1 00:00:35,911 --> 00:00:37,697 They're coming. 2 00:00:49,216 --> 00:00:53,926 700 SHARKS INTO THE DARK 3 00:00:58,350 --> 00:01:02,389 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: 5 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 7 00:01:22,708 --> 00:01:26,371 with breaches connecting its lagoon to the ocean. 8 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 10 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, 12 00:01:46,940 --> 00:01:50,853 a valley of corals declared a UNESCO biosphere reserve. 13 00:01:53,947 --> 00:01:55,938 Why are there so many? 14 00:02:00,037 --> 00:02:02,574 What causes them to group together? 15 00:02:16,887 --> 00:02:18,297 To solve this enigma, 16 00:02:18,472 --> 00:02:20,884 20 divers and scientists join forces, 17 00:02:21,058 --> 00:02:23,891 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. 56 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. 64 00:06:30,515 --> 00:06:33,097 It was the rumor of thousands of groupers 65 00:06:37,397 --> 00:06:40,104 a moon which tells them to spawn. 66 00:06:42,152 --> 00:06:44,268 The rumor was true. We estimated 67 00:06:44,446 --> 00:06:47,108 a world record of 18,000 groupers. 68 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 71 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, 74 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... 77 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, 79 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 82 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, 86 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 111 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 113 00:10:44,394 --> 00:10:46,305 when shoals of fish arrive, 114 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 161 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, 173 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