Growing up to 40 feet (12 m)—longer than your average jeepney—and weighing about 20.6 tons (18.7 metric tonnes), the whale shark (Rhincodon typus, also called balilan or butanding) is the world’s largest living fish species. It has a noteworthy trait that marine scientists and conservationists use to distinguish and track them in the wild: Like how our fingerprints are believed to be unique, no two butanding have been known to share the same constellation-like spot pattern.
Found in the warm tropical waters of the Philippines (such as those in southern Leyte, Palawan, Sorsogon, and Cebu), the butanding features a flattened head, a blunt snout, short whisker-like sensory organs called barbels, a dark-colored backside, and a white belly. Complementing its countershading is its aforementioned trait: the white spot pattern behind its gills.
Besides its massive size, this carpet shark species has another thing in common with whales: It’s a filter feeder. It opens its 5-foot-wide (1.5 m) mouth, full of over 300 teeth, to take in water. It then filters out food—plankton, shrimp, algae, small fish, and even fish eggs—and expels water and debris after it’s done.
Known for its docile temperament, the butanding is popular with tourists. Travelers from different parts of the world go on whale shark tours, paying for the chance to feed and swim with these gentle giants.
However, a number of ethical and environmental issues surround whale shark tourism. For starters, butanding are an endangered species, protected by Philippine law since 1998. Researchers have noted that tourism has made them associate boats with free food; they may mistakenly approach shark-fishing vessels and poachers. Increased human activity has also negatively affected coral density and biodiversity in butanding habitats, with the resulting nitrogen input stunting coral growth and disrupting coral-algae symbiosis.
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Cover photo: Sam Farkas/National Geographic