Tiger Shark Migration Secrets Revealed in 7-year Study

After spending seven years tracking the movement of tiger sharks around Hawaii, researchers have uncovered a wealth of information about the predatory fish, including some data that may offer insight into tiger shark attacks in the area.

Researchers from the universities of Florida and Hawaii learned that male and female tiger sharks have different migration patterns around the Hawaiian island chain: males tend to stay in one area, while female tigers sharks move around more, especially during late summer and fall, when they travel between the remote French Frigate Shoals atoll and the main Hawaiian islands.

"We have previously analyzed data to see which sharks are hanging around shark tours with cage divers on Oahu, and one of the things we noticed was that you'd get a spike in how many tiger sharks are seen in October, which would match our predicted model that you're having an influx of big, pregnant females coming from the northwestern Hawaiian Islands," said Yannis Papastamatiou, a marine biologist in the division of ichthyology at the Florida Museum of Natural History at University of Florida. "There even tends to be a spike in the number of shark bites that occur during that season."

The conclusion of the study comes at a time when Hawaiian shark attacks have received international media attention. In late August a 20-year-old German woman died after a shark bit her arm off while she was snorkeling off the shores of Maui. It was unclear what type shark bit the woman.

Prior to this year, the last time a person was killed by a shark in Hawaii was in 2004 when a tiger shark attacked a surfer, The Associated Press reported, adding that prior to the 2004 incident the last fatal shark attack in Hawaii was in 1992.

So far this year there have been eight reported shark attacks in Hawaii, while there were 10 attacks reported in 2012, the researchers said, citing data from the International Shark Attack File. The highest number of reported shark attacks in Hawaii have historically occurred in October, November and December.

"We knew tiger sharks had fairly complicated movement patterns and it seemed to be sort of a free-for-all," Papastamatiou said. "Once we looked at data for the full seven years and used the right analysis, everything started to make sense. Now we have a much better understanding of the migration patterns of these sharks."

The data revealed a complex pattern of partial migration among the tiger sharks, said Papastamatiou, noting that they believe about one-quarter of female tiger sharks swim from French Frigate Shoals atoll to the main Hawaiian Islands in the fall, potentially to give birth. He said other individual sharks may stray to other islands as well, perhaps to find more suitable water temperatures or because of more ample food sources.

"When you think of migration patterns, you think of all the animals in a population getting up at a certain time and migrating somewhere else, and then they all come back together - so everybody does the same thing," Papastamatiou said. "But that's actually rarely how it happens."

Papastamatiou and his colleagues' research is scheduled for publication in the November edition of the journal Ecology.