Filter Feeding Sharks
- bioworld090
- Feb 27, 2023
- 4 min read
Sharks are fascinating creatures that have captured the imagination of people for centuries. While many people think of sharks as fierce predators, not all sharks feed solely on the prey they actively hunt. Some sharks, known as filter-feeding sharks, have evolved a unique way of feeding that sets them apart from other species. Filter-feeding sharks use specialized structures in their mouths to filter tiny organisms from the water, such as plankton and small fish, making them an important part of marine ecosystems. Below is a list of all the three extant filter-feeding sharks.
MEGAMOUTH SHARK
The first on the list is the megamouth shark that also goes by its scientific name, Megachasma pelagios. It is the smallest of the three extant filter-feeding sharks. Even though it is the smallest shark on the list, it is still pretty big with bigger individuals reaching a length of nearly 7 m. Females are larger than males and measure 3.41-7.10 m as compared to males who reach a length of around 6 m.
A creature of this size is fairly easy to spot but the megamouth shark is rare and has been spotted very few times since its accidental discovery in 1976. According to Florida Museum, there have been only 273 confirmed sightings since its discovery, most of which are from Taiwan.
The megamouth shark possesses a big mouth that can reach up to a width of 1.3 m. The upper lip is silvery in color. The upper jaw of this animal is lined by 50 rows of teeth and the lower jaw by 75 rows of teeth. The body is tapering which ends in an asymmetrical caudal fin with a big upper lobe. The dorsal surface of the megamouth shark is black or dark grey and the belly is white.
The megamouth shark inhabits the Pacific, Atlantic, and Indian Oceans. The exact depth ranges at which this animal can be found seem to be a bit uncertain. Some sources say this shark is found in the epipelagic and mesopelagic zones or at depths of 0-1000 m while other sources say it is a deepwater shark and can be found as deep as 4600 m.
Now, the most unique thing about this animal is its diet. With such a big size and mouth, it might seem that this shark is some sort of top predator in its habitat and thrives on animals it hunts. But, in reality, this animal thrives mainly on a few cm long creatures, the euphausiid krill. It also sometimes feeds on jellyfish and copepods.
BASKING SHARK
The second animal on the list is the basking shark, the second largest filter-feeding shark. Its scientific name is Cetorhinus maximus. The basking shark is a big creature with adults typically reaching a length of around 8 m. Some individuals can even reach a length of 9-11 m.
The large body of this shark is usually dark brown or black on top and dull white on the belly. The mouth is large like that of the megamouth shark and can reach a width of up to 1 m. The inside of the mouth is lined by 100 small, hooked teeth per row and there are six and nine rows of teeth in the upper and lower jaw respectively. The basking shark has 5 big gills that almost encircle the head and each gill has highly developed gill rakers that are used to capture food.
As a cosmopolitan species, the basking shark is found in temperate waters all over the world. It is found in the pelagic zone, i.e., from the surface down to a depth of nearly 1000 m.
The diet of the basking shark is composed of copepods, small crustaceans, fish eggs, and larvae. It is a ram feeder, meaning it swims with its mouth open to draw plankton along with water over its gills. It filters its food with its 3 inches long gill rakers. Unlike the other two filter-feeding sharks, the megamouth and whale shark, it cannot actively pump water through its gills.
WHALE SHARK
The last on the list of filter-feeding sharks is the whale shark. It is also known by its scientific name, Rhincodon typus, and is the largest extant species of fish. The maximum length can be around 20 meters.
The huge body of a whale shark is dark grey on top and white on the ventral surface. Many spots and stripes cover the body and are unique to each individual just like human fingerprints. The head of the whale shark is flat and behind it are five gills on both sides. The mouth is lined by 300 rows of tiny teeth which are considered non-functional. 20 food filtering structures known as filtering pads lie inside the mouth. Each filtering pad has a net-like appearance with several small holes.
The whale shark’s diet consists of a variety of small animals including copepods, krill, fish eggs, small crabs, squids, and fishes. A study also suggests that algae are also a part of its diet. The food is taken in along with water and it can be done in three ways:
Surface ram filter feeding
Stationary or vertical filter feeding
Sub-surface ram filter feeding
After the food particles are taken in, they pass through the filtering pads. Unlike other filter-feeding sharks, the flow of water and food is parallel to the filtering structures and this type of filtering process is known as cross-flow filtration. This causes a shear force to act upon the food particles and they end up near the esophagus.
REFERENCES:
Megamouth Sightings – Discover Fishes (ufl.edu) –> sightings by date
https://onlinelibrary.wiley.com/doi/abs/10.1111/jfb.14007
https://peerj.com/articles/4432/
https://en.wikipedia.org/wiki/Megamouth_shark
https://www.floridamuseum.ufl.edu/discover-fish/sharks/megamouths/
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