1. Let students know that today they will be learning about sharks. Ask students to work in small groups to discuss some of the things they know about sharks. Ask for volunteers to share some of their thoughts. Write their ideas on the board. (Ask students if they think sharks, for the most part tend to be patient or impatient? Gentle or aggressive? Take out pictures of two sharks-a whale shark and a bull shark. (Whale sharks can grow up to 40 feet in length while bull sharks can be up to 13 feet long.) Let your students know that one of these sharks is not dangerous to humans, while the other is extremely dangerous to humans. Ask students to predict which shark is the gentle one. Let your students know that they will find the answer to this question during the lesson.
2. FRAME the first clip by asking students if they can think of any ways that shark are similar to other fish. Ask them to think of how sharks are different from other fish. Write down their answers. Explain that you are now going to show them a video segment with information about how sharks and fish differ. Provide students with a FOCUS by asking them to look for 3 ways that sharks and fish differ and to write them down.
3. PLAY Video Segment 1 “Fish, Sharks and Rays.” After the segment, FOLLOW UP by asking students to share some ways that sharks and fish are different. Revise your original list to add the new information from the segment.
(Possible answers: Most fish have hard bony skeletons, while sharks and rays are entirely boneless and have skeletons made of flexible cartilage. Bony fish can hover in one place and swim backwards, while sharks cannot. Most bony fish have an air bladder that controls their buoyancy, while sharks do not have this. Sharks must either swim or sink. Bony fish have compact bodies and good mobility, which have contributed to their success. There are over 24,000 species of bony fish. Sharks come in an array of shapes and sizes and are 3 times older than dinosaurs.)
Ask students if they noticed any other ways that fish and sharks are similar that they hadn’t included on their list already. If so, add them to the list.
4. Ask students if they remember the name of the cousin of the shark that was featured in the segment. (The ray.) Ask students to list some ways that rays and sharks are similar. (Possible answers: Both sharks and rays are entirely boneless and have skeletons made of cartilage.) Ask students to point out some ways that rays differ from their cousins, the sharks. (Possible answers: Their fins and body have merged into a single, flatter design. In almost all rays, their mouths and gills are located on the underside of their bodies.)
LEARNING ACTIVITY 1
1. Explain that sharks have been in the oceans for 400 million years-about 200 million years before the dinosaurs. Ask students to suggest some hypotheses for why these creatures have survived for so long while other animals have become extinct. Write their answers on a board and discuss the students’ hypotheses. During the discussion, define the term “adaptation” (an evolutionary change in a species that improves its chances for survival) and explain that the theory of evolution states that different animal and plant species have changed, over millions of years, in response to changes in the environment.
2. FRAME Video Segment 2, “A Close Look at Sharks,” by letting students know that you will now be showing them a video segment which features several different sharks. Provide a FOCUS for the clip by asking students to look for the following as they watch the segment:
o name of each shark
o adaptations that have helped this shark survive
o other interesting facts about the shark
3. PLAY Video Segment 2. After the segment, FOLLOW UP by asking students to name the three featured sharks. (Angel shark, wobbegong shark and saw shark.) Lead a discussion with students about some of the things they learned about each shark and what has helped it survive.
Possible facts to include in the discussion:
o Angel sharks are very patient and camouflaged which helps them catch prey. They have teeth that curve backward, to prevent their prey from escaping.
o Wobbegong sharks have wiggly projections around their mouth, which look like seaweed and also have spots on their bodies, which help them to blend in with the reefs. Both the projections and the spots help to camouflage them, so that prey do not see them as the sharks lie still, waiting for potential prey to swim by.
o Saw sharks have a long, sharp and spiky snout that looks like a power saw and is used for slashing at fish and digging up the bottom to search for prey. They also have two long sensory organs, used for feeding and tasting, which hang from their snout.
LEARNING ACTIVITY 2:
1. FRAME the next segment, by asking the students if they remember the name of the shark’s cousin. (The ray.) Explain that, although rays have not existed as long as sharks, they have been around for many years-about 150 million years. Just like there are different types of sharks, there are also different types of rays, with varied eating habits and survival techniques. FOCUS the students by asking them to write down the names of the featured rays as they watch the next segment. They should also write down some physical features, skills and behaviors that have helped them survive.
2. PLAY Video Segment 3, “A Close Look at Rays.” FOLLOW UP with students by asking them to identify the featured rays. (Electric ray, sting ray and manta ray.)
3. Lead a discussion with students about some of the physical features, skills and behaviors that have helped each of the featured rays survive. Remind your students that rays have been around for 150 million years and, as mentioned in the video, there are more than 500 species of rays (and hundreds of different kinds of sharks).
Possible facts to include in the discussion:
- Electric Rays have gills underneath their bodies and two honeycombed organs filled with a jellylike tissue which, when combined, can give an electric shock of more than 200 volts. The ray shocks and paralyzes its prey and then swallows the fish whole. Electric rays often hide under the sand.
- Sting Rays inflict more harm on people than all other rays and sharks combined. They lie in secret in shallow waters around the world. Sting rays have a venomous barb on their tail-up to a foot long. Aside from this feature, the sting rays are harmless. When stepped on by humans, sting rays can protect themselves by putting their barb through the humans’ feet.
- Manta Rays are very large (20 feet across from wingtip to wingtip and weighing 4000 lbs), graceful, gentle and fast. They have two frontal lobes, used to help scoop food into their mouth. Manta rays feed on plankton and do back flips to gather the food. The manta rays have a long tail which is harmless. They are not a danger to humans. Their wings help them move quickly when they want to.
1. Explain to your students that they are now going to conduct their own research on sharks and rays. Divide students into small groups of 2-3 students. Each group should pick a shark or ray to study. When students make their selections, make sure that at least one group chooses a whale shark and at least one group chooses a bull shark (so that they will be able to see if their predictions made at the beginning of the lesson were accurate). Encourage students to select a species that sounds intriguing to them. Here are a few possibilities:
Sharks: basking shark, blacktip reef shark, blue shark, bull shark, dwarf shark, great white shark, hammerhead shark, nurse shark, spiny dogfish shark, tiger shark, whale shark
Rays: eagle ray, bat ray, butterfly ray, bluespotted ribbontail ray, eagle ray
2. Instruct students to use books, reference materials, Web sites, etc. to find the information. Here are some sites that have good information and photographs of sharks and rays:
- The biological profiles page on the Ichthyology at the Florida Museum of Natural History site at: http://www.flmnh.ufl.edu/fish/Education/bioprofile.htm
- The shark page on the National Geographic Web site at: http://animals.nationalgeographic.com/animals/article/sharks-index.html.
- The shark facts page on the Kidzone Fun Facts for Kids site at: http://www.kidzone.ws/sharks/facts9.htm
3. Provide students with 20-30 minutes to conduct their research. Instruct each group to find a photo and the following information about one shark or ray:
- information about what it eats and how it gets its food
- its size
- whether or not it is dangerous to humans
- ways that it defends itself
- special features that help it survive
- any other interesting facts
4. Each student or pair of students should hold up a photo of their shark or ray. Ask the students who researched a shark to line up in size order of their sharks from smallest to largest. The students who researched rays should do the same in another line. (If their species of sharks or rays has a range of sizes, ask the group to select the highest number as the size of its species.)
5. Ask each group to present its species to the class, starting with the smallest and ending with the largest. Each group should briefly describe the name of the shark or ray, its size, what it likes to eat, how it catches its prey and how it defends itself. Ask the groups to point out interesting physical features and characteristics (such as camouflage and patience) which help it survive.
6. Optional: Create a large chart or graph on which students can add their findings, grouping the sharks and rays by size and including photographs and information about their temperaments, diets, means of protection, how they catch prey, etc.
7. Lead a discussion about the different sharks and rays that the students presented, as well as the other sharks and rays discussed during the lesson. Ask students to reflect on some of the findings and to discuss some of the things that have helped sharks and rays survive over such a long period of time. During the discussion, point out the following:
o Some sharks and rays are dangerous to humans, while others are not.
o Some of the largest species eat the smallest prey.
o Some of the largest sharks, such as the basking shark and the whale shark, are the least harmful to humans.
Return to the sheet with all the students’ predictions about sharks that they made at the beginning of the class. Revisit their original answers to the question about which shark-the whale or bull shark-is gentler and pose the question again. (Correct answer: The whale shark.)