How Angel Sharks Work

As we mentioned, the angelsharkslive up to their "squatty" name, with most species ofsquatinameasuring only about 5 feet (1.5 meters). A few species, such as the Japanese angel shark and the Mediterranean angel shark, may be as long as 6.5 feet (2 meters), but that's about as long as they get. While most weigh about 60 pounds (27 kilograms), the biggest angel shark, found in Europe, has been known to weigh 170 pounds (77 kilograms) [source:Lineaweaver].

Angel sharks look more likeraysthangreat whites, but they have all the same basic equipment as sharks. It just happens that the equipment is flattened dorsoventrally, or from top to bottom. Thepectoral finsthat give the angel shark its name are probably the first thing to strike your eye. To review, these fins aren't attached to the head, as they are in rays. Thepelvic finsare similarly flattened and expand outward from the body.

The mouth is located at the very tip of the snout, and inside are some truly scaryteeth. Shaped like triangles, the teeth are extremely sharp and come to needlelike points. On either side of the mouth arebarbels, which are whiskerlike antennae that sniff out the chemical reactions of prey along the bottom of the ocean floor.

Along the side of the head aregill slitsthat allow the angel shark to breathe. The positioning of the gill slits represents another important distinction from rays and skates, which have gill slits on the bottom of their heads. Unlike many other sharks that must constantly swim to pullwaterover their gill slits, the angel shark uses its muscles to pull water over the gill slits while in a resting position. This shark also has aspiracle, or a tube behind the eyes that can pull in water when the shark's mouth is closed.

One way that angel sharks do differ from other sharks is theircaudal fin, or tail. Most sharks' tails are top-heavy, meaning that the top lobe of the fin is bigger than the second one. The opposite holds true for angel sharks. They have a longer lower lobe, which may help them achieve a quick liftoff when they attack their prey from below.

一个成功的攻击从下面一个一个的关键gel shark's next meal. Many of the angel shark's features, from its flattened body to its barbels to a tail that helps it move upward quickly, allow it to live at the bottom of the ocean floor, waiting for prey to swim by. Even its coloring providescamouflage. Angel sharks are various shades of white, gray, brown and black, colors that blend in with the ocean floor. Some have red spotting, which may provide even more coordination with their habitat.

Find out where they're lying in wait, and what exactly they're waiting for, on the next page.

Angelsharksare found all over the world, including both the western and eastern sides of the Atlantic and Pacific oceans. They're generally not found in the Indian Ocean, except for one southwestern corner. To learn exactly where angel sharks are found, see the sidebar.

Of all the angel sharks, the Pacific angel shark is probably the most studied and best known, although many of these species are likely the same except for location. Even if they make their homes in different parts of the world, in waters ranging from cool to tropical, angel sharks are still seeking out the same parts of the ocean. They're found on the very bottom of the ocean floor, either in shallow areas or at depths of up to 4,265 feet (1,300 meters).

The angel shark buries itself into the sand and mud at the bottom of the ocean floor, with only its eyes poking out. They can lie there for days at a time, waiting for the perfect meal to swim by. When this shark strikes its prey -- normally鱼,如比目鱼和大比目鱼,甲壳类动物ormollusks-- its front half rises suddenly to ambush the prey from below. It can attack and capture its prey in a tenth of a second [source:Martin]. Angel sharks seem to favor one hunting spot strongly, but if the local fish figure out where the shark is hiding, then the angel shark will temporarily move several miles away.

While their barbels are constantly working, the most important sense to a hunting angel shark is its sense of sight. In a study, Pacific angel sharks were presented with rubber fish, which didn't contain any of the same olfactory,electricalor vibratory cues of a regular fish. The angel shark struck at virtually all of the targets [source:Martin]. When hunting at night, angel sharks are tipped off to a fish's presence by the生物荧光plankton in the fish's wake. Some angel sharks are probably exclusively nocturnal.

When provoked, the angel shark turns its sharp bite on humans, but generally, angel sharks have much more to fear in terms of us taking a big bite out of them. Find out about angel shark fishing on the next page.

Largersharks, including the大白鲨, may prey on the angel shark, but the angel shark's real threat is. Or more specifically, one man, by the name of Michael Wagner. Until the 1970s, angel sharks were thought of as a "junk fish," something that got caught in a fishermen's net by accident. Fishermen threw them back, until Wagner, a seafood processor in California, began to spread the word about the tastiness of the Pacific angel shark.

Wagner's campaign was almost single-handedly responsible for bringing the angel shark to millions of plates. In 1977, only about 366 pounds (166 kilograms) of Pacific angel shark were caught, but by 1984, that had become 700,000 pounds (317,545 kilograms) [source:Monterey Bay Aquarium]. When鱼ing for this sharkreached its peak in 1985 and 1986, about 1.2 million pounds (544,311 kilograms) of sharks were being caught each year [source:Martin].

While this was good news for inventive cooks and shark connoisseurs, it was extremely bad news for angel shark populations, which were nearly decimated when the high fishing rate was combined with their low reproductive rate and slow growth.

Pacific angel sharks typicallygive birthto litters of about 8 to 13, while other species may have litters of just six or up to 25 [sources:Martin,Awruch et al.,Hansen]. The gestation period varies among species but is generally between eight and 10 months. Angel sharks areovoviviparous, which means that the females carries the eggs, but the eggs hatch inside and the pups are born live. Angel shark pups measure only about 9 inches (23 centimeters) at birth. Adults try to protect the small pups by giving birth in deeper waters [source:Martin]. Still, only about 20 percent of Pacific angel sharks survive to maturity [source:Bester].

不是每一个gel shark is subject to this kind of fishing, but many angel shark populations have been declining [source:Morey et al.]. In some areas, the fish appears to have vanished completely, but specific numbers are hard to come by. These sharks are listed as "vulnerable" by the International Union for Conservation of Nature (IUCN), and some of the fisheries are subject to increased regulation. When not caught, it's estimated that angel sharks live about 25 years [source:Kay].

You can fish for more information on angel sharks and other shark species on the next page.