Goblin shark
The goblin shark is a rare species of deep-sea shark. Sometimes called a "living fossil", it is the only extant representative of the family Mitsukurinidae, a lineage some 125 million years old. This pink-skinned animal has a distinctive profile with an elongated, flattened snout, and highly protrusible jaws containing prominent nail-like teeth. It is usually between long when mature, though it can grow considerably larger. Goblin sharks inhabit upper continental slopes, submarine canyons, and seamounts throughout the world at depths greater than, with adults found deeper than juveniles.
Various anatomical features of the goblin shark, such as its flabby body and small fins, suggest that it is sluggish in nature. This species hunts for teleost fishes, cephalopods, and crustaceans both near the sea floor and in the middle of the water column. Its long snout is covered with ampullae of Lorenzini that enable it to sense minute electric fields produced by nearby prey, which it can snatch up by rapidly extending its jaws. Small numbers of goblin sharks are unintentionally caught by deepwater fisheries. The International Union for Conservation of Nature has assessed it as Least Concern, despite its rarity, citing its wide distribution and low incidence of capture.
Taxonomy
American ichthyologist David Starr Jordan described the goblin shark in an 1898 issue of Proceedings of the California Academy of Sciences, recognizing the peculiar fish not only as a new species, but also a new genus and family. He based his account on an immature male long caught in Sagami Bay near Yokohama, Japan. The specimen had been acquired by shipmaster and naturalist Alan Owston, who had given it to Professor Kakichi Mitsukuri at the University of Tokyo, who in turn had brought it to Jordan. Thus, Jordan named the shark Mitsukurina owstoni in honor of these two men.The generic name honors Keigo Mitsukuri, a Japanese zoologist who studied at University College London during the 1860s. The specific name honors Alan Owston, an English collector of Asian wildlife. The common name "goblin shark" is a translation of its old Japanese name tenguzame, a tengu being a Japanese mythical creature often depicted with a long nose and red face. Another name for this species is elfin shark.
Soon after Jordan's description was published, several scientists noted the similarity between Mitsukurina and the extinct Mesozoic shark Scapanorhynchus. For a time, the prevailing opinion was to treat Mitsukurina as a junior synonym of Scapanorhynchus. Eventually, more complete fossils revealed many anatomical differences between Scapanorhynchus and Mitsukurina, causing modern authors to again regard them as distinct genera. Several goblin shark specimens were described as separate species from 1904 to 1937, none of which are now considered valid. This taxonomic confusion began because the specimens' jaws were fixed at varying degrees of protrusion during preservation, giving the appearance of proportional differences among the heads.
Phylogeny and evolution
studies based on morphology have generally classified the goblin shark as the most basal member of the order Lamniformes, known as mackerel sharks. Studies using genetic data have also confirmed a basal classification for this species. The family Mitsukurinidae, represented by Mitsukurina, Scapanorhynchus, and Anomotodon, dates back to the Aptian age of the Cretaceous period. Mitsukurina itself first appears in the fossil record during the period Middle Eocene ; extinct species include M. lineata and M. maslinensis. Striatolamia macrota, which lived in warm shallow waters during the Paleogene period, may also be a Mitsukurina species. As the last member of an ancient lineage, and one that retains several "primitive" traits, the goblin shark has been described as a "living fossil".Description
The goblin shark has a distinctively long and flat snout, resembling a sword blade. The proportional length of the snout decreases with age. The eyes are small and lack protective nictitating membranes; behind the eyes are spiracles. The large mouth is parabolic in shape. The jaws are very protrusible and can be extended almost to the end of the snout, though normally they are held flush against the underside of the head. It has 35–53 upper and 31–62 lower tooth rows. The teeth in the main part of the jaws are long and narrow, particularly those near the symphysis, and are finely grooved lengthwise. The rear teeth near the corners of the jaw are small and have a flattened shape for crushing. Much individual variation of tooth length and width occurs, as for whether the teeth have a smaller cusplet on each side of the main cusp, and regarding the presence of toothless gaps at the symphysis or between the main and rear teeth. The five pairs of gill slits are short, with the gill filaments inside partly exposed; the fifth pair is above the origin of the pectoral fins.The body is fairly slender and flabby. The two dorsal fins are similar in size and shape, both being small and rounded. The pectoral fins are also rather small and rounded. The pelvic and anal fins have long bases and are larger than the dorsal fins. The caudal peduncle is flattened from side-to-side and lacks keels or notches. The asymmetric caudal fin has a long upper lobe with a shallow ventral notch near the tip, and an indistinct lower lobe. The soft, semitranslucent skin has a rough texture from a covering of dermal denticles, each shaped like a short upright spine with lengthwise ridges. Living sharks of this species are pink or tan due to visible blood vessels beneath the skin; the color deepens with age, and young sharks may be almost white. The fins' margins are translucent gray or blue, and the eyes are black with bluish streaks in the irises. After death, the coloration fades quickly to dull gray or brown. Adult sharks usually measure between long. However, the capture of an enormous female estimated at long during 2000 showed this species can grow far larger than suspected previously. The maximum weight recorded is for a 3.8-m-long shark.
Distribution and habitat
The goblin shark has been caught in all three major oceans, indicating a wide global distribution. In the Atlantic Ocean, it has been recorded from the northern Gulf of Mexico, Suriname, French Guiana, and southern Brazil in the west, and France, Portugal, Madeira, and Senegal in the east. It has also been collected from seamounts along the Mid-Atlantic Ridge. In the Indo-Pacific and Oceania, it has been found off South Africa, Mozambique, Japan, Taiwan, Australia and New Zealand. This species has been recorded from off East Cape to Kaikoura Canyon and from the Challenger Plateau near New Zealand. A single eastern Pacific specimen is known, collected off southern California. This species is most often found over the upper continental slope at depths of. It has been caught as deep as, and a tooth has been found lodged in an undersea cable at a depth of. Adults inhabit greater depths than juveniles. Immature goblin sharks frequent the submarine canyons off southern Japan at depths of, with individuals occasionally wandering into inshore waters as shallow as. On the 19 April 2014 fishermen in Key West, Florida, while fishing in the Gulf of Mexico, caught a goblin shark in their fishing net, only the second one ever to be caught in the Gulf. The shark was photographed and released back into the water.During July 2014, a goblin shark was found in a fishery net in Sri Lanka, near the eastern coast of Sri Lanka. The shark was about long and weighed about. The shark was given to the NARA for further research.
Biology and ecology
Although observations of living goblin sharks are scant, its anatomy suggests its lifestyle is inactive and sluggish. Its skeleton is reduced and poorly calcified, the muscle blocks along its sides are weakly developed, and its fins are soft and small. Its long caudal fin, held at a low angle, is also typical of a slow-swimming shark. The long snout appears to have a sensory function, as it bears numerous ampullae of Lorenzini that can detect the weak electric fields produced by other animals. Due to the snout's softness, it is unlikely to be used for stirring up prey from the bottom as has been proposed. Vision seems to be less important than other senses, considering the relatively small optic tectum in the shark's brain. Yet unlike most deep-sea sharks, it can change the size of its pupils, thus probably does use its sight in some situations. Goblin sharks may be the prey of blue sharks. Parasites documented from this species include the copepod Echthrogaleus mitsukurinae, and the tapeworms Litobothrium amsichensis and Marsupiobothrium gobelinus.Feeding
The goblin shark feeds mainly on teleost fishes such as rattails and dragonfishes. It also consumes cephalopods and crustaceans, including decapods and isopods. Garbage has been recorded from the stomachs of some specimens. Its known prey includes bottom-dwelling species such as the blackbelly rosefish, and midwater species such as the squid Teuthowenia pellucida and the ostracod Macrocypridina castanea rotunda. Thus, the goblin shark appears to forage for food both near the sea floor and far above it.Since it is not a fast swimmer, the goblin shark may be an ambush predator. Its low-density flesh and large oily liver make it neutrally buoyant, allowing it to drift towards its prey with minimal motions so as to avoid detection. Once prey comes into range, the shark's specialized jaws can snap forward to capture it. The protrusion of the jaw is assisted by two pairs of elastic ligaments associated with the mandibular joint, which are pulled taut when the jaws are in their normal retracted position; when the shark bites, the ligaments release their tension and essentially "catapult" the jaws forward. At the same time, the well-developed basihyal on the floor of the mouth drops, expanding the oral cavity and sucking in water and prey. Striking and prey capture events were videotaped and recorded for the first time during 2008 and 2011 and helped to confirm the use and systematics of the protrusible jaws of goblin sharks. The video evidence suggests that while the jaws are definitely unique, goblin sharks use ram feeding, a type of prey capture that is typical of many mackerel sharks. What makes the goblin shark unique is the kinematics of their jaw when feeding. The lower jaw seems to undergo more complex movements and is important in capturing the prey. The measured protrusions of the upper and lower jaw combined put the goblin shark jaws at 2.1–9.5 times more protrusible than other sharks. The lower jaw has a velocity about two times greater than the upper jaw because it not only protrudes forward, but also swings upward to capture the prey, and the maximum velocity of the jaws is 3.14 m/s. The goblin shark has a re-opening and re-closing pattern during the strike, a behavior that has never been seen in other sharks before and could be related to the extent with which the goblin shark protrudes its jaws. This “slingshot” style of feeding could be an adaptation to compensate for poor swimming ability by allowing the goblin shark to catch elusive, fast prey without having to chase the prey.