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Pupping guides tiger sharks’ movement in isles, study finds

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    Researchers tracked more than 100 tiger sharks over the course of seven years, tagging each animal with a transmitter that emits a high-frequency sound in a unique code.
    University of Hawaii scientist Carl Meyer, left, and the University of Florida's Yannis Papastamatiou, co-authored a study that shows female tiger sharks swim to the main Hawaiian Islands when it's time to give birth -- a period that correlates with an increase in shark bites.

Anew studyhas found female tiger sharks migrate from the Northwestern Hawaiian Islands to the main Hawaiian islands during fall pupping season — a period that historically coincides with a higher frequency of shark bites in Hawaii.

The findings from the University of Hawaii and University of Florida are scheduled to be published in November in the scientific journal Ecology.

UH-Manoa marine biologist Carl Meyer, co-author of the study, said although a rise in shark bites roughly coincides with the pupping season for female tiger sharks, there’s no conclusive evidence showing these sharks are responsible for a seasonal rise in shark bites.

"From a scientific perspective, there’s no conclusive proof that these events are linked," he said in an interview.

Researchers said the increase in frequency could be tied to a number of other factors.

Meyer said scientists don’t know the number of tiger sharks that migrate to the main Hawaiian islands or the birthing areas. Very little scientific information exists about the behavior of tiger sharks in Hawaii, partially because their far-ranging underwater migratory pattern makes tracking them difficult.

"It’s just impossible to come up with a meaningful number," Meyer said.

The pupping season research advances scientists’ understanding of migration patterns of tiger sharks in Hawaii waters. The species has been linked to a number of shark attacks in the islands, and public officials have been looking for ways to reduce shark bites.

Meyer said while tiger sharks are present throughout the islands at all times of the year, traditional Hawaiian knowledge warns of danger during the fall months.

Scientists estimate about a quarter of mature tiger sharks migrate annually to the main Hawaiian islands, while the others remain in the Northwest Hawaiian Islands.

About one-third of the female tiger sharks are pregnant in the fall, according to research estimates.

"Some are resident and some are transient," said Yannis Papastamatiou, the study’s lead author and a University of Florida researcher, in a news release Thursday. "When we think of animal migrations, we tend to think of all individuals in a population getting up and leaving at the same time, but it’s not as simple as that."

Scientists say among migrating animals from birds to ocean predators, some portion of the population remains behind when the rest leave on the seasonal journey.

Scientists said the study and other research have solidly dispelled ideas that tiger sharks stick to chosen territories such as specific coves and bays.

In the 1960s and 1970s, the false assumption that sharks were territorial led to culls under the belief that killing sharks in locations where people had been hurt meant killing the shark that had attacked them, eliminating a "problem" shark.

In the new study, scientists tracked more than 100 tiger sharks for seven years by tagging each animal with a transmitter that emitted high-frequency sound in a unique code.

Some 143 listening stations would record the time, date and identity of the shark when it passed within detection range.

Only glimpses of each animal were caught.

"They could leave Hawaii altogether and we wouldn’t know," said Papastamatiou.

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