The Blue Planet 1x3

1. These seas

2. - thousands of miles from nearest land

3. - are the most sterile on our planet.

4. These are marine deserts.

5. But here live the swiftest and the most powerful of all ocean hunters

6. Simply finding them is an immense challenge

7. but we are about to follow them as they search for their food

8. in this little known part of the seas - the open ocean.

9. Striped marlin - voracious predators... that can grow to three metres long.

10. They hunt mainly in daylight

11. searching the tropical oceans from close

12. to the surface down to depths of a hundred metres or so.

13. Normally the fish they feed on are widely dispersed

14. but sometimes their prey gathers in dense shoals, like these sardines.

15. This feast may last for over an hour,

16. time enough for other hunters to reach the scene.

17. Juvenile tuna join in the feeding frenzy.

18. The noise attracts a giant - a sei whale.

19. It's fourteen metres long and twenty tonnes in weight

20. - and has an appetite to match.

21. Soon the only sign that the sardines ever existed are scales

22. sinking down into the abyss.

23. Such feasts don't last long.

24. Within a few short days, waters that once swarmed...

25. with food will have been cleaned out.

26. The hunters must move elsewhere and once again

27. start their search of the seemingly featureless open ocean.

28. A manta ray - immense - five metres

29. across from the tip of one wing-like fin to the tip of the other.

30. It's travelling economy, wasting as little energy as possible,

31. as it glides through the waters of the tropics.

32. The remora fish that accompany it travel

33. more economically still - by hitching a lift.

34. Their host is searching for food - plankton,

35. the minute fish and invertebrates that float near the surface.

36. It needs lots of them and may cruise for days before...

37. it finds a good feeding ground.

38. Dusk, at the edge of a Pacific Island

39. three thousand miles from the nearest continent.

40. Here surgeon fish have assembled to spawn.

41. As they perform their nuptial dances

42. they discharge clouds of eggs and sperm into the water.

43. The manta must have known this was about

44. to happen for it arrived at exactly this critical moment.

45. And it is not the only one to do so.

46. Others are here too.

47. Now all they need to do is to sweep the water into their mouths

48. and sieve out the eggs.

49. Within an hour, the whole event will be over...

50. Any surviving eggs will be so dispersed

51. that they are not worth collecting.

52. But other perils await them as they join

53. the clouds of eggs and larvae and tiny fish

54. that drift through the surface waters of the open ocean.

55. These are the eggs of yellow fin tuna.

56. If the hatchlings survive, it will take them two years to become adults.

57. In three years, they could be nearly two metres long

58. and weigh two hundred kilograms.

59. Perhaps only one in a million will live as long as that.

60. They and the other animals and microscopic plants of the plankton

61. constitute the basis of all life out on the open ocean.

62. A storm petrel dancing on the water.

63. But this is no amiable waltz.

64. It's a hunt.

65. As they hover facing into the wind,

66. they pick out morsels from near the surface, including eggs.

67. Only a tiny percentage of the developing eggs

68. will survive long enough to hatch.

69. These newly emerged tuna are only three millimetres long

70. and although they can swim they're still very vulnerable.

71. It will be many weeks before they can swim

72. strongly enough to make any real headway in the ocean.

73. After the sun goes down,

74. other predators rise from the depths to attack the floating multitudes.

75. Darkness shrouds the arrival of battalions of dangerous drifting predators

76. These shimmering comb jellies - sea gooseberries

77. - trap their prey with sticky net-like webs

78. One ill-timed fin-stroke could bring certain death to a hatchling fish.

79. There are many kinds of these comb jellies

80. - all of them very effective hunters.

81. By dawn, most of the nocturnal feeders

82. will have returned to the depths.

83. The surviving hatchlings,

84. however, have already started on their travels.

85. Vast current systems,

86. like immense rivers, carry them around the ocean basins.

87. The boundaries between these masses of moving water...

88. form invisible barriers that can trap

89. both plankton and nutrients carried up from the depths.

90. So parts of the ocean become rich

91. with food for days or even weeks at a time

92. This attracts vast schools of plankton-feeding fish - like these sardine

93. They take in water through their mouths

94. and expel it through their gills

95. sieving out the plankton which is then funnelled down their throats.

96. The immense schools travel along the boundaries of the currents

97. - seeking the spots where the plankton is thickest.

98. As the position of the current boundaries changes constantly,

99. so does both the supply of plankton and the numbers of fish.

100. A small pod of Pacific Spotted Dolphin

101. - twenty miles from the coast of Panama.

102. Like all predators, they seek parts of the ocean

103. where their food is thickest.

104. They cover as much as hundred miles in a day.

105. And while they travel, they play.

106. They have detected the sound of schooling fish from hundreds of metres away

107. and start to track down the shoals using sonar

108. - leaving their toys behind them.

109. For the hunted there are few places to hide.

110. Schooling mackerel.

111. They have already sensed the sonar beams of approaching dolphin.

112. Their only defence is to gather into a ball.

113. Any individual that stayed out of the shoal would be quickly picked off.

114. Within it, there is at least some chance of survival.

115. The noise of the attack alerts another predator

116. - a sailfish, one of the fastest fish in the ocean.

117. It has detected rapid vibrations in the water

118. and is searching for the cause.

119. Sailfish rely on eyesight

120. for their final approach

121. so they hunt mainly in daylight.

122. When sailfish become excited they change colour

123. lighting up with bright blue stripes.

124. Since mackerel eyes are especially sensitive

125. to blue and ultraviolet, these colours confuse them

126. - making them easier to catch.

127. Far below, a blue shark returns from a squid-hunting trip in the

128. cold darkness three hundred metres down.

129. It's heading for the surface to reheat in the warmer water.

130. As it ascends, it detects the smell of oils

131. and proteins shed into the water by the panicked mackerel.

132. The trail leads both the shark

133. and its attendant pilot fish towards an easy meal.

134. Scraps and casualties float

135. in the wake of the passing mackerel school

136. Throughout the ocean, predators and prey are locked

137. in a deadly three-dimensional contest of hide and seek

138. played out over immense distances.

139. To survive they must travel.

140. The huge four metre long blue-fin tuna

141. has special blood vessels that enable it

142. to keep its body temperature significantly warmer than the surrounding water.

143. As a result, they can survive in much colder conditions

144. than any other tuna and they travel thousands of

145. miles away from their spawning grounds

146. in the tropics to hunt in cold seas

147. where the food supply is richest.

148. Ocean travellers come in many guises

149. - and few are stranger than this...

150. crab that spends much of its life afloat.

151. It is a worrying passer-by for booby birds with delicate toes.

152. Many floaters are little more than jelly,

153. enclosed in membranes, but they may drift for vast distances.

154. And turtles, like these olive ridleys, migrate thousands of miles every year.

155. The ocean is full of such wanderers,

156. riding the currents, and doing their best

157. to avoid enemies while they search for food

158. and a safe place to breed...

159. Which is exactly what these rays are doing

160. - forming the two-mile-high-club,

161. gathering together for courtship on the wing,

162. far above the ocean floor.

163. More nomads - flying fish.

164. They seem to be on every large predator's menu,

165. so their whole life is spent on the run in the open ocean.

166. They don't scatter their eggs

167. but lay them on pieces of flotsam like this palm frond.

168. If the quality of water is right,

169. they will attach their eggs to the frond,

170. which will then serve as a kind of life-raft for their offspring.

171. But it's not only flying fish that seek nurseries.

172. Any piece of floating debris can serve as a shelter under which baby fish can hide

173. The only draw back, is that predators

174. like this wahoo always check up on

175. who's hanging about in the shadows.

176. The wahoo may trail the flotsam for weeks.

177. Few bits of flotsam are without their

178. quota of lodgers - even man-made junk attracts them.

179. And some, like this oceanic trigger fish,

180. defend their squatters rights with vigour

181. The triggers, in fact, tend to claim all the prime residences.

182. Out here, even discarded netting can provide

183. valuable shelter, so

184. - in a bizarre twist

185. - a wrecked trawl net like this can end up as a sanctuary for fish

186. - until such time as it finally sinks.

187. Indeed, a single large piece of flotsam

188. can be the reason why several square miles of open ocean,

189. instead of being empty, will support a fish population of hundreds of tonnes.

190. This huge clump of seaweed is doing exactly that.

191. It is a giant kelp plant, ripped from the rocks off the coast of California.

192. Now, it's floating above thousands of metres of water,

193. held up by its gas filled floats.

194. Clouds of young rockfish are growing up in the safety of its shadow.

195. Giants also seek out this algal flotsam.

196. This is a sunfish.

197. It can measure as much as four metres from fin-tip to fin-tip.

198. Rather surprisingly, it has the record as the heaviest bony fish in the sea.

199. Sunfish spend much of their time at depth where they feed on jellyfish;

200. but it is cold and dark down there so from time to time,

201. they seek a little rest and recuperation and warm up near the surface.

202. They too are looking for floating kelp plants.

203. Not for shelter but because here they

204. can find a particular kind of fish that only lives in such places.

205. Half moon fish.

206. The sunfish form up in an orderly queue.

207. They have a problem.

208. Their skin is covered in parasites.

209. The hungry half-moons will help.

210. The sunfish turn their heads towards

211. the surface as a clear invitation to their personal hygienists.

212. The half-moons nip off - and eat

213. - every parasite they can find.

214. If the half moons don't do the job

215. - there is another rather drastic treatment available here.

216. Gulls rest on the floating kelp.

217. And if the sunfish send the right signals...

218. the gulls will investigate.

219. Their beaks can dig out the most stubborn parasites.

220. But even the very best of health clinics can only trade on a temporary basis.

221. The seaweed rafts are rotting

222. and will eventually lose their buoyancy.

223. Then their lodgers will have to find a new home.

224. If they can't, they will be eaten,

225. or die and sink down into the abyss.

226. But the open ocean is not entirely devoid of permanent shelter.

227. A volcano is erupting from the seafloor and it is still growing.

228. It has formed an island some seventy miles from the coast of New Zealand.

229. Some juvenile reef fish have already arrived,

230. carried here by a lucky current.

231. Now they are growing up in the shelter of

232. the weeds growing around the island's fringes.

233. More plankton and juvenile fish

234. are being swept by currents straight towards the island.

235. But now there is a welcoming committee.

236. Schools of trevally and blue maomao

237. are patrolling the surface water.

238. All are in search of a meal.

239. These one kilo fish snap up every morsel of plankton they find.

240. At times, the currents sweeping in from

241. the open ocean bring with them all kinds of small creatures in dense concentrations

242. These are mysid shrimps.

243. Very little that is edible is left after such feasts.

244. Islands are far from being safe havens for plankton.

245. The Pacific Ocean, however,

246. is peppered with over twenty three thousand...

247. slands as well as countless other submerged mountains

248. - sea mounts - whose summits do not break the surface.

249. Juvenile fish, for their first few months

250. would do well to avoid such places.

251. These yellow-fin tuna, however,

252. are now more than six months old and forty centimetres long

253. - big enough to be able to eat fry,

254. - so sea mounts for them are promising

255. feeding grounds where they may hunt for several months.

256. The base of a seamount.

257. As currents sweep towards it they are deflected up its towering walls.

258. The water, coming from the depths,

259. carries both nutrients and plankton to the surface.

260. Numerous reef fish take up permanent residence here,

261. feeding where the currents are strongest

262. and the plankton most dense.

263. Where the cold water mixes with warmer water at the surface,

264. there is a strange shimmering effect

265. - a clear sign that the currents are running strongly.

266. But these currents attract more than just coastal fish.

267. Giants come here from the open ocean...

268. Hammerhead sharks - and in great numbers.

269. During the day, they circle the sea mount looking for small fish at the reef edges.

270. But not in order to eat them.

271. They, like the sunfish,

272. are looking for cleaners to rid them of their parasites.

273. White-tip reef sharks gather here too.

274. They do eat reef fish.

275. But they prefer to hunt at night,

276. when the reef fish are sleepy and easier to catch.

277. Far better to rest by day and allow the cleaners to do their work...

278. Even swarms of breeding trigger aren't a serious temptation.

279. These triggers spend much of their time in open water,

280. but they have come to the seamount to spawn.

281. Trigger eggs are good food

282. and the plankton-feeders gather what they can before the current sweeps them away.

283. This whole community is only here

284. because of the nutrients and plankton

285. that the seamount deflected into the surface waters.

286. But ocean-going hunters are never far away.

287. Silky shark specialise in picking off

288. injured fish and constantly check over

289. the residents around the seamount.

290. At some times of the year,

291. seasonal changes make the currents especially rich in nutrients

292. and then the ocean around the seamount

293. becomes a virtual soup of plankton.

294. At such times, hunters gather in astonishing numbers.

295. Bonito, smaller relatives of the tuna.

296. They are searching for still smaller plankton

297. feeders that have been attracted by the bloom.

298. So are these jacks - and their prey is nearby.

299. A school of anchovetta has strayed up near the surface,

300. even though it is broad daylight

301. and hunters are on the prowl.

302. These small fish can already feel

303. the vibrations of the approaching predators.

304. Swimming at speed, they have formed into a ball

305. and now they must wait for whatever comes.

306. They're been detected.

307. At first the sheer scale of the bait ball seems to daunt the predators.

308. But now the bonito arrive and launch the first attack.

309. Still the bait ball holds together.

310. The young yellow fin tuna move in.

311. The speed of this attack is so great

312. that gradually groups of anchovetta are splintered from the main fish ball.

313. Before long the currents will shift

314. and the ocean will become once more a blue tropical desert, plankton free.

315. And the hunters will have to move on.

316. Spinner dolphins, still searching for food.

317. Their twisting leaps are, apparently, purely social displays.

318. Since the hunting has been good

319. many hundred have gathered together in this exuberant super-pod.

320. But now the spinners are starting to hunt once more.

321. Their skill in tracking food is not a secret.

322. Yellow-fin tuna must be aware of it for they regularly follow them.

323. But only adult tuna in their second

324. or third year of life have sufficient stamina

325. to keep up with the fast-moving spinners.

326. These are another kind - Common Dolphin.

327. They too are on the move.

328. As they travel - ever inquisitive

329. they pay a call on one of their larger relations

330. - a pilot whale.

331. The whale is not hunting.

332. It's on its way to its breeding grounds in the Mediterranean.

333. Pilot whales normally hunt in small family groups but in mid-summer

334. they head for traditional socialising grounds

335. where they will assemble in super herds several hundred strong.

336. Already two families have joined together.

337. The males are starting to compete for the favours of the females.

338. As the weeks pass by these group rubbing- sessions will become more overtly sexual.

339. But now - it's just flirting in the sun.

340. Timing in the ocean can be crucial.

341. In summer, the northern Atlantic waters are beginning to warm.

342. The hunting is good here and by June predators

343. from southern waters are heading towards the Azores.

344. These are more Common Dolphin.

345. Like most oceanic dolphins

346. they too often travel in huge herds containing many different families.

347. There is seldom enough prey in any one place to feed such numbers.

348. So small groups leave the super-pod and set off on hunting expeditions.

349. This group will be away from the main herd for several hours.

350. By mid-day they're nearing the Islands of the Azores

351. - nine hundred miles west of the Portuguese coast.

352. Other hunters are already here - Cory's Shearwaters.

353. Half a million of these birds breed on the Azores every year

354. and scour the nearby ocean for food.

355. Right now there is insufficient wind

356. to support gliding flight and since flapping

357. is a waste of energy they sit out the calm

358. clustered in rafts and riding the gentle swells.

359. By mid-afternoon the dolphin are starting to hunt in earnest.

360. As the sea breeze picks up,

361. the shearwaters take to the air once more.

362. Out to sea, the dolphin have found prey...

363. They are driving a shoal of small mackerel up towards the surface.

364. The shearwaters crowd the skies above,

365. following the dolphins' every turn.

366. The mackerel are still some metres down.

367. But when the baitfish come sufficiently close,

368. the airborne division makes its move.

369. Far from being mere bystanders,

370. the shearwaters can now become underwater predators themselves.

371. Incredibly they can dive down to depths of several metres.

372. The hunting dolphin prevent the mackerel

373. from escaping downwards and both predators gorge themselves.

374. Soon the diving birds outnumber the dolphin and even drive them away from their meal.

375. But another squadron of predators arrives to replace the dolphin.

376. Adult yellow-fin tuna.

377. These are giants - two metres long.

378. They are heading directly for the bait ball.

379. Despite the arrival of the giant fish,

380. the shearwater continue to press home their attack unfazed.

381. Eventually the tuna move on, leaving the shearwaters to battle among themselves.

382. As long as a predatory fish or a dolphin

383. remains at the scene the mackerel can't escape to safety.

384. But when the little skipjack tuna start to move away,

385. gradually the bait ball begins to sink in to the depths towards safety.

386. The shearwaters follow it down to the very limit of their breath-holding ability

387. perhaps as deep as fifteen metres.

388. At last, even they are forced to leave their quarry.

389. However good or bad this summer's feeding may be

390. within three months winter will be

391. on its way and the temperature of these waters will drop by a few degrees.

392. Then the ocean hunters will abandon the Azores once more.

393. As ever, they will move on - searching for another feeding opportunity,

394. the next pulse of life in the distant reaches of the Open Ocean.