Species of the Week
This week we are going to take a look into the world’s largest living fish, the Whale Shark.
Common name: Whale shark
Species: Rhincondon typus (named by Smith in 1828)
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Orectolobiformes
Family: Rhincodontidae
Genus: Rhincodon
Conservation status: Endangered (A2bd+4bd; see more here)
Size: 4 to 12 m (specimens rare above 12m, but were found some individuals up to 18m)
Weight: average 20600 kg
Average life span in the wild: around 70 years (still in study)
Depth range: 0-1928 m (usually 0-100m)
This highly mobile species can be found in both coastal and oceanic habitats, with mean daily movement up to 28 km. They are strongly correlated with temperatures in the Atlantic and Indian oceans, with most occurring in the Indian (temperatures between 26,5-30ºC).
Diet
Filter feeder, usually feed upon planktonic and small nektonic organisms (krill, crab, jellyfish, larvae, sardines, anchovies, mackerels, small tunas and squid).
Geographic Range
Present in all tropical and warm temperate seas, excluding the Mediterranean. In Africa, they have been observed in several countries as for example: Mozambique, Angola, Cabo Verde, South Africa and many others.
Reproduction
Whale sharks are polygynandrous (multiple mating) and obligate lecithtrophic livebearers, meaning that the eggs are fertilized internally and develop in the female, until the end of the embryonic phase or even later. Due to their oviparous reproductive strategy, female whale sharks provide protection to their internally developing young until they hatch from their eggs and are born. Like all sharks, there is no parental care shown by the females towards pups after they are born.
Migratory habits
These gentle giants are known as a highly migratory species. Mature pregnant females undergo long migrations to the middle of the ocean, near seamounts or remote islands, and it is where they supposedly give birth.
Threats
- Directed fisheries
- Significant by-catch in nets
- Vessel strikes
- Inappropriate tourism (interference, crowding or provisioning)
- Marine pollution events (example: oil spills)
Curiosity
- Whale sharks are in no way related to whales. Although they are sharks, they are very docile and pose no real threats to humans. Sometimes they even allow swimmers to hitch a ride.
- They have about 3000 tiny teeth (less than 6mm long), but they don’t use them to eat
- In July 1996 a female was captured pregnant with 300 eggs!!!!
- They grow up really fast!
- They have an incredibly thick skin (ranging from 2-14cm).
- This species was one of the characters of the movie “Finding Dori”, called Destiny
- See video about the species
References:
http://www.iucnredlist.org/details/19488/0
http://www.arkive.org/whale-shark/rhincodon-typus/image-G1989.html
http://animals.nationalgeographic.com/animals/fish/whale-shark/
http://www.marinemegafauna.org/whale-sharks-boring-come-check-fun-facts/
http://www.fao.org/fishery/species/2801/en
https://www.worldwildlife.org/species/whale-shark
http://www.marinespecies.org/aphia.php?p=taxdetails&id=105847
Chang, W., M. Leu, L. Fang. 1997. Embryos of the whale shark, Rhincodon typus: early growth and size distribution. Copeia, 2: 44-446.
Rowat, D., K. Brooks. 2012. A review of the biology, fisheries and conservation of the whale shark Rhincodon typus. Journal of Fish Biology, 80: 1019–1056
Figures:
http://www.arkive.org/whale-shark/rhincodon-typus/image-G70657.html
http://www.iucnredlist.org/details/19488/0