About The Whale Shark

The whale shark (Rhincodon typus) is a filter feeding shark and the largest living fish. However, despite its large size (up to 18 m) and popularity with tourists most aspects of its biology and ecology are poorly known.

Indeed such is the extent of our lack of knowledge of the whale shark that most questions about its life could be legitimately answered: ‘’we don’t know’’!  Read on to learn some fast facts about what we do know about whale shark biology and ecology.

The whale shark (Rhincodon typus) is a massive filter-feeding shark, and takes the title as the largest fish in the world. However, it is still a poorly understood species. Prior to 1986 there were only 320 records of whale sharks worldwide. Since then science has been trying to catch up, but most of what we know remains limited to basic biology.

All sharks are grouped as elasmobranches, along with skates and rays. They differ from all other teleost fishes in their unique skeleton, which is comprised of tough, flexible cartilage, as opposed to bone. Defined ridges can be clearly seen running along almost the entire length of a whale shark, a characteristic also seen in the bottom-dwelling leopard shark (Stegostoma fasciatum). In fact, these two are closely related, within the predominately bottom-dwelling order Orectolobiformes (meaning lengthened tail lobe).

Whale sharks have a broad distribution throughout tropical and warm temperate seas, and can be found in both coastal and oceanic waters. Some unconfirmed reports give a maximum size of up to 18 m, although the largest whale sharks are more commonly thought to grow to between 12 and 15 m. The lifespan of these sharks is not known, but some estimate they may live for more than 100 years.

Feeding

Whale sharks are filter feeders, a feeding strategy they share with only two other known shark species; the basking shark (Cetorhinus maximus) and the mysterious megamouth shark (Megachasma pelagios). All three feed by continually swimming through food-rich water, channelling tiny organisms into their mouths; a process called ram filter-feeding. Whale sharks also employ a second feeding method, known as suction feeding. In areas of high food concentration they may hang almost motionless near the surface, simply sucking prey into their mouths.

Whale sharks are able to consume larger prey than the other two filter feeding sharks, and are thought to include small fish, squid and jellyfish in their diet. Because whale shark filter-feeding apparatus is better suited to catching this larger prey using the suction feeding method, and less so to filtering tiny planktonic organisms, they probably depend more on dense, seasonal aggregations of prey than the other filter feeding sharks.

Movements

In some parts of the world it is possible to predict when whale sharks will visit coastal areas to feed for a few weeks or months at a time, but out of these seasons we have very little knowledge of their movements.

Whale sharks are capable of travelling over a huge range (see map), and advantage bestowed by their massive size. They are powerful swimmers, and can swim steadily and continuously for extended periods, theoretically allowing them to travel huge distances between food aggregations. Their large size also allows them to tolerate a great variation in water temperature. Although many studies have shown whale sharks spend much of their time in surface waters, they regularly dive to extraordinary depths, sometimes exceeding 1,200m where the water temperature may drop as low as 4°C.

There have been several projects carried out in the last decade using satellite tagging to track whale shark movements, with varied success. Many tags detach prematurely from the whale shark after only a few days or weeks, but some have persisted for many months or even years, and show these animals are capable of moving over huge distances. One shark tagged in the Sea of Cortez was tracked for over 3 years and travelled 13,000 km out into the Pacific during that time. Another study in the Sulu Sea tracked two sharks thousands of kilometres through several political boundaries, highlighting the need for conservation efforts for these sharks to be on an international level.