Lecture 1: SHARKS

1. Angel Shark Lecture 1: SHARKS Hammerhead Sharks Leopard Shark Corresponding Reading Material ~ Shark section in Lab Manual ~ Levinton: Chapter 8 Thresher Shark

2. Three groups of fish: • Jawless fish (lampreys) • Sharks, skates, rays (Class Chondrichthyes) • Bony Fish (Class Osteichthyes) There are more than 20,000 species of fish and are the most diverse group of vertebrates. 850 species are cartilaginous fishes.

3. What Are Sharks? Sharks are fish. They are ecotherms, have fins, have a calcified skeleton, live in the water, and respire with gills. . ~ Characteristics of sharks that are different from bony fish: 1. Their skeleton is only composed of cartilage. 2. They can only swim forward. 3. They have a large oily liver for buoyancy. 4. They have gill slits but no gill cover. 5. The eggs are fertilized within the female’s body. 6. Their skin is made of rough, sandpaper-like placoid scales called dermal denticles . 7. Skulls lack sutures and teeth are not fused to the jaws like bony fish skulls.

4. The Evolution of Sharks • The first sharks appeared 400 mya. (200 million years before any of the dinosaurs, reptiles, or birds appeared.) Fossil evidence of early sharks is from fossilized teeth and a few skin impressions • Modern forms of sharks evolved during the Jurassic period about 150 mya. At the beginning of the Jurassic period Pangaea was still intact, but the continents were beginning to drift apart. The climate was hot and dry and strongly seasonal.

5. Megalodon (“Giant Tooth”) • The Megalodon is an ancient shark that lived between 25-1.6 million years ago. It is now extinct. • The Megalodon is thought to have grown to length as great as 40 ft (12m). Possibly longer (up to 100 ft). • Due to the similarity between the Great White’s teeth and that of the Megalodon it is thought that the Megalodon may have resembled a huge, streamlined version of the Great White Shark. • Megalodon’s jaw could open 6 ft. (1.8 m) wide and 7 ft. (2.1 m) high. It could easily swallow a Great White Shark whole.

6. Megalodon Continued… • Megalodon’s diet consisted of whales. Sharks eat about 2% of their body weight a day. • Fossilized Megalodon teeth up to 6.5 in. long have been found in Europe, India, general area around Australia, North America, and South America. • The cause of the Megalodon’s extinction is still being debated. One hypothesis is that the Megalodon was confined to warmer water and so could not follow the whales it preyed upon to cooler waters.

7. The Diversity of Sharks • Sharks range in size from the size of a person’s hand to larger than a bus. The Spined Pygmy shark is 7 in. (18cm) long while the Whale shark can grow up to 50 ft. (15m) long. • Sharks have a variety of different body shapes. Most have streamlined, torpedo shaped bodies to glide easily through the water. Others have flattened bodies for bottom dwelling. Sawsharks have elongated snouts. Hammerheads have extremely wide heads. • Sharks have a variety of diets, but they are all carnivores. Some are fast swimmers that eat fish, squid, other sharks, and marine mammals. Some are slower swimmers and eat shellfish off the ocean floor. Others are filter feeders that sieve tiny bits of plankton and small animals from the water.

8. The Great White Shark • The Great White is a torpedo-shaped shark with a pointed snout and crescent shaped tail. • Only the underbelly of the Great White is actually white. • It usually strikes its prey from below and its grayish top coloration helps it blend in with the darker water. • Great Whites average 12-16 ft (3.7-4.9 m) long. The largest on record was 23 ft. (7 m) and weighed 7.000 lbs (3200 kg). • They have 3,000 teeth at a time. • They are found near shore along most of the temperate coastlines around the world. • They average 2 mph but can swim 15 mph in short bursts. • Great Whites are usually solitary animals but are occasionally spotted in pairs. • In fall females migrate to warmer waters to give birth.

9. The Tiger Shark • The tiger shark has tiger-like markings on a dark back with an off-white underbelly. • Tiger sharks are found worldwide in warm seas (tropical and subtropical). • They can grow up to 20 ft (6 m) long but average 10 ft (3 m). • They are solitary animals except during mating. • Tiger sharks do not remain in one area (have territories). They can migrate over 1,000 miles. • They eat just about anything they can catch alive.

10. The Whale Shark • The Whale Shark is the largest shark and fish in the world. It can grow up to 46 ft. (14 m) but averages 25 ft. (7.6 m). It can weigh up to 15 tons. • It has a huge mouth that can be up to 4 ft (1.4 m) wide. It is a filter feeder and sieves enormous amounts of plankton to eat through its gills as it swims.. • Whale sharks live in warm waters both along the coasts and in the open oceans. They spend most of their time near the surface. • It is estimated that they live up to 100-150 years.

11. Finding Prey:The Shark’s Senses Sharks have 5 main senses that they use to process the waters around them. 1. Nares: This is the shark’s nose which it uses to smell. They can detect minute quantities of substances in the water like blood. Sharks can detect some concentrations as low as one part per billion. 2. Eyes: The sharks have a basic vertebrate eye to see. They are well- suited to see in dim light and are particularly sensitive to moving objects. In clear waters they can see up to 50 ft. (15 m). 3. Ears: The shark only has an inner ear that it uses to detect sound, acceleration, and gravity.

12. Finding Prey:The Shark’s Senses 4. Ampullae de Lorenzini: This is a complex and extensive sensory system around the shark’s head. It can detect weak electrical fields at short ranges. They are external pores cover the surface of a shark’s head, filled with jelly. 5. Lateral Line: This is a system of fluid filled canals that run along the side of a shark. Tiny hair-like structures stick out of this canal. The shark can detect water movements created by turbulence, currents, or vibrations by displacing this hair-like structure. This line system detects low-frequency vibrations and helps mainly with distance perception.

13. The Physiology of Sharks • There are 5-7 gill slits on either side of a sharks head. • The skin of sharks is covered with placoid scales called dermal denticles. The alignment of the denticles channels the water, resulting in a flow that acts to reduce friction as a shark swims through the water. • The shark also has a heterocercal tail to aid with buoyancy. • The liver is a very oily organ of the body. It can make up as much as 25% of the shark’s body weight. This decreases the shark’s density and help make it more buoyant. Sharks do not have a swim bladder. • Sharks have a spiral valve located inside the intestine. • Claspers are finger-like structures found on the outside of male sharks next to the pelvic fins and are used for reproduction.

14. Shark Reproduction Sharks can reproduce in one of three ways: 1.Oviparous = The shark secretes a shell or casing around the eggs and then deposits the egg into the ocean (Ex: Horn Sharks). 2.Ovoviviparous = A thin membrane is secretes around the eggs inside the sharks. This is called the candle. After a time the membrane is shed and the eggs remain inside the shark and develop in the mother’s uterus. (Ex: Spiny Dogfish) 3.Viviparous = The eggs hatch within the mother shark. (Ex: Hammerhead)

15. Conservation • The largest sharks are decreasing in numbers around the world because of being hunted by humans. People have used sharks for food, medicines, vitamins, weapons, and jewelry. • Thousands of sharks are caught each year by accident in nets set out to catch other fish. • Some sharks are caught for finning. The shark is caught and the fins are removed. The remainder of the shark is tossed back into the ocean. • Sharks grow slowly compared to other fish and do not produce as many young. Thus it takes their populations years to recover. • The Great White Shark, Basking Shark, and Whale Shark are all currently endangered.