Biology of the Goblin Shark
(Mitsukurina owstoni)
| Field Marks | Snout greatly elongated and flattened, forming a dagger-like blade; jaws highly protrusible; teeth slender and fang-like, without lateral cusplets; body flabby with soft skin; ventral lobe of caudal fin not developed; anal fin large and broadly rounded. Color in life pinkish-grey. |
| Size | Length at birth unknown (smallest free-swimming specimen was 42 in [107 cm] long ); average length about 5 ft (1.6 m); largest on record is a 12.6-ft (3.8-m) long male, females may grow even larger. |
| Range | Widely but patchily distributed; about half of known specimens from Sagami and Suruga Bays, Japan, most of the remainder from Kaikura, New Zealand, and southern Africa; a substantial population apparently occurs off Madeira. |
| Habitat | Demersal to mesopelagic inhabitant of outer continental shelves and slopes; known depth range is 130 to 3 940 ft (40 to 1 200 m); most individuals have been caught off Honshu, Japan, at depths of 200 to 920 ft (60 to 280 m); there is curious record of a 42-in (107-cm) specimen supposedly netted near the mouth of the Murray River, South Australia, but there is some doubt about its capture locality. |
| Feeding | Records of stomach contents are rare; known prey includes small mesopelagic teleosts; myodocopid ostracods and a juvenile cranchiid squid (both of species known to be vertical migrators), and an unidentified crab. Apparently sluggish, feeding in mid-water and possibly on or near the bottom (teeth have been found embedded in submarine cables), probably using the electrosensitive rostrum to detect prey and capturing it from close range using a combination of protrusible jaws and pharyngeal suction. |
| Reproduction | Almost certainly ovoviviparous, as in other lamnoids; no pregnant specimen has been collected, thus no data available on gestation period, number of pups, pupping season, or nursery grounds. |
| Age & Growth | Males are immature to 7.5 ft (2.3 m), one 12.6-ft (3.8-m) specimen had sperm in the seminal vesicles and calcified claspers, indicating probable maturity; no data on size at maturity in females. No data on growth rate, age at maturity, or longevity for either sex. |
| Danger to Humans | Probably minimal. |
| Utilization | Minimal; apparently fished commercially off Japan and sporadically taken as bycatch while deep-sea longlining for scabbardfish (Trichiuridae) off Portugal. Elsewhere, taken primarily as bycatch of deep-water trawls and occasionally with deep-water longlines, deep-set gill nets, and possibly purse seines. Utilized dried salted. |
| Remarks | Although probably common, this species is rarely seen and is thus poorly known; catches should be preserved and reported. |
By any standard, the Goblin Shark is a bizarre creature. Growing to a length of over 10 feet (3 metres), it has a soft, flabby body, is colored bubblegum pink, and has a peculiar, blade-like snout overhanging long, highly protrusible jaws bristling with slender, fang-like teeth. This species is usually depicted with its jaws fully extended, resembling a forceps-jawed, snaggle-toothed demon wearing a papal mitre. One would expect that any specimen of this weird shark turning up anywhere on the planet would be as instantly recognizable as would a stegosaur. But, with the exception of serious shark enthusiasts, few people have ever heard of let alone anticipated encountering such a piscine gargoyle.
The Goblin Shark is generally regarded as being quite rare. Only about 45 Goblin Sharks have been described in the scientific literature. Over half of them (25 specimens) were taken off the coast of Japan, with most of the others from off New Zealand (6) and southern Africa (4). The remaining ten or so known Goblin Shark specimens came from scattered locations around the globe. Yet our planet is shrinking at an alarming rate. With modern telecommunications technologies such as fax-modems, the Internet, e-mail, and special-interest list-severs becoming ever more widespread, it is increasingly unlikely that rare or unusual sharks will go unreported, no matter where they turn up. But sometimes the unprecedented turns up virtually in one's lap . . . or laptop, as the case may be.
In September 1998, biologist John Ugoretz of the California Department of Fish and Game sent out the following cyber-plea on ELASMO-L, a list-server dedicated to academic discussions about cartilaginous fishes:
Weird California Shark
The attached photos are of a shark caught by a drift gillnet boat in Southern California. I have already sent them to Jeffrey Seigel at the LA County Museum, but I thought I'd try this list also.
The fish was approximately 8 to 9 feet [2.4 to 2.7 metres] long. The body was discarded, and I'm not sure if the fisherman still has the head. I'm checking into the details of the catch location and will post them later if I get any.
If you cannot open the file (I'm sending it two different ways, as a "bmp" and a "jpg" file, I don't have much luck with computers) I'll describe it as best I can:
The skin is pale, white/grey and appears very soft. The eyes are small and highly reflective (like in deep water species). The teeth are impressive, long narrow and highly pointed. The snout is about two feet [60-centimetres] long, flat and shovel-like. "nostrils" are located the front of the upper jaw, at the base of the long snout.
Any guesses?
Within hours, Ugoretz received dozens of responses from helpful people (including yours truly) who recognized the fish in question. Despite John's computer misgivings, both his image files opened just fine, and sure enough they showed the head of a large Goblin Shark, jaws retracted but bristling with stiletto-shaped teeth and looking fierce even in death (had its jaws been protruded, it is quite likely that the creature's identity would have been recognized instantly). As this capture represents the first known occurrence of the Goblin Shark in the eastern Pacific and the first in American waters, I suggested that such an important range extension for this little-known species should be written up for the scientific literature. I am pleased to report that, as I write this, a short scientific paper on this capture is being prepared by Ugoretz and Seigel for publication in the journal, California Fish & Game.
Perhaps the Goblin Shark is not nearly as 'rare' as catch records would seem to indicate and its apparently patchy distribution may be an artifact of reportage. It may even be fairly abundant at some locations. Although officially only one Goblin Shark has been recorded from Portuguese waters, recent reports suggest that this species is not at all uncommon in deep waters off Madeira. According to Portuguese naturalist Pedro Miguel Niny Cambaira Duarte, a total of four confirmed catches of Goblin Shark none longer than 5 feet (1.5 metres) are known from Sesimbra, one of Portugal's most prominent fishing localities. In addition, between December 1995 and February 1996, Duarte observed, or was reliably informed of, three additional Goblin Shark specimens ranging from 5.4 to 6.6 feet (1.6 to 2 metres) in length captured in the "Sea of Bombaldes", 15 miles (24 kilometres) west of Cape Espichel. The sharks were caught at a depth of about 1 800 feet (600 metres) on deep-water longlines set for Black Scabbardfish (Aphanopus carbo) an elongate, ferociously predatory fish known locally as 'espada' and considered quite a gastronomic delicacy. Portuguese espada fishermen attest that they catch an average of four Goblin Sharks per year while fishing for espada in this part of the eastern Atlantic. Based on these recent catches and the pescado's credible reports, Duarte speculates that there may be a substantial population of Goblin Sharks in deep waters off the Iberian Peninsula.
Even if they are fairly abundant at certain locations, Goblin Sharks are no less bizarre. But as ever more specimens are examined, the form and function of many of this species' stranger features are coming to light. Consider the Goblin Shark's odd coloration. As long as the species was known only from long-dead representatives, its color in life was presumed to be the same drab greyish-brown observed in preserved specimens. But in March 1976, ichthyologists Teruya Uyeno, Kazue Nakamura, and Susumu Mikami published a short paper which included spectacular color photographs of a living (though moribund) Goblin Shark, revealing for the first time this species' completely unexpected pigmentation: soft pinkish or purplish-grey, with translucent peacock-blue margins on the fins. Several other fresh specimens (including John Ugoretz' partial one from California and a whole individual from off New Zealand) have revealed that this decidedly unshark-like coloration is indeed typical of this species when alive or freshly dead. The color is not due to pink pigments in the skin, however, but largely due to oxygenated blood in capillaries (tiny blood vessels) close to the body surface and visible through the translucent dermis. Were it not for advances in freezing and shipping technologies, we would never suspect that the ocean is home to a pink Goblin.
Arguably, color is not the Goblin Shark's most conspicuous or surprising feature. Its combination of elongated, trowel-shaped snout overhanging snaggle-toothed, forceps-like jaws is quite unique. Small wonder that this improbable beast is sometimes known by such fanciful names as "elfin shark", requin lutin (French for "imp shark"), and tiburσn duende (Spanish for "hobgoblin shark"). The first known specimen a 42-inch (107-centimetre) juvenile male was caught by Japanese fishermen in 1898, hauled up from deep water in the "Black Current" off Yokohama. These fishermen, who were quite accustomed to strange things pulled from the deep-sea, called this weird fish tenguzame, which means "goblin shark". This descriptive moniker has become its common name in English, but does nothing to explain the creature's perplexing countenance.
In fresh Goblin Shark specimens, the jaws are loosely slung beneath the head and can easily be pulled outward or pushed back into place. In preserved specimens, however, much of this oral flexibility disappears. Most Goblin Shark specimens have been preserved with their jaws protruded to varying degrees (Perhaps because many died trying to bite the net that had cruelly and unceremoniously ensnared them?). Since the degree of jaw protrusion radically changes the appearance of the shark's whole head, it is not surprising that such variation in preserved specimens generated much confusion about how many species of goblin shark there are. During the early 20th Century, it seemed as though each new goblin shark capture represented a new species, thus we had, Odontaspis nasutus de Braganza 1904 (from off Portugal), Scapanorhynchus jordani Hussakof 1909 (Japan), Scapanorhynchus dofleinii Engelhardt 1912 (Japan), and Scapanorhynchus mitsukurii White 1937 (Japan). All these nominal species are now known to represent a single, widely distributed species: Mitsukurina owstoni Jordan 1898. What had misled each of those erecting a new species was specimen-to-specimen variation in jaw protrusion.
With its jaws protruded, the Goblin Shark looks like nothing else on earth.
With its jaws retracted, however, it looks considerably less bizarre superficially resembling certain deep-sea sharks, such as the ghost catsharks
(genus Apristurus) or the birdbeak dogfishes (Deania). The retracted jaws fit
snugly into a depression on the underside of the long, blade-like snout. It is
tempting to envision a Goblin Shark swimming just above the substrate and using
its nose tip like a prod to flush benthic fishes and crustaceans hiding in
bottom crevices, then snapping them up using its loosely slung jaws like a
spring-loaded trap. Unfortunately for this nifty scenario, the snout itself is
surprisingly soft, being almost rubbery in texture. The snout's upper and especially
lower surfaces are studded with electrosensitive ampullae of
Lorenzini, suggesting that this rhinal protrusion may function primarily in
prey-detecting rather than prey-stabbing or prodding. Unfortunately, until quite
recently, virtually nothing was known about what Goblin Sharks eat, let alone
how.
Stomach contents are recovered from sharks relatively infrequently. This may be due to the tendency of many line- or net-caught sharks to regurgitate as they are hauled to the surface. Even when they are found, shark stomach contents are often reduced by digestion to a thick, smelly 'soup' with barely-to-quite unidentifiable globs of prey remains in suspension. Despite these logistical difficulties, more-or-less identifiable stomach contents have been reported for seven Goblin Shark specimens from four countries. Stomachs of Japanese individuals contained mostly half-digested teleost parts (fin rays, muscle blocks, and vertebrae), but one large individual also contained crab remains; a large specimen from southeastern Australia contained only an elongate silvery structure with a central lumen, apparently a teleost swim bladder; a small specimen from off South Africa contained pelagic octopus, crabs, and a deep-water rockfish known as a Jacopever (Helicolenus dactylopterus), while a small specimen from New Zealand contained a single, unidentifiable eye lens. From such meager data, few worthwhile conclusions about the feeding habits of Goblin Sharks could be drawn.
In April 1998, a 50-inch (128-cm) immature female Goblin Shark was taken off Kaikoura, New Zealand, in a bottom gillnet set at a depth of 1,050-1,445 feet (320-440 metres). Evidence contained in the gut of that one specimen was to challenge virtually everything we thought we knew about Goblin Shark dining habits. In a 1997 paper, biologist Clinton J. Duffy described the stomach contents of this specimen and speculated about what the identifiable prey items imply about the feeding biology of Goblin Sharks in general. Duffy found that the little Goblin's stomach was mostly empty, but included the following: the beak of an immature squid from a species called Teuthowenia pellucida, two relatively large and three smaller eye lenses, a small number of fish scales of a type known as cycloid (smooth, without tooth-like projections on the edges and exposed surfaces), two relatively intact and two disarticulated ostracods (a subclass of planktonic crustacean) of a species called Macrocypridina castanea rotunda, and 16 mostly decalcified Goblin Shark teeth (probably dislodged and swallowed with prey).
From these gut contents, Duffy was able to deduce that the juvenile female Goblin Shark had been feeding, not near the bottom as had been widely supposed of her species but in mid-water. The beak and large eye lenses were probably the remains of a single immature Teuthowenia pellucida. Juveniles and early subadults of this species are vertical migrators, remaining in mid-water depth of 2,300 to 2,950 feet (700 to 900 metres) during the day and moving surfaceward to depths less than 985 feet (300 metres) at night. The cycloid scales were deemed typical of small, mid-water teleosts such as lanternfishes (family Myctophidae); whatever their identity, most mid-water teleosts are vertical migrators. Similarly, the ostracod Macrocypridina castanea rotunda which grows to a diameter of about 1/4 inch (0.7 centimetres), or about the same as a pea is a vertical migrator, typically inhabiting depths of 655 to 1,640 feet (200 to 500 metres) by day and as shallow as 115 feet (35 metres) by night. As little else was found in the little Goblin Shark's stomach and the ostracods were relatively intact, it seems unlikely that these delicate crustaceans were ingested in the stomach contents of another prey item.
The Goblin Shark's anatomy also suggests a mid-water habitat. The majority of squaloids found at similar depths to Mitsukurina owstoni are active species sharing the following features: a solid, well-muscled, fusiform (spindle-shaped) body; large eyes with permanently dilated irises; compact, powerful jaws of limited protrusibility and equipped with blade-like lower teeth; and a powerful tail with a short, almost symmetrical caudal fin (ideal for facilitating bursts of acceleration). In contrast, the Goblin Shark has soft, flabby body with weakly developed myotomes (muscle blocks); small eyes with contractile irises; long, rather delicate and highly protrusile jaws armed with slender, spike-like teeth; and a long, highly asymmetrical caudal fin with a low thrust-angle (a feature common in sharks known to be rather languid swimmers). Taken in concert, these features indicate that the Goblin Shark is a relatively inactive species with a density close to seawater. Its prey and anatomy strongly suggest that the Goblin Shark is a sluggish beast and that at least some individuals visit mid-water zones well off the bottom, possibly vertically migrating along with their prey.
Now that he had a clear 'snapshot' of what Goblin Sharks eat, Duffy could better speculate on how this mysterious species feeds. Detecting prey in the vast blackness of the deep-sea, however, is no easy task. At mid-water depths, precious little light filters down from the surface, rendering vision all but useless. Duffy speculates that the Goblin Shark's spatulate, ampulla-peppered snout may function as a forward-projecting prey detector, in much the same way as certain halfbeaks (teleost fishes of the family Hemiramphidae) use the lateral line organs along their elongated lower jaws to feed at night. However, the Goblin Shark possesses small but functional eyes, perhaps able to capture the faintest glimmer that may betray the presence of prey. Like many mid-water animals, both the squid Teuthowenia pellucida and the ostracod Macrocypridina castanea rotunda are bioluminescent, so perhaps the Goblin Shark detects such prey visually. But it is probably not an either/or matter. It seems likely that, in the vastness of the deep-sea, Goblin Sharks would take advantage of as many prey-detecting strategies as they are able.
Given its apparent sluggishness and near-neutral buoyancy, Duffy speculates that the Goblin Shark probably hangs nearly motionless in the water, ambushing its prey from close range like a pink crocodile. A 1990 paper by shark systematist Leonard Compagno suggests that, as in the related Megamouth Shark (Megachasma pelagios), prey capture in Mitsukurina is probably affected by highly co-ordinated movements of the protrusible jaws, expandable pharynx (throat) and associated structures. According to Compagno, as the Goblin Shark's loosely-slung jaws protrude forward, the pharynx expands downward. These paired actions greatly expand throat volume and thereby create a strong negative pressure inside the pharynx that sucks prey animals into the mouth. Most of the Goblin Shark's lower jaw is filled by a large, highly mobile basihyal ('tongue'), which probably enhances the creation of a powerful pharyngeal suction to hoover up hapless prey. The Goblin Shark's wicked-seeming, fang-like teeth ensure prey capture, grasping it securely as the jaws retract into the head. Thus, considered in context of the challenges posed by its deep-sea habitat, the Goblin Shark ceases to be a grotesque or freakish 'monster', becoming instead a remarkable example of lamnoid biomechanics and adaptability.
The Goblin shark has long been assumed to be a deep-sea, bottom-dwelling species. But a careful examination of catch records suggests that such may not be the case at least in some parts of its range. The greatest depth from which a Goblin Shark has been taken is 4,265 feet (1,300 metres), caught off Sydney, Australia. That's deep by swimming-pool standards, but represents only a little more than one-third as deep as the greatest depth recorded for any shark -12,060 feet (3,675 metres), a record held by the Portuguese Shark (Centroscymnus coelolepis) and is about the same as the greatest depth recorded for the White Shark (4,200 feet or 1,280 metres), a species no ichthyologist considers to be a deep-sea shark. Most specimens of Goblin Shark recorded to date, however, have been taken from Sagami and Suruga Bays, on the south-east coast of Honshu Island, Japan, at depths of 200 to 920 feet (60 to 280 metres). Off the Izu Shichito islands located a mere 40 miles (64 kilometres) from downtown Tokyo a 6-foot (1.75-metre) female and an 8-foot (2.5-metre) male Goblin Shark were captured at a depth of only 130 feet (40 metres). That's near the safe depth limit for recreational scuba divers, and it may be only a matter of time before some lucky underwater photographer snaps the first portrait of a free-swimming Goblin Shark.
From those images and the diver's first-person account of an encounter with a living Goblin, we would probably learn more about the behavior of this mysterious species than in the entire century since it was first discovered. Here's hoping that, within a few hours of being captured on film, such tantalizing images will be digitized and available on the Internet to inspire amazement, awe, speculation, debate and above all a deep sense of wonder. What brave new world, that has such pixels in it.
