A University of New Hawaii study confirms that “Sharktober” is real and reveals a statistically significant spike in shark bites in Hawaiian waters every October. The study analyzed 30 years of data (1995-2024) and found that about 20% of all recorded bites occurred during that month, far more frequently than at any other time of the year. University of Manoa researchers Hawaii Marine Biological Institute (HIMB) Shark Research Institute Their findings were published in Frontiers of marine science.

The study, led by HIMB Professor Carl G. Mayer, determined that this striking pattern, informally known as “Sharktober,” is primarily driven by the tiger sharks’ seasonal movements and biological needs (Galeocerdo Cuvier), accounting for at least 63% of incidents this month.

“While the October surge is real and statistically significant, the overall risk remains very low,” Meyer said. “This pattern appears to be driven by the ecology of the tiger sharks, rather than by an increase in the number of people entering the water.”

The findings suggest a strong link between the October spike and the tiger shark’s reproductive cycle, particularly with calving (birth), which occurs between September and October. Evidence indicates that two major mechanisms act in concert. First, there has been a temporary increase in the abundance of large adult females in near-shore habitats, including a partial migration of adult females from the northwestern Hawaiian Islands to mainland Hawaii. Second, bearing a large number of offspring is energetically taxing, which may leave postpartum females in a state of poor nutritional status and increased motivation to actively forage to restore energy reserves. This conclusion is supported by multiple independent lines of evidence, including that peak tiger shark sightings at ecotourism sites coincide precisely with the spawning season.

requires special attention

This study uses Hawaii-specific data to address Hawaii-specific concerns and provides science-based information that allows residents and visitors to make informed decisions about ocean use during this time, supporting awareness and coexistence without sensationalism.

“Understanding when there is a slight increase in risk can help people make informed choices rather than fear,” Meyer said.

Ocean users are advised to be aware that large tiger sharks are more likely to be present in the coastal waters of mainland Hawaii in October. During this month, it is recommended to be especially careful about high-risk solo activities such as surfing and swimming, especially in coastal areas.

Future research will focus on directly studying adult female tiger sharks during spawning season, tracking their movements and using non-invasive tools to assess their reproductive status and body condition. The study was conducted as part of the University of Hawai’i at Mānoa’s HIMB Shark Lab program using publicly available shark incident data compiled by the Hawai’i Department of Land and Natural Resources.