1 00:00:25,967 --> 00:00:28,595 A 56-year-old scuba diver was reported missing 2 00:00:28,836 --> 00:00:30,929 by his diving partner this morning. 3 00:00:33,675 --> 00:00:35,836 The man's body was found this afternoon. 4 00:00:36,177 --> 00:00:39,704 Police say his injuries are consistent with a crocodile attack. 5 00:00:42,150 --> 00:00:44,414 There's a growing problem in Northern Australia. 6 00:00:45,553 --> 00:00:48,021 Saltwater crocodile numbers have exploded. 7 00:00:51,225 --> 00:00:52,453 If you get in the water, 8 00:00:52,694 --> 00:00:55,857 you run the real, serious risk of getting eaten. 9 00:00:58,666 --> 00:01:01,362 Crocodiles are now moving into new territory, 10 00:01:02,103 --> 00:01:04,128 travelling hundreds of kilometres. 11 00:01:04,372 --> 00:01:07,830 They are pushing up river, along the coast. 12 00:01:08,142 --> 00:01:10,201 Even far out to sea. 13 00:01:11,145 --> 00:01:14,444 And now they are coming into conflict with people. 14 00:01:14,682 --> 00:01:16,946 It's a nice-looking croc. A ten-footer. 15 00:01:18,286 --> 00:01:20,254 Looks like it's heading towards Darwin. 16 00:01:20,588 --> 00:01:24,991 Last year, rangers pulled 253 crocs out of Darwin Harbour. 17 00:01:25,560 --> 00:01:28,290 Many of the crocs are around three metres long. 18 00:01:30,331 --> 00:01:31,229 As far as I'm concerned, 19 00:01:31,466 --> 00:01:33,991 anybody that swims in Darwin Harbour is mad. 20 00:01:34,535 --> 00:01:37,629 Croc expert Adam Britton is about to spend the next year 21 00:01:37,872 --> 00:01:41,273 following every move the saltwater crocodiles make. 22 00:01:42,076 --> 00:01:43,407 In the last week alone, 23 00:01:43,745 --> 00:01:46,236 six crocodiles were pulled out of Darwin Harbour. 24 00:01:46,481 --> 00:01:49,939 There have been two fatal attacks on swimmers out at sea. 25 00:01:51,285 --> 00:01:53,310 This is a new and dangerous situation. 26 00:01:53,888 --> 00:01:55,480 To manage it, we have to find out 27 00:01:55,723 --> 00:01:57,714 how and why crocodiles are moving. 28 00:01:59,927 --> 00:02:01,758 What he discovers could hold the key 29 00:02:01,996 --> 00:02:04,191 to managing this ancient predator. 30 00:02:19,414 --> 00:02:21,939 One of the most ambitious studies ever to be conducted 31 00:02:22,183 --> 00:02:25,710 on saltwater-crocodile movements is about to start. 32 00:02:26,154 --> 00:02:29,146 - There's a good one in there. - Just there, look. 33 00:02:29,557 --> 00:02:31,525 - Big male. - He's pretty awesome. 34 00:02:31,759 --> 00:02:33,750 He's about 30 foot, 40 foot. 35 00:02:33,995 --> 00:02:34,984 16 crocodiles will be fitted 36 00:02:35,229 --> 00:02:37,789 with state-of-the-art tracking devices. 37 00:02:38,032 --> 00:02:41,399 It'll be fantastic to get a satellite transmitter on him. 38 00:02:41,636 --> 00:02:43,934 Hour by hour, they will allow Adam and his team 39 00:02:44,172 --> 00:02:46,572 to follow the crocodiles' every move. 40 00:02:46,841 --> 00:02:49,036 I'll put a GPS position in here 41 00:02:49,277 --> 00:02:52,007 and then come back at night and look for it. 42 00:02:53,247 --> 00:02:56,410 They're targeting two river systems in Northern Australia. 43 00:02:58,486 --> 00:03:00,078 East of the capital, Darwin, 44 00:03:00,388 --> 00:03:02,253 the Mary and South Alligator Rivers 45 00:03:02,490 --> 00:03:05,618 have been chosen for their high number of saltwater crocodiles. 46 00:03:07,929 --> 00:03:11,330 There's a good one down here. He's a good-size one, that one. 47 00:03:11,566 --> 00:03:13,557 Yeah. What, 12 foot, 13 foot? 48 00:03:13,901 --> 00:03:17,234 If Adam can discover where and when the crocodiles are moving, 49 00:03:17,472 --> 00:03:20,407 they'll be closer to solving the escalating conflict 50 00:03:20,641 --> 00:03:22,609 between crocodiles and people. 51 00:03:30,818 --> 00:03:32,012 For millions of years, 52 00:03:32,253 --> 00:03:34,983 saltwater crocodiles have stalked the tidal rivers 53 00:03:35,223 --> 00:03:36,952 of Australia's Northern Territory. 54 00:03:40,461 --> 00:03:42,258 Growing up to six metres, they're 55 00:03:42,497 --> 00:03:45,557 the largest and most aggressive of reptiles. 56 00:03:49,937 --> 00:03:52,963 It's very easy for crocodiles to capture attention. 57 00:03:53,241 --> 00:03:55,641 They're just such incredible masters 58 00:03:55,877 --> 00:03:58,004 of the domain that they live in. 59 00:03:58,446 --> 00:04:00,880 And When I was young, I used to dream 60 00:04:01,115 --> 00:04:02,309 how incredible it would be 61 00:04:02,550 --> 00:04:04,745 to be able to follow these animals around, 62 00:04:04,986 --> 00:04:07,216 to really learn what they were doing. 63 00:04:12,827 --> 00:04:14,727 If you're a saltwater crocodile today, 64 00:04:15,396 --> 00:04:16,863 you've got a dilemma. 65 00:04:17,398 --> 00:04:20,367 The best place to live is the tidal rivers. 66 00:04:20,601 --> 00:04:22,694 That's where the best food is and the best habitat is. 67 00:04:23,204 --> 00:04:25,900 The problem is, it's full of other crocodiles. 68 00:04:26,140 --> 00:04:28,005 There's a lot of big, dominant males. 69 00:04:28,376 --> 00:04:29,365 If you want to stay there, 70 00:04:29,610 --> 00:04:31,407 you've got a serious fight on your hands. 71 00:04:34,148 --> 00:04:35,240 And it's these fights 72 00:04:35,483 --> 00:04:37,644 which are at the heart of the crocodile problem. 73 00:04:49,764 --> 00:04:51,026 Sizing each other up, 74 00:04:51,265 --> 00:04:53,893 two males puff their bodies high out of the water 75 00:04:54,535 --> 00:04:57,299 and emit low-frequency warning calls. 76 00:05:11,052 --> 00:05:14,317 It's all about territory, a resource so precious 77 00:05:14,555 --> 00:05:17,991 many crocs are killed in these violent confrontations. 78 00:05:19,794 --> 00:05:22,354 The loser's only chance is to move out. 79 00:05:25,600 --> 00:05:28,433 And it's these outcasts, often young males, 80 00:05:28,669 --> 00:05:30,227 that this study is targeting. 81 00:05:39,480 --> 00:05:41,448 As twilight comes to the Mary River, 82 00:05:41,882 --> 00:05:43,440 the team head out on the first night 83 00:05:43,684 --> 00:05:45,174 of the tagging operation. 84 00:06:02,403 --> 00:06:04,803 Night is when crocodiles are most active. 85 00:06:05,406 --> 00:06:07,738 It's also the best time to catch them. 86 00:06:12,346 --> 00:06:14,405 It's quite easy to get nervous when you're doing this. 87 00:06:15,316 --> 00:06:17,409 This is potentially very dangerous. 88 00:06:17,652 --> 00:06:20,177 This animal could cause us very serious injury 89 00:06:20,421 --> 00:06:22,616 or kill us if we don't do this right. 90 00:06:27,194 --> 00:06:29,128 We've got a crocodile on the bank right here. 91 00:06:33,134 --> 00:06:36,535 He's a good size. Yeah, three and a half metres. 92 00:06:36,837 --> 00:06:38,361 It's OK. We'll get him. 93 00:06:39,073 --> 00:06:41,507 For a moment, the crocodile is blinded. 94 00:06:46,714 --> 00:06:47,806 OK. Neutral. 95 00:06:48,983 --> 00:06:51,281 - Get the pole. - You got the snout rope? 96 00:06:51,886 --> 00:06:52,944 Keep reversing it out. 97 00:06:53,187 --> 00:06:55,781 OK, slide it on. Get your hands out of the water. 98 00:07:00,127 --> 00:07:00,957 Hang on. 99 00:07:02,563 --> 00:07:03,928 Ah-ah. Hands up. 100 00:07:06,067 --> 00:07:07,398 It's dangerous work. 101 00:07:09,437 --> 00:07:10,734 The crocodile's bite is even more 102 00:07:10,971 --> 00:07:13,064 powerful than a great white shark's. 103 00:07:13,307 --> 00:07:15,639 At least that means he can't bite you. 104 00:07:17,645 --> 00:07:18,373 Hang on. 105 00:07:19,980 --> 00:07:20,674 That's it. 106 00:07:21,849 --> 00:07:23,043 - You all right? - Yeah. 107 00:07:23,284 --> 00:07:26,879 - Pull him up. Bit more. - He'll be perfect for the transmitter. 108 00:07:30,424 --> 00:07:31,288 Got him? 109 00:07:31,826 --> 00:07:34,260 An adult male can weigh over half a ton. 110 00:07:34,895 --> 00:07:38,661 Just keep that head forward. Take him up the back. 111 00:07:42,870 --> 00:07:45,737 This is definitely a feisty crocodile. 112 00:07:47,908 --> 00:07:49,899 1305. 113 00:07:50,377 --> 00:07:54,177 We've got a 2.6m male saltwater crocodile just here. 114 00:07:54,915 --> 00:07:57,042 He's really an ideal animal for us. 115 00:07:57,284 --> 00:07:59,582 So We're going to put a satellite transmitter 116 00:07:59,887 --> 00:08:01,081 onto him and release him. 117 00:08:05,259 --> 00:08:06,226 He's not light. 118 00:08:10,164 --> 00:08:12,826 So if I pull this rope, it should release his jaws. 119 00:08:14,301 --> 00:08:15,393 And now he can go. 120 00:08:17,705 --> 00:08:20,868 The first crocodile to be tagged, they've called Wills. 121 00:08:25,813 --> 00:08:27,007 See you later, alligator. 122 00:08:28,482 --> 00:08:29,847 For the next 12 months, 123 00:08:30,084 --> 00:08:32,644 Adam and the team will follow his every move. 124 00:08:46,400 --> 00:08:48,561 When we get new technology like this, 125 00:08:48,903 --> 00:08:51,371 what we're able to do really for the first time, 126 00:08:51,605 --> 00:08:55,063 is have a look at the secret lives of crocodiles. 127 00:08:56,777 --> 00:08:59,837 We can put a tracking device on the back of a crocodile. 128 00:09:00,481 --> 00:09:04,178 We can watch it from the safety of our computer screens, 129 00:09:04,418 --> 00:09:06,249 swimming up and down rivers 130 00:09:06,487 --> 00:09:09,854 and we are able to really learn a huge amount 131 00:09:10,090 --> 00:09:12,217 about what makes a crocodile tick. 132 00:09:13,260 --> 00:09:16,821 And I just found that absolutely hypnotically compelling. 133 00:09:24,138 --> 00:09:25,070 By the end of the night, 134 00:09:25,306 --> 00:09:28,707 four more crocodiles are tagged in the Mary River. 135 00:09:32,813 --> 00:09:33,871 For the next year, 136 00:09:34,114 --> 00:09:37,743 a satellite deep in space will track their exact positions. 137 00:09:50,431 --> 00:09:52,865 Next morning, they head to Kakadu National Park 138 00:09:53,434 --> 00:09:56,562 and the second study area, the South Alligator River. 139 00:10:01,976 --> 00:10:04,240 Controversy continues in the Northern Territory 140 00:10:04,478 --> 00:10:07,709 over some of Kakadu National Park's top tourism spots. 141 00:10:07,948 --> 00:10:08,880 A record number of saltwater 142 00:10:09,116 --> 00:10:11,311 crocodiles are being found in the area. 143 00:10:17,191 --> 00:10:18,749 The vast South Alligator River 144 00:10:18,993 --> 00:10:21,086 cuts a path through the heart of Kakadu. 145 00:10:23,163 --> 00:10:24,494 At the end of the dry season, 146 00:10:24,732 --> 00:10:26,029 its upstream waters dwindle 147 00:10:26,267 --> 00:10:28,497 to a series of pools called billabongs. 148 00:10:39,113 --> 00:10:42,981 As these water holes dry out, birds, fish and crocodiles 149 00:10:43,217 --> 00:10:45,708 are drawn together in ever-denser numbers. 150 00:10:52,059 --> 00:10:54,584 For the crocodiles, it makes for easy pickings. 151 00:11:32,766 --> 00:11:33,528 Ten years ago, 152 00:11:33,767 --> 00:11:36,429 these billabongs marked the end of the salties' range. 153 00:11:38,839 --> 00:11:39,567 But every year, 154 00:11:39,807 --> 00:11:42,037 they are moving further and further up river. 155 00:11:47,114 --> 00:11:48,604 50 kilometres upstream, 156 00:11:48,849 --> 00:11:52,376 Jim Jim Falls lies at the source of the South Alligator. 157 00:11:57,491 --> 00:12:00,255 It's one of Kakadu's most popular swimming holes. 158 00:12:02,863 --> 00:12:05,661 But now crocodiles are moving dangerously close. 159 00:12:11,171 --> 00:12:13,867 As concern mounts over the safety of the falls, 160 00:12:14,308 --> 00:12:16,105 Kakadu ranger, Garry Linder, 161 00:12:16,343 --> 00:12:19,835 hopes the study will reveal how and when the crocs are moving. 162 00:12:22,549 --> 00:12:24,016 Over the next two weeks, 163 00:12:24,251 --> 00:12:27,152 11 more crocs are tagged in the South Alligator River. 164 00:12:41,035 --> 00:12:44,562 The last to be released, they've called Munmalary. 165 00:13:06,026 --> 00:13:09,962 It's mid-November and one month since the tags were deployed. 166 00:13:11,799 --> 00:13:13,289 Now is the moment of truth. 167 00:13:14,268 --> 00:13:16,498 The first set of data is coming in. 168 00:13:22,009 --> 00:13:24,978 Five crocodiles are sending back signals from the Mary River. 169 00:13:25,779 --> 00:13:27,872 and 11 from the South Alligator. 170 00:13:28,682 --> 00:13:31,549 Already, some interesting stories are emerging. 171 00:13:33,153 --> 00:13:35,417 Adam and data analyst Corey Bradshaw 172 00:13:35,656 --> 00:13:39,148 are surprised by the results coming from one Mary River croc. 173 00:13:39,960 --> 00:13:42,326 This is Wills and he was really interesting. 174 00:13:42,563 --> 00:13:45,555 because He did a couple of really interesting moves. 175 00:13:45,799 --> 00:13:47,790 He spent most of the time after release 176 00:13:48,035 --> 00:13:49,764 around the spot that he was released. 177 00:13:50,003 --> 00:13:52,528 Then he moved upstream towards the barrage. 178 00:13:53,874 --> 00:13:54,704 In just three hours, 179 00:13:54,942 --> 00:13:57,376 Wills covers an incredible 15 kilometres. 180 00:13:58,512 --> 00:14:00,742 The crocodile equivalent of a fast jog. 181 00:14:03,150 --> 00:14:05,448 Now he is sitting close to a manmade barrage 182 00:14:05,686 --> 00:14:07,711 that divides the Mary River in two. 183 00:14:18,732 --> 00:14:21,200 It's exciting to finally start getting some data 184 00:14:21,435 --> 00:14:23,096 and to see that the crocodiles are moving. 185 00:14:23,871 --> 00:14:25,930 What's interesting about this crocodile 186 00:14:26,173 --> 00:14:27,640 is that it's moved such a long way 187 00:14:27,875 --> 00:14:29,467 in such a short period of time. 188 00:14:29,710 --> 00:14:32,975 And I'm hoping when we go there, we can find out why. 189 00:14:41,755 --> 00:14:43,086 This is amazing. 190 00:14:43,624 --> 00:14:45,888 The number of eye shines, it's incredible. 191 00:14:46,126 --> 00:14:49,823 There must be maybe 60, maybe 70 crocodiles out there. 192 00:14:50,831 --> 00:14:54,130 Somewhere amongst them is Adam's tagged crocodile, Wills. 193 00:15:01,542 --> 00:15:04,136 As a high spring tide briefly floods the barrage, 194 00:15:04,478 --> 00:15:07,038 an extraordinary event begins to unfold... 195 00:15:07,948 --> 00:15:11,509 one that has never recorded in saltwater crocodiles before. 196 00:15:17,324 --> 00:15:19,315 This is absolutely incredible to see. 197 00:15:19,660 --> 00:15:23,096 The mullet are flying over the barrage. 198 00:15:23,564 --> 00:15:24,997 There are hundreds of them, 199 00:15:25,232 --> 00:15:27,029 and the crocodiles are lined up. 200 00:15:28,001 --> 00:15:30,299 We've got a crocodile feeding frenzy here. 201 00:15:30,771 --> 00:15:32,363 I've never seen saltwater crocodiles 202 00:15:32,606 --> 00:15:33,664 do this before. 203 00:15:38,312 --> 00:15:40,473 Our tagged croc is actually in this area. 204 00:15:41,415 --> 00:15:44,407 And I'm pretty sure now I know why he is here. 205 00:15:49,256 --> 00:15:52,453 The mullet are heading down river and out to the ocean to spawn. 206 00:15:53,794 --> 00:15:57,252 It's a seasonal event that only occurs on an extreme high tide. 207 00:15:58,398 --> 00:16:02,391 It's just incredible to see these animals, normally so territorial, 208 00:16:02,636 --> 00:16:03,500 tolerating each other 209 00:16:03,737 --> 00:16:05,967 because there is so much free food available. 210 00:16:10,744 --> 00:16:14,077 How have so many crocodiles tuned in to this one event? 211 00:16:16,116 --> 00:16:18,482 Wills travelled 30 kilometres in two days 212 00:16:18,719 --> 00:16:20,311 just to be here on this night. 213 00:16:24,625 --> 00:16:26,024 Not only does it suggest crocs 214 00:16:26,260 --> 00:16:28,990 have a remarkable understanding of their environment 215 00:16:29,863 --> 00:16:32,627 but also, that their movements are far from random. 216 00:16:36,770 --> 00:16:39,603 As the tide turns and the flow begins to subside, 217 00:16:39,840 --> 00:16:42,468 the crocodiles turn their attention to the bank. 218 00:16:50,984 --> 00:16:52,042 Oh! 219 00:16:53,487 --> 00:16:54,749 A lucky escape. 220 00:16:59,726 --> 00:17:02,251 Just one month in, the discovery of this event 221 00:17:02,496 --> 00:17:05,488 offers remarkable new insights into crocodile behaviour. 222 00:17:14,908 --> 00:17:15,636 The next morning, 223 00:17:15,876 --> 00:17:17,810 some of the world's most aggressive predators 224 00:17:18,045 --> 00:17:21,845 are lying side by side, digesting the night's catch. 225 00:17:27,120 --> 00:17:29,213 Nowhere else are saltwater crocodiles known 226 00:17:29,456 --> 00:17:31,515 to tolerate each other in such numbers. 227 00:17:38,699 --> 00:17:39,666 30 years ago, 228 00:17:39,900 --> 00:17:41,993 crocodiles were hunted to the brink of extinction 229 00:17:42,235 --> 00:17:43,532 in Northern Australia. 230 00:17:44,571 --> 00:17:45,970 But thanks to a hunting ban, 231 00:17:46,206 --> 00:17:49,972 their numbers have increased from 3,000 to 75,000. 232 00:17:54,614 --> 00:17:56,639 It's a conservation success story. 233 00:17:58,585 --> 00:18:00,348 But has it now gone too far? 234 00:18:12,199 --> 00:18:15,327 It's now December and the monsoon is taking hold. 235 00:18:20,974 --> 00:18:23,636 For weeks at a time, the rain is almost constant. 236 00:18:34,588 --> 00:18:38,422 Overnight, the billabongs are transformed into flowing rivers. 237 00:18:43,430 --> 00:18:46,797 The crocodiles' world has changed beyond all recognition. 238 00:18:52,105 --> 00:18:53,504 Released from their billabongs, 239 00:18:53,740 --> 00:18:56,641 they're starting to explore the newly-flooded landscape. 240 00:19:08,922 --> 00:19:10,412 Cattle ranchers are keen to see 241 00:19:10,657 --> 00:19:14,286 the reintroduction of controlled culling of saltwater crocodiles. 242 00:19:14,528 --> 00:19:16,223 They say the high number of stock attacks 243 00:19:16,463 --> 00:19:18,090 is becoming a serious problem 244 00:19:18,331 --> 00:19:21,300 with some stations reporting hundreds of losses. 245 00:19:22,769 --> 00:19:26,068 The Mary River runs through the heart of cattle-station country. 246 00:19:29,109 --> 00:19:30,736 Just Upstream from the barrage, 247 00:19:30,977 --> 00:19:34,344 ranchers are concerned at the rise in attacks on livestock. 248 00:19:38,351 --> 00:19:40,979 The crocodile population up here is getting out of hand. 249 00:19:41,221 --> 00:19:42,882 There's far, far too many of them. 250 00:19:43,123 --> 00:19:46,581 It is getting to a stage now where anywhere you go up here, 251 00:19:46,827 --> 00:19:48,317 there's crocodiles in the water. 252 00:19:50,197 --> 00:19:53,860 We've always got someone on watch and if they do see a crocodile, 253 00:19:54,100 --> 00:19:55,226 we don't shoot at the crocodile, 254 00:19:55,469 --> 00:19:57,437 we shoot around it to try and deter it away. 255 00:19:57,971 --> 00:19:59,734 You're not allowed to shoot 256 00:19:59,973 --> 00:20:02,771 them unless one's got hold of you, and then it's too late. 257 00:20:07,914 --> 00:20:09,848 As temperatures and humidity rise, 258 00:20:10,083 --> 00:20:13,109 the distant thunder triggers the crocs to start breeding. 259 00:20:36,510 --> 00:20:40,037 Blowing bubbles, a dominant male gently woos the female, 260 00:20:42,716 --> 00:20:45,810 until finally, the love match is played out underwater. 261 00:20:47,320 --> 00:20:49,515 An arching back and the joining of bubbles 262 00:20:49,756 --> 00:20:51,951 are the only visible sign of their union. 263 00:20:54,861 --> 00:20:57,762 The mating season will continue for another two months. 264 00:20:59,699 --> 00:21:00,791 During this time, 265 00:21:01,034 --> 00:21:04,367 the males will have to fight hard to defend breeding rights. 266 00:21:07,941 --> 00:21:09,431 And for those that lose out, 267 00:21:09,676 --> 00:21:12,304 the struggle to find new territory continues. 268 00:21:17,584 --> 00:21:18,573 It's now January, 269 00:21:18,818 --> 00:21:20,752 and three months since the study began. 270 00:21:20,987 --> 00:21:23,046 ..the Mary River, about 20 miles away at the moment. 271 00:21:24,024 --> 00:21:26,549 The first crocodile we're gonna be looking for... 272 00:21:26,793 --> 00:21:29,523 Adam's team have just received some exciting new data. 273 00:21:31,031 --> 00:21:32,293 It's Wills again, 274 00:21:32,532 --> 00:21:34,500 who was last located at the feeding frenzy 275 00:21:34,734 --> 00:21:35,758 next to the barrage. 276 00:21:37,971 --> 00:21:40,371 What we're seeing just outside the helicopter 277 00:21:40,640 --> 00:21:43,040 This is Shady Camp. This is the barrage. 278 00:21:43,376 --> 00:21:46,174 We were standing on this only recently, 279 00:21:46,413 --> 00:21:48,074 looking for one of the crocodiles. 280 00:21:48,381 --> 00:21:50,144 Now the crocodile has moved from here 281 00:21:50,383 --> 00:21:52,510 all the way downstream, out to the coast, 282 00:21:52,752 --> 00:21:54,845 so we're gonna fly all the way to the coast 283 00:21:55,088 --> 00:21:56,749 to see if we can find this animal. 284 00:22:01,227 --> 00:22:04,685 In one week, Wills has moved 85 kilometres. 285 00:22:08,468 --> 00:22:09,230 From the barrage, 286 00:22:09,469 --> 00:22:12,199 he travelled downriver reaching the sea at 2am, 287 00:22:12,439 --> 00:22:13,906 on the 18th of January. 288 00:22:17,510 --> 00:22:20,035 Since then he has been hugging the muddy coastline, 289 00:22:20,280 --> 00:22:22,441 steadily moving west towards Darwin. 290 00:22:27,587 --> 00:22:29,953 We do know that crocodiles move around the coast. 291 00:22:30,190 --> 00:22:31,657 That much isn't a mystery. 292 00:22:31,891 --> 00:22:34,724 What is a mystery is how much time they spend around here 293 00:22:34,961 --> 00:22:37,191 and how they actually do it. 294 00:22:37,831 --> 00:22:39,924 We know that they can tolerate saltwater 295 00:22:40,166 --> 00:22:42,862 but we don't know how much they can tolerate it. 296 00:22:45,238 --> 00:22:46,330 Saltwater crocodiles 297 00:22:46,573 --> 00:22:48,666 are the only ocean-going crocs in the world. 298 00:22:50,810 --> 00:22:52,778 But battering waves and salty water 299 00:22:53,013 --> 00:22:54,776 make it a gruelling place to be. 300 00:22:57,917 --> 00:23:00,112 More accustomed to life in tidal rivers, 301 00:23:00,353 --> 00:23:03,618 crocodiles can't drink and rarely eat whilst at sea. 302 00:23:07,594 --> 00:23:10,927 How is Wills surviving out here and where is he going? 303 00:23:12,465 --> 00:23:14,558 We are getting a pretty good signal from this croc. 304 00:23:14,801 --> 00:23:16,200 This is looking pretty hopeful. 305 00:23:18,104 --> 00:23:21,073 Look at this guy. This guy is actually... 306 00:23:22,375 --> 00:23:24,673 He's pretty much buried in the mud. Look, there he goes! 307 00:23:24,911 --> 00:23:25,935 This is one of the crocs. 308 00:23:26,179 --> 00:23:28,044 He's got a transmitter on the back of his neck. 309 00:23:28,782 --> 00:23:30,272 OK, that's fantastic. 310 00:23:36,956 --> 00:23:38,787 If this crocodile keeps moving west, 311 00:23:39,025 --> 00:23:40,390 he'll end up in Darwin Harbour. 312 00:23:40,627 --> 00:23:42,288 Then he'll be a problem crocodile. 313 00:23:44,964 --> 00:23:48,456 In a five-kilometre stretch, Adam spots ten more crocodiles. 314 00:23:50,937 --> 00:23:51,961 There's another one. 315 00:23:52,806 --> 00:23:55,104 I'm actually amazed how many crocodiles are out here. 316 00:23:55,341 --> 00:23:56,535 They're all over the place. 317 00:23:57,610 --> 00:23:59,202 It's an unexpected result. 318 00:23:59,913 --> 00:24:01,813 It not only confirms that the Mary River 319 00:24:02,048 --> 00:24:03,777 crocodiles are pushing into the sea 320 00:24:04,350 --> 00:24:06,648 but they're doing so in huge numbers. 321 00:24:08,888 --> 00:24:10,412 I'm really stoked by all this. 322 00:24:10,657 --> 00:24:12,147 We've got some fantastic data. 323 00:24:12,392 --> 00:24:15,054 To see so many out here is just fantastic. 324 00:24:15,295 --> 00:24:16,728 It tells us a huge amount 325 00:24:16,963 --> 00:24:19,022 about the populations of crocs in these rivers. 326 00:24:20,567 --> 00:24:23,627 It's strong evidence that the Mary River is now full. 327 00:24:25,105 --> 00:24:26,868 But where are the crocodiles going? 328 00:24:34,647 --> 00:24:37,241 Parks and wildlife rangers have had a busy start to the year, 329 00:24:37,484 --> 00:24:40,578 catching 19 crocodiles in the last month alone. 330 00:24:41,054 --> 00:24:43,750 Saltwater crocodile numbers are at an all-time high. 331 00:24:44,224 --> 00:24:48,422 Last year, rangers pulled 253 crocs out of Darwin Harbour. 332 00:24:49,929 --> 00:24:52,557 Darwin is on the front line of the crocodile invasion. 333 00:24:55,635 --> 00:24:58,968 And keeping its waters safe is a never-ending task. 334 00:25:02,976 --> 00:25:04,944 As soon as one crocodile is removed, 335 00:25:05,178 --> 00:25:06,941 another quickly takes its place. 336 00:25:08,982 --> 00:25:11,917 Yeah, terrified. I'm terrified of crocodiles. 337 00:25:14,687 --> 00:25:17,053 I wouldn't swim in Darwin Harbour. 338 00:25:17,290 --> 00:25:18,348 Not if you paid me. 339 00:25:23,163 --> 00:25:26,189 As the croc problem escalates, the pressure is building 340 00:25:26,432 --> 00:25:28,491 for the study to deliver some answers. 341 00:25:34,808 --> 00:25:37,242 It's now February, and the satellite tags 342 00:25:37,477 --> 00:25:39,911 have been sending back data for four months. 343 00:25:40,480 --> 00:25:43,540 As the Mary River crocs continue to move along the coast, 344 00:25:43,983 --> 00:25:47,680 Adam receives news of crocs being sighted far out to sea. 345 00:25:51,658 --> 00:25:53,888 We have reports, fairly frequently, 346 00:25:54,427 --> 00:25:56,588 that people who work on oil rigs, 347 00:25:56,830 --> 00:25:57,728 people in ships, 348 00:25:57,964 --> 00:25:59,864 they'll see crocodiles swimming past. 349 00:26:00,366 --> 00:26:04,530 Now, those animals can be 300-400 kilometres from the nearest land. 350 00:26:05,205 --> 00:26:06,365 What are they doing out there? 351 00:26:08,274 --> 00:26:11,368 Adam is on his way to investigate some unusual sightings 352 00:26:11,611 --> 00:26:13,841 on the Tiwi Islands, north of Darwin. 353 00:26:25,525 --> 00:26:28,119 To make the 100-kilometre journey from the mainland 354 00:26:28,361 --> 00:26:30,386 would take a crocodile around a week. 355 00:26:39,505 --> 00:26:40,563 Millions of years ago, 356 00:26:40,807 --> 00:26:43,139 the crocodiles' ancestors were giant reptiles 357 00:26:43,376 --> 00:26:44,707 that ruled the seas. 358 00:26:51,751 --> 00:26:53,343 Travelling huge distances, 359 00:26:53,586 --> 00:26:56,020 they colonised the tropical world. 360 00:27:00,526 --> 00:27:02,153 And today's saltwater crocodiles 361 00:27:02,395 --> 00:27:04,556 retain many of their prehistoric features. 362 00:27:09,002 --> 00:27:12,028 Inside their mouths, tiny glands are working overtime 363 00:27:12,272 --> 00:27:13,500 to excrete enough salt 364 00:27:13,740 --> 00:27:16,265 to overcome the oceans' saline waters. 365 00:27:20,213 --> 00:27:21,111 Along its back, 366 00:27:21,347 --> 00:27:23,611 blood-filled plates absorb the sun's heat, 367 00:27:24,050 --> 00:27:26,518 warming its muscles for the journey ahead. 368 00:27:28,454 --> 00:27:30,945 And with a tail that makes up half its body length, 369 00:27:31,224 --> 00:27:32,486 it can move through the waves 370 00:27:32,725 --> 00:27:35,057 at speeds of up to 10 kilometres an hour. 371 00:27:38,998 --> 00:27:42,229 Just like their ancestors, today's saltwater crocodiles 372 00:27:42,468 --> 00:27:45,198 are once again moving into the oceans. 373 00:27:59,018 --> 00:28:00,986 As night comes to the Tiwi Islands, 374 00:28:01,754 --> 00:28:03,949 a crocodile is waiting in the surf. 375 00:28:36,155 --> 00:28:37,315 It's 9:00 at night. 376 00:28:37,957 --> 00:28:40,653 We're on a beach on the north of the Tiwi Islands. 377 00:28:41,027 --> 00:28:43,325 I'm with turtle biologist Scott Whiting 378 00:28:43,596 --> 00:28:45,427 because Scott has witnessed 379 00:28:45,665 --> 00:28:48,896 saltwater crocodiles attacking flatback turtles. 380 00:28:50,203 --> 00:28:52,797 I think it's 100% that we'll see turtles. 381 00:28:53,039 --> 00:28:55,473 Whether we see crocodiles is another thing. 382 00:28:59,245 --> 00:29:01,645 But as they approach the turtle nesting site, 383 00:29:01,981 --> 00:29:03,881 they realise they're being followed. 384 00:29:05,485 --> 00:29:06,611 A crocodile, just there. 385 00:29:07,620 --> 00:29:08,587 It's gone. 386 00:29:09,022 --> 00:29:10,455 There was an eye shine just there. 387 00:29:20,099 --> 00:29:24,536 Yep, there is he is, look. No, he's gone again. Look. 388 00:29:25,204 --> 00:29:27,172 He's just bobbing up and down in the water. 389 00:29:28,341 --> 00:29:30,639 But he's definitely moving this way, and he's going quite fast. 390 00:29:32,678 --> 00:29:33,736 It's very exciting to see a crocodile 391 00:29:33,980 --> 00:29:35,538 in this kind of a situation. 392 00:29:36,916 --> 00:29:38,042 To be honest, it's the first time 393 00:29:38,284 --> 00:29:39,945 I've ever seen a croc on a beach at night. 394 00:29:40,953 --> 00:29:42,944 It's made me a little bit uneasy. 395 00:29:43,289 --> 00:29:44,847 You just couldn't see the crocs coming. 396 00:29:45,091 --> 00:29:46,991 They'd be able to launch themselves out of the water 397 00:29:47,427 --> 00:29:50,726 so I'm gonna stay a safe distance away from the edge. 398 00:30:00,873 --> 00:30:01,931 Further down the beach, 399 00:30:02,175 --> 00:30:04,507 a flatback turtle hauls herself out. 400 00:30:05,411 --> 00:30:07,777 Now she is at her most vulnerable. 401 00:30:16,789 --> 00:30:19,053 It takes just half an hour to lay her eggs. 402 00:30:20,460 --> 00:30:22,485 But every second she is out of the water, 403 00:30:22,728 --> 00:30:24,855 she is in danger from the crocodiles. 404 00:30:51,791 --> 00:30:53,952 - Wow, look at these tracks, Adam. - Whoa. 405 00:30:54,360 --> 00:30:55,486 We're standing on them. 406 00:30:56,562 --> 00:30:58,689 You can see what's happened. Turtle's come up, 407 00:30:58,931 --> 00:31:00,364 crocodile's followed it. 408 00:31:00,600 --> 00:31:02,693 You can see clearly the imprint from his scales 409 00:31:02,935 --> 00:31:05,096 between each of these footprints. 410 00:31:05,638 --> 00:31:08,072 There's no signs of a struggle or no blood, 411 00:31:08,307 --> 00:31:10,605 or anything,so obviously the croc missed its target. 412 00:31:10,843 --> 00:31:11,502 Yeah, I think so. 413 00:31:11,744 --> 00:31:13,712 It's pretty exciting to see these tracks, 414 00:31:13,946 --> 00:31:15,777 to see this story in the sand here. 415 00:31:16,015 --> 00:31:19,781 Um... It's just a bit frustrating that we missed, unfortunately. 416 00:31:22,021 --> 00:31:25,047 I think what this shows is that saltwater crocodiles 417 00:31:25,291 --> 00:31:27,759 are not only using the coastline for moving 418 00:31:27,994 --> 00:31:30,292 but there's also a potential source of food here. 419 00:31:30,563 --> 00:31:32,895 So it really raises the possibility 420 00:31:33,132 --> 00:31:35,464 that crocodiles use islands such as this 421 00:31:35,701 --> 00:31:38,033 as staging posts on a longer journey. 422 00:31:40,072 --> 00:31:43,371 With increasing evidence of crocs spending long periods at sea, 423 00:31:43,976 --> 00:31:46,240 could this be the start of a wider problem? 424 00:31:47,213 --> 00:31:50,546 Are crocs now leaving Australia to colonise new continents? 425 00:32:01,093 --> 00:32:01,957 It's now April. 426 00:32:02,962 --> 00:32:05,089 Two more crocodiles from the Mary River 427 00:32:05,331 --> 00:32:07,060 have joined Wills on the coast. 428 00:32:10,269 --> 00:32:11,964 And as water levels rise, 429 00:32:12,205 --> 00:32:14,400 the billabong crocs on the South Alligator 430 00:32:14,640 --> 00:32:17,074 are becoming more and more active. 431 00:32:20,846 --> 00:32:21,676 But it's a crocodile 432 00:32:21,914 --> 00:32:25,042 that's barely moved at all that attracts the team's attention. 433 00:32:25,651 --> 00:32:27,118 He's called Munmalary. 434 00:32:27,353 --> 00:32:31,687 Do you remember that animal, he was a male about 3.5 metres? 435 00:32:31,924 --> 00:32:33,949 - We got him about 30 kilometres... - I remember. 436 00:32:34,193 --> 00:32:35,353 The South Alligator here. 437 00:32:35,595 --> 00:32:38,758 And He's moved five or six kilometres 438 00:32:38,998 --> 00:32:41,091 up that area and he hasn't moved at all. 439 00:32:46,038 --> 00:32:48,768 To find out why Munmalary is so in active, 440 00:32:49,041 --> 00:32:51,532 Adam and Garry head back to the South Alligator. 441 00:33:01,587 --> 00:33:05,079 They suspect Munmalary is either trapped between the territory 442 00:33:05,324 --> 00:33:06,484 of two dominant males 443 00:33:08,294 --> 00:33:13,288 or that he is the boss croc, and this is his area. 444 00:33:25,144 --> 00:33:26,702 As the signal gets stronger, 445 00:33:27,079 --> 00:33:30,173 Adam spots signs of a crocodile nest near by. 446 00:33:33,119 --> 00:33:35,280 It looks like there might be one just over here. 447 00:33:35,521 --> 00:33:36,954 In fact, there is. I can see it. 448 00:33:38,724 --> 00:33:40,658 There. A nest back there. 449 00:33:43,229 --> 00:33:45,561 I can't see the female but she might be in a wallow, 450 00:33:45,798 --> 00:33:46,492 hidden there. 451 00:33:46,966 --> 00:33:49,799 So it's going to be very dangerous for us to go in here. 452 00:33:50,036 --> 00:33:51,594 She might rush out at us, 453 00:33:51,837 --> 00:33:54,704 so what we're gonna do is go a little bit further upstream 454 00:33:55,074 --> 00:33:58,202 and then we can walk along the bank and we can come from behind. 455 00:33:59,045 --> 00:34:02,503 To find out if the nest is active, they must open it. 456 00:34:08,354 --> 00:34:10,322 It's extremely dangerous. 457 00:34:13,893 --> 00:34:15,155 From a standing start, 458 00:34:15,394 --> 00:34:17,487 a crocodile can explode at speeds of up 459 00:34:17,730 --> 00:34:19,357 to seven metres per second. 460 00:34:20,366 --> 00:34:21,458 It's a fairly big one. 461 00:34:22,068 --> 00:34:24,832 It's a good-size nest which means it's a good-size female. 462 00:34:25,137 --> 00:34:27,765 They still have no idea where the female is hiding. 463 00:34:32,545 --> 00:34:34,809 It's often a good idea to bang the ground like this, 464 00:34:35,147 --> 00:34:37,081 because if she is hidden, 465 00:34:37,316 --> 00:34:39,876 the vibrations from this can bring her out 466 00:34:40,119 --> 00:34:42,087 or even make her flee. 467 00:34:43,656 --> 00:34:46,955 - Adam, she is coming out of the water. - OK. Come here. 468 00:34:59,472 --> 00:35:01,337 A nice-looking female. 469 00:35:03,075 --> 00:35:05,373 Well, this is the female. 470 00:35:05,911 --> 00:35:07,037 She's actually come back to the nest. 471 00:35:07,279 --> 00:35:10,407 So Us disturbing it has attracted her. 472 00:35:11,851 --> 00:35:14,115 So she's obviously a little unsure what to do now. 473 00:35:14,820 --> 00:35:17,288 There's a good chance she's going to come up towards us. 474 00:35:17,523 --> 00:35:18,785 We have to be very careful. 475 00:35:22,094 --> 00:35:24,358 You want to check those eggs and I'll give you a yell? 476 00:35:35,274 --> 00:35:38,869 OK, well, this is your classic saltwater-crocodile nest. 477 00:35:39,845 --> 00:35:43,542 She has grabbed all of this grass, this vegetation, from around here, 478 00:35:44,116 --> 00:35:46,778 and she's just stacked it all together and compressed it down. 479 00:35:48,220 --> 00:35:49,710 Hopefully, she laid some eggs. 480 00:35:49,955 --> 00:35:52,856 That's what we're looking for. Is this an active nest? 481 00:35:59,932 --> 00:36:01,957 It's incredible how tightly they pack 482 00:36:02,201 --> 00:36:04,362 the vegetation when they build these nests. 483 00:36:05,838 --> 00:36:08,204 It's often a really good indication 484 00:36:08,441 --> 00:36:10,306 that the female needs to be here to open it 485 00:36:10,543 --> 00:36:12,534 when the eggs hatch out because imagine 486 00:36:12,778 --> 00:36:15,747 being a baby crocodile trying to get out of this. 487 00:36:16,115 --> 00:36:18,208 OK, we've got some eggs. 488 00:36:20,219 --> 00:36:21,777 Excellent. 489 00:36:31,497 --> 00:36:32,225 So basically, 490 00:36:32,465 --> 00:36:36,162 this is a very good reason for Munmalary to stay in this area. 491 00:36:36,402 --> 00:36:37,460 to stay in this area. 492 00:36:38,304 --> 00:36:40,101 The ability to breed. 493 00:36:42,975 --> 00:36:47,378 Munmalary could father as many as 300 crocodiles this season. 494 00:36:48,180 --> 00:36:49,511 And with up to 1,000 nests 495 00:36:49,748 --> 00:36:51,875 being laid in Northern Australia this year, 496 00:36:52,151 --> 00:36:54,415 salty numbers continue to rise. 497 00:36:57,923 --> 00:37:00,255 But before the team can locate Munmalary, 498 00:37:00,493 --> 00:37:02,085 they are forced to return to Darwin. 499 00:37:09,401 --> 00:37:11,266 Residents in the Northern Territory capital, 500 00:37:11,504 --> 00:37:12,835 Darwin, are on high alert 501 00:37:13,072 --> 00:37:16,098 as Cyclone Monica continues on its destructive path. 502 00:37:16,575 --> 00:37:18,167 The category-five tropical cyclone 503 00:37:18,410 --> 00:37:21,504 is one of the biggest in the Territory's history. 504 00:37:22,281 --> 00:37:25,580 The cyclone cuts a path straight through the study site, 505 00:37:26,185 --> 00:37:27,777 decimating the landscape. 506 00:37:28,687 --> 00:37:31,554 It's still not clear what effect it's had on the crocodiles. 507 00:37:34,026 --> 00:37:38,053 Early this morning, severe tropical cyclone Monica 508 00:37:38,330 --> 00:37:40,628 passed across the South Alligator River. 509 00:37:40,933 --> 00:37:41,763 At that point, 510 00:37:42,001 --> 00:37:45,061 it was packing winds of 350 kilometres an hour. 511 00:37:45,738 --> 00:37:48,036 In extreme weather conditions like this, 512 00:37:48,407 --> 00:37:50,898 it's going to be very difficult for crocodiles. 513 00:37:54,213 --> 00:37:56,181 It's an unprecedented opportunity 514 00:37:56,415 --> 00:37:59,646 to study crocodile behaviour in cyclone conditions. 515 00:38:02,154 --> 00:38:03,348 As the data comes in, 516 00:38:03,789 --> 00:38:06,417 it reveals that two days before the storm, 517 00:38:06,659 --> 00:38:08,854 the Mary River crocs, Wills and Kelly, 518 00:38:09,094 --> 00:38:11,585 moved to the relative safety of the river. 519 00:38:15,334 --> 00:38:18,098 It suggests they knew the bad weather was approaching. 520 00:38:20,940 --> 00:38:22,464 But the data is limited. 521 00:38:23,542 --> 00:38:26,568 Only half the satellite tags were able to transmit. 522 00:38:29,081 --> 00:38:30,605 It's likely their aerials were hidden 523 00:38:30,849 --> 00:38:33,010 as the crocs sought refuge underwater. 524 00:38:36,155 --> 00:38:38,919 Large crocs can dive to around ten metres 525 00:38:39,358 --> 00:38:42,225 and hold their breath for more than two hours. 526 00:38:44,396 --> 00:38:48,833 Deep underwater, the storm passes by barely detected. 527 00:38:51,470 --> 00:38:53,438 This ability to predict severe weather 528 00:38:53,672 --> 00:38:57,005 has never been reported in saltwater crocodiles before. 529 00:39:05,117 --> 00:39:06,744 As the study draws to a close, 530 00:39:07,119 --> 00:39:10,748 Adam and Garry make one final expedition down river. 531 00:39:14,059 --> 00:39:15,720 Across Northern Australia, 532 00:39:15,961 --> 00:39:17,758 it's the crocodile hatching season, 533 00:39:18,464 --> 00:39:20,955 and Munmalary's babies are about to emerge. 534 00:39:27,940 --> 00:39:31,398 The female has been guarding her nest for the last 80 days. 535 00:39:34,279 --> 00:39:37,214 - Strange calls fill the air. - (Bleating) 536 00:39:38,117 --> 00:39:40,517 It's the sound she's been waiting for. 537 00:39:50,829 --> 00:39:52,888 Ripping into the compacted grass, 538 00:39:53,132 --> 00:39:55,191 she sets the young crocodiles free. 539 00:40:11,784 --> 00:40:13,183 Then, by one by one, 540 00:40:13,485 --> 00:40:15,953 she gently carries them down to the water. 541 00:40:29,101 --> 00:40:34,129 Within 24 hours, her clutch of more than 50 eggs have hatched. 542 00:40:36,608 --> 00:40:38,269 All over the Northern Territory, 543 00:40:38,544 --> 00:40:40,876 thousands more are taking to the water. 544 00:40:51,356 --> 00:40:54,757 Garry, there's a bunch of eye shines on the bank here. 545 00:40:54,993 --> 00:40:57,291 - That's mum there, is it? - Yeah, that's the female. 546 00:41:04,303 --> 00:41:06,168 It's pretty impressive when they move like that. 547 00:41:09,141 --> 00:41:10,665 There's about three of them here, Garry. 548 00:41:13,779 --> 00:41:15,542 Oh, wow, there's so many of them. 549 00:41:15,781 --> 00:41:16,805 It's incredible. 550 00:41:17,249 --> 00:41:19,217 I've seen the odd hatchling here and there. 551 00:41:19,718 --> 00:41:21,276 I've never seen so many hatchlings 552 00:41:21,520 --> 00:41:23,420 like this, together, feeding at once. 553 00:41:23,655 --> 00:41:26,180 It's an amazing site, to be honest. 554 00:41:26,558 --> 00:41:28,822 Baby crocodiles grow up fast. 555 00:41:30,062 --> 00:41:32,030 Already they're skilled hunters, 556 00:41:32,831 --> 00:41:35,527 killing these mudskippers with a single bite. 557 00:41:38,971 --> 00:41:41,667 For the moment, their mother watches over them. 558 00:41:44,243 --> 00:41:45,608 But in three months' time, 559 00:41:45,844 --> 00:41:48,142 these tiny crocs will be on their own. 560 00:41:55,654 --> 00:41:56,746 It's pretty exciting. 561 00:41:57,022 --> 00:42:00,355 This could possibly be one of Munmalary's young. 562 00:42:01,460 --> 00:42:03,519 It's a bit frightened now, doesn't know what's going on, 563 00:42:03,762 --> 00:42:05,821 so it's producing this ''ow-ow''. 564 00:42:06,064 --> 00:42:09,227 It's calling out for the female, the mother, 565 00:42:09,468 --> 00:42:10,560 who is just over there. 566 00:42:11,804 --> 00:42:14,068 Something like this looks so cute and innocent. 567 00:42:14,840 --> 00:42:18,708 And yet ultimately, this could be the animal 568 00:42:19,044 --> 00:42:20,705 that becomes a real problem. 569 00:42:21,880 --> 00:42:25,611 OK, I'm just going to release this one here. Good luck, fella. 570 00:42:28,120 --> 00:42:29,382 No, you've got to go that way. 571 00:42:32,257 --> 00:42:33,747 Well, it's been an amazing night. 572 00:42:33,992 --> 00:42:37,621 We've seen that there are a lot of hatchlings on this river. 573 00:42:38,163 --> 00:42:40,256 We've found several groups of them 574 00:42:40,499 --> 00:42:42,262 and we've seen some pretty amazing behaviour, 575 00:42:42,501 --> 00:42:43,991 we've seen all these animals feeding 576 00:42:44,236 --> 00:42:45,828 and they're doing it now in front of us, 577 00:42:46,071 --> 00:42:47,504 taking all of these mudskippers, 578 00:42:47,739 --> 00:42:49,104 it's something I've never seen before. 579 00:42:50,175 --> 00:42:51,403 What it's proven to us is that this is 580 00:42:51,643 --> 00:42:53,907 an incredibly productive river system. 581 00:42:57,783 --> 00:42:58,715 Latest estimates 582 00:42:58,951 --> 00:43:03,047 put the salty population in Northern Australia at 75,000. 583 00:43:03,789 --> 00:43:05,518 Whilst only half of these hatchlings 584 00:43:05,757 --> 00:43:07,281 will survive their first year, 585 00:43:07,793 --> 00:43:10,819 there's clearly a lot more problem crocs on the way. 586 00:43:16,468 --> 00:43:19,164 For the past year, 16 crocodiles 587 00:43:19,404 --> 00:43:21,599 have been transmitting their daily positions. 588 00:43:22,341 --> 00:43:25,037 Now the study is coming to a close. 589 00:43:34,620 --> 00:43:36,110 As the data comes in, 590 00:43:36,355 --> 00:43:38,516 finally some patterns are emerging. 591 00:43:40,425 --> 00:43:43,622 We've got the biggest movements from the river 592 00:43:43,862 --> 00:43:45,295 with the highest density of crocs. 593 00:43:45,530 --> 00:43:48,556 - Which is what you'd expect. - It's a fantastic result. 594 00:43:48,834 --> 00:43:51,428 The crocodiles in the overcrowded Mary River 595 00:43:51,670 --> 00:43:55,162 have moved further and faster than anyone had expected. 596 00:43:56,642 --> 00:43:59,509 Moving up and down the coastline, they've surprised the team 597 00:43:59,745 --> 00:44:02,213 by crossing the difficult waters of Cape Hoffen. 598 00:44:04,483 --> 00:44:06,314 It's a crucial piece of information. 599 00:44:07,052 --> 00:44:09,816 It suggests that crocodiles from the Mary River 600 00:44:10,055 --> 00:44:13,616 are capable of swimming the 150 kilometres to Darwin. 601 00:44:14,192 --> 00:44:17,457 And they can do it in less than a week. 602 00:44:19,364 --> 00:44:22,026 For Darwin's residents, it's sobering news. 603 00:44:23,068 --> 00:44:25,901 It means that crocodiles could turn up at any time. 604 00:44:28,407 --> 00:44:31,808 But on the South Alligator, it's quite a different story. 605 00:44:33,712 --> 00:44:35,009 Adam and Corey are surprised 606 00:44:35,247 --> 00:44:37,078 at how little the crocs have moved. 607 00:44:38,116 --> 00:44:41,643 This inactivity can only be good news for Kakadu. 608 00:44:43,755 --> 00:44:45,814 But then some alarming data comes in. 609 00:44:51,463 --> 00:44:53,454 The Northern Territory had its wetest April 610 00:44:53,699 --> 00:44:56,167 since records began 65 years ago. 611 00:44:56,401 --> 00:44:58,392 Extensive Flooding in the top end has closed 612 00:44:58,637 --> 00:45:00,468 major highways and swimming holes, 613 00:45:00,706 --> 00:45:03,072 disrupting the start of the tourist season. 614 00:45:09,648 --> 00:45:11,411 We've just got some very interesting data 615 00:45:11,650 --> 00:45:12,708 from one of our crocodiles. 616 00:45:13,251 --> 00:45:14,718 The crocodile called 617 00:45:14,953 --> 00:45:17,581 Mullet has moved about 20 kilometres upstream 618 00:45:17,823 --> 00:45:20,758 and is swimming straight towards the Jim Jim Falls swimming area. 619 00:45:21,426 --> 00:45:23,291 That means he's going to be a big problem. 620 00:45:26,231 --> 00:45:27,357 It's frightening news. 621 00:45:28,800 --> 00:45:32,201 A late flush of rain has allowed Mullet to push upstream, 622 00:45:32,471 --> 00:45:35,565 covering 20 kilometres in just ten hours. 623 00:45:40,245 --> 00:45:40,973 This area here, 624 00:45:41,213 --> 00:45:43,943 We're just coming up to Jim Jim Falls, which is ahead of us, 625 00:45:44,182 --> 00:45:47,379 it's very rocky, very stony escarpment country. 626 00:45:48,587 --> 00:45:49,884 It's not the kind of habitat 627 00:45:50,122 --> 00:45:52,113 that you'd associate with saltwater crocodiles. 628 00:45:53,792 --> 00:45:55,157 Ten years ago, 629 00:45:55,394 --> 00:45:58,488 you wouldn't have found salties moving this far upstream. 630 00:45:58,730 --> 00:46:00,129 But they're certainly there now. 631 00:46:11,543 --> 00:46:12,567 To get to the falls, 632 00:46:12,811 --> 00:46:15,609 Mullet has to climb several stretches of rapids. 633 00:46:17,549 --> 00:46:19,779 It's a difficult and exhausting journey. 634 00:46:25,724 --> 00:46:27,487 But with the sudden rise in water levels, 635 00:46:27,726 --> 00:46:29,694 he does it with unexpected ease. 636 00:46:37,702 --> 00:46:40,967 As 11 more potential man-eaters are spotted in the area, 637 00:46:41,339 --> 00:46:43,170 Garry closes the falls. 638 00:46:45,644 --> 00:46:47,509 It's the first time in the park's history 639 00:46:47,746 --> 00:46:51,204 that so many crocodiles have been found this far up river. 640 00:46:55,487 --> 00:46:58,820 It suggests that salty behaviour is changing. 641 00:47:02,661 --> 00:47:05,858 For Garry, this new information could save lives. 642 00:47:11,236 --> 00:47:13,033 Now, when water levels rise, 643 00:47:13,371 --> 00:47:15,896 he'll be putting Kakadu on high alert. 644 00:47:24,182 --> 00:47:26,173 I think the most surprising result for me 645 00:47:26,418 --> 00:47:30,047 was the speed at which these crocodiles were capable of moving. 646 00:47:31,690 --> 00:47:34,352 And it's raised a very interesting management issue. 647 00:47:35,060 --> 00:47:38,052 That is that even if you find an area 648 00:47:38,296 --> 00:47:39,786 has no crocodiles in one day, 649 00:47:40,031 --> 00:47:40,759 it doesn't mean to say 650 00:47:40,999 --> 00:47:43,695 there isn't going to be one in there the next day. 651 00:47:46,438 --> 00:47:49,464 I think Crocodiles have got a place in the Northern Territory 652 00:47:49,708 --> 00:47:53,166 but we obviously have to make sure that crocodiles and people 653 00:47:53,411 --> 00:47:55,174 are not coming into conflict. 654 00:47:55,413 --> 00:47:58,041 That means there are places where we have to control them, 655 00:47:58,283 --> 00:48:00,717 to keep them from killing people. 656 00:48:03,455 --> 00:48:04,513 It's a balancing act 657 00:48:05,023 --> 00:48:06,820 and if we don't get the balance right, 658 00:48:07,159 --> 00:48:09,957 then the consequences for either species could be fatal. 659 00:48:13,331 --> 00:48:16,061 Getting the balance right is never going to be easy. 660 00:48:16,735 --> 00:48:19,226 But this study is a critical first step 661 00:48:19,471 --> 00:48:22,907 in managing the future of this ancient predator.