Whale Shark

Large sharks that eat plankton

Baleen whales are known to be the biggest animals on Earth that feed on plankton, but they are not the only big animals that eat these tiny organisms. In this post, you will discover three species of shark that consume plankton. 

WHAT IS PLANKTON?

Plankton refers to those tiny organisms that drift in the water with the currents. They can be classified as phytoplankton, which include the planktonic algae and other autotrophs or producers that may be the most important producers in many marine ecosystems, or as zooplankton, which include the heterotrophic plankton (the primary consumers). There are so many groups of organisms that spend all their life in the plankton, but other may be present just in some phases.

Organisms included in the zooplankton (Picture: Sci-news).
Organisms included in the zooplankton (Picture: Sci-news).

So many marine groups of animals feed on plankton, but baleen whales are known to be among the biggest animals that eat these small creatures. Some sharks are known to eat these little organisms: the famous Whale shark (Rhincodon typus), the awesome Basking shark (Cetorhinus maximus) and the stunning Megamouth shark (Megachasma pelagios). Did you know about these three species of planktophagous sharks? 

THE BIGGEST FISH IN THE WORLD

The biggest fish in the world usually is 12 meters long (but may achieve a length of 15 meters), weights 22 tonnes and its mouth is so wide that could swallow a car. We are referring to the famous whale shark (Rhincodon typus).

Whale sharks are true sharks, so they breathe using gills and are cold-blooded fishes. The reason of their name is the fact that they feed on plankton in a similar way of whales: they swim slowly (1,5-5 km per hour) with the mouth opened (which has dense filter screens) and swallow the small organisms present in the water, like coral and teleost spawn, krill, copepods, jellyfishes, small cephalopods and schooling fishes. They are also reported to feed almost vertically in the water. They can be identified so easily for their colossal size and for their dark blue colouration with white spots all over the body.

The whale shark is the biggest fish in the world (Picture: Mauricio Handler).
The whale shark (Rhincodon typus) is the biggest fish in the world (Picture: Mauricio Handler).

Little is known about the biology of these big animals. They live usually alone in coastal, pelagic and oceanic waters of the tropics and warm temperate zones, except the Mediterranean sea. They migrate extremely large distances. Every spring, they migrate to the continental shelf of the central west coast of Australia.

Due to direct and indirect fishing, their populations have reduced and the IUCN classifies them as a vulnerable species. Nowadays, their fishing is widely forbidden. Do you know that swimming with whale sharks has a negative impact on their populations? 

THE BASKING SHARK

The world’s second largest fish is also a filter feeder and is also a shark: it is the basking shark (Cetorhinus maximus). This shark lives in coastal and pelagic of temperate and boreal waters, but is a migratory species.

They can be distinguished from other sharks for their big mouth, small teeth and long gill slits. They are solitary animals, but sometimes they can form a small group of animals. Basking sharks consume small fish, fish eggs and zooplankton. They capture them on their gill rakers with the help of mucus secreted in the pharynx. In average, they swim at 3,7 km per hour. So, how many tonnes of water filter per hour? 

The basking shark (Cetorhinus maximus) is the second biggest fish in the world (Picture: FLMNH).
The basking shark (Cetorhinus maximus) is the second biggest fish in the world (Picture: FLMNH).

Their conservation status is vulnerable, but is considered to be endangered in the North Pacific and the Northeast Atlantic subpopulations. The fact that their fins are among the most valuable in international trade explains their conservation status. Moreover, accidental fishing is a threat to consider.   In some regions, such us European Union, they are protected by law.

THE MEGAMOUTH SHARK

The megamouth shark (Megachasma pelagios) is a large oceanic shark (at least 5 metres long) with long pectoral fins, but sometimes is littoral on the continental shelves. They live in tropical and subtropical waters. Little is known about this species because it was discovered in 1976.

The megamouth shark (Megachasma pelagios) is a strange planktophagous shark (Picture: ).
The megamouth shark (Megachasma pelagios) is a strange planktophagous shark (Picture: Theethogram).
Its low-flow filter apparatus suggest it is less active than the whale and basking sharks. Megamouth might swim slowly with its jaws wide open to capture their preys by suction. A surprising feature of this shark is its bioluminescent mouth, which acts to attract prey. Its conservation status is unknown, but accidental fishing might be a threat.

REFERENCES

  • Camhi, MD; Pikitch, EK & Babcock, EA (2008). Sharks of the Open Ocean: Biology, Fisheries & Conservation. Blackwell Publishing.
  • Carrier, JC; Musick, JA & Heithaus, MR (2010). Sharks and their relatives II: Biodiversity, adaptive physiology and conservation. CRC Press.
  • Castro, P & Huber ME (2003). Marine biology. The McGraw-Hill (4 ed).
  • Fundación Squalus (2011). Guía para la identificación de especies del Programa de avistamiento de tiburones y rayas de la Reserva de Biosfera SEAFLOWER.
  • IUCN: Cetorhinus maximus 
  • IUCN: Megachasma pelagios
  • IUCN: Rhincodon typus
  • National Geographic: Whale sharks 
  • Oceana (2008). Guía de los Elasmobranquios de Europa.

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