#pelagic

Two entwined pelagic sea snakes, now classified as Hydrophis platurus. Icones amphibiorum. 1835.

Known as the Yellow-Bellied Sea Snake.

Echeneis naucrates

Sharksucker

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Status: Least concern

Whale shark

Rhincodon typus

Family: Rhincodontidae

The whale shark is a massive, gentle filter-feeding shark and the largest living fish in the world, but despite its enormous size, this docile giant is not a predator but a specialist that feeds on some of the ocean's smallest creatures.

Physical Description and Size

The whale shark has a massive, stout, cylindrical body with a broad, flattened head and a very short, squarish snout. The body coloration of this species is dark gray to gray-brown dorsally with a white or yellowish underside and is covered with a unique pattern of white or yellowish spots and transverse stripes, which are as distinctive as human fingerprints.

The distinctive features of this shark include three prominent longitudinal ridges that run along each side of the body, and an enormous mouth located nearly at the tip of the snout. The first dorsal fin is positioned behind the midbody; the tail fin is crescent-shaped with a longer upper lobe and no subterminal notch. Its teeth are very small and numerous, but play no role in feeding, as the whale shark is a filter feeder.

Size and Weight: ◦ Length: Maximum size remains uncertain, but lengths of up to 18.3 meters have been reported as credible, while a common length is 10 to 15.5 meters. ◦ Weight: They can weigh more than 10 tons.

Distribution and Habitat

The whale shark has a circumtropical distribution, found in warm temperate and tropical oceans worldwide.

Genetic analysis shows two distinct populations: one in the Atlantic Ocean and one in the Indo-Pacific Ocean. The species has been seen throughout tropical and subtropical waters of the Atlantic, Pacific, and Indian Oceans. In the eastern Pacific, they range from off the coast of California and Mexico to northern Chile and the Galapagos Islands.

They are epipelagic sharks that prefer open ocean waters; often in regions of upwelling, they have also been found near continental shelves and coastal aggregation sites where food is abundant.

Behavior and Diet

The whale shark is a slow-moving filter feeder that is not a top predator but a specialist on small organisms.

They swim slowly, typically at about 5 kilometers per hour, and are generally solitary but can form seasonal aggregations in areas with abundant food, and some populations migrate vast distances, timing their visits around annual plankton blooms or fish spawning events.

Whale sharks are filter feeders that use two primary feeding methods:

Active suction feeding: By rapidly opening and closing the mouth to suck water in.

Ram filter feeding: While swimming with the mouth agape, allowing water to flow in passively.

As the water enters the enormous mouth and passes over specialized filter pads located between the gill arches, the food particles are trapped while the water is expelled through the gills.

They feed primarily on small pelagic prey. Diet: ◦ Primary: Phytoplankton, zooplankton (copepods, krill), fish eggs, and crab larvae. ◦ Secondary: Small crustaceans, squid, and small schooling fishes (anchovies, herrings, and sprats).

Reproduction and Life Cycle

Whale sharks are ovoviviparous; their have an unknown gestation period and litter size, but the pups measure approximately 40 to 60 cm at birth.

Also, where whale sharks give birth remains a mystery, scientists believed they relied on coastal nursery areas., but a nine-year tagging study suggests they may give birth in the open ocean, which is unusual for sharks.

The whale shark’s life cycle and lifespan are still largely an enigma.

Relationship with Humans

Whale sharks are considered harmless to humans; they are docile, gentle giants, that are easily approached by swimmers, snorkelers, and divers, and in many locations, swimming with whale sharks is a popular ecotourism activity valued at US$1.9 billion worldwide, attracting over 25.5 million people annually at 46 sites in 23 countries. While this provides economic incentives for conservation, unregulated tourism can cause stress, behavioral changes, and boat-related injuries to the sharks.

Whale sharks are rarely kept in captivity due to their enormous size, specialized filter-feeding requirements, and need for vast amounts of space. Only a few large public aquariums such as the Okinawa Churaumi Aquarium in Japan and the Georgia Aquarium in the USA have successfully housed them for extended periods.

⚠️Conservation Status

The International Union for Conservation of Nature (IUCN) classifies the whale shark as Endangered.

The major threats are anthropogenic (human-caused) such as overfishing, bycatch, boat strikes, habitat loss and pollution, and climate change.

Conservation Efforts: The whale shark is protected in several countries' waters, including the United States (prohibited species), Mexico (threatened status under NOM-059-SEMARNAT), Ecuador (Galapagos Marine Reserve), and the Bahamas (all sharks protected), and is listed in Appendix II of CITES, which regulates international trade.

🦈Fascinating Facts

Small fish such as remoras (suckerfish), pilot fish, and juvenile golden trevallies are often seen "hitching a ride" on whale sharks' skin, and even inside their mouths; these fish feed on parasites attached to the shark's skin, keeping the shark clean while getting free food and protection.

The presence of whale sharks indicates an abundance of plankton, which in turn reflects the overall health of the ocean. They serve as bioindicators for marine ecosystem health.

The Galapagos Marine Reserve is one of the only places in the world where the vast majority of visiting whale sharks are mature females, many of which appear pregnant. This makes Galapagos a critically important site for research into whale shark reproduction.