The cookiecutter shark is a deep-sea creature. This article explores its characteristics and addresses whether it poses a threat to people.
Meet the Cookiecutter Shark
The cookiecutter shark, scientifically known as Isistius brasiliensis, is a small, cigar-shaped shark growing to about 50 centimeters (20 inches) in length. Its body is dark brown or gray with a prominent dark collar around its throat and gill slits. It is bioluminescent, with photophores on its underside emitting a vivid green glow.
This species inhabits the warm, oceanic waters worldwide, particularly around islands. During the day, cookiecutter sharks reside in deep waters, often between 1,000 to 3,700 meters (3,280 to 12,139 feet) below the surface. At night, they migrate vertically to shallower depths, usually remaining below 85 meters (279 feet), to feed. This behavior minimizes their encounters with surface dwellers.
Assessing the Danger to Humans
Encounters between cookiecutter sharks and humans are uncommon, and bites are rare. These sharks are not considered a significant danger to people, due to their deep-water habitat and feeding strategy, which doesn’t involve attacking large prey like humans. When bites do occur, they are not life-threatening.
Bites result in small, superficial, circular wounds, 5 to 10 centimeters (2 to 4 inches) in diameter and around 7 centimeters (2.8 inches) deep. While such wounds can be painful and may require medical attention, they are distinct from the more severe injuries inflicted by larger predatory sharks. Documented cases are rare, including a few incidents involving swimmers in Hawaiian channels.
Unique Feeding Habits and Non-Human Targets
The cookiecutter shark employs a unique parasitic feeding strategy, which is the origin of its name. It uses suctorial lips and pharynx to attach firmly to a larger marine animal. Once attached, it uses razor-sharp lower teeth to slice into the flesh, while its upper teeth act as anchors. The shark then rotates its body, excising a perfectly circular plug of flesh, leaving a distinctive “cookie-cutter” shaped wound.
This feeding method allows the shark to feed on a wide range of marine megafauna without killing its host. Its diet includes large animals such as whales, dolphins, tuna, seals, and other sharks. Beyond living organisms, cookiecutter sharks are also known to interact with inanimate objects. They have damaged submarine sonar domes and undersea telecommunications cables. This behavior highlights their opportunistic nature in biting various objects encountered in their deep-sea environment.