Scuba Diving

Whale Sharks: Gentle Giants of the Ocean

Whale Shark

The first whale shark known to science was a five-meter fish harpooned off the South African coast in 1828.[i] British military doctor Andrew Smith boasted that his discovery was the largest fish in the ocean, and named it accordingly. Notwithstanding the glory of the whale shark’s title, almost two centuries would pass before this prehistoric species got much attention.

Nowadays, everyone wants to see a whale shark. The world’s desire to lay eyes on a thirteen-meter, gracefully majestic, bus-sized fish creates an estimated 42 million dollars in annual tourism revenue globally.[ii] This is mostly good news for whale sharks, which are endangered species. Without advocates, fans, or conservation plans, the fishing industry was harvesting them into nonexistence. Now, scientists are racing to gather information about the largest non-mammal on Earth which, despite its enormous size, has proven to be very mysterious.

Whale sharks are commonly referred to as the “gentle giants” of the ocean. They nourish their 10-ton[iii] bodies with small fish and zooplankton (animal life that drifts through the ocean, like fish larvae, krill, and jellyfish). They are filter-feeders, which means that they simply open their 5-foot wide mouths and swim into their food, relying on rows of filter pads to separate dinner from seawater. The water gets expelled through the gills, and the food gets swallowed. Baleen whales feed in the same way, as do basking and megamouth sharks.

The maximum length of a whale shark is hard to pin down. Multiple historical and modern accounts claim shark lengths of 18 to 21 meters, but usually with a degree of inaccuracy. It’s generally accepted that the largest accurately measured whale shark was 12.65 meters, landed in Karachi, Pakistan in 1949. The heaviest shark, according to independent researcher Victor Lin, clocks in at 39 tons in Taiwan- which could mean it was over 20 meters long.[iv]

Whale Sharks off the coast of Isla Mujeres, Mexico
Whale Sharks off the coast of Isla Mujeres, Mexico

The geographical range of whale sharks encircles the globe, but it doesn’t stretch from pole to pole. Whale sharks inhabit tropical and subtropical waters. Within this equatorial zone, they migrate to feed and breed, though their exact travel patterns are still largely unknown. Most whale shark sightings occur in coastal locations with seasonal spawning events. A spawning event is phenomenon in which, at a certain time of year, fish, coral, or other animals spew out eggs and sperm for a mass reproduction party- and whale sharks gather to gorge on the feast. The abundance of food can draw hundreds of sharks (a 2011 survey off the coast of Yucatán, Mexico counted around 420 individuals)[v], and hundreds of tourists too. At a few of these locations, whale sharks are said to be entertainingly rambunctious; reports from Cenderawasih Bay in east Indonesia recount rolling and frolicking behavior.

However, whale sharks become much less conspicuous once they leave shallow water. According to data from body tags, sharks may dive as deep as 1928 meters to feed on deep-ocean prey or swim long distances.[vi] When sharks stay so deep, they are difficult to track. Whale sharks also spend time in the vast open ocean, where data collection relies on fishing vessels with independent observers, or on the word of fisher-people themselves. To make matters more complicated, whale shark migration patterns seem to change based on variations in temperature and weather. Long-term monitoring in the Azores showed that a local increase in whale sharks was correlated with the location of the 22 C isotherm.[vii] After 2013’s “Super-typhoon” Haiyan in the Philippines, a reliable whale shark population in Southern Leyte virtually disappeared for a season, perhaps because the storm changed the local ecosystem.

Perhaps the most mysterious aspect of whale sharks is their reproduction. Whale sharks have never been observed mating or giving birth, and scientists have no conclusive evidence for the location of their breeding or birthing grounds. However, apparently pregnant females have been consistently observed at Darwin Island in the Galapagos, and last month (July 2017), researchers performed ultrasounds on three females to find proof of pregnancy; the data will be analyzed soon.[viii] The only pregnant female physically examined was a 10.6 meter shark landed in Taiwan. She had a whopping 304 pups, which is the largest reported litter of any shark species. From this examination, scientists determined that whale sharks are aplacental viviparous, meaning that their babies develop and hatch inside the uterus, but are nourished by the egg, not a placental connection. Length at birth seems to be around 50 centimeters.[ix]

Whale sharks’ docile nature and enormous size make them a star attraction for divers and snorkelers. Even tourists who don’t usually do watersports consider whale shark encounters a once in a lifetime opportunity. Swimming alongside the enormity of the shark’s intricately patterned body, witnessing its incredibly powerful, yet slow and stately grace, is undeniably, overwhelmingly wonderful. It’s no wonder that whale shark tourism has boomed, and that young and old scientists and volunteers are dedicating their lives to the species.

Whale Shark Isla Mujeres Mexico
Whale Shark Isla Mujeres Mexico

Unfortunately, even with all this enthusiasm and support, whale sharks have heavy odds against them. The Atlantic subpopulation, which holds a quarter of the world’s whale sharks, dropped by 30% over 75 years. The Indo-Pacific subpopulation, holding the bulk 75% of the world’s whale sharks, dropped by more than 50% in the same time.[x] In 2016, the International Union for Conservation of Nature (IUCN) shifted whale sharks’ status from vulnerable to endangered.

  • Targeted fisheries are one major cause of decline. A targeted whale shark fishery (meaning that the vessels specifically hunt whale sharks) didn’t exist on a large scale until Taiwan developed a booming market for whale shark meat; in 1997, one 10-ton whale shark could fetch $70,000. The Taiwanese shark population steadily declined, and the fishery was outlawed in 2007. The Philippines and India caught and sold their own whale sharks to Taiwan until 1998 and 2001, respectively. Nowadays, the most whale sharks (up to 1000 per year) are caught by Chinese fleets, which may or may not be “targeting” the animals- it’s likely that the remaining markets (including illegal ones) offer fisher-people enough reason to kill a whale shark when they see one.[xi]
  • Shark fin soup, a runny broth which uses shark fin simply to thicken its consistency, was a luxury item in China for generations. The huge upswing in demand for this dish is usually attributed to China’s growing middle class. Whale shark fins are fetching high prices today, which drives legal and illegal trade. All shark populations are rapidly losing individuals to this industry, in which a shark’s fins are sliced off and the body thrown overboard; unable to swim- and therefore breathe- the shark slowly sinks and drowns.
  • Bycatch fisheries, in which a vessel targeting one species accidentally traps another, also kill whale sharks. Tuna purse-seines (huge, weighted nets that fishing boats lay in a circle around tuna schools) are especially dangerous; fisher-people know that tuna travel with whale sharks, and sometimes encircle whale sharks and tuna together for the sake of convenience. Some of these vessels let the whale shark go after they pull in the tuna, but the physical and mental stress of the experience can be fatal.
  • Boats can also kill whale sharks simply by sailing into them. Surface-feeding whale sharks have been impaled on slow-moving vessels throughout history, resulting in some gruesome drawings and firsthand accounts.[xii] Nowadays, powerful shipping boats may not even know they have struck a whale shark because it sinks upon death.
  • Harmful tourism is also a growing concern for whale shark conservation. Crowding has always caused boat collisions and stressed animals, but the most alarming trend is shark-feeding. In whale shark-feeding sites like Oslob, Cebu in the Philippines, the sharks have modified their behavior significantly in ways which could change their migration patterns, diet, and life cycle.[xiii] Sharks have also started intentionally to bump boats and humans in their demand for food.

Conservation programs are trying to spring to the rescue. One of the most inspiring citizen-science efforts is the Wildbook for Whale Sharks,[xiv] an online photo database which keeps records of individual sharks, each identified by the completely unique spot pattern on its side. Anyone can contribute photos to the site. Advocacy, publicity, and research have won victories in recent years, like Air China’s refusal to carry shark fin cargo, and the sharks’ 2016 status shift to “endangered.” But for a species that has captured the world’s fascination and passion, whale sharks are still suffering more than they should. To help them, scientists need to know them much better, and powerful people in government and business need to be convinced that they are worth more alive than dead.

Whale Sharks Isla Mujeres Sony A6300
Whale Sharks in Isla Mujeres, taken with Sony A6300

[i] http://www.environment.gov.au/marine/marine-species/sharks/whale-shark

[ii] http://www.iucnredlist.org/details/summary/19488/0

[iii] http://news.nationalgeographic.com/2016/11/brad-norman-explorer-moments-identification-system-helps-protect-whale-sharks/

[iv] http://elasmollet.org/Rt/Rt_large.html

[v] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3084747/

[vi] http://www.iucnredlist.org/details/summary/19488/0

[vii] http://www.iucnredlist.org/details/summary/19488/0

[viii] http://www.discoverwildlife.com/news/wildlife-first-wild-whale-shark-ultrasounds

[ix] http://www.iucnredlist.org/details/summary/19488/0

[x] http://www.iucnredlist.org/details/summary/19488/0

[xi] http://www.iucnredlist.org/details/summary/19488/0

[xii] http://elasmollet.org/Rt/Rt_large.html

[xiii] www.lamave.org, Learning from a provisioning site: code of conduct compliance and behaviour of whale sharks in Oslob, Cebu, PhilippinesSchleimer, A., Araujo, G., Penketh, L., Heath, A., McCoy, E., Labaja, J., Lucey, A., Ponzo, A.; Peer J, 2015

[xiv] https://www.whaleshark.org/


Jacqueline Dodd

Jacqueline Dodd

Jacqueline is a PADI Open Water Scuba Instructor. She specializes in conservation, sustainability, and community development. Co-Founder at Experiential Education and Conservation Organization
Jacqueline Dodd

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