Spending day-time in deep waters between 1000 and 3700 meters deep/ 3280– 12139 feet deep, it is difficult to get first-hand information from cookiecutter sharks in the wild, as very few have been recorded alive. Due to this, most of the information we have about their feeding mechanism comes from inflicted wounds and jaw analysis of dead specimens.
What Do Cookiecutter Sharks Eat?
What we know is that a cookiecutter shark’s menu is diverse: dolphins, pinnipeds, orcas, great white sharks, swordfish and many other species have been spotted with shark-inflicted crater-shaped wounds on their body.
How is it that such massive ocean animals repeatedly fall prey to such tiny sharks, and which technique used by the cookiecutter shark makes it such an efficient predator?
Tiny, But Efficient Preditors
It has been discovered that cookiecutter sharks undergo a vertical migration everyday, one of the longest in the animal kingdom, to take advantage of the presence of wildlife near the surface. Here, they can make the best use of their bioluminescence, the strongest one out of any shark, in order to lure animals bigger than themselves. They use the so-called counterillumination technique, which is a camouflaging technique used by many other marine animals, such as a lanternfish, the lucifer shark and a variety of squid (and even has been prototyped on military planes & ships), during which light is produced by photophores on the animals underside in order to hide its dark silhouette from predators underneath.
The cookie-cutter sharks collar being the only non-bioluminescent part of its underside, it is believed that it acts as lure mimicking a smaller fish, attracting animals which the shark can prey on.They sometimes travel in schools, which may increase the effectiveness of its lure, mimicking a fish school. With the help of their large caudal fin, which allows for short speed bursts, they are able to surprise larger prey and bite them before they get caught.
But which unique anatomical features allows it to leave such distinguishable, round wounds on its prey?
Cookiecutter Shark Jaws
Such a unique technique needs specialised equipment: the cookiecutter shark’s jaw is highly specialised and perfect for this parasitic feeding method. It consists of two very different sets of teeth: the upper jaw consists of 21-31 small, hook-like teeth who serve the purpose of holding firmly onto the prey. The 30-37 upper teeth are much bigger, sharper and of triangular shape. It is with these teeth the shark cuts its cookiecutter shaped bite, rotating its body in order to complete the circular cut. Remember each of these teeth evolved to fuse together at their base, which likely makes them more resistant during these attacks.
The cookiecutter shark also has the largest teeth-to-body ratio out of all sharks. The very strong cartilage in its skull and lips are another of the many adaptations that create a strong bite. Other specializations, such as closing the spiracles (small openings behind the eyes that help some species breathe by drawing water into the gills when the shark is at rest) and retracting the tongue to create a low pressure, and sealing it off with the suction mechanism of their large, fleshy lips. Such bites, while not deadly, can seriously injure if the sharks attack in a group. It is not rare to find animals with multiple scars, such as an unfortunate dolphin which has been found with a dozen of such wounds on its body!
However, cookiecutter sharks don’t use all of this complex weaponry to only hunt for megafauna chunks. As a matter of fact, most of the shark’s diet consists of smaller fish and squid. The technical term for this is adaptive ectoparasite, meaning it doesn’t rely entirely on a parasitic lifestyle, but also on a more traditional hunting technique for which its specialised teeth can also be used for.
Written by Emmanuel Ballif.