Author: Smith, 1828
Field Marks:
An unmistakable huge shark, one of three large filterfeeding species, with a broad, flat head and truncated snout, immense transverse, virtually terminal mouth in front of eyes, minute, extremely numerous teeth, and unique filter screens on its internal gill slits, prominent ridges on sides of body with the lowermost one expanding into a prominent keel on each side of the caudal peduncle, a large first dorsal and small second dorsal and anal fin, lunate or semilunate caudal fin without a prominent subterminal notch, and a unique checkerboard pattern of light spots, horizontal and vertical stripes on a dark background.
Diagnostic Features:
Body cylindrical or moderately depressed, with prominent ridges on sides. Head very broad and flattened, without lateral flaps of skin, snout truncated; eyes laterally situated on head, without subocular pockets; spiracles much smaller than eyes, behind but not below them; gill slits very large, fifth well separated from fourth; internal gill slits with unique filter screens, consisting of transverse lamellae that cross each gill slit, with ramose processes on their inner surfaces that interconnect to form the filters; nostrils with rudimentary barbels and no circumnarial folds and grooves; mouth ext'remely large, terminal on head, and transverse, without a symphyseal groove on chin; teeth not strongly differentiated in jaws, with a medial cusp, no cusplets and no labial root lobes; tooth rows extremely numerous, in over 300 rows in either jaw of adults and subadults. Caudal peduncle with strong lateral keels and an upper precaudal pit. First dorsal much larger than second, first dorsal with origin well anterior to the pelvic origins, and insertion over the pelvic bases; pectoral fins very large, relatively narrow and falcate, much larger than pelvic fins, with fin radials expanded into fin web nearly to its distal edge; pelvic fins somewhat smaller than first dorsal but slightly larger than second dorsal and anal fins; anal fin about as large as second dorsal, with its origin about opposite first third of second dorsal base; anal fin with broad base and angular apex, separated by a space somewhat greater than base length from lower caudal origin; caudal fin with its upper lobe at a high angle above the body axis, less than a third as long as the entire shark, with a vestigial terminal lobe and subterminal notch and a very strong ventral lobe or a very short one. Supraorbital crests present on cranium, these laterally expanded. Valvular intestine probably of ring type. A unique colour pattern of light spots and vertical and horizontal stripes, in the form of a checkerboard.
Geographical Distribution:
Circumglobal in tropical and warm temperate seas, oceanic and coastal. Western Atlantic: New York to central Brazil and including Gulf of Mexico and Caribbean. Eastern Atlantic: Senegal, Mauritania, Cape Verde Islands, Gulf of Guinea. Indo-West and central Pacific: South Africa and Red Sea to Pakistan, India, Sri Lanka, Malaysia, Thailand, China, Japan, Philippines, Indonesia (Kalimantan, Java, Irian Jaya), Papua New Guinea, Australia (Queensland, Northern Territory), New Caledonia, Hawaiian Islands. Eastern Pacific: Southern California, to northern Chile.
Habitat and Biology:
An epipelagic oceanic and coastal, tropical and warm-temperate pelagic shark, often seen far offshore but coming close inshore and sometimes entering lagoons of coral atolls. It is generally seen or otherwise encountered close to or at the surface, as single individuals or in schools or aggregations of up to hundreds of sharks. In the Indian Ocean it is common around the Seychelles, Mauritius, Zanzibar, Madagascar, Mozambique and northernmost Natal. In the western Pacific it is common in the Kuroshio current in the fishing grounds for skipjack. It is reportedly abundant from Cabo San Lucas to Acapulco in the eastern Pacific, and in the Gulf of Mexico and the Caribbean in the western Atlantic. It apparently prefers areas where the surface temperature is 21 to 25°C with cold water of 17°C or less upwelling into it, and salinity of 34 to 34.5 ppt; these conditions are probably optimal for production of plankton and small nektonic organisms, all of which are prey of the whale shark. Whale sharks are apparently highly migratory, with their movements probably timed with blooms of planktonic organisms and changes in temperatures of water masses. They are often associated with schools of pelagic fishes, especially scombrids.
Development uncertain, possibly oviparous or ovoviviparous. In 1953 a large eggcase, 30 cm long, 14 cm wide and 9 cm thick containing a nearly full-term 36 cm embryo whale shark was collected from the Gulf of Mexico, and the assumption was made that the species is oviparous (cf. Baughman, 1955, Garrick, 1964, Bass, d'Aubrey and Kistnasamy (1975c). However, the rarity of 'free-living' whale-shark eggs, the extreme thinness and lack of tendrils on the only known case, the considerable yolk and partially developed gill sieve in the only known embryo, and the presence of umbilical scars on larger free living specimens 55 cm long suggests an alternative explanation (Wolfson, 1983), that the Gulf of Mexico egg was aborted before term, and that the whale shark is ovoviviparous. The type of ovoviviparity practiced by the whale shark would be a relatively simple sort very similar to that of the related nurse sharks (Ginglymostomatidae), with retention of the egg case in utero until the embryo hatches. Alternatively, the egg cases of the whale shark might be retained in utero for most of the development of their embryos, then ejected at a late stage of development. Hence the mode of reproduction of the whale shark must be considered uncertain, with ginglymostomatid-like ovoviviparity a distinct possibility. The smallest free-living whale sharks are from 55 to 56 cm long, the smallest of which has an umbilical scar (properly vitelline scar). One adult female whale shark was recorded as having 16 egg cases in its uteri.
The whale shark is a versatile suction filter-feeder, and feeds on a wide variety of planktonic and nektonic organisms. Masses of small crustaceans are regularly reported, along with small and not so small fishes such as sardines, anchovies, mackerels, and even small tunas and albacore as well as squids. The whale shark feeds at or close to the surface, and often assumes a vertical position with its mouth above. Phytoplankton often occurs in the stomachs of whale sharks, but whether this is a major component of the diet of this shark is rather doubtful. The suction-filter mechanism of the whale shark is more versatile than the dynamic filter mechanism of the basking shark in the range of prey species that can be taken. The basking shark, with its scooplike mouth, hydrodynamically 'clean' gillrakers, and huge gill slits, has little if any suction capacity and must depend on its relatively slow forward motion to carry animals into its mouth; this limits it to eating small planktonic crustaceans and other invertebrates. The whale shark is not dependent on forward motion to operate its filters, and can probably achieve relatively high intake velocities of water into its mouth, that enable it to readily ingest larger, active nektonic prey in addition to masses of planktonic crustaceans. A disadvantage of the suction plankton feeding of the whale shark over the dynamic method used by the basking shark is that the structures involved can filter a far smaller volume of water per unit time and hence are far less efficient in concentrating diffuse plankters. Hence the whale shark may be more dependent on high concentrations of plankters than the basking shark to optimally utilize such food, but has the option of utilizing nektonic organisms for prey.
The whale shark is generally considered harmless, and very large individuals have been examined and ridden by divers without the sharks reacting aggressively, although they may show curiosity and approach divers to apparently examine them. However, there have been a few cases of whale sharks butting sportsfishing boats, possibly after being excited by hooked fishes being played from the boats or by bait. More often human beings inadvertently assault whale sharks, by ramming them with ships and boats as they bask on the surface.
The whale shark has been kept in captivity in Japan; at the time of writing this account a good-sized individual has been housed in a large oceanarium tank in Okinawa for over a year, and feeds readily at the surface of the tank.
Size:
Maximum total length uncertain, possibly to 18 m, but specimens rare above 12 m; 13.7 m is often given as the maximum measured, 12.1 m the most recently accurately measured. Most reported in the literature are between 4 and 12 m. Females of 438 to 562 cm are immature. This is by far the world's largest fish.
Interest to Fisheries:
Apparently of relatively limited interest for fisheries. Small harpoon fisheries exist in Pakistan and India; it may also be taken in China, and has been captured and utilized in Senegal; it is eaten by people either fresh or dried salted and used to treat boat hulls in Pakistan.
Type material:
Holotype: Museum National d'Histoire Naturelle, Paris, MNHN 9855, 4600 mm male; mounted, stuffed specimen. Type Locality: Table Bay, South Africa.