The basking shark, a slow-moving filter feeder, is the second-largest fish in the world after the whale shark. With its enormous mouth and seemingly fearsome appearance, it is often mistakenly regarded as a threat.
However, these sharks are known for their peaceful nature, often seen “basking” at the ocean’s surface, passively filtering the plankton, their primary food source.
This article delves into the mesmerizing life of the basking shark, revealing fascinating details about its biology, behavior, and conservation.
The Basking Shark at a Glance
Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes (Cartilaginous fish) |
| Order: | Lamniformes |
| Family: | Cetorhinidae |
| Genus: | Cetorhinus |
| Species: | C. maximus |
Essential Information
| Average Size: | 20-26 feet (6-8 meters) |
| Average Weight: | 11,000 lbs (5,000 kg) – 19,000 lbs (8,600 kg) |
| Average Lifespan: | 50 years |
| Geographical Range: | Global; typically in temperate oceans |
| Conservation Status: | Endangered (IUCN Red List) |
Species and Subspecies
The basking shark, Cetorhinus maximus, is the sole member of its genus Cetorhinus and does not have any recognized subspecies. It is unique within its family, Cetorhinidae. Thus, when referring to the basking shark, one is invariably referring to Cetorhinus maximus, and there are no subspecies or variants to differentiate.
Description
The basking shark is a colossal and imposing fish, second only to the whale shark in terms of size among all extant fish species. Adult basking sharks typically measure between 20-26 feet (6-8 meters) in length, although there have been unverified reports of individuals reaching up to 40 feet (12 meters). Their weight can vary significantly, with adults usually weighing between 11,000 lbs (5,000 kg) and 19,000 lbs (8,600 kg).
Their bodies are torpedo-shaped, streamlined, and predominantly greyish-brown, often with mottled skin patterns. This coloration provides some degree of camouflage in the open ocean.
The most distinguishing feature of the basking shark is its enormous, gaping mouth, which can open up to 3 feet (1 meter) wide. This wide mouth, paired with a series of long gill slits, allows it to filter vast amounts of water for plankton, its primary food.
Another notable feature is the shark’s dorsal fin, which is large, triangular, and often visible above the water’s surface when the shark is feeding. The basking shark also has a crescent-shaped caudal (tail) fin and smaller pectoral fins.
In terms of sexual dimorphism, females tend to be slightly larger than males. The males have claspers, a pair of modified pelvic fins, which are used for mating. These claspers are absent in females. However, aside from these reproductive structures and slight size differences, males and females are generally similar in appearance.
Habitat and Distribution
Basking sharks inhabit temperate coastal and shelf waters worldwide, ranging from the Arctic to the Antarctic. These massive creatures are pelagic, meaning they spend most of their time in the open ocean, but they do occasionally venture closer to shore, especially during feeding seasons.
While they are known to dive to depths of up to 3,280 feet (1,000 meters), they are most commonly spotted near the surface, especially when feeding. Seasonal migrations are a key aspect of the basking shark’s life, often influenced by the availability of their primary food source: zooplankton.
Behavior
Basking sharks are predominantly diurnal, actively feeding during the day. This daytime feeding often leads to their misperception as “sunbathing” sharks, further lending to their name, although they do not bask in the sun in the traditional sense.
They are generally solitary creatures but can sometimes be seen in groups, especially in areas with high concentrations of plankton. During peak feeding seasons, these gatherings can comprise dozens of individuals. Despite their massive size and ominous appearance, basking sharks are incredibly docile and pose no threat to humans.
Basking sharks primarily rely on passive filtration to feed. They swim with their vast mouths open, funneling water through their gill rakers to trap and consume zooplankton. The process is efficient, allowing them to filter thousands of tons of water per hour.
Communication among basking sharks is not well-documented, and their vocalization (if any) is yet to be detailed. They are believed to communicate primarily through body language and physical signals, especially during mating rituals. The presence of scars and marks on many mature males suggests that aggressive interactions, possibly related to mating competitions, occur.
An interesting aspect of their behavior relates to their shedding of gill rakers. Basking sharks shed and regrow their gill rakers multiple times throughout their lives, particularly when transitioning between feeding and fasting periods. This phenomenon ensures they always have effective tools for filtration when they’re in plankton-rich regions.
Diet and Feeding Behavior
The basking shark is a filter feeder, primarily consuming zooplankton. This puts them in the category of carnivores, albeit passive ones. Their diet mainly consists of copepods, barnacle larvae, decapod larvae, and other small marine organisms. They’ve also been known to consume small fish on occasion.
Unlike many other sharks, basking sharks don’t actively “hunt” their prey. Instead, they swim with their enormous mouths wide open, passively filtering water as they go. The water enters the mouth and passes over specialized structures known as gill rakers, which trap the tiny organisms.
The filtered water then exits through their gills. This method of feeding requires the shark to move continuously to ensure a steady flow of water and food. A basking shark can process up to 1,500 tons of water per hour when feeding in plankton-rich areas.
Predators
Given the basking shark’s significant size, adult individuals face few threats from marine predators. However, orcas (killer whales) have been known to prey on basking sharks occasionally. The primary threat to young basking sharks comes from larger sharks, including the great white shark.
Human interactions, primarily through fishing, pose a more substantial threat to basking sharks than natural predators. Although they are not typically targeted for their meat, they are often caught as bycatch in fishing nets. Additionally, their fins and liver are highly valued in some cultures. As slow-moving creatures, they are also at risk of injury or death from boat strikes.
Reproduction and Life Cycle
Basking sharks exhibit ovoviviparity, a reproductive mode where embryos develop inside eggs that remain in the mother’s body until they are ready to hatch. The exact breeding habits of basking sharks remain somewhat enigmatic due to the limited observation of their reproductive behaviors in the wild. However, it’s believed that these sharks engage in a courtship ritual, which includes parallel swimming.
The gestation period for basking sharks is thought to be long, possibly up to three years, although concrete data on this aspect is still limited. When it’s time to give birth, the female releases fully-formed pups, typically ranging from four to six in number, although litters of up to 15 have been recorded. These pups can be quite large at birth, often measuring over 5 feet (1.5 meters) in length.
After birth, basking sharks receive no parental care. The young are born well-developed and capable of fending for themselves immediately.
Conservation and Threats
The basking shark is currently listed as “Endangered” on the IUCN Red List of Threatened Species. This designation stems from a history of commercial exploitation for their liver oil, meat, and fins. Populations were significantly reduced in the 20th century due to intensive fisheries.
The primary threats facing basking sharks today include bycatch in fisheries, boat strikes, and marine pollution. Climate change, which affects the distribution and abundance of plankton, their primary food source, can also influence their migration and feeding patterns.
Conservation efforts for basking sharks are ongoing. Numerous countries have implemented protective measures to prevent targeted fishing and reduce bycatch.
These include fishing moratoriums, protective legislation, and the establishment of marine protected areas. Public awareness campaigns and ongoing research also play vital roles in conserving and understanding this enigmatic and gentle giant of the sea.
Fun Facts
- The basking shark is the second-largest fish in the world, only surpassed by the whale shark.
- Despite their formidable size, basking sharks feed primarily on tiny plankton, filtering water through their enormous mouths.
- Basking sharks are known for their propensity to “bask” near the ocean’s surface, giving them their name, although the reason for this behavior is still a matter of scientific discussion.
- They have a unique, three-pronged tail fin, with the upper lobe being much longer than the lower one, giving it an almost crescent shape.
- The basking shark’s liver can weigh up to 2,000 pounds (907 kilograms) and makes up nearly 25% of its total body weight.
Frequently Asked Questions
How did the basking shark get its name?
The basking shark got its name from its behavior of swimming slowly near the surface, or “basking” in the sun, especially during warmer months.
Are basking sharks dangerous to humans?
No, basking sharks are not dangerous to humans. They are filter-feeders and have no interest in larger prey. There have been no reported incidents of basking sharks attacking humans.
Why are basking sharks important to the ecosystem?
Basking sharks play a crucial role in marine ecosystems. As filter feeders, they help maintain plankton populations and contribute to the health and balance of the marine food web.
How fast can a basking shark swim?
Basking sharks are generally slow swimmers, moving at speeds of about 2 to 3 mph (3 to 5 km/h). However, they are capable of short bursts of speed when needed.
How do basking sharks eat without teeth?
Basking sharks have very small teeth, but they don’t use them for feeding. Instead, they swim with their mouths wide open, taking in vast amounts of water filled with plankton. The water is then expelled through their gills, while tiny organisms are trapped by gill rakers and swallowed.
