The gentle giant of the sea
Whale sharks (Rhincodon typus) are the world’s largest fish, growing up 12 metres in length and weighing up to 12,500 kg. They are known for their gentle nature, sometimes letting divers swim with them and even remove parasites from them. Whilst the whale shark looks a lot like a whale, hence the name, it is actually a fish. Like other fish, it takes in oxygen from the water through its gills gives birth to young that have hatched from eggs within the body.
Distribution and Habitat
The whale shark has a wide distribution and can be found throughout the world’s oceans in temperate and tropical waters. Most commonly, the whale shark can be found at latitudes between 30 and degrees around the equator. Within these areas whale sharks occupy shallow coastal areas and the open ocean, with a preference for warmer water in the 21-30 degree Celsius range. The species can tolerate waters as low as 3 degrees C however, which are mostly encountered when the animal is deep diving.
Whale sharks are fairly solitary animals; however they have been spotted in groups of up to 100 individuals. They are known to be migratory, travelling up to thousands of kilometres but it is not clear whether whales are following the migrations of prey species or migrating for other reasons. Whale sharks are classed as ovoviviparous, a reproductive strategy where young hatch from eggs inside the mother so that she gives birth to live young. Details of this process are poorly known in whale sharks.
In order to feed, whale sharks employ a method known as filter feeding, where suspended matter and food particles are strained from water, typically through passing the water over a specialized filtering structure. In the case of whale sharks, the filtering structure is the filtering pads that comprise black sieve like structures and separate food from water which is then expelled through the gills. Food items include plankton, fish and the eggs and sperm of spawning fish. Though these sharks possess around 300 tiny teeth, they are not used in the feeding process and their function remains unknown.
As in many other species of large fish, smaller fish including remoras are known to attach to the whale shark through a sucker on the top of their head and feed on the whales external parasites. This is a mutually beneficial arrangement, as in return for removal harmful parasites the smaller fish receive protection from predators.
Threats and conservation
Whale sharks are currently classified as vulnerable by the IUCN Red List. The largest threat to whale sharks is fishing, as their flesh is highly valued in some parts of Asia. Shark watching tourism may also be a threat though the implications of tourism are not well understood in this species. The catching of whale sharks is now prohibited in the Philippines and international conservation and management plans are encouraged by its listing on Appendix II of the Convention on Migratory Species (CMS) The Australian Department of Conservation and Land Management (CALM) has laid out guidelines and protection measures in order to minimise the impact of shark-watching tours, and research projects in the area hope to aid our understanding of the species. Small numbers of whale shark exist in aquaria both in the Asia and in the USA.
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