‘Sharktober’: tiger shark parturition drives seasonality in shark bite incidents in Hawaiian waters

Shark bite incidents in Hawaiian waters exhibit a significant seasonal pattern, with October experiencing a disproportionate spike in bites despite no corresponding increase in ocean recreational activity. Analysis of 30 years of bite records (1995–2024) reveals that 20% of all incidents occurred in October, a frequency 2 to 4 times higher than in any other month. Statistical modeling confirms October’s significantly elevated bite probability and count. Tiger sharks ( Galeocerdo cuvier ) are the primary driver of this pattern, accounting for at least 63% of October bites. This seasonal trend aligns with peak tiger shark sightings at ecotourism sites and the partial migration of mature females from the Northwestern Hawaiian Islands, suggesting a potential link to reproductive cycles. Parturition during September–October may increase encounters via two mechanisms: (1) a temporary rise in nearshore adult female abundance and (2) heightened foraging by postpartum individuals recovering from energy depletion. These findings provide ecological insight into seasonal shark bite risk and highlight potential biological drivers warranting further investigation.