1
00:00:33,360 --> 00:00:36,956
These seas, thousands of miles
from nearest land,

2
00:00:37,120 --> 00:00:39,351
are the most sterile on our planet.

3
00:00:39,520 --> 00:00:41,910
These are marine deserts.

4
00:00:43,760 --> 00:00:48,516
But here live the swiftest
and most powerful of all ocean hunters.

5
00:00:54,760 --> 00:00:58,310
Simply finding them
is an immense challenge...

6
00:00:59,760 --> 00:01:01,752
but we are about to follow them

7
00:01:01,920 --> 00:01:03,912
as they search for their food

8
00:01:04,080 --> 00:01:06,595
in this little known part
of the seas...

9
00:01:08,360 --> 00:01:09,999
the open ocean.

10
00:01:26,160 --> 00:01:27,913
Striped marlin —

11
00:01:28,080 --> 00:01:29,594
voracious predators

12
00:01:29,760 --> 00:01:32,434
that can grow to three metres long.

13
00:01:35,920 --> 00:01:37,912
They hunt mainly in daylight,

14
00:01:38,080 --> 00:01:40,117
searching the tropical oceans

15
00:01:40,280 --> 00:01:42,272
from close to the surface

16
00:01:42,440 --> 00:01:44,591
down to depths of 100 metres or so.

17
00:01:45,480 --> 00:01:48,871
Normally, the fish they feed on
are widely dispersed,

18
00:01:49,040 --> 00:01:52,351
but sometimes their prey
gathers in dense shoals,

19
00:01:52,520 --> 00:01:54,477
like these sardines.

20
00:03:25,920 --> 00:03:28,958
This feast may last
for over an hour...

21
00:03:35,560 --> 00:03:38,792
time enough for other hunters
to reach the scene.

22
00:03:39,600 --> 00:03:42,957
Juvenile tuna join in
the feeding frenzy.

23
00:04:00,360 --> 00:04:02,352
The noise attracts a giant —

24
00:04:02,520 --> 00:04:04,637
a sei whale.

25
00:04:12,160 --> 00:04:15,153
It's 14 metres long
and 20 tonnes in weight,

26
00:04:15,320 --> 00:04:17,312
and has an appetite to match.

27
00:05:19,400 --> 00:05:23,838
Soon, the only sign
that the sardines ever existed

28
00:05:24,000 --> 00:05:27,550
are scales sinking
down into the abyss.

29
00:05:29,760 --> 00:05:31,752
Such feasts don't last long.

30
00:05:31,920 --> 00:05:33,912
Within a few short days,

31
00:05:34,080 --> 00:05:36,311
waters that once swarmed with food

32
00:05:36,480 --> 00:05:38,472
will have been cleaned out.

33
00:05:38,640 --> 00:05:40,711
The hunters must move elsewhere

34
00:05:40,880 --> 00:05:44,794
and once again search the seemingly
featureless open ocean.

35
00:05:48,240 --> 00:05:50,232
A manta ray — immense,

36
00:05:50,800 --> 00:05:52,200
five metres across

37
00:05:52,360 --> 00:05:55,956
from the tip of one wing—like fin
to the tip of the other.

38
00:05:56,120 --> 00:06:00,194
It's travelling Economy,
wasting as little energy as possible

39
00:06:00,360 --> 00:06:03,353
as it glides through the waters
of the tropics.

40
00:06:08,120 --> 00:06:10,715
The remora fish that accompany it

41
00:06:10,880 --> 00:06:14,396
travel more economically still
by hitching a lift.

42
00:06:15,080 --> 00:06:18,790
Their host is searching for food —
plankton,

43
00:06:18,960 --> 00:06:23,034
the minute fish and invertebrates
that float near the surface.

44
00:06:23,200 --> 00:06:24,714
It needs lots of them

45
00:06:24,880 --> 00:06:28,794
and may cruise for days before
it finds a good feeding ground.

46
00:06:30,880 --> 00:06:34,157
Dusk, at the edge
of a Pacific island,

47
00:06:34,320 --> 00:06:36,915
3,000 miles
from the nearest continent.

48
00:06:37,080 --> 00:06:40,152
Here, surgeon fish
have assembled to spawn.

49
00:06:42,320 --> 00:06:44,755
As they perform
their nuptial dances,

50
00:06:44,920 --> 00:06:48,470
they discharge clouds of eggs
and sperm into the water.

51
00:06:49,040 --> 00:06:52,272
The manta must have known
this was about to happen,

52
00:06:52,440 --> 00:06:55,478
for it arrived at exactly
this critical moment,

53
00:06:55,640 --> 00:06:57,711
and it is not the only one
to do so.

54
00:06:57,880 --> 00:06:59,872
Others are here, too.

55
00:07:03,760 --> 00:07:08,039
Now, they just need to sweep
the water into their mouths

56
00:07:08,200 --> 00:07:09,998
and sieve out the eggs.

57
00:07:35,360 --> 00:07:38,273
Within an hour,
the whole event will be over.

58
00:07:39,560 --> 00:07:42,075
Any surviving eggs
will be so dispersed

59
00:07:42,240 --> 00:07:44,550
that they are not worth collecting.

60
00:07:51,840 --> 00:07:53,832
But other perils await them

61
00:07:54,000 --> 00:07:56,959
as they join the clouds of eggs
and larvae and tiny fish

62
00:07:57,120 --> 00:07:59,635
that drift through
the surface waters of the open ocean.

63
00:08:02,520 --> 00:08:05,319
These are the eggs
of yellow—fin tuna.

64
00:08:05,480 --> 00:08:07,472
If the hatchlings survive,

65
00:08:07,640 --> 00:08:10,474
it will take them two years
to become adults.

66
00:08:14,960 --> 00:08:16,440
In three years,

67
00:08:16,600 --> 00:08:20,514
they could be nearly two metres long
and weigh 200 kilograms.

68
00:08:23,440 --> 00:08:26,911
Perhaps only one in a million
will live as long as that.

69
00:08:27,960 --> 00:08:29,952
They and the other animals

70
00:08:30,120 --> 00:08:32,635
and microscopic plants
of the plankton

71
00:08:32,800 --> 00:08:36,271
constitute the basis of all life
out on the open ocean.

72
00:08:41,280 --> 00:08:43,590
A storm petrel
dancing on the water.

73
00:08:43,760 --> 00:08:45,752
But this is no amiable waltz.

74
00:08:45,920 --> 00:08:47,400
It's a hunt.

75
00:08:51,360 --> 00:08:53,795
As they hover facing into the wind,

76
00:08:53,960 --> 00:08:57,874
they pick out morsels from near
the surface, including eggs.

77
00:09:05,880 --> 00:09:08,793
Only a tiny percentage
of the developing eggs

78
00:09:08,960 --> 00:09:11,191
will survive long enough to hatch.

79
00:09:11,360 --> 00:09:15,240
These newly emerged tuna
are only three millimetres long,

80
00:09:15,400 --> 00:09:17,392
and although they CAN swim,

81
00:09:17,560 --> 00:09:19,631
they're stillvery vulnerable.

82
00:09:20,680 --> 00:09:24,356
It will be many weeks before
they can swim strongly enough

83
00:09:24,520 --> 00:09:26,910
to make any real headway
in the ocean.

84
00:09:36,480 --> 00:09:38,199
After the sun goes down,

85
00:09:38,360 --> 00:09:40,750
other predators
rise from the depths

86
00:09:40,920 --> 00:09:43,230
to attack the floating multitudes.

87
00:10:01,440 --> 00:10:03,432
Darkness shrouds the arrival

88
00:10:03,600 --> 00:10:06,832
of battalions of dangerous,
drifting predators.

89
00:10:20,800 --> 00:10:24,237
These shimmering comb jellies —
sea gooseberries —

90
00:10:24,400 --> 00:10:27,234
trap their prey
with sticky, net—like webs.

91
00:10:27,640 --> 00:10:29,199
One ill—timed fin stroke

92
00:10:29,360 --> 00:10:32,398
could bring certain death
to a hatchling fish.

93
00:10:34,120 --> 00:10:36,874
There are many kinds
of these comb jellies —

94
00:10:37,040 --> 00:10:39,714
all of them very effective hunters.

95
00:10:50,960 --> 00:10:52,360
By dawn,

96
00:10:52,520 --> 00:10:56,594
most of the nocturnal feeders
will have returned to the depths.

97
00:11:00,640 --> 00:11:02,916
The surviving hatchlings, however,

98
00:11:03,080 --> 00:11:05,720
have already started
on their travels.

99
00:11:16,560 --> 00:11:19,473
Vast current systems
like immense rivers

100
00:11:19,640 --> 00:11:21,950
carry them around the ocean basins.

101
00:11:23,960 --> 00:11:27,397
The boundaries between
these masses of moving water

102
00:11:27,560 --> 00:11:31,554
form invisible barriers that
can trap plankton and nutrients

103
00:11:31,720 --> 00:11:33,518
carried up from the depths.

104
00:11:38,200 --> 00:11:41,238
So, parts of the ocean
become rich with food

105
00:11:41,400 --> 00:11:43,676
for days or even weeks at a time.

106
00:11:45,840 --> 00:11:49,390
This attracts vast schools
of plankton—feeding fish,

107
00:11:49,760 --> 00:11:51,274
like these sardine.

108
00:11:57,200 --> 00:11:59,715
They take in water
through their mouths

109
00:11:59,880 --> 00:12:01,997
and expel it through their gills,

110
00:12:02,160 --> 00:12:06,154
sieving out the plankton which is
then funnelled down their throats.

111
00:12:11,760 --> 00:12:15,993
The immense schools travel
along the boundaries of the currents,

112
00:12:16,160 --> 00:12:19,392
seeking the spots
where the plankton is thickest.

113
00:12:22,200 --> 00:12:26,274
As the position of the current
boundaries changes constantly,

114
00:12:26,440 --> 00:12:30,195
so does both the supply of plankton
and the numbers of fish.

115
00:12:44,360 --> 00:12:47,592
A small pod
of Pacific spotted dolphin,

116
00:12:47,760 --> 00:12:49,911
20 miles from the coast of Panama.

117
00:12:50,080 --> 00:12:53,152
Like all predators,
they seek parts of the ocean

118
00:12:53,320 --> 00:12:55,312
where their food is thickest.

119
00:13:04,680 --> 00:13:07,149
They cover as much
as 100 miles in a day,

120
00:13:07,320 --> 00:13:09,312
and while they travel,

121
00:13:09,480 --> 00:13:10,960
they play.

122
00:13:26,720 --> 00:13:29,713
They have detected
the sound of schooling fish

123
00:13:29,880 --> 00:13:31,872
from hundreds of metres away,

124
00:13:32,040 --> 00:13:35,033
and start to track down the shoals
using sonar,

125
00:13:35,200 --> 00:13:37,271
leaving their toys behind them.

126
00:13:41,440 --> 00:13:44,274
For the hunted,
there are few places to hide.

127
00:13:50,320 --> 00:13:52,118
Schooling mackerel.

128
00:13:52,280 --> 00:13:56,513
They have already sensed the sonar
beams of approaching dolphin.

129
00:14:00,440 --> 00:14:03,194
Their only defence
is to gather into a ball.

130
00:14:03,360 --> 00:14:07,513
Any fish that stayed out of the
shoal would be quickly picked off.

131
00:14:07,680 --> 00:14:11,071
Within it, there is
at least SOME chance of survival.

132
00:14:20,160 --> 00:14:23,358
The noise of the attack
alerts another predator —

133
00:14:23,520 --> 00:14:26,592
a sailfish, one of the fastest fish
in the ocean.

134
00:14:31,040 --> 00:14:34,636
It has detected rapid vibrations
in the water,

135
00:14:34,800 --> 00:14:36,792
and is searching for the cause.

136
00:14:50,000 --> 00:14:53,391
Sailfish rely on eyesight
for their final approach,

137
00:14:53,560 --> 00:14:55,631
so they hunt mainly in daylight.

138
00:15:00,320 --> 00:15:03,631
When sailfish become excited,
they change colour,

139
00:15:03,800 --> 00:15:05,917
lighting up with blue stripes.

140
00:15:06,080 --> 00:15:10,711
Since mackerel eyes are especially
sensitive to blue and ultraviolet,

141
00:15:10,880 --> 00:15:14,556
these colours confuse them,
making them easier to catch.

142
00:15:54,680 --> 00:15:58,356
Far below, a blue shark
returns from a squid—hunting trip

143
00:15:58,520 --> 00:16:00,193
in the cold darkness

144
00:16:00,360 --> 00:16:02,113
300 metres down.

145
00:16:02,280 --> 00:16:06,035
It's heading for the surface
to reheat in the warmer water.

146
00:16:07,680 --> 00:16:10,718
As it ascends, it detects the smell

147
00:16:10,880 --> 00:16:12,314
of oils and proteins

148
00:16:12,480 --> 00:16:15,393
shed into the water
by the panicked mackerel.

149
00:16:18,760 --> 00:16:22,515
The trail leads both the shark
and its attendant pilot fish

150
00:16:22,680 --> 00:16:24,399
towards an easy meal.

151
00:16:29,360 --> 00:16:30,999
Scraps and casualties

152
00:16:31,160 --> 00:16:34,312
float in the wake
of the passing mackerel school.

153
00:16:38,320 --> 00:16:40,994
Throughout the ocean,
predators and prey

154
00:16:41,160 --> 00:16:44,551
are locked in a deadly
three—dimensional contest

155
00:16:44,720 --> 00:16:48,077
of hide and seek, played out
over immense distances.

156
00:16:48,240 --> 00:16:50,232
To survive, they must travel.

157
00:16:56,840 --> 00:17:00,993
The huge four—metre—long
blue—fin tuna has special blood vessels

158
00:17:01,160 --> 00:17:04,631
that enable it to keep
its body temperature warmer

159
00:17:04,800 --> 00:17:06,792
than the surrounding water.

160
00:17:10,840 --> 00:17:14,277
As a result, they can survive
in much colder conditions

161
00:17:14,440 --> 00:17:17,990
than any other tuna,
and they travel thousands of miles

162
00:17:18,160 --> 00:17:22,632
away from their spawning grounds
in the tropics to hunt in cold seas

163
00:17:22,800 --> 00:17:25,110
where the food supply is richest.

164
00:17:26,280 --> 00:17:28,795
Ocean travellers
come in many guises —

165
00:17:28,960 --> 00:17:31,555
and few are stranger than this...

166
00:17:37,240 --> 00:17:40,199
a crab that spends
much of its life afloat.

167
00:17:47,000 --> 00:17:49,037
It's a worrying passer—by

168
00:17:49,200 --> 00:17:51,999
for booby birds with delicate toes.

169
00:18:10,200 --> 00:18:14,274
Many floaters are little more
than jelly enclosed in membranes

170
00:18:14,440 --> 00:18:17,035
but they may drift
for vast distances.

171
00:18:18,360 --> 00:18:21,080
And turtles,
like these olive Ridleys,

172
00:18:21,240 --> 00:18:24,472
migrate thousands of miles
every year.

173
00:18:27,360 --> 00:18:29,636
The ocean is full of such wanderers

174
00:18:29,800 --> 00:18:33,476
riding the currents and doing
their best to avoid enemies

175
00:18:33,640 --> 00:18:35,632
while they search for food

176
00:18:35,800 --> 00:18:37,792
and a safe place to breed...

177
00:18:39,960 --> 00:18:42,714
which is exactly
what these rays are doing —

178
00:18:42,880 --> 00:18:44,951
forming the two—mile high club,

179
00:18:45,120 --> 00:18:48,113
gathering together
for courtship on the wing,

180
00:18:48,280 --> 00:18:50,272
far above the ocean floor.

181
00:19:15,160 --> 00:19:18,437
More nomads — flying fish.
They seem to be

182
00:19:18,600 --> 00:19:20,671
on every large predator's menu,

183
00:19:20,840 --> 00:19:24,390
so their whole life is spent
on the run in the open ocean.

184
00:19:27,360 --> 00:19:29,352
They don't scatter their eggs

185
00:19:29,520 --> 00:19:32,991
but lay them on pieces of flotsam
like this palm frond.

186
00:19:35,280 --> 00:19:37,351
If the quality of water is right,

187
00:19:37,520 --> 00:19:39,989
they will attach their eggs
to the frond

188
00:19:40,160 --> 00:19:44,313
which will then serve as a kind
of life—raft for their offspring.

189
00:19:45,840 --> 00:19:49,072
But it's not only flying fish
that seek nurseries.

190
00:19:54,640 --> 00:19:56,996
Any piece of floating debris

191
00:19:57,160 --> 00:20:00,631
can serve as a shelter
under which baby fish can hide.

192
00:20:04,000 --> 00:20:05,480
The only drawback

193
00:20:05,640 --> 00:20:07,791
is that predators like this wahoo

194
00:20:07,960 --> 00:20:10,953
check up on who's hanging about
in the shadows.

195
00:20:12,440 --> 00:20:15,114
The wahoo may trail the flotsam
for weeks.

196
00:20:20,480 --> 00:20:24,156
Few bits of flotsam
are without their quota of lodgers,

197
00:20:24,320 --> 00:20:26,516
even man—made junk attracts them,

198
00:20:26,680 --> 00:20:29,275
and some,
like this oceanic trigger fish,

199
00:20:29,440 --> 00:20:32,274
defend their squatters' rights
with vigour.

200
00:20:40,440 --> 00:20:44,434
The triggers, in fact, tend
to claim all the prime residences.

201
00:20:49,320 --> 00:20:53,473
Out here, even discarded netting
can provide valuable shelter,

202
00:20:53,920 --> 00:20:55,400
so, in a bizarre twist,

203
00:20:55,560 --> 00:20:57,552
a wrecked trawl net like this

204
00:20:57,720 --> 00:20:59,791
can end up as a sanctuary for fish

205
00:20:59,960 --> 00:21:01,792
until it finally sinks.

206
00:21:07,440 --> 00:21:09,432
A single large piece of flotsam

207
00:21:09,600 --> 00:21:12,991
can be the reason why several
square miles of open ocean,

208
00:21:13,160 --> 00:21:14,560
instead of being empty,

209
00:21:14,720 --> 00:21:18,191
will support a fish population
of hundreds of tonnes.

210
00:21:22,360 --> 00:21:25,512
This huge clump of seaweed
is doing exactly that.

211
00:21:26,280 --> 00:21:27,999
It's a giant kelp plant,

212
00:21:28,160 --> 00:21:31,153
ripped from rocks
off the coast of California.

213
00:21:35,200 --> 00:21:38,750
Now, it's floating
above thousands of metres of water,

214
00:21:38,920 --> 00:21:41,389
held up by its gas—filled floats.

215
00:21:45,240 --> 00:21:49,439
Young rockfish are growing up in
the safety of its shadow.

216
00:21:54,920 --> 00:21:58,880
Giants also seek out
this algal flotsam.

217
00:22:01,160 --> 00:22:02,640
This is a sunfish.

218
00:22:02,800 --> 00:22:06,714
It can measure as much as four
metres from fin tip to fin tip.

219
00:22:06,880 --> 00:22:08,519
Rather surprisingly,

220
00:22:08,680 --> 00:22:12,071
it has the record as
the heaviest bony fish in the sea.

221
00:22:14,040 --> 00:22:18,592
Sunfish spend much of their time
at depth, where they feed on jellyfish,

222
00:22:18,760 --> 00:22:20,797
but it's cold and dark down there

223
00:22:20,960 --> 00:22:24,715
so from time to time, they seek
a little rest and recuperation

224
00:22:24,880 --> 00:22:26,872
and warm up near the surface.

225
00:22:27,040 --> 00:22:30,556
They too are looking
for floating kelp plants...

226
00:22:32,040 --> 00:22:33,520
not for shelter,

227
00:22:33,680 --> 00:22:37,276
but because here they can find
a particular kind of fish

228
00:22:37,440 --> 00:22:39,432
that only lives in such places.

229
00:22:43,440 --> 00:22:44,954
Half—moon fish.

230
00:22:46,840 --> 00:22:48,354
The sunfish form up

231
00:22:48,520 --> 00:22:50,239
in an orderly queue.

232
00:22:50,400 --> 00:22:52,232
They have a problem.

233
00:22:52,400 --> 00:22:54,710
Their skin is covered in parasites.

234
00:23:05,000 --> 00:23:07,390
The hungry half—moons will help.

235
00:23:07,960 --> 00:23:09,952
The sunfish turn their heads

236
00:23:10,120 --> 00:23:13,875
as a clear invitation
to their personal hygienists.

237
00:23:14,040 --> 00:23:17,875
The half—moons nip off and eat
every parasite they can find.

238
00:23:35,640 --> 00:23:37,871
If the half—moons don't do the job,

239
00:23:38,040 --> 00:23:41,875
there is another rather
drastic treatment available here.

240
00:23:43,760 --> 00:23:46,275
Gulls rest on the floating kelp...

241
00:23:48,160 --> 00:23:50,834
and if the sunfish
send the right signals,

242
00:23:51,000 --> 00:23:53,754
the gulls will investigate.

243
00:24:00,240 --> 00:24:03,631
Their beaks can dig out
the most stubborn parasites.

244
00:24:24,600 --> 00:24:27,399
But even the very best
of health clinics

245
00:24:27,560 --> 00:24:30,155
can only trade
on a temporary basis.

246
00:24:30,320 --> 00:24:32,437
The seaweed rafts are rotting

247
00:24:32,600 --> 00:24:35,274
and will eventually lose
their buoyancy.

248
00:24:42,680 --> 00:24:45,673
Then their lodgers
will have to find a new home.

249
00:24:45,840 --> 00:24:48,116
If they can't, they will be eaten

250
00:24:48,280 --> 00:24:49,680
or die

251
00:24:49,840 --> 00:24:51,718
and sink down into the abyss.

252
00:25:03,600 --> 00:25:07,719
But the open ocean is not entirely
devoid of permanent shelter.

253
00:25:12,960 --> 00:25:15,475
A volcano is erupting
from the sea floor

254
00:25:15,640 --> 00:25:17,632
and it's still growing.

255
00:25:51,760 --> 00:25:53,752
It has formed an island

256
00:25:53,920 --> 00:25:56,674
some 70 miles
from the coast of New Zealand.

257
00:26:00,360 --> 00:26:03,353
Some juvenile
reef fish have already arrived,

258
00:26:03,520 --> 00:26:05,591
carried here by a lucky current.

259
00:26:05,760 --> 00:26:08,912
Now they are growing up
in the shelter of the weeds

260
00:26:09,080 --> 00:26:11,072
around the island's fringes.

261
00:26:17,560 --> 00:26:21,395
More plankton and juvenile fish
are being swept by currents

262
00:26:21,560 --> 00:26:23,552
straight towards the island,

263
00:26:23,720 --> 00:26:26,235
but now there's
a welcoming committee.

264
00:26:29,360 --> 00:26:33,752
Schools of trevally and blue maomao
are patrolling the surface water.

265
00:26:41,440 --> 00:26:43,432
All are in search of a meal.

266
00:26:49,520 --> 00:26:51,318
These one—kilo fish

267
00:26:51,480 --> 00:26:54,234
snap up every morsel
of plankton they find.

268
00:27:03,400 --> 00:27:07,280
At times, the currents
sweeping in from the open ocean

269
00:27:07,440 --> 00:27:12,071
bring with them all kinds of small
creatures in dense concentrations.

270
00:27:12,240 --> 00:27:14,277
These are mysid shrimps.

271
00:27:48,000 --> 00:27:51,471
Very little that is edible
is left after such feasts.

272
00:27:51,640 --> 00:27:55,031
Islands are far from being
safe havens for plankton.

273
00:28:00,960 --> 00:28:02,952
The Pacific Ocean, however,

274
00:28:03,120 --> 00:28:05,589
is peppered
with over 23,000 islands,

275
00:28:05,760 --> 00:28:09,674
as well as countless other
submerged mountains — sea mounts —

276
00:28:09,840 --> 00:28:12,355
whose summits do not break
the surface.

277
00:28:14,760 --> 00:28:17,355
Juvenile fish
for their first few months

278
00:28:17,520 --> 00:28:19,751
would do well to avoid such places.

279
00:28:21,600 --> 00:28:25,594
These yellow—fin tuna, however,
are now more than six months old

280
00:28:25,760 --> 00:28:27,752
and 40 centimetres long —

281
00:28:28,920 --> 00:28:30,957
big enough to be able to eat fry,

282
00:28:31,120 --> 00:28:34,511
so sea mounts for them
are promising feeding grounds

283
00:28:34,680 --> 00:28:37,195
where they may hunt
for several months.

284
00:28:43,720 --> 00:28:45,439
The base of a sea mount.

285
00:28:45,600 --> 00:28:47,592
As currents sweep towards it,

286
00:28:47,760 --> 00:28:50,434
they're deflected
up its towering walls.

287
00:28:57,320 --> 00:28:59,391
The water coming from the depths

288
00:28:59,560 --> 00:29:02,951
carries both nutrients
and plankton to the surface.

289
00:29:07,960 --> 00:29:11,112
Numerous reef fish
take up permanent residence,

290
00:29:11,280 --> 00:29:14,318
feeding where the currents
are strongest

291
00:29:14,480 --> 00:29:16,472
and the plankton most dense.

292
00:29:25,840 --> 00:29:29,754
Where the cold water mixes
with warmer water at the surface,

293
00:29:29,920 --> 00:29:32,435
there's a strange,
shimmering effect —

294
00:29:32,600 --> 00:29:35,991
a clear sign that the currents
are running strongly.

295
00:29:52,880 --> 00:29:56,510
But these currents attract
more than just coastal fish.

296
00:29:59,960 --> 00:30:02,680
Giants come here
from the open ocean —

297
00:30:03,840 --> 00:30:07,754
hammerhead sharks,
and in great numbers.

298
00:30:13,960 --> 00:30:15,474
During the day,

299
00:30:15,640 --> 00:30:19,998
they circle the sea mount looking
for small fish at the reef edges...

300
00:30:20,160 --> 00:30:22,880
but not in order to eat them.

301
00:30:24,080 --> 00:30:25,799
They, like the sunfish,

302
00:30:25,960 --> 00:30:29,556
are looking for cleaners
to rid them of their parasites.

303
00:30:33,840 --> 00:30:37,151
White—tip reef sharks
gather here, too.

304
00:30:37,320 --> 00:30:39,471
They DO eat reef fish...

305
00:30:48,960 --> 00:30:51,520
but they prefer to hunt at night,

306
00:30:51,680 --> 00:30:54,832
when the reef fish are sleepy
and easier to catch.

307
00:30:55,040 --> 00:30:57,032
Far better to rest by day

308
00:30:57,200 --> 00:30:59,874
and allow the cleaners
to do their work.

309
00:31:06,800 --> 00:31:11,352
Even swarms of breeding trigger
aren't a serious temptation.

310
00:31:19,920 --> 00:31:23,914
These triggers spend
much of their time in open water,

311
00:31:24,120 --> 00:31:26,794
but they've come to the sea mount
to spawn.

312
00:31:35,480 --> 00:31:37,392
Trigger eggs are good food,

313
00:31:37,560 --> 00:31:40,394
and the planton feeders
gather what they can

314
00:31:40,560 --> 00:31:42,836
before the current
sweeps them away.

315
00:31:43,000 --> 00:31:46,914
This community is here because
of the nutrients and plankton

316
00:31:47,080 --> 00:31:50,118
the sea mount deflected
into the surface waters.

317
00:31:52,960 --> 00:31:54,679
But ocean—going hunters

318
00:31:54,840 --> 00:31:56,320
are never far away.

319
00:31:59,240 --> 00:32:01,960
Silky sharks specialise
in picking off injured fish

320
00:32:02,120 --> 00:32:05,397
and constantly check over
the residents around the sea mount.

321
00:32:09,560 --> 00:32:11,199
At some times of the year,

322
00:32:11,360 --> 00:32:15,593
seasonal changes make the currents
especially rich in nutrients,

323
00:32:15,760 --> 00:32:19,720
and the ocean around the sea mount
becomes a virtual soup of plankton.

324
00:32:28,360 --> 00:32:31,990
At such times, hunters gather
in astonishing numbers.

325
00:32:41,960 --> 00:32:44,600
Bonito, smaller relatives
of the tuna.

326
00:32:44,760 --> 00:32:48,310
They are searching
for still smaller plankton feeders

327
00:32:48,480 --> 00:32:50,915
that have been attracted
by the bloom.

328
00:32:52,960 --> 00:32:54,474
So are these jacks,

329
00:32:54,640 --> 00:32:56,996
and their prey is nearby.

330
00:33:01,600 --> 00:33:05,150
A school of anchovetta
has strayed up near the surface,

331
00:33:05,320 --> 00:33:09,234
even though it's broad daylight
and hunters are on the prowl.

332
00:33:12,680 --> 00:33:14,160
These small fish

333
00:33:14,320 --> 00:33:18,394
can already feel the vibrations
of the approaching predators.

334
00:33:18,560 --> 00:33:21,632
Swimming at speed,
they have formed into a ball,

335
00:33:21,800 --> 00:33:24,474
and now they must wait
for whatever comes.

336
00:33:33,320 --> 00:33:34,959
They've been detected.

337
00:33:50,280 --> 00:33:53,000
At first, the sheer scale
of the bait ball

338
00:33:53,160 --> 00:33:55,152
seems to daunt the predators...

339
00:34:08,440 --> 00:34:12,593
but now the bonito arrive
and launch the first attack.

340
00:34:19,000 --> 00:34:21,390
Still the bait ball holds together.

341
00:34:30,440 --> 00:34:32,591
The young yellow—fin tuna move in.

342
00:34:32,760 --> 00:34:34,991
The speed of this attack
is so great

343
00:34:35,160 --> 00:34:39,393
that groups of anchovetta are
splintered from the main fish ball.

344
00:35:41,200 --> 00:35:43,760
Before long,
the currents will shift,

345
00:35:43,920 --> 00:35:46,230
and the ocean will become once more

346
00:35:46,400 --> 00:35:49,074
a blue tropical desert,
plankton—free,

347
00:35:49,240 --> 00:35:51,709
and the hunters
will have to move on.

348
00:36:01,040 --> 00:36:04,112
Spinner dolphins,
still searching for food.

349
00:36:11,240 --> 00:36:15,393
Their twisting leaps are,
apparently, purely social displays.

350
00:36:15,560 --> 00:36:20,032
Since the hunting has been good,
many hundred have gathered together

351
00:36:20,200 --> 00:36:22,192
in this exuberant super—pod.

352
00:37:25,560 --> 00:37:29,634
But now the spinners
are starting to hunt once more.

353
00:37:34,760 --> 00:37:37,832
Their skill in tracking food
is not a secret.

354
00:37:38,000 --> 00:37:40,151
Yellow—fin tuna must be aware of it,

355
00:37:40,320 --> 00:37:42,391
for they regularly follow them,

356
00:37:42,560 --> 00:37:45,997
but only adult tuna in their
second or third year of life

357
00:37:46,160 --> 00:37:50,473
have sufficient stamina to keep up
with the fast—moving spinners.

358
00:38:07,840 --> 00:38:10,560
These are another kind —
common dolphin.

359
00:38:10,720 --> 00:38:12,837
They too are on the move.

360
00:38:14,960 --> 00:38:18,636
As they travel— ever inquisitive —
they pay a call

361
00:38:18,800 --> 00:38:21,872
on one of their larger relations,
a pilot whale.

362
00:38:23,600 --> 00:38:25,592
The whale is not hunting.

363
00:38:25,760 --> 00:38:29,674
It's on its way to its breeding
grounds in the Mediterranean.

364
00:38:29,840 --> 00:38:33,151
Pilot whales normally hunt
in small family groups,

365
00:38:33,320 --> 00:38:38,031
but in mid—summer they head
for traditional socialising grounds,

366
00:38:38,200 --> 00:38:41,989
where they will assemble in
super—herds several hundred strong.

367
00:38:42,760 --> 00:38:45,673
Already, two families
have joined together.

368
00:38:45,840 --> 00:38:49,311
The males are competing
for the favours of the females.

369
00:39:20,360 --> 00:39:21,760
As the weeks pass by,

370
00:39:21,920 --> 00:39:25,960
these group rubbing sessions
will become more overtly sexual,

371
00:39:26,120 --> 00:39:28,555
but now
it's just flirting in the sun.

372
00:39:50,360 --> 00:39:52,591
Timing in the ocean can be crucial.

373
00:39:52,760 --> 00:39:56,834
In summer, the northern Atlantic
waters are beginning to warm.

374
00:39:57,000 --> 00:39:58,992
The hunting is good here,

375
00:39:59,160 --> 00:40:00,674
and by June,

376
00:40:00,840 --> 00:40:04,993
predators from southern waters
are heading towards the Azores.

377
00:40:13,920 --> 00:40:16,389
These are more common dolphin.

378
00:40:23,240 --> 00:40:27,473
Like most oceanic dolphins,
they too often travel in huge herds

379
00:40:27,640 --> 00:40:30,155
containing many different families.

380
00:40:35,320 --> 00:40:39,633
There is seldom enough prey in any
one place to feed such numbers...

381
00:40:44,800 --> 00:40:47,315
so small groups leave the super—pod

382
00:40:47,480 --> 00:40:49,790
and set off on hunting expeditions.

383
00:40:52,560 --> 00:40:55,951
This group will be away
from the main herd for many hours.

384
00:41:06,280 --> 00:41:09,956
By midday, they're nearing
the islands of the Azores,

385
00:41:10,120 --> 00:41:13,431
900 miles west
of the Portuguese coast.

386
00:41:16,760 --> 00:41:20,754
Other hunters are already here —
Cory's shearwaters.

387
00:41:27,360 --> 00:41:31,115
Half a million of these birds
breed on the Azores every year

388
00:41:31,280 --> 00:41:33,590
and scour the nearby ocean
for food.

389
00:41:33,760 --> 00:41:37,151
There's insufficient wind
to support gliding flight,

390
00:41:37,320 --> 00:41:40,996
and since flapping is a waste
of energy, they sit out the calm,

391
00:41:41,160 --> 00:41:44,312
clustered in rafts
and riding the gentle swells.

392
00:42:01,440 --> 00:42:05,480
By mid—afternoon, the dolphin
are starting to hunt in earnest.

393
00:42:12,760 --> 00:42:14,479
As the sea breeze picks up,

394
00:42:14,640 --> 00:42:17,314
the shearwaters
take to the air once more.

395
00:42:27,600 --> 00:42:30,593
Out to sea,
the dolphin have found prey.

396
00:42:35,600 --> 00:42:39,833
They are driving a shoal of small
mackerel up towards the surface.

397
00:42:47,800 --> 00:42:50,076
The shearwaters crowd the skies,

398
00:42:50,240 --> 00:42:52,800
following the dolphins' every turn.

399
00:43:00,720 --> 00:43:03,599
The mackerel
are still some metres down...

400
00:43:05,880 --> 00:43:09,157
but when the baitfish
come sufficiently close,

401
00:43:09,320 --> 00:43:11,755
the airborne division
makes its move.

402
00:43:13,240 --> 00:43:15,118
Far from being mere bystanders,

403
00:43:15,280 --> 00:43:18,910
the shearwaters become
underwater predators themselves.

404
00:43:22,760 --> 00:43:26,595
Incredibly, they can dive
down to depths of several metres.

405
00:43:28,360 --> 00:43:32,752
The hunting dolphin prevent the
mackerel from escaping downwards,

406
00:43:32,920 --> 00:43:35,799
and both predators
gorge themselves.

407
00:44:00,960 --> 00:44:04,431
Soon, the diving birds
outnumber the dolphin

408
00:44:04,600 --> 00:44:07,354
and even drive them away
from their meal...

409
00:44:07,520 --> 00:44:12,549
but another squadron of predators
arrives to replace the dolphin —

410
00:44:13,520 --> 00:44:15,671
adult yellow—fin tuna.

411
00:44:18,040 --> 00:44:20,396
These are giants, two metres long.

412
00:44:26,640 --> 00:44:29,792
They are heading
directly for the bait ball.

413
00:45:28,120 --> 00:45:30,555
Despite the arrival
of the giant fish,

414
00:45:30,720 --> 00:45:34,714
the shearwater continue
to press home their attack unfazed.

415
00:45:51,520 --> 00:45:53,398
Eventually, the tuna move on,

416
00:45:53,560 --> 00:45:56,997
leaving the shearwaters
to battle among themselves.

417
00:46:04,960 --> 00:46:08,795
As long as a predatory fish
or a dolphin remains at the scene,

418
00:46:08,960 --> 00:46:11,350
the mackerel can't escape to safety,

419
00:46:11,520 --> 00:46:14,911
but when the little skipjack tuna
start to move away,

420
00:46:15,080 --> 00:46:19,154
gradually the bait ball sinks
into the depths towards safety.

421
00:46:29,720 --> 00:46:31,791
The shearwaters follow it down

422
00:46:31,960 --> 00:46:35,271
to the very limit
of their breath—holding ability,

423
00:46:35,440 --> 00:46:37,432
perhaps as deep as 15 metres.

424
00:46:44,000 --> 00:46:47,789
At last, even they are forced
to leave their quarry.

425
00:46:58,840 --> 00:47:02,038
However good or bad
this summer's feeding may be,

426
00:47:02,200 --> 00:47:04,999
within three months,
winter will be on its way

427
00:47:05,160 --> 00:47:09,154
and the temperature of these waters
will drop by a few degrees.

428
00:47:09,320 --> 00:47:13,075
Then the ocean hunters
will abandon the Azores once more.

429
00:47:13,240 --> 00:47:15,232
As ever, they will move on,

430
00:47:15,400 --> 00:47:18,313
searching for another
feeding opportunity —

431
00:47:18,480 --> 00:47:22,793
the next pulse of life in the distant
reaches of the open ocean.