For years, surfers and ocean-goers in Hawaiʻi have talked about “Sharktober,” a time when shark encounters seem more common.
Now, scientists say the pattern is real.
New research from the University of Hawaiʻi confirms that shark bite incidents in Hawaiian waters rise sharply every October, driven largely by the natural behavior of tiger sharks.
The study, published in Frontiers in Marine Science, analyzed 30 years of shark bite records from 1995 to 2024.
Researchers found that roughly one in five recorded shark bites occurred in October alone, a much higher share than in any other month of the year.
This increase is statistically significant and cannot be explained by chance.
The research was led by Professor Carl G. Meyer at the Hawaiʻi Institute of Marine Biology’s Shark Lab at UH Mānoa. According to the study, tiger sharks are responsible for at least 63 percent of the October incidents.
“The October spike is real,” Meyer said. “But it’s important to stress that the overall risk of a shark bite is still very low. This pattern is linked to shark biology, not to more people being in the water.”
The findings are based entirely on Hawaiʻi-specific data, using publicly available shark incident records compiled by the Hawaiʻi Department of Land and Natural Resources.
The goal, researchers say, is not to alarm people but to provide clear, science-based information that helps residents and visitors make informed choices about ocean activities.
October appears to be a key month in the life cycle of tiger sharks, particularly adult females. The study points to a strong connection between the bite increase and the sharks’ reproductive cycle. Tiger sharks typically give birth during September and October, a process known as parturition.
During this time, large adult females are more likely to be found in nearshore waters around the main Hawaiian Islands.
Some migrate from the Northwestern Hawaiian Islands, temporarily increasing the number of big sharks close to shore. Giving birth to a large litter also requires a great deal of energy, which may leave females hungry and more actively searching for food.
This explanation is supported by other observations, including a noticeable rise in tiger shark sightings at ecotourism sites during the same period. The timing closely matches the pupping season, strengthening the link between reproduction and increased shark activity near shore.
Meyer emphasizes that awareness, not fear, is the key takeaway. Knowing that risk is slightly higher in October allows people to be more cautious, especially during solo activities like surfing or swimming close to shore.
Future research will focus on tracking adult female tiger sharks during the pupping season and using non-invasive methods to better understand their movements, health, and behavior.
By learning more about when and why sharks come closer to shore, scientists hope to improve coexistence between humans and these important ocean predators—especially during Sharktober.
