What Do Basking Sharks Eat?

By D.C. Demetre •  Updated: 09/02/22 •  7 min read

Basking sharks, the second largest shark species, are filter feeders. Their diet is mainly small plankton. Basking sharks (scientific name Cetorhinus Maximus), represent one of the three shark species that filter seawater to feed (the other two being the megamouth shark and the whale shark).

They eat both zooplankton and phytoplankton, but basking sharks’ preferred food is zooplankton, especially copepods. Zooplankton is minuscule animals or larvae that live freely floating in the water. Copepods are a kind of zooplankton, planktonic crustaceans slightly related to crabs and shrimps. Copepods include around 9000 different species, ranging in size from 0.5 to 15 mm.

Fish eggs, marine worms called chaetognaths, and deep-water ocean shrimp are also known to be consumed by these sharks.

How Much Do Basking Sharks Eat?

Comparison of size of basking shark (Cetorhinus maximus) and human

Comparison of size of basking shark (Cetorhinus maximus) and human. Credit: The Nature Box, CC-BY

An average adult basking shark filters about 2,000 tons of water per hour through its food strainers. The amount of water that passes over it’s gill rakers in one hour could fill two Olympic-sized swimming pools. That is because a basking shark must eat millions of individual microscopic plankton per day. The amount eaten has been estimated by marine ecologist David W. Sims to be 31 kilograms a day, about 68 pounds.

The basking shark’s name comes from its distinct habit of “basking”, or slowly swimming at the surface, while it feeds. Although it is also called the bone shark, elephant shark, sail-fish, or sun-fish in different parts of the world.

In patches of the ocean where there are high concentrations of plankton, these sharks have been seen in numbers from single individuals, small groups, and hundreds of individuals.

How Does Filter-feeding Work?

Filter-feeding is a method of feeding where an animal uses a filter to separate food from the water. The basking shark has gill slits on its head almost completely circling the body. These gill slits allow water to flow into the mouth of the basking shark while it is swimming with its mouth wide open.

Filter-feeding sharks eat by swimming with their mouths open and filtering the water through their gills. Attached to the bones supporting the gills are densely spaced, bony projections, called gill rakers, that look like a comb. The gill rakers trap the planktonic organisms, which are then drawn into the mouth and swallowed.

Gill rakers can reach lengths of 6 inches, reaching across the gaps between the shark’s five gill arches when the shark opens it’s mouth to feed. Each arch has between 1,000 and 1,300 gill rakers that form a sieve when extended.

The basking shark will periodically close its mouth, after about 30 to 60 seconds of feeding. The gill rakers then fold down flat and the biomatter that was strained from the seawater is collected by mucus secretions from cells at the raker’s base, squeezed out and then swallowed.

One unique fact about the basking shark is that is the only fish known to have seasonal moulting. As Karl Shuker writes in his book, The Hidden Powers of Animals:

“Torpor or hibernation in fish is rare, but the most remarkable case features the basking shark (Cetorhinus maximus). It swallows great quantities of plankton, straining it from the water via specialized filters called gill-rakers. A common sight drifting just beneath the sea surface during the plankton-rich summer months, these sharks are rarely seen during the winter, when plankton is scarce. This is because they descend to deeper waters where, scientists assumed, they spend the season in a torpid state. However, when scientists examined two basking sharks during winter they lacked gill-rakers and thus couldn’t feed. This unexpected finding suggests that basking sharks hibernate, shedding their gill-rakers and regrowing them in spring.”

Can Basking Sharks Eat Humans?

Basking sharks are the world’s second-largest type of shark, after the whale shark. They can grow to be up to 40 feet long and weigh up to 7 tons. Despite their size, basking sharks are harmless to humans and pose no threat. In fact, basking sharks are filter feeders and only eat small fish and plankton. So, no, basking sharks cannot eat humans.

C. Maximus is not an aggressive species and is not bothered by approaching boats and divers. However, its ability to jump entirely out of the water could endanger passengers of smaller boats and sea kayaks.

Basking sharks grow to an average size of 26 feet long, and can reach up to 30 feet. The huge size and power of the baskets command a healthy caution and respect, as anyone who has seen one in person can testify.

Do Basking Sharks Have Teeth

The mouth of a basking shark features jaws lined with hundreds of small teeth that curve backwards. These teeth measure around a quarter of an inch in length, puny compared with other shark species.

In total, there are roughly 1,500 teeth, arranged along 6 rows of teeth on their upper jaw, with 9 rows on the lower jaw. The teeth do not appear to have any function, as the basking shark’s food does not need to be chewed or torn apart. Scientists speculate that they may be used before the shark embryo is born as they probably feed on unfertilized eggs in utero., a practice called oophagy.

After being born, baby basking sharks are called pups. Basking shark pups are estimated to be about 1.5 to 2 m long when they are born and take 12 to 16 years to reach adulthood for males and for females between 16 to 20 years.

The life cycle and reproduction of the species are actually still not well understood, but with the advent of tracking technologies, such as biologging and satellite-based tagging, more and more of the knowledge gap is being filled in.

What Eats Basking Sharks?

Does anything eat the world’s second largest fish? The answer is yes, there are a few creatures that prey on these massive fish.

Orcas, or killer whales, could possibly be one of the few predators of the basking shark. There have been scattered verbal reports of people witnessing orcas or great white sharks feeding on a basking shark’s dead body.

However, basking sharks are not a common prey for either of these predators, and no such kills have ever been recorded.

There is one other predator of these gentle giants, namely humans. Due to its slow swimming speed, easygoing nature, and formerly plentiful numbers, the species has been a mainstay of fisheries. Basking sharks may be used by humans for many things, including as a food source, with the flesh and fins (for shark fin soup) being eaten, and the liver used in shark liver oil. The hide has also been used, for leather, and shark cartilage is used in traditional Chinese medicine.

Due to rapidly decreasing numbers, the basking shark has been declared protected in certain territorial waters and trade in its products is restricted in many countries under CITES, including the United Kingdom and the Gulf regions of the United States.

Is A Basking Shark A Carnivore?

Basking sharks are not true carnivores, nor true herbivores, because they don’t distinguish between the two forms of plankton (zooplankton and phytoplankton) that they consume. We can call them omnivores, or perhaps, planktivores.

One study from 2001 reports anecdotally basking sharks feeding on small fishes that travel in schools, like herring. There is at least one case of an eel being found in the stomach contents of a basking shark. So yes, omnivores would be the way to classify them.

Sources:

  1. Basking Shark Factsheet. The Shark Trust. February 2013.
  2. Compagno, L.J.V. 2001. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Volume 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO Species Catalogue for Fishery Purposes. No. 1, Vol. 2. Rome, FAO
  3. Hallacher, L.E., 1977. On the feeding behavior of the basking shark, Cetorhinus maximus. Environ. Biol. Fishes 2(3):297-298.
  4. GE & RC Newell, Marine Plankton: A Practical Guide, Hutchinson Educational 1963
  5. Karl P. N. Shuker, The Hidden Powers of Animals: Uncovering the Secrets of Nature, Marshall Editions Ltd. 1970
  6. Siders ZA, Westgate AJ, Johnston DW, Murison LD, Koopman HN (2013) Seasonal Variation in the Spatial Distribution of Basking Sharks (Cetorhinus maximus) in the Lower Bay of Fundy, Canada. PLoS ONE 8(12): e82074.
  7. Sims, D. W. 2008. Sieving a Living: A Review of the Biology, Ecology and Conservation Status of the Plankton-Feeding Basking Shark Cetorhinus maximus. Adv. Mar. Biol. 54: 171-220

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