Species Profile: Basking Shark

Hello again, welcome back to animals under threat. Today, we will be covering the second largest species of shark that feeds on plankton. Reaching over 40 feet/12m in length and weight of 10,000/4.5 metric tons, this species of shark has reach endangered status from boat collisions, overfishing and harvesting of fins and livers. Say hello to the Basking Shark (Cetorhinus maximus).

Being the second largest shark in the world, the Basking shark is characterized by their pointed snout, enormous mouth, 5 gill slits that almost encircle its head, rows of minute curved teeth in jaws, large first dorsal, pectoral and pelvic fins and small second dorsal/anal fins (Bray, 2018). This species of shark is mostly found worldwide in temperate/arctic oceanic waters (australianmuseum, 2020).

Basking sharks are normally seen swimming close to the surface with its mouth open and are known to swim in pairs or large groups up to 100 members. This species of shark does breach similar to great white sharks and whales, although scientists have not figured out why they do this (floridamuseum, 2020).

Basking shark by Greg Skomal and world distribution by floridamuseum.

The current population of the Basking shark is unknown leading them to classed as endangered by the IUCN red list. Basking sharks feed in a unusual way as they have their mouth open while swimming which allows water to flow through its pharynx. By suction/pumping the water through the pharynx, zooplankton is strained from the water by gill rakers that is located in the gills (floridamuseum, 2020).

Zooplankton and gill rakers by Floridamuseum

Basking sharks’ mate via internal fertilization and females give birth to live young. Unlike Whale sharks which give birth to hundreds of small young, Basking sharks give birth to large young and in fewer numbers (Oceana.org, 2020). Basking sharks are also ovoviviparous which means developing embryos rely on a yolk sack but have no placental connection to the mother. This also means that embryos that are developing in the eggs remain in their mother’s body until they are ready to hatch (Matthews, 1950).

Breaching Basking shark by Nat Geo Wild.

This species of shark is endangered due to boat collisions, overfishing and harvesting of fins and livers. Due to the Basking shark’s nature of feeding and swimming near the surface, commercial ships/boats have collided with the sharks leaving them injury/dead. Overfishing for the shark’s liver and fins is also having an impact on the species population as the fins are harvested for shark fin soup and other meals/medicine which can be worth over US$57,000 while the liver was collected to use the oil for lamps in early industrial era (Rigby et al, 2019).

Feeding shark (above) by Martin Prochazkac and Caught shark (below) by Michihiko Yano

Next time, we will be covering a well-known species of sea turtle.

References
https://australianmuseum.net.au/learn/animals/fishes/basking-shark-cetorhinus-maximus-gunnerus-1765/ retrieved 21/03/2020

Bray, D.J. 2018, Cetorhinus maximus in Fishes of Australia, accessed 21 Mar 2020, http://136.154.202.208/home/species/1847

https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/cetorhinus-maximus/ retrieved 21/03/2020

Gore, M.A., Frey, P.H., Ormond, R.F., Allan, H. & Gilkes, G. 2016, "Use of photo-identification and mark-recapture methodology to assess basking shark (Cetorhinus maximus) populations", PLoS ONE, vol. 11, no. 3, pp. e0150160.

Matthews, L.H. 1950, "Reproduction in the Basking Shark, Cetorhinus maximus (Gunner)", Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, vol. 234, no. 612, pp. 247-316.

https://oceana.org/marine-life/sharks-rays/basking-shark retrieved 21/03/2020

Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Romanov, E. & Kyne, P.M. 2019. Cetorhinus maximus. The IUCN Red List of Threatened Species 2019: e.T4292A2988471.

Picture references
https://fishesofaustralia.net.au/home/species/1847 (gill rakers)
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/cetorhinus-maximus/ (Michihiko Yano) (caught Basking shark).
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/cetorhinus-maximus/ (zooplankton)
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/cetorhinus-maximus/ (world map)
https://oceana.org/marine-life/sharks-rays/basking-shark (Martin Prochazkac) (feeding shark)
https://en.wikipedia.org/wiki/Basking_shark
https://www.youtube.com/watch?v=zsC61g36EqM (video)