The Whale Shark
By Tammy Peluso
One would suspect it would be relatively easy to spot a 40 foot fish with a gaudy black and white checkerboard design, swimming casually at or near the surface. Surprisingly, Whale Shark encounters are extremely uncommon. Whale Sharks (Rhincodon typus), pelagic and migratory in nature, are circumglobal, appearing in every temperate ocean except the Mediterranean. Driven by a constant need for food, Whale Sharks are instinctively drawn to upwellings, plankton blooms and coral spawning in the open ocean waters, shallow reefs and atoll lagoons.
In the Sea of Cortez; the deep trench between mainland Mexico and the Baja Peninsula, Whale Sharks are seen most often in the spring when warming waters spur massive plankton blooms. Local operators typically see several dozen Whale Sharks each season between May and November. Another popular Whale Shark stomping ground is Ningaloo Reef off Western Australia; huge numbers of Whale Sharks appear each year, like clockwork, after the coral spawn following the March full moon.
Whale Sharks usually travel alone and, occasionally, in small groups. Although seemingly solitary, the Whale Shark typically travels with an entourage of remoras, jacks, tuna, mackerel and Pilotfish; all enjoying protection from the Whale Shark and a meal from its leftovers. Most Whale Sharks are covered with dozens of remoras that cling tightly with disk-shaped suckers; the remoras assist the shark by removing bothersome parasites.
The Whale Shark has more than 300 rows of tiny, one-eighth inch long teeth but it doesn't use them for eating. Since it's a filter feeder, it effortlessly captures plankton, pelagic crustaceans, squid and tiny baitfish just by moving through the water; the spongy tissue between the gill arches acts as a giant sieve. Anything undigestible or too big, such as a careless jack or remora, can be purged by the shark's stomach. Occasionally, Whale Sharks feed in a vertical position; thrusting themselves wildly toward the surface, ingesting congregating baitfish.
Although Whale Sharks resemble whales in size, they are actually sharks, members of the order Orectolobiformes. Whale Sharks are related to some of the more unusual shark species such as Wobbegongs, Carpetsharks, Nurse Sharks, Zebra Sharks and Blind Sharks.
The Whale Shark is unusual in design with a broad, flat, spotted head and a huge, cavernous mouth in front of its eyes. The top of the body is charcoal gray, patterned with bold whitish spots and stripes; the underside is completely white.
It is speculated the Whale Shark's method of reproduction is ovoviviparous (the egg cases are retained in the uterus for most of the embryonic development). The smallest recorded living Whale Shark was 21 inches in length and the largest more than 60 feet; most animals encountered are 30 to 40 feet.
Whether you see the Whale Shark as a fleeting shadow or are lucky enough to spend an hour, any encounter with this big fish is guaranteed to be dramatic.