Researchers from the University of Florida and the University of Hawaii say they've spent seven years analyzing the predators' movements in the Hawaiian archipelago where recent shark incidents -- including a fatal attack in August -- have gained international attention.
About 25 percent of mature females move from the remote French Frigate Shoals atoll to the main Hawaiian Islands during late summer and early fall, they said.
"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," UF marine biologist Yannis Papastamatiou said. "There even tends to be a spike in the number of shark bites that occur during that season."
Eight reported attacks have occurred so far this year. The August fatality was the state's first since 2004.
Since 1926, the highest numbers of reported attacks in Hawaii occurred in October, November and December, the researchers said.
"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."
Tiger sharks, found worldwide in tropical and subtropical waters, are one of the largest predatory fish in the ocean, and mature females give birth about every three years.