Last modified on 21 August 2019, at 22:16

Shark

Shark
Oceanic whitetip.jpg
Oceanic whitetip shark
(Carcharhinus longimanus)
Scientific classification
Kingdom Information
Domain Eukaryota
Kingdom Animalia
Subkingdom Biliteria
Branch Deuterostomia
Phylum Information
Phylum Chordata
Sub-phylum Vertebrata
Infraphylum Gnathostomata
Class Information
Class Chondrichthyes
Sub-class Elasmobranchii
Order Information
Superorder Selachimorpha
Population statistics

Sharks are approximately 350 species of cartilaginous fish of the superorder Selachimorpha, inhabiting the world's oceans and several freshwater lakes and rivers.

Description

Sharks vary in appearance, shape, and size, so there is no absolute description of a typical shark. In general, all sharks with several exceptions share the following characteristics:

Cartilaginous skeleton

All sharks possess a skeletal system made entirely of cartilage; there is no solid bone anywhere. The vertebrate extends to and forms the upper lobe of the claudal (tail) fin. The skull has no sutures, and in nearly all species the mouth is ventrally-located, i.e. under and behind the snout. The upper jaw is unattached to the skull, enabling the animal to extend both jaws forward to take in prey.

Placoid scales

Shark skin is covered in thousands of tiny placoid or dentical scales related to teeth; these scales are pointed backward and sharp.

Lifetime of teeth

The only hard part of a shark's body, their teeth are arranged in a "conveyor belt"-fashion, enabling continual replacement over the lifetime of the animal.

Sensory organs

external anatomy of a typical shark

Sharks possess several sensory organs which enable them to bear down on their prey or scavenge, often from miles away. Their eyesight is extremely sensitive to light and shadow. Their sense of smell enables them to detect a drop of blood in water a quarter-mile away, while their lateral lines (a nerve line extending along their flanks) enable them to detect the vibrations from distressed fish several miles away. The ampullae of Lorenzini are small pits on the snout, enabling sharks to detect weak electrical signals produced by the muscle contractions of bony fish.

Diet

With the exception of the two largest sharks - the plankton-feeding whale and basking sharks - all sharks are predatory. Most species eat fish; some, such as the bullhead sharks, eat shellfish. One species (great white) routinely eats warm-blooded prey. And nearly all sharks scavenge dead remains found anywhere, in effect cleaning up the area quickly.

Behavior

Many species of sharks give birth to a few dozen live young, others lay a similarly small number of eggs; these are often washed ashore and are known as mermaid's purses.

Sharks are reputed to be able to detect minute amounts of blood in water, and to be able to follow blood trails for miles. In fact, although sharks can detect blood at concentrations of as little as a few parts per billion, a very considerable quantity must be spilt before it is detectable amongst billions of gallons of seawater. Sharks actually use sounds and vibrations to locate most of their prey.

Classification

Sharks belong to the holobaramin that also includes skates and rays.

Orders and Families

Squaliformes

Dogfish; order representing 7 families and 113 species of shark, with the spiny dogfish possibly the most abundant fish of any kind in the world's oceans. They are characterized by a lack of an anal fin, and range in size from 7.5 inches (Dwarf lanternshark, Etmopterus perryi) to 21 feet (Greenland shark, Somniosus microcephalus).

  • Bramble sharks (Echinorhinidae, 2 species)
  • Dogfish (Squalidae, 20 species)
  • Roughsharks (Oxynotidae, 5 species)
  • Gulper Sharks (Centrophoridae, 15 species)
  • Lantern Sharks (Etmopteridae, 51 species)
  • Sleeper sharks (Somniosidae, 18 species)
  • Kitefin sharks (Dalatiidae, 10 species)

Hexanchiformes

Broadnose sevengill shark (Notorynchus cepedianus)

Deep-water sharks, identifiable by the presence of six or seven gill slits (cow sharks); or a shape reminiscent of an eel (frilled sharks)

  • Frilled sharks (Chlamydoselachidae, 2 species)
  • Cow sharks (Hexanchidae, 3 species)

Pristiophoriformes

Sharks identified by a long snout bearing variably-sized teeth on either side, similar in appearance to sawfish.

  • Sawsharks (Pristiophoridae, 6 species)

Squatiniformes

Identified by their flattened, ray-like appearance, lack of anal fins, and the lower lobe of the tail fin longer than the upper lobe.

  • Angelsharks (Squatinidae, 16 species)

Heterodontiformes

Sharks which have a characteristic pig-like snout, short face, and bovine-like ridges above the eyes. All species have a spine in front of their dorsal fins.

  • Bullhead sharks (Heterodontidae, 9 species)

Orectolobiformes

Zebra shark (Stegostoma fasciatum)

Carpet sharks, so-named for the intricate patterns resembling oriental carpeting. Most species are small bottom dwellers; the exception is the whale shark (Rhincodon typus), at up to 60 feet in length it is the largest living fish.

  • Collared carpetsharks (Parascyllidae, 8 species)
  • Blind sharks (Brachaeluridae, 2 species)
  • Wobbegongs (Orectolobidae, 12 species)
  • Bamboosharks (Hemiscyllidae, 16 species)
  • Zebra shark (Stegostomatidae, 1 species)
  • Nurse sharks (Ginglymostomatidae, 3 species)
  • Whale shark (Rhiniodontidae, 1 species)

Lamniformes

Shortfin mako shark (Isurus oxyrinchus)

Mackerel sharks. Most species identified by a robust appearance; all lack a nictating membrane over the eyes.

  • Sandtigers (Odontaspididae, 4 species)
  • Goblin shark (Mitsukurinidae, 1 species)
  • Crocodile shark (Pseudocarchariidae, 1 species)
  • Megamouth shark (Megachasmidae, 1 species)
  • Thresher sharks (Alopiidae, 3 species)
  • Basking shark (Cetorhinidae, 1 species)
  • Mackerel sharks (Lamnidae, 5 species)

Carcharhiniformes

Atlantic sharpnose shark (Rhizoprionodon terraenovae)

Ground or common sharks, characterized by a nictating membrane over the eyes; several species have been implicated in attacks on man.

  • Catsharks (Scyliorhinidae, 150 species)
  • Finback catsharks (Proscylliidae, 7 species)
  • False catsharks (Pseudotriakidae, 4 species)
  • Barbelled houndshark (Leptochariidae, 1 species)
  • Houndsharks (Triakidae, 40 species)
  • Weasel sharks (Hemigaleidae, 8 species)
  • Requiem sharks (Carcharhinidae, 52 species)
  • Hammerhead sharks (Sphyrnidae, 9 species)

Worse shark attacks case in history: Sinking of USS Indianapolis

The sinking of the USS Indianapolis is considered to be the worst case of shark attacks in history.[1] Most of the shark-related causalities came from oceanic whitetips which are one of the most aggressive types of sharks.[2]

Of the 1,195 crewmen aboard the USS Indianapolis, about 300 went down with the ship.[3]

USS Indianapolis: Excerpt of a sermon related to the phrase "There are no atheists on a sinking ship"

See also: There are no atheists on a sinking ship and Edgar Harrell

The USS Indianapolis is considered to be the worst case of shark attacks in history.[4] Most of the shark-related causalities came from oceanic whitetips which are one of the most aggressive types of sharks.[5]

Of the 1,195 crewmen aboard the USS Indianapolis, which sank due to a torpedo attack, only 300 survived.[3]

The website Sermon Central gives the following excerpt of a sermon:

NO ATHEISTS IN THE WATER

David Harrell wrote a book telling the story of his father, Edgar Harrell. Edgar was one of the 300 survivors of the sinking of the USS Indianapolis, the last US ship sunk by enemy contact in WW2. 600 of the 900 men who survived the ship's sinking were stranded in the water for five days - many with only a life vest - all facing thirst, hunger, injuries, dehydration and sharks. They all came face to face with fear and their own mortality.

Edgar testifies of those days alone in the ocean, 'Clearly there were no atheists in the water that day. Gone was that damnable attitude of pride that deceives men into thinking that there is no God...'[6]

Video of Edgar Harrell, USS Indianapolis Survivor

USS Indianapolis National Memorial

USS Indianapolis National Memorial

Environmental Concerns

Worldwide, sharks suffer threats from over-fishing, mercury poisoning, ocean acidification, and habitat disruption.[7] Many individual shark species are currently threatened or endangered, often because of human activities such as careless fishing practices and coal fired plants dumping tones of toxic mercury into the oceans.

References

  1. The Worst Shark Attack in History, Smithsonian website
  2. The Worst Shark Attack in History, Smithsonian website
  3. 3.0 3.1 Neuman, Scott. "Navy Admits To 70-Year Crew List Error In USS Indianapolis Disaster", NPR.org, 23 March 2018. (en) 
  4. The Worst Shark Attack in History, Smithsonian website
  5. The Worst Shark Attack in History, Smithsonian website
  6. No Atheists In The Water, Sermon Central
  7. http://www.ceibahamas.org/shark-ecology.aspx