New University of Hawaiʻi research confirms that "Sharktober" is real, revealing a statistically significant spike in shark bite incidents in Hawaiian waters every October. The study, which analyzed 30 years of data (1995–2024), found that about 20% of all recorded bites occurred in that single month, a frequency far exceeding any other time of the year. Researchers at UH Mānoa's Hawaiʻi Institute of Marine Biology (HIMB) Shark Lab published their findings in Frontiers in Marine Science .
The research, led by HIMB Professor Carl G. Meyer, determined that this pronounced pattern, informally known as "Sharktober," is primarily driven by the seasonal movements and biological needs of tiger sharks (Galeocerdo cuvier), which account for at least 63% of the incidents during this month.
"The October spike is real and statistically significant, but the overall risk remains very low," said Meyer. "This pattern appears to be driven by tiger shark biology, not by more people being in the water."
Extra caution advised
The study uses Hawaiʻi-specific data to provide science-based information that allows residents and visitors to make informed decisions about ocean use during this time of year, supporting awareness and coexistence without sensationalism.
"Understanding when risk is slightly elevated helps people make informed choices, not fearful ones," said Meyer.
Ocean users are advised to be aware that tiger sharks are more likely to be present in the nearshore waters of the main Hawaiian Islands during October, and extra caution is advised during this month, particularly for high-risk, solo activities such as surfing or swimming in coastal areas.
Postpartum tiger sharks
The findings suggest a strong link between the October spike and the tiger shark's reproductive cycle, specifically parturition (giving birth), which occurs during the months of September and October. The evidence indicates two primary mechanisms acting together.
First, there is a temporary increase in the abundance of large adult females in nearshore habitats, including a partial migration of mature females from the Northwestern Hawaiian Islands to the main Hawaiian Islands.
Second, giving birth to a large litter is energetically taxing, likely leaving postpartum females in a state of poor nutritional condition and increasing their motivation to forage actively to recover energy reserves.
This conclusion is supported by multiple independent lines of evidence, including the peak in tiger shark sightings at ecotourism sites that aligns precisely with the pupping season.
Future research will focus on directly studying adult female tiger sharks during the pupping season, including tracking their movements and using non-invasive tools to assess their reproductive status and body condition. The work was conducted as part of the HIMB Shark Lab program at UH Mānoa, utilizing publicly available shark incident data compiled by the Hawaiʻi Department of Land and Natural Resources.
The post Sharktober: UH scientists confirm spike in tiger shark bites in October first appeared on University of Hawaiʻi System News .
