Cookiecutter Shark - Biology and Ecology

Biology and Ecology

Best known for biting neat round chunks of tissue from marine mammals and large fish, the cookiecutter shark is considered a facultative ectoparasite, as it also wholly ingests smaller prey. It has a wide gape and a very strong bite, by virtue of heavily calcified cranial and labial cartilages. With small fins and weak muscles, this ambush predator spends much of its time hovering in the water column. To maintain neutral buoyancy, its liver, which can comprise some 35% of its weight, is rich in low-density lipids. As this species has higher skeletal density than Euprotomicrus or Squaliolus, its body cavity and liver are proportionately much larger, and the oil content is much higher. Its large caudal fin allows for a quick burst of speed to catch larger, faster prey that come in range.

The cookiecutter shark regularly replaces its teeth like other sharks, but sheds its lower teeth in entire rows rather than one at a time. A cookiecutter shark 14 cm (5.5 in) long has been calculated to have shed 15 sets of lower teeth by the time it is 50 cm (20 in) long, totaling 435–465 teeth. This represents a significant investment of resources and is probably why the old sets of teeth are swallowed, so that the shark can recycle the calcium content. Unlike other sharks, the retina of the cookiecutter shark has ganglion cells concentrated in a concentric area rather than in a horizontal streak across the visual field; this may help to focus on prey in front of the shark. This shark has been known to travel in schools, which may increase the effectiveness of its lure (see below), as well as discourage counterattacks by much larger predators.