1 00:00:36,138 --> 00:00:37,179 These seas 2 00:00:37,180 --> 00:00:40,306 - thousands of miles from nearest land 3 00:00:40,307 --> 00:00:42,402 - are the most sterile on our planet. 4 00:00:42,403 --> 00:00:46,562 These are marine deserts. 5 00:00:47,615 --> 00:00:51,774 But here live the swiftest and the most powerful of all ocean hunters 6 00:00:59,091 --> 00:01:03,261 Simply finding them is an immense challenge 7 00:01:04,314 --> 00:01:07,440 but we are about to follow them as they search for their food 8 00:01:07,441 --> 00:01:11,600 in this little known part of the seas - the open ocean. 9 00:01:31,437 --> 00:01:35,606 Striped marlin - voracious predators... that can grow to three metres long. 10 00:01:41,871 --> 00:01:43,965 They hunt mainly in daylight 11 00:01:43,966 --> 00:01:46,050 searching the tropical oceans from close 12 00:01:46,051 --> 00:01:50,210 to the surface down to depths of a hundred metres or so. 13 00:01:52,305 --> 00:01:55,442 Normally the fish they feed on are widely dispersed 14 00:01:55,443 --> 00:01:59,602 but sometimes their prey gathers in dense shoals, like these sardines. 15 00:03:36,649 --> 00:03:40,818 This feast may last for over an hour, 16 00:03:46,041 --> 00:03:50,220 time enough for other hunters to reach the scene. 17 00:03:50,221 --> 00:03:54,380 Juvenile tuna join in the feeding frenzy. 18 00:04:12,132 --> 00:04:16,291 The noise attracts a giant - a sei whale. 19 00:04:24,651 --> 00:04:28,820 It's fourteen metres long and twenty tonnes in weight 20 00:04:28,821 --> 00:04:32,990 - and has an appetite to match. 21 00:05:35,607 --> 00:05:39,766 Soon the only sign that the sardines ever existed are scales 22 00:05:40,819 --> 00:05:44,988 sinking down into the abyss. 23 00:05:46,041 --> 00:05:48,125 Such feasts don't last long. 24 00:05:48,126 --> 00:05:51,252 Within a few short days, waters that once swarmed... 25 00:05:51,253 --> 00:05:54,390 with food will have been cleaned out. 26 00:05:54,391 --> 00:05:56,474 The hunters must move elsewhere and once again 27 00:05:56,475 --> 00:06:00,634 start their search of the seemingly featureless open ocean. 28 00:06:04,825 --> 00:06:07,951 A manta ray - immense - five metres 29 00:06:07,952 --> 00:06:12,111 across from the tip of one wing-like fin to the tip of the other. 30 00:06:13,164 --> 00:06:16,301 It's travelling economy, wasting as little energy as possible, 31 00:06:16,302 --> 00:06:20,461 as it glides through the waters of the tropics. 32 00:06:25,694 --> 00:06:28,820 The remora fish that accompany it travel 33 00:06:28,821 --> 00:06:32,980 more economically still - by hitching a lift. 34 00:06:34,033 --> 00:06:36,127 Their host is searching for food - plankton, 35 00:06:36,128 --> 00:06:40,296 the minute fish and invertebrates that float near the surface. 36 00:06:40,297 --> 00:06:43,424 It needs lots of them and may cruise for days before... 37 00:06:43,425 --> 00:06:47,594 it finds a good feeding ground. 38 00:06:49,689 --> 00:06:52,816 Dusk, at the edge of a Pacific Island 39 00:06:52,817 --> 00:06:55,943 three thousand miles from the nearest continent. 40 00:06:55,944 --> 00:07:00,113 Here surgeon fish have assembled to spawn. 41 00:07:01,166 --> 00:07:03,250 As they perform their nuptial dances 42 00:07:03,251 --> 00:07:07,410 they discharge clouds of eggs and sperm into the water. 43 00:07:08,473 --> 00:07:10,557 The manta must have known this was about 44 00:07:10,558 --> 00:07:14,727 to happen for it arrived at exactly this critical moment. 45 00:07:14,728 --> 00:07:17,864 And it is not the only one to do so. 46 00:07:17,865 --> 00:07:22,024 Others are here too. 47 00:07:24,120 --> 00:07:27,246 Now all they need to do is to sweep the water into their mouths 48 00:07:27,247 --> 00:07:31,416 and sieve out the eggs. 49 00:07:56,465 --> 00:08:00,644 Within an hour, the whole event will be over... 50 00:08:00,645 --> 00:08:02,729 Any surviving eggs will be so dispersed 51 00:08:02,730 --> 00:08:06,889 that they are not worth collecting. 52 00:08:14,207 --> 00:08:16,290 But other perils await them as they join 53 00:08:16,291 --> 00:08:19,417 the clouds of eggs and larvae and tiny fish 54 00:08:19,418 --> 00:08:23,588 that drift through the surface waters of the open ocean. 55 00:08:24,641 --> 00:08:28,809 These are the eggs of yellow fin tuna. 56 00:08:28,810 --> 00:08:32,980 If the hatchlings survive, it will take them two years to become adults. 57 00:08:38,202 --> 00:08:40,286 In three years, they could be nearly two metres long 58 00:08:40,287 --> 00:08:44,457 and weigh two hundred kilograms. 59 00:08:46,552 --> 00:08:50,711 Perhaps only one in a million will live as long as that. 60 00:08:51,774 --> 00:08:54,900 They and the other animals and microscopic plants of the plankton 61 00:08:54,901 --> 00:08:59,061 constitute the basis of all life out on the open ocean. 62 00:09:05,336 --> 00:09:07,420 A storm petrel dancing on the water. 63 00:09:07,421 --> 00:09:10,547 But this is no amiable waltz. 64 00:09:10,548 --> 00:09:14,717 It's a hunt. 65 00:09:15,770 --> 00:09:17,854 As they hover facing into the wind, 66 00:09:17,855 --> 00:09:22,014 they pick out morsels from near the surface, including eggs. 67 00:09:31,416 --> 00:09:33,511 Only a tiny percentage of the developing eggs 68 00:09:33,512 --> 00:09:35,595 will survive long enough to hatch. 69 00:09:35,596 --> 00:09:39,756 These newly emerged tuna are only three millimetres long 70 00:09:40,808 --> 00:09:44,978 and although they can swim they're still very vulnerable. 71 00:09:46,031 --> 00:09:48,115 It will be many weeks before they can swim 72 00:09:48,116 --> 00:09:52,275 strongly enough to make any real headway in the ocean. 73 00:10:02,720 --> 00:10:04,814 After the sun goes down, 74 00:10:04,815 --> 00:10:08,974 other predators rise from the depths to attack the floating multitudes. 75 00:10:28,811 --> 00:10:32,970 Darkness shrouds the arrival of battalions of dangerous drifting predators 76 00:10:48,637 --> 00:10:51,763 These shimmering comb jellies - sea gooseberries 77 00:10:51,764 --> 00:10:55,933 - trap their prey with sticky net-like webs 78 00:10:55,934 --> 00:11:00,103 One ill-timed fin-stroke could bring certain death to a hatchling fish. 79 00:11:03,241 --> 00:11:05,325 There are many kinds of these comb jellies 80 00:11:05,326 --> 00:11:09,495 - all of them very effective hunters. 81 00:11:20,982 --> 00:11:23,066 By dawn, most of the nocturnal feeders 82 00:11:23,067 --> 00:11:27,226 will have returned to the depths. 83 00:11:30,374 --> 00:11:32,458 The surviving hatchlings, 84 00:11:32,459 --> 00:11:36,618 however, have already started on their travels. 85 00:11:47,063 --> 00:11:48,104 Vast current systems, 86 00:11:48,105 --> 00:11:52,275 like immense rivers, carry them around the ocean basins. 87 00:11:54,370 --> 00:11:57,496 The boundaries between these masses of moving water... 88 00:11:57,497 --> 00:12:00,634 form invisible barriers that can trap 89 00:12:00,635 --> 00:12:04,794 both plankton and nutrients carried up from the depths. 90 00:12:10,027 --> 00:12:12,111 So parts of the ocean become rich 91 00:12:12,112 --> 00:12:16,271 with food for days or even weeks at a time 92 00:12:17,324 --> 00:12:21,493 This attracts vast schools of plankton-feeding fish - like these sardine 93 00:12:29,843 --> 00:12:31,937 They take in water through their mouths 94 00:12:31,938 --> 00:12:34,022 and expel it through their gills 95 00:12:34,023 --> 00:12:38,182 sieving out the plankton which is then funnelled down their throats. 96 00:12:44,457 --> 00:12:48,626 The immense schools travel along the boundaries of the currents 97 00:12:48,627 --> 00:12:52,796 - seeking the spots where the plankton is thickest. 98 00:12:55,934 --> 00:12:59,060 As the position of the current boundaries changes constantly, 99 00:12:59,061 --> 00:13:03,230 so does both the supply of plankton and the numbers of fish. 100 00:13:18,887 --> 00:13:22,013 A small pod of Pacific Spotted Dolphin 101 00:13:22,014 --> 00:13:25,151 - twenty miles from the coast of Panama. 102 00:13:25,152 --> 00:13:27,236 Like all predators, they seek parts of the ocean 103 00:13:27,237 --> 00:13:31,396 where their food is thickest. 104 00:13:39,756 --> 00:13:42,882 They cover as much as hundred miles in a day. 105 00:13:42,883 --> 00:13:47,053 And while they travel, they play. 106 00:14:02,709 --> 00:14:06,888 They have detected the sound of schooling fish from hundreds of metres away 107 00:14:06,889 --> 00:14:11,058 and start to track down the shoals using sonar 108 00:14:11,059 --> 00:14:15,218 - leaving their toys behind them. 109 00:14:17,324 --> 00:14:21,483 For the hunted there are few places to hide. 110 00:14:27,758 --> 00:14:28,799 Schooling mackerel. 111 00:14:28,800 --> 00:14:32,960 They have already sensed the sonar beams of approaching dolphin. 112 00:14:38,192 --> 00:14:41,319 Their only defence is to gather into a ball. 113 00:14:41,320 --> 00:14:45,488 Any individual that stayed out of the shoal would be quickly picked off. 114 00:14:45,489 --> 00:14:49,659 Within it, there is at least some chance of survival. 115 00:14:59,061 --> 00:15:02,187 The noise of the attack alerts another predator 116 00:15:02,188 --> 00:15:06,347 - a sailfish, one of the fastest fish in the ocean. 117 00:15:10,538 --> 00:15:12,622 It has detected rapid vibrations in the water 118 00:15:12,623 --> 00:15:16,782 and is searching for the cause. 119 00:15:29,322 --> 00:15:31,405 Sailfish rely on eyesight 120 00:15:31,406 --> 00:15:32,448 for their final approach 121 00:15:32,449 --> 00:15:36,608 so they hunt mainly in daylight. 122 00:15:40,798 --> 00:15:43,925 When sailfish become excited they change colour 123 00:15:43,926 --> 00:15:47,052 lighting up with bright blue stripes. 124 00:15:47,053 --> 00:15:49,147 Since mackerel eyes are especially sensitive 125 00:15:49,148 --> 00:15:52,274 to blue and ultraviolet, these colours confuse them 126 00:15:52,275 --> 00:15:56,434 - making them easier to catch. 127 00:16:37,140 --> 00:16:41,319 Far below, a blue shark returns from a squid-hunting trip in the 128 00:16:41,320 --> 00:16:44,446 cold darkness three hundred metres down. 129 00:16:44,447 --> 00:16:48,606 It's heading for the surface to reheat in the warmer water. 130 00:16:50,701 --> 00:16:53,838 As it ascends, it detects the smell of oils 131 00:16:53,839 --> 00:16:57,998 and proteins shed into the water by the panicked mackerel. 132 00:17:02,188 --> 00:17:03,230 The trail leads both the shark 133 00:17:03,231 --> 00:17:07,390 and its attendant pilot fish towards an easy meal. 134 00:17:12,623 --> 00:17:14,707 Scraps and casualties float 135 00:17:14,708 --> 00:17:18,867 in the wake of the passing mackerel school 136 00:17:23,057 --> 00:17:25,141 Throughout the ocean, predators and prey are locked 137 00:17:25,142 --> 00:17:29,301 in a deadly three-dimensional contest of hide and seek 138 00:17:30,354 --> 00:17:32,438 played out over immense distances. 139 00:17:32,439 --> 00:17:36,608 To survive they must travel. 140 00:17:41,831 --> 00:17:43,925 The huge four metre long blue-fin tuna 141 00:17:43,926 --> 00:17:47,052 has special blood vessels that enable it 142 00:17:47,053 --> 00:17:51,212 to keep its body temperature significantly warmer than the surrounding water. 143 00:17:56,445 --> 00:17:59,571 As a result, they can survive in much colder conditions 144 00:17:59,572 --> 00:18:02,698 than any other tuna and they travel thousands of 145 00:18:02,699 --> 00:18:04,793 miles away from their spawning grounds 146 00:18:04,794 --> 00:18:08,963 in the tropics to hunt in cold seas 147 00:18:08,964 --> 00:18:12,090 where the food supply is richest. 148 00:18:12,091 --> 00:18:14,175 Ocean travellers come in many guises 149 00:18:14,176 --> 00:18:18,346 - and few are stranger than this... 150 00:18:23,568 --> 00:18:27,737 crab that spends much of its life afloat. 151 00:18:34,002 --> 00:18:38,172 It is a worrying passer-by for booby birds with delicate toes. 152 00:18:58,009 --> 00:19:00,092 Many floaters are little more than jelly, 153 00:19:00,093 --> 00:19:04,252 enclosed in membranes, but they may drift for vast distances. 154 00:19:06,348 --> 00:19:10,517 And turtles, like these olive ridleys, migrate thousands of miles every year. 155 00:19:16,782 --> 00:19:18,876 The ocean is full of such wanderers, 156 00:19:18,877 --> 00:19:20,961 riding the currents, and doing their best 157 00:19:20,962 --> 00:19:24,088 to avoid enemies while they search for food 158 00:19:24,089 --> 00:19:28,268 and a safe place to breed... 159 00:19:28,269 --> 00:19:31,395 Which is exactly what these rays are doing 160 00:19:31,396 --> 00:19:34,523 - forming the two-mile-high-club, 161 00:19:34,524 --> 00:19:36,607 gathering together for courtship on the wing, 162 00:19:36,608 --> 00:19:40,778 far above the ocean floor. 163 00:20:05,827 --> 00:20:07,910 More nomads - flying fish. 164 00:20:07,911 --> 00:20:11,048 They seem to be on every large predator's menu, 165 00:20:11,049 --> 00:20:15,208 so their whole life is spent on the run in the open ocean. 166 00:20:18,346 --> 00:20:20,440 They don't scatter their eggs 167 00:20:20,441 --> 00:20:24,600 but lay them on pieces of flotsam like this palm frond. 168 00:20:26,695 --> 00:20:28,779 If the quality of water is right, 169 00:20:28,780 --> 00:20:30,874 they will attach their eggs to the frond, 170 00:20:30,875 --> 00:20:35,034 which will then serve as a kind of life-raft for their offspring. 171 00:20:38,172 --> 00:20:42,342 But it's not only flying fish that seek nurseries. 172 00:20:46,522 --> 00:20:50,681 Any piece of floating debris can serve as a shelter under which baby fish can hide 173 00:20:56,956 --> 00:20:59,040 The only draw back, is that predators 174 00:20:59,041 --> 00:21:01,124 like this wahoo always check up on 175 00:21:01,125 --> 00:21:05,304 who's hanging about in the shadows. 176 00:21:05,305 --> 00:21:09,465 The wahoo may trail the flotsam for weeks. 177 00:21:13,655 --> 00:21:15,739 Few bits of flotsam are without their 178 00:21:15,740 --> 00:21:19,908 quota of lodgers - even man-made junk attracts them. 179 00:21:19,909 --> 00:21:21,993 And some, like this oceanic trigger fish, 180 00:21:21,994 --> 00:21:26,164 defend their squatters rights with vigour 181 00:21:34,524 --> 00:21:38,683 The triggers, in fact, tend to claim all the prime residences. 182 00:21:43,916 --> 00:21:47,042 Out here, even discarded netting can provide 183 00:21:47,043 --> 00:21:48,084 valuable shelter, so 184 00:21:48,085 --> 00:21:49,127 - in a bizarre twist 185 00:21:49,128 --> 00:21:53,287 - a wrecked trawl net like this can end up as a sanctuary for fish 186 00:21:54,350 --> 00:21:58,509 - until such time as it finally sinks. 187 00:22:02,689 --> 00:22:05,826 Indeed, a single large piece of flotsam 188 00:22:05,827 --> 00:22:08,953 can be the reason why several square miles of open ocean, 189 00:22:08,954 --> 00:22:13,113 instead of being empty, will support a fish population of hundreds of tonnes. 190 00:22:18,346 --> 00:22:21,472 This huge clump of seaweed is doing exactly that. 191 00:22:21,473 --> 00:22:25,632 It is a giant kelp plant, ripped from the rocks off the coast of California. 192 00:22:31,907 --> 00:22:35,034 Now, it's floating above thousands of metres of water, 193 00:22:35,035 --> 00:22:39,204 held up by its gas filled floats. 194 00:22:42,342 --> 00:22:46,501 Clouds of young rockfish are growing up in the safety of its shadow. 195 00:22:52,776 --> 00:22:56,935 Giants also seek out this algal flotsam. 196 00:22:59,041 --> 00:23:00,082 This is a sunfish. 197 00:23:00,083 --> 00:23:04,242 It can measure as much as four metres from fin-tip to fin-tip. 198 00:23:05,295 --> 00:23:09,465 Rather surprisingly, it has the record as the heaviest bony fish in the sea. 199 00:23:12,602 --> 00:23:16,771 Sunfish spend much of their time at depth where they feed on jellyfish; 200 00:23:16,772 --> 00:23:20,951 but it is cold and dark down there so from time to time, 201 00:23:20,952 --> 00:23:25,111 they seek a little rest and recuperation and warm up near the surface. 202 00:23:26,164 --> 00:23:30,333 They too are looking for floating kelp plants. 203 00:23:31,386 --> 00:23:33,470 Not for shelter but because here they 204 00:23:33,471 --> 00:23:37,630 can find a particular kind of fish that only lives in such places. 205 00:23:42,863 --> 00:23:47,032 Half moon fish. 206 00:23:47,033 --> 00:23:50,169 The sunfish form up in an orderly queue. 207 00:23:50,170 --> 00:23:52,254 They have a problem. 208 00:23:52,255 --> 00:23:56,414 Their skin is covered in parasites. 209 00:24:05,816 --> 00:24:07,900 The hungry half-moons will help. 210 00:24:07,901 --> 00:24:09,995 The sunfish turn their heads towards 211 00:24:09,996 --> 00:24:14,156 the surface as a clear invitation to their personal hygienists. 212 00:24:15,208 --> 00:24:17,292 The half-moons nip off - and eat 213 00:24:17,293 --> 00:24:21,463 - every parasite they can find. 214 00:24:38,162 --> 00:24:40,246 If the half moons don't do the job 215 00:24:40,247 --> 00:24:44,416 - there is another rather drastic treatment available here. 216 00:24:45,469 --> 00:24:49,628 Gulls rest on the floating kelp. 217 00:24:50,681 --> 00:24:52,775 And if the sunfish send the right signals... 218 00:24:52,776 --> 00:24:56,935 the gulls will investigate. 219 00:25:03,210 --> 00:25:07,370 Their beaks can dig out the most stubborn parasites. 220 00:25:28,249 --> 00:25:32,408 But even the very best of health clinics can only trade on a temporary basis. 221 00:25:34,514 --> 00:25:35,555 The seaweed rafts are rotting 222 00:25:35,556 --> 00:25:39,715 and will eventually lose their buoyancy. 223 00:25:48,075 --> 00:25:51,201 Then their lodgers will have to find a new home. 224 00:25:51,202 --> 00:25:53,286 If they can't, they will be eaten, 225 00:25:53,287 --> 00:25:57,457 or die and sink down into the abyss. 226 00:26:08,944 --> 00:26:13,103 But the open ocean is not entirely devoid of permanent shelter. 227 00:26:19,378 --> 00:26:23,537 A volcano is erupting from the seafloor and it is still growing. 228 00:26:59,031 --> 00:27:03,190 It has formed an island some seventy miles from the coast of New Zealand. 229 00:27:08,423 --> 00:27:10,506 Some juvenile reef fish have already arrived, 230 00:27:10,507 --> 00:27:13,634 carried here by a lucky current. 231 00:27:13,635 --> 00:27:15,718 Now they are growing up in the shelter of 232 00:27:15,719 --> 00:27:19,889 the weeds growing around the island's fringes. 233 00:27:26,154 --> 00:27:28,248 More plankton and juvenile fish 234 00:27:28,249 --> 00:27:32,417 are being swept by currents straight towards the island. 235 00:27:32,418 --> 00:27:36,578 But now there is a welcoming committee. 236 00:27:38,683 --> 00:27:40,767 Schools of trevally and blue maomao 237 00:27:40,768 --> 00:27:44,927 are patrolling the surface water. 238 00:27:51,202 --> 00:27:55,362 All are in search of a meal. 239 00:27:59,552 --> 00:28:03,711 These one kilo fish snap up every morsel of plankton they find. 240 00:28:14,156 --> 00:28:17,282 At times, the currents sweeping in from 241 00:28:17,283 --> 00:28:21,453 the open ocean bring with them all kinds of small creatures in dense concentrations 242 00:28:23,548 --> 00:28:27,707 These are mysid shrimps. 243 00:29:00,063 --> 00:29:04,242 Very little that is edible is left after such feasts. 244 00:29:04,243 --> 00:29:08,402 Islands are far from being safe havens for plankton. 245 00:29:13,635 --> 00:29:15,718 The Pacific Ocean, however, 246 00:29:15,719 --> 00:29:17,803 is peppered with over twenty three thousand... 247 00:29:17,804 --> 00:29:21,973 slands as well as countless other submerged mountains 248 00:29:21,974 --> 00:29:26,143 - sea mounts - whose summits do not break the surface. 249 00:29:28,239 --> 00:29:30,322 Juvenile fish, for their first few months 250 00:29:30,323 --> 00:29:34,493 would do well to avoid such places. 251 00:29:36,588 --> 00:29:38,672 These yellow-fin tuna, however, 252 00:29:38,673 --> 00:29:41,799 are now more than six months old and forty centimetres long 253 00:29:41,800 --> 00:29:44,937 - big enough to be able to eat fry, 254 00:29:44,938 --> 00:29:48,064 - so sea mounts for them are promising 255 00:29:48,065 --> 00:29:52,224 feeding grounds where they may hunt for several months. 256 00:29:58,499 --> 00:30:00,583 The base of a seamount. 257 00:30:00,584 --> 00:30:04,743 As currents sweep towards it they are deflected up its towering walls. 258 00:30:13,103 --> 00:30:14,145 The water, coming from the depths, 259 00:30:14,146 --> 00:30:18,315 carries both nutrients and plankton to the surface. 260 00:30:24,580 --> 00:30:27,716 Numerous reef fish take up permanent residence here, 261 00:30:27,717 --> 00:30:29,801 feeding where the currents are strongest 262 00:30:29,802 --> 00:30:33,961 and the plankton most dense. 263 00:30:42,321 --> 00:30:46,500 Where the cold water mixes with warmer water at the surface, 264 00:30:46,501 --> 00:30:48,585 there is a strange shimmering effect 265 00:30:48,586 --> 00:30:52,745 - a clear sign that the currents are running strongly. 266 00:31:10,497 --> 00:31:14,656 But these currents attract more than just coastal fish. 267 00:31:17,804 --> 00:31:21,964 Giants come here from the open ocean.... 268 00:31:23,016 --> 00:31:27,176 Hammerhead sharks - and in great numbers. 269 00:31:32,408 --> 00:31:36,567 During the day, they circle the sea mount looking for small fish at the reef edges. 270 00:31:39,715 --> 00:31:41,799 But not in order to eat them. 271 00:31:41,800 --> 00:31:43,884 They, like the sunfish, 272 00:31:43,885 --> 00:31:48,044 are looking for cleaners to rid them of their parasites. 273 00:31:54,319 --> 00:31:56,403 White-tip reef sharks gather here too. 274 00:31:56,404 --> 00:32:00,574 They do eat reef fish. 275 00:32:08,923 --> 00:32:11,018 But they prefer to hunt at night, 276 00:32:11,019 --> 00:32:15,187 when the reef fish are sleepy and easier to catch. 277 00:32:15,188 --> 00:32:19,347 Far better to rest by day and allow the cleaners to do their work... 278 00:32:27,707 --> 00:32:31,877 Even swarms of breeding trigger aren't a serious temptation. 279 00:32:41,279 --> 00:32:44,405 These triggers spend much of their time in open water, 280 00:32:44,406 --> 00:32:48,565 but they have come to the seamount to spawn. 281 00:32:56,925 --> 00:32:59,009 Trigger eggs are good food 282 00:32:59,010 --> 00:33:03,180 and the plankton-feeders gather what they can before the current sweeps them away. 283 00:33:05,275 --> 00:33:07,359 This whole community is only here 284 00:33:07,360 --> 00:33:09,444 because of the nutrients and plankton 285 00:33:09,445 --> 00:33:13,614 that the seamount deflected into the surface waters. 286 00:33:15,709 --> 00:33:19,868 But ocean-going hunters are never far away. 287 00:33:21,964 --> 00:33:24,058 Silky shark specialise in picking off 288 00:33:24,059 --> 00:33:26,143 injured fish and constantly check over 289 00:33:26,144 --> 00:33:30,303 the residents around the seamount. 290 00:33:34,493 --> 00:33:35,535 At some times of the year, 291 00:33:35,536 --> 00:33:38,662 seasonal changes make the currents especially rich in nutrients 292 00:33:38,663 --> 00:33:40,747 and then the ocean around the seamount 293 00:33:40,748 --> 00:33:44,917 becomes a virtual soup of plankton. 294 00:33:52,224 --> 00:33:56,394 At such times, hunters gather in astonishing numbers. 295 00:34:06,839 --> 00:34:08,922 Bonito, smaller relatives of the tuna. 296 00:34:08,923 --> 00:34:12,050 They are searching for still smaller plankton 297 00:34:12,051 --> 00:34:16,220 feeders that have been attracted by the bloom. 298 00:34:17,273 --> 00:34:21,432 So are these jacks - and their prey is nearby. 299 00:34:27,707 --> 00:34:30,834 A school of anchovetta has strayed up near the surface, 300 00:34:30,835 --> 00:34:32,918 even though it is broad daylight 301 00:34:32,919 --> 00:34:37,089 and hunters are on the prowl. 302 00:34:40,226 --> 00:34:42,310 These small fish can already feel 303 00:34:42,311 --> 00:34:44,395 the vibrations of the approaching predators. 304 00:34:44,396 --> 00:34:47,533 Swimming at speed, they have formed into a ball 305 00:34:47,534 --> 00:34:51,693 and now they must wait for whatever comes. 306 00:35:01,095 --> 00:35:05,254 They're been detected. 307 00:35:17,794 --> 00:35:21,953 At first the sheer scale of the bait ball seems to daunt the predators. 308 00:35:36,568 --> 00:35:40,737 But now the bonito arrive and launch the first attack. 309 00:35:48,044 --> 00:35:52,214 Still the bait ball holds together. 310 00:35:59,532 --> 00:36:01,615 The young yellow fin tuna move in. 311 00:36:01,616 --> 00:36:04,743 The speed of this attack is so great 312 00:36:04,744 --> 00:36:08,903 that gradually groups of anchovetta are splintered from the main fish ball. 313 00:37:13,614 --> 00:37:15,698 Before long the currents will shift 314 00:37:15,699 --> 00:37:19,858 and the ocean will become once more a blue tropical desert, plankton free. 315 00:37:21,954 --> 00:37:26,123 And the hunters will have to move on. 316 00:37:34,483 --> 00:37:38,642 Spinner dolphins, still searching for food. 317 00:37:44,917 --> 00:37:49,086 Their twisting leaps are, apparently, purely social displays. 318 00:37:49,087 --> 00:37:51,171 Since the hunting has been good 319 00:37:51,172 --> 00:37:55,341 many hundred have gathered together in this exuberant super-pod. 320 00:39:03,170 --> 00:39:07,329 But now the spinners are starting to hunt once more. 321 00:39:12,562 --> 00:39:16,730 Their skill in tracking food is not a secret. 322 00:39:16,731 --> 00:39:20,910 Yellow-fin tuna must be aware of it for they regularly follow them. 323 00:39:20,911 --> 00:39:22,995 But only adult tuna in their second 324 00:39:22,996 --> 00:39:26,122 or third year of life have sufficient stamina 325 00:39:26,123 --> 00:39:30,293 to keep up with the fast-moving spinners. 326 00:39:45,950 --> 00:39:50,129 These are another kind - Common Dolphin. 327 00:39:50,130 --> 00:39:54,298 They too are on the move. 328 00:39:54,299 --> 00:39:56,383 As they travel - ever inquisitive 329 00:39:56,384 --> 00:39:59,520 they pay a call on one of their larger relations 330 00:39:59,521 --> 00:40:03,690 - a pilot whale. 331 00:40:03,691 --> 00:40:04,732 The whale is not hunting. 332 00:40:04,733 --> 00:40:08,902 It's on its way to its breeding grounds in the Mediterranean. 333 00:40:08,903 --> 00:40:13,082 Pilot whales normally hunt in small family groups but in mid-summer 334 00:40:13,083 --> 00:40:16,209 they head for traditional socialising grounds 335 00:40:16,210 --> 00:40:20,369 where they will assemble in super herds several hundred strong. 336 00:40:23,517 --> 00:40:25,601 Already two families have joined together. 337 00:40:25,602 --> 00:40:29,761 The males are starting to compete for the favours of the females. 338 00:41:02,128 --> 00:41:06,287 As the weeks pass by these group rubbing- sessions will become more overtly sexual. 339 00:41:07,340 --> 00:41:11,499 But now - it's just flirting in the sun. 340 00:41:33,431 --> 00:41:37,599 Timing in the ocean can be crucial. 341 00:41:37,600 --> 00:41:40,726 In summer, the northern Atlantic waters are beginning to warm. 342 00:41:40,727 --> 00:41:43,864 The hunting is good here and by June predators 343 00:41:43,865 --> 00:41:48,024 from southern waters are heading towards the Azores. 344 00:41:57,426 --> 00:42:01,586 These are more Common Dolphin. 345 00:42:07,861 --> 00:42:09,945 Like most oceanic dolphins 346 00:42:09,946 --> 00:42:14,105 they too often travel in huge herds containing many different families. 347 00:42:20,380 --> 00:42:24,539 There is seldom enough prey in any one place to feed such numbers. 348 00:42:29,772 --> 00:42:33,931 So small groups leave the super-pod and set off on hunting expeditions. 349 00:42:39,164 --> 00:42:43,323 This group will be away from the main herd for several hours. 350 00:42:52,725 --> 00:42:56,904 By mid-day they're nearing the Islands of the Azores 351 00:42:56,905 --> 00:43:01,064 - nine hundred miles west of the Portuguese coast. 352 00:43:04,202 --> 00:43:08,372 Other hunters are already here - Cory's Shearwaters. 353 00:43:14,636 --> 00:43:17,773 Half a million of these birds breed on the Azores every year 354 00:43:17,774 --> 00:43:20,900 and scour the nearby ocean for food. 355 00:43:20,901 --> 00:43:22,985 Right now there is insufficient wind 356 00:43:22,986 --> 00:43:26,112 to support gliding flight and since flapping 357 00:43:26,113 --> 00:43:28,207 is a waste of energy they sit out the calm 358 00:43:28,208 --> 00:43:32,367 clustered in rafts and riding the gentle swells. 359 00:43:50,119 --> 00:43:54,279 By mid-afternoon the dolphin are starting to hunt in earnest. 360 00:44:01,596 --> 00:44:03,680 As the sea breeze picks up, 361 00:44:03,681 --> 00:44:07,840 the shearwaters take to the air once more. 362 00:44:17,242 --> 00:44:21,412 Out to sea, the dolphin have found prey.... 363 00:44:25,592 --> 00:44:29,751 They are driving a shoal of small mackerel up towards the surface. 364 00:44:38,111 --> 00:44:40,195 The shearwaters crowd the skies above, 365 00:44:40,196 --> 00:44:44,365 following the dolphins' every turn. 366 00:44:52,725 --> 00:44:56,885 The mackerel are still some metres down. 367 00:44:57,937 --> 00:45:00,021 But when the baitfish come sufficiently close, 368 00:45:00,022 --> 00:45:04,201 the airborne division makes its move. 369 00:45:04,202 --> 00:45:06,286 Far from being mere bystanders, 370 00:45:06,287 --> 00:45:10,446 the shearwaters can now become underwater predators themselves. 371 00:45:14,637 --> 00:45:18,796 Incredibly they can dive down to depths of several metres. 372 00:45:21,933 --> 00:45:22,985 The hunting dolphin prevent the mackerel 373 00:45:22,986 --> 00:45:27,145 from escaping downwards and both predators gorge themselves. 374 00:45:54,289 --> 00:45:58,448 Soon the diving birds outnumber the dolphin and even drive them away from their meal. 375 00:46:01,586 --> 00:46:05,755 But another squadron of predators arrives to replace the dolphin. 376 00:46:07,851 --> 00:46:12,019 Adult yellow-fin tuna. 377 00:46:12,020 --> 00:46:16,190 These are giants - two metres long. 378 00:46:21,412 --> 00:46:25,571 They are heading directly for the bait ball. 379 00:47:25,061 --> 00:47:27,144 Despite the arrival of the giant fish, 380 00:47:27,145 --> 00:47:31,315 the shearwater continue to press home their attack unfazed. 381 00:47:50,109 --> 00:47:54,268 Eventually the tuna move on, leaving the shearwaters to battle among themselves. 382 00:48:03,671 --> 00:48:06,797 As long as a predatory fish or a dolphin 383 00:48:06,798 --> 00:48:09,935 remains at the scene the mackerel can't escape to safety. 384 00:48:09,936 --> 00:48:13,062 But when the little skipjack tuna start to move away, 385 00:48:13,063 --> 00:48:17,222 gradually the bait ball begins to sink in to the depths towards safety. 386 00:48:29,751 --> 00:48:33,921 The shearwaters follow it down to the very limit of their breath-holding ability 387 00:48:34,974 --> 00:48:39,133 perhaps as deep as fifteen metres. 388 00:48:44,366 --> 00:48:48,525 At last, even they are forced to leave their quarry. 389 00:49:00,012 --> 00:49:03,149 However good or bad this summer's feeding may be 390 00:49:03,150 --> 00:49:05,233 within three months winter will be 391 00:49:05,234 --> 00:49:09,394 on its way and the temperature of these waters will drop by a few degrees. 392 00:49:10,446 --> 00:49:14,625 Then the ocean hunters will abandon the Azores once more. 393 00:49:14,626 --> 00:49:18,786 As ever, they will move on - searching for another feeding opportunity, 394 00:49:19,838 --> 00:49:24,008 the next pulse of life in the distant reaches of the Open Ocean.