New research from the University of Hawaiʻi has confirmed a statistically significant increase in shark bite incidents in Hawaiian waters during October, a phenomenon informally termed "Sharktober." The study analyzed 30 years of data (1995–2024), revealing that approximately 20% of all recorded shark bites occurred in October, a frequency higher than any other month of the year.
The findings, published in Frontiers in Marine Science by researchers at UH Mānoa's Hawai'i Institute of Marine Biology (HIMB) Shark Lab, indicate that this pattern is primarily driven by the seasonal behaviors and biological requirements of tiger sharks (Galeocerdo cuvier), which are responsible for at least 63% of incidents during this period. HIMB Professor Carl G. Meyer, who led the research, stated that while the October spike is significant, the overall risk remains very low and is linked to tiger shark biology rather than increased human presence in the water.
The study suggests a strong connection between the October surge and the tiger shark's reproductive cycle, specifically parturition (giving birth), which takes place from September to October. Two main mechanisms are believed to be at play:
- A temporary rise in the presence of large adult female tiger sharks in nearshore habitats, including a partial migration of mature females from the Northwestern Hawaiian Islands to the Main Hawaiian Islands.
- The energetically demanding process of giving birth to a large litter likely leaves postpartum females in a depleted nutritional state, increasing their motivation to forage actively to replenish energy reserves.
This conclusion is supported by independent evidence, such as a peak in tiger shark sightings at ecotourism sites coinciding with the pupping season.
Safety Recommendations
The study utilized Hawaiʻi-specific data to address a local concern, providing scientific information for residents and visitors to make informed decisions about ocean use. Ocean users are advised that large tiger sharks are more likely to be present in the nearshore waters of the Main Hawaiian Islands during October. Extra caution is recommended during this month, particularly for high-risk, solo activities such as surfing or swimming in coastal areas.
Future research will concentrate on direct studies of adult female tiger sharks during the pupping season, including tracking their movements and using non-invasive methods to assess their reproductive status and body condition. The work was conducted as part of the HIMB Shark Lab program and utilized publicly available shark incident data compiled by the Hawaiʻi Department of Land and Natural Resources.