharias, migrate here from the coastal waters of California and Mexico, where they hunt seals.

But males and females have different migration patterns, according to research by Kevin Weng of the UH-Manoa School of Ocean and Earth Science and Technology and Randy Honebrink of the state Division of Aquatic Resources. Their findings were published in April in the Journal of Marine Biology.

Males have been recorded in Hawaii from December through June, but females have been observed here year-round, Weng said.

The males may be drawn to the state by the humpback calving season.

Female great white visits to Hawaii may be related to a two-year reproductive cycle in which they return to the California or Mexico coasts in alternating years. That leaves them with more time to spend in Hawaii, where warmer water may speed up fetal development, the researchers said.

But the pregnant females apparently don’t give birth here. That could be because they don’t want their pups to have to swim all the way back to California with very little food on the way.

In fact, separate research from UH indicates great whites have to live on their fat stores during their migrations between Hawaii and the West Coast. Using satellite tag data, oceanography graduate student Gen Del Raye and colleagues calculated that changes in the shark’s buoyancy correlate to a reduction of liver fat volume along the way.

Their findings were published July 17 in the Proceedings of the Royal Society B.

Weng and Honebrink compiled their information from sighting and attack records, shark culling program data, remote cameras, submersibles and published satellite tag records. The gender of the shark was recorded if the ventral surface showed the presence or absence of male sex organs called claspers.

Altogether, there have been 13 confirmed great white sightings in Hawaii since statehood, and 22 others were tracked by satellite tag to Hawaii from the coast of North America, they reported.

They found eight other reports of white sharks from 1995 to 2012, but couldn’t confirm them. (News reports of a great white off Kaena Point in January 2012 were wrong, they say; it was a shortfin mako.)

One of the recent sightings, on Jan. 4, 2005, was here at Molokini, an idyllic, crescent-shaped crater off the south coast of Maui.

Just as happy we weren’t diving that day.

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Jim Borg is the author of "Tigers of the Sea: Hawaii’s Deadly Sharks," Mutual Publishing, Honolulu, 1993.