The unique cookiecutter shark, Part II
Marks made by cookiecutter sharks have been found on a wide variety of marine mammals and fishes, as well as on submarines, undersea cables and even human bodies. Though rarely encountered because of its oceanic habitat, there are a handful of documented attacks on humans that were apparently caused by cookiecutter sharks.
Similar reports have come from shipwreck survivors of suffering small, clean, deep bites during nighttime. In March 2009, Maui resident Mike Spalding was bitten by a cookiecutter shark while swimming across the Alenuihaha Channel. Nevertheless, this diminutive shark is not regarded as highly dangerous.
One of the earliest accounts of the wounds left by the cookiecutter shark on various animals is in ancient Samoan legend, which held that atu (skipjack tuna) entering Palauli Bay would leave behind pieces of their flesh as a sacrifice to Tautunu, the community chief. In later centuries, various other explanations for the wounds were advanced, including lampreys, bacteria and invertebrate parasites.
In 1971, Everet Jones of the U.S. Bureau of Commercial Fisheries (a predecessor of the National Marine Fisheries Service) discovered that the cigar shark, as it was then generally known, was responsible.
Shark expert Stewart Springer thus popularized the name “cookiecutter shark” for this species, though he originally called them “demon whale-biters.” Other common names used for this shark include luminous shark, smalltooth cookiecutter shark and smooth cookiecutter shark.
Cookiecutter sharks have adaptations for hovering in the water column and likely rely on stealth and deception to capture prey that is more active. It is an ambush predator. This shark feeds on larger pelagic animals such as mahi, wahoo (ono), tuna, billfishes and marine mammals. It is a facultative ectoparasite, which means that it feeds on the flesh of other species, causing them harm but not death, and it is not dependent on these species for survival.
The name “cookiecutter shark” refers to its feeding habit of gouging round plugs, like a cookie cutter, out of larger animals. The shark first secures itself to the body surface of its prey by closing its spiracles (breathing holes) and retracting its basihyal (tongue) to create negative pressure; its suctorial lips ensure a tight seal. It then bites, using its narrow upper teeth as anchors and its bandsaw-like set of lower teeth. The suctorial lips and large lower teeth are adaptations for its parasitic lifestyle.
The action of the lower teeth may also be assisted by back-and-forth vibrations of the jaw, a mechanism akin to that of an electric carving knife. This shark’s ability to create strong suction into its mouth is useful in capturing smaller prey such as squid. Finally, the shark twists and rotates its body to complete a circular cut, quite possibly aided by the initial forward momentum and subsequent struggles of its prey.
The mouth is short, forming a nearly transverse line, and is surrounded by enlarged, fleshy, suctorial lips. It has a wide gape and a very strong bite by virtue of heavily calcified cranial and labial cartilages.
There are 30-37 tooth rows in the upper jaw and 25-31 tooth rows in the lower jaw, increasing with body size. The upper and lower teeth are extremely different. The upper teeth are small, narrow and upright, tapering to a single, smooth-edged cusp. The lower teeth are also smooth-edged but much larger, broader and knife-like, with their bases interlocking to form a single saw-like cutting edge.
The cookiecutter shark regularly replaces its teeth like other sharks, but sheds its lower teeth in entire rows rather than one at a time. It has been calculated that a cookiecutter shark 14 centimaters (5.5 inches) long would have shed 15 sets of lower teeth by the time it is 50 centimeters (20 inches) long, totaling 435-465 teeth.
This represents a significant investment of resources, and it’s probably why the old sets of teeth are swallowed so that the shark can recycle the calcium content.