Sharks 101 | National Geographic — Transcript

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1. 0:00(ominous music)
2. 0:02- [Narrator] They glide through the water
3. 0:03with unmistakable grace,
4. 0:06remnants of an ancient past,
5. 0:08they dive and they rise
6. 0:11from the ocean's murky depths
7. 0:13to it's sun-kissed shallows,
8. 0:15rousing fear and awe
9. 0:19like no other creature in the sea.
10. 0:23The world's biggest living fish is a shark.
11. 0:28Of the estimated 34,000 species of fish,
12. 0:31the largest are whale sharks.
13. 0:35These gentle giants usually grow to about 40 feet long
14. 0:39and weigh an estimated 15 tons.
15. 0:42Their mouths alone can span four feet wide.
16. 0:47The gigantic whale shark however,
17. 0:49pales in comparison to the largest fish
18. 0:52that ever existed, the megalodon.
19. 0:55Dating to over 20 million years ago,
20. 0:58it's thought that the prehistoric shark
21. 1:00could of reached 80 feet long,
22. 1:02weighing up to around 70 tons.
23. 1:05Unlike whale sharks, the megalodon was carnivorous,
24. 1:08and consumed any creature that fit
25. 1:10into it's nearly 10 foot wide mouth.
26. 1:15Throughout their lives some species of shark
27. 1:17can shed over 30,000 teeth.
28. 1:21Unlike humans who are born
29. 1:23with a set number of teeth in their jaws,
30. 1:25sharks have a seemingly limitless supply.
31. 1:29They can grow, lose, and replace their teeth as needed.
32. 1:33Furthermore, most sharks
33. 1:35have multiple rows of teeth in their jaws.
34. 1:38The jaws of a great white shark,
35. 1:40the largest predatory fish in the sea,
36. 1:42can contain up to seven rows
37. 1:44that hold up to 300 teeth at any one point.
38. 1:48Most sharks, as they hunt their prey,
39. 1:51end up losing their teeth individually.
40. 1:53However, the cookiecutter shark loses
41. 1:56and replaces the teeth in it's lower jaw all at once.
42. 2:03Sharks are built for speed.
43. 2:06The fastest known shark, the mako shark,
44. 2:09can reach speeds of up to 46 miles per hour.
45. 2:13This speed is largely due
46. 2:15to their body's hydrodynamic design.
47. 2:17Many sharks have torpedo shaped heads
48. 2:19that allow them to cut through the water
49. 2:21with little resistance.
50. 2:23Plus, shark skin is covered with flat, v-shaped scales,
51. 2:27called dermal denticles.
52. 2:29The denticles help water flow smoothly over the skin,
53. 2:32which reduces friction
54. 2:34and helps sharks swim quickly and quietly.
55. 2:38Sharks also have skeletons
56. 2:40made of cartilage instead of bone.
57. 2:43Cartilage is a much lighter material than bone
58. 2:46so sharks have less weight to carry.
59. 2:51Sharks may lay eggs, or bear live young.
60. 2:55Egg laying sharks only lay a few large eggs.
61. 2:58They may come in various forms,
62. 3:00such as sacks called mermaid purses or corkscrews.
63. 3:06These eggs act as external wombs
64. 3:08in which shark embryos complete their development.
65. 3:11However, most sharks give birth to live young.
66. 3:15Called pups, the young of most live bearing species
67. 3:19gestate for around one year.
68. 3:22Some even begin practicing their predation skills
69. 3:25while in the womb.
70. 3:27Before they are born, the sand tiger shark pups compete
71. 3:30with their siblings.
72. 3:32In fact, the strongest pup in each of the two wombs
73. 3:35devours its weaker brothers and sister.
74. 3:40Some sharks are at risk of extinction.
75. 3:44Every year an estimated 100 million sharks
76. 3:48are killed worldwide, in large part
77. 3:50for the shark fin trade.
78. 3:54The sharks are caught and their dorsal fins
79. 3:56are removed and sold at a hefty price,
80. 3:58primarily in Asia.
81. 4:01In traditional Chinese culture,
82. 4:03serving and eating shark fin is a sign
83. 4:05of status and wealth.
84. 4:07Because of the high demand and value of shark fins,
85. 4:11some shark populations have plummeted
86. 4:13by up to 70% causing a ripple effect
87. 4:16in ecosystems and endangering at least 74 shark species.
88. 4:22However, measures are being taken to protect sharks
89. 4:26with a number of countries and jurisdictions cracking down
90. 4:29on unsustainable shark fishing.
91. 4:32In China, shark fin soup is no longer allowed
92. 4:35to be served at government banquets.
93. 4:37A move hailed by shark conservationists.
94. 4:41Through continued international conservation efforts,
95. 4:44the loss of sharks may be curbed,
96. 4:47allowing the creatures in all their power and grace
97. 4:50to survive for many generations to come.