Coral Reefs: Diversity on Display
The vast majority of shark species are recognizably ‘sharky’, but the Spotted Wobbegong (Orectolobus maculatus) doesn’t look much like anything. Flat as a struggling artist’s wallet and sporting a fleshy ‘beard’ of tassels, it vaguely resembles a weird three-way cross between a bad 1950’s space monster, a cricket paddle with fins, and a Navajo quilt. The name ‘wobbegong’ is Aboriginal in origin but, despite the fact that the same name is used by Aborigines around the coast of Australia (a continental uniformity which is rather unusual), no one seems to know precisely what it means. One theory is that wobbegong means “living rock” and, indeed, if the Spotted Wobbegong resembles anything at all, it is a weed-overgrown rock.
Just the Facts:
Habitat: Intertidal, Estuaries, Sandy Plains, Rocky Reefs, Coral Reefs
Depth: Intertidal - 360 ft (110 m)
Distribution: Southeast Asian, Western Australian, Southeast Australian/New Zealand, Northern Australian, Japanese
The Spotted Wobbegong is an absolute master of escaping notice in plain sight. Resting quietly on the bottom, this species is almost undetectable. Its flattened body, enlarged pectoral and pelvic fins drape over the rocky or coral substrate, barely adding to the vertical relief of the bottom. The shark’s variegated brownish-grey markings and pale ring-like spots break up the body into irregular, unrecognizable shapes that blend imperceptibly with the riotous irregularity of the surrounding underwater terrain. Even the eyes — which would ordinarily be a dead giveaway — are rendered tough to detect by being hooded and surrounded by eye-shaped markings. A beard of fleshy tassels further obscures the outline of the shark’s head, making it extremely difficult to tell where the animal stops and the bottom begins. All these features conspire to make the Spotted Wobbegong seem to ‘melt’ into the bottom.
The only thing that betrays the presence of a concealed Spotted Wobbegong is the regular expansion and contraction of its gill pouches. But even this unavoidable action is muted, made easier by drawing in water through large, crescent-shaped spiracles behind the eyes. A wobbegong’s spiracles free the prone shark of the need to pump water in through its mouth, which might suck in sand or other particulate that could damage its delicate gill tissues. As in other wobbegongs, the Spotted Wobby’s eyes are located on top of its head and raised above the plane of its body. This arrangement grants it an excellent view of the surrounding area, the better to detect approaching prey.
The Spotted Wobbegong is a formidable ambush predator. Its strategy consists of lying quietly in wait until an unwary crab, lobster, octopus, teleost, or smaller shark blunders too close. When a suitable prey animal ventures within striking range (about 2 feet or 60 centimetres from the shark’s head), the formerly quiescent Spotted Wobby is suddenly transformed into a formidable killer. With mind-stuttering swiftness (within 25 milliseconds), the fang-toothed jaws are protruded forward and down by a third of the cranial length as the powerful throat and gill muscles are expanded, bellows-like. These lightning-fast, paired actions create a powerful pharyngeal suction from which there is little hope of escape. The prey is grasped firmly with the Wobby’s long, smooth-edged teeth and swallowed whole.
The Spotted Wobbegong is most often encountered resting in near-shore caves off New South Wales, Australia, during daylight hours. Each individual Spotted Wobby seems to favor specific daytime resting caves. These caves are often shared with small schooling fishes, such as bullseyes (Pempheris spp.), which are hoovered up opportunistically. But the Spotted Wobbegong is primarily nocturnal. At night, individuals venture forth from their caves, moving over the reef face by ‘walking’ on highly mobile pectoral and pelvic fins. While hunting, the touch-, taste-, and electrically-sensitive nasal barbels are splayed outward, like the whiskers of a cat. When prey is detected within a rocky or coral crevice, the Spotted Wobby presses its broad, flat head against the opening and forcibly sucks out the hiding or sleeping prey. By sunrise, each Spotted Wobbegong has ceased its active hunting and returned to its favored daytime resting cave, there to digest the fruits of that night’s hunting.
Little is known of courtship and mating in the Spotted Wobbegong. Captive males of this species from the Sydney area are said to fight vigorously among one another while courting females. A wild male Spotted Wobby was reported to attempt repeatedly to enter the wire enclosure in which a mature female of the same species was kept. This behavior suggests that the female gave off a pheromone or other attractive chemical signal. In captive specimens of Spotted Wobby from central New South Wales, mating reportedly occurs during the month of July. As in many other sharks, the mating behavior of the Spotted Wobbegong is quite rough. An aroused male Spotted Wobby typically bites and holds onto a receptive female’s gill region and arches his body to insert a single clasper into her vent.
After an undetermined gestation period, a large number of small Spotted Wobbegong pups are born in shallow coastal areas. Juvenile Spotted Wobbies occur in estuaries, on seagrass beds, and on low-profile reefs inshore from the usual habitats haunted by adults of the same species. Avoiding their elders may be a sound survival strategy, as Spotted Wobbegongs have been known to consume smaller conspecifics. Growth during the first few years of life is probably fairly rapid, but this needs to be confirmed. At present, no data are available for this species on age at maturity for either sex, nor on longevity.
Despite the obvious lack of life history information on the Spotted Wobbegong and the fact that its flesh is regarded as poor quality for human consumption, it is increasingly sought as a source of leather. It is ironic that the variegated skin pattern that renders this species nearly invisible in the wild makes it highly attractive to manufacturers of shark-skin purses, vests, belts, and hat-bands. Perhaps the diurnally lethargic Spotted Wobby will ultimately save its skin due to basic human laziness — the hide is exceptionally labor-intensive to remove without puncturing it, thereby reducing its value. As such, it may eventually be deemed not worth the effort. But it can be argued that the skin looks much better on the shark anyway.