You rarely catch a cookiecutter shark in action. Instead, you notice the marks it leaves behind: neat, circular holes resembling the cut of a cookie cutter. But scientists have managed to use the few clues available to sketch out the shark’s behavioral patterns—a task that required some impressive detective work.

For the new study, published in Marine Ecology Progress Series, marine biologist detectives from the University of Hawaii at Manoa collected and studied data on cookiecutter shark bites and sighting records. The analysis revealed critical patterns in the location, timing, and frequency of cookiecutter shark bites on prized fish caught in Hawaiian waters. As the most extensive investigation on these sharks thus far, the findings present critical insights for both researchers and the fishing industry, the paper concluded.

A truly weird shark

Common cookiecutter sharks (Isistius brasiliensis) typically measure up to around 20 inches. Their most distinctive feature, of course, is their teeth: between 30 and 37 small, erect teeth in the upper jaw and 25 to 31 larger, jagged triangular teeth in the lower jaw. Using their chompers like a suction cup, the sharks bite off circular sections of larger fish and even mammals like whales, dolphins, and seals.

Cookiecutter sharks are known for their distinctively shaped teeth. Credit: University of Hawaii at Manoa

Here’s where things get weirder. Unlike other sharks, the cookiecutter’s teeth are actually a single unit, so the shark sheds all its teeth at once. Then it eats the teeth (or tooth?) it just lost, which researchers believe helps it maintain calcium levels.

Generally speaking, cookiecutters—like most sharks—don’t attack humans, but their tendency to take out chunks of prized fish like tuna or swordfish has made them a nuisance to longline fisheries across Hawaii. But they’ve occasionally had run-ins with submarines and oceanographic devices.

When the cookiecutter bites

Cookiecutter shark bites on a bigeye tuna. Credit: University of Hawaii Manoa

That said, these (arguably) minor inconveniences haven’t—and likely won’t—prompt population control measures. Although cookiecutter sharks are currently listed as on the IUCN Red List, some experts project that increased fishing may lead to a population decline for the sharks in the future.