Sadc Whale Shark Handout

Whale Shark (Rhincodon typus)

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hale sharks—which can grow bigger than some whales—were first discovered in 1829 off the coast of South Africa. Massive but harmless to humans, they are, like many other sharks, in decline. Listed as vulnerable by the IUCN (International Union for the Conservation of Nature and Natural Resources), their placid nature makes them an easy target for fisheries for both their meat and fins, which are highly valued in the international shark-fin trade. Gathering information on whale sharks is critical to their international protection. However, due to the difficulty and cost of studying them, very little is known about whale shark biology. Description The whale shark is the biggest fish in the world. The largest one on scientific record was 12 m long, but there are reports of sharks up to 20 m long and weighing 34 tonnes! The whale shark’s blue-grey back is covered with pale spots and stripes. It has a whitish underbelly. This two-tone coloration helps camouflage the animal whether seen from the top or the bottom. The whale shark has a broad, flattened head. Its large mouth is up to 1.5 m wide and sits at the front of the short snout (rather than below, as in most other sharks). The first dorsal fin is larger than the second, and three prominent ridges run the length of either side of the body. Reproduction and life span Whale sharks are ovoviviparous: eggs are fertilized and hatched internally but gain no additional nutrition from the female before she gives birth to fullydeveloped, live pups. It is estimated that whale sharks live from 60–100 years, reaching sexual maturity after 30 years—at around 6 m in length in males and 8 m in females. Whale sharks seem to segregate by size and sex, probably mixing only when mating. Whale shark mating, however, has never been observed. The only pregnant whale shark on record was caught by fishermen in Taiwan. It carried over 300 embryos measuring 42–63 cm long. Pups are thought to be 55–64 cm long at birth. It is unknown how often whale sharks reproduce, where they mate or give birth, or how many pups survive to maturity. Diet and feeding Whale sharks are filter-feeders, sucking water in through the mouth and sieving it through the gill-rakers to trap the tiny zooplankton—mainly krill and larvae, as small as 1 mm—that they feed on.

Whale sharks find food through their sense of smell. They have tiny eyes and relatively poor vision, but their well-developed nostrils, located at either side of the upper jaw, are thought to sense plankton density. They often sweep their heads from side to side as they swim to maximize plankton intake. Distribution Whale sharks are found in all tropical and warm seas (except the Mediterranean) and have been sighted as far north as New York and as far south as Tasmania. Usually seen offshore, they occasionally come inshore or enter lagoons and coral atolls. Whale sharks inhabit surface waters with temperatures of 18–30°C, but spend most of their time diving to depths greater than 1000 m, where the water can be as cool as 10°C.

Global whale shark range (red) and the 14 main regions where you are likely to spot a

whale shark while snorkeling or diving. Whale sharks are migratory and travel vast distances. The longest recorded journey spanned 13 000 km and took longer than 36 months. It is thought that males migrate more than females. Migrations are probably related to feeding and mating, and linked to plankton blooms and spawning events.

Despite their vast habitats, whale sharks are regularly sighted in a few favoured “hotspots” scattered around the tropics. They are spotted year round in some locations and seasonally at others. This is thought to be determined by the plankton density in each region. Want to know more? To learn more about whale sharks, visit the following online resources: The Whale Shark Project (www.whalesharkproject.org): Read up on whale shark biology and ongoing research and conservation efforts; learn how to take photos that can be used to identify individual whale sharks; and download research papers, fact sheets and the whale shark Code of Conduct. ECOCEAN (www.whaleshark.org): The ECOCEAN Whale Shark Photo-identification Library is a visual database of individual whale sharks from around the world. Whale shark encounter data submitted to the database is analysed by marine biologists to learn more about these mysterious fish. If you submit photos of a whale shark encounter, you will be informed whenever “your” whale shark is resighted. Information you provide will contribute to global whale shark conservation efforts. Project Aware (www.projectaware.org): Use Project Aware’s search engine to find a registered Whale Shark Project Operator for your next holiday. You can also download a Whale Shark Data Reference Sheet to help you capture important information about your whale shark encounters.

Whale Shark Photo Identification

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hale sharks are born with a unique pattern of spots on their bodies that, like fingerprints, do not change over time. This “bodyprint” can be used, along with information on scars, sex and size, to identify individual whale sharks. This ability to identify individual whale sharks led to the development, in 1995, of a whale shark photoID library at Western Australia’s Ningaloo Marine Park, one of the world’s whale shark hotspots. At the time, researchers identified individual sharks by examining dot patterns and other identifying characteristics by eye—a time-consuming task.

Different photos of the same whale shark showing matching spot patterns.

Marine biology meets the space age By adapting a computer algorithm originally developed by astronomers to map star patterns in images of the night sky, accurate computer matching is now possible. The software maps individual spot patterns and compares them with other whale shark patterns already in the photo library. The result is the Interactive Individual Identification System (I3S), which has helped researchers identify over 100 individual whale sharks in the Maldives and more than 1500 whale sharks around the world. “Virtual” tagging: better than the real thing The I3S pattern-matching software means a shark can be “virtually tagged” simply by taking a photo. Unlike physical tagging, there is no physical contact with the animal, leaving it unharmed. And, considering the high cost and short lifespan of plastic shark tags (typically less than one year), and the great distances whale sharks are known to travel, virtual tagging is far more useful for long-term, global population monitoring. Click, you’re a whale shark research assistant Submitting photos and information about your whale shark encounters helps researchers understand the movements and overall numbers of whale sharks around the world. The results can be used by conservation authorities to understand the pressures on whale sharks and to take action to protect them. You can help by simply taking a photo of a whale shark’s unique skin pattern, or “bodyprint,” in the area directly behind the gills and above the pectoral fins. If possible, try to get three or four shots of the patterning. Both photos and frame grabs from video can be used for identification.

Target area (behind the gills, above the pectoral fin). Position yourself perpendicular to this area for the perfect whale shark mug shot.

Left-side spot patterning is the most important type of identifying photo. You will get the best photos by being perpendicular to the spot patterning area above the left pectoral fin.

Right-side spot patterning can identify a shark previously identified by a left-side spot patterning photo if it also has a right-side pattern in the database. (To avoid doublecounting sharks with left-side and right-side photos submitted separately, new shark IDs are only allocated to left-side patterns. Unmatched right-side photos remain in the database until the shark is sighted again and identified with a left-side pattern.) Submit your whale shark photos to the dive centre, along with as much information about the encounter as you remember (use the Whale Shark Data Reference Sheet to help capture as many details as possible), and we will run them through the I3S software program and identify the sharks for you. Alternately, you can submit your whale shark photos to the global ECOCEAN Whale Shark Photo-identification Library at: www.whaleshark.org Remember, it is vital that you do not harm the sharks during your interaction with them! Please respect the whale shark interaction guidelines.

Whale shark interaction guidelines

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hen swimming or diving with whale sharks, following these guidelines ensures that the shark is disturbed as little as possible, prolonging your encounter and maximizing the chances of seeing the same shark in the future: • Keep a minimum of 3 m from the shark’s body and 4 m from the tail. • Keep splashing and noise to a minimum. • Do not use flash photography. • Don’t touch the shark or block its path, as this may cause it to dive. •

Never swim across the path of the shark. Only dive under a whale shark from the middle of the body, behind the pectoral fins. 

Make sure you understand these guidelines before you enter the water. If you have any questions, please ask one of the dive guides on board the boat.