Whale Shark

Rhincodon typus

A whale shark illustration.
Type: Fish Litter size: Up to 304 Other common names: ‘papa shillingi’ - Swahili Life span: 70 years Diet description: Krill, fish spawn, jellyfish, other plankton, small fish Max length: 18 metres Habitat and range: Found worldwide in tropical and subtropical waters apart from the Mediterranean. They occupy both coastal and oceanic habitats, from the surface to dives of at least 1,900 m. Relative size: Image IUCN status: Endangered (EN) - Decreasing population Endangered (EN)
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Identification

Named after a body size more common in marine mammals, whale sharks are the largest fish in the ocean. This, combined with their whole top side being covered in an intricate spot pattern, makes them one of the most easily identified shark species. They also have a very wide, blunt head, with a large filter-feeding mouth. It is thought that their spot patterns may be a form of camouflage and, since each one is unique, the patterns are useful for identifying individuals.

Photo © Byron Dilkes
Photo © Byron Dilkes

Special behaviour

Despite being so conspicuous, whale sharks are remarkably elusive and little is known about their behaviour and ecology. They do, however, aggregate to feed in large numbers when plankton is seasonally abundant in certain locations. They perform migrations across ocean basins, and are capable of regularly diving to 1,900 m and possibly more (this record is restricted by tagging technology).

Reproduction

Whale sharks are ovoviviparous, meaning they grow their embryos internally and nourish them from a yolk sack before giving birth to live, independent young. Very little else is known about whale shark reproduction, and much of our knowledge comes from a single pregnant female in Taiwan, which gave birth to the largest litter of any shark species at 304 pups. Curiously, the 304 pups were all at different stages of development. Genetic analysis suggests they were sired by the same male, indicating that whale sharks may be able to store sperm and sequentially fertilise their eggs, essentially creating a conveyor belt of pups. Pupping areas remain largely unknown.

Habitat and geographical range

Whale sharks are found worldwide in tropical and subtropical waters apart from the Mediterranean. They occupy both coastal and oceanic habitats, from the surface to dives of at least 1,900 m.

Image

Diet

Whale sharks are filter feeders, essentially feeding on whatever plankton they can filter from the water with their gill rakers. They can often be seen feeding on fish spawn and have even been recorded feeding on baitfish. While they can ram feed like basking sharks (swimming forward with their mouth open to push water through their gills), they are also capable of suction feeding, where they remain stationary in a productive prey patch and pump plankton-rich water over their gills with their mouth. They are able to filter an impressive 600,000 litres of water per hour.

Threats

The primary threat to whale sharks is overfishing, both by fisheries and as incidental bycatch. Even though their meat is considered to be of low quality, it is still in demand along with their large fins, which are highly valued as trophy and display pieces. They are also at significant risk of vessel strikes, especially in shipping lanes as they regularly feed at the surface and are slow moving. Although whale shark population declines vary regionally, it is estimated that global populations have fallen by more than 50%, and they are considered Endangered by the IUCN.

Relationship with humans

Although exploited opportunistically, whale sharks are primarily sought out for in-water interactions through ecotourism operators. Since reliable aggregation spots have been identified in many locations worldwide, whale shark tourism has boomed, with many countries (e.g. Maldives, Mexico, Australia) reporting millions of dollars in revenue. It is estimated that whale shark tourism may globally be worth more than $42 million annually. They are also listed on Appendix II of CITES, restricting their international trade.

References

David A. Ebert. et al, 2021, Sharks of the World: A Complete Guide.

IUCN Red List of Threatened Species, Whale shark: Rhincodon typus

Florida Museum, 2018, Rhincodon typus

National Geographic, Whale Shark

Britannica, Whale Shark

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