October has a reputation in Hawaii that makes locals uneasy. For decades, this month has seen a noticeable spike in unprovoked shark attacks, enough that researchers started digging through long-term data to figure out what keeps repeating itself enough to dub the month “Sharktober.”
A new study published in Frontiers in Marine Science examined 165 unprovoked shark attacks recorded in Hawaiian waters between 1995 and 2024. Roughly one-fifth happened in October. That number raised some alarms because it didn’t correspond with a rise in swimming, surfing, or other ocean recreation. People weren’t flooding the water. Something else was.
That “something” appears to be tiger sharks.
Marine biologist Carl Meyer of the University of Hawai’i at Manoa found that tiger sharks accounted for 47 percent of all unprovoked attacks across the 30-year dataset. In October, that figure jumped higher. At least 63 percent of the bites that month involved tiger sharks, with additional incidents attributed to unidentified species that might also have included them.
“The October spike appears to be driven by tiger shark biology rather than changes in human ocean use,” Meyer told Live Science via email.
October is when large, mature female tiger sharks move into waters closer to the main Hawaiian Islands to give birth. These aren’t little sharks. Tiger sharks can grow well over 10 feet long and weigh hundreds of pounds. Their increased presence near shore raises the odds of encounters with humans who already use those same coastal areas.
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The reproductive process complicates things. Tiger sharks carry their young for roughly 15 to 16 months and give birth to an average of about 30 pups. Pregnant and postpartum females need to feed aggressively to rebuild reserves, which means active foraging in areas where reef fish and other prey are available.
None of this involves protecting their offspring. Once born, tiger shark pups fend for themselves and usually remain shallow to avoid larger predators, including adult sharks.
According to Daryl McPhee at Bond University, the issue comes down to proximity. When large sharks share the same shallow water as humans, of course bite risk is going to increase. He says comparable seasonal surges show up in other places in the world when coastal sharks move shoreward during reproduction.
On a global scale, shark bite numbers have risen over time, according to data from the Florida Museum, mostly because humans spend far more time in the ocean than they did decades ago. Hawaii’s October increase stands apart because it reflects shark behavior, not a surge in human activity.
Meyer emphasizes awareness rather than fear. Extra caution in October, particularly for solo surfers and swimmers, is a reasonable response. The sharks aren’t out to get you. They’re following biological demands that predate surfboards and tourism.
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