1. There is a force sufficiently
powerful to move the oceans
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2. of this world.
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3. It is a force not of this Earth.
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4. The Moon is large enough
to generate gravity
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5. and with sufficient force to pull
on the Earth 230,000 miles away.
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6. As the Moon orbits the Earth,
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7. its gravity sweeps across
the face of our planet.
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8. Its power drags a great bulge
of oceanic water in its wake...
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9. the rising tide.
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10. The River Amazon in Brazil.
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11. On some special days,
the gravitational forces
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12. of the Moon and the sun combine,
to extraordinary effect.
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13. A growing tidal wave from the ocean
is being forced 200 miles inland.
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14. This is a tidal bore.
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15. Fortunately, tidal bores are rare,
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16. but the Moon does create strong tides
out in the world's oceans
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17. on every day of the year.
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18. The Bay of Fundy in Nova Scotia.
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19. The tides here
are the largest in the world,
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20. and have a profound effect
on marine life,
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21. creating a rich feeding ground.
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22. A feast that attracts some
of the largest diners on the planet...
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23. humpback whales.
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24. But they are not the biggest threat
to the herring.
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25. These are finback whales.
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26. At 70 tons, they are the second
largest animal on Earth,
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27. but so streamlined they are
the fastest of the great whales.
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28. This combination of speed
and immense size
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29. makes the finback a voracious hunter
of schooling fish.
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30. The Bay of Fundy
can attract so many fish
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31. that, during the summer,
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32. as many as 500 of these magnificent
whales hunt here every day.
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33. The feeding is best
where the tides run strongly.
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34. So the whales
move further into the bay,
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35. following tidal rips
and searching for fish.
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36. Their movements are closely watched
by flocks of Cory shearwaters.
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37. As the whales dive down towards
the fish, more and more birds gather,
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38. anxious to pick up scraps.
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39. The flowing tide
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40. may provide a feast,
but, before long, it will turn.
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41. In just six hours,
100 billion tons of water
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42. will flow out of the bay,
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43. the sea level falling
by as much as 15 meters
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44. and exposing vast tracts
of mud and sand.
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45. At first sight, a barren place,
entirely devoid of life.
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46. In fact, the clamp sand
is packed with microscopic life,
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47. the meiofauna,
feeding in a sandy underworld,
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48. quite unaffected
by the departure of the sea.
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49. But life is not all roses
in this miniature world.
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50. A sand bubbler crab
in Northern Australia.
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51. It hunts meiofauna,
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52. Just a centimeter across,
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53. the sand bubbler
works at breakneck speed,
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54. filtering out the meiofauna
and kicking aside the waste.
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55. The crab will clean
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56. every grain of sand
within a meter of its burrow.
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57. Endless practice for the best
backheel in the natural world.
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58. The crabs work fast
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59. because they can only sieve
when the sand is damp.
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60. Remarkably, they work
the entire surface of the beach
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61. within a couple of hours
of the tide retreating.
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62. Then they simply return to their
burrows and await the next tide.
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63. Underwater,
the falling tide is the cue
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64. for some bizarre activity.
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65. These slow-moving clams
use their muscular feet
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66. to bury themselves under the sand.
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67. If they fail to get under cover,
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68. the tide will leave them exposed
to the air and they will perish.
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69. But once underground,
they can wait,
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70. safe beneath the beach,
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71. And not a moment too soon.
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72. June in south east Alaska.
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73. In just four hours, a vast beach
is exposed by the falling tide.
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74. The bears are hungry.
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75. At this time of year, the pickings
on land are few and far between.
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76. But any food here has long since
buried itself deep under the sand.
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77. To a hungry adult bear,
that is no barrier.
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78. They smell the clams through
the sand and simply dig them out.
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79. For such large animals,
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80. they show
quite extraordinary dexterity
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81. at opening
the unfortunate shellfish.
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82. Cubs try their luck, too,
none too successfully.
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83. But for the adults,
the shellfish feast
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84. lasts as long
as the tide remains out.
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85. Table Mountain in South Africa.
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86. Every day, the retreating waves
leave flotsam on the beach.
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87. And this creature
is scenting the currents
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88. for the odor of rotting fish.
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89. The tide carries the scent
far into the surf zone.
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90. Responding to the smell,
snails emerge from the sand.
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91. This is a race against the tide.
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92. The snails need to find their meal
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93. before the tide
leaves it beyond reach.
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94. But snails are slow
and the tides fall rapidly.
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95. These, however,
are no ordinary snails.
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96. They can surf!
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97. They ride the waves up the beach
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98. but, all too soon, the tide leaves
the fish beyond the surf zone.
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99. Without the sea, there's a danger
the snails will lose the scent,
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100. but as long
as the sand remains damp,
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101. they can still follow
a faint trail to the food.
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102. Once there,
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103. they tuck in with macabre relish.
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104. Good things come to those who wait.
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105. Soon, the heat of the sun
forces them to retreat into the sand
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106. to await the return
of the next tide.
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107. February in Britain.
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108. The falling tide is eagerly awaited
by these knot.
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109. As the water retreats,
countless small invertebrates
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110. seek shelter under the mud.
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111. And with good reason.
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112. Waders are specialists
at probing in the mud,
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113. their variety of beak shapes
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114. designed for reaching
different invertebrates -
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115. keys that unlock the safety
of the tidal flats.
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116. But within a few hours,
the tide will turn again.
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117. Soon, the waders
are out of their depth.
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118. The creatures of the mud
are safe once more.
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119. Underwater, incoming tides
can create a strong current,
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120. and flounder are experts
at hitching a tidal lift.
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121. They are shaped
rather like a kite,
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122. a perfect design
for gliding on the tide.
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123. In Newfoundland
on the east coast of Canada,
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124. large numbers of flounder ride
the currents up into the shallows.
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125. They've come to hunt invertebrates
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126. that will emerge
now that the water is back.
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127. The pickings in the shallows
can be very good.
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128. The activity
has not gone unnoticed.
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129. But ospreys can't dive deeply.
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130. As long as the water is more than
a meter deep, the flounder is safe.
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131. Going too far inshore
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132. can be a risky business.
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133. This fish buries itself
completely in the sand
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134. at any sign of danger.
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135. But when the tide floods in again,
as long as the coast is clear,
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136. these sand lancet will re-emerge.
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137. After a wait of six hours
under the sand,
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138. they are desperate for food.
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139. Unlike flounder,
they head out to sea,
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140. looking for shallow, open water
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141. where the tidal currents will
concentrate their food - plankton.
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142. In untold thousands, they stream
towards the best feeding grounds,
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143. where they simply pick up
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144. tiny planktonic creatures
from the water.
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145. But, if they swim too far off-shore
in search of food,
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146. they risk meeting large predators
that live in deeper water.
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147. Dogfish - small sharks.
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148. The sand lancet have strayed
out of their safe depth.
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149. The effect of the turning tide
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150. can be totally different
on a rocky shore.
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151. Here, on the coast
of Vancouver Island in Canada,
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152. the sun bakes the exposed rock.
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153. It's almost impossible to dig
underground when the sea retreats,
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154. so these mussels and barnacles
are fully exposed to the sun's heat,
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155. literally cooking
in their own shells.
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156. And the seaweed
simply dry to a crisp.
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157. It can be a wait of many hours
before the water returns.
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158. Throughout each month, the size
and strength of the tide changes.
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159. The biggest tides of all happen
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160. when the gravities of the sun
and Moon pull in unison.
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161. That happens immediately
after the new moon...
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162. and again after the full moon.
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163. These are called the spring tides.
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164. They reveal vast tracts of seabed
that would normally be covered.
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165. For these raccoons, it's a chance
to look for a seafood feast.
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166. A mother ventures forth
with her kits.
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167. With the spring tide,
they've come further down
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168. than smaller tides
would normally allow.
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169. Searching
with their sensitive paws,
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170. they look for suitable prey.
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171. With the extreme low tide,
they could find something special.
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172. And what could be better
than a red rock crab?
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173. That is, if it weren't
for the risk of a painful pinch.
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174. With crabs, there's no substitute
for experience.
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175. The mother
makes an expert's catch.
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176. But the kits learn fast.
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177. And for those that don't,
begging is always worth a try.
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178. All too soon, the returning tide
will cover the raccoon's table.
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179. For the invertebrates,
it's a welcome relief,
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180. but in rough weather,
they are exposed
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181. to the worst of the waves.
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182. Even when there are no waves,
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183. the incoming tide can create
considerable forces underwater.
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184. The gaps between these islands
on the east coast of Vancouver Island
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185. channel the tidal flow.
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186. As the tide keeps rising,
gradually the water flows faster,
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187. and soon these 30-meter-long
bull kelp plants
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188. bend to the current.
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189. They are sufficiently flexible
to cope without too much damage,
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190. but there are some spots where
the currents are especially powerful.
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191. This is the Nakwakto Rapids.
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192. At the turn of the tide, water from
almost 700 miles of coastal fjords
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193. will have to empty through a gap
half a mile wide.
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194. Within a few minutes, the current
is already picking up speed,
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195. until water roars by
at over 17 miles an hour.
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196. Tidal currents
are not always damaging.
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197. Here, in the Poor Knight Islands
of New Zealand,
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198. weak tides run through rock arches,
making it an ideal resting place
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199. for Stingrays.
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200. These rays congregate here
in huge numbers every March.
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201. They've come to breed.
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202. The arches funnel the current,
which the rays can ride
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203. with the minimum of effort,
so saving energy.
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204. Nearby, out in open water,
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205. a school of two spotted demoiselle
fish are feeding on plankton,
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206. and the current is perfect
for sweeping their food past them.
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207. Once the current starts to weaken,
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208. there is insufficient food
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209. to warrant the risks
of swimming out in the open.
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210. So, the demoiselles head off
to find shelter en masse.
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211. Safety is in numbers.
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212. More and more demoiselles
pour towards the cave entrances
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213. that riddle the Poor Knight Islands.
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214. Safe at last. Inside the cave,
they are less exposed
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215. to attack from predators.
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216. Thousands of demoiselles
and blue mao mao
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217. wait for the return of the current,
when, once again,
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218. they will head out
into the open to feed.
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219. The Moon's gravitational pull
is weaker
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220. nearer to the Earth's equator.
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221. So, the more equatorial the location,
the smaller the tides.
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222. Out in the Caribbean Sea,
the tidal movements are slight.
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223. Even so, they are sufficient
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224. to push free swimming plankton
in their path.
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225. These are thimble jellyfish.
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226. They swim towards sunlight,
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227. and invisible boundaries
formed by the tidal motion
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228. help to herd them together,
until they gather in immense swarms.
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229. They put the tropical sunshine
to good use.
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230. Their brown color comes from algae
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231. that live inside
the jellyfish's body
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232. and photosynthesize
energy from the sun.
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233. In open water they are fairly safe,
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234. but the tide is sweeping the whole
swarm gently towards the Bahamas,
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235. where hungry mouths are waiting.
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236. Although the sea level
doesn't change much,
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237. the tides are still pushing
an enormous volume of ocean water
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238. through the small gaps
between the island cays.
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239. Underwater, the tidal currents
race past soft corals...
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240. and on over
the sandy banks themselves.
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241. It is an immense area of coral sand
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242. that is only just submerged
at high tide.
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243. This incoming tide is bringing in
a fresh supply of oceanic plankton.
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244. Razorfish gather at the best spots
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245. to catch the pick
of the microscopic feast.
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246. Although there's plenty here
for these small fish to eat,
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247. gathering in one place
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248. makes it easy
for their predators to find them.
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249. A nurse shark is little threat.
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250. But this sound...
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251. heralds a quite different danger.
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252. A bottlenose dolphin.
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253. It's using its sonar
to locate razorfish beneath the sand.
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254. Once it finds a suitable target,
it simply digs out its prey.
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255. The buried fish have no defense
against this attack.
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256. They simply have to wait
and hope they aren't found out.
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257. This dolphin appears to have
a razorfish craving.
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258. Well, she is pregnant.
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259. Success at last.
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260. The incoming tide
sweeps on towards America,
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261. flooding across vast flat
plains of seagrass.
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262. They are so shallow
that, at low tide,
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263. all large fish are forced
to retreat into deep water channels,
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264. like these nurse shark...
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265. and stingrays.
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266. Both predators hunt crustaceans
on the seagrass beds,
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267. but until the tide
brings enough water,
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268. they will have to wait.
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269. So now, for this tulip snail,
it appears safe
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270. to patrol the shallows
in search of a meal.
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271. But is it?
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272. This is a rather bigger snail.
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273. At five kilograms in weight,
the giant horse conch
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274. has little to fear from any shark,
and it has a taste for tulip snail.
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275. Sensing the approaching danger,
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276. the snail flees.
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277. But, in a world of snail paces,
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278. the conch
is something of a Ferrari.
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279. It calls for desperate measures.
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280. Exhausted by the effort
of its last-ditch attempt,
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281. the tulip snail
is slowly gunned down.
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282. The tide has to rise
for another hour
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283. before the big predators can feed.
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284. But out on the flats, the scent of
dying snail wafts away on the tide.
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285. It's a scent these hermit crabs
are particularly partial to.
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286. It's vital that the crabs
have the best possible protection
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287. from the heavy teeth
of the waiting sharks and rays.
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288. For that, they need the shell
with the perfect fit.
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289. Today, there is new real estate
on offer -
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290. and competition
in this housing market is fierce.
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291. The action becomes
even more desperate
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292. when the shell of the devoured
snail is ready for release.
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293. This crab simply can't wait
any longer.
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294. But it's a decidedly risky
acquisition.
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295. The risk paid off handsomely.
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296. The new shell is both lighter
and stronger than the old home.
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297. It's not a moment too soon,
because the tide is flooding the plains.
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298. At last, the predators are free
to start their foraging.
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299. Both stingrays and shark
have an electrical sense
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300. which they use to search
for buried invertebrates.
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301. They can sense minute movements
beneath the sand.
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302. Finding a promising signal,
this ray digs out its meal.
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303. An unprotected hermit crab
would have no chance.
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304. Within a few hours,
the tide ebbs out once more
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305. and all the predators
are forced to leave.
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306. They will have to wait
until the next high tide
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307. before making
another feeding foray.
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308. At certain times of the year,
called the equinox,
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309. spring tides are exceptionally large
and rise higher than normal.
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310. Predators can reach the shallowest
fringes of the seagrass flats.
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311. These two-meter-long tarpon
are going further inshore still.
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312. They are heading for the mangroves.
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313. These flooded forests cover
huge areas of the coastal shallows.
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314. Extraordinarily, the roots of
the mangrove can live in saltwater,
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315. and they make a perfect nursery
for small fish.
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316. Silversides and snapper
find sanctuary in the maze of roots.
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317. Big predators
seldom find a way in here.
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318. And now the tide
is falling once more.
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319. The water starts losing
what little oxygen it contained,
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320. and quickly becomes stagnant.
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321. Most predators
have abandoned the mangroves,
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322. but the tarpon are still here,
trapped by the falling tide.
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323. Dissolved oxygen
is fast running out,
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324. but they have a vital survival
technique...
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325. they can breathe air.
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326. Pumped up with fresh oxygen,
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327. they can easily out-maneuver
the dozy silversides.
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328. The tide has turned again.
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329. And this is no ordinary tide.
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330. Since it is the equinox,
the tide is rising fast,
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331. but now, out to sea,
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332. a hurricane is on its way,
forcing the tide yet higher.
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333. The passing storm leaves large
areas of the coast flooded.
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334. Low-lying islands,
like the Bahamas,
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335. are particularly prone
to the storm flooding.
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336. The sun's power here is immense.
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337. As the tide recedes and the
remaining flood water evaporates,
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338. a remarkable transformation
takes place.
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339. The mud is coated
with a magical world of salt.
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340. Any remaining water
is extremely salty.
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341. Very few creatures
can survive here...
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342. except brine shrimp.
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343. And, on the water's edge -
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344. brine flies.
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345. Both are the favorite food
of an extraordinary animal.
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346. The Caribbean flamingo.
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347. Remarkably, they actually seek out
such briny places.
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348. They are the best spots
for them to find their food.
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349. They also provide the protection
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350. the flamingos need
to raise their young.
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351. Nesting sites like this
are surrounded by corrosive brine.
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352. It's a formidable barrier
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353. to any predator
seeking to dine on flamingo chicks.
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354. The flamingos take the precaution
of building raised nests
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355. just in case of further flooding.
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356. Strangely, it's actually
the power of the storm tides
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357. that gives the flamingos food and
a perfect habitat in which to breed.
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358. The breeding of many animals
in the ocean
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359. is closely coordinated
with the tidal cycles.
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360. The half moon in November.
It's the time of small tides.
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361. Christmas Island in the Pacific.
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362. Strange happenings are afoot.
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363. It's one of only
a few nights each year
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364. when female Christmas Island crabs
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365. risk heading down towards the sea.
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366. They number in tens of thousands
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367. and all of them are laden
with hundreds of eggs.
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368. They have to shed them
into the ocean
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369. if the eggs are to develop
into baby crabs.
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370. But these are land crabs
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371. and they can neither swim
nor breathe underwater.
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372. There's a great risk of drowning.
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373. That is why they pick the smallest
tides, to minimize the danger.
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374. The eggs will develop far offshore.
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375. And, in exactly one month's time,
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376. a swarm of baby crabs will return,
again choosing the perfect tide.
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377. Whether it's the daily
or monthly cycle,
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378. tides are the rhythm of the ocean -
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379. its pulsing clock.
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380. For every tide brings opportunity
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381. to marine life
somewhere in the world.
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382. Now, a spring tide
is flooding the shallows,
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383. and hunters are on the prowl.
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384. A small group of bottlenose dolphin
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385. are working their way inshore
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386. to start a quite extraordinary
hunting campaign.
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387. After one successful pass,
the dolphin move off to start again.
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388. One animal peels off from the group
and swims in a circle,
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389. stirring up the mud and driving
the mullet towards the other dolphins.
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390. It's a remarkable team effort
and it's extremely effective.
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391. The dolphin will feed like this
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392. for as long as the tide grants them
access to the shallows.
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393. Eventually,
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394. the falling tide will force
the dolphin to leave the flats
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395. and the mullet will be safe
once more, until the next high tide.
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396. Because, in the ocean,
every turn of the tide
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397. spells the difference
between life and death somewhere.
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