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Whale Shark
[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]Read more about the whale shark one of the most sought-after sightings on any cruise in our oceans in our marine life blogs. Did you know that Harlequin Shrimp, one of the most colourful crustaceans in the ocean keep the starfish they prey on alive? They devour one leg at a time and turn them upside down to prevent them from running away. Read more Fascinating Facts about Harlequin Shrimp. [/vc_column_text][vc_separator][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]
Whale Shark - Rhincodon typus
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The Whale Shark is the worlds largest fish in the ocean and can reach a size of 12m. But on average 10m in length and weigh up to 18.7 metric tonnes. The maximum length is not known, but some estimates put it at 20m.
These plankton feeders travel vast distances, usually alone, to feed. Their mouths open to around 1.5m and contain approximately 300 to 250 rows of teeth plus ten pairs of pads to filter food.
There are some places in the ocean where multiple whale sharks can be found as they have high levels of plankton. This attracts them for feeding, and the tourist to view them. The congregation of whale sharks is, as a result, an indicator of the overall health of the ocean. An example of this is in Baa Atoll in the Maldives or Cendrawasih Bay in Indonesia.
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Diet
The method of feeding is passive, so they just swim with the mouths open and suck the water. Once inside the mouth is closed and the plankton gets trapped in the filtering organs. The water is then just pushed out through the gills. The reason they have teeth is not understood as they are not used in feeding. A juvenile can consume up to 21kg of plankton per day. They also feed on small fish and spawning fish shoal that are producing eggs and sperm.
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Whale sharks prefer warmer tropical waters with about 75 % found in the Indian and Pacific Oceans, but can also be seen in some of the cooler water locations. They have a preference for water above 21 C. They are found in most locations except for the Mediterranean Sea.
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Unique
The skin of each whale shark has a unique pattern of light spots meaning that each individual can be identified and tracked. In the Philippines alone over 450 individuals have been identified by this method. Any photos of whale sharks can be added to the database. The best position is to photo the skin above the pectoral fins being the gills and submit them for identification.
The migration patterns of the whale sharks were not fully understood until around ten years ago. This is when the use of tagging allowed scientists to observe this. Now it is seen that they migrate thousands of miles, one was observed travelling over 8,000miles in 3 years. They stay mainly within 125 miles of the coast and mostly above 40m of depth, but have been observed going to below 1000m.
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Reproduction
Whale shark reproduction has not been observed, but it is known they give birth to live pups. Where this actually happens is unknown as they are rarely seen. They mature sexually at around 30 years of age and may live to about 100 years old.
Research has shown that the female delivers the pups at 40 to 60cm in length and can have up to 300 inside her. They are not born at the same time but stored to develop over a time period. This way she can produce a continuous stream of pups over an extended period. A captured female was found to have over 300 inside her in the 90’s.
In 2009 the smallest whale shark was found in an area of the Philippines measuring only 38cm. Also observed in the area where several pregnant females. This has led scientist to believe the whale sharks do have breeding grounds that are as yet undiscovered.
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Despite being the largest fish, whale sharks also have predators. Orcas, blue sharks, white sharks and blue marlin have all been known to attack young individuals. But it is humans who pose a significant threat. The meat is highly valued in Asia, and the fins are sought after for soup and alleged medicinal and aphrodisiac properties. Bycatch is also an issue as well as unregistered tourism where boat propellers can damage them.
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As a result, the whale sharks were registered under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 2003. It is believed that their population has fallen by 63% in the past 75 years. They are also listed as vulnerable on the IUCN Red List.
Conservation efforts are in place in many countries like the Philippines and Australia.
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Aquarium trade
Despite their size, some whale sharks have been kept in captivity notably in Japan, but also in the USA and Dubai. This started in 1934 in Japan with a netted area of a bay where a whale shark was kept for four months. The first aquarium whale shark was in 1980. Specialised feeding and huge tanks are required, and many of whale sharks do die early. They are usually taken from bycatch or standings. After the early difficulties the aquariums have managed to keep the whale sharks of up to 19 years in captivity, but they have had behavioural changes. These intelligent animals began to swim in circles and have “coughing” activities thought to be them clearing the filter pads for feeding.
There is much opposition to the captive whale sharks especially since some of the Japanese aquarium tanks are relatively small and cause early deaths of the creatures.
[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]Images were provided by Amos Nachoum, Maki Cat, Debbie Arriaga and Dennis Whitestone.[/vc_column_text][/vc_column][/vc_row]