When considering the ocean's apex predators, creatures such as killer whales and great white sharks often come to mind. However, wobbegong sharks, with their unique hunting strategies and significant presence in their ecosystems, deserve equal recognition. This article delves into the dietary habits of wobbegong sharks, exploring their hunting techniques, preferred prey, and ecological importance.
Wobbegong Sharks: Masters of Camouflage
Belonging to the Orectolobidae family, wobbegong sharks are commonly referred to as carpet sharks due to their flattened bodies and ornate patterns. The name "wobbegong" itself is believed to have originated from an Australian Aboriginal word, potentially meaning "shaggy beard," referring to the tassel-like skin flaps around their snouts.
These sharks primarily inhabit the eastern Indian Ocean, western Queensland, and southern Australia. One species, the Japanese wobbegong, is found near Japan and the South China Sea. They typically reside on coral and rocky reefs and sandy ocean bottoms in shallow waters.
Wobbegongs have a unique body shape; their head and body are very flattened, and their pectoral and pelvic fins are broad. Most wobbegongs grow to be 3 to 5 feet long, but they can reach a maximum length of 10 feet.
Hunting and Feeding Behavior
Wobbegongs are masters of camouflage, blending seamlessly with their surroundings. Their flattened bodies, broad fins, and variegated brownish-grey markings with pale ring-like spots help them remain almost undetectable on the ocean floor. Even their eyes are camouflaged by eye-shaped markings, making them difficult to spot. This remarkable camouflage is essential for their ambush predation strategy.
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These sharks are generally docile and sluggish during the day, often resting in specific caves, sometimes shared with small schooling fishes. As nocturnal hunters, wobbegongs become active at night, lying in wait for unsuspecting prey. They capture food by remaining motionless and blending in with their surroundings. When prey swims nearby, the wobbegong opens its huge jaws and sucks in the surrounding water and the prey. They create suction by opening their mouths at lightning speed, causing pressure differences in the water.
About 50-80% of the wobbegongs examined have empty stomachs, which isn't surprising for an ambush predator. They are champions at doing nothing, but when an unwary fish swims past, they strike with incredible speed.
Diet Composition
Wobbegongs are opportunistic feeders with a diverse diet that includes:
- Benthic Fish: As bottom-dwelling predators, wobbegongs primarily feed on fish that inhabit the seabed.
- Invertebrates: Their diet also consists of various invertebrates, such as crayfish, crabs, lobsters, and octopus. Octopi are among their preferred prey items.
- Other Sharks: Even other sharks can be an important component of their diet. Smaller wobbegongs and other species like Port Jackson sharks have been found in the stomachs of larger wobbegongs.
They eat other sharks! A scientist conducting a survey of reef fish came across a tasselled wobbegong chowing down on a brown-banded bamboo shark, which is almost 80% of the wobbegong’s own size! It was a real case of ‘eyes bigger than your belly’ - 30 minutes later, the wobbegong had only managed to engulf the head.
Wobbegongs can extend their mouth by as much as 30% of the nasal distance from its anterior most point to the anterior edge of the pectoral fin, to capture prey. This is equivalent to the combined length of the head and branchial arches. Prey have even been known to nibble on this shark’s dermal lobes before being eaten.
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Regional Variations and Specific Species
The diet of wobbegongs can vary depending on their location and the availability of prey. For example, the tasselled wobbegong (Eucrossorhinus dasypogon), found in New Guinea and northern Australia, feeds on benthic fish, invertebrates, and occasionally other sharks.
The spotted wobbegong (Orectolobus maculatus), native to the western Pacific Ocean around Australia, also consumes invertebrates such as crabs, lobsters, and octopi, as well as bony fish and even other small sharks.
Ecological Role
Wobbegongs play a crucial role in their ecosystems as high-level predators. Marine biologist Charlie Huveneers found that wobbegongs fit into the food web at a similarly-high level to marine mammals.
There are high densities of these large predators at sites such as Julian Rocks off Byron Bay. It is plausible that their density compares to the 14-40 grey reef sharks per hectare documented at near-pristine French Polynesian atolls, which creates an ‘inverted trophic pyramid’ at that incredible site. Neglecting the ecological importance of these "Rugs of Doom" on subtropical and temperate reefs seems unwise.
Conservation Status and Threats
The International Union for Conservation of Nature (IUCN) lists the wobbegong shark as a data-deficient species. They are sometimes caught as bycatch in commercial fisheries, but fishermen do not typically target them. In New South Wales wobbegongs were targeted in the early 90’s by trawl fisheries. After numbers declined locally it was listed as “vulnerable”. As fishing intensity decreased the population stabilized. In the mid 2000’s New South Wales saw a drop in harvest numbers again.
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Threats to tasselled wobbegongs are thought to be minimal, mainly because of their association with coral reefs (a substantial part of their range falls within the Great Barrier Reef Marine Park). They are caught as by-catch occasionally by fisheries, but are not a target species. Habitat loss is thought to be more of a threat, especially as climate change advances.
Human Interactions
Wobbegongs are generally not aggressive toward humans. However, they have been known to bite when stepped on or provoked. The spotted wobbegong can be aggressive. There are multiple accounts of unprovoked attacks on divers well above the bottom. There are also reports of wobbegongs biting people if stepped on, or when limbs come close to the mouth and are mistaken for prey. This shark is often reluctant to let go once it bites, causing severe lacerations.
Incidents usually occur when divers have accidentally strayed too close to a well-camouflaged wobbegong or when they have deliberately provoked one.
Reproduction and Life Cycle
Spotted wobbegongs are ovoviviparous, meaning they produce eggs that hatch inside them before giving birth to live young. A female can give birth to up to 20-37 pups at a time, each of which becomes self-sufficient immediately after birth.
During breeding season, the male is attracted to the female by chemical pheromones that she releases into the water. The male attaches to the female by biting near the gills and then copulates. Females have a triennial reproductive cycle, follicles take two years to mature before ovulation. Gestation lasts 10-11 months, with pups being born September-October. New pups are born at 23 cm (9 in.).
Interesting Facts
- Tasselled wobbegongs are nocturnal and are only active at night. During the day, they rest in caves and under ledges, with their tail curled up. However, tasselled wobbegongs never miss the opportunity for a snack - sometimes they’ll catch and eat the fish they share the cave with!
- The shark’s latin name - Eucrossorhinus dasypogon - roughly translates as ‘well-fringed nose with a shaggy head’.