The cookiecutter shark, a creature of the deep ocean, fascinates due to its unusual appearance and feeding habits. This small shark leaves a distinctive mark on the marine world. Its adaptations allow it to thrive in an environment rarely seen by humans.
Physical Characteristics
The cookiecutter shark, also known as the cigar shark due to its elongated, cylindrical body, is a small species. Males reach about 42 centimeters (16.5 inches), while females grow up to 56 centimeters (22 inches). Its body is dark brown or greyish-brown, lighter on its underside, with a distinct dark band or “collar” around its throat and gill region. It has a short, blunt snout, large, oval, green eyes positioned forward, and two small, spineless dorsal fins set far back.
The cookiecutter shark’s bioluminescence, produced by light-emitting organs called photophores, covers its entire ventral surface, excluding the dark collar. This greenish glow is among the strongest known for any shark. Scientists believe this bioluminescence, combined with the non-glowing dark collar, serves as counter-illumination, helping the shark blend with dim downwelling light when viewed from below. The dark collar is thought to mimic the silhouette of a smaller fish, attracting larger prey.
The shark’s mouth is adapted for its feeding method. Its large, fleshy, suctorial lips create a tight seal. Teeth differ between the upper and lower jaws: the upper has 30-37 small, pointed teeth, while the lower has 25-31 larger, triangular, serrated teeth interconnected at their bases. These lower teeth are shed as a complete unit and ingested by the shark.
Unique Feeding Strategy
The cookiecutter shark is named for its feeding method, which involves extracting circular plugs of flesh from larger marine animals. It uses its suctorial lips to attach to prey, creating a vacuum by retracting its tongue and closing its spiracles. With upper teeth as anchors, the shark uses its lower teeth to slice into the flesh.
Once attached, the shark rotates its body, carving out a cookie-shaped plug of flesh. This parasitic behavior allows the shark to feed on animals much larger than itself without killing them. Distinctive circular wounds have been observed on a wide variety of marine animals, including whales, dolphins, seals, large fish like tuna and marlin, and other sharks, including great whites.
In addition to parasitic bites, the cookiecutter shark also consumes smaller prey like squid, small fish, and crustaceans. This dual strategy classifies it as a facultative ectoparasite, meaning it can feed on other species without solely depending on them. It hovers in the water column, using its bioluminescent lure to ambush prey.
Habitat and Behavior
Cookiecutter sharks inhabit warm, deep waters of tropical and warm-temperate oceans worldwide. Their global distribution includes the Atlantic, Pacific, and Indian Oceans, often found near islands. During the day, they reside at depths below 1,000 meters (3,281 feet), with some recorded as deep as 3,700 meters (2.3 miles).
Their daily vertical migration is significant. As night falls, they ascend into the upper water column, often reaching depths of 85 to 300 meters (279 to 984 feet) to feed, before descending back to deeper waters before dawn. This nocturnal ascent allows them to access a wider range of vertically migrating prey.
The cookiecutter shark’s small fins and weak muscles suggest it is not a fast swimmer. Its large, oil-filled liver contributes to neutral buoyancy, reducing the energy needed to stay suspended. This adaptation supports its ambush predatory style, where it waits for prey to be lured by its bioluminescent display before launching a quick attack.
Encounters and Impact
Encounters between cookiecutter sharks and humans are infrequent. Documented instances of bites on humans have occurred, typically on long-distance swimmers in open ocean environments at night. These bites result in small, circular wounds and are generally not life-threatening. Such incidents are rare and often attributed to mistaken identity in the dark.
Cookiecutter sharks have also left marks on man-made objects. Bites have been reported on rubber sonar domes of submarines, deep-sea cables, and oceanographic equipment. Scars on marine creatures provide valuable information for researchers, acting as biological markers to track larger animals’ movements. While damage to commercial fish is minor, the shark’s widespread presence and feeding habits highlight its role in the oceanic ecosystem.