Cookie-cutter sharks, tiny but fearless, are a unique shark species as they are parasitic. Its name comes from its feeding habit that involves pulling out the flesh from the prey’s body, making the wound appear as if cut with a cookie cutter.
Head: The eyes of these sharks are large, round, and green in color. Its nostrils are covered with a short flap of skin. There are two spiracles behind the eyes, which help in breathing.
Mouth: They have a short mouth extending to form a transverse line, fleshy suctorial lips, and a round, bulbous snout.
Teeth: There are 30-37 rows of small, narrow teeth in the upper jaw, attached to a single cusp. The lower jaw has 25-31 large and smooth teeth rows, resembling a knife.
Body and Coloration: It is long and shaped like a cigar, marked with two small trapezoid-like pectoral fins. They also have two spineless dorsal fins, one located in front of the pectoral fins and the other behind. A large, broad caudal fin is present at the end, while the anal fin remains absent. The scales are concave and raised, and the fins are translucent, except the caudal fin, which is darker.
Overall, cookie-cutter sharks are chocolate-brown, with the underside being lighter. There is a dark collar around the gill regions. Photophores or light-emitting organs are present in the underside except for the collar.
It is pelagic and native to both the Pacific and Atlantic oceans. Specimens were spotted in several places worldwide, including the Bahamas, Japan, Australasia, Mauritius, Southern Brazil, Fiji, South Africa, southern Angola, and near Galápagos, Easter, and Guadalupe Islands.
They inhabit parts of the sea where the water is warm, with a temperature of around 64–79°F (18–26°C).
Due to its unique feeding style, the cookie-cutter shark has a wide variety of prey including cetaceans like dolphins, porpoises, and whales, other sharks such as megamouth sharks, great white sharks, and blue sharks, seals like the leopard seals, fur seals, and elephant seals, stingrays, bony fishes such as dolphinfishes and pomfrets, as well as dugongs. They can even eat an entire squid as big as their own size.
Their exact lifespan remains unrecorded yet, but they may live up to 25 years as per estimations.
These sharks are solitary, only meeting their fellowmates during the breeding season. However, while foraging they have been observed travelling in schools.
The cookie-cutter shark follows diel vertical migration, staying deep underwater below 1000m during the day and coming closer to the surface at about 300m at night.
They swallow teeth that they lose to raise their calcium levels and maintain the development of new teeth.
Cookie cutters have a unique biting technique that helps them acquire food. The sharks attach themselves to their prey with the help of their lips. They then use their lower teeth to extract flesh, 2 inches wide and 7 inches deep, which they hold in place with their upper jaw, leaving behind a circular wound in their victims.
Do they attack humans
Cookie-cutter sharks are generally not deadly to humans due to their small size, but there have been several biting incidences. In 2019, these sharks reportedly attacked three swimmers on separate occasions while they tried to cross the Kaiwi channel. Eric Schall, one of the victims, was severely wounded in his stomach.
Some of the creatures that prey on them include other sharks and bony fish.
Their fleshy lips are large and suctorial, allowing them to attach themselves to their prey.
The tiny, upright upper teeth, and sharp lower teeth forming a saw-like cutting edge, help these sharks tear onto the flesh with ease.
Cookie-cutter sharks have green bioluminescence, stronger than any other known shark, helping to disguise themselves. It accomplishes this through the photophores present in their ventral regions.
These sharks have a huge liver that covers 35% of their weight, letting them stay buoyant, reducing the need to swim constantly.
Unlike most other sharks, their cartilaginous skeleton is calcified, helping them to adjust to deeper waters while foraging for food.
The ganglion cells in the retina are focused concentrically, giving them the ability to focus on their prey.
Dark collar-like bands that taper off are present on both sides of their throat, mimic a small fish’s silhouette luring prey towards them.
Mating and Reproduction
These sharks breed through internal fertilization, which involves the male inserting its claspers into the female’s cloaca to impregnate her.
Like other small sharks, the cookie cutter is oviparous and lays eggs that hatch after 12-22 months. Upon hatching, the young are fully developed and capable of fending for themselves. Males reach sexual maturity when they become 14 inches long, while females do so at 16 inches.
The IUCN lists this species as “LC” or “Least Concern”. These sharks are rarely encountered, are not illegally fished, and seem to have a stable population.
Submarines have sometimes been detected with cookie-cutter bite marks as the latter mistook it for their food. They have even damaged nuclear submarines, exposing cables and rubber sonar domes.