Sharks: The Animal Answer Guide

Contents

Acknowledgments xi Introduction xiii 1 Introducing Sharks, Skates, Rays, and Chimaeras 1 What is this book about? 1 What are sharks and how are they classified? 3 How many kinds of sharks are there? 10 How did sharks get their name? 11 Where do sharks live? 12 When did sharks evolve? 13 What are the largest and smallest sharks alive today? 14 What is the fastest shark? 17 What is the largest shark that ever lived? 18 Where can I find fossil shark teeth? 19 How can you tell whether a fossil shark lived in a river, a lake, or an ocean? 20 Why are sharks important? 21 Why should people care about sharks? 21 2 Form and Function of Sharks 23 What is the metabolism of a shark? 23 Are sharks cold-blooded or warm-blooded? 24 What kind of teeth do sharks have? 25 How many teeth does a shark have during its lifetime? 29 Do a shark’s teeth change during its life? 30 What is the skeleton of a shark made of? 32 Does a shark have senses like ours? 32 How good is a shark’s sense of smell? 33 How well can sharks hear? 35 How well can sharks see? 36 Can sharks see color? 37 How do sharks detect electric fields? 38 Do sharks sleep? 41 Do sharks have scales like other fishes? 41 How do sharks breathe under water? 42 Must a shark keep swimming to breathe? 43 Contents How do sharks swim? 43 How do a shark’s fins function during swimming? 47 How long can a shark live out of water? 47 Why do hammerhead sharks have such strange heads? 48 What kind of brains do sharks have? 51 How large is a shark’s brain? 51 3 Shark Colors 53 Why are so many sharks dark on top and light on the bottom? 53 Which sharks aren’t countershaded? 54 Are any sharks colorful? 57 Are any sharks colorless? 61 What causes the different colors of sharks? 62 Is there a reason for the color patterns of sharks? 63 What color are a shark’s eyes? 64 Do a shark’s colors change as it grows? 65 Do a shark’s colors change at different times of the day or in different seasons? 66 Is there much geographic variation in the color of a shark species? 66 4 Shark Behavior 68 Are sharks social? 68 Do sharks form schools? 70 Can sharks tell one another apart? 71 Do sharks fight? 73 Are any sharks territorial? 75 Do sharks socialize with other kinds of animals? 77 Why do sharks swim at the surface with their dorsal fins sticking out? 79 How smart are sharks? 79 Do sharks use tools? 81 Do sharks play? 82 Do sharks talk? 82 What is “tonic immobility”? 83 5 Shark Ecology 84 Do sharks migrate? 84 How do sharks navigate? 90 How many shark species live in rivers and lakes? 91 How far down in the ocean do sharks live? 94 vi Contents Which geographic regions have the most species of sharks? 95 Which sharks are most or least abundant? 97 When during the day are sharks most active? 99 How do sharks survive the winter? 99 How do sharks survive droughts? 100 Are there sharks in the desert? 100 Do sharks have any enemies other than humans? 101 How do sharks avoid predators? 104 Do sharks get sick? 107 Do sharks have parasites? 108 How can you tell if a shark is sick? 111 Are sharks good for the environment? 111 6 Reproduction and Development 112 How do sharks reproduce? 112 Do sharks lay eggs or do they give birth to live young? 115 How long do female sharks hold young in their body? 118 How long does it take for a baby shark to hatch from an egg case? 119 Where do sharks lay their egg cases or give birth? 120 Do sharks give birth or lay their egg cases at the same times and places every year? 121 How many young does a mother shark produce? 121 How often do sharks reproduce? 124 What is a baby shark called? 125 Are all the baby sharks in a mother full siblings? 125 Do sharks care for their young? 125 How is the sex of a shark determined? 126 Can sharks reproduce asexually? 127 Is there such a thing as a hybrid...