Hear the word “shark” and, if you are like most people, you probably think of hair-raising scenes filled with snapping jaws and mouths full of razor-sharp teeth. You might envision a great white shark “leaping” out of the water with a sea lion pup dangling from its jaws or a big school of scalloped hammerheads. Perhaps a close-up of the frightening face of a gray nurse or mako shark comes to mind. Or maybe it’s a scene of a tiger shark or oceanic whitetip pursuing its prey, or possibly a gang of blue sharks feeding on squid.
Most people are not very likely to think of rather innocuous animals like horn sharks, Port Jackson sharks, nurse sharks, angel sharks or filetail catsharks. The same is true for the species commonly known as the swell shark, spiny dogfish and zebra shark. Even though these species don’t look as fierce as many, more highly publicized sharks, they are sharks, every bit as much as great whites, tigers, makos and all the rest.
It is relatively easy for film and television producers to make some sharks appear to be big, bad and dangerous — the on-air qualities that draw large viewing audiences. But even with the marvels of modern technology it’s hard to make many other sharks look fierce enough to keep us tuned in. In a world with more than 370 species of sharks, the vast majority of sharks get overlooked for this very reason most of the time, which leads to a lot of misunderstandings about sharks.
They’re Not All “Jaws”
Three species that are not going to get a lot of exposure on television are commonly referred to as nurse sharks. All are regularly encountered by sport divers in a variety of tropical and subtropical locations. Nurse sharks are bottom-dwelling, nocturnal creatures that chiefly prey on bottom fishes and invertebrates including lobsters, crabs, snails, octopuses, squids and various echinoderms. When encountered during the day these lethargic sharks tend to be tucked under ledges or resting in caves or on the sea floor.
However, at night they transform themselves into determined predators that routinely knock over coral heads and big boulders to get to their intended prey that they “vacuum” into their mouths while using a powerful, suction-feeding technique. This feeding method has earned them the nickname “sucker shark” due to the sucking noise nurse sharks make while trying to steal fishermen’s baits.
As is the case with many bottom-dwelling sharks, nurse sharks are equipped with sensory barbels, whiskerlike appendages that project downward from their nostrils. The barbels are used to taste the bottom as the sharks look for chemical cues that indicate the presence of prey. Barbels are indicative of the fact that when hunting, nurse sharks rely heavily upon olfactory clues and visual information.
Ginglymostoma cirratum, the species of nurse shark that is commonly seen by sport divers in North Carolina, Florida, the Bahamas and Caribbean, ranges all the way from Rhode Island to Brazil and is found throughout the Caribbean Sea. A surprising number of divers have been bitten by nurse sharks and other bottom-dwelling sharks over the years. Not surprisingly, the cause of the “attack” is usually teasing the animals with bait or grabbing the sharks by their tail. A word to the wise here: Don’t let their sluggish nature fool you. Nurse sharks are very well-equipped to take care of themselves. After all, they can bite a lobster in half in a heartbeat.
To clear up a point of potential confusion, the gray nurse shark (a.k.a. sand tiger and ragged tooth), Carcharias taurus, a species that is commonly encountered on many shipwrecks in North Carolina’s “Graveyard of the Atlantic,” is not a type of nurse shark. The gray nurse is described in a different family of sharks than true nurse sharks.
The zebra shark (Stegostoma fasciatum) is frequently encountered by sport divers throughout Indo-Pacific waters. The most notable feature of this spotted, bottom shark is a tail that is almost half as long as the rest of the body. This vigorous side-to-side movement of the tail helps zebra sharks gain a lot of power and leverage when they try to capture prey that is hiding in tough-to-get-to places under coral heads and ledges.
While the Southern California Pacific is inhabited by a number of “headline grabbing” sharks such as great whites, threshers, shortfin makos and blues, it is also blessed with a number of smaller, less publicized species. A list of these includes the horn, swell, leopard and Pacific angel shark. All are commonly encountered by divers.
Horn sharks (Heterodontus francisci) are named for both the horny ridges over their eyes and the white, spinelike appendages that protrude from each of two dorsal fins. When held in an erect position these spikes can be a strong deterrent to predators. On several occasions I have seen a horn shark that was grabbed by a large angel shark be spat out as the hunter was thwarted by the pain inflicted by the spines of the much smaller horn shark.
Bottom dwellers, horn sharks are also characterized by their brownish bodies (with numerous black spots on some specimens), short, blunt heads, piglike faces and pursed lips. Most horn sharks are 2-3 feet long (0.67-1 m), but they are documented to 4 feet (1.2 m). Primarily nocturnal hunters, horn sharks prey upon a variety of crustaceans, mollusks, echinoderms and smaller reef fishes. Their mouths are equipped with two types of teeth: front teeth with sharp cusps for grasping prey and rear teeth with rounded cusps used for crushing.
To describe horn sharks as docile and easy to approach is understating the facts. They are often encountered with their head tucked into a crevice or buried under a kelp blade that has come to rest on the sea floor. Neither pose does much to enhance the fierce reputation of sharks.
The horn shark found in Southern California waters is described in the same family of sharks as its more highly publicized and larger Australian relative, the Port Jackson shark (Heterodontus portjacksoni). A temperate-water species, Port Jacksons are known for gathering in huge concentrations in cold-water bays south of Sydney, Australia, when they mate and lay their eggs in the middle of the Australian winter. Port Jacksons share those waters with another member of the horn shark family, the crested bullhead (Heterodontus galeatus). While sharks reproduce in a variety of ways including live birth, horn sharks, Port Jacksons and crested bullheads are egg layers.
Like horn sharks, swell sharks (Cephaloscyllium ventriosum) are docile bottom dwellers that are most active at night in waters off the California coast. Attaining a maximum length of about 3 feet (1 m), swell sharks are characterized by their yellow-brown body covered with brown spots, flattened head and wide mouths. Swell sharks swallow water to inflate their bodies, much like balloonfish, to ward off predators. Not exactly the type of defensive action one expects a big, bad shark to take.
But just because they are small and defend themselves by inflating their bodies with water does not mean these relatively small sharks can be taken for granted. They are well-equipped to prey on small fishes, and more than one misbehaving diver has lost a fingernail or fingertip to the teeth of an agitated swell shark.
Leopard sharks (Triakis semifasciata) are occasionally mistaken for swell sharks because of their relatively flattened heads and their spots. However, leopard sharks tend to be considerably larger and generally far more active than swell sharks. Female leopard sharks reach lengths of 6 feet (2 m) while the smaller males are only half that length when full grown. Leopard sharks are live bearers. They prey primarily upon a variety of crustaceans, clams, worms and fishes.
The Pacific angel shark (Squatina californica), can be identified by its extremely flattened body and its greatly enlarged pectoral fins. In fact, these large fins lead many first-time observers to believe that angel sharks are types of rays, but specialists consider all 13 species of angel sharks to be sharks.
Angel sharks routinely bury themselves in the sand, mud and other soft bottoms leaving only part of their heads and eyes protruding from the sea floor. The sharks wait in that position for unsuspecting prey to venture within striking at which time the sharks “leap” up off the bottom, open their mouths much wider than seems possible and grab their prey before it can react. Then they settle back down, rebury and play the waiting game once more.
Angel sharks are masters of camouflage and their general body color tends to closely match the bottoms they inhabit. Pacific angel sharks attain maximum proportions of about 5 feet (1.5 m) and 60 pounds (27 kg).
The species commonly known both as wobbegongs and carpet sharks also have greatly flattened bodies. A variety of Indo-Pacific species, especially the spotted wobbegong (Orectolobus maculatus) and the tasseled wobbegong (Orectolobus ornatus) are encountered by sport divers exploring reef communities. “Wobbes,” as the Australians like to call them, are lie-in-wait, ambush predators that capture prey in much the same fashion as angel sharks. However, these reef dwellers do not bury themselves when hunting. Instead, they use their well-camouflaged bodies to blend with surrounding reefs in their attempt to go undetected by their prey of fishes, mollusks and crustaceans.
Wobbegongs might not look like the fiercest of sharks, but once you see them capture prey, you will understand why the Australians give them plenty of room and hold them in high regard.
Some prawns (large shrimp) are as large as filetail catsharks (Parmaturus xaniurus) and spiny dogfish (Squalus acanthias). Both of these sharks commonly end up as the fish in servings of “fish and chips.” “How cute!” is the reaction of many people the first time they see a picture of the deep-water species, the longnose sawshark (Pristiophorus cirratus). These 3-foot- (1-m-) long sharks are equipped with sensory chemosensory barbels that resemble those of nurse sharks. However, the most outstanding feature of the longnose sawshark is its elongated snout that is armed with a number of highly modified teeth that are used as spikes to impale prey.
Epaulette sharks are extremely slender, small, bottom-dwelling animals that occur in numerous Indo-Pacific locations where they feed on a variety of benthic invertebrates. But even this tiny shark is a monster compared with the spined pygmy shark (Squaliolus laticaudus). Full-grown males reach a length of only 7 inches (18 cm). The spined pygmy shark inhabits deep waters where it preys upon shrimps, squids and a variety of lanternfishes.
As you now know, there are many small, rather innocuous species of sharks that have not gained the notoriety of many larger, more dramatic species. However, the more you know about any and all sharks, the better your understanding of the marine kingdom.
What Makes a Fish a Shark?
It surprises a lot of people to learn that sharks are fishes. Worldwide, there are about 24,000 species of fishes. Of these, the vast majority are bony fishes. A little more than 370 are classified as sharks. So, the logical question is “what makes a fish a shark?”
The most important factor that distinguishes sharks and their close cousins, the rays and skates, from bony fishes is the cartilaginous composition of the skeletons of sharks, rays and skates compared with the bony skeletons of bony fishes. A tricky part in classifying sharks is distinguishing sharks from rays and skates. In general, the gill slits of sharks are on the sides of their head, and sharks have fleshy, lobed, muscular tails. The gill slits of most rays are on the underside of their head and their tails are whiplike. The gill slits of skates are on the underside of the head while their tails are fleshy and lobed.