Parasitic Cookiecutter Sharks Terrorize Not Only Great White Sharks, Whales, but Animals of All Sizes in Varying Ocean Depths

Despite their adorable names, cookiecutter sharks are terrifying creatures well known for ripping small, cookie-shaped chunks out of whales and sharks significantly larger than the sharks themselves. However, a new study suggests that the scourge of the deep terrorizes animals of all sizes.

What Are Cookiecutter Sharks?

Isistius brasiliensis or cookiecutter sharks are small deepwater sharks that are named according to the cookie-shaped wounds it inflicts on other larger marine animals such as great white sharks and orcas.

According to OCEANA, the shark is parasitic since it feeds off of larger animals without killing them. It uses its sharp specialized upper teeth to latch onto larger animal's skin and its triangular lower teeth to scoop out mouth-sized chunks of blubber.

Several species, including great white sharks, bluefin tuna, and spinner dolphins, have been observed to have at least one scar caused by cookiecutter sharks. It grows up to 20 inches in length and is not commercially fished.

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Elucidating Dietary Habits of Cookiecutter Sharks

Researchers frequently observed cookiecutter markings on much larger marine animals assuming that these were the sharks' primary diet.

However, in a study published in the journal Scientific Reports, titled "Integrating Multiple Chemical Tracers To Elucidate the Diet and Habitat of Cookiecutter Sharks," it appears that these unique sharks prey on animals from the bottom of the food chain as well, giving them a one-of-a-kind role in the oceanic ecosystem.

Aaron Carlisle, lead author and assistant professor at the University of Delaware's School of Marine Science and Policy, explained that cookiecutter sharks feed on every animal, from the biggest of the apex predators, like orcas, great whites, and everything you can imagine, down to the smallest of prey. In addition, not many animals have been credited with a huge prey selection, reports LiveScience.

Isistius brasiliensis live in tropical waters and inhabit depths of at least 4,920 feet, according to the study. If humans observe cookiecutter sharks near the surface by coincidence, it is usually at night when they are hunting much larger prey in the upper ocean.

To test the assumptions on cookiecutter shark's dietary habits, researchers studied 14 cookiecutter sharks caught near Hawaii by the Monterey Bay Aquarium.

However, the stomachs of these parasitic sharks were mostly empty of food. Hence, researchers used chemical tracers to identify what the sharks have been eating. Additionally, researchers analyzed the presence of environmental DNA left behind in the shark's stomach even when there was no tissue to study.

Carlisle explained that environmental DNA is a powerful and increasingly popular tool that works under the premise that if an animal swims in the ocean, it will shed DNA in the water. Hence, by taking water samples and filtering out the DNA, researchers can identify which species were there. Researchers tried this method on the cookiecutter shark's stomach.

Researchers found that these parasitic sharks mostly fed on smaller species at lower depths, including small fish, squids, crustaceans, and Ariomma and Cololabis genera members.

In contrast, 10% of the shark's diet is comprised of large upper ocean animals. These findings shed light on the cryptic oceanic creature's behavior.