The Smalltooth Cookiecutter Shark is named after the cookie-shaped wounds that it leaves on the bodies of larger animals. It attaches itself to its prey with its suctorial lips and then spins to cut out a cookie-shaped plug of flesh from the larger animal.
Identification of the Cookiecutter shark
The species has a small cigar-shaped body, a conical snout and two low, spineless dorsal fins positioned posteriorly on the body. It is dark brown dorsally, lighter below, and has a distinct dark collar around the gill region. The entire ventral surface, except for the dark collar, is covered in a dense network of tiny photophores, which in life produce an even greenish glow. The genus name Isistius, is derived from Isis, the Egyptian goddess of light.
This species has small, erect teeth in the upper jaw and large triangular teeth in the lower jaw. The appropriately named Largetooth Cookiecutter Shark is the second species in the genus Isistius. The two species can be separated by tooth numbers, colouration and fin positions.
Habitat of the Cookiecutter Shark
They vertically migrate, being found in deep water, probably below 1000 m during the day, and migrating into surface waters at night.
Distribution of the Cookiecutter Shark
Cookiecutter Sharks are recorded from scattered localities around the world. In Australia, they have been recorded from Queensland, New South Wales, Tasmania and Western Australia.
Feeding and diet
The Smalltooth Cookiecutter Shark attaches itself to its prey with its suctorial lips and then spins to cut out a cookie-shaped plug of flesh. Many species show evidence of attacks, including White Sharks.
Widder (1998) suggested that the feeding behaviour of the Smalltooth Cookiecutter Shark may be even stranger than originally thought. The fish is counterilluminated – the ventral light organs make the fish appear darker above and lighter below.
The dark-pigmented collar is not illuminated, so would appear silhouetted against the light from above. The theory suggests that this dark area would look like a small fish from below, and the Smalltooth Cookiecutter Shark would wait for a larger predator to attack the “small fish”. As the predator is about to attack, the Smalltooth Cookiecutter Shark would turn and attack the attacker. The forward motion of the larger animal may even assist the Smalltooth Cookiecutter Shark in removing a plug of flesh.
In addition to plugs of flesh from larger animals, the Smalltooth Cookiecutter Shark is also known to eat squid. There are even reports of this species leaving crater marks on the sonar domes of submarines.