For years, October headlines in Hawaii seem to repeat a familiar and unsettling pattern: another shark bite, another close call, another reminder of the uneasy overlap between humans and one of the ocean’s most powerful predators. The timing often feels uncanny, giving rise to the local shorthand “Sharktober.”
Now, a new peer-reviewed study suggests that “Sharktober” is a real thing. However, this seasonal spike is not a coincidence or due to more surfers and swimmers crowding the water. Still, it may instead be driven by the biology and reproductive rhythms of tiger sharks themselves.
The research, published in Frontiers in Marine Science by marine biologist Dr. Carl G. Meyer of the Hawaii Institute of Marine Biology, analyzed 30 years of shark-bite records in Hawaiian waters.
The findings reveal a striking and consistent pattern: October stands out as an outlier, with far more shark bite incidents than any other month of the year, even though ocean recreation does not increase during that period.
In other words, something is changing in the water each fall—but it is not human behavior.
“Of the 165 unprovoked shark bites recorded in Hawaiian waters between January 1995 and October 2024, 32 (20%) occurred in October, a frequency 2 to 4 times higher than in any other month,” Dr. Meyer writes. Statistical analysis confirms that this seasonal pattern is significantly different from an even distribution of bites throughout the year.”
The analysis draws on bite records collected by the Hawaii Department of Land and Natural Resources and combines them with statistical modeling to test several competing explanations.
The result is a clear rejection of some common assumptions. Sea surface temperature, often cited as a driver of shark behavior, does not explain the October spike. Neither does a surge in swimmers or surfers. October’s elevated risk persists even after controlling for these factors.
Instead, the data points toward a specific species—and a specific life stage—as the primary driver.
Tiger sharks dominate Hawaii’s shark bite statistics year-round, but their role becomes especially pronounced in October. The study found that tiger sharks accounted for at least 63% of all shark bites in October.
Of the confirmed tiger shark bites over the 30-year period, more than a quarter occurred in October alone. By comparison, outside of October, tiger shark bite counts rarely exceed 1 per month.
The sharks involved also tended to be large. Where size estimates were available, October incidents involved tiger sharks ranging from roughly 8 to 15 feet in length, with many described as exceeding known size thresholds associated with sexual maturity in females.
Although it is impossible to determine the sex of sharks involved in bite incidents with certainty, the pattern aligns closely with independent tracking and ecological data on tiger shark movements around Hawaii.
The data show that October marks a seasonal shift in tiger shark abundance near the Main Hawaiian Islands. Acoustic tagging studies have documented a partial migration of mature female tiger sharks from the remote Northwestern Hawaiian Islands into nearshore waters around the populated islands during late summer and early autumn.
At the same time, shark ecotourism operators off Oahu’s north shore report their highest tiger shark sighting rates of the year in October, sometimes observing multiple recognizable individuals in a single day after months of near-zero detections.
Significantly, this convergence lines up with tiger shark reproduction.
In Hawaii, tiger sharks give birth primarily between September and October. Dr. Meyer argues that parturition—the process of giving birth—may temporarily increase shark-human encounters through two overlapping mechanisms.
First, the arrival of late-term pregnant females into nearshore waters used by swimmers and surfers increases the sheer number of large sharks in those areas. Second, the energetic cost of pregnancy may drive heightened foraging behavior after birth, making postpartum females more active and potentially more likely to interact with unfamiliar stimuli, including humans.
Tiger shark reproduction is unusually demanding. Females carry embryos for 15 to 16 months, and litters can range from a handful of pups to dozens. During gestation, embryos grow dramatically, drawing on maternal energy reserves stored largely in the liver.
Evidence from tiger sharks and other species suggests that these reserves decline as pregnancy progresses, leaving females in poorer condition after giving birth. Unlike some sharks, tiger sharks do not appear to reduce feeding late in pregnancy, and there is no indication that they suppress foraging around parturition.
Taken together, these biological pressures may help explain why October stands out so sharply in the bite record.
Dr. Meyer is careful to emphasize that, even during “Sharktober,” shark bites remain extremely rare. In Hawaiian waters, there have been only 165 documented unprovoked shark bites over nearly three decades, and typical years see just a handful of incidents despite thousands of people swimming, surfing, and diving annually.
According to data compiled by the Hawaii Department of Land and Natural Resources and shark encounter records, the probability of an individual being bitten in Hawaii is on the order of less than one in a million per ocean visit, and serious injuries are even less common.
At a global scale, the International Shark Attack File records roughly 70 to 100 unprovoked shark bites worldwide each year across all oceans, with only a small fraction resulting in fatalities. In fact, deaths from jellyfish stings—while themselves extremely rare—are 300%-700% more likely than fatal shark attacks. This underscores just how incredibly uncommon shark-related deaths are in absolute terms.
This underscores that “Sharktober” only becomes visible when decades of data are aggregated and analyzed statistically. The baseline risk is so low that modest increases in a short period can produce a statistically detectable pattern, while the absolute risk to any given ocean user remains exceptionally small.
The research also does not suggest that tiger sharks are becoming more aggressive in any intentional sense, nor that they are “targeting” humans.
Instead, it frames shark bites as the byproduct of overlapping habitats and shifting ecological conditions. When large predators move closer to shore and increase their foraging activity, the probability of accidental encounters rises, even if human behavior remains constant.
The study also detected a small but statistically significant long-term increase in the likelihood that any given month will record at least one shark bite, averaging about 0.1 additional bites per year. However, that increase does not explain October’s dominance or “Sharktober,” which persists independently of long-term change.
For policymakers, lifeguards, and ocean safety officials, the findings offer a more nuanced way to think about risk. Rather than treating shark bites as random or purely temperature-driven events, the research highlights the value of ecological context. Seasonal awareness, particularly during October, could inform public guidance, targeted warnings, and personal decision-making without resorting to fear-based narratives.
Dr. Meyer concludes that greater vigilance during “Sharktober” is warranted, especially for solo activities like surfing, swimming, or diving in nearshore waters.
At the same time, he calls for further research to directly test the reproductive hypothesis, including non-invasive techniques such as ultrasound to assess pregnancy status in large female sharks observed close to shore.
Ultimately, the study reframes “Sharktober” not as a media phenomenon or an anomaly, but as a predictable outcome of shark biology intersecting with human presence.
Understanding that intersection, the research suggests, is the key to coexistence—not only in Hawaii, but in coastal ecosystems around the world where people and apex predators increasingly share the same space.
“The takeaway message is always, when we enter the ocean, we enter a wilderness area, and it’s the natural habitat of those predators,” Dr. Meyer tells the Hawaii Tribune Herald. “They don’t have a choice. That’s where they live. We choose to go and play in the ocean, and so, we’re making informed decisions about our risks.”
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com