It’s easy to accept that sharks, an order of animals with more than 440 described species, must be diverse in shape, size, and behavior. Indeed, a cartilaginous skeleton is one of the only characteristics all sharks share; the rest is up to nature’s creativity. Some sharks act and look completely different than the stereotypical torpedo-shaped predator we imagine zooming around the reef after hapless fish. Below are a couple details on some of the most un-“shark-like” sharks in the ocean.
Dwarf Lantern Shark
At a maximum length of around 20 centimeters, the dwarf lantern shark is the world’s smallest shark. Most specimens fit upon a human hand. Dwarf lanterns have only been observed a few times, and live at depths greater than 250 meters in the Caribbean Sea.[i] However, they belong to a wider family of 28 deep-sea lantern sharks, some of which are easier to study. Within this family, scientists have found relatively high diversity and many interesting traits, such as pack-hunting behavior and hermaphrodism.[ii]
All lantern sharks enjoy bioluminescence- the ability to produce light. Bioluminescence is a common survival and hunting strategy in the deep sea, used either to attract prey, distort one’s silhouette, or recognize one’s own species. When dwarf lantern sharks are near the surface, for example, they use photophores (light-producing organs) on their bellies to help them blend in with sunlight streaming down; a predator below them can’t distinguish between the lantern shark’s body and the sunrays.[iii] Some lanternsharks even carry photophores on the sharp spines of their backs, perhaps so predators can see how painful it would be to swallow them.[iv]
These sharks may be small, with a maximum length of 50 centimeters, but they would fit better in a horror movie than great whites or hammerheads. Imagine a cookie, not of gingerbread or oatmeal, but of fish flesh, neatly sawed into a thick, perfectly circular patty. This “fish cookie” is the main dish of the parasitic, morbidly-named cookiecutter shark. Cookiecutters, or Isistius brasiliensis, are fearless predators of whales, seals, tuna, squid, and other sharks, but they never kill their prey. Instead, they hook on to the bigger animal with suction-specialized lips and saw out a circle of flesh with their oversized lower teeth. These lower teeth function as a unit, and are replaced as a unit as well, so the shark is never without a fully stocked and sharpened “saw-jaw.”
Cookiecutter sharks also use bioluminescence to attract their prey. Some scientists have recently proposed that the pattern of photophores on the sharks’ bellies makes them look smaller than they are- perhaps as a way to lure big fish into suction-and-saw range. Because cookiecutters participate in the daily vertical migration of deep-sea creatures toward and away from the ocean surface, they get the chance to feast on a huge range of animals. Some anecdotal evidence even recounts cookiecutter attacks on humans.[v]
Greenland sharks may be one of the better-known strange sharks, but scientists still can’t agree on the facts. We know that they look perfectly at home in an Arctic habitat, where their mottled, gray skin camouflages with rock and ice, but while they usually inhabit waters around Greenland and northern Canada, reported sightings in Scotland, France, and as far south as Florida, USA, have brought even the simple question of range into dispute.[vi] Greenland sharks are commonly called the world’s slowest sharks, cruising between 1 and 3.5 kilometers per hour. This leisurely swimming speed has only added to the shark’s mystery, since its stomach contents often include fast-swimming prey like seals and powerful creatures like reindeer and polar bear. To explain this discrepancy, scientists have concluded that Greenland sharks usually scavenge for dead animals. However, some maintain that even slow Greenland sharks can speed up when they want to catch something.[vii]
Another controversy revolves around the eyes of Greenland sharks. Their eyes are often infested with parasitic copepods (shrimp-like creatures) which cause partial or full blindness. Some scientists believe that the copepods are bioluminescent and attract prey for the shark. Others disagree, saying such a mutual relationship has never been proven. Further controversy centers on the “corkscrew killer” phenomenon near Nova Scotia, Canada. When dead seals started washing ashore with flesh spirally stripped from one half of their bodies, some pointed to Greenland sharks, asserting that the sharks were ambushing seals at their ice holes. However, other researchers say these “ambushes” have never been observed, and hypothesize that the seals were sliced up by the propellers of local boats.[viii]
Perhaps the most incredible fact about Greenland sharks is their age. In 2016, scientists established that Greenland sharks are the longest-living vertebrates on Earth. The oldest specimen they examined was a 400 year old female shark; the former record-holder was a 211 year old bowhead whale. It seems that Greenland sharks don’t even reach maturity until they are 150 years old. This news has dire implications for conservation management; we need to make sure that the sharks are not accidentally or intentionally caught before they reproduce.[ix]
Megamouth sharks are one of the most mysterious animals on the planet. The first sighting of these dinosaur-like fish, with their huge jaws and rubbery lips, was recorded in 1976; since then, only 16 additional specimens have been observed. Most of the 17 megamouths were already dead when scientists accessed them, whether from stranding or accidental fishing capture. That’s why one satellite tag, placed on a megamouth for two days in 1990, is so momentous; it’s almost the only information we have about megamouth shark behavior.
Though they reach 4 or 5 meters at maturity, megamouths are the smallest of the plankton-eating sharks (the largest of which is the whale shark). As its name indicates, the megamouth has a huge mouth and head in relation to the rest of its body. The 1990 tag tracked a megamouth migrating vertically from around 130 meters during daylight hours to a shallow 15 meters at night. Scientists hypothesize that it was following the rise and fall of plankton like many other plankton-eating creatures.
The frilled shark is barely recognizable as a shark. Its eel-like body is elongated and measures up to 2 meters with almost no visible fins, and the blunt head looks more like a lizard than a fish. In the inky black of the deep ocean (down to 1500 meters), frilled sharks hunt squid and other slippery prey with their 300 needle-sharp, hooked teeth. Their name derives from the frilly borders of their gills, as well as a frilly collar around the base of the head.
As scientists slowly gathered information about this deep-sea dweller, they uncovered an incredible fact: frilled shark females in a Japanese population were found to gestate for 3.5 years! This makes frilled shark pregnancies the longest of any vertebrate in the world. Such long pregnancies are made possible by the freezing cold of the deep sea, which slows down metabolism and all other life processes. A female’s body is longer than a male’s in order to make room for up to 6 shark pups at a time.[x]
The goblin shark may be one of the most grotesque animals on earth. It has a relatively flabby, pink body, colored not by dermal pigment, but by the sheen of oxygenated capillary blood under translucent skin. Its claim to fame, however, is its horn-like snout and projectile jaw. The snout of a goblin shark extends from the front of its eye like a flattened, blade-like unicorn horn. Its jaws lie neatly tucked away underneath the snout until the shark strikes its prey; then, both jaws pop forward and clamp down with fang-like teeth.
Besides its unnerving and dramatic jaw projection and generally alien appearance, the goblin shark is not intimidating. It grows to around 1.6 meters average length. It’s also relatively slow and lives at 60 to 280 meters depth, though we know it can descend to 1200 meters as well. Most specimens are found through accidental capture by Japanese fisheries. [xi]
Once one starts to delve into such a diverse group of animals, there are intriguing creatures around every corner. Sharks deserve to be known for more than “Jaws,” and spreading the word about strange sharks can also spread fascination and care. Many of these strange sharks are classified as “data-deficient” by the IUCN (International Union for Conservation of Nature); because of their deep-sea habitats, it’s hard for us to study them and figure out how human activity is impacting their populations. The best way to protect shark diversity is to convince governments and fisheries to tread lightly into the unknown. This way, we can preserve the mysteries that are here now, and those that are waiting to be discovered.
Cover photo By © Citron /, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11142485
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