Rare and Elusive Cookiecutter Shark Leaves a Round Wound in Its Prey

When we think of shark bites, we often think of jagged teeth that tear at skin. However, this is not the case for the cookiecutter shark (Isistius brasiliensis). Though elusive, the cookiecutter shark sure does leave its mark. Spotted on larger fish such as tuna and swordfish, this shark takes a nearly perfect circular bite from its prey, leaving a shape resembling a cookiecutter behind.

Although the cookiecutter shark is rarely observed, new research published in Marine Ecology Progress Series from the University of Hawai’i integrates ʻike Hawaiʻi (Hawaiian knowledge) and ʻōlelo Hawaiʻi (Hawaiian language) with western marine science to bring more knowledge of I. brasiliensis to the surface.

“What makes this species so fascinating is that we almost never see the shark itself,” said Justin Suca, an assistant professor in oceanography at UH Mānoa, in a press release. “We’re learning about it by studying when and where those bite marks appear.”

Learning From the Cookiecutter Shark’s Bite

Silver Tuna with cookiecutter shark bite taken out of its side — Tuna with cookiecutter shark bite
(Image Courtesy of the University of Hawaiʻi)

Cookiecutter sharks are rather small when compared to white sharks or tiger sharks. According to the Shark Research Institute, male cookiecutter sharks reach a maximum length of about 1.3 feet, while females can grow to 1.6 feet. They have a bulbous snout and can have 25 to 31 rows of sharp, triangular teeth on their lower jaw.

These daunting teeth are what leave circular wounds in the shark’s prey. These wounds are also helping researchers better understand this small predator.

Cookiecutter Sharks Hunt Best Without the Moon

For this study, the research team analyzed a broader data set than in previous research. The team examined recorded bite patterns from longline fisheries in Hawai’i — a fishing method that uses extremely long lines and thousands of bait hooks to catch species such as tuna — over several years.

“I’ve been intrigued by these small sharks for over 40 years, when I first learned about them while a graduate student in oceanography at UH Mānoa, and we would encounter them in net tows,” Donald R. Kobayashi from NOAA’s Pacific Island Fisheries Science Center (PIFSC) said in a press release. “These enigmatic creatures have resisted formal study due to their habitat, behavior, and apparent rarity, so it is quite gratifying to personally contribute some solid scientific knowledge towards understanding them and their ways!”

The results indicated that cookiecutter sharks typically attack their prey at night and attack most often when there is little to no moonlight. According to the research team, this builds on previous research that links cookiecutter shark bites on humans during moonless nights.

These findings, which were published in a 2024 PLOS One study, suggest that cookiecutter sharks mostly hunt on moonless nights, and though the bites to humans are very rare, the majority happen in Hawai’i’s ocean channels.

Indigenous Knowledge and Modern Science Working Together

In addition to scientific research, the team analyzed historical Hawaiian-language newspapers (nūpepa) and other Hawaiian-language sources for evidence of past shark bites. While no references were identified, the team thinks that Hawaiian ancestors were likely familiar with the cookiecutter shark's bite.

“Our kūpuna (elders) may never have encountered the shark itself,” said Suca, J. Hauʻoli Lorenzo-Elarco, an assistant professor of ʻōlelo Hawaiʻi at Honolulu Community College, in a press release. “But they almost certainly encountered the evidence it left behind, the distinctive bite marks on fish they brought in from the open ocean.”

From this study, the research team assigned the cookiecutter shark a new name — nahunaiki, which means ‘little bites.’ They also created a Hawaiian proverb (ʻōlelo noʻeau) about the shark: Muku ka malama, nanahu ka nahunaikio o ka pō, When the new moon arises, the cookiecutter shark bites.

This research highlights how Indigenous knowledge and modern science can collaborate on new discoveries.

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