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Whale Shark Research on the Belize Barrier Reef


Whale Shark Biology


whale shark
Photo © Jeremy Stafford-Deitsch

Whale Shark Biology

Whale sharks (Rhincodon typus) range throughout the world's tropical waters and are thought to have evolved around 200 million years ago. With nurse and zebra sharks as some of their closest relatives (the Orectolobiforms or carpet sharks), whale sharks are the only species in their family (Rhincodontidae). They are the largest of the three planktivorous sharks (feeding on microscopic organisms floating in the sea), the other two being the Basking shark (Cetorhinus maximus) and the Megamouth (Megachasma pelagios) that inhabit more temperate waters.

Whale sharks are the largest fish in the sea, purported to reach 20m, although the most accurate measurement made is 14.2 m. Whale sharks feed on a variety of tiny animals including zooplankton, thimble jellyfish, baitfish and squid. The whale shark is ovoviviparous, where the young develop in eggcases in the uterus and are then born live. Although sharks in general produce very few young compared to bony fish, whale sharks have been known to produce an estimated 300 live young in one litter. Although no one knows how long they live or where they reproduce, they are thought to reach sexual maturity at about 30 years of age, or when they reach close to 30 ft/9-10m in length, and may live beyond 100 years old. World population estimates are unknown but they are thought by shark scientists to be very low.

Although whale sharks appear to be solitary animals, they will congregate to feed. Whale sharks appear to target high-density food sources such as thick "soups" of plankton, zooplankton at-tracted to coral blooms off Ningaloo Reef, and blooms of zoo-plankton such as copepods off of Baja, Mexico. Whale sharks are now known to undertake large-scale migrations possibly in search of, or targeting, these patches of food. Predictable aggregations are rare although several have been recently identified offshore near the Philippines, Australia, Maldives, Baja/Mexico, South Africa, Honduras and now Belize. In Belize, research has shown that whale sharks seasonally aggregate at Gladden Spit to feed on the spawn of aggregating snappers. Apart from snapper eggs, whale sharks at Gladden also feed on thimble jellyfish, pelagic baitfish and zooplankton.


Gladden Spit's Whale Sharks

Predictable aggregations of feeding whale sharks at Gladden Spit have been known by fishermen for decades. Gladden Spit forms a promontory on the barrier reef, 46 km from the coast. Research undertaken by scientists with local fishermen, revealed that whale sharks aggregate to feed on freshly released spawn of aggregating dog and cubera snappers. This is the first documented observation of cubera snappers spawning, and of whale sharks specifically targeting fish spawn for food. Whale sharks are able to feed by filtering large volumes of water across their gills while moving, or by gulping water and filtering food in a stationary horizontal or vertical position.


Research worldwide

Elucidating the behaviour of elusive whale sharks requires a range of techniques. Conventional tags have been used to look at site fidelity and large-scale movements in South Africa, Belize, Honduras and the Seychelles. Acoustic tags have been used to track whale sharks from boats in Australia and the Seychelles yielding information on fine-scale movements in relation to food sources. Acoustic tags used with passive underwater acoustic monitors (in Belize) and satellite-linked tags (Australia, Belize, the Seychelles, Baja California) have provided information on whale shark site fidelity and movements independent of researchers and sightings. Satellite tags deployed to date reveal that sharks are highly migratory (e. g. Seychelles to Thailand) even making trans-oceanic crossings of over 12,000 km (Baja California to Tonga). They are capable of moving in a rapid and directed manner between patches of abundant food and across deep bodies of water indicating that they are outstanding navigators.


Whale Shark Conservation

Due to their life history, populations of whale sharks are highly susceptible to any fishing pressures. Yet whale sharks are currently fished primarily in India and Asia to supply the Asian fin and meat markets. They do not benefit from any global protection at this time mainly because so little is known about them. Yet, most countries are slowly realizing that whale sharks are worth far more alive through the tourist trade, than dead. Consequently, several countries, such as the Maldives and the Philippines, passed laws protecting whale sharks. The impacts of tourism on whale sharks are not yet known in Belize but to avoid them, many local whale shark tour-guides have undergone training to promote safe & sustainable tours. Whale sharks were recently listed on Appendix II of the Convention for the International Trade for Endangered Species which monitors and regulates trade in listed species.


For more information on whale sharks, see the Whale Shark Biological Profile.