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They're coming.
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700 SHARKS
INTO THE DARK
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In the middle of the vast Pacific,
700 sharks congregate
4
00:01:02,563 --> 00:01:04,929
around an island
invisible from space:
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00:01:05,107 --> 00:01:09,100
Fakarava Atoll
in the Tuamotu Archipelago.
6
00:01:20,706 --> 00:01:22,537
The atoll is a crown of coral
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with breaches connecting
its lagoon to the ocean.
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00:01:27,671 --> 00:01:29,662
The deepest are called passes,
9
00:01:31,133 --> 00:01:33,169
and the southern pass at Fakarava
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00:01:33,302 --> 00:01:37,215
contains the highest density
of grey sharks in the world.
11
00:01:42,644 --> 00:01:46,808
Seven hundred of them
gather in the pass,
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a valley of corals declared
a UNESCO biosphere reserve.
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Why are there so many?
14
00:02:00,037 --> 00:02:02,574
What causes them to group together?
15
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To solve this enigma,
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20 divers and scientists join forces,
17
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led by Laurent Ba/Iesta.
18
00:02:41,328 --> 00:02:44,411
They set up a scientific HQ
on the island.
19
00:02:54,341 --> 00:02:58,801
Charlie Huveneers, from Australia,
is an expert on great white sharks.
20
00:03:00,097 --> 00:03:02,930
He and Laurent
discuss the aims of the mission.
21
00:03:03,100 --> 00:03:04,385
Amazing photo.
22
00:03:04,601 --> 00:03:09,311
I want to know what distinguishes
an organized pack
23
00:03:09,481 --> 00:03:10,812
from total anarchy.
24
00:03:10,941 --> 00:03:13,978
If this were a pack of wolves,
25
00:03:14,820 --> 00:03:19,280
there would be
some kind of sharing of the prey,
26
00:03:19,449 --> 00:03:22,316
with the leader of the pack
given priority.
27
00:03:22,869 --> 00:03:27,488
Here, I don't know if they use tactics
to hunt together,
28
00:03:27,624 --> 00:03:29,455
but once a prey is caught,
29
00:03:29,751 --> 00:03:31,287
it's a free-for—all.
30
00:03:31,420 --> 00:03:33,786
-They fight over it.
-Yes.
31
00:03:35,173 --> 00:03:38,165
What causes these sharks
to hunt together?
32
00:03:38,301 --> 00:03:41,543
Is it cooperation or competition?
33
00:03:42,013 --> 00:03:46,006
Could this wild horde
actually be an organized pack?
34
00:03:49,938 --> 00:03:53,806
These crates contain the centerpiece
of the headquarters:
35
00:03:53,942 --> 00:03:56,979
a detailed model of the pass.
36
00:04:07,372 --> 00:04:09,488
That's the lagoon end.
37
00:04:09,666 --> 00:04:11,531
Put it on the table.
38
00:04:11,710 --> 00:04:15,168
It's the wrong way, turn it round.
39
00:04:16,798 --> 00:04:20,461
-You say that about every piece.
-This is the next one.
40
00:04:29,269 --> 00:04:32,432
The model maker
followed real contour lines.
41
00:04:32,939 --> 00:04:36,227
We’ll use this to show
where the sharks hunt
42
00:04:36,401 --> 00:04:38,266
and where they rest.
43
00:04:38,987 --> 00:04:41,729
I hope the model
will bring the team together,
44
00:04:42,240 --> 00:04:44,276
so everyone can share ideas.
45
00:04:44,451 --> 00:04:45,861
It goes very deep.
46
00:04:48,038 --> 00:04:50,620
This section should be raised a bit.
47
00:04:54,252 --> 00:04:56,368
We make a gentle slope.
48
00:04:58,340 --> 00:04:59,921
I’ve come to this pass
49
00:05:00,091 --> 00:05:02,423
four years in a row,
and this year,
50
00:05:02,677 --> 00:05:06,386
we have 50 days
and 50 nights ahead of us.
51
00:05:14,189 --> 00:05:18,148
Surveying the valley of the sharks
again and again,
52
00:05:18,360 --> 00:05:21,477
like an adventure
that thrives on routine,
53
00:05:21,696 --> 00:05:23,232
revealing its secrets
54
00:05:23,698 --> 00:05:27,441
and fulfilling a childhood ambition.
55
00:05:28,036 --> 00:05:33,247
I didn't play cowboys and Indians,
but Commandant Cousteau's adventures.
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00:05:33,416 --> 00:05:37,750
Now, in my forties,
the game has become my profession,
57
00:05:37,921 --> 00:05:40,162
but the dream is the same:
58
00:05:40,340 --> 00:05:43,798
trying to solve mysteries
of the unden/vater world.
59
00:05:57,607 --> 00:06:01,270
The number of sharks
seems to vary during the year.
60
00:06:02,487 --> 00:06:04,728
What draws them to the pass?
61
00:06:18,044 --> 00:06:21,377
I'm just borrowing this, Sané.
I'll bring it back.
62
00:06:22,591 --> 00:06:24,798
I'm obsessed with these sharks,
63
00:06:25,010 --> 00:06:30,004
but they weren’t the reason
we came here four years ago.
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00:06:30,515 --> 00:06:33,097
It was the rumor
of thousands of groupers
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a moon which tells them to spawn.
66
00:06:42,152 --> 00:06:44,268
The rumor was true.
We estimated
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a world record of 18,000 groupers.
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00:06:48,867 --> 00:06:53,156
We knew such a mass of groupers
would attract sharks.
69
00:06:54,623 --> 00:06:58,332
But we didn’t expect so many.
We were spellbound.
70
00:07:03,089 --> 00:07:06,707
We made counts
from one end of the pass to the other
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00:07:07,260 --> 00:07:10,673
and obtained
the amazing figure of 700.
72
00:07:10,847 --> 00:07:12,929
705, to be exact.
73
00:07:14,893 --> 00:07:18,727
All those sharks in a valley
barely 200 meters wide,
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00:07:18,980 --> 00:07:22,564
the highest density
anywhere in the world.
75
00:07:26,071 --> 00:07:27,436
Two.
76
00:07:27,739 --> 00:07:28,979
One, two...
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00:07:29,199 --> 00:07:30,814
Five plus three, eight.
78
00:07:31,493 --> 00:07:36,157
Seven hundred sharks,
a silent army deployed along the pass,
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00:07:36,331 --> 00:07:38,617
impossible to behold in one glance.
80
00:07:40,543 --> 00:07:45,503
Driven by our curiosity,
we went to observe them at night.
81
00:07:45,674 --> 00:07:48,211
We noticed that sharks
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00:07:48,343 --> 00:07:53,133
which were at mid-depth by day
would suddenly swim to the bottom
83
00:07:53,348 --> 00:07:56,806
and start raiding
around the bottom of the pass.
84
00:07:57,352 --> 00:07:59,183
We didn't dare approach them.
85
00:07:59,354 --> 00:08:02,096
We filmed from 10 meters above,
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00:08:02,482 --> 00:08:05,974
with our knees pulled up
underneath our chins,
87
00:08:06,152 --> 00:08:09,110
afraid to dangle anything
near all those jaws.
88
00:08:09,656 --> 00:08:12,398
It was an impenetrable ball of sharks.
89
00:08:24,713 --> 00:08:27,420
We started daring to go deeper,
on the edges.
90
00:08:27,632 --> 00:08:30,419
Keeping a distance,
but nearer the bottom.
91
00:08:34,055 --> 00:08:37,639
It was still impenetrable.
What goes on in the center
92
00:08:37,809 --> 00:08:38,844
when we're here?
93
00:08:40,895 --> 00:08:45,309
Filming that close,
we got bashed by the sharks.
94
00:08:52,115 --> 00:08:53,696
Damn!
95
00:09:02,292 --> 00:09:06,376
We realized that we weren't targets,
96
00:09:06,504 --> 00:09:08,415
we were just obstacles.
97
00:09:19,100 --> 00:09:22,183
We figured there was
some sort of social system.
98
00:09:22,353 --> 00:09:26,892
We were seeing
various predatory strategies.
99
00:09:27,317 --> 00:09:29,933
We had a hunch, an intuition.
100
00:09:30,111 --> 00:09:34,480
Now I want to confirm it
and see if it's scientific fact.
101
00:09:36,993 --> 00:09:39,200
Laurent has 50 days.
102
00:09:39,370 --> 00:09:41,782
For now,
there are less than 400 sharks,
103
00:09:41,956 --> 00:09:44,493
enough to observe their attacks,
104
00:09:44,667 --> 00:09:48,410
before the major hunt
during the June full moon.
105
00:09:51,591 --> 00:09:55,379
This natural satellite
is the expedition ’s stopwatch,
106
00:09:55,553 --> 00:09:57,760
a reference for the scientists
107
00:09:57,931 --> 00:10:00,923
and a metronome
for life in the pass.
108
00:10:12,821 --> 00:10:14,857
The countdown has begun.
109
00:10:15,031 --> 00:10:18,523
The team plan positions
for 3 surveillance cameras.
110
00:10:19,786 --> 00:10:24,530
Where do you want the cameras?
We said we could put one
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00:10:24,874 --> 00:10:27,331
at the entrance to the deep canyon.
112
00:10:41,724 --> 00:10:44,215
The cameras will tell the biologists
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00:10:44,394 --> 00:10:46,305
when shoals of fish arrive,
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00:10:46,604 --> 00:10:50,017
how the sharks react
to this potential prey,
115
00:10:50,191 --> 00:10:52,933
and of possible increases
in shark numbers.
116
00:11:01,744 --> 00:11:03,860
There's Thibault.
117
00:11:04,038 --> 00:11:07,155
-A few adjustments.
—Cedric is positioning it.
118
00:11:10,420 --> 00:11:11,409
That's not bad.
119
00:11:18,678 --> 00:11:21,715
The 700 sharks
are not here by accident.
120
00:11:25,560 --> 00:11:28,723
Their presence is linked
to the island’s history.
121
00:11:29,189 --> 00:11:33,808
Its geological past helps us
to understand its biology today.
122
00:11:34,777 --> 00:11:38,110
Fakarava was created
70 million years ago.
123
00:11:38,281 --> 00:11:41,819
After the volcano emerged
from the Pacific Ocean,
124
00:11:42,076 --> 00:11:44,567
coral reefs colonized the coast.
125
00:11:46,456 --> 00:11:50,290
The island was quickly ringed
by a belt of coral.
126
00:11:50,460 --> 00:11:54,544
In the north, freshwater from rivers
prevented coral growth,
127
00:11:54,714 --> 00:11:58,502
causing a three-kilometer wide gap
in the coral barrier.
128
00:11:59,469 --> 00:12:04,008
The volcano, by then extinct,
disappeared after 2 million years,
129
00:12:04,140 --> 00:12:06,597
while the reef kept growing.
130
00:12:06,768 --> 00:12:11,307
Traces of those estuaries still remain.
They are the passes.
131
00:12:13,024 --> 00:12:16,232
The northern pass receives
almost all of the tide.
132
00:12:16,527 --> 00:12:21,521
As a result, the current
in the southern pass is less violent.
133
00:12:36,089 --> 00:12:38,876
This gentle current is a godsend.
134
00:12:39,050 --> 00:12:43,339
It’s weak enough for coral to grow
and for fish to shelter in,
135
00:12:44,013 --> 00:12:46,971
but strong enough to create
a nourishing flow
136
00:12:47,558 --> 00:12:49,924
that benefits everyone.
137
00:13:09,455 --> 00:13:12,993
The current also helps the sharks.
138
00:13:13,459 --> 00:13:17,828
By day, they use it to rest,
by night, it helps them to hunt.
139
00:13:25,346 --> 00:13:27,302
Part of the enigma of our 700 sharks
140
00:13:28,224 --> 00:13:30,681
is this miraculously suitable current.
141
00:13:36,858 --> 00:13:39,895
The current allows sharks
to breathe effortlessly.
142
00:13:40,069 --> 00:13:42,276
They just need to face into it,
143
00:13:42,530 --> 00:13:45,317
which requires less energy
than swimming.
144
00:13:45,867 --> 00:13:49,451
If the current is too weak,
the sharks leave the pass.
145
00:13:51,039 --> 00:13:53,655
To build a 3D map
of their movements,
146
00:13:53,833 --> 00:13:56,700
Laurent hopes
to fit some sharks with tags
147
00:13:56,878 --> 00:13:59,415
and install receivers in the pass.
148
00:14:01,549 --> 00:14:06,543
He enlists Charlie Huveneers
and shark experts Yannis Papastamatiou
149
00:14:07,388 --> 00:14:10,095
and Johann Mourrier to help him.
150
00:14:10,641 --> 00:14:14,429
The current isn't equal.
If we know roughly where they are
151
00:14:14,937 --> 00:14:17,269
in the channel
and how active they are,
152
00:14:17,440 --> 00:14:20,398
and we have
an idea of current strength,
153
00:14:20,568 --> 00:14:23,685
then we can really see
how their behavior varies
154
00:14:23,863 --> 00:14:28,197
based on the energetic state of
the water flowing through the channel.
155
00:14:28,451 --> 00:14:32,444
Based on the range testing we did,
we should space the receivers
156
00:14:32,830 --> 00:14:35,196
-100 meters apart.
-Yeah, exactly.
157
00:14:35,375 --> 00:14:38,082
So this is about 100 meters.
158
00:14:40,380 --> 00:14:42,666
You don't want them too close.
159
00:14:43,841 --> 00:14:45,797
Let‘s say here.
160
00:14:47,053 --> 00:14:50,386
We want to position
the acoustic receivers
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00:14:51,599 --> 00:14:54,466
where the sharks spend
most of their time,
162
00:14:54,685 --> 00:14:56,801
on the hotspots around the walls,
163
00:14:56,979 --> 00:14:59,937
but also where they hunt at night,
164
00:15:00,066 --> 00:15:03,354
so we can compare the activity
from day and night.
165
00:15:03,569 --> 00:15:08,939
We have a big school of sharks
usually staying all along here.
166
00:15:09,158 --> 00:15:12,070
So all these receivers
can get that detection.
167
00:15:12,286 --> 00:15:17,576
There‘s always a smaller school
of sharks by the edge of the drop-off.
168
00:15:18,668 --> 00:15:22,536
We assume there is a connection
between the two schools.
169
00:15:23,381 --> 00:15:25,372
We just have to deploy them now.
170
00:15:30,763 --> 00:15:34,676
This is done with the permission
of the Polynesian government.
171
00:15:34,851 --> 00:15:37,593
The sharks here are protected by law.
172
00:15:45,486 --> 00:15:48,899
22 is one, zero, one,
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00:15:49,157 --> 00:15:50,897
seven, nine, nine.
174
00:15:54,120 --> 00:15:56,907
One, one, three, one, two, two.
175
00:15:57,707 --> 00:16:02,952
These 25 receivers will pick up
signals from tags on the sharks.
176
00:16:03,629 --> 00:16:04,744
Three, three, four.
177
00:16:13,014 --> 00:16:14,845
We hope to tag 40 sharks.
178
00:16:15,183 --> 00:16:18,050
Fewer wouldn't be representative,
179
00:16:18,186 --> 00:16:22,429
more could cause interference
and skew the results.
180
00:16:31,532 --> 00:16:33,864
The grey sharks keep their distance.
181
00:16:34,243 --> 00:16:36,108
Like us, they are wary.
182
00:16:38,206 --> 00:16:40,788
These predators are also prey
183
00:16:40,958 --> 00:16:43,324
for large hammerhead sharks.
184
00:17:04,857 --> 00:17:07,519
The VHF works just fine.
185
00:17:07,693 --> 00:17:10,184
The first receivers are installed.
186
00:17:10,363 --> 00:17:13,651
Yannis, Johann and Charlie
can now tag the sharks.
187
00:17:14,325 --> 00:17:17,817
They want to know
when the predators go into action,
188
00:17:17,995 --> 00:17:21,533
if they leave the pass,
if some stay together,
189
00:17:21,707 --> 00:17:24,744
and if there are leaders
and followers.
190
00:17:25,461 --> 00:17:28,919
Many of the answers
could come from these tags
191
00:17:29,090 --> 00:17:31,297
placed in the sharks' abdomens.
192
00:17:31,759 --> 00:17:35,172
If it works,
they will see each shark's movements,
193
00:17:35,972 --> 00:17:37,928
like the demo on this screen.
194
00:17:38,849 --> 00:17:41,807
We can see three axes.
195
00:17:42,228 --> 00:17:44,765
For example,
if the shark is moving up,
196
00:17:46,983 --> 00:17:51,022
we can see the red line moving.
197
00:17:51,529 --> 00:17:53,485
If it's going that way,
198
00:17:53,948 --> 00:17:56,781
the green one,
and that way, the blue.
199
00:17:56,951 --> 00:18:00,739
So that's the data
we are going to have.
200
00:18:00,913 --> 00:18:04,371
If it is beating its tail,
you can see the frequency.
201
00:18:04,625 --> 00:18:08,288
If it gets more active,
if it's doing it faster,
202
00:18:08,462 --> 00:18:11,078
you can see that change in there.
203
00:18:13,759 --> 00:18:16,250
The team has another
more accurate tool:
204
00:18:16,429 --> 00:18:20,889
a spy camera
that can be fixed to the shark.
205
00:18:22,059 --> 00:18:25,347
This will go
on the shark's dorsal fin.
206
00:18:25,521 --> 00:18:27,978
It measures depth, water temperature,
207
00:18:28,899 --> 00:18:32,437
and there's a video camera
that will run for 5 hours.
208
00:18:32,862 --> 00:18:35,274
That will show us what it sees.
209
00:18:35,990 --> 00:18:40,575
Laurent is going to try
and put the shark in tonic immobility,
210
00:18:40,703 --> 00:18:42,443
underwater.
211
00:18:43,539 --> 00:18:46,372
The shark is going to be like this.
212
00:18:46,500 --> 00:18:52,245
Do you think you'd be able to put
the clamp on a shark like that?
213
00:18:52,882 --> 00:18:56,249
l have no idea.
We'll try it and see.
214
00:18:56,427 --> 00:18:58,543
If not,
we'll do it the old way.
215
00:18:58,721 --> 00:19:03,886
But the goal is that we come in,
I can open up the clamp,
216
00:19:04,060 --> 00:19:07,427
over the dorsal fin like that,
and it's spring-loaded,
217
00:19:07,605 --> 00:19:09,311
to clamp together.
218
00:19:09,482 --> 00:19:12,064
We release the shark,
it goes off.
219
00:19:13,319 --> 00:19:17,187
Once we turn it back the normal way,
it will swim off.
220
00:19:17,365 --> 00:19:21,153
There will be a release
connecting the tag to the clamp
221
00:19:21,327 --> 00:19:23,613
which, after two days, will dissolve.
222
00:19:24,580 --> 00:19:30,075
So then, the whole tag
should come off of the clamp
223
00:19:30,753 --> 00:19:32,869
and float up to the surface.
224
00:19:33,047 --> 00:19:36,164
Within a week,
there's nothing left on the shark.
225
00:19:36,300 --> 00:19:38,291
Let's try it and see.
226
00:19:45,101 --> 00:19:47,513
It's Yannis's first dive, at night,
227
00:19:48,104 --> 00:19:50,015
in the middle of the pack.
228
00:19:52,566 --> 00:19:55,603
Together,
we’ll try to attach the spy camera
229
00:19:55,778 --> 00:19:58,360
by immobilizing a shark underwater.
230
00:19:59,699 --> 00:20:03,658
One year ago,
this would’ve seemed impossible to me.
231
00:20:10,626 --> 00:20:13,288
The sharks are too wary by day,
232
00:20:14,088 --> 00:20:17,876
but at night
they are emboldened by the hunt.
233
00:20:57,089 --> 00:20:58,295
Other researchers
234
00:20:58,424 --> 00:21:02,008
have shown how a shark turned
on its back can be placed
235
00:21:02,261 --> 00:21:03,421
in a tonic state.
236
00:21:03,596 --> 00:21:07,339
But those sharks were used to it
and fed by divers.
237
00:21:07,516 --> 00:21:09,882
Is it possible in all this excitement?
238
00:21:13,481 --> 00:21:15,346
Amazingly, it works.
239
00:21:21,989 --> 00:21:25,948
This circus trick could become
a scientific procedure.
240
00:21:40,841 --> 00:21:42,331
We want a big shark,
241
00:21:42,551 --> 00:21:45,384
so I ask Yannis to be patient.
242
00:22:04,198 --> 00:22:06,109
Each shark reacts differently.
243
00:22:06,283 --> 00:22:09,992
Some resist hypnosis
and there’s a risk of being bitten.
244
00:22:15,042 --> 00:22:19,126
Yannis says this one is too small,
so I let it go.
245
00:22:25,010 --> 00:22:27,501
As I'm looking for a compliant shark,
246
00:22:27,680 --> 00:22:30,672
we witness something
never filmed before.
247
00:22:43,487 --> 00:22:47,526
No grey shark would attack
a moray eel this size on its own,
248
00:22:47,783 --> 00:22:50,946
but with the school
comes greater audacity.
249
00:22:58,335 --> 00:22:59,996
After two hours, we give up.
250
00:23:01,005 --> 00:23:03,417
Attaching the camera is too difficult.
251
00:23:03,632 --> 00:23:05,418
We need another method.
252
00:23:14,435 --> 00:23:16,096
Still got all ten fingers?
253
00:23:16,270 --> 00:23:17,555
l have gloves.
254
00:23:20,024 --> 00:23:24,734
I've been fortunate to dive
all over the world with sharks.
255
00:23:24,862 --> 00:23:27,854
l have never in my life
seen something like that.
256
00:23:29,283 --> 00:23:31,615
That was beyond belief.
257
00:23:33,037 --> 00:23:36,450
I'm happy to hear that,
coming from a guy like you.
258
00:23:36,582 --> 00:23:37,788
My God.
259
00:23:43,464 --> 00:23:45,876
Look at his face
260
00:23:46,050 --> 00:23:52,011
In 25 years of diving, I've probably
seen one or two predation events.
261
00:23:52,181 --> 00:23:57,426
-And here?
—I stopped counting!
262
00:23:58,562 --> 00:23:59,517
Unbelievable.
263
00:23:59,730 --> 00:24:02,016
Probably the best dive I've ever done.
264
00:24:02,191 --> 00:24:03,180
-Best dive?
-Yeah.
265
00:24:03,484 --> 00:24:07,898
You judged that it wasn't
the right way to place the camera?
266
00:24:08,072 --> 00:24:13,157
We could have done it,
but if it wasn‘t perfect first time,
267
00:24:13,327 --> 00:24:17,195
you wouldn't have been able
to keep on holding it.
268
00:24:17,373 --> 00:24:23,164
I realize with the small ones,
I can really immobilize them.
269
00:24:23,337 --> 00:24:26,454
With the big ones,
I can just hold them.
270
00:24:26,632 --> 00:24:28,213
And you want a big one.
271
00:24:28,342 --> 00:24:32,176
I‘m sorry. When I held one,
it moved and jumped on you.
272
00:24:32,304 --> 00:24:36,923
That‘s right, I just stopped moving
and hoped for the best.
273
00:24:37,434 --> 00:24:40,551
It's funny now,
but it could've been serious.
274
00:24:58,789 --> 00:25:01,656
The endless night dives
are exhausting.
275
00:25:02,042 --> 00:25:04,784
By dawn,
tiredness catches up with us.
276
00:25:04,962 --> 00:25:07,874
Like the sharks, we rest by day.
277
00:25:29,194 --> 00:25:31,981
The moon continues its course.
278
00:25:32,239 --> 00:25:35,652
We need to be ready
for when the shoals arrive.
279
00:25:37,327 --> 00:25:39,409
After a short nap,
280
00:25:39,580 --> 00:25:43,619
Antonin and Thibault continue
installing receivers in the pass.
281
00:25:51,675 --> 00:25:54,633
At HQ,
Yannis examines our first images.
282
00:25:54,803 --> 00:25:56,543
A hypothesis emerges.
283
00:25:56,722 --> 00:25:59,464
The idea of sharks forming duos
284
00:25:59,641 --> 00:26:01,552
that hunt together.
285
00:26:02,061 --> 00:26:04,143
There are so many sharks here,
286
00:26:04,772 --> 00:26:07,058
and so much predation going on,
287
00:26:07,232 --> 00:26:10,816
that for the first time,
we can try and understand
288
00:26:11,612 --> 00:26:15,901
sharks' hunting tactics,
and, more importantly,
289
00:26:16,116 --> 00:26:19,859
how that applies to the social system
of the sharks.
290
00:26:23,373 --> 00:26:28,834
One of the most fascinating things
about the sharks in Fakarava channel
291
00:26:29,004 --> 00:26:31,541
is the social systems of the sharks.
292
00:26:32,299 --> 00:26:34,756
Why do they form social associations?
293
00:26:34,927 --> 00:26:37,043
By remaining close to each other,
294
00:26:37,221 --> 00:26:42,056
one shark could see another shark
taking some prey and benefit from that.
295
00:26:42,226 --> 00:26:46,344
Imagine there's a reef fish here,
one shark sees it,
296
00:26:46,688 --> 00:26:50,397
charges, goes after the reef fish,
it escapes.
297
00:26:50,567 --> 00:26:54,901
Another shark sees that shark
chasing the reef fish,
298
00:26:55,447 --> 00:26:58,985
then it sees the reef fish
and successfully gets it.
299
00:26:59,243 --> 00:27:01,108
By being close to each other,
300
00:27:01,286 --> 00:27:05,029
I can see if you get some food
and that can benefit me.
301
00:27:05,290 --> 00:27:09,784
Very simple, but that could still
drive us to form social associations.
302
00:27:12,005 --> 00:27:14,246
The duo theory seems plausible.
303
00:27:16,218 --> 00:27:20,962
Are the hunting pairs always
made up of the same individuals
304
00:27:21,140 --> 00:27:23,222
and active every night?
305
00:27:23,809 --> 00:27:28,018
Grey sharks only need to eat
3 to 5 kilos of fish per week.
306
00:27:28,188 --> 00:27:31,897
In theory, they don't need
to hunt every night.
307
00:27:33,777 --> 00:27:36,519
Electronic tags
will tell the team more.
308
00:27:36,697 --> 00:27:39,279
Laurent has a plan for fitting them.
309
00:27:39,449 --> 00:27:42,566
I grab the shark,
turn it over, and rope it.
310
00:27:43,829 --> 00:27:47,572
I'm not sure I can tighten
the slipknot with one hand.
311
00:27:49,960 --> 00:27:52,667
Do you know this knot?
312
00:27:53,338 --> 00:27:55,169
It works.
313
00:27:55,340 --> 00:27:57,626
But that also means
314
00:27:58,260 --> 00:28:01,502
I need some slack
to get it off my wrist.
315
00:28:01,763 --> 00:28:04,755
He lets go of the tail
and you guys pull.
316
00:28:04,933 --> 00:28:09,973
-Not before that.
—Then we really go for it.
317
00:28:10,689 --> 00:28:15,683
The most important part
of the expedition is at stake here.
318
00:28:15,986 --> 00:28:20,730
Will this non-violent method work?
319
00:28:20,866 --> 00:28:22,197
Or won't it?
320
00:28:24,244 --> 00:28:25,734
It's a trial.
321
00:28:25,913 --> 00:28:28,825
It's a trial,
but it would help if it works.
322
00:28:31,210 --> 00:28:32,666
You got the bag?
323
00:28:39,051 --> 00:28:40,257
Good luck!
324
00:28:53,732 --> 00:28:57,020
Most scientists catch sharks
with hooks to tag them.
325
00:28:57,486 --> 00:29:02,276
We aim to immobilize them by hand
then put a lasso on them.
326
00:29:02,491 --> 00:29:05,654
It’s less violent,
but also untested,
327
00:29:05,827 --> 00:29:08,409
and there's a risk of being bitten.
328
00:29:20,425 --> 00:29:24,043
One of the difficulties
is the weight of the animal.
329
00:29:25,180 --> 00:29:28,047
A shark sinks
when it stops swimming.
330
00:29:28,183 --> 00:29:31,300
When I immobilize it,
it sinks downwards
331
00:29:31,478 --> 00:29:34,015
and its jaws are close to my legs.
332
00:29:40,779 --> 00:29:41,859
Damn it!
333
00:29:48,996 --> 00:29:50,577
It has to work tonight,
334
00:29:50,872 --> 00:29:54,785
to convince Yannis and Charlie
who doubt our method.
335
00:30:06,471 --> 00:30:09,713
-Yannis, you can do the slack.
-Yeah.
336
00:30:11,018 --> 00:30:13,509
I'll pull it from the other side.
337
00:30:13,687 --> 00:30:15,018
-Here.
-Good.
338
00:30:20,444 --> 00:30:22,685
Pick up the slack!
339
00:30:26,950 --> 00:30:29,487
Another one, guys.
We're on.
340
00:30:30,454 --> 00:30:32,365
A little bit more.
341
00:30:32,581 --> 00:30:34,492
One, two, three.
342
00:30:47,804 --> 00:30:49,089
There goes the...
343
00:30:50,724 --> 00:30:52,260
Good boy!
344
00:30:53,185 --> 00:30:55,426
-Don‘t touch...
-There we go.
345
00:30:55,604 --> 00:30:56,684
Close! Close!
346
00:31:01,651 --> 00:31:06,486
When the shark is belly-up,
it's much easier for us to work.
347
00:31:06,740 --> 00:31:10,653
And the shark is less stressed
when he's belly-up.
348
00:31:12,454 --> 00:31:16,413
Yannis Papastamatiou
fits the shark with an electronic tag.
349
00:31:16,875 --> 00:31:20,288
This will reveal
all of the shark's movements
350
00:31:20,420 --> 00:31:23,457
and periods of activity and rest.
351
00:31:25,675 --> 00:31:27,836
The surface of the skin is very hard.
352
00:31:28,512 --> 00:31:32,630
A really thick muscle layer
until you get to the body cavity.
353
00:31:32,933 --> 00:31:36,846
Although these incisions
look quite dramatic,
354
00:31:37,020 --> 00:31:38,635
you must remember,
355
00:31:38,897 --> 00:31:42,810
first of all, sharks naturally have
pretty violent lives,
356
00:31:42,943 --> 00:31:45,150
especially when they mate.
357
00:31:45,404 --> 00:31:50,524
The male will bite the female,
females can get pretty torn up.
358
00:31:50,700 --> 00:31:53,157
We get females with huge scars,
359
00:31:53,328 --> 00:31:56,946
much larger than anything
we're inflicting with this blade.
360
00:31:57,416 --> 00:32:01,375
They're naturally adapted
to having a lot of damage.
361
00:32:01,711 --> 00:32:04,874
So they have
very impressive immune systems
362
00:32:05,132 --> 00:32:07,874
and very fast healing rates.
363
00:32:08,051 --> 00:32:12,090
We've caught sharks
a couple of days after tagging
364
00:32:12,222 --> 00:32:15,464
and the wound is already healed up.
365
00:32:21,940 --> 00:32:23,851
Lassoing sharks like this
366
00:32:23,984 --> 00:32:26,851
is more than
an underwater rodeo show,
367
00:32:27,237 --> 00:32:30,650
it allows us to catch
the specimens we want.
368
00:32:30,782 --> 00:32:35,617
We need a range of sizes,
from small to large sharks,
369
00:32:35,787 --> 00:32:37,778
but also males and females
370
00:32:38,123 --> 00:32:41,365
to have a good population sample.
371
00:32:41,835 --> 00:32:46,204
It also means
we don't have to fish for the sharks.
372
00:32:46,339 --> 00:32:49,547
Not having a hook in its mouth,
373
00:32:49,718 --> 00:32:52,209
the shark will recover more easily.
374
00:32:52,345 --> 00:32:54,176
-Ready to let go?
-Yeah.
375
00:32:54,306 --> 00:32:57,139
One, two, three.
Flip it out.
376
00:32:57,392 --> 00:33:00,509
Flip it, and let it go.
Perfect.
377
00:33:00,729 --> 00:33:02,640
At least we know she's healthy.
378
00:33:02,856 --> 00:33:05,142
OK, guys,
get ready for the next one.
379
00:33:05,317 --> 00:33:08,650
-How many sharks have you tagged?
-In my life?
380
00:33:08,862 --> 00:33:10,523
Probably over 2,000.
381
00:33:10,697 --> 00:33:13,439
And these?
Are they easy to handle?
382
00:33:13,617 --> 00:33:17,155
You know,
you have to be cautious with them.
383
00:33:17,621 --> 00:33:21,489
But, as you see, they will
switch their behavior in a second.
384
00:33:21,666 --> 00:33:25,409
They'll go from being calm,
and then, suddenly,
385
00:33:25,587 --> 00:33:30,456
if you don‘t watch the head,
your hand's going to be in the mouth.
386
00:33:36,515 --> 00:33:39,006
The tagged sharks will be monitored
387
00:33:40,018 --> 00:33:41,724
for one year.
388
00:33:41,895 --> 00:33:45,729
It should tell us
if they leave the pass,
389
00:33:45,899 --> 00:33:47,935
if they hunt together every night
390
00:33:48,568 --> 00:33:51,935
and if the lunar cycles
influences them.
391
00:34:13,176 --> 00:34:15,383
The lasso method works.
392
00:34:16,221 --> 00:34:18,052
The other sharks don't attack.
393
00:34:18,181 --> 00:34:22,390
The school shows no solidarity
in defending its members.
394
00:34:33,488 --> 00:34:35,274
One, two, three.
395
00:34:38,368 --> 00:34:40,609
There it goes.
396
00:34:42,205 --> 00:34:47,199
This shark may have been bitten
while mating or while attacking prey.
397
00:34:47,377 --> 00:34:49,584
Sometimes they snap at each other.
398
00:34:51,339 --> 00:34:53,796
It‘s a male, guys.
First male.
399
00:34:54,968 --> 00:34:59,928
This shark is bigger,
time for Yannis to try his spy camera.
400
00:35:01,725 --> 00:35:03,056
Come back to me.
401
00:35:04,978 --> 00:35:06,843
Turn it up.
402
00:35:15,030 --> 00:35:16,611
-Good?
-Yeah.
403
00:35:20,076 --> 00:35:21,907
It's the best way to do it.
404
00:35:23,788 --> 00:35:25,028
OK.
405
00:35:25,206 --> 00:35:26,946
Push forward and let go.
406
00:35:40,764 --> 00:35:44,723
When Johann told me divers
could catch sharks for us to tag,
407
00:35:45,143 --> 00:35:48,260
l was like:
"No, that's not going to happen."
408
00:35:48,480 --> 00:35:51,438
So you've proved me wrong.
409
00:35:52,984 --> 00:35:54,315
He didn't know us.
410
00:35:54,486 --> 00:35:59,196
You didn't know me.
Us, I mean. Us.
411
00:35:59,366 --> 00:36:03,405
We're smiling now,
but we could easily have been bitten.
412
00:36:03,620 --> 00:36:06,703
-We were close.
-You had some close calls.
413
00:36:06,998 --> 00:36:08,363
They turn on you.
414
00:36:08,833 --> 00:36:12,621
-They go like this...
-We had a few close calls too.
415
00:36:15,215 --> 00:36:17,080
We don't want to get bitten.
416
00:36:22,180 --> 00:36:24,262
This first night is encouraging.
417
00:36:24,432 --> 00:36:26,889
We tag nine sharks.
418
00:36:27,060 --> 00:36:31,474
But we 7] need more nights like this
to reach our target of 40.
419
00:36:37,028 --> 00:36:38,643
Careful, now.
420
00:36:39,114 --> 00:36:42,277
Raise this end
so the other end is lower.
421
00:36:43,326 --> 00:36:46,113
Is it clear? Careful, now.
422
00:36:46,621 --> 00:36:49,408
Easy.
Wait until we get it undennater.
423
00:36:52,043 --> 00:36:56,286
It took nine months to build
this arch conceived by Laurent.
424
00:36:56,631 --> 00:36:59,668
Antonin Guilbert and Thibault Rauby
are the pilots.
425
00:37:01,219 --> 00:37:04,336
The arch combines
photography and video
426
00:37:04,597 --> 00:37:07,304
to film a predation
in 100ths of second,
427
00:37:07,475 --> 00:37:09,386
using synchronized cameras
428
00:37:10,103 --> 00:37:12,560
to circle around the image in 3D.
429
00:37:13,732 --> 00:37:17,850
How will the sharks react
to this imposing oddity?
430
00:37:20,655 --> 00:37:25,649
Two laser beams help the divers
to aim and focus on the predation.
431
00:37:26,619 --> 00:37:30,282
The two lasers
will really help us to aim it.
432
00:37:32,751 --> 00:37:36,494
If we manage to put it down
on the bottom,
433
00:37:36,671 --> 00:37:40,459
what it films will be the middle.
434
00:37:43,052 --> 00:37:46,920
You position it where you think
it's going to happen,
435
00:37:47,140 --> 00:37:51,349
you focus the cameras,
then switch off the lasers.
436
00:37:51,519 --> 00:37:55,933
We can't see them now,
but in murky water or at night,
437
00:37:56,065 --> 00:38:00,479
they'll look like Jedi light sabers
in the shot.
438
00:38:03,823 --> 00:38:06,485
Johann’s counts reveal 413 sharks,
439
00:38:06,910 --> 00:38:08,616
then 480.
440
00:38:08,787 --> 00:38:12,154
That number should rise
as the full moon approaches.
441
00:38:12,415 --> 00:38:16,909
By day, the sharks form three groups
which divers call "walls”.
442
00:38:17,086 --> 00:38:19,998
The term was coined by explorers
in the 19603
443
00:38:20,173 --> 00:38:23,961
who first saw
hundreds of sharks in formation.
444
00:38:26,054 --> 00:38:28,796
A scary sight at the time.
445
00:38:43,321 --> 00:38:46,859
The "walls” form at precise points
in the current flows.
446
00:38:52,956 --> 00:38:56,744
Every time a shark leaves the flow,
it returns to join it again,
447
00:38:56,918 --> 00:39:01,082
like migrating birds
flying in a ”V" formation.
448
00:39:05,760 --> 00:39:09,048
They pause for dental attention
from cleaner fish.
449
00:39:28,825 --> 00:39:32,989
The spy camera detaches itself
from the shark as planned.
450
00:39:38,042 --> 00:39:42,376
Yannis Papastamatiou looks for clues
to the school’s behavior.
451
00:39:43,339 --> 00:39:46,957
One of the things we can see
when we take a look at this video
452
00:39:47,176 --> 00:39:49,838
is that our shark
is often associating
453
00:39:50,013 --> 00:39:53,130
with this individual
with the damaged dorsal fin.
454
00:39:53,308 --> 00:39:57,176
That may mean there is a social bond
between those two sharks.
455
00:39:57,520 --> 00:40:02,731
We need to know if that association
occurs more than just by chance alone.
456
00:40:03,192 --> 00:40:08,277
That could suggest there is a social
network for the shark population here.
457
00:40:08,448 --> 00:40:11,940
Next, we want to know
if that also applies at night,
458
00:40:12,118 --> 00:40:14,609
if they form social bonds
while hunting.
459
00:41:13,262 --> 00:41:15,218
The arch is finally ready.
460
00:41:15,431 --> 00:41:17,171
With Antonin and Thibault,
461
00:41:17,392 --> 00:41:20,054
we start the buoyancy tests.
462
00:41:20,228 --> 00:41:22,264
Designing it was a challenge.
463
00:41:22,438 --> 00:41:26,022
We needed the right cun/ature
and camera spacing
464
00:41:26,985 --> 00:41:30,352
and materials
that were both light and strong.
465
00:41:32,991 --> 00:41:37,109
-Not bad.
—It floats. It's not moving.
466
00:41:37,286 --> 00:41:40,778
We don’t know how easy it will be
to film a predation,
467
00:41:40,957 --> 00:41:43,915
but it feels like we are holding
468
00:41:44,210 --> 00:41:45,700
a futuristic machine,
469
00:41:45,878 --> 00:41:50,247
a magic key to seeing
the undenivater world differently.
470
00:41:53,761 --> 00:41:58,346
/ can't wait to see the images,
to show them to the scientists
471
00:41:58,516 --> 00:42:00,802
and to see their reaction.
472
00:42:04,063 --> 00:42:05,678
The full moon approaches.
473
00:42:09,360 --> 00:42:10,725
Everything gathers pace.
474
00:42:10,862 --> 00:42:13,478
Shoals of fish arrive in the pass.
475
00:42:13,656 --> 00:42:17,399
They will soon spawn
and attract more and more sharks.
476
00:42:18,578 --> 00:42:20,864
After crossing our minds as an idea,
477
00:42:21,039 --> 00:42:23,371
the arch now crosses the pass.
478
00:42:23,583 --> 00:42:26,825
The idea has become a reality.
479
00:42:27,587 --> 00:42:30,750
We'll soon be ready
to use it with the sharks.
480
00:42:32,300 --> 00:42:34,882
Antonin and Thibault are the pilots.
481
00:42:35,344 --> 00:42:38,302
Even undenivater,
I hear their excitement.
482
00:42:49,400 --> 00:42:51,311
The results are promising.
483
00:42:51,569 --> 00:42:56,563
It will give us a more precise idea
of the sharks’ position as they attack.
484
00:43:13,049 --> 00:43:16,507
The pass is not like
a well-stocked larder,
485
00:43:16,803 --> 00:43:18,714
it is a conveyor belt of food
486
00:43:18,888 --> 00:43:21,925
that speeds up
as the full moon approaches,
487
00:43:22,100 --> 00:43:27,060
finally providing enough
to satisfy our school of sharks.
488
00:43:28,106 --> 00:43:32,315
One after another, dozens of species
arrive from the lagoon,
489
00:43:32,527 --> 00:43:34,984
as if they have synchronized agendas.
490
00:43:35,154 --> 00:43:37,736
The pass brims with life.
491
00:43:37,949 --> 00:43:41,658
At the entrance to the ocean
they discharge eggs and sperm
492
00:43:41,786 --> 00:43:44,528
into the current,
towards the open sea,
493
00:43:45,081 --> 00:43:47,447
giving the larvae
a chance to survive
494
00:43:47,750 --> 00:43:50,241
far from predators on the reef.
495
00:44:15,528 --> 00:44:19,942
So far, there are only a few groupers,
but there will soon be 18,000.
496
00:44:21,200 --> 00:44:24,283
The sharks know it.
This romantic rendezvous
497
00:44:24,495 --> 00:44:26,702
is about to become an ambush.
498
00:44:34,046 --> 00:44:36,537
By day, the fish are too alert.
499
00:44:36,716 --> 00:44:38,672
The sharks save their energy.
500
00:44:38,843 --> 00:44:41,459
A tacit truce is obsen/ed.
501
00:44:45,600 --> 00:44:48,342
While Antonin and Thibault
master the arch,
502
00:44:49,270 --> 00:44:52,103
Yannis,
on his last night on the expedition,
503
00:44:52,356 --> 00:44:55,894
fits the last
of the 40 electronic tags.
504
00:45:06,245 --> 00:45:10,454
At night, the fish are half asleep,
they don 't spot danger.
505
00:45:13,085 --> 00:45:17,419
Hunting alone, the majority
of the sharks' attacks fail.
506
00:45:19,634 --> 00:45:24,799
Filmed at 1, 000 frames per second,
we see the different phases.
507
00:45:26,265 --> 00:45:30,008
The shark is attracted
by noise and movement,
508
00:45:30,353 --> 00:45:33,686
but in the dark,
it has another advantage.
509
00:45:33,898 --> 00:45:36,890
lt detects electromagnetic energy
from the fish
510
00:45:37,068 --> 00:45:41,107
thanks to sensory cells
all around its snout
511
00:45:41,781 --> 00:45:44,363
called Ampullae of Lorenzini.
512
00:45:50,122 --> 00:45:54,741
This electric stimulation only works
10 to 20 cm from the shark's snout.
513
00:46:09,558 --> 00:46:11,264
Beyond that distance,
514
00:46:11,686 --> 00:46:14,348
the shark only detects movements.
515
00:46:16,565 --> 00:46:19,432
If the fish plays dead,
it goes unnoticed.
516
00:46:32,832 --> 00:46:35,790
The shark on its own is clumsy.
517
00:46:36,168 --> 00:46:39,660
The team shows
that salvation lies in the pack.
518
00:46:42,133 --> 00:46:43,998
Analysis of our images
519
00:46:44,176 --> 00:46:47,885
shows that the pack succeeds
in 25 percent of attacks.
520
00:46:48,180 --> 00:46:52,048
By comparison, a pack of wolves,
despite its reputation,
521
00:46:52,184 --> 00:46:54,266
only reaches 14 percent.
522
00:46:54,562 --> 00:46:58,680
But wolves, unlike sharks,
will share their quarry.
523
00:47:00,109 --> 00:47:04,398
Our photos show how they circle
the prey to block any escape.
524
00:47:04,780 --> 00:47:07,112
While the group is clearly a force,
525
00:47:07,283 --> 00:47:09,990
it is a handicap
once the prey is caught
526
00:47:10,161 --> 00:47:12,527
and everyone wants a piece.
527
00:47:12,663 --> 00:47:15,029
At Fakarava, prey is abundant.
528
00:47:15,249 --> 00:47:17,456
Sooner or later,
all mouths are fed.
529
00:47:28,179 --> 00:47:31,137
To understand the pack,
no stone is left unturned.
530
00:47:32,391 --> 00:47:36,259
Eric Parmentier,
from Liege University in Belgium,
531
00:47:36,437 --> 00:47:39,304
has a passion for shark morphology.
532
00:47:39,482 --> 00:47:41,814
His specialty: Jaws.
533
00:47:51,952 --> 00:47:54,659
Everyone has this idea that sharks
534
00:47:55,289 --> 00:47:57,951
are streamlined,
especially the head.
535
00:47:58,167 --> 00:48:00,408
But when the animal is feeding,
536
00:48:00,586 --> 00:48:02,952
it can change shape.
537
00:48:03,130 --> 00:48:08,045
It's no longer a straight line,
there is a step here
538
00:48:08,219 --> 00:48:10,551
preceding the opening of the mouth.
539
00:48:10,721 --> 00:48:13,963
As a morphologist,
I want to know
540
00:48:14,100 --> 00:48:16,136
how the animal manages
541
00:48:16,310 --> 00:48:19,894
to deform its body
in order to feed on fish.
542
00:48:20,064 --> 00:48:22,476
If sharks feed on small prey,
543
00:48:22,650 --> 00:48:27,610
they do what many fish do
and just open their mouths wide.
544
00:48:27,780 --> 00:48:30,613
The wide mouth
sucks in a lot of water
545
00:48:30,741 --> 00:48:34,654
and any prey contained in the water.
546
00:48:38,874 --> 00:48:40,705
That suction is essential
547
00:48:41,293 --> 00:48:44,376
to get the prey into the mouth.
548
00:48:44,505 --> 00:48:48,168
Take your favorite rubber duck,
for example.
549
00:48:48,300 --> 00:48:52,009
Lie in the bath,
with your hands behind you,
550
00:48:52,179 --> 00:48:54,465
and try catching it in your mouth.
551
00:48:54,682 --> 00:48:57,264
It won't work.
You need suction
552
00:48:57,435 --> 00:49:01,019
to draw water into the mouth
and the duck will follow.
553
00:49:02,064 --> 00:49:04,146
For large prey like groupers,
554
00:49:04,316 --> 00:49:06,932
suction alone isn't enough,
555
00:49:07,111 --> 00:49:10,899
the shark has to use
a different technique.
556
00:49:11,073 --> 00:49:16,659
We need to understand how
a shark's upper and lowerjaws work.
557
00:49:17,037 --> 00:49:20,200
What happens when it opens its mouth?
558
00:49:20,374 --> 00:49:23,241
The lowerjaw ligaments tighten,
559
00:49:23,419 --> 00:49:25,876
the upperjaw ligaments tighten,
560
00:49:26,046 --> 00:49:30,881
and that tension
makes the teeth stick up straight.
561
00:49:31,051 --> 00:49:35,010
As well as that,
the shark has a muscle
562
00:49:35,222 --> 00:49:37,884
between its upper jaw and its eye.
563
00:49:38,058 --> 00:49:41,642
When this muscle contracts,
the jaws are projected out.
564
00:49:41,812 --> 00:49:45,555
Like unfastening false teeth
and pulling them fonnard.
565
00:49:50,571 --> 00:49:54,189
The jaws shift and the teeth
stick out towards the front.
566
00:49:54,450 --> 00:49:59,444
With the upper teeth and lower teeth
all biting vertically
567
00:50:00,080 --> 00:50:02,366
the prey is completely caught.
568
00:50:02,500 --> 00:50:03,990
Like the groupers.
569
00:50:10,591 --> 00:50:13,048
But only half of it is in the mouth.
570
00:50:13,469 --> 00:50:16,381
The shark shakes its head
from side to side
571
00:50:16,555 --> 00:50:18,466
and these rows of teeth
572
00:50:18,641 --> 00:50:22,884
act like saws
and slice through the prey.
573
00:50:39,787 --> 00:50:42,028
The jaws are ultra-efficient.
574
00:50:42,206 --> 00:50:45,619
but they’re no use
if the prey remains hidden.
575
00:50:46,335 --> 00:50:49,827
Our observations led us
to a shocking discovery.
576
00:50:50,589 --> 00:50:54,252
The grey sharks follow
white-tip reef sharks,
577
00:50:54,385 --> 00:50:58,594
or "mamaru",
that can swim into small gaps.
578
00:50:59,181 --> 00:51:03,049
Only they can flush out a prey
hidden in the reef.
579
00:51:18,492 --> 00:51:19,652
A bit of action!
580
00:51:20,411 --> 00:51:25,280
When we started
really getting into the melee,
581
00:51:25,541 --> 00:51:27,827
we noticed these guys underneath.
582
00:51:28,669 --> 00:51:31,411
They‘re "mamaru“,
whitetip reef sharks.
583
00:51:31,672 --> 00:51:34,459
They rummage around in the coral.
584
00:51:35,426 --> 00:51:39,169
The grey sharks
hang around above them.
585
00:51:39,305 --> 00:51:41,921
-They‘re always first.
-At every melee.
586
00:51:42,099 --> 00:51:44,260
There are two possible outcomes.
587
00:51:44,435 --> 00:51:48,724
Either the whitetip finds
a small prey inside the coral
588
00:51:48,897 --> 00:51:50,888
and he just eats it there.
589
00:51:51,108 --> 00:51:52,814
The grey sharks get nothing.
590
00:51:52,943 --> 00:51:55,685
Or he flushes out
a grouper too big for him
591
00:51:55,821 --> 00:51:58,608
and the grey sharks
are waiting for it.
592
00:51:58,741 --> 00:52:03,576
When the "mamaru" hunt in the coral
they flush out other fish by accident.
593
00:52:03,996 --> 00:52:08,114
The whitetips
search the coral thoroughly,
594
00:52:08,292 --> 00:52:09,702
every nook and cranny.
595
00:52:09,877 --> 00:52:12,789
-They flush out other prey.
-They're flexible.
596
00:52:21,555 --> 00:52:24,092
They're smashing the corals.
597
00:52:24,266 --> 00:52:25,472
Biting everything.
598
00:52:30,064 --> 00:52:35,400
This opportunism is another facet
of the school’s behavior.
599
00:52:35,569 --> 00:52:37,355
It's a significant discovery.
600
00:52:37,529 --> 00:52:41,488
The school is able to exploit
the virtues of another species.
601
00:53:29,665 --> 00:53:32,156
The electronic tags in our 40 sharks
602
00:53:32,501 --> 00:53:37,495
send back data each time
they pass one of the receivers.
603
00:53:38,507 --> 00:53:39,587
After a week,
604
00:53:39,758 --> 00:53:42,591
Johann and Antonin extract the data.
605
00:53:44,263 --> 00:53:46,424
The receivers are then put back.
606
00:53:51,061 --> 00:53:55,475
There's a different color
for each of the sharks we tagged.
607
00:53:55,649 --> 00:53:58,857
By day, they're by the wall,
as we saw.
608
00:53:59,069 --> 00:54:00,309
We see them looping
609
00:54:00,529 --> 00:54:02,736
and returning to the same spot.
610
00:54:03,365 --> 00:54:09,281
You can really see two groups.
One stays here by the drop-off,
611
00:54:09,455 --> 00:54:13,073
and the other group
is much more mobile.
612
00:54:13,292 --> 00:54:17,160
They mainly use these waters
during the day,
613
00:54:17,337 --> 00:54:22,172
and at night,
they swim into this area a lot more.
614
00:54:22,384 --> 00:54:24,591
It would be great if we noticed
615
00:54:24,762 --> 00:54:29,096
specimens who leave the pass
for a few weeks or months.
616
00:54:29,308 --> 00:54:32,141
We will.
A percentage of them at least.
617
00:54:32,311 --> 00:54:36,645
We now have the peak number
of sharks for the year.
618
00:54:36,857 --> 00:54:39,940
For the management of the pass,
619
00:54:40,194 --> 00:54:43,061
if we could show
the reserve authorities
620
00:54:43,238 --> 00:54:45,354
that sharks don't only live here.
621
00:54:45,532 --> 00:54:49,400
Some leave
and need to go somewhere else
622
00:54:49,578 --> 00:54:51,239
to complete their cycle.
623
00:54:51,413 --> 00:54:54,905
That could be positive and create
624
00:54:55,542 --> 00:54:59,376
an interest in extending
the protected area.
625
00:55:00,047 --> 00:55:02,333
We'll see if there are leaders,
626
00:55:02,508 --> 00:55:06,501
if there are groups of sharks
that move together.
627
00:55:06,678 --> 00:55:09,340
Is it always the same one leading?
628
00:55:09,515 --> 00:55:12,222
We'll try to identify interactions,
629
00:55:12,392 --> 00:55:17,637
like these two playing around
at the mouth of the pass.
630
00:55:17,815 --> 00:55:19,271
Must be buddies.
631
00:55:19,566 --> 00:55:21,602
Plenty to get your teeth into!
632
00:55:24,488 --> 00:55:28,151
Nine days from the full moon,
all our experiments are set up.
633
00:55:29,701 --> 00:55:33,569
We have just enough time
to complete our scientific mission.
634
00:55:37,334 --> 00:55:39,871
Are there other schools of sharks?
635
00:55:40,128 --> 00:55:42,870
Do they also hunt in packs
after sunset?
636
00:55:43,048 --> 00:55:46,290
There are rumors,
so I need to go check
637
00:55:46,635 --> 00:55:48,796
with Thibault, Cedric and Yanick.
638
00:55:53,183 --> 00:55:57,017
One, two, three,
four, five, six,
639
00:55:57,688 --> 00:56:01,431
seven, eight atolls worth visiting.
640
00:56:01,608 --> 00:56:03,098
We'll start with Toau.
641
00:56:03,277 --> 00:56:04,642
There are two spots.
642
00:56:04,820 --> 00:56:07,812
A few days here and there,
643
00:56:08,031 --> 00:56:09,362
then back to Fakarava.
644
00:56:09,533 --> 00:56:12,991
The interesting pass at Toau,
for groupers and sharks
645
00:56:13,203 --> 00:56:15,444
and deep dives,
is very exposed.
646
00:56:15,581 --> 00:56:19,119
I know we have
three years' experience at Fakarava,
647
00:56:20,544 --> 00:56:24,833
but that doesn't mean a thing,
it could even be dangerous.
648
00:56:25,090 --> 00:56:28,207
The outgoing current at Toau
is way too strong.
649
00:56:28,385 --> 00:56:29,374
Like a catapult.
650
00:56:30,220 --> 00:56:33,303
Like being fired through a blowpipe.
651
00:56:33,682 --> 00:56:36,389
We'll start with the most difficult.
652
00:56:36,685 --> 00:56:39,597
-Great.
—No, seriously. Why not?
653
00:56:39,771 --> 00:56:42,638
We'll be very careful after that.
654
00:56:47,696 --> 00:56:50,813
They are only just visible on the map.
655
00:56:51,617 --> 00:56:56,281
Atolls are low-lying rings of land,
but in my dreams of empty oceans,
656
00:56:57,122 --> 00:57:00,910
they are mountains
of which we see only the peaks.
657
00:57:02,628 --> 00:57:06,746
To understand the pass,
we have to consider the outer reef
658
00:57:06,924 --> 00:57:11,588
How can we appreciate an oasis
without the desert around it?
659
00:57:29,529 --> 00:57:33,442
Do sharks have any reason
to go to these depths?
660
00:57:34,159 --> 00:57:36,070
Fish are rare down here.
661
00:57:36,828 --> 00:57:39,365
This 2,000 meter high fortress
662
00:57:39,539 --> 00:57:42,030
is just a pile of fossilized corals,
663
00:57:42,250 --> 00:57:46,243
the giant skeleton of a reef
which has grown over 70 million years
664
00:57:46,380 --> 00:57:48,746
as the original island subsided.
665
00:57:52,761 --> 00:57:57,471
On the surface, corals build
and erode at the same time,
666
00:57:57,641 --> 00:58:02,010
crying endless tears of sand
into the abyss below.
667
00:58:05,440 --> 00:58:07,772
A vertiginous void.
668
00:58:07,943 --> 00:58:13,154
These barren depths make the life
in the pass even more precious.
669
00:58:13,323 --> 00:58:14,733
Are the sharks here
670
00:58:15,492 --> 00:58:18,325
from a school that lives higher up?
671
00:58:19,121 --> 00:58:21,157
At 100m, there's no current,
672
00:58:22,541 --> 00:58:25,533
but in the Toau pass,
it's another story.
673
00:58:25,711 --> 00:58:30,171
No chance of seeing sharks
resting here like they do at Fakarava.
674
00:59:13,300 --> 00:59:17,464
It sucks you up
and then pushes you down.
675
00:59:17,637 --> 00:59:19,593
Your fins are pushed up.
676
00:59:20,140 --> 00:59:23,348
It was hard enough
with the lighting rig.
677
00:59:23,518 --> 00:59:27,056
I could see Yanick with the camera,
like this...
678
00:59:27,814 --> 00:59:30,351
It's hard to dive in this current.
679
00:59:30,525 --> 00:59:34,814
It's not like Fakarava
where we can always dive.
680
00:59:34,988 --> 00:59:38,697
You can‘t work here.
You just drift.
681
00:59:39,159 --> 00:59:43,243
Drifting is OK,
but you can't stop to do anything.
682
00:59:43,455 --> 00:59:45,821
There‘s less predation here.
683
00:59:45,999 --> 00:59:50,993
Fewer hiding places for coral fish
than at Fakarava.
684
00:59:51,213 --> 00:59:53,124
Fakarava is full of them.
685
00:59:58,095 --> 01:00:01,508
Nothing here is like
what we see at Fakarava by day.
686
01:00:03,058 --> 01:00:04,639
But what about at night?
687
01:00:04,810 --> 01:00:08,177
Myself, Thibault,
Cedric and Yanick are going to see.
688
01:00:08,647 --> 01:00:12,105
If I get injured,
I'll use this as a tourniquet.
689
01:00:13,568 --> 01:00:17,026
Or a band-aid for a shark bite.
690
01:00:19,074 --> 01:00:22,487
-Imagine your arm hanging off.
-Put your hood on.
691
01:00:24,079 --> 01:00:26,195
Getting lost is not allowed.
692
01:00:26,373 --> 01:00:27,863
We stay together.
693
01:00:28,041 --> 01:00:30,282
Nobody tries to get lost.
694
01:00:30,460 --> 01:00:32,792
Or fall off a boat, but it happens.
695
01:00:35,757 --> 01:00:38,339
Yellow card. OK?
696
01:00:38,885 --> 01:00:40,921
If you don't put your hood on.
697
01:00:50,147 --> 01:00:54,106
I hope we won‘t be
fired through the pass in 25 minutes.
698
01:00:59,906 --> 01:01:01,942
Is the drop-off at 25 meters?
699
01:01:05,245 --> 01:01:08,703
Guys, I'm struggling with the map.
700
01:01:10,917 --> 01:01:12,623
What‘s the depth?
701
01:01:16,590 --> 01:01:18,296
30 meters.
702
01:01:37,903 --> 01:01:42,317
All the passes we visit are scraped
and eroded by powerful currents.
703
01:01:42,741 --> 01:01:44,777
The coral has nothing to hang onto.
704
01:01:44,951 --> 01:01:48,159
Sharks have little to gain
from hanging around here.
705
01:02:09,100 --> 01:02:12,809
The current catapults us
out of the pass in under 20 minutes.
706
01:02:18,902 --> 01:02:20,392
Let's get the others.
707
01:02:21,488 --> 01:02:22,898
20 meters.
708
01:02:23,073 --> 01:02:25,985
Impossible.
709
01:02:32,040 --> 01:02:34,031
It's disappointing.
710
01:02:34,209 --> 01:02:39,044
We hoped to find something similar
to the southern pass at Fakarava
711
01:02:39,214 --> 01:02:43,423
at some of these other atolls
we're visiting.
712
01:02:45,178 --> 01:02:47,009
We haven't found it yet.
713
01:02:47,264 --> 01:02:48,925
The current isn't linear.
714
01:02:49,099 --> 01:02:52,307
It pulls you up and down
and rips you in half.
715
01:02:52,477 --> 01:02:57,016
We didn't realize its potential.
Fakarava is the perfect pass.
716
01:02:57,357 --> 01:02:59,518
You were scared.
717
01:03:02,612 --> 01:03:05,570
There! Now I‘m scared.
718
01:03:06,658 --> 01:03:09,320
No more dives like that, thanks.
719
01:03:10,537 --> 01:03:13,074
It's late. Let's sleep.
720
01:03:53,955 --> 01:03:56,913
With its moderate currents
and burgeoning corals,
721
01:03:57,083 --> 01:03:59,916
Fakarava is unrivalled.
722
01:04:02,005 --> 01:04:05,748
The 700 sharks are here
and only here.
723
01:04:10,513 --> 01:04:14,051
Three days to go until the full moon
and the spawning,
724
01:04:14,225 --> 01:04:16,807
a major event for the pass.
725
01:04:18,021 --> 01:04:22,765
Acousticians have set up microphones
from the entrance to the lagoon
726
01:04:22,942 --> 01:04:24,478
to the ocean drop-off.
727
01:04:24,819 --> 01:04:28,107
The aim is to see
if the acoustic intensity changes
728
01:04:28,281 --> 01:04:32,900
when shark attacks increase
during the spawning.
729
01:04:55,892 --> 01:04:59,476
This acoustic backdrop
is formed by dozens of species.
730
01:05:00,438 --> 01:05:04,852
Eric Parmentier and Loi'c Kever
hope to record them one at a time,
731
01:05:05,026 --> 01:05:06,812
to decipher the brouhaha
732
01:05:07,112 --> 01:05:09,569
and produce an acoustic barcode
733
01:05:09,739 --> 01:05:13,448
at different moments of the day
and the lunar cycle.
734
01:05:33,138 --> 01:05:36,301
Cousteau's "Silent World"
is actually really noisy.
735
01:05:37,225 --> 01:05:40,058
I'm sure Cousteau knew it too.
736
01:05:40,270 --> 01:05:42,511
Can you pass me the triggerfish?
737
01:05:50,530 --> 01:05:53,647
What we observe in the pass
is that day and night
738
01:05:53,867 --> 01:05:56,233
have different sounds.
739
01:05:56,411 --> 01:05:58,948
That's understandable.
740
01:05:59,122 --> 01:06:03,536
Fish can't spend
24 hours a day yelling,
741
01:06:03,710 --> 01:06:05,746
they have other things to do.
742
01:06:05,920 --> 01:06:07,831
We noticed straightaway
743
01:06:08,006 --> 01:06:11,999
that the fish have specific periods
744
01:06:12,177 --> 01:06:16,090
during which they make sounds.
745
01:06:16,222 --> 01:06:20,090
It might be afternoon for some,
nightfall for others,
746
01:06:20,268 --> 01:06:23,010
or between 10 o'clock and midday.
747
01:06:23,271 --> 01:06:25,387
It's cool there's so much sound
748
01:06:25,565 --> 01:06:26,975
because we can study
749
01:06:27,150 --> 01:06:31,484
what happens by day and by night
and with the tides and the moon.
750
01:06:31,779 --> 01:06:36,569
But we find ourselves
with a big problem:
751
01:06:36,701 --> 01:06:38,532
Who is saying what?
752
01:06:38,661 --> 01:06:41,824
We can compare stress sounds
with the sounds
753
01:06:41,998 --> 01:06:44,410
a fish makes
when hunted by a shark.
754
01:06:51,257 --> 01:06:53,464
-Tell me if you hear anything.
-OK.
755
01:07:00,517 --> 01:07:03,179
From an acoustic point of view,
756
01:07:03,353 --> 01:07:07,187
we can try to detect
the attacks of different sharks
757
01:07:07,357 --> 01:07:09,188
on the groupers.
758
01:07:09,859 --> 01:07:11,645
The long term objective
759
01:07:11,986 --> 01:07:15,729
is to be able
to just clip a microphone in the water
760
01:07:15,865 --> 01:07:18,151
and describe what's happening.
761
01:07:18,326 --> 01:07:22,615
Identify the species present,
understand what they're saying
762
01:07:22,789 --> 01:07:26,657
and monitor the evolution
of the pass at Fakarava.
763
01:07:37,929 --> 01:07:39,465
One possibility,
764
01:07:39,639 --> 01:07:42,597
which is what we're starting here,
765
01:07:42,809 --> 01:07:44,970
is a sort of sound library,
766
01:07:45,103 --> 01:07:48,345
that could be used
5 or 10 years from now
767
01:07:48,523 --> 01:07:51,481
to compare biodiversity in the pass.
768
01:07:51,693 --> 01:07:55,231
Financially,
it works out a lot cheaper
769
01:07:55,530 --> 01:07:58,112
than putting divers in the water
770
01:07:58,324 --> 01:07:59,780
at various depths.
771
01:07:59,951 --> 01:08:02,317
You just send down a microphone,
772
01:08:02,495 --> 01:08:06,704
record for 24 hours,
or at a certain time,
773
01:08:06,874 --> 01:08:10,332
then use comparisons
to make an inventory
774
01:08:10,461 --> 01:08:12,793
of the health of the pass.
775
01:08:14,549 --> 01:08:15,789
Sharks are mute
776
01:08:16,009 --> 01:08:20,628
and swim silently,
making them stealthy predators.
777
01:08:21,306 --> 01:08:25,595
Eric hopes to detect
and count the sharks indirectly,
778
01:08:25,810 --> 01:08:29,849
by the quantity and nature
of the sounds they provoke in fish.
779
01:08:45,872 --> 01:08:48,204
Briefing with Laurent at the HQ.
780
01:08:49,083 --> 01:08:53,201
Eric has isolated
the stress sound of the Myripristis
781
01:08:53,379 --> 01:08:55,119
or soldier fish.
782
01:08:55,298 --> 01:08:58,756
A soldier fish in this position
would be making a sound.
783
01:08:58,926 --> 01:09:01,633
Yes, and, unfortunately for him,
784
01:09:02,013 --> 01:09:05,130
in the frequency
detected by sharks.
785
01:09:08,311 --> 01:09:11,929
Sharks can feel sound
but not hear it.
786
01:09:12,106 --> 01:09:15,519
If you go to a concert
and stand by the speakers,
787
01:09:16,486 --> 01:09:18,772
you feel the sound
and you hear it.
788
01:09:18,946 --> 01:09:21,858
If you move further back,
you only hear it.
789
01:09:22,075 --> 01:09:24,407
It only works at a certain distance.
790
01:09:24,994 --> 01:09:26,279
Exactly.
791
01:09:26,454 --> 01:09:30,367
Like all fish,
sharks have a lateral line
792
01:09:31,042 --> 01:09:32,532
the length of their body
793
01:09:32,752 --> 01:09:34,788
which ends at their snout.
794
01:09:34,962 --> 01:09:37,669
They're pressure sensors.
795
01:09:37,840 --> 01:09:41,332
Pressure and movement sensors,
good for hunting.
796
01:09:41,511 --> 01:09:42,751
Sharks are mute.
797
01:09:42,929 --> 01:09:44,669
Nobody has ever recorded
798
01:09:44,847 --> 01:09:48,760
sharks producing sounds
to communicate.
799
01:09:50,937 --> 01:09:54,145
When you eat, when you chew,
you make sounds.
800
01:09:54,315 --> 01:09:57,352
That‘s a consequence
not a produced sound.
801
01:09:57,527 --> 01:10:00,769
There's a thin line between the two.
802
01:10:01,322 --> 01:10:05,440
A woman in high heels walks in a room,
all the men turn to look.
803
01:10:05,618 --> 01:10:07,700
Did she send a message?
804
01:10:07,995 --> 01:10:09,576
She hasn‘t spoken.
805
01:10:09,747 --> 01:10:11,203
But we know she's there.
806
01:10:11,374 --> 01:10:14,787
Sharks don't produce sounds
but they do make
807
01:10:14,961 --> 01:10:16,747
hydrodynamic sounds.
808
01:10:16,921 --> 01:10:19,333
You displace water,
you make a wave.
809
01:10:23,720 --> 01:10:24,709
Outside HQ,
810
01:10:25,388 --> 01:10:29,722
the last instrument to be installed
needs no light
811
01:10:29,892 --> 01:10:31,974
to take ultrasounds of the pass.
812
01:10:32,812 --> 01:10:37,397
Laurent wants to know
if their lights affect the sharks.
813
01:10:38,735 --> 01:10:40,942
Belgian biologist Damien Sonny
814
01:10:41,112 --> 01:10:45,151
observes what happens
before and after the divers arrive.
815
01:10:47,201 --> 01:10:50,614
I'm using the ultrasound camera
to observe
816
01:10:50,788 --> 01:10:54,451
the middle of the pass,
right by the wall of sharks.
817
01:10:54,834 --> 01:10:58,418
Using this camera, I can see,
like a gynecologist,
818
01:10:58,588 --> 01:11:00,499
a shark gynecologist.
819
01:11:00,673 --> 01:11:04,541
I'm not disturbing the animals,
but I can see their echoes.
820
01:11:05,136 --> 01:11:07,673
I can even see their shapes
821
01:11:07,847 --> 01:11:10,805
and distinguish the sharks
from other fish.
822
01:11:18,232 --> 01:11:20,769
with his acoustic camera.
823
01:11:41,255 --> 01:11:42,836
Here come the divers.
824
01:11:43,299 --> 01:11:45,255
The sharks are all around them.
825
01:11:51,140 --> 01:11:53,301
The sharks are not afraid of the arch.
826
01:11:53,476 --> 01:11:55,432
They continue hunting around us.
827
01:11:57,271 --> 01:11:59,432
Whether while resting by day,
828
01:11:59,607 --> 01:12:01,268
or attacking by night,
829
01:12:01,442 --> 01:12:04,650
it’s becoming clear
they operate in pairs.
830
01:12:04,821 --> 01:12:08,234
Accomplices swimming together.
831
01:12:09,867 --> 01:12:12,153
The arch finally pays off,
832
01:12:12,328 --> 01:12:15,536
showing what happens
at the heart of an attack.
833
01:12:17,834 --> 01:12:20,075
The beater on the right,
834
01:12:23,297 --> 01:12:25,288
the recipient on the left.
835
01:12:27,927 --> 01:12:31,294
Slow motion
shows these hunting duos in action.
836
01:12:31,472 --> 01:12:34,805
As well as the general
organization of the school,
837
01:12:35,226 --> 01:12:40,095
another level of cooperation
arises from fleeting common interests.
838
01:12:41,232 --> 01:12:44,850
The prey can get away once,
maybe twice,
839
01:12:47,655 --> 01:12:49,691
but not forever.
840
01:12:52,201 --> 01:12:56,490
This behavior is a mixture
of cooperation and competition.
841
01:12:56,622 --> 01:12:59,955
Watching,
more than helping each other.
842
01:13:00,126 --> 01:13:02,742
If one loses out,
the other profits.
843
01:13:13,180 --> 01:13:14,716
Johann '3 latest count
844
01:13:15,016 --> 01:13:16,847
reveals nearly 600 sharks.
845
01:13:17,018 --> 01:13:20,351
The predators are closing ranks.
846
01:13:25,776 --> 01:13:26,856
They fascinate us.
847
01:13:27,612 --> 01:13:29,819
How many sharks could there be
848
01:13:30,197 --> 01:13:31,937
in this one photo
849
01:13:32,116 --> 01:13:33,902
that is brimming with them?
850
01:14:16,410 --> 01:14:20,699
We don't dive amongst the pack.
851
01:14:21,332 --> 01:14:23,163
-We are the pack!
-True.
852
01:14:23,334 --> 01:14:27,247
-We're part of the pack.
-That‘s how it felt.
853
01:14:27,922 --> 01:14:32,382
When you're in the middle...
you're with them.
854
01:14:32,677 --> 01:14:36,670
You want to go like this
and hang out with them.
855
01:14:38,349 --> 01:14:41,432
You want to be with them,
they're your mates.
856
01:14:41,727 --> 01:14:45,936
I think I might have a dorsal fin
growing on my back.
857
01:14:46,482 --> 01:14:49,019
They were all over us.
858
01:14:49,652 --> 01:14:51,483
There are more every year.
859
01:14:51,654 --> 01:14:56,694
-Lots of youngsters.
—Yes, lots about this big.
860
01:14:57,785 --> 01:15:02,119
-I think one called you daddy!
-I wasn't going to mention it.
861
01:15:02,498 --> 01:15:06,116
It's now we‘re in the middle
that we have perspective.
862
01:15:08,254 --> 01:15:10,290
-l‘m writing that down.
-Go for it!
863
01:15:10,423 --> 01:15:15,292
He's going to say that tomorrow,
or in two days.
864
01:15:16,178 --> 01:15:19,762
He‘ll be like:
"Damn, I'm clever."
865
01:15:32,862 --> 01:15:36,104
Hi, Damien.
What does the pass gynecologist say?
866
01:15:36,323 --> 01:15:38,939
-You went in the water at 01:55.
-Yes.
867
01:15:39,118 --> 01:15:41,109
This is at 02:05.
868
01:15:41,287 --> 01:15:43,869
Still no light affecting the area.
869
01:15:44,457 --> 01:15:47,540
The moving shapes
are the fish, the prey.
870
01:15:47,710 --> 01:15:50,326
As you see, they're fairly active.
871
01:15:51,088 --> 01:15:55,252
This second sequence is from 02:13.
872
01:15:55,718 --> 01:15:57,879
Light is edging into my area.
873
01:15:58,095 --> 01:15:59,676
Prey still quite active.
874
01:15:59,847 --> 01:16:01,963
Guess what happens next.
875
01:16:03,768 --> 01:16:06,225
-The fish disappear.
-It goes quiet.
876
01:16:06,395 --> 01:16:09,808
In one minute,
there are almost no prey.
877
01:16:10,191 --> 01:16:11,931
Wow! No more fish.
878
01:16:12,109 --> 01:16:16,819
They don't leave,
they just disappear from the screen.
879
01:16:17,406 --> 01:16:20,398
In the next sequence,
you move away,
880
01:16:20,576 --> 01:16:23,989
and we gradually see
the prey reappear.
881
01:16:24,747 --> 01:16:27,363
The storm has passed.
882
01:16:27,541 --> 01:16:31,955
It confirms a hunch we had
that when we switched off our lights,
883
01:16:32,129 --> 01:16:33,915
we saw the fish reappear.
884
01:16:34,298 --> 01:16:37,335
It contradicts the common belief
885
01:16:37,510 --> 01:16:39,717
that lights attract fish.
886
01:16:40,596 --> 01:16:43,508
Is it the light that makes them hide,
887
01:16:43,682 --> 01:16:48,051
or is it the light attracting sharks
that scares the fish?
888
01:16:48,229 --> 01:16:50,595
They anticipate the threat.
889
01:16:50,773 --> 01:16:54,436
Even before the sharks arrive,
they hide.
890
01:16:54,777 --> 01:16:58,565
I don't think
the amount of light matters.
891
01:16:58,739 --> 01:17:00,695
It's about being able to see.
892
01:17:00,825 --> 01:17:03,817
Diving at full moon,
you don't need lights.
893
01:17:03,994 --> 01:17:06,576
We add lighting for our cameras.
894
01:17:06,705 --> 01:17:09,913
But to find your way
and see what's around you,
895
01:17:10,084 --> 01:17:12,496
the light of the full moon is enough.
896
01:17:12,962 --> 01:17:16,750
When you dive with a full moon,
897
01:17:17,758 --> 01:17:21,125
you don't see fish in open water,
they're hiding.
898
01:17:21,428 --> 01:17:25,137
So maybe our artificial lighting
899
01:17:25,307 --> 01:17:28,470
sometimes recreates
full moon conditions.
900
01:17:28,644 --> 01:17:32,011
We don‘t attract the sharks,
they're already there.
901
01:17:32,189 --> 01:17:34,225
In that one little spot
902
01:17:34,400 --> 01:17:37,858
we make an ordinary night
like a full moon.
903
01:17:38,070 --> 01:17:40,356
We give them a full moon
every night.
904
01:17:41,115 --> 01:17:44,357
This is great.
It's so clear.
905
01:18:13,898 --> 01:18:15,980
Fifty nights of diving.
906
01:18:16,150 --> 01:18:18,106
Tonight is the full moon.
907
01:18:18,277 --> 01:18:21,895
The most important night
for the sharks and for us.
908
01:18:27,620 --> 01:18:29,952
Everyone is busy, quietly working,
909
01:18:30,122 --> 01:18:33,910
as if a month here and 3 years
of planning wasn't enough.
910
01:19:08,327 --> 01:19:10,693
The surveillance cameras alert us.
911
01:19:10,871 --> 01:19:14,489
Like last year,
the groupers arrive en-masse.
912
01:19:16,168 --> 01:19:20,662
Solitary all year, they group together
for their annual spawning.
913
01:19:21,048 --> 01:19:24,916
They always know the date.
The full moon in June.
914
01:19:25,094 --> 01:19:29,212
No need to check the sky,
all the females are full of eggs.
915
01:19:37,564 --> 01:19:41,807
This collective spawning presages
a peak in the number of sharks.
916
01:19:41,944 --> 01:19:46,404
Johann ’3 latest count approaches
the 700 of three years ago.
917
01:19:47,199 --> 01:19:49,235
The predations will increase
918
01:19:49,410 --> 01:19:51,617
allowing us to observe more
919
01:19:51,745 --> 01:19:55,784
and test our latest hypotheses
about the school's behavior.
920
01:20:00,963 --> 01:20:05,673
The attack will come tonight
from inside the pass.
921
01:20:14,643 --> 01:20:17,635
The countdown to the massacre
has begun.
922
01:20:20,149 --> 01:20:22,265
The groupers are packed in the pass.
923
01:20:22,443 --> 01:20:25,059
A one year wait
for 30 minutes of spawning.
924
01:20:25,237 --> 01:20:27,273
What is the sharks' battle plan?
925
01:20:29,575 --> 01:20:32,817
-The groupers are here.
-On the right.
926
01:20:33,162 --> 01:20:36,325
A few days before,
this area empties out
927
01:20:36,498 --> 01:20:38,659
and they're all concentrated here.
928
01:20:38,834 --> 01:20:41,416
Right at the entrance to the pass.
929
01:20:41,545 --> 01:20:44,457
During the day,
there are fewer sharks than this.
930
01:20:45,007 --> 01:20:46,747
They're by the drop-off.
931
01:20:46,925 --> 01:20:51,294
I counted 100 there last time.
Not that many.
932
01:20:52,556 --> 01:20:53,921
Right on the edge.
933
01:20:54,266 --> 01:20:55,301
And at night?
934
01:20:55,476 --> 01:20:58,183
At night, they come over here.
935
01:20:58,354 --> 01:20:59,764
All dispersed.
936
01:20:59,938 --> 01:21:01,519
Night falls...
937
01:21:03,942 --> 01:21:07,526
What if it is actually like this
before we arrive,
938
01:21:07,821 --> 01:21:09,732
and when we go in the water,
939
01:21:09,907 --> 01:21:11,863
it goes like this?
940
01:21:13,535 --> 01:21:17,119
-No, I don't believe that.
-Why not?
941
01:21:17,831 --> 01:21:20,288
Sometimes, you go in the water
942
01:21:20,459 --> 01:21:23,747
and you think your lights
are causing the predation,
943
01:21:23,921 --> 01:21:26,833
then you go back
the next night
944
01:21:27,216 --> 01:21:31,004
and they only hunt
outside the areas you light up.
945
01:21:31,553 --> 01:21:34,420
In the end,
it feels like us being there
946
01:21:35,099 --> 01:21:37,090
doesn't always influence them.
947
01:21:40,437 --> 01:21:42,393
In three hours,
we’ll join the pack
948
01:21:42,940 --> 01:21:45,682
for the long-awaited full moon.
949
01:22:39,246 --> 01:22:42,033
50 nights of diving
has taken its toll.
950
01:22:43,750 --> 01:22:45,081
Our faces are drawn
951
01:22:45,461 --> 01:22:47,417
but our spirit is resolute.
952
01:22:47,671 --> 01:22:50,128
We know that tonight is the last.
953
01:23:14,364 --> 01:23:16,150
Slaves to their instinct,
954
01:23:16,325 --> 01:23:19,283
the groupers dare to spawn here
once a year.
955
01:23:21,914 --> 01:23:22,903
While they wait,
956
01:23:23,290 --> 01:23:24,951
they must hide.
957
01:23:25,125 --> 01:23:27,707
To do othenivise would be suicide.
958
01:23:30,839 --> 01:23:34,878
At night, the school comes alive
with ravenous energy.
959
01:23:43,101 --> 01:23:44,181
The sharks form
960
01:23:44,353 --> 01:23:46,810
a deadly spiral
around their prey.
961
01:23:57,199 --> 01:24:00,487
Tornadoes of teeth
producing clouds of scales.
962
01:24:10,837 --> 01:24:12,373
The voracious vortex feeds
963
01:24:13,215 --> 01:24:15,957
again and again,
throughout the night.
964
01:25:35,255 --> 01:25:38,622
One grouper manages to evade
three sets of jaws,
965
01:25:39,968 --> 01:25:41,424
but not four.
966
01:25:57,152 --> 01:26:00,986
A half-asleep parrot fish
bumps into this shark.
967
01:26:05,994 --> 01:26:07,985
The parrot fish escapes,
968
01:26:08,163 --> 01:26:10,745
and the grey shark
bites the reef shark.
969
01:26:17,923 --> 01:26:20,460
Encumbered by her swollen belly,
970
01:26:20,926 --> 01:26:23,417
this female grouper cannot get away.
971
01:26:31,353 --> 01:26:34,265
Her eggs are strewn around
and lost forever.
972
01:27:09,141 --> 01:27:11,006
The full moon is a paradox.
973
01:27:11,143 --> 01:27:12,724
At its midnight zenith,
974
01:27:12,894 --> 01:27:14,384
it lights up the seabed,
975
01:27:14,563 --> 01:27:18,021
but at five in the morning,
it no longer penetrates.
976
01:27:18,191 --> 01:27:19,852
The sharks are in darkness,
977
01:27:20,026 --> 01:27:22,984
tired, almost blind, they ease off,
978
01:27:23,780 --> 01:27:25,441
and the groupers react.
979
01:27:25,615 --> 01:27:27,822
The time has come for them to spawn.
980
01:27:43,008 --> 01:27:46,375
In the darkness,
the sharks are less reactive.
981
01:27:46,553 --> 01:27:49,920
The lights for our cameras
don 't change a thing.
982
01:27:55,395 --> 01:27:56,851
Sharks have evolved
983
01:27:56,980 --> 01:28:00,564
over generations to be more efficient.
984
01:28:00,734 --> 01:28:02,850
But so have their prey.
985
01:28:03,069 --> 01:28:05,936
Groupers use speed
and perfect timing
986
01:28:06,114 --> 01:28:08,856
to spawn at just the right moment.
987
01:28:09,034 --> 01:28:13,118
These clever adaptations
show that we had a false idea
988
01:28:13,288 --> 01:28:15,529
of both prey and predator.
989
01:28:17,125 --> 01:28:19,662
Both have strengths and weaknesses.
990
01:28:20,128 --> 01:28:22,164
Groupers are not as vulnerable,
991
01:28:23,215 --> 01:28:26,582
and sharks are not as fearsome
as we thought.
992
01:28:35,685 --> 01:28:38,597
The spectacle ends at daybreak.
993
01:28:38,772 --> 01:28:40,637
The moon continues its course
994
01:28:40,816 --> 01:28:43,933
and the groupers and sharks
will meet again next year.
995
01:28:44,986 --> 01:28:46,476
That this wild spectacle
996
01:28:47,072 --> 01:28:48,858
still exists
997
01:28:49,032 --> 01:28:52,490
frightens us,
dazzles us and reassures us.
998
01:28:53,245 --> 01:28:55,736
After four years of observations,
999
01:28:55,914 --> 01:28:59,782
this miracle of existence
has emerged from the shadows.
1000
01:29:06,299 --> 01:29:08,631
Five months after the expedition,
1001
01:29:08,802 --> 01:29:11,464
the electronic tags
reveal their secrets.
1002
01:29:11,638 --> 01:29:14,846
Despite its wild nature,
the school follows rules.
1003
01:29:15,016 --> 01:29:18,008
The sharks departed
in three different groups.
1004
01:29:19,187 --> 01:29:23,897
The behavior of the 40 tagged sharks
is extrapolated to the school.
1005
01:29:24,693 --> 01:29:27,810
By day, they circle around, resting.
1006
01:29:27,946 --> 01:29:30,904
There are pairs who swim together.
1007
01:29:31,658 --> 01:29:34,525
When night falls,
they come together to hunt
1008
01:29:34,661 --> 01:29:39,200
and new associations are formed,
like sub-units of the school.
1009
01:29:39,666 --> 01:29:42,624
These associations
are a new discovery.
1010
01:29:42,794 --> 01:29:45,877
They produce spectacular spirals,
1011
01:29:46,298 --> 01:29:50,792
but, over time, the results reveal
something even more remarkable.
1012
01:29:50,969 --> 01:29:54,086
The sharks' behavior
depends on the lunar cycle.
1013
01:29:54,222 --> 01:29:56,759
More than the quantity of prey,
1014
01:29:56,933 --> 01:30:01,176
it is the amount of moonlight
that affects how intense/y they hunt.
1015
01:30:01,521 --> 01:30:04,888
It is the first time
research has shown this.
1016
01:30:05,442 --> 01:30:10,732
Each morning, the sharks dutifully
return to their respective "walls",
1017
01:30:10,864 --> 01:30:12,729
except for at least two,
1018
01:30:12,866 --> 01:30:16,905
who left the pass
and have yet to return.
1019
01:30:21,333 --> 01:30:24,245
The electronic tags
will transmit for one year.
1020
01:30:25,003 --> 01:30:27,710
We will also return next year.
1021
01:30:27,881 --> 01:30:30,588
These 700 sharks
are not so unpredictable.
1022
01:30:30,842 --> 01:30:32,503
They do not have a leader,
1023
01:30:32,677 --> 01:30:36,670
but they obey the moon
and march to the rhythm of pass.
1024
01:30:36,890 --> 01:30:40,599
Understanding their routines
was our adventure.
1025
01:30:41,353 --> 01:30:43,059
We spent 3,000 hours undenivater
1026
01:30:43,229 --> 01:30:45,220
to witness and then prove
1027
01:30:45,941 --> 01:30:50,025
that the shark pack
is more efficient than the wolf pack.
1028
01:30:50,612 --> 01:30:53,399
For the first time,
we can see that their hunts
1029
01:30:53,573 --> 01:30:56,235
are actually
a sort of collective effort,
1030
01:30:56,409 --> 01:30:59,526
macabre dances
which are orchestrated
1031
01:30:59,663 --> 01:31:01,904
by a need to survive
1032
01:31:02,082 --> 01:31:04,573
and the existence of a special place:
1033
01:31:04,960 --> 01:31:07,702
the pass at Fakarava.
1034
01:31:57,053 --> 01:32:02,047
Translation: Daniel Murray
Subtitles: Diane Bardinet
81733
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