Angel sharks, belonging to the genus Squatina, are a unique group of sharks characterized by their flattened bodies and wing-like fins, giving them a striking resemblance to rays. These fascinating creatures are found in temperate and tropical oceans worldwide, often dwelling on sandy or muddy seabeds. This article delves into the dietary habits of angel sharks, exploring their feeding strategies, preferred prey, and the ecological factors that influence their diet.
Angel Shark Anatomy and Hunting Adaptations
Angel sharks are perfectly designed for ambush predation. Their large, stocky, and flattened body, coupled with expansive pectoral fins, allows them to create a depression in the seabed. Here, they lie in wait, partially buried in the sand, prepared to strike at any unsuspecting prey that ventures too close.
One remarkable adaptation is the angel shark's unusually flexible 'neck,' enabling them to quickly raise their heads and snap their trap-like jaws to capture prey with remarkable speed.
These sharks are masters of camouflage, boasting skin mottled with brown, grey, black, green, and often white spots. This intricate pattern allows them to seamlessly blend into the mud or sand, remaining undetected by their prey. They spend most of their time concealed just beneath the surface, with their eyes positioned prominently on the top of their head, keeping them above the sand.
Adding to their stealth, angel sharks are mostly nocturnal hunters.
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Another incredible adaptation found in sharks is their spiracles, located behind their eyes. These openings allow them to draw water over their gills even when buried in the sand, a crucial adaptation for their ambush lifestyle.
Feeding Behavior and Diet
Angel sharks are opportunistic feeders with a diet primarily consisting of bottom-dwelling organisms. They employ a "lie-in-wait" strategy, remaining motionless and camouflaged until prey approaches. Their diet includes:
- Bony Fishes: A significant portion of their diet comprises various bony fishes found on the seabed. Flatfishes are a particularly favored prey.
- Crustaceans: Crabs, shrimp, and other crustaceans are also common food items.
- Mollusks: Mollusks like squid form a part of the angel shark's diet, especially for those residing in the Mediterranean and Canary Islands.
- Skates: Some species also prey on skates.
The specific composition of their diet can vary depending on geographic location and the availability of prey. For instance, studies have shown regional variations in their diet. In the Mediterranean, they additionally consume hake, mullet, crabs, and squid, while in the Canary Islands, bony fish and squid are dominant. They have strong jaws and numerous small, sharp teeth that help them secure and consume their food.
Hunting Techniques
Angel sharks are ambush predators, relying on stealth and camouflage to capture their meals. They typically bury themselves partially in the sandy or muddy substrate, leaving only their eyes and spiracles exposed.
When prey approaches, the angel shark rapidly lunges forward, using its large, protrusible jaws to capture and swallow the prey. They are not fast swimmers, relying more on their ambush hunting technique rather than actively pursuing their prey. Their flattened body and broad pectoral fins allow them to glide along the bottom efficiently while minimizing disturbance to the surrounding sediment.
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Angel sharks can lie camouflaged on the seafloor for extended periods, striking within a tenth of a second to catch any prey that ventures too close. They can wait for days but strike passing prey within a tenth of a second. Their color patterns and body shape allow them to lie flat and camouflaged on the sand. They can pump water over their gills, allowing them to remain perfectly still.
Their hunting areas are relatively small, around 45-60 meters.
Specific Species and Their Diets
While the general feeding habits are similar across angel shark species, some variations exist:
- Atlantic Angel Shark (Squatina dumeril): This species feeds on a variety of bottom-dwelling organisms.
- Japanese Angelshark (Squatina japonica): The diet of this species consists of demersal fishes, cephalopods, and crustaceans.
- Common Angelshark (Squatina squatina): Their diet appears to consist primarily of flatfish, but there is also some regional variation. For instance, in the Mediterranean, they feed additionally on hake, mullet, crabs, and squid. In the Canary Islands, bony fish and squid are dominant in their diet.
Habitat and Distribution Influences
Angel sharks are typically found in shallow, coastal habitats, often in sand or mudflats of less than 5 m, in the eastern North Atlantic, throughout European waters and the West African coast down to Gambia. Lagoon and seagrass habitats also appear to be important to this species. However, their current distribution appears to be largely reduced from this historic range. Although they are still sighted regularly in the Canary Islands, they are now considered locally extinct in the North Sea.
Angel sharks, Squatina squatina, have a relatively broad distribution in the northeastern Atlantic Ocean. Their world range extends from the southern coasts of Norway and the British Isles, the Mediterranean Sea, and south to Morocco.
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These sharks are primarily found in coastal waters, preferring shallow areas rather than deep oceanic regions. They inhabit a variety of habitats, including sandy or muddy bottoms, rocky areas, and seagrass beds. They are particularly adept at adapting to environments with soft substrates, which allows them to bury themselves and camouflage effectively.
Angel sharks are known to occur at depths ranging from a few meters to around 150 meters (490 feet), although they are typically found at shallower depths. They have been observed in areas such as bays, estuaries (brackish waters), and coastal shelves, as well as near offshore islands and reefs.
The availability of prey and the type of habitat greatly influence the diet of angel sharks. Those living in areas with abundant flatfish will likely consume more flatfish, while those in areas with more crustaceans will consume more crustaceans.
Conservation Status and Threats
Unfortunately, angel sharks are among the most threatened families of sharks. The Angel shark, Squatina squatina, is classified as Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List. Of the 23 species, 12 are on the UICNT Red List of Threatened Species.
Several factors contribute to their decline:
- Overfishing: Angel sharks are often caught as bycatch in fishing gear intended for other species. They are particularly vulnerable to bottom trawling, a fishing method that involves dragging nets along the seabed, as they are bottom-dwelling species. Being accidentally caught in fishing gear significantly reduces their numbers.
- Habitat Loss and Degradation: Destruction and alteration of their coastal habitats, such as the destruction of seagrass beds and damage to sandy and muddy areas, have a negative impact on Angel sharks. These habitats provide important foraging and nursery grounds for the species.
- Coastal Development: Urbanization and coastal development can lead to increased pollution, sedimentation, and disturbance of coastal ecosystems. These factors can disrupt the natural habitat of Angel sharks and have detrimental effects on their survival.
- Climate Change: Climate change impacts various aspects of Angel shark ecology, including changes in sea temperature, ocean acidification, and alterations in prey availability. These factors can affect their distribution, reproduction, and overall population health.
- Illegal Fishing and Trade: Angel sharks are also targeted for their meat, fins, and other body parts, which are in demand in illegal wildlife trade markets.
Conservation efforts are focused on protecting their habitats, implementing fishing regulations, and raising awareness about the importance of preserving this species. In some countries, scuba divers are helpful to angel shark conservation strategies. If there are several divers: they do not go around it and do not stand in front of it.
Reproduction and Life Cycle
Angel sharks are lecithotrophic viviparous, also called ovoviviparous. It means the mother carries the fertilized eggs in a gestation period between 8 and 10 months. The eggs then hatch inside it. In each birth, between 7 and 25 pups of 24â34 cm in length are born. Scientists think Angel sharks breed biennially.
The life history of Angel sharks, Squatina squatina, encompasses various aspects of their reproductive behavior, growth, and longevity. Here is an overview of their life cycle:
Reproduction: Angel sharks are ovoviviparous, meaning that they give birth to live young. The females have internal fertilization, where males transfer sperm to the femaleâs reproductive tract. After mating, the embryos develop inside eggs within the femaleâs body. The gestation period is estimated to be around 8 to 10 months.
Birth and Growth: When the embryos are fully developed, the female Angel shark gives birth to live pups. The litter size typically ranges from 7 to 25 individuals, depending on the size and condition of the female. The newborns measure about 24 to 30 centimeters (9.4 to 11.8 inches) in length and are already capable of swimming and hunting on their own.
Growth and Development: As the young Angel sharks grow, they feed on small fishes and invertebrates in their habitat. They undergo a slow growth rate, with males reaching sexual maturity at 147.5 cm (4.8 feet) or around 8 to 10 years of age and females at approximately 12 to 15 years. The growth rate is influenced by various factors, including food availability, temperature, and genetic factors.
Longevity: Angel sharks have a relatively long lifespan compared to many other shark species. They can live up to 30 years or more, although the exact lifespan in the wild is not well-documented.
Angel Sharks and Humans
Historically their meat was also valued in Europe, where it was referred to as âwhite tunaâ. Once abundant throughout their range, declines are now so severe that the last angel shark recorded in the North Sea was in 1966. Angel sharksâ relationship with people has primarily been one of exploitation. However, in a few remaining refuges such as the Canary Islands, there is a burgeoning ecotourism trade around diving and snorkelling with them. They are generally placid and reliably observed. There is also increasing recognition of the severe population declines and urgent need for effective conservation measures. They are now listed on both Appendix I and II of CITES, which severely restricts international trade.