Frequently Asked Questions - Shark FAQ's
Fequently asked questions on sharks
(source: Florida Museum of Natural History Ichthyology Department)
Sharks have several adaptations that can aid their ability to be neutrally buoyant. Sharks lack true bone but instead have cartilaginous skeletons that are much lighter. Sharks also have large livers full of low-density oils, which provide some buoyancy. While sharks lack a swim bladder, some species of shark, like the Ragged-tooth or sand tiger (Carcharias taurus), can actually gulp air into their stomach, which can provide additional buoyancy.
Above: Ragged-tooth Shark
Male sharks have paired intromittent organs called claspers. Claspers are modifications of the pelvic fins and are located on the inner margin of the pelvic fins. Females do not have claspers.
Sharks have five different types of fins: pectoral, pelvic, dorsal, anal, and caudal. These fins are rigid and supported by cartilaginous rods.
- The paired pectoral fins are located ventrally near the anterior (front) end of the shark. They are used primarily for lift as the shark swims.
- The paired pelvic fins located behind the pectoral fins are used for stabilization while the shark swims.
- The dorsal fin is the one that commonly appears skimming along the water's surface. Sharks may have one or two dorsal fins that act to stabilize the shark during swimming. The second dorsal fin is usually smaller than the first dorsal fin and is located posteriorly (toward the
tail) to the first larger dorsal.
- Stability is the main function of the anal fin for sharks that have one, other sharks may lack this fin. It is located on the ventral (bottom) side between the pelvic and caudal fins.
- The caudal fin is also called the tail fin. The upper half and the lower half of the shark' tail are not equal in size with the upper portion usually the larger. This is especially pronounced in the thresher shark that has an upper tail lobe longer than the shark's body. This fin is responsible for propelling the shark through the water as it swims.
All sharks have internal fertilization. Mating has been observed in relatively few species of sharks, but both hormonal and behavioral cues are likely involved.
The female is typically passive as the male bites and grasps her with his teeth to hold on during copulation. Then, the male inserts a clasper into the female's cloaca and releases sperm. Depending on species, sperm may or may not be stored in the female prior to fertilization of the oocyte, or ovum.
During ovulation, the female releases oocytes from the ovary. Then, these oocytes are fertilized by sperm, and the fertilized ova are encapsulated in an egg case in a specialized organ called the nidamental or shell gland. In all oviparous species and most viviparous species, a yolk sac is packaged in the egg case along with the ovum.
Development of the embryo then proceeds according to the mode of reproduction and embryonic nutrition of the particular species. In oviparous species, eggs are laid. In viviparous species, gestation takes place in the uterus. Sharks are hatched or born as juveniles, or smaller versions of the adult. There is no larval stage.
Most sharks live only in the marine environment in full-strength saltwater. Some coastal shark species can survive in brackish estuaries with mixed fresh- and saltwater. Many juvenile sharks use these brackish areas as nursery grounds. There are only a couple shark species that are capable of surviving in freshwater for any length of time, and these have special physiological adaptations that allow this. These species are the bull shark (Carcharhinus leucas) and the speartooth shark (Glyphis sp.). Bull sharks have been captured ~2,100 miles (3,480 km) up the Amazon River, and ~1,700 miles (2,800 km) up the Mississippi River. Bull sharks have also been documented to
traverse ~108 miles (175 km) of rapids in the Rio San Juan leading up to Lake Nicaragua from the Caribbean Sea. The speartooth shark has been captured over ~60 miles (100 km) up the Adelaide River in Australia. Though these sharks are capable of surviving in freshwater, there are no populations living in completely landlocked freshwater lakes. They always have a route that will connect them to the ocean.
Above: Baby bull shark caught in an estuary
Sharks have a tongue referred to as a "basihyal". The basihyal is a small, thick piece of cartilage located on the floor of the mouth of sharks and other fishes. It appears to be useless for most sharks with the exception of the cookiecutter shark. The cookiecutter shark uses the basihyal to rip chunks of flesh out of their prey. Taste is sensed by taste buds located on the papillae lining the mouth and throat of the shark. The taste receptors help the shark decide if the prey item is suitable or not prior to ingesting the item.
Above: Blacktip eating a piece of sardine
Currently there are approximately 400 described species of sharks, however new species are being described all the time. In addition, there are around 400 species of rays, a close relative of sharks. For detailed information on individual species, check out our bioprofiles!
Above: Different Shark Species
Fossil records indicate that ancestors of modern sharks swam the seas over 400 million years ago, making them older than dinosaurs! Throughout time sharks have changed very little.
Elasmobranchs are a closely related group of fishes, differing from bony fishes by having cartilaginous skeletons and five or more gill slits on each side of the head. In contrast, bony fishes have bony skeletons and a single gill cover. Elasmobranchs include sharks, rays, and skates.
No, sharks and all other fishes belonging to the class Chondrichthyes lack true bone, but rather have cartilaginous skeletons.
Cartilage is a type of connective tissue strong enough to give support but softer than true bone. Cartilage is found in the human ear and nose. Due to cartilage being softer than bone, it is very rare to find complete fossil remains of sharks.