The Cookiecutter shark attacks almost anything.
Cookiecutter sharks are known for tearing small, cookie-shaped blocks out of sharks and whales much larger than themselves, but a new study shows they actually terrorize animals of all sizes.
The blue-eyed alien sharks look like sinister sock puppets made of pastry dough and grow up to 20 inches (50 centimeters) long. These strange creatures use their sharp teeth to eat great white sharks 10 times their size and have even been known to gnaw on human flesh, Live Science previously reported.
Scientists regularly observe cookiecutter markings on larger animals and therefore assume that this is what sharks primarily eat. But as it turns out, these sharks also gnaw at animals at the bottom of the food chain, giving them a unique role in ocean ecosystems, a new analysis of shark specimens finds.
Lead author Aaron Carlisle, an assistant professor in the School of Marine Science and Policy at the University of Delaware, said in a statement. “There aren’t many animals that do things like this.”
According to research, the Cookiecutter shark (Isistius brasiliensis) lives in tropical and subtropical waters and can live at depths of more than 4,920 feet (1,500 meters). If humans see cookiecutter sharks, it is usually near the surface at night when they come to hunt larger prey in the upper ocean.
The researchers tested the hypothesis that these sharks primarily feed on larger animals in the upper ocean by studying 14 cookiecutter sharks caught around Hawaii by the Monterey Bay Aquarium.
The sharks’ stomachs were mostly devoid of food, but the team figured out what they ate by looking at the chemical composition of their tissues. The team also tested for environmental DNA (eDNA), or the presence of DNA left behind even when no tissue was available to study.
“Environmental DNA is an increasingly popular and powerful tool that works on the idea that, if an animal swims in the ocean, it disperses the DNA in the water,” Carlisle said.
“So if you take a sample of water and filter it out, you can extract the DNA of everything that’s in that water and determine what species was there. So we tried that on their stomach contents.”
The researchers found that cookiecutter sharks mainly fed on smaller species at lower depths, including crustaceans, squid, and small fish, such as members of the genera Ariomma and Cololabis. Some of these prey may be small enough for the shark to swallow them whole. In contrast, the study found that large animals from the upper ocean make up less than 10% of a shark’s diet.
These findings shed new light on the behavior of this puzzling ocean creature. But the shark sample is small and geographically limited, so it’s unclear whether this feeding trend is the same across the global range for cookiecutter sharks, according to the study.