An Open Water Swimmer’s Nightmare: the Cookiecutter Shark
By Veronica Becerra and David McGuire, Shark Stewards (Image FAO)
22, March 2023
There are over 450 described species of sharks, yet many still lurk in the depths or in the back of museum collections, as yet unknown or undescribed. For example, a new shark, the recently identified catshark (Scyliorhinus hachijoensis sp. nov), has been described as a different subspecies in 2022 by morphological details, and confirmed by nucleotide sequence analysis of three mitochondrial DNA regions. This small shark, hails from the islands of Mikurajima, Hachijojima, and Torishima in southeastern Japan. It was lumped in as a single species with S. hachijoensis before DNA sequencing confirmed it as a unique subspecies. Other sharks, like the deep-water megamouth shark was unknown to science until 1976, when it was fished up at the end of an anchor by the US Navy in Honolulu. This large, filter feeding shark lives across the globe with a pan-tropical distribution, yet even today, fewer than 300 specimens have been recorded. There is a lot we do not know about how sharks are related, their natural history, and especially their behavior!
One shark, a strange species of dogfish, the cookiecutter shark, (Isistius brasiliensis) is invisible to daytime surface dwellers. Their behavior is poorly known, but it does leave a tell-tale signature bite mark.
First discovered during an exploratory voyage between 1817-1820 by French naturalists Jean René Constant Quoy and Joseph Paul Giamard, the cookiecutter shark is one of the more bizarre species of shark to rise from the depths.
Cookiecutter shark jaws, quite specialized for an unusual feeding method. Specimen caught during trawl operations during OES1104 (Integrated Ecosystem Assessment survey; Chief Scientist Evan Howell, summer 2011) aboard the NOAA vessel Oscar Elton Sette. Photo by Don Kobayashi, NOAA / PIFSC.
Quoy and Gaimard’s discovery
Circa 1817, Jean René Constant Quoy and Joseph Paul Gaimard, set sail as ship’s doctors and naturalists aboard an exploratory voyage on the vessel S.M. Uranie. While off the coast of Brazil, the two naturalists encountered an odd specimen of shark in which they named Symnus brasiliensis (after the coast in which they found it) in their published account of the voyage in 1824. However, it wasn’t until 1865 when American Ichthyologist, Theodore Nicholas Gill, created a new genus for the species, Isistius (after Isis, the Egyptian goddess of light).
The cookiecutter’s hunting habits are equally as odd as this member of the Dogfish family’s (Dalatidae) strange appearance. Though small in size, the shark will typically go after medium to large size fish or mammals including other sharks, tuna, and seals. The cookiecutter shark will attach itself to its host, turn its body in a circle and removing a plug of flesh, leaving a signature scar on its victim and earning its name. This shark latches on with its upper teeth, using its lower teeth to “suck and scoop” out the flesh. The tell-tale scar of the cookiecutter shark is observed on whales, sealions and dolphins. Since the host escapes without mortality, this shark is considered a parasite and not a predator. The dentition is unique. The upper teeth are individual like other sharks, but the bottom tooth is a single is an integrated saw-like tooth that falls out whole. Interestingly, the cookiecutter shark is the only shark that sheds all its teeth simultaneously, and is also known to swallow its own teeth. Like other sharks, the cookiecutter loses and regrows its teeth regularly, however, scientists believe that they swallow their own teeth as a recycled source of calcium.
The cookiecutter, also known as the cigar shark, has an unusual anatomy with a short conical snout, unique mouth and suction lips. The eyes are set forward close to the front of the head which is different from the typical shark whose eyes are on the opposite sides of the shark’s snout. It has an elongated fusiform body shape, giving it the moniker cigar shark. These sharks are typically brown in color with an even darker brown collar. The dark patch of the throat, contrasting against the glow of the underside, is thought to appear like a small fish when viewed from deeper waters. Interestingly, this species of shark is also known to have photophores, a light producing organ present in many bioluminescent fish.
While female cookiecutters can grow up to 22 in (56 cm), the males are only reach 16.5 inches (42 cm). This species of shark is ovoviviparous, meaning they give live-birth from eggs that hatch and develop internally. Litter size is typically between 6-12 pups. Like many deepwater species, not much is known about their birthing sites or where the pups forage and develop.
Where do they live?
These sharks have a broad geographical range and are observed mostly around the eastern Pacific and Indo-Pacific ocean, and found off the coasts of equatorial, and oceanic islands. They have also been recorded around Mauritius, and in temperate waters off New Zealand, and Japan. The cookiecutter is rarely observed due to its tendency to dwell in deep waters more than 1000 m down during the day. They rise vertically to feed 300 m to feed, although they are also known to enter the shallow photic zone up to the surface at night. It’s believed that the shark uses its bioluminescence as a form of aggressive mimicry, where the shark will imitate the appearance of a harmless species, attracting and tricking would-be predators that become the cookiecutter’s prey.
Although not fatal, the cookiecutter shark exhibits an especially gruesome kind of bite, leaving symmetrical crater wounds on the surfaces of larger fishes, open-water swimmers, other sharks, and sometimes drowning victims. These wounds bleed profusely and heal slowly and are quite painful, although attacks on humans are extremely rare.
The first description of an incident involving a cookiecutter shark occurred on March 16, 2009 after sunset, when one bit a long-distance swimmer attempting to cross the Alenuihaha Channel from Hawaii to Maui. The Florida Museum International Shark Attack File (ISAF) lists two other incidents involving cookiecutters, both judged to be inflicted post-mortem. An unusually rare event occurred during daylight in 2017 in shallow waters when a 7 year old boy was bitten on the calf while snorkeling in North Queensland Australia. According to records maintained by ISAF, 2019 was the year of the cookiecutter shark. This species was responsible for three of the 64 global attacks in 2019. All three bites were on long-distance swimmers training in Hawaii’s Ka’iwi Channel at night.
The cookiecutter shark is killed as occasional bycatch in oceanic trawl and longline fisheries, including mid-water trawls. Given that its is not a targeted fishery, and the species is broadly distributed, it is assessed by the IUCN as Least Concern.
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