Why are cookiecutter sharks called that?

Next to a great white shark, its cookiecutter cousin looks like a piece of cake. Better-known shark species like the great whites and tiger sharks dwarf the cookiecutter shark that maxes out around 20 inches (50 centimeters) of length. Judging by its brown, slender profile, a cookiecutter looks almost docile, sometimes referred to as a "cigar fish" because of its brown body.

Shark Image Gallery

These small sharks reside in the deep sea, around 11,500 feet (3,500 meters) below the surface [source: ReefQuest Centre for Shark Research]. At night, however, they migrate toward the top of the water where they find their meals. Mostly calling tropical and subtropical waters home, cookiecutter sharks have been spotted in the Pacific and Atlantic Oceans, as well as the Caribbean Sea and Amazon River [source: ReefQuest Centre for Shark Research].

Get a load of that grin! Cookiecutter sharks leave cookie-shaped bite mark in their victims.
Bill Curtsinger/Getty Images

But the diminutive name and size belie this shark's bite. As soon as you see a cookiecutter shark's smile, you immediately understand how it upholds the shark family reputation associated with ferocious hunting. Surrounded by relatively large, flabby lips, the cookiecutter's mouth houses a formidable set of pearly whites. On the top, 30 to 37 teeth stretch across like a set of dentures, and 25 to 31 larger ones extend along the bottom.

Equipped with weak fins and a puny body, cookiecutter sharks wouldn't make successful predators. Instead, they are the only parasitic fish in the shark family that feed off hunks of flesh ripped out of larger fish [source: Parker]. The bites don't kill their hosts, but are enough to satisfy the small sharks' appetites.

Cookiecutter sharks get their name from the almost perfectly round, cookie-shaped wound they leave on their victims. Think of the cookiecutter shark as the Zorro of the sea, slashing its signature marks onto foes that generally include marlin, dolphin, tuna, stingrays, seals and other sharks [source: Florida Museum of Natural History]. Some fish scientists even suspect that cookiecutter sharks have taken bites out of almost every tropical sea dweller [source: ReefQuest Centre for Shark Research].

How Cookiecutter Sharks Hunt

Cookiecutter sharks are one of many species of bioluminescent fish in the sea. Bioluminescence means their bodies glow. Among sharks, cookiecutters glow the brightest [source: Parker]. In fact, its scientific name Isistius brasiliensis comes from the Greek goddess Isis, the goddess of light [source: ReefQuest Centre for Shark Research].

Bioluminescence occurs in cookiecutter sharks because of the presence of photopores glands, particularly concentrated on its lower belly. These glands produce an enzyme called luciferose that converts chemical energy to light energy, causing the glow. Transparent cells surrounding the glands also allow the light to shine through the cookiecutter shark's skin [source: Parker].

Since the shark swims closer to the surface of the water at night, predator fish will see it from below. From this vantage point, the glowing belly of the cookiecutter shark looks like a spot of sunlight or moonlight shining through the water. That perspective makes the luminous part of its body virtually invisible to predators. Other fish aside from cookiecutters also practice this camouflage called counterillumination [source: Milius].

However, one wide stripe around the cookiecutter shark's neck does not glow. Fish can distinguish that non-glowing part, which may seem like an evolutionary pitfall. But this is actually the cookiecutter shark's trump card. Because the rest of its body is camouflaged by the bioluminescence, to other fish, it looks like the cookiecutter's body only consists of that small portion around its head and neck. Since it appears much smaller than it is, the shark attracts predator fish looking for an easy snack. By luring the fish to come to it, the cookiecutter then has more power to bite them than if it tried to use its feeble strength to approach [source: Milius].

Once the predator goes in for the kill, the shark whips around and latches on to its opponent's flesh with the suction power from its fleshy lips. Digging its razor-sharp teeth into fish, the cookiecutter shark then spins its body around, carving out a cookie-shaped lump of meat like a wild melon baller. After the cookiecutter shark has taken its fill, it releases the fish. Fish can usually survive a cookiecutter attack, but the wound may fester or become infected.

To keep them primed for attacks, cookiecutter sharks periodically lose their teeth. Their interconnected chompers fall out as a unit like dentures. When that happens, cookiecutters actually swallow their teeth to absorb the extra calcium [source: Florida Museum of Natural History].

If you'd like to learn more about cookiecutters and their shark family members, see the links on the next page.

Why are cookiecutter sharks called that?

How Cookiecutter Sharks Hunt

Lots More Information

Related HowStuffWorks Articles:

More Great Links: