1 00:00:05,558 --> 00:00:08,630 DAVID ATTENBOROUGH: The power of the sun drives the seasons, 2 00:00:08,718 --> 00:00:10,788 transforming our planet. 3 00:00:12,118 --> 00:00:15,508 Vast movements of ocean and air currents 4 00:00:15,598 --> 00:00:18,431 bring dramatic change throughout the year. 5 00:00:22,838 --> 00:00:26,797 And in a few special places, these seasonal changes 6 00:00:26,878 --> 00:00:31,030 create some of the greatest wildlife spectacles on Earth. 7 00:00:38,638 --> 00:00:40,993 Here on the western coast of North America 8 00:00:41,078 --> 00:00:42,796 in the spring of each year, 9 00:00:42,878 --> 00:00:46,473 one of the Earth's greatest travellers comes home. 10 00:00:47,918 --> 00:00:51,388 Over half a billion salmon in the Pacific Ocean 11 00:00:51,478 --> 00:00:54,117 start on a 3,000-mile journey, 12 00:00:54,198 --> 00:00:57,713 returning to spawn in the rivers where they were born. 13 00:01:03,718 --> 00:01:05,754 Travelling deep into the continent, 14 00:01:05,838 --> 00:01:09,877 these fish will not only provide food for millions of animals, 15 00:01:14,358 --> 00:01:16,155 they will also bring life 16 00:01:16,238 --> 00:01:19,947 to one of the richest habitats on Earth. 17 00:01:46,598 --> 00:01:49,670 The coast of British Columbia and Alaska 18 00:01:49,758 --> 00:01:52,955 is rimmed by spectacular mountains. 19 00:01:57,038 --> 00:01:58,596 Although it will be months 20 00:01:58,678 --> 00:02:02,512 before the salmon enter the rivers below these frozen peaks, 21 00:02:03,198 --> 00:02:07,111 one species that has spent the winter sleeping up here 22 00:02:07,198 --> 00:02:09,792 is already anticipating their return. 23 00:02:14,638 --> 00:02:17,789 In January, snug in their dens, 24 00:02:17,878 --> 00:02:20,153 the females have given birth 25 00:02:20,238 --> 00:02:23,389 and now the family is beginning to stir. 26 00:02:41,438 --> 00:02:43,349 Grizzly bears. 27 00:02:47,278 --> 00:02:52,306 Whether the cubs will live or die depends largely on one key event, 28 00:02:52,598 --> 00:02:54,111 the salmon run. 29 00:02:54,398 --> 00:02:55,797 For the next five months, 30 00:02:55,878 --> 00:02:58,711 the bears will be focused on making their appointment 31 00:02:58,798 --> 00:03:00,834 with the returning salmon. 32 00:03:19,998 --> 00:03:23,627 Surviving the first year is hard. 33 00:03:23,718 --> 00:03:27,427 Half of all grizzly cubs don't make it. 34 00:03:41,478 --> 00:03:44,436 Throughout Alaska and British Columbia, 35 00:03:44,518 --> 00:03:48,477 thousands of bear families are emerging from their winter sleep. 36 00:03:51,078 --> 00:03:53,387 There is nothing to eat up here, 37 00:03:53,478 --> 00:03:56,595 but the conditions were ideal for hibernation - 38 00:03:58,678 --> 00:04:02,148 lots of snow in which to dig a den. 39 00:04:06,198 --> 00:04:10,589 To find food, mothers must lead their cubs down to the coast 40 00:04:10,678 --> 00:04:13,476 where the snow will already be melting. 41 00:04:18,198 --> 00:04:22,908 But getting down can be a challenge for small cubs. 42 00:04:51,678 --> 00:04:54,556 These mountains are dangerous places. 43 00:04:55,158 --> 00:04:58,389 But ultimately, the fate of these bear families 44 00:04:58,478 --> 00:05:02,153 and indeed that of all bears around the North Pacific, 45 00:05:02,238 --> 00:05:04,388 depends on the salmon. 46 00:05:05,958 --> 00:05:10,986 Right now, those salmon are more than 2,000 miles away. 47 00:05:15,998 --> 00:05:17,875 After four years at sea, 48 00:05:17,958 --> 00:05:21,428 half a billion Pacific salmon are going home, 49 00:05:21,518 --> 00:05:23,793 back to fresh water 50 00:05:23,878 --> 00:05:28,110 to lay their eggs in the rivers where they themselves were hatched. 51 00:05:39,878 --> 00:05:42,438 How the salmon manage to find their way back home 52 00:05:42,518 --> 00:05:46,397 across the open ocean is still largely a mystery. 53 00:05:48,718 --> 00:05:52,154 It has only recently been discovered that a salmon's brain 54 00:05:52,238 --> 00:05:56,675 contains small particles of iron that, like a compass, 55 00:05:56,758 --> 00:05:59,591 help it steer the magnetic lines of the Earth, 56 00:05:59,678 --> 00:06:02,556 showing them exactly where to go. 57 00:06:22,558 --> 00:06:26,312 For many of these salmon, that destination is here 58 00:06:26,398 --> 00:06:30,471 along the western coast of North America in British Columbia. 59 00:06:37,358 --> 00:06:40,395 They are making their way back to their birthplace 60 00:06:40,478 --> 00:06:44,266 in one of its many freshwater rivers and streams. 61 00:06:48,238 --> 00:06:51,628 Here, amongst the network of lakes and waterways, 62 00:06:51,718 --> 00:06:56,792 lies the largest expanse of temperate rainforest left in the world. 63 00:06:59,718 --> 00:07:04,633 It stretches from southern British Columbia to Alaska. 64 00:07:11,878 --> 00:07:15,996 It's one of the most fertile landscapes on the planet. 65 00:07:28,358 --> 00:07:33,512 The temperate rainforest supports even more life than its tropical counterpart. 66 00:07:39,398 --> 00:07:43,232 For thousands of years, salmon have returned to this country 67 00:07:43,318 --> 00:07:47,596 because of the abundance of one element: fresh water. 68 00:08:13,198 --> 00:08:16,634 This is some of the purest water in the world, 69 00:08:16,718 --> 00:08:18,913 thanks to these forests. 70 00:08:33,518 --> 00:08:36,396 Where the forests are still undisturbed, 71 00:08:36,478 --> 00:08:39,709 the soil, held by millions of tree roots, 72 00:08:39,798 --> 00:08:44,349 filters the water, keeping the rivers flowing clean and pure. 73 00:08:54,758 --> 00:08:58,353 In May, grizzly bears come down to the coast 74 00:08:58,438 --> 00:09:02,954 to find something to eat while they await the arrival of the salmon. 75 00:09:04,198 --> 00:09:07,349 This is where spring arrives first. 76 00:09:15,078 --> 00:09:18,548 The cubs, still feeding on nothing but their mother's milk, 77 00:09:18,638 --> 00:09:20,594 have grown considerably. 78 00:09:25,638 --> 00:09:30,507 But it has been six months since their mother had anything to eat. 79 00:09:40,718 --> 00:09:42,709 Now they need other food 80 00:09:42,798 --> 00:09:45,915 and the search for it can lead them into danger. 81 00:09:50,278 --> 00:09:53,429 Some males will try to kill cubs. 82 00:09:57,078 --> 00:09:59,638 The breeding season has begun, 83 00:10:00,678 --> 00:10:03,795 and big males are here looking for females. 84 00:10:03,878 --> 00:10:05,357 (GROWLING) 85 00:10:20,558 --> 00:10:23,516 But at least there is something to eat here, 86 00:10:23,598 --> 00:10:26,237 even if it's only grass and sedges. 87 00:10:28,878 --> 00:10:32,587 These greens, in fact, can keep them going for months, 88 00:10:32,678 --> 00:10:34,828 but they will need something more nutritious 89 00:10:34,918 --> 00:10:36,556 if they are to put on enough fat 90 00:10:36,638 --> 00:10:39,516 to enable them to survive the next winter. 91 00:10:44,958 --> 00:10:49,907 In some places along the coast, bears find much richer food. 92 00:10:53,278 --> 00:10:57,635 It's buried, but bears have an extremely acute sense of smell 93 00:10:57,718 --> 00:11:02,314 and can sniff out a meal even if it's beneath the wet sand. 94 00:11:08,318 --> 00:11:09,512 Clams. 95 00:11:17,558 --> 00:11:20,072 It's not only bears that are drawn to the coast 96 00:11:20,158 --> 00:11:21,989 in search of food. 97 00:11:26,478 --> 00:11:31,108 There are more than 2,000 grey wolves in the Great Forest. 98 00:11:35,198 --> 00:11:39,396 They leave their cubs in the tidal areas while they hunt. 99 00:11:47,158 --> 00:11:50,150 This wolf is the pups' eldest brother. 100 00:11:50,238 --> 00:11:53,628 He's baby-sitting while the adults are away hunting. 101 00:11:53,798 --> 00:11:55,948 He doesn't have any food for the cubs, 102 00:11:56,038 --> 00:11:58,347 so they eat whatever they can find, 103 00:11:58,438 --> 00:12:01,236 even chewing the barnacles off the rocks. 104 00:12:10,078 --> 00:12:14,708 They, like the bears, are awaiting the arrival of the salmon. 105 00:12:17,918 --> 00:12:19,670 (HOWLING) 106 00:12:23,718 --> 00:12:27,836 The adults return and find an intruder. 107 00:12:29,278 --> 00:12:32,236 A hungry bear has wandered into their patch. 108 00:12:32,318 --> 00:12:33,637 (GROWLING) 109 00:12:36,758 --> 00:12:40,467 Coastal wolves will often kill and eat small bears. 110 00:12:49,918 --> 00:12:52,432 But this bear is very big. 111 00:13:11,558 --> 00:13:15,836 Eventually, they decide that this one is just too big. 112 00:13:26,918 --> 00:13:30,911 By July, the bears are all getting very hungry indeed. 113 00:13:31,718 --> 00:13:34,391 And still the salmon are not here. 114 00:13:43,198 --> 00:13:47,237 And then, after two months of travelling across the open ocean, 115 00:13:47,318 --> 00:13:49,434 the salmon reach the coast. 116 00:13:55,278 --> 00:13:59,351 As they near the shore, they begin to smell fresh water. 117 00:14:08,158 --> 00:14:10,797 There are thousands of rivers flowing into the sea, 118 00:14:10,878 --> 00:14:13,676 and the salmon have to find the particular one 119 00:14:13,758 --> 00:14:16,511 that will lead them to their birthplace. 120 00:14:19,598 --> 00:14:23,193 They have a truly extraordinary sense of smell. 121 00:14:26,238 --> 00:14:29,628 They can distinguish a single drop from their home river 122 00:14:29,718 --> 00:14:33,427 amongst eight million litres of sea water. 123 00:14:37,838 --> 00:14:42,593 As they detect the waters of home, they converge into the narrow fjords, 124 00:14:42,678 --> 00:14:45,067 which act as underwater corridors. 125 00:14:47,878 --> 00:14:51,587 But other creatures also know these corridors. 126 00:14:55,718 --> 00:14:59,711 Killer whales. They eat a lot of salmon. 127 00:15:07,838 --> 00:15:10,591 And so do Steller sea lions. 128 00:15:25,678 --> 00:15:30,627 Salmon sharks are here, too, specifically to feed on salmon. 129 00:15:36,838 --> 00:15:40,990 But there is one predator that they can never see coming. 130 00:15:44,798 --> 00:15:46,789 The bald-headed eagle. 131 00:16:33,878 --> 00:16:36,438 Once past these coastal predators, 132 00:16:36,518 --> 00:16:39,669 there is little to prevent them from reaching their home river. 133 00:16:39,758 --> 00:16:41,476 It's now late July 134 00:16:41,558 --> 00:16:45,710 and the salmon are poised at the edge of their inland realm. 135 00:16:51,918 --> 00:16:54,148 In the estuaries of the larger rivers, 136 00:16:54,238 --> 00:16:58,356 all five species of Pacific salmon mingle together. 137 00:16:58,838 --> 00:17:03,673 Pink, chum, coho, sockeye and Chinook. 138 00:17:10,158 --> 00:17:13,195 The drive to get into the rivers is strong. 139 00:17:13,278 --> 00:17:16,270 Their eggs will only survive in fresh water. 140 00:17:23,878 --> 00:17:27,393 In late July, however, the water level is often too low 141 00:17:27,478 --> 00:17:30,788 for the first salmon to enter the smaller rivers. 142 00:17:38,478 --> 00:17:40,753 That doesn't stop them trying. 143 00:17:44,798 --> 00:17:48,347 But the very water that has drawn them back home 144 00:17:48,438 --> 00:17:50,633 will eventually kill them. 145 00:17:53,318 --> 00:17:58,392 As their kidneys and other organs adjust to the sudden lack of salt water, 146 00:17:58,878 --> 00:18:01,472 they stop eating and even drinking. 147 00:18:03,198 --> 00:18:06,907 So the energy stored in their bodies is all they have 148 00:18:06,998 --> 00:18:09,990 to power their swim upriver and spawn. 149 00:18:13,798 --> 00:18:16,949 However, the salmon in the smaller streams 150 00:18:17,038 --> 00:18:19,632 have a more immediate problem. 151 00:18:21,318 --> 00:18:23,070 The low water has stopped them 152 00:18:23,158 --> 00:18:26,275 before their journey upstream can even begin. 153 00:18:34,638 --> 00:18:39,268 But their coast, every year, is swept by great storms. 154 00:18:42,918 --> 00:18:47,469 In the skies above the North Pacific, a huge eddy is forming. 155 00:18:49,518 --> 00:18:54,194 It moves towards the coast and the high coastal mountains. 156 00:19:17,078 --> 00:19:21,276 The clouds are driven up and over this massive barrier, 157 00:19:21,358 --> 00:19:24,191 and they drop their load of water. 158 00:19:50,678 --> 00:19:55,957 The Great Forest gets up to three metres of rainfall a year. 159 00:20:03,878 --> 00:20:05,834 Bears have thick coats 160 00:20:05,918 --> 00:20:09,308 and the heavy rain doesn't seem to bother them at all. 161 00:20:17,558 --> 00:20:21,710 The steep Rocky Mountains funnel the rainwater into the rivers 162 00:20:21,798 --> 00:20:23,914 and levels quickly rise. 163 00:20:35,358 --> 00:20:38,350 This is what the salmon have been waiting for. 164 00:20:47,998 --> 00:20:51,434 The first wave of travellers advance upstream. 165 00:20:58,078 --> 00:20:59,955 No sooner do they start 166 00:21:00,038 --> 00:21:02,871 than they are faced with another challenge. 167 00:21:07,478 --> 00:21:12,552 But six million years of evolution have prepared the salmon well. 168 00:21:33,878 --> 00:21:38,235 Their bodies are solid muscle and perfectly streamlined. 169 00:21:42,078 --> 00:21:44,034 Clearing these falls for a salmon 170 00:21:44,118 --> 00:21:48,111 is like a human being jumping over a four-storey building. 171 00:22:01,638 --> 00:22:06,666 In many of these falls, however, the salmon face more than just water. 172 00:22:10,358 --> 00:22:12,155 The bears know that this is 173 00:22:12,238 --> 00:22:15,833 where they can get the first proper meal of the season. 174 00:22:18,398 --> 00:22:20,309 But it's not easy. 175 00:22:23,238 --> 00:22:26,548 There is an art to catching a leaping salmon. 176 00:22:30,758 --> 00:22:33,636 And this young bear hasn't yet acquired it. 177 00:22:40,598 --> 00:22:43,635 This is what salmon were born to do. 178 00:22:51,198 --> 00:22:55,635 They are driven to get up these rivers to their spawning grounds. 179 00:22:56,558 --> 00:22:59,994 Their parents made it up here, and nothing short of death 180 00:23:00,078 --> 00:23:02,990 will stop them from repeating that journey. 181 00:23:07,478 --> 00:23:11,676 They are trying to get to the exact stretch of gravel where they hatched. 182 00:23:14,918 --> 00:23:18,991 Some lucky ones may only have to go a few miles inland. 183 00:23:19,158 --> 00:23:22,867 But others are faced with a truly daunting journey. 184 00:23:28,358 --> 00:23:31,668 The farthest that salmon have been known to swim upriver 185 00:23:31,758 --> 00:23:34,477 is 2,000 miles. 186 00:23:38,438 --> 00:23:41,828 Summer rains can be short, and when they stop 187 00:23:41,918 --> 00:23:46,355 the water levels in many of the rivers along the coast drop quickly. 188 00:23:49,158 --> 00:23:53,356 The first salmon in the rivers are once again trapped by shallow water. 189 00:23:53,438 --> 00:23:56,589 And worse, they're in bear country now. 190 00:24:00,078 --> 00:24:04,390 In early August, mother bears begin to patrol the rivers looking for fish. 191 00:24:04,478 --> 00:24:08,107 Like this one, they are usually skinny and starving. 192 00:24:17,558 --> 00:24:20,868 She and her cubs have eaten nothing but plants 193 00:24:20,958 --> 00:24:23,188 since they emerged from their den. 194 00:24:23,278 --> 00:24:26,509 They are in desperate need of a proper meal. 195 00:24:30,758 --> 00:24:35,707 Bears of all ages and experience come to the rivers to look for salmon. 196 00:24:40,278 --> 00:24:44,476 The first fish of the season, however, are hard to catch. 197 00:24:47,278 --> 00:24:50,315 This young bear is still learning how to do it. 198 00:24:50,758 --> 00:24:54,148 Step number one is spotting a salmon. 199 00:24:57,238 --> 00:24:59,957 A higher perspective usually helps. 200 00:25:03,398 --> 00:25:07,107 In these early days, fish are few and far between. 201 00:25:10,718 --> 00:25:14,506 And when they do appear, they are moving very fast. 202 00:25:43,478 --> 00:25:46,550 The salmon also have lots of places to hide. 203 00:25:46,998 --> 00:25:49,387 The rivers are only shallow in short stretches 204 00:25:49,478 --> 00:25:53,949 and they can quickly shoot across them and escape into the deep pools. 205 00:26:02,078 --> 00:26:03,909 This mother and her cubs 206 00:26:03,998 --> 00:26:05,750 are going to have to wait a little longer 207 00:26:05,838 --> 00:26:09,069 for the conditions to change before they can get the meals 208 00:26:09,158 --> 00:26:10,876 they so badly need. 209 00:26:18,198 --> 00:26:19,472 But for the salmon, 210 00:26:19,558 --> 00:26:22,914 these deep-water refuges are becoming prisons. 211 00:26:30,198 --> 00:26:34,510 It may be weeks before it rains again and they can move on. 212 00:26:40,318 --> 00:26:43,594 Their bodies are now beginning to change. 213 00:26:44,198 --> 00:26:48,749 As their sex hormones stimulate the production of eggs and sperm, 214 00:26:48,838 --> 00:26:50,988 their skin changes colour. 215 00:26:53,718 --> 00:26:57,552 Some develop a humped back and a hooked nose. 216 00:27:00,158 --> 00:27:03,309 All these changes use up precious energy. 217 00:27:03,718 --> 00:27:06,073 The longer the fish wait in these pools, 218 00:27:06,158 --> 00:27:07,876 the less likely they will be able 219 00:27:07,958 --> 00:27:11,268 to complete the journey to their spawning grounds. 220 00:27:16,078 --> 00:27:19,275 The mother bear and her cubs, finding little in the shallows, 221 00:27:19,358 --> 00:27:23,192 now try their luck in the deeper salmon-filled pools. 222 00:27:29,678 --> 00:27:32,431 The salmon are easy enough to see. 223 00:27:36,278 --> 00:27:37,996 With so many fish here, 224 00:27:38,078 --> 00:27:41,673 this young bear should surely be able to catch something. 225 00:27:46,838 --> 00:27:50,433 But finding the salmon is only part of the problem. 226 00:27:53,438 --> 00:27:55,793 Bears must pin a salmon to the stream bed 227 00:27:55,878 --> 00:27:57,391 in order to catch it. 228 00:27:57,478 --> 00:28:00,197 Not easy in deep water. 229 00:28:03,478 --> 00:28:05,867 Older bears know that it's almost impossible 230 00:28:05,958 --> 00:28:07,994 to get a meal this way. 231 00:28:11,118 --> 00:28:14,827 But while the salmon here may be relatively safe from the bears, 232 00:28:14,918 --> 00:28:16,988 they are not out of danger. 233 00:28:21,878 --> 00:28:26,508 The late summer sun is warming the water so that levels are dropping 234 00:28:26,598 --> 00:28:30,307 and the amount of dissolved oxygen is decreasing. 235 00:28:34,398 --> 00:28:38,949 The time spent in these worsening conditions is beginning to show. 236 00:28:44,558 --> 00:28:48,915 The experienced bears show the youngsters what to do. 237 00:28:49,878 --> 00:28:52,870 Catching live salmon in these pools may be difficult, 238 00:28:52,958 --> 00:28:55,028 but there are dead ones for the taking, 239 00:28:55,118 --> 00:28:57,507 if only the bears can reach them. 240 00:29:03,398 --> 00:29:07,949 The problem is that most bears don't like to get their ears wet. 241 00:29:21,838 --> 00:29:25,513 However, the old bears know a trick or two. 242 00:29:34,078 --> 00:29:37,514 It just needs a little fancy footwork. 243 00:30:02,598 --> 00:30:06,227 This year, the water levels are particularly low 244 00:30:06,318 --> 00:30:09,867 and by September, the salmon are in real trouble. 245 00:30:11,998 --> 00:30:14,717 In the confined oxygen-poor water, 246 00:30:14,798 --> 00:30:18,427 there is an increased risk of parasites and infections. 247 00:30:22,678 --> 00:30:25,750 In some years, these conditions can get so bad 248 00:30:25,838 --> 00:30:30,354 that most of the salmon die before they even reach the spawning grounds. 249 00:30:36,038 --> 00:30:40,554 What they need is more rain. And soon. 250 00:30:44,358 --> 00:30:49,113 Luckily, this year the autumn rains arrive on time. 251 00:31:15,038 --> 00:31:18,235 The salmon can set off once again. 252 00:31:20,918 --> 00:31:25,230 However, so much rain brings different challenges. 253 00:31:30,718 --> 00:31:34,870 The fish now have to battle against powerful torrents. 254 00:31:46,758 --> 00:31:51,036 But the salmon know how to turn this swift, turbulent water 255 00:31:51,118 --> 00:31:53,154 to their own advantage. 256 00:32:06,078 --> 00:32:10,674 Scarcely beating their tails, they manage to propel themselves forward 257 00:32:10,758 --> 00:32:12,828 by using the energy of the water, 258 00:32:12,918 --> 00:32:16,706 much as a sailboat does when tacking into the wind. 259 00:32:42,838 --> 00:32:45,591 But that doesn't mean there will be no further problem 260 00:32:45,678 --> 00:32:48,238 in reaching the spawning grounds. 261 00:33:09,558 --> 00:33:14,029 This is going to be the end of the road for a lot of salmon. 262 00:33:15,798 --> 00:33:18,073 These bears are really hungry. 263 00:33:18,158 --> 00:33:20,626 They haven't tasted salmon for 1 0 months 264 00:33:20,718 --> 00:33:24,393 and the big males battle for the best fishing spots. 265 00:33:24,598 --> 00:33:26,077 (GROWLING) 266 00:33:30,998 --> 00:33:34,308 The longer the salmon take over their journey upstream, 267 00:33:34,398 --> 00:33:36,468 the weaker they become. 268 00:33:39,798 --> 00:33:43,347 And these falls present them with their biggest challenge yet. 269 00:33:45,118 --> 00:33:49,430 Although the falls aren't very tall, the bears hold the high ground. 270 00:33:52,158 --> 00:33:56,913 The salmon make short exploratory leaps to see where the bears are. 271 00:34:11,798 --> 00:34:14,266 But they don't always get it right. 272 00:34:19,558 --> 00:34:23,676 This mother bear has been waiting months for this moment. 273 00:34:25,878 --> 00:34:28,915 Competition is fierce for these first salmon, 274 00:34:28,998 --> 00:34:31,751 even between a mother and her own cubs. 275 00:34:37,438 --> 00:34:40,987 More and more fish arrive at the foot of the falls. 276 00:34:51,598 --> 00:34:56,308 Eventually they have to go for it, regardless of the danger. 277 00:35:34,478 --> 00:35:37,436 But numbers are on their side. 278 00:35:37,518 --> 00:35:42,228 For every salmon that gets caught, hundreds make it past the bears. 279 00:36:15,038 --> 00:36:16,596 By early September, 280 00:36:16,678 --> 00:36:20,307 the salmon have almost reached their spawning grounds, 281 00:36:20,398 --> 00:36:25,313 that one particular patch of gravel where they hatched four years ago. 282 00:36:30,238 --> 00:36:33,275 The salmon have now travelled far inland 283 00:36:33,358 --> 00:36:36,748 and can be found from California to the Arctic Ocean, 284 00:36:36,838 --> 00:36:41,389 across a fifth of the entire continent of North America. 285 00:36:58,518 --> 00:37:01,669 But the journey has taken a heavy toll. 286 00:37:02,958 --> 00:37:07,952 For every thousand that hatched, only four manage to return. 287 00:37:11,838 --> 00:37:15,035 And even for those salmon that have made it back, 288 00:37:15,118 --> 00:37:16,870 there are still more dangers. 289 00:37:16,958 --> 00:37:19,677 They have finally reached the end of their road 290 00:37:19,758 --> 00:37:23,307 and are so tired and battered that they are easy prey. 291 00:37:23,798 --> 00:37:26,949 The advantage is fully to the bears now. 292 00:38:34,958 --> 00:38:38,030 The bears are spoiled for choice. 293 00:38:42,278 --> 00:38:43,950 In the best spawning areas, 294 00:38:44,038 --> 00:38:47,394 there are thousands of salmon in every mile of river. 295 00:38:51,278 --> 00:38:55,032 The bears here will gorge themselves for the next two months 296 00:38:55,158 --> 00:38:58,753 and the mothers with their cubs can now gain the weight they will need 297 00:38:58,838 --> 00:39:02,035 if they are to make it through the coming winter. 298 00:39:13,998 --> 00:39:18,992 The salmon are so abundant that even the little cub is having a go. 299 00:39:28,798 --> 00:39:33,349 He has caught a female pink, the smallest of the salmon species. 300 00:39:35,998 --> 00:39:40,310 He is already learning the skills he will need to survive as an adult. 301 00:39:46,478 --> 00:39:49,117 But he's got a little way to go yet. 302 00:39:53,118 --> 00:39:56,428 Although the salmon are now at the mercy of the bears, 303 00:39:56,518 --> 00:39:58,634 they will not leave this place. 304 00:39:58,718 --> 00:40:01,357 Their nature impels them to lay their eggs 305 00:40:01,438 --> 00:40:03,793 where they themselves were born. 306 00:40:11,638 --> 00:40:13,868 Even though the bears eat their fill, 307 00:40:13,958 --> 00:40:17,837 there are so many salmon that most will survive to spawn. 308 00:40:23,998 --> 00:40:28,867 The sockeye salmon's brilliant colour signals that they are ready to breed. 309 00:40:30,318 --> 00:40:34,675 Males battle with each other for position behind the females. 310 00:40:43,078 --> 00:40:47,276 The female digs out a shallow scoop as a nest. 311 00:40:57,798 --> 00:41:02,997 The male nestles up against the female, stimulating her to release her eggs. 312 00:41:06,158 --> 00:41:09,468 When she's ready, she lowers herself over the nest. 313 00:41:09,558 --> 00:41:11,788 She begins to turn out her eggs 314 00:41:11,878 --> 00:41:15,507 and the male releases a cloud of sperm into the water. 315 00:41:33,838 --> 00:41:36,432 These salmon are the lottery winners, 316 00:41:37,278 --> 00:41:41,237 the lucky ones that have succeeded in returning here to spawn. 317 00:41:42,198 --> 00:41:46,157 But there are enough of them to seed the next generation. 318 00:41:53,118 --> 00:41:56,747 The spawning season is a time of extreme abundance, 319 00:41:56,838 --> 00:41:59,716 for in the course of ensuring their own survival, 320 00:41:59,798 --> 00:42:03,996 the salmon provide food for a horde of other creatures. 321 00:42:11,198 --> 00:42:16,033 These Bonaparte gulls are collecting one of the season's great delicacies... 322 00:42:16,518 --> 00:42:18,429 salmon eggs. 323 00:42:37,918 --> 00:42:42,867 For the bears, the salmon spawning season is the pinnacle of the year. 324 00:42:49,478 --> 00:42:51,434 But for the salmon, 325 00:42:51,518 --> 00:42:55,033 it's the pinnacle of their entire lives. 326 00:43:01,158 --> 00:43:02,477 All that have reached it 327 00:43:02,558 --> 00:43:06,392 will end their days in the very place where they began them. 328 00:43:17,998 --> 00:43:21,593 The wear and tear of their long journey is now showing. 329 00:43:27,278 --> 00:43:30,395 Their bodies have been deteriorating for weeks 330 00:43:30,478 --> 00:43:34,596 and with this last act of reproduction, they are finally spent. 331 00:43:55,998 --> 00:43:57,989 But even in death, 332 00:43:58,078 --> 00:44:02,071 the salmon continue to benefit the animals of the forest. 333 00:44:07,478 --> 00:44:12,347 The mother and her cubs will continue to fatten themselves on the carcasses 334 00:44:12,438 --> 00:44:15,077 until they are ready to head back up the mountain 335 00:44:15,158 --> 00:44:17,069 to den in November. 336 00:44:22,238 --> 00:44:26,231 Why Pacific salmon have to die after they reproduce 337 00:44:26,318 --> 00:44:28,434 is not clearly understood. 338 00:44:29,158 --> 00:44:34,186 Atlantic salmon don't. They return year after year to spawn. 339 00:44:34,278 --> 00:44:37,907 But the Pacific salmons' decaying bodies nourish the rivers, 340 00:44:37,998 --> 00:44:41,434 providing abundant food for their growing eggs. 341 00:44:43,358 --> 00:44:47,397 And that is what it has been all about for the salmon. 342 00:44:48,318 --> 00:44:52,516 All their trials and tribulations have ensured that the baby salmon, 343 00:44:52,598 --> 00:44:56,034 when they emerge from these beautiful orange globes, 344 00:44:56,118 --> 00:45:00,157 will have everything they need to begin this incredible journey 345 00:45:00,238 --> 00:45:02,308 all over again. 346 00:45:11,198 --> 00:45:16,067 But the legacy of the salmon extends far beyond the rivers and streams. 347 00:45:19,238 --> 00:45:22,947 They are at the heart of a massive network of life. 348 00:45:25,398 --> 00:45:29,357 There are more than 200 species in the Great Forest alone, 349 00:45:29,518 --> 00:45:34,194 plants and insects, birds and mammals, that depend on the salmon. 350 00:45:40,038 --> 00:45:42,154 It's possible that Pacific salmon, 351 00:45:42,238 --> 00:45:45,355 between their time out at sea and their time inland, 352 00:45:45,438 --> 00:45:49,750 feed more life than any other animal species on the planet. 353 00:45:54,358 --> 00:45:58,795 And there is one more beneficiary of the salmon's legacy. 354 00:46:04,638 --> 00:46:08,756 The fish are a unique link between the ocean and the forest. 355 00:46:15,038 --> 00:46:18,951 Born in fresh water, they live their life in the sea 356 00:46:19,038 --> 00:46:22,951 and there gather nutrients with which they build their bodies. 357 00:46:29,598 --> 00:46:33,477 Now, scattered by feeding bears and wolves, 358 00:46:33,558 --> 00:46:37,471 the last bequest of these salmon is to the forest. 359 00:46:47,558 --> 00:46:51,995 Nitrogen, carbon and phosphorus that was gathered in the ocean 360 00:46:52,078 --> 00:46:55,150 is now released from their decaying bodies, 361 00:47:00,398 --> 00:47:05,188 providing the nutrients that enable these trees, 362 00:47:05,278 --> 00:47:09,157 Sitka spruce, red cedar, 363 00:47:10,598 --> 00:47:12,554 and western hemlock, 364 00:47:13,758 --> 00:47:16,909 to grow to such prodigious heights. 365 00:47:20,678 --> 00:47:25,035 It is now known that 80% of the nitrogen in these coastal forests 366 00:47:25,118 --> 00:47:28,906 where the salmon spawn, comes from the sea, 367 00:47:28,998 --> 00:47:32,115 carried in the bodies of the returning fish. 368 00:47:37,478 --> 00:47:40,993 The trees may be growing hundreds of miles from the ocean, 369 00:47:41,078 --> 00:47:44,195 but they are still nourished by its richness. 370 00:47:48,438 --> 00:47:50,349 The rivers of the Great Forest, 371 00:47:50,438 --> 00:47:54,750 like the veins and arteries of an animal, carry its lifeblood, 372 00:47:54,838 --> 00:47:57,671 the Pacific salmon, throughout. 373 00:48:05,478 --> 00:48:10,233 And no animal relies on them more than the grizzly bear. 374 00:48:15,198 --> 00:48:19,271 Thanks in large part to the abundance of the salmon run, 375 00:48:19,358 --> 00:48:23,829 these cubs have survived their first and most difficult year. 376 00:48:25,318 --> 00:48:28,037 The bears will sleep easy each winter 377 00:48:28,438 --> 00:48:33,466 as long as the Pacific salmon are able to continue their epic run. 378 00:48:34,438 --> 00:48:37,589 One of nature's great events.