Sharks, rays, skates

Sharks

Rays

Skates

Class Chondrichthyes

• Members of the Chondrichthyes all lack true bone and have a skeleton made of cartilage (the flexible material you can feel in your nose and ears). Only their teeth, and sometimes their vertebrae, are calcified.

• They also have jaws, paired fins, and paired nostrils.• Cartilaginous fish also have thick, fleshy fins, unlike bony

fish. The tail of cartilaginous fish is also distinctive: the tail is divided into two lobes. The vertebrae extend into the upper lobe, which is elongated past the lower half. Such a tail is called heterocercal.

More Characteristics

• They have five to seven gill slits on each side of the body. Sharks and rays reproduce by passing sperm from the male to the female, the male using modified fins called claspers. Some species produce large egg cases while others produce live young.

• There are about 600 species. Most are marine, some live in mid-water, while many live on or near to the sea bed.

• Sharks must swim constantly or they will sink to the bottom of the ocean. Unlike fish, which have a gas-filled swim bladder that keeps them afloat in the water, sharks rely upon a huge, oily liver to provide some buoyancy.

Senses• Sharks have acute senses, befitting their carnivorous

lifestyle.

• Sharp vision (no color).

• Olfactory nostrils used only for smelling.

• can detect electric fields set up by other animals.

• Lateral line system, a row of microscopic organs spanning the length of the animals that are sensitive to water pressure.

• Sharks have auditory organs.

Digestive System

• Digestive system with a j-shaped stomach; intestine short but surface area increased by a spiral valve.

Locomotion

• Sharks are known for their speed and maneuverability in the water. Most species can swim at speeds of 30 to 50 kilometer per hour. The speed of the Mako when attacking has been recorded at more than 90 kilometer per hour!

• With a few exceptions, sharks have torpedo-shaped bodies, an efficient, streamlined design for fast-swimming predators.

Respiratory System

• Sharks and rays have "plate-gills". Typically, sharks pull water in through their mouths and spiracles (small holes on top of the head in some species) as they swim, and pass it through five to seven gill slits on each side of the head. As water passes over the gills, oxygen is extracted. Most sharks, but not all (the nurse shark is one exception), must swim all the time to keep water flowing over their gills and oxygen moving through their circulatory system.

Circulatory System

• Sharks have a two-chambered heart, with an atrium (also called the auricle) and a ventricle. The heart is an S-shaped tube that is located in the head region of the shark.

• The blood is pumped by the heart through the afferent branchial arteries (ventral aorta) to capillaries in the gills (where the blood is oxygenated). The blood then flows through efferent branchial arteries (paired dorsal aorta), then through the tissues of the body, and then back to heart in veins.

Shark Attacks

Attacks continued

• Contrary to popular belief, only a few species of sharks are potentially dangerous to humans, and most attacks are due to the shark confusing a human for a seal or another animal; this is typical in case of an attack against a surfer. While sharks cause a few dozen human deaths yearly, in the same time millions of sharks are killed by fishing.

Attacks

• Most shark attacks occur on the inshore side of a sandbar or between sandbars because fish congregate there and because sharks can become trapped at low tide. Sharp drop-offs also attract lots of fish and, therefore, sharks.

• The most common type of attack is the so-called "hit and run" assault. The shark bites and then quickly releases the person and disappears. These attacks usually involve injuries to the leg below the knee and are not usually fatal. Humans are usually considered too bony to be a good meal for a shark.

• Considering that tens of thousands of people come in close contact with sharks each year while swimming, surfing, or boating, numbers of shark attacks are negligible. In 2004, there were 61 confirmed "unprovoked" shark attacks in the world, resulting in 7 deaths

Number of Attacks• Region Confirmed Attacks/Deaths•  • United States 761,390• Hawaii 100,150• Australia        294,134• Africa  264,690• Asia    116,550 • Europe 38,180• South America          96,220• Antilles and the Bahamas     59,190• Bermuda        4,000• Mexico and Central America  58,310• Pacific Islands, Oceania       114,470• New Zealand  45,900• Other  20,600• World  1969,464

2008 Attacks

• For 2008, the Global Shark Attack File records 69 unprovoked attacks of which five were fatal.

Realistic Facts

• The fact is, you're more likely to get hit by pieces of an airplane falling out of the sky while on your way to the mailbox, then you are getting bit by a shark. If you don't have a mailbox, then here's another one; you are more likely to get struck by lightening or drown in the bath tub, then you are getting attacked by a shark.

• Out of 350 species of sharks, there are only a handful that have actually been know to attack people. They include the Great White, Maco, Tiger, Bull, Dusky Brown, Lemon, and Nurse Sharks.