1 00:00:07,200 --> 00:00:09,220 This vast stretch of water 2 00:00:09,220 --> 00:00:12,060 is the mouth of our mightiest river, 3 00:00:12,060 --> 00:00:13,220 the Tay. 4 00:00:15,180 --> 00:00:18,660 Its flow is greater than the Thames and the Severn combined. 5 00:00:20,980 --> 00:00:24,860 The wildest and most unspoiled of all our great rivers. 6 00:00:28,140 --> 00:00:31,820 Its waters give life to countless curious creatures... 7 00:00:33,300 --> 00:00:34,980 ..from birds that swim... 8 00:00:36,460 --> 00:00:37,900 ..to fish that fly. 9 00:00:40,740 --> 00:00:42,460 I'm a writer and naturalist 10 00:00:42,460 --> 00:00:44,020 and, ever since I was tiny, 11 00:00:44,020 --> 00:00:46,340 I have been obsessed with the natural world. 12 00:00:47,940 --> 00:00:51,260 I've always wanted to follow a river from its source to sea... 13 00:00:53,740 --> 00:00:57,140 ..to explore the incredible connections that a running ribbon 14 00:00:57,140 --> 00:00:59,500 of water has to the wider world. 15 00:01:03,220 --> 00:01:06,540 From its birth in Scotland's Western Highlands, 16 00:01:06,540 --> 00:01:10,980 the Tay flows for 120 miles through some of our most remote 17 00:01:10,980 --> 00:01:12,820 and stunning landscapes... 18 00:01:15,620 --> 00:01:19,460 ..until its final dissolution in the cold North Sea. 19 00:01:21,260 --> 00:01:25,180 Unlocking the mysteries of this vast river, I'll explore what makes 20 00:01:25,180 --> 00:01:28,460 these threads of wildness so vital for our world. 21 00:01:31,700 --> 00:01:35,380 Travelling from spring onward to winter, new technology 22 00:01:35,380 --> 00:01:38,740 will unlock incredible perspectives on the river. 23 00:01:41,260 --> 00:01:44,100 From the vantage of a soaring hawk 24 00:01:44,100 --> 00:01:46,260 to microscopic marvels... 25 00:01:47,700 --> 00:01:51,060 ..I'll meet the people drawn to the river's silvery waters... 26 00:01:53,460 --> 00:01:57,180 ..the Tay guardians striving to uncover why its legendary 27 00:01:57,180 --> 00:01:59,780 salmon are disappearing... 28 00:02:01,940 --> 00:02:05,660 ..and the scientists searching for new knowledge hidden 29 00:02:05,660 --> 00:02:07,460 in the beauty of the natural world. 30 00:02:09,020 --> 00:02:11,140 This is making me feel quite emotional. 31 00:02:13,900 --> 00:02:15,660 Four seasons, 32 00:02:15,660 --> 00:02:18,380 wonderful wildlife, 33 00:02:18,380 --> 00:02:22,340 and the answers to some of the biggest questions of our time. 34 00:02:24,060 --> 00:02:26,700 All connected by the living thread 35 00:02:26,700 --> 00:02:28,980 of one extraordinary river. 36 00:02:50,580 --> 00:02:52,140 I'm starting with the search 37 00:02:52,140 --> 00:02:54,380 for the source of Britain's biggest river. 38 00:02:57,780 --> 00:02:59,780 Unlike some other great rivers, 39 00:02:59,780 --> 00:03:02,500 there's no signpost at the Tay's beginning. 40 00:03:02,500 --> 00:03:04,140 Not even a path. 41 00:03:08,020 --> 00:03:11,620 To reach a river's source, you have to follow its longest 42 00:03:11,620 --> 00:03:13,740 stream to its very end. 43 00:03:16,300 --> 00:03:20,740 It sounds an easy task, but this boggy, misty place 44 00:03:20,740 --> 00:03:22,860 is full of uncertainties. 45 00:03:27,660 --> 00:03:30,860 The Tay's source lies somewhere on Ben Lui. 46 00:03:30,860 --> 00:03:33,740 It's one of Britain's tallest mountains 47 00:03:33,740 --> 00:03:35,540 and one of our wettest places. 48 00:03:41,700 --> 00:03:45,780 All around me, water is rushing down hillsides. 49 00:03:45,780 --> 00:03:49,020 Quite a lot of the future River Tay is in the sky above me 50 00:03:49,020 --> 00:03:50,620 and falling onto me. 51 00:03:54,300 --> 00:03:58,860 I'm only ten miles from Atlantic waters to the West but these slopes 52 00:03:58,860 --> 00:04:02,460 send the Tay on an eastward course, 53 00:04:02,460 --> 00:04:07,300 flowing for 120 miles until it meets the North Sea. 54 00:04:17,220 --> 00:04:20,260 I've been hiking uphill for about two hours now 55 00:04:20,260 --> 00:04:21,940 in all weathers. 56 00:04:21,940 --> 00:04:24,380 There's been sun and rain and hail 57 00:04:24,380 --> 00:04:26,180 but I'm nearly there. 58 00:04:31,260 --> 00:04:33,500 It's almost impossible to pinpoint 59 00:04:33,500 --> 00:04:36,060 exactly which trickling rill of meltwater 60 00:04:36,060 --> 00:04:37,940 extends furthest up the hill. 61 00:04:39,580 --> 00:04:42,500 But one of these thawing patches of snow marks 62 00:04:42,500 --> 00:04:45,260 the furthest the Tay reaches from the sea. 63 00:04:55,020 --> 00:04:57,420 And there's so much water pouring down the hill here 64 00:04:57,420 --> 00:04:59,420 that I kind of... 65 00:04:59,420 --> 00:05:02,420 It makes me wonder why it is that, when a river's beginnings 66 00:05:02,420 --> 00:05:06,180 so clearly is multiple, we really want it to have this single 67 00:05:06,180 --> 00:05:07,620 point where it starts. 68 00:05:08,860 --> 00:05:12,100 And, I guess, you know, we're human. 69 00:05:12,100 --> 00:05:14,180 We're born, we live, we die. 70 00:05:14,180 --> 00:05:16,460 And we, kind of, can't help but see rivers 71 00:05:16,460 --> 00:05:18,540 through that lens of our own lives. 72 00:05:23,980 --> 00:05:26,060 A river doesn't care where it begins. 73 00:05:27,700 --> 00:05:31,780 What makes the Tay our greatest river isn't a single dot on the map 74 00:05:31,780 --> 00:05:35,940 marking its source, it's the sheer profusion 75 00:05:35,940 --> 00:05:38,860 of trickling rivulets that feed into its waters. 76 00:05:42,780 --> 00:05:44,780 Thousands of running, silver threads 77 00:05:44,780 --> 00:05:47,820 joining together as gravity pulls them downhill. 78 00:05:53,060 --> 00:05:57,380 These streams merge into larger tributaries that collectively drain 79 00:05:57,380 --> 00:06:00,620 2,500 square miles of soil. 80 00:06:05,100 --> 00:06:08,580 The Tay is not just a single ribbon of moving water, 81 00:06:08,580 --> 00:06:10,860 it's a whole geographic region. 82 00:06:12,580 --> 00:06:15,220 One vast, living ecosystem. 83 00:06:29,060 --> 00:06:32,140 The first streams that flow from this barren landscape 84 00:06:32,140 --> 00:06:35,180 are little more than rain and melting snow. 85 00:06:35,180 --> 00:06:37,780 Fast-flowing, cold and pure, 86 00:06:37,780 --> 00:06:40,060 they support very little life. 87 00:06:45,340 --> 00:06:47,140 With one famous exception. 88 00:06:49,420 --> 00:06:53,660 The Tay system's most iconic resident, 89 00:06:53,660 --> 00:06:55,620 the legendary king of fish. 90 00:06:57,060 --> 00:07:00,700 Salmons' lives both begin and end in mountain streams. 91 00:07:02,860 --> 00:07:05,340 But their extraordinary life story 92 00:07:05,340 --> 00:07:07,140 carries them into faraway oceans. 93 00:07:09,140 --> 00:07:13,180 And this vast domain begins just two miles below the source. 94 00:07:19,780 --> 00:07:22,020 This is The Hole In The Wall waterfall. 95 00:07:23,340 --> 00:07:26,460 In the 18th century, it was marked on maps as the source of the Tay. 96 00:07:26,460 --> 00:07:28,620 For salmon, it is the beginning of the Tay. 97 00:07:28,620 --> 00:07:31,540 They can't actually get any higher up the river than the bottom 98 00:07:31,540 --> 00:07:32,820 of that waterfall. 99 00:07:32,820 --> 00:07:34,980 They can't jump that kind of length of water. 100 00:07:37,660 --> 00:07:42,140 Every autumn, adult Atlantic salmon lay eggs in riverbed gravel. 101 00:07:44,660 --> 00:07:48,020 All winter they lie buried, waiting for their moment. 102 00:07:58,380 --> 00:08:01,460 Spring is the season of awakenings and, 103 00:08:01,460 --> 00:08:04,140 even in a barren mountain stream, 104 00:08:04,140 --> 00:08:06,620 the changing year sparks new life. 105 00:08:08,420 --> 00:08:11,580 Warmer water triggers the hatching of tiny salmon fry. 106 00:08:19,980 --> 00:08:23,540 These fish will spend the next two years in these upland streams. 107 00:08:25,860 --> 00:08:28,340 Yet they'll never grow much larger than minnows. 108 00:08:30,780 --> 00:08:33,380 To become the king of fish, they need to move 109 00:08:33,380 --> 00:08:35,060 to richer waters to feed. 110 00:08:44,380 --> 00:08:47,660 Those few creatures that can thrive here are specially equipped 111 00:08:47,660 --> 00:08:49,500 for this hostile territory. 112 00:08:53,060 --> 00:08:55,140 Like this mayfly nymph. 113 00:08:55,140 --> 00:08:58,020 It's a very different shape from its downstream cousins. 114 00:09:01,180 --> 00:09:05,660 Its dirty front legs are shaped like racing car aerofoils. 115 00:09:05,660 --> 00:09:08,940 So, instead of washing it away, the rushing water 116 00:09:08,940 --> 00:09:11,100 pins it harder to the riverbed. 117 00:09:19,820 --> 00:09:22,260 Another animal built for fast-flowing water 118 00:09:22,260 --> 00:09:24,860 is the world's only swimming songbird. 119 00:09:26,780 --> 00:09:29,700 BIRD TWEETS 120 00:09:34,540 --> 00:09:39,100 Bright, bold and decidedly odd, it's one of my favourite birds - 121 00:09:39,100 --> 00:09:40,620 the dipper. 122 00:09:46,100 --> 00:09:49,420 Dippers dive into the icy water to hunt. 123 00:09:49,420 --> 00:09:53,220 Young mayfly and tiny salmon are among their favourite snacks. 124 00:09:57,260 --> 00:09:59,700 Thanks to denser bones than other birds, 125 00:09:59,700 --> 00:10:01,420 they sink rather than float. 126 00:10:16,460 --> 00:10:20,220 This pair built their nest right at the edge of a 20-metre waterfall. 127 00:10:36,700 --> 00:10:39,900 And the first chicks are just emerging onto the riverside. 128 00:10:56,260 --> 00:10:59,660 Soon, the chicks will hunt these turbulent waters on their own. 129 00:11:06,060 --> 00:11:08,620 Those that can adapt can thrive here. 130 00:11:13,540 --> 00:11:15,020 But, in recent decades, 131 00:11:15,020 --> 00:11:16,980 the Tay's most famous resident 132 00:11:16,980 --> 00:11:18,740 has been disappearing, 133 00:11:18,740 --> 00:11:21,340 here and right across the ecosystem. 134 00:11:26,700 --> 00:11:28,500 As in many UK rivers, 135 00:11:28,500 --> 00:11:32,700 numbers of once-abundant salmon have dropped by 70% 136 00:11:32,700 --> 00:11:35,340 over the past 30 years. 137 00:11:35,340 --> 00:11:38,300 Because their life cycle covers such a vast area, 138 00:11:38,300 --> 00:11:41,820 it's been hard to pinpoint an exact cause. 139 00:11:47,620 --> 00:11:51,300 But on one of the Tay's upland tributaries, the River Garry, 140 00:11:51,300 --> 00:11:53,900 a team are trying to unravel the mystery. 141 00:11:59,820 --> 00:12:04,140 The Tay Fisheries Board have placed this trap here to gently gather 142 00:12:04,140 --> 00:12:06,460 juvenile salmon, known as smolts. 143 00:12:10,020 --> 00:12:13,340 Spring's floods and the rising water temperature are triggering them 144 00:12:13,340 --> 00:12:15,620 to move downstream in search of food. 145 00:12:22,500 --> 00:12:24,540 Mike, what have you got in the bucket here? 146 00:12:24,540 --> 00:12:26,980 We have five, wild Atlantic salmon smolts. 147 00:12:26,980 --> 00:12:28,460 These little fish are about 148 00:12:28,460 --> 00:12:30,420 two years old and they're starting 149 00:12:30,420 --> 00:12:32,860 their migration to sea. Ah, they're marvellous. 150 00:12:34,340 --> 00:12:37,540 In preparation for the ocean, the young fishes' bodies 151 00:12:37,540 --> 00:12:40,220 are undergoing an incredible transformation 152 00:12:40,220 --> 00:12:43,260 with a wonderful name - smoltification. 153 00:12:45,260 --> 00:12:48,420 The body becomes elongated, its head changes shape, 154 00:12:48,420 --> 00:12:51,100 its eyes get bigger because this fish has to hunt 155 00:12:51,100 --> 00:12:52,380 in salt water. 156 00:12:52,380 --> 00:12:54,420 And also there are cells within the body 157 00:12:54,420 --> 00:12:56,300 that alter because a fish travelling 158 00:12:56,300 --> 00:12:59,380 from a freshwater lifestyle to a saltwater lifestyle 159 00:12:59,380 --> 00:13:01,140 is a big change for a fish. 160 00:13:02,740 --> 00:13:05,980 This team hope hi-tech surveillance can help pinpoint 161 00:13:05,980 --> 00:13:07,860 where fish are disappearing. 162 00:13:07,860 --> 00:13:09,460 We take a length and a weight before 163 00:13:09,460 --> 00:13:10,860 we tag them. So, this one's... 164 00:13:10,860 --> 00:13:13,100 Under anaesthetic, Mike places 165 00:13:13,100 --> 00:13:15,340 a tiny transponder tag harmlessly 166 00:13:15,340 --> 00:13:17,580 into the body cavity of each smolt. 167 00:13:17,580 --> 00:13:19,980 Just going to make a very small... Tiny incision. 168 00:13:19,980 --> 00:13:22,060 ..tiny incision in their belly. 169 00:13:24,620 --> 00:13:25,740 Amazing. 170 00:13:25,740 --> 00:13:27,180 And done with such care and skill. 171 00:13:27,180 --> 00:13:28,420 It's really wonderful. 172 00:13:28,420 --> 00:13:31,420 Then you put the fish into the recovery bucket. Wonderful. 173 00:13:31,420 --> 00:13:35,860 The project basically involves us tagging migrating salmon smolts. 174 00:13:35,860 --> 00:13:38,380 They'll obviously migrate to sea with the other smolts 175 00:13:38,380 --> 00:13:40,300 and then we can record these fish 176 00:13:40,300 --> 00:13:42,700 as adults as they return into freshwater. 177 00:13:44,980 --> 00:13:48,340 The tagging project has only been running for two years. 178 00:13:48,340 --> 00:13:51,860 Too soon to tell whether the cause is more predators 179 00:13:51,860 --> 00:13:53,580 catching young salmon 180 00:13:53,580 --> 00:13:57,460 or other changes affecting adults downstream or at sea. 181 00:13:59,100 --> 00:14:01,060 But the proportion of tagged fish 182 00:14:01,060 --> 00:14:03,060 that eventually return will help 183 00:14:03,060 --> 00:14:05,540 pinpoint the most likely problem. 184 00:14:05,540 --> 00:14:08,900 We've tagged 2,300 salmon this year. 185 00:14:08,900 --> 00:14:12,380 Wow. So, we should see a fairly vast number of these 186 00:14:12,380 --> 00:14:15,020 returning next year and the year after. 187 00:14:16,460 --> 00:14:19,380 Mike is determined to bring back the fish whose abundance here 188 00:14:19,380 --> 00:14:20,740 was once taken for granted. 189 00:14:24,260 --> 00:14:26,860 How does it feel to know that the fish with your transponder in 190 00:14:26,860 --> 00:14:30,700 is swimming around the ocean somewhere? Do you think about them? 191 00:14:30,700 --> 00:14:33,820 Yes, I do. I do think about them, yeah. What they're up to? 192 00:14:33,820 --> 00:14:35,540 I'm hoping that they come back. 193 00:14:42,780 --> 00:14:46,580 Adult salmon are rightly renowned for their heroic upstream journeys. 194 00:14:51,500 --> 00:14:56,620 But the first migration of these tiny fish downstream, 195 00:14:56,620 --> 00:14:59,380 moving up to 100 miles in a fortnight... 196 00:15:01,540 --> 00:15:05,140 ..is perhaps even more moving and miraculous. 197 00:15:20,940 --> 00:15:24,340 Salmon are one of the Tay's great treasures 198 00:15:24,340 --> 00:15:25,940 but the river has other gifts, 199 00:15:25,940 --> 00:15:27,300 if you know where to look. 200 00:15:31,820 --> 00:15:34,540 Spring's melting snow is unleashing 201 00:15:34,540 --> 00:15:36,660 torrents of fast-flowing water. 202 00:15:38,500 --> 00:15:42,380 It draws weekend hunters to these upland streams 203 00:15:42,380 --> 00:15:44,220 looking for flakes of pure gold. 204 00:15:54,980 --> 00:15:56,340 Four wee bits. 205 00:15:58,140 --> 00:15:59,860 Worth crashing that up. Yeah. 206 00:15:59,860 --> 00:16:01,300 I haven't got a pocket. 207 00:16:01,300 --> 00:16:03,100 I haven't got one either. 208 00:16:04,780 --> 00:16:07,460 It's in the quartz veins and then, over millions of years, 209 00:16:07,460 --> 00:16:11,300 the rocks rolling down the river erode the quartz 210 00:16:11,300 --> 00:16:13,460 and then that brings the gold up. 211 00:16:13,460 --> 00:16:16,100 And then the force of the water washes the gold 212 00:16:16,100 --> 00:16:18,060 and, then, cos it's heavy, 213 00:16:18,060 --> 00:16:20,780 it settles down into the bedrock 214 00:16:20,780 --> 00:16:23,260 and stays there until... 215 00:16:23,260 --> 00:16:25,100 ..until it's found. 216 00:16:27,900 --> 00:16:30,380 Panning for commercial gain is not allowed here. 217 00:16:32,940 --> 00:16:36,300 The few flakes they sift from the cold water are strictly 218 00:16:36,300 --> 00:16:38,220 for passion projects. 219 00:16:38,220 --> 00:16:43,580 I'm due to get married in less then two weeks to my fiancee, Charlotte. 220 00:16:43,580 --> 00:16:47,100 Instead of going to a goldsmith's to buy our wedding bands, 221 00:16:47,100 --> 00:16:48,380 I'm actually going to use 222 00:16:48,380 --> 00:16:50,740 the gold that I've collected. 223 00:16:50,740 --> 00:16:53,900 Currently, Charlotte's ring is looking like this and I've got 224 00:16:53,900 --> 00:16:58,580 less than two weeks to get that into a wedding band for her, 225 00:16:58,580 --> 00:17:00,300 which looks like this. 226 00:17:00,300 --> 00:17:02,620 And she's quite happy with that because I'm actually 227 00:17:02,620 --> 00:17:05,260 using my gold instead of it being sat there in my collection. 228 00:17:08,020 --> 00:17:10,740 To preserve the river's most precious creatures, 229 00:17:10,740 --> 00:17:12,620 restrictions ensure panners do not 230 00:17:12,620 --> 00:17:14,900 disturb streams where salmon eggs 231 00:17:14,900 --> 00:17:16,500 might hide in the gravel. 232 00:17:29,860 --> 00:17:33,580 It's late April and, just a few miles from the source, 233 00:17:33,580 --> 00:17:36,180 the warming air and melting snow 234 00:17:36,180 --> 00:17:39,020 are unleashing all sorts of hidden wonders. 235 00:17:45,180 --> 00:17:47,940 There's something about the smell of this place that reminds me 236 00:17:47,940 --> 00:17:50,060 of every other spring I've ever had. 237 00:17:50,060 --> 00:17:54,180 It's a very pungent, earthy smell that's so evocative. 238 00:17:54,180 --> 00:17:56,620 It takes me back to all the springs I've ever known. 239 00:18:00,140 --> 00:18:03,660 In this high, wet country there are few obvious signs 240 00:18:03,660 --> 00:18:06,140 of the changing season. 241 00:18:06,140 --> 00:18:08,780 No bright daffodils to catch the eye. 242 00:18:10,180 --> 00:18:12,340 Spring's awakening is more subtle, 243 00:18:12,340 --> 00:18:14,540 where mosses and lichens carpet 244 00:18:14,540 --> 00:18:16,340 the river bank rocks and trees. 245 00:18:24,540 --> 00:18:27,540 We tend to see beauty in the landscape in a, kind of, big scale. 246 00:18:27,540 --> 00:18:30,620 We look at hills and waterfalls and rock formations. 247 00:18:30,620 --> 00:18:33,900 But I think, if you get your eye in, the really true, exquisite beauty 248 00:18:33,900 --> 00:18:36,940 in these particular landscapes is very small. 249 00:18:36,940 --> 00:18:38,500 So, if you look at this tree here, 250 00:18:38,500 --> 00:18:39,740 you'll see it's covered 251 00:18:39,740 --> 00:18:41,780 in mosses, in wonderful lichens. 252 00:18:41,780 --> 00:18:44,340 These ones are foliose, they're branching lichens. 253 00:18:44,340 --> 00:18:46,580 These are woodrush, these are ground-dwelling species 254 00:18:46,580 --> 00:18:48,220 that are growing on the tree. 255 00:18:48,220 --> 00:18:50,260 We've got so many different species of mosses. 256 00:18:51,580 --> 00:18:52,700 We could just spend ages! 257 00:18:52,700 --> 00:18:54,340 This is a lovely one, here. 258 00:18:54,340 --> 00:18:55,700 It's called feather moss. 259 00:18:56,980 --> 00:18:58,380 Exquisite branching. 260 00:19:01,060 --> 00:19:02,300 It's magical! 261 00:19:08,260 --> 00:19:11,460 And there are marvels here at an even smaller scale. 262 00:19:13,420 --> 00:19:15,500 Responding to spring's warmth, 263 00:19:15,500 --> 00:19:17,620 networks of microscopic life 264 00:19:17,620 --> 00:19:20,580 are branching and spreading through the wet river bank. 265 00:19:25,180 --> 00:19:28,900 Professor Paul Hoskisson's lab at the University of Strathclyde 266 00:19:28,900 --> 00:19:30,900 studies a soil-dwelling bacteria 267 00:19:30,900 --> 00:19:33,140 that's given us astonishing gifts. 268 00:19:35,140 --> 00:19:36,820 Wow! What am I seeing? 269 00:19:36,820 --> 00:19:41,100 So, you're seeing the streptomyces magnified about 1,000 times. 270 00:19:41,100 --> 00:19:43,980 That's the main growing part 271 00:19:43,980 --> 00:19:46,620 of the organism that forages 272 00:19:46,620 --> 00:19:48,180 in soil for nutrients. 273 00:19:48,180 --> 00:19:51,300 And then you can see, stained in red, the spores as they start 274 00:19:51,300 --> 00:19:53,220 to make their fruiting bodies. 275 00:19:53,220 --> 00:19:54,580 Exquisitely beautiful. 276 00:19:56,380 --> 00:19:58,300 Paul's team are interested in 277 00:19:58,300 --> 00:20:01,980 the chemical streptomyces bacteria release as they grow. 278 00:20:05,020 --> 00:20:07,980 These organisms are competing with lots of other bacteria, 279 00:20:07,980 --> 00:20:10,660 fungi, worms, all within the soil, 280 00:20:10,660 --> 00:20:13,300 and they need to make chemicals in order to give them an advantage 281 00:20:13,300 --> 00:20:15,140 in that environment. 282 00:20:15,140 --> 00:20:18,380 So, the antibiotics that they make kill bacteria, 283 00:20:18,380 --> 00:20:21,540 they make antifungals to kill the fungal competitors. 284 00:20:24,340 --> 00:20:26,580 Antibiotics, such as streptomycin, 285 00:20:26,580 --> 00:20:29,260 are a by-product of this chemical warfare 286 00:20:29,260 --> 00:20:31,700 and have become life-savers to us. 287 00:20:34,740 --> 00:20:37,220 But one of the other chemicals streptomyces makes 288 00:20:37,220 --> 00:20:39,580 transports me straight back to the riverside. 289 00:20:39,580 --> 00:20:41,820 Streptomyces for you. 290 00:20:41,820 --> 00:20:44,260 Oh, my goodness, that waft of smell. 291 00:20:47,220 --> 00:20:49,820 It smells like spring in the incubator. That's astonishing. 292 00:20:49,820 --> 00:20:53,260 Yes, that's a molecule that streptomyces makes called geosmin. 293 00:20:53,260 --> 00:20:56,740 It's the smell of wet, spring soil. 294 00:20:56,740 --> 00:20:57,900 They're so beautiful. 295 00:20:57,900 --> 00:20:59,860 Little silvery lines of colonies, here. 296 00:21:02,220 --> 00:21:05,260 Geosmin is one of these chemicals that we don't really know 297 00:21:05,260 --> 00:21:06,820 the full function of. 298 00:21:06,820 --> 00:21:09,660 But we believe it's there to repel insects that may come and eat 299 00:21:09,660 --> 00:21:11,820 the streptomyces spores. 300 00:21:11,820 --> 00:21:14,900 I remember many years ago being in a desert 301 00:21:14,900 --> 00:21:18,340 in one of the Gulf states and it rained very heavily after 302 00:21:18,340 --> 00:21:20,180 a lot of hot weather and I smelt this smell. 303 00:21:20,180 --> 00:21:22,260 It was almost overpowering. 304 00:21:22,260 --> 00:21:26,300 Yeah, the human nose is very sensitive to the smell of geosmin 305 00:21:26,300 --> 00:21:28,780 and lots of animals are very sensitive to it. 306 00:21:28,780 --> 00:21:31,500 I mean, it's been hypothesised that it's one of the ways 307 00:21:31,500 --> 00:21:34,020 that animals like camels can find water in the desert, 308 00:21:34,020 --> 00:21:36,020 is by following the smell of geosmin. 309 00:21:41,820 --> 00:21:45,780 I love this theory that, deep in our evolutionary past, 310 00:21:45,780 --> 00:21:48,420 we developed the ability to sense water, 311 00:21:48,420 --> 00:21:50,420 we can, kind of, smell it, 312 00:21:50,420 --> 00:21:53,540 even when it's not in sight, and be drawn towards it. 313 00:22:06,020 --> 00:22:09,540 There's something so magnetic about rivers. 314 00:22:09,540 --> 00:22:11,540 They're the only moving things in the landscape. 315 00:22:13,260 --> 00:22:15,140 This one looks like a, kind of, river of mercury, 316 00:22:15,140 --> 00:22:16,820 it's reflecting the sky. 317 00:22:19,220 --> 00:22:21,340 There's white noise all around me. 318 00:22:23,620 --> 00:22:25,380 I could watch this for hours. 319 00:22:29,380 --> 00:22:30,660 It's just magic! 320 00:22:41,340 --> 00:22:45,300 The transformation from winter to spring is now complete. 321 00:22:47,100 --> 00:22:49,460 But the water's flow is constant. 322 00:22:54,380 --> 00:22:58,460 And, two centuries ago, on a Tay tributary called the Tilt, 323 00:22:58,460 --> 00:23:02,940 the river's ceaseless flow helped spark an idea that shook our world 324 00:23:02,940 --> 00:23:05,420 to its core - deep time. 325 00:23:12,100 --> 00:23:14,340 This is a beautiful little river. 326 00:23:14,340 --> 00:23:17,500 And I've come here to find a spot where the power of running water 327 00:23:17,500 --> 00:23:19,300 helped fundamentally change 328 00:23:19,300 --> 00:23:21,860 our understanding of the age of the Earth. 329 00:23:25,660 --> 00:23:30,260 In 1785, an Edinburgh man of science named James Hutton arrived 330 00:23:30,260 --> 00:23:32,020 here on horseback. 331 00:23:34,260 --> 00:23:37,500 He was pondering one of the big questions of his time - 332 00:23:37,500 --> 00:23:39,180 how old is the Earth? 333 00:23:42,100 --> 00:23:46,580 Back then, the consensus pretty much was that the Earth's rocks formed 334 00:23:46,580 --> 00:23:50,700 from the worldwide sea left behind after Noah's flood. 335 00:23:50,700 --> 00:23:55,260 All the rocks crystallised and were left behind as the sea drained away. 336 00:23:58,020 --> 00:24:01,740 But, for Hutton, the idea that all Earth's rocks were created 337 00:24:01,740 --> 00:24:05,020 in one single, biblical moment didn't stack up. 338 00:24:07,540 --> 00:24:11,820 He suspected new rock could form inside the Earth. 339 00:24:14,340 --> 00:24:16,060 But he needed evidence. 340 00:24:17,860 --> 00:24:21,060 Here, on the River Tilt, he found it. 341 00:24:21,060 --> 00:24:23,740 Here, the river's worn through layers of rock, 342 00:24:23,740 --> 00:24:25,860 giving us a glimpse back through time. 343 00:24:34,100 --> 00:24:36,820 It looks like I'm standing amidst just rocks, 344 00:24:36,820 --> 00:24:39,860 but there is actually evidence of an unimaginably 345 00:24:39,860 --> 00:24:42,420 violent, ancient event. 346 00:24:42,420 --> 00:24:46,460 This pale-coloured granite was once a finger of molten lava 347 00:24:46,460 --> 00:24:49,180 flooding its way through the cracks in the layered bedrock. 348 00:24:49,180 --> 00:24:51,100 You can see where it's met weak points, 349 00:24:51,100 --> 00:24:53,700 fissures in that rock, it's prising them apart. 350 00:24:55,420 --> 00:24:59,180 This could only be the aftermath of an eruption. 351 00:24:59,180 --> 00:25:04,060 Hot liquid rock prising apart cold, old bedrock. 352 00:25:08,940 --> 00:25:12,220 Hutton had seen back through time and found 353 00:25:12,220 --> 00:25:14,580 the smoking gun he needed. 354 00:25:16,300 --> 00:25:20,140 The Earth's landscape wasn't created in a single event. 355 00:25:20,140 --> 00:25:24,060 New rocks are constantly being created, then worn away. 356 00:25:27,580 --> 00:25:32,660 What we see in our brief lives is just a moment in a constant cycle 357 00:25:32,660 --> 00:25:34,820 of destruction and renewal. 358 00:25:37,180 --> 00:25:41,540 Hutton's revelation in this place introduced a new concept for us. 359 00:25:41,540 --> 00:25:43,500 A new concept of time. 360 00:25:43,500 --> 00:25:45,060 Deep time. 361 00:25:45,060 --> 00:25:47,900 The understanding that the Earth was way more ancient 362 00:25:47,900 --> 00:25:50,540 than the 6,000 years of biblical time. 363 00:25:58,140 --> 00:26:01,260 Hutton radically shifted our comprehension of our place 364 00:26:01,260 --> 00:26:02,660 in the world. 365 00:26:07,300 --> 00:26:10,340 He's known now as the grandfather of geology 366 00:26:10,340 --> 00:26:13,220 and I think you can put him amongst that select group of legendary 367 00:26:13,220 --> 00:26:15,340 figures who changed the way we see ourselves in relation 368 00:26:15,340 --> 00:26:16,740 to the universe. 369 00:26:16,740 --> 00:26:20,620 Like Copernicus, who moved the Earth from the centre of all things. 370 00:26:20,620 --> 00:26:24,700 Or Darwin, who placed humans among other animals on the tree of life. 371 00:26:24,700 --> 00:26:27,140 But Hutton? Something special. 372 00:26:27,140 --> 00:26:30,580 These rocks and this river, he gave us a new understanding 373 00:26:30,580 --> 00:26:33,300 of the unimaginably vast sweep of history. 374 00:26:40,900 --> 00:26:45,100 As the Tay's many upland tributaries tumble on downstream, 375 00:26:45,100 --> 00:26:49,660 they merge, one by one, to create an ever larger river. 376 00:26:53,580 --> 00:26:56,020 But, just as these waters gather power, 377 00:26:56,020 --> 00:26:58,420 there's an unexpected transformation. 378 00:27:04,940 --> 00:27:09,140 15 miles long and 150 metres deep, 379 00:27:09,140 --> 00:27:11,060 this is Loch Tay, 380 00:27:11,060 --> 00:27:14,700 the tenth largest volume of freshwater in the UK. 381 00:27:14,700 --> 00:27:17,700 Lying only 23 miles from the source, 382 00:27:17,700 --> 00:27:19,940 the pure mountain streams that feed 383 00:27:19,940 --> 00:27:22,660 into the loch carry very few nutrients. 384 00:27:24,620 --> 00:27:28,860 So, it may look like an oasis but it's really more 385 00:27:28,860 --> 00:27:30,460 of a wet desert. 386 00:27:41,180 --> 00:27:44,260 Life is sparse in this vast volume of water. 387 00:27:47,340 --> 00:27:51,660 Salmon smolts race through here en route to the sea's riches. 388 00:27:54,980 --> 00:27:59,460 And the loch's beautiful, silent waters exert a pull that I find 389 00:27:59,460 --> 00:28:01,060 hard to resist. 390 00:28:04,500 --> 00:28:07,060 There's something about standing next to a body of water 391 00:28:07,060 --> 00:28:11,220 like this that does something very strange to the soul. 392 00:28:13,020 --> 00:28:14,380 And it's not just me. 393 00:28:15,540 --> 00:28:17,740 These waters have drawn people for millennia. 394 00:28:21,300 --> 00:28:27,780 2,500 years ago, our Iron Age ancestors constructed huge wooden 395 00:28:27,780 --> 00:28:29,580 buildings over the water. 396 00:28:31,460 --> 00:28:34,900 This is a reconstruction of one of 18 crannogs 397 00:28:34,900 --> 00:28:36,420 that once lined the loch. 398 00:28:41,580 --> 00:28:45,260 What motivated people to create these huge feats of engineering 399 00:28:45,260 --> 00:28:46,860 remains deeply mysterious. 400 00:28:48,540 --> 00:28:52,220 Perhaps they were compelled by the water's spiritual significance? 401 00:28:56,380 --> 00:28:59,100 There's something about water, something about rivers and lakes, 402 00:28:59,100 --> 00:29:01,100 that draws us deeply to them. 403 00:29:01,100 --> 00:29:03,260 And, if you look at nearly all the world's religions, 404 00:29:03,260 --> 00:29:07,460 they all seem to have a spring or a river or a lake at their heart. 405 00:29:09,860 --> 00:29:13,460 But, looking out at the loch here, this implacable grey surface 406 00:29:13,460 --> 00:29:17,980 and a very low misty cloud, I certainly feel a, kind of, stirring. 407 00:29:29,300 --> 00:29:32,780 At the loch's easterly edge, the water gathers speed again. 408 00:29:34,740 --> 00:29:40,100 For the first time this river is now officially named the Tay. 409 00:29:40,100 --> 00:29:42,740 And it's packed with power and energy. 410 00:29:51,420 --> 00:29:54,620 12 miles from the crannogs lie Grandtully Rapids. 411 00:29:56,980 --> 00:29:59,300 The draw here is pure thrill. 412 00:30:00,660 --> 00:30:03,060 The noise and force of whitewater. 413 00:30:45,140 --> 00:30:49,860 It's one of the last stretches of fast running water on the Tay 414 00:30:49,860 --> 00:30:54,140 and marks the beginnings of a new kind of river 415 00:30:54,140 --> 00:30:56,900 where life's challenges are very different, 416 00:30:56,900 --> 00:30:58,860 especially at this time of year. 417 00:31:12,020 --> 00:31:13,100 It's late June. 418 00:31:14,980 --> 00:31:18,020 Summer means longer, warmer days. 419 00:31:18,020 --> 00:31:22,140 A few months for the river's life, in all its forms, to flourish. 420 00:31:30,380 --> 00:31:34,420 This river is far from the raging torrents of the mountain burns. 421 00:31:34,420 --> 00:31:37,180 It's moving here, this water, through a much calmer, 422 00:31:37,180 --> 00:31:38,860 gentler landscape. 423 00:31:42,180 --> 00:31:44,940 These are gentle waters to inhabit. 424 00:31:44,940 --> 00:31:47,660 Here, summertime really is easy living. 425 00:31:50,420 --> 00:31:53,260 Life thrives in the long sunny days. 426 00:31:57,740 --> 00:32:00,420 The salmon smolts that set out two months ago are already 427 00:32:00,420 --> 00:32:02,140 far out at sea. 428 00:32:03,940 --> 00:32:07,180 But these wide waters teem with trout, pike, 429 00:32:07,180 --> 00:32:10,820 perch and adult salmon now returning from their fattening trips 430 00:32:10,820 --> 00:32:12,980 to the sea. 431 00:32:12,980 --> 00:32:15,500 And the ospreys high above know it. 432 00:32:31,860 --> 00:32:36,020 Their pale, keen eyes scan for a sliver of shadow moving 433 00:32:36,020 --> 00:32:37,780 against the riverbed. 434 00:33:24,660 --> 00:33:29,660 It's a food chain connecting water and sky 435 00:33:29,660 --> 00:33:33,860 and fuelling all this abundance is one simple ingredient... 436 00:33:33,860 --> 00:33:35,500 ..summer sun. 437 00:33:37,940 --> 00:33:41,140 Light streaming into the river is feeding a great gathering 438 00:33:41,140 --> 00:33:42,860 of green creatures. 439 00:33:47,300 --> 00:33:50,660 Some float free, others cling to the rocks. 440 00:33:54,100 --> 00:33:56,980 Along with bacteria, algae are the foundation 441 00:33:56,980 --> 00:33:58,660 of all the river's food. 442 00:34:04,340 --> 00:34:05,780 Miniature predators 443 00:34:05,780 --> 00:34:07,620 suck them into their jaws. 444 00:34:10,500 --> 00:34:14,620 These then become meals for larger river dwellers 445 00:34:14,620 --> 00:34:15,700 and so on. 446 00:34:17,500 --> 00:34:19,980 But algae aren't just underwater fodder. 447 00:34:21,460 --> 00:34:25,180 They're among Earth's oldest life forms 448 00:34:25,180 --> 00:34:28,700 and these tiny creatures are helping to solve one 449 00:34:28,700 --> 00:34:31,700 of the great mysteries of science - 450 00:34:31,700 --> 00:34:35,900 how cells first joined together to form bodies. 451 00:34:39,220 --> 00:34:42,340 Many are just a single cell 452 00:34:42,340 --> 00:34:45,140 but in some species cells link up 453 00:34:45,140 --> 00:34:47,620 into cooperating colonies. 454 00:34:50,140 --> 00:34:53,700 And it's this ability that fascinates scientists. 455 00:35:00,700 --> 00:35:04,380 This is an algae called volvox 456 00:35:04,380 --> 00:35:08,460 found in ponds, puddles and streams all over the world. 457 00:35:08,460 --> 00:35:13,220 Each of these spheres is a colony of around 1,000 cells. 458 00:35:18,460 --> 00:35:21,540 At the University of Cambridge, Professor Ray Goldstein 459 00:35:21,540 --> 00:35:24,580 leads a team that studies them. 460 00:35:24,580 --> 00:35:28,420 We've got volvox on the microscope live, for you to see. 461 00:35:28,420 --> 00:35:30,460 And there they are. And they're really beautiful. 462 00:35:30,460 --> 00:35:32,060 You can see the spinning motion. 463 00:35:32,060 --> 00:35:33,740 Beautiful. 464 00:35:33,740 --> 00:35:35,940 I've seen still photographs of them before 465 00:35:35,940 --> 00:35:38,180 but they've always looked a little bit like, sort of, 466 00:35:38,180 --> 00:35:42,060 expensive lampshades. But these, in motion, are astonishing! 467 00:35:42,060 --> 00:35:44,900 They look like little transparent planets. 468 00:35:48,540 --> 00:35:52,420 Each cell that makes up volvox's surface is identical. 469 00:35:54,260 --> 00:35:58,660 What's amazing is that, even though there is no brain or nervous system 470 00:35:58,660 --> 00:36:02,860 in overall control, the entire sphere can move 471 00:36:02,860 --> 00:36:04,260 in a purposeful way. 472 00:36:08,460 --> 00:36:10,900 Here, hundreds of volvox colonies 473 00:36:10,900 --> 00:36:13,460 are all swimming towards a light. 474 00:36:21,020 --> 00:36:25,180 To find out how a single colony of cells can swim with purpose, 475 00:36:25,180 --> 00:36:26,780 Ray's team are studying 476 00:36:26,780 --> 00:36:28,580 the parts of volvox's cells 477 00:36:28,580 --> 00:36:30,260 that generate movement. 478 00:36:31,980 --> 00:36:33,380 So, each of the cells on the surface 479 00:36:33,380 --> 00:36:34,940 has two hair-like appendages called 480 00:36:34,940 --> 00:36:37,220 flagella, that beat roughly like this, 481 00:36:37,220 --> 00:36:39,780 and they're organised on the surface in a very regular 482 00:36:39,780 --> 00:36:41,940 pattern so that the beating is basically from the North Pole 483 00:36:41,940 --> 00:36:43,300 to the South pole. 484 00:36:45,460 --> 00:36:49,620 The flagella beat very fast to make the colony move. 485 00:36:49,620 --> 00:36:52,620 But, slowing down footage of a single cell, 486 00:36:52,620 --> 00:36:54,500 you can see them in action. 487 00:37:01,060 --> 00:37:04,260 When two cells are positioned at a distance apart, 488 00:37:04,260 --> 00:37:06,980 their flagella beat independently. 489 00:37:11,140 --> 00:37:13,180 But, when they're moved closer together, 490 00:37:13,180 --> 00:37:15,340 something magical happens. 491 00:37:21,340 --> 00:37:24,100 The neighbouring cell's flagella reacts to the movement 492 00:37:24,100 --> 00:37:25,940 of the fluid around them. 493 00:37:27,100 --> 00:37:30,740 Like a team of rowers, the cells beat in synchrony. 494 00:37:32,300 --> 00:37:36,260 When we look at these organisms in enough detail to see 495 00:37:36,260 --> 00:37:38,140 their individual flagella, we see that they are 496 00:37:38,140 --> 00:37:39,820 synchronised with each other. 497 00:37:42,500 --> 00:37:45,980 So, that seems to be the basic underlying mechanism 498 00:37:45,980 --> 00:37:48,020 by which they talk to each other. 499 00:37:48,020 --> 00:37:50,860 They're actually talking to each other through the fluid 500 00:37:50,860 --> 00:37:52,460 in which they are immersed. 501 00:37:54,100 --> 00:37:56,700 From the combined reactions of 1,000 502 00:37:56,700 --> 00:37:59,100 perfectly arranged individual cells, 503 00:37:59,100 --> 00:38:02,100 the entire colony moves as one. 504 00:38:06,500 --> 00:38:09,540 And, once colonies of linked cells found ways to move, 505 00:38:09,540 --> 00:38:13,900 it's possible to imagine how cells could start to combine 506 00:38:13,900 --> 00:38:16,940 into ever larger and more complicated bodies. 507 00:38:21,540 --> 00:38:24,340 And, over vast expanses of time, 508 00:38:24,340 --> 00:38:27,140 evolve into creatures like us 509 00:38:27,140 --> 00:38:30,860 with 37 trillion cooperating cells. 510 00:38:34,100 --> 00:38:37,660 You know, the more I look at the tiniest kinds of life, 511 00:38:37,660 --> 00:38:42,260 the more I feel incredibly humbled about how little I know 512 00:38:42,260 --> 00:38:46,980 and how complex and beautiful all those diverse creatures are. 513 00:38:46,980 --> 00:38:48,740 It's quite astonishing. 514 00:39:03,420 --> 00:39:05,220 It's early July. 515 00:39:05,220 --> 00:39:07,780 I am now more than halfway along the river. 516 00:39:11,660 --> 00:39:15,820 The calm, deep waters are ideal resting grounds for mature salmon 517 00:39:15,820 --> 00:39:17,460 returning from the sea. 518 00:39:24,020 --> 00:39:26,500 And there's another species waiting for them. 519 00:39:31,380 --> 00:39:35,180 Anglers are drawn from all over the world to the Tay's waters. 520 00:39:39,780 --> 00:39:41,740 And, at nearby Glendelvine, 521 00:39:41,740 --> 00:39:44,820 nearly 100 years ago a record was set. 522 00:39:47,140 --> 00:39:51,340 Salmon fishing history was made right here on the Tay. 523 00:39:51,340 --> 00:39:54,260 On the 7th of October 1922 local angler 524 00:39:54,260 --> 00:39:57,420 Georgina Ballantyne sat with her father in a boat. 525 00:39:57,420 --> 00:40:01,460 It was getting late and she made one last cast before going home. 526 00:40:01,460 --> 00:40:03,500 Just behind that rock in the rapids. 527 00:40:05,580 --> 00:40:07,220 And she felt a tug on the line. 528 00:40:07,220 --> 00:40:08,980 She'd hooked a fish. 529 00:40:08,980 --> 00:40:11,780 And what happened was, in her own words, 530 00:40:11,780 --> 00:40:14,260 a Homeric battle. 531 00:40:14,260 --> 00:40:17,260 The fish raced 300 yards downstream, closely followed 532 00:40:17,260 --> 00:40:19,740 by Georgina and her father in their boat, 533 00:40:19,740 --> 00:40:23,580 and then what happened was two hours and five minutes of nerve-racking 534 00:40:23,580 --> 00:40:27,220 anxiety, thrilling excitement and stiff work. 535 00:40:32,540 --> 00:40:35,580 It was completely dark by the time Georgina hauled her prize 536 00:40:35,580 --> 00:40:37,060 into the boat. 537 00:40:37,060 --> 00:40:38,660 It was an astonishing fish. 538 00:40:38,660 --> 00:40:41,060 When she hooked it she must've had no idea that she would break 539 00:40:41,060 --> 00:40:43,020 a record that still stands. 540 00:40:43,020 --> 00:40:46,980 That fish was 64lb in weight, nearly five feet long 541 00:40:46,980 --> 00:40:48,940 and 28 inches in girth. 542 00:40:50,620 --> 00:40:52,220 It's still the biggest salmon 543 00:40:52,220 --> 00:40:54,220 ever landed in British freshwater... 544 00:40:57,260 --> 00:40:59,100 ..despite nearly a century of anglers 545 00:40:59,100 --> 00:41:00,900 trying to beat Georgina's record. 546 00:41:07,180 --> 00:41:10,860 A little way downstream, another female angler, 547 00:41:10,860 --> 00:41:13,860 Claire Mercer Nairne, fishes at Meikleour. 548 00:41:16,020 --> 00:41:17,780 She's passionate about encouraging 549 00:41:17,780 --> 00:41:20,060 more women into angling. 550 00:41:20,060 --> 00:41:23,700 Like many fly-fishers, she ties her own flies. 551 00:41:26,380 --> 00:41:28,620 So, what are you making on that particular fly? 552 00:41:28,620 --> 00:41:30,580 What kind of fly are you making? A Munro Killer. 553 00:41:30,580 --> 00:41:32,180 A Munro Killer. 554 00:41:32,180 --> 00:41:34,620 It's an extraordinarily violent name! 555 00:41:37,940 --> 00:41:41,180 Fishing for Atlantic salmon is especially challenging for one 556 00:41:41,180 --> 00:41:42,660 very big reason. 557 00:41:44,580 --> 00:41:45,860 They don't eat. 558 00:41:47,140 --> 00:41:50,740 Once fish return to fresh water, their stomachs shrink 559 00:41:50,740 --> 00:41:53,580 and they survive entirely off fat put on at sea. 560 00:42:00,660 --> 00:42:02,740 No-one knows exactly why salmon 561 00:42:02,740 --> 00:42:05,060 snatch at a combination of brightly 562 00:42:05,060 --> 00:42:07,100 coloured feathers and thread. 563 00:42:08,460 --> 00:42:11,660 It may be simple curiosity, it may be aggressive 564 00:42:11,660 --> 00:42:13,180 defence of territory. 565 00:42:15,580 --> 00:42:19,780 I'm hoping my Munro Killer is the right mix of flash and fancy 566 00:42:19,780 --> 00:42:22,020 to help me catch my very first salmon. 567 00:42:26,260 --> 00:42:27,700 Give a little tug. 568 00:42:27,700 --> 00:42:30,900 Now, you just... Forward here like this? 569 00:42:30,900 --> 00:42:32,140 Forward. Yeah. 570 00:42:33,180 --> 00:42:34,820 Back... 571 00:42:34,820 --> 00:42:36,660 ..and go. 572 00:42:36,660 --> 00:42:37,940 Lovely. 573 00:42:37,940 --> 00:42:39,220 Shall I have a go? 574 00:42:40,300 --> 00:42:42,940 This is the most terrifying thing I've ever done in my life. 575 00:42:42,940 --> 00:42:44,540 This side? See, slowly you retrieve. 576 00:42:44,540 --> 00:42:45,980 Slowly retrieve. 577 00:42:45,980 --> 00:42:47,340 You retrieve a little line. 578 00:42:47,340 --> 00:42:49,380 And then bi-i-ig, big... 579 00:42:50,780 --> 00:42:52,740 Slow! Slowly. 580 00:42:52,740 --> 00:42:55,100 Like that, but slowly and better! 581 00:42:55,100 --> 00:42:57,860 No, it looked like you were missing your train. I know! OK. 582 00:42:57,860 --> 00:43:00,180 So, slowly, slowly, slowly. 583 00:43:00,180 --> 00:43:01,820 So, rod here, hand here. OK. 584 00:43:01,820 --> 00:43:03,580 Slow, slow, slow. 585 00:43:05,060 --> 00:43:06,660 OK. Yep. 586 00:43:06,660 --> 00:43:07,940 And then back. 587 00:43:07,940 --> 00:43:09,420 Wait, wait! 588 00:43:09,420 --> 00:43:10,700 OK. I'm too fast! You did it! 589 00:43:10,700 --> 00:43:11,940 I did it? OK. 590 00:43:13,060 --> 00:43:14,740 Then slowly, slowly. 591 00:43:14,740 --> 00:43:16,140 Watch the time. 592 00:43:17,900 --> 00:43:19,980 Much better! Yeah, yeah, it's much easier... 593 00:43:19,980 --> 00:43:21,220 Watch the time. 594 00:43:25,380 --> 00:43:28,340 I've been a falconer all my life. 595 00:43:28,340 --> 00:43:31,780 Like angling, it's a pursuit traditionally dominated by men. 596 00:43:33,620 --> 00:43:36,420 So, it's personally so satisfying to find out 597 00:43:36,420 --> 00:43:39,060 that, despite their scarcity on the river bank, 598 00:43:39,060 --> 00:43:41,340 women often land the biggest fish. 599 00:43:43,340 --> 00:43:45,860 This fact has been the source of much debate. 600 00:43:50,500 --> 00:43:54,180 Entire books have been written on the topic. 601 00:43:54,180 --> 00:43:58,580 One suggestion is that female pheromones might somehow entice 602 00:43:58,580 --> 00:44:00,260 salmon onto the hook. 603 00:44:03,300 --> 00:44:09,100 There's so many stories of women 604 00:44:09,100 --> 00:44:12,340 attracting these absolute monsters. 605 00:44:12,340 --> 00:44:14,580 This is very, very funny. This is like, erm... 606 00:44:14,580 --> 00:44:16,860 It's not the women's skill that's making them catch it, 607 00:44:16,860 --> 00:44:19,500 it's the fact that they're just passively attracting the fish. 608 00:44:19,500 --> 00:44:21,860 This sounds to be like a very suspicious theory! 609 00:44:21,860 --> 00:44:27,060 And so I believe that men had to come up 610 00:44:27,060 --> 00:44:30,020 with this pheromones theory 611 00:44:30,020 --> 00:44:33,100 simply because they were annoyed. 612 00:44:38,860 --> 00:44:41,980 Because there are such worries about salmon numbers in the Tay, 613 00:44:41,980 --> 00:44:48,020 anglers are heavily encouraged to return every fish to the river 614 00:44:48,020 --> 00:44:51,340 so as many as possible have a chance to breed. 615 00:45:00,420 --> 00:45:03,100 80 miles from its source, the Tay flows through 616 00:45:03,100 --> 00:45:04,540 a flatter landscape. 617 00:45:07,580 --> 00:45:11,980 Farmland covers the fertile soil of the gently sloping river valley. 618 00:45:15,100 --> 00:45:17,500 Order and straight lines contrast 619 00:45:17,500 --> 00:45:19,500 with the soft curve of the waterway. 620 00:45:24,340 --> 00:45:27,180 But farmers aren't the only ones making their mark 621 00:45:27,180 --> 00:45:28,540 on the Tay's landscape. 622 00:45:31,580 --> 00:45:34,100 They've recently been joined by a creature whose industry 623 00:45:34,100 --> 00:45:35,620 matches our own. 624 00:45:42,700 --> 00:45:45,460 After a 500 year absence, 625 00:45:45,460 --> 00:45:47,140 beavers are back. 626 00:45:51,380 --> 00:45:55,100 It's late July and this adult pair have two new kids. 627 00:45:56,620 --> 00:45:59,060 They're making their first, tentative splashes 628 00:45:59,060 --> 00:46:00,780 outside the home lodge. 629 00:46:08,860 --> 00:46:12,220 Beavers don't eat salmon, they're vegetarians. 630 00:46:12,220 --> 00:46:15,300 Their diet consists of tree bark and fresh branches. 631 00:46:20,500 --> 00:46:24,860 But, nevertheless, their presence here is highly divisive. 632 00:46:29,900 --> 00:46:32,860 Beaver country looks like a modernist sculpture park 633 00:46:32,860 --> 00:46:34,900 carved by rodent teeth. 634 00:46:44,500 --> 00:46:46,700 Animals the size of a pet spaniel 635 00:46:46,700 --> 00:46:48,860 have moved more than a tonne of mud 636 00:46:48,860 --> 00:46:51,060 and wood to build this dam. 637 00:47:00,700 --> 00:47:04,860 This used to be a tiny stream trickling down towards the Tay 638 00:47:04,860 --> 00:47:07,580 but beavers have been here for the last decade 639 00:47:07,580 --> 00:47:10,700 and they have done some serious river engineering in that time. 640 00:47:10,700 --> 00:47:12,620 It's a very eerie landscape. 641 00:47:12,620 --> 00:47:14,420 It's quite an unusual one. 642 00:47:14,420 --> 00:47:16,980 It's not what I expect a river up here to look like. 643 00:47:16,980 --> 00:47:19,220 There are fallen trees across the river. 644 00:47:19,220 --> 00:47:22,660 Behind the dam, here, that they've built, there is a drowned tree. 645 00:47:22,660 --> 00:47:25,100 Everywhere there are little stumps with chips of wood around them 646 00:47:25,100 --> 00:47:27,700 where they've been hammering away with their incredibly sharp 647 00:47:27,700 --> 00:47:29,180 incisors. 648 00:47:29,180 --> 00:47:32,620 It's a weird, open landscape and it's astonishingly new 649 00:47:32,620 --> 00:47:34,220 and yet very old. 650 00:47:36,420 --> 00:47:39,380 And why do they create such extraordinary feats of engineering? 651 00:47:41,740 --> 00:47:44,940 Because they feel intensely vulnerable out of water. 652 00:47:48,220 --> 00:47:51,700 Their dams flood the land so they can safely reach evermore trees 653 00:47:51,700 --> 00:47:53,860 and other plants for their food. 654 00:47:56,380 --> 00:47:58,860 This can devastate riverside crops. 655 00:48:02,540 --> 00:48:05,260 Beavers don't care for our neat, orderly division between 656 00:48:05,260 --> 00:48:06,660 river and land. 657 00:48:09,220 --> 00:48:13,460 But the truth is a landscape shaped by beavers is probably closer 658 00:48:13,460 --> 00:48:16,860 to how the Tay would have looked before any human walked here. 659 00:48:22,180 --> 00:48:24,820 This transformation has done extraordinary things 660 00:48:24,820 --> 00:48:27,140 for the biodiversity in this place. 661 00:48:27,140 --> 00:48:29,340 As soon as the water slows down, different creatures begin 662 00:48:29,340 --> 00:48:30,620 to live in it. 663 00:48:37,500 --> 00:48:40,300 Beneath the beaver pond surface dwell life forms 664 00:48:40,300 --> 00:48:43,060 that would be washed away in a fast-moving stream. 665 00:48:50,220 --> 00:48:53,700 And that means a completely different cast of animals occupy 666 00:48:53,700 --> 00:48:55,580 the world above the water. 667 00:49:00,420 --> 00:49:03,580 There are damselflies here, dragonflies here, newts here. 668 00:49:03,580 --> 00:49:07,460 These are all species that would not otherwise be here. 669 00:49:09,420 --> 00:49:11,340 Without the beavers, this would be a cold, 670 00:49:11,340 --> 00:49:13,460 dark bit of forest with a trickle of water 671 00:49:13,460 --> 00:49:16,340 and with them it's kind of a wonderland. 672 00:49:31,740 --> 00:49:36,060 The beavers' return to the Tay hasn't been welcomed by everyone. 673 00:49:36,060 --> 00:49:37,740 Farmers, in particular. 674 00:49:39,460 --> 00:49:42,060 But my hope is that, over time, 675 00:49:42,060 --> 00:49:43,900 there'll be room for us all. 676 00:49:53,820 --> 00:49:57,460 As the days shorten, summer's heat is slipping away. 677 00:50:16,540 --> 00:50:19,380 Because the water stays warm for a little while longer 678 00:50:19,380 --> 00:50:23,540 than the sky above, on clear mornings clouds of steam fog 679 00:50:23,540 --> 00:50:25,580 rise up from the river. 680 00:50:26,900 --> 00:50:29,940 It's a bewitching sight for early risers on the river bank. 681 00:50:36,020 --> 00:50:39,220 But it also heralds the beginning of a season that will transform 682 00:50:39,220 --> 00:50:41,500 the river and all the life within it. 683 00:50:49,860 --> 00:50:53,500 The clear waters of spring and summer are growing darker 684 00:50:53,500 --> 00:50:55,140 and richer in hue. 685 00:50:57,740 --> 00:51:00,460 It's trees that are driving this change. 686 00:51:03,060 --> 00:51:05,900 The days are getting shorter, the temperature is getting much 687 00:51:05,900 --> 00:51:08,580 colder and the trees really can't support the kind 688 00:51:08,580 --> 00:51:10,980 of existence they had in the summer. 689 00:51:10,980 --> 00:51:13,820 The chemical that they used to turn sunlight into food, 690 00:51:13,820 --> 00:51:17,260 chlorophyll, breaks down, goes back into the tree 691 00:51:17,260 --> 00:51:20,100 and what's left behind are the chemicals that are always 692 00:51:20,100 --> 00:51:23,980 in the tree but we never see, which make them this colour. 693 00:51:23,980 --> 00:51:27,580 One by one these leaves go, they're not needed, 694 00:51:27,580 --> 00:51:29,620 and what's left behind... 695 00:51:31,220 --> 00:51:34,260 ..are the buds for the new leaves for next spring. 696 00:51:34,260 --> 00:51:38,460 It's like winter and spring and autumn and summer all at once 697 00:51:38,460 --> 00:51:39,740 on one tree. 698 00:51:47,340 --> 00:51:51,340 Millions of leaves find their way into the Tay and its tributaries, 699 00:51:51,340 --> 00:51:53,900 some falling onto the river's surface, 700 00:51:53,900 --> 00:51:55,700 others washed in by rain. 701 00:52:02,780 --> 00:52:07,020 As they float, they reveal new secrets about the river, 702 00:52:07,020 --> 00:52:11,300 tracing currents, showing subtle eddies and whirls in the flow 703 00:52:11,300 --> 00:52:14,940 that relate to the depth and shape of the riverbed. 704 00:52:24,180 --> 00:52:25,900 Not every leaf that falls 705 00:52:25,900 --> 00:52:27,980 into the river is washed out to sea. 706 00:52:29,180 --> 00:52:32,900 In backwaters, where the water slows, leaves build up. 707 00:52:38,140 --> 00:52:41,780 Each leaf attracts a miniature army of decomposers. 708 00:52:46,420 --> 00:52:49,900 Insects, worms and fungi break the leaves into 709 00:52:49,900 --> 00:52:51,580 ever-smaller fragments. 710 00:52:55,420 --> 00:52:58,300 Even a single leaf is a vast source of food 711 00:52:58,300 --> 00:53:00,540 for the river's microscopic decomposers. 712 00:53:07,980 --> 00:53:12,260 But millions of leaves in the delicate balance of the river? 713 00:53:12,260 --> 00:53:15,500 Too much of anything is often bad news. 714 00:53:19,020 --> 00:53:22,780 The danger is that vast multiplying decomposers could use up 715 00:53:22,780 --> 00:53:24,860 the water's vital oxygen. 716 00:53:27,660 --> 00:53:29,660 If oxygen levels fall too low, 717 00:53:29,660 --> 00:53:31,940 many creatures will suffocate. 718 00:53:33,580 --> 00:53:37,380 Including salmon, biding their time in river pools before moving 719 00:53:37,380 --> 00:53:39,260 upstream to spawn. 720 00:53:47,580 --> 00:53:50,140 But the river has an unusual saviour. 721 00:53:51,900 --> 00:53:54,700 A creature that can keep the river in balance. 722 00:53:54,700 --> 00:53:57,340 And, to find it, it's wader time. 723 00:54:10,820 --> 00:54:14,220 I'm searching for freshwater pearl mussels. 724 00:54:17,900 --> 00:54:20,940 And when you look for them you can see what looks like a kind of 725 00:54:20,940 --> 00:54:23,700 an oval dark stone covered in weed. 726 00:54:23,700 --> 00:54:25,860 If you look on the top of it, it's got a crack on the top 727 00:54:25,860 --> 00:54:27,700 and little, kind of, feelers, kind of, 728 00:54:27,700 --> 00:54:29,420 filaments coming out and scooping 729 00:54:29,420 --> 00:54:31,900 in the water to filter it. 730 00:54:34,860 --> 00:54:36,620 It's such a treat. 731 00:54:39,380 --> 00:54:42,860 Cousins of the more familiar saltwater species, 732 00:54:42,860 --> 00:54:46,060 these mussels play an important role in keeping rivers clean. 733 00:54:49,620 --> 00:54:53,420 But, because one in 1,000 contains a pearl, mussels have traditionally 734 00:54:53,420 --> 00:54:55,420 suffered from overharvesting. 735 00:54:58,060 --> 00:55:02,300 More recently, many rivers are suffering huge variations. 736 00:55:02,300 --> 00:55:04,420 Either sudden floods or droughts due 737 00:55:04,420 --> 00:55:06,820 to changing climate or being drained 738 00:55:06,820 --> 00:55:08,540 for hydroelectric power. 739 00:55:10,900 --> 00:55:15,020 In extreme cases, mussels can dry out or be washed away. 740 00:55:17,180 --> 00:55:20,220 They're now so precious their remaining strongholds 741 00:55:20,220 --> 00:55:21,500 are kept secret. 742 00:55:27,100 --> 00:55:30,060 Scientists at this research station on Loch Lomond are mobilising 743 00:55:30,060 --> 00:55:31,740 to save them. 744 00:55:34,180 --> 00:55:40,100 Each individual mussel can filter up to about 50 litres of water a day. 745 00:55:40,100 --> 00:55:43,420 So, that's equivalent to the amount of water you would use 746 00:55:43,420 --> 00:55:45,420 in a shower every day. 747 00:55:45,420 --> 00:55:47,940 So, it cleans the water, basically. 748 00:55:47,940 --> 00:55:53,940 It siphons in the water, it filters out all the organic particles, 749 00:55:53,940 --> 00:55:58,460 which it uses as food, and then it releases cleaner water 750 00:55:58,460 --> 00:56:02,020 into the river system to the benefit of other organisms, 751 00:56:02,020 --> 00:56:04,140 like fish, like invertebrates. 752 00:56:07,260 --> 00:56:10,580 But sudden river level changes are a potential disaster 753 00:56:10,580 --> 00:56:12,620 for these sensitive molluscs. 754 00:56:12,620 --> 00:56:15,300 They will only thrive in the right conditions. 755 00:56:18,540 --> 00:56:21,740 Fortunately, freshwater mussels have a secret weapon 756 00:56:21,740 --> 00:56:23,980 that could be their saviour - 757 00:56:23,980 --> 00:56:25,740 a flexible foot. 758 00:56:30,100 --> 00:56:33,700 The team on Loch Lomond are monitoring how mussels respond 759 00:56:33,700 --> 00:56:36,980 to water dropping five centimetres every hour. 760 00:56:50,620 --> 00:56:53,380 The mussels have previously been thought as very 761 00:56:53,380 --> 00:56:57,300 sedentary species, so that they don't move around much. 762 00:56:57,300 --> 00:57:01,780 But what we're seeing in our experiments is that, as the flow 763 00:57:01,780 --> 00:57:05,460 rates are changing and the flow levels are changing, 764 00:57:05,460 --> 00:57:08,780 the mussels are moving around quite a bit and they are moving, 765 00:57:08,780 --> 00:57:11,100 using their foot, to move around. 766 00:57:14,780 --> 00:57:18,820 Now we know how fast these wonderful molluscs can move, 767 00:57:18,820 --> 00:57:22,860 where possible, we can safely control water levels. 768 00:57:22,860 --> 00:57:25,660 So, the mussels can continue to benefit the river. 769 00:57:30,220 --> 00:57:34,460 Sadly, they have already disappeared from many UK waters. 770 00:57:36,380 --> 00:57:38,940 But, on this secret Tay tributary, 771 00:57:38,940 --> 00:57:41,220 thanks to careful conservation, 772 00:57:41,220 --> 00:57:43,420 there are promising signs for the future. 773 00:57:46,900 --> 00:57:50,580 So, under licence, I'm able to show you these little beauties. 774 00:57:50,580 --> 00:57:52,460 This is a very rare sight. 775 00:57:53,980 --> 00:57:55,580 Baby mussels. 776 00:57:55,580 --> 00:57:59,340 This one's maybe three years old, this one's maybe eight 777 00:57:59,340 --> 00:58:00,860 to ten years old. 778 00:58:01,940 --> 00:58:04,340 And it's a real sign that this river's thriving. 779 00:58:04,340 --> 00:58:05,900 I'll put them back. 780 00:58:18,340 --> 00:58:20,580 As the air grows ever colder, 781 00:58:20,580 --> 00:58:22,740 many species are finding a fresh 782 00:58:22,740 --> 00:58:24,220 burst of energy. 783 00:58:29,140 --> 00:58:31,980 Red squirrels are gathering food to see them through 784 00:58:31,980 --> 00:58:33,580 the leaner months. 785 00:58:40,940 --> 00:58:44,420 Warming water drove salmon smolts out of the river to sea 786 00:58:44,420 --> 00:58:45,580 in the spring. 787 00:58:49,660 --> 00:58:52,980 Now, autumn's cooling water is drawing adult salmon 788 00:58:52,980 --> 00:58:54,700 upstream to spawn. 789 00:58:57,340 --> 00:58:59,940 One of nature's most extraordinary sights. 790 00:59:26,900 --> 00:59:30,340 The fish are guided back to this waterfall by the unique 791 00:59:30,340 --> 00:59:33,700 scent of their birth stream imprinted on their memory 792 00:59:33,700 --> 00:59:35,100 as they left it. 793 00:59:36,980 --> 00:59:39,140 Now, pure strength and luck determine who makes it 794 00:59:39,140 --> 00:59:41,020 over this final hurdle. 795 01:00:18,540 --> 01:00:23,380 As fish head upstream, my journey continues down to catch up 796 01:00:23,380 --> 01:00:25,940 with the Tay District Salmon Board 797 01:00:25,940 --> 01:00:28,900 now carrying out a very different kind of fishing. 798 01:00:32,460 --> 01:00:33,540 OK. 799 01:00:35,900 --> 01:00:38,700 This net is rigged with a mild electric current. 800 01:00:40,740 --> 01:00:43,580 It attracts and temporarily stuns the fish, 801 01:00:43,580 --> 01:00:45,820 making them easier to catch. 802 01:00:48,020 --> 01:00:50,100 Like tagging the smolts upriver, 803 01:00:50,100 --> 01:00:52,460 this work is part of the determined 804 01:00:52,460 --> 01:00:54,500 effort to stop salmon disappearing. 805 01:00:59,460 --> 01:01:03,020 And it gives me a rare chance to get close to the fish whose presence 806 01:01:03,020 --> 01:01:05,900 seems to define this river system. 807 01:01:05,900 --> 01:01:07,340 Hello, Mike. 808 01:01:07,340 --> 01:01:08,580 Really excited to see this. 809 01:01:08,580 --> 01:01:12,260 This is a cock fish that you've caught. Yes, this is a cock salmon. 810 01:01:12,260 --> 01:01:15,100 So, this is a male Atlantic salmon, getting quite close 811 01:01:15,100 --> 01:01:16,940 to being ready to breed. 812 01:01:16,940 --> 01:01:18,980 That's extraordinary. 813 01:01:18,980 --> 01:01:21,500 It's just the most prehistoric, kind of, eerie... 814 01:01:21,500 --> 01:01:24,140 You know, I've been reading a lot about salmon and I've seen them 815 01:01:24,140 --> 01:01:29,820 from a distance but seeing this cock salmon in all its finery so close... 816 01:01:29,820 --> 01:01:31,700 So, I remember those beautiful silver smolts 817 01:01:31,700 --> 01:01:33,020 that we saw earlier in the year 818 01:01:33,020 --> 01:01:35,380 and this was one very like that 819 01:01:35,380 --> 01:01:36,900 only 14 months ago? 820 01:01:36,900 --> 01:01:39,660 Yeah, just last May he would have gone to sea. 821 01:01:39,660 --> 01:01:42,460 Travelled the big distance across the sea to his feeding grounds 822 01:01:42,460 --> 01:01:44,140 and this is what he's become. 823 01:01:44,140 --> 01:01:45,940 He's eaten a lot of food out there. 824 01:01:45,940 --> 01:01:48,580 He's eaten a lot of food, he's quite a healthy-looking fish 825 01:01:48,580 --> 01:01:52,100 as well, so, yeah, it's amazing how successful these fish 826 01:01:52,100 --> 01:01:53,860 are in saltwater. 827 01:01:53,860 --> 01:01:57,340 He's gone from, as a smolt, as you saw, about four inch long, 828 01:01:57,340 --> 01:02:01,460 four inches long? A small silver fish and he's spent about a year 829 01:02:01,460 --> 01:02:05,300 at sea and came back as a fish about five pounds in weight. Wow. 830 01:02:05,300 --> 01:02:07,340 So, yeah, there's good feeding in the sea. 831 01:02:07,340 --> 01:02:10,580 Come on, mister, there we are. 832 01:02:10,580 --> 01:02:14,780 This beautiful animal has returned to the river 100 times heavier 833 01:02:14,780 --> 01:02:16,420 than when it left for the sea. 834 01:02:19,940 --> 01:02:23,660 If left in the wild, this male would be competing to mate with 835 01:02:23,660 --> 01:02:26,180 egg-laden females in the next few weeks. 836 01:02:28,100 --> 01:02:33,580 After spawning, both males and females would most likely expire 837 01:02:33,580 --> 01:02:37,220 from the exhaustions of their journey. 838 01:02:37,220 --> 01:02:41,620 But these fish will be reproducing in a slightly different way. 839 01:02:46,700 --> 01:02:49,300 This is the Salmon Board's hatchery. 840 01:02:52,980 --> 01:02:55,260 The team here are dedicated to boosting fish numbers 841 01:02:55,260 --> 01:02:56,740 in the river. 842 01:03:01,900 --> 01:03:06,100 When a female fish is ready to release eggs, hatchery manager, 843 01:03:06,100 --> 01:03:08,780 Steve Kaye, delicately removes 844 01:03:08,780 --> 01:03:11,740 around 6,000 of these orange spheres. 845 01:03:17,580 --> 01:03:20,140 This is Steve's 48th year working 846 01:03:20,140 --> 01:03:22,780 with salmon and he takes great care 847 01:03:22,780 --> 01:03:24,260 not to harm the fish. 848 01:03:28,060 --> 01:03:30,220 A male fish from the same river 849 01:03:30,220 --> 01:03:32,180 is relieved of his sperm. 850 01:03:34,180 --> 01:03:36,140 And the result? 851 01:03:36,140 --> 01:03:41,180 Over 1 million fertilised eggs loaded in trays each autumn 852 01:03:41,180 --> 01:03:44,900 and watched over by Steve's experienced eye. 853 01:03:47,340 --> 01:03:49,380 Wow, they're beautiful. 854 01:03:50,460 --> 01:03:54,220 There are a couple in here which are infertile. Oh, right. 855 01:03:54,220 --> 01:03:56,700 You can see... Oh, yeah, they've got a white spot on them. 856 01:03:56,700 --> 01:03:59,020 They've got a little white spot, so it's quite important 857 01:03:59,020 --> 01:04:04,500 that I remove these, otherwise a secondary infected 858 01:04:04,500 --> 01:04:07,020 fungus can come in on them. 859 01:04:12,420 --> 01:04:14,740 In the unpredictable river environment, 860 01:04:14,740 --> 01:04:17,660 not every egg will make it through the winter. 861 01:04:20,020 --> 01:04:23,340 Whereas these million eggs will be safe until just before 862 01:04:23,340 --> 01:04:26,620 hatching next spring 863 01:04:26,620 --> 01:04:29,420 when they'll be released into the Tay tributaries most 864 01:04:29,420 --> 01:04:31,580 in need of a population boost. 865 01:04:40,500 --> 01:04:43,140 Not everyone agrees that stocking rivers by hand 866 01:04:43,140 --> 01:04:45,380 is the best long-term solution. 867 01:04:47,500 --> 01:04:50,660 But the hope is that it can give a much-needed boost to a fish 868 01:04:50,660 --> 01:04:52,220 that's in trouble. 869 01:05:05,540 --> 01:05:09,780 I'm reaching some of the last turns of the river 870 01:05:09,780 --> 01:05:13,340 and, as autumn comes to an end, 871 01:05:13,340 --> 01:05:14,940 a chance to reflect. 872 01:05:17,580 --> 01:05:19,940 So, I have a confession to make. 873 01:05:19,940 --> 01:05:22,380 People sometimes ask me what my favourite season is 874 01:05:22,380 --> 01:05:25,660 and I know I should say summer, or spring in particular, 875 01:05:25,660 --> 01:05:28,060 but it's not. It's none of those things. 876 01:05:28,060 --> 01:05:30,500 It's always been autumn for me. 877 01:05:30,500 --> 01:05:34,180 And there's something about the changing of the seasons, 878 01:05:34,180 --> 01:05:37,380 these days, that really gets me here. 879 01:05:37,380 --> 01:05:39,940 Everything's slowing down, shutting down. 880 01:05:39,940 --> 01:05:42,180 Things are leaving. 881 01:05:42,180 --> 01:05:44,620 Everything about it reminds me that winter's coming 882 01:05:44,620 --> 01:05:47,380 and that our lives will eventually come to an end. 883 01:05:47,380 --> 01:05:49,860 It's not very cheerful but it's sobering, you know? 884 01:05:49,860 --> 01:05:52,740 To remind ourselves that life's very short. 885 01:05:54,620 --> 01:05:57,460 What we see in the world... It's glorious but I think, also, 886 01:05:57,460 --> 01:05:59,060 it's always slightly about us. 887 01:05:59,060 --> 01:06:01,340 We always think of it in relation to our own lives. 888 01:06:01,340 --> 01:06:02,940 We can't help but do it. 889 01:06:02,940 --> 01:06:05,540 So, standing by the river right now, 890 01:06:05,540 --> 01:06:07,860 I think I'm just loving it more. 891 01:06:07,860 --> 01:06:11,060 I'm loving it more because, eventually, none of us will be able 892 01:06:11,060 --> 01:06:12,660 to see anything like this anymore. 893 01:06:12,660 --> 01:06:14,380 We'll all be gone. 894 01:06:25,860 --> 01:06:28,580 As I follow this immense river downstream, 895 01:06:28,580 --> 01:06:31,700 the seasons are turning once more and the Tay 896 01:06:31,700 --> 01:06:34,100 is beginning its final chapter. 897 01:06:50,540 --> 01:06:53,060 Cooler air and shorter days trigger 898 01:06:53,060 --> 01:06:55,220 river bank life to slow down. 899 01:07:01,260 --> 01:07:05,340 30 miles from its end, the Tay passes the first major 900 01:07:05,340 --> 01:07:07,500 settlement on its long journey... 901 01:07:08,980 --> 01:07:10,020 ..Perth. 902 01:07:11,700 --> 01:07:14,380 The city marks the point where the river's fresh water 903 01:07:14,380 --> 01:07:15,820 meets the sea. 904 01:07:24,140 --> 01:07:27,460 As the river pushes downstream, it becomes increasingly mixed 905 01:07:27,460 --> 01:07:32,060 with the incoming saltwater in this wonderfully open landscape. 906 01:07:34,940 --> 01:07:37,820 But, even as the sea starts to dominate, 907 01:07:37,820 --> 01:07:41,060 the river still has enormous power to sustain life. 908 01:07:45,180 --> 01:07:48,740 One of the few species that thrive in this brackish water 909 01:07:48,740 --> 01:07:50,900 are common reeds. 910 01:07:50,900 --> 01:07:54,980 Able to tolerate both salt and the changing tide, 911 01:07:54,980 --> 01:07:58,300 they blur the boundary between land and river. 912 01:08:02,500 --> 01:08:04,980 This half world feels wild, 913 01:08:04,980 --> 01:08:08,380 but this is an industrial landscape. 914 01:08:11,540 --> 01:08:14,500 Reeds were planted here in the 19th-century to stop 915 01:08:14,500 --> 01:08:16,740 the river washing away farmed fields. 916 01:08:20,180 --> 01:08:24,260 The plants now stretch for 15 miles along the Tay, 917 01:08:24,260 --> 01:08:26,620 the largest continuous bed in Britain. 918 01:08:36,500 --> 01:08:40,060 For decades, the reeds have also provided thatch for roofs. 919 01:08:43,380 --> 01:08:46,460 Graham Craig started harvesting here in the 1970s. 920 01:08:48,700 --> 01:08:52,340 He's come to check the crop he's lived beside all his life. 921 01:08:57,900 --> 01:09:02,660 Reed-cutting always begins in winter, once the sap has fallen. 922 01:09:06,140 --> 01:09:09,340 An ideal way to tell when the reed is ready to cut is it usually 923 01:09:09,340 --> 01:09:12,140 has a nice rattle to it. 924 01:09:12,140 --> 01:09:14,460 And you can tell when most of the moisture is out of it. 925 01:09:14,460 --> 01:09:17,340 Also, obviously, we're looking for the leaf to come 926 01:09:17,340 --> 01:09:19,620 off the reed, as well. There's still one or two bits. 927 01:09:19,620 --> 01:09:22,860 If we do cut it with that on, it tends to make the bunch that bit 928 01:09:22,860 --> 01:09:25,860 bulkier and it's not ideal for thatching with. So... 929 01:09:27,140 --> 01:09:29,340 We harvest from December to April, 930 01:09:29,340 --> 01:09:32,020 which is the worst months of the year! 931 01:09:32,020 --> 01:09:34,020 But, I mean, you can be out here in January 932 01:09:34,020 --> 01:09:37,020 with sunshine and it's beautiful out here. 933 01:09:37,020 --> 01:09:40,460 And with the reed and the wildlife going about, 934 01:09:40,460 --> 01:09:42,300 absolutely brilliant. 935 01:09:46,140 --> 01:09:48,260 Despite their man-made origins, 936 01:09:48,260 --> 01:09:50,500 these vast reed forests have become 937 01:09:50,500 --> 01:09:53,820 a sanctuary for one of the UK's rarest birds... 938 01:09:53,820 --> 01:09:55,580 ..the bearded reedling. 939 01:09:59,620 --> 01:10:01,340 Hundreds nest here, 940 01:10:01,340 --> 01:10:03,620 30% of the UK's population. 941 01:10:05,860 --> 01:10:07,860 They're bewitching birds, 942 01:10:07,860 --> 01:10:11,980 with long legs and huge feet to clamber amongst stems 943 01:10:11,980 --> 01:10:15,100 and the males have glorious, feathery moustaches. 944 01:10:18,180 --> 01:10:21,300 With summer's flying insects long gone, 945 01:10:21,300 --> 01:10:24,340 reed seeds provide most of the bird's winter diet. 946 01:10:26,340 --> 01:10:29,820 Because they don't have teeth to grind away the tough seed cases, 947 01:10:29,820 --> 01:10:33,900 the birds must swallow grit to do the same job in their stomach 948 01:10:33,900 --> 01:10:37,900 and the nearest source is this crumbling old sewer pipe. 949 01:10:53,580 --> 01:10:56,420 These rare birds have people like Graham to thank 950 01:10:56,420 --> 01:10:57,940 for their stronghold. 951 01:10:59,620 --> 01:11:03,140 Left to nature, accumulated dead reeds would provide a base 952 01:11:03,140 --> 01:11:07,340 for less salt-tolerant plants and slowly turn to woodland. 953 01:11:09,620 --> 01:11:12,700 Only regular cutting preserves the reed bed. 954 01:11:18,060 --> 01:11:23,140 I love the idea that this wild haven is created and maintained by us. 955 01:11:23,140 --> 01:11:25,700 Giving something back to the river. 956 01:11:28,460 --> 01:11:31,100 It seems to me the wildest of all places, you know? 957 01:11:31,100 --> 01:11:33,180 It's an impenetrable area for humans. 958 01:11:33,180 --> 01:11:35,220 We can't really walk in it. 959 01:11:35,220 --> 01:11:39,300 It's, sort of, neither land nor water, it's... 960 01:11:39,300 --> 01:11:40,700 It's kind of exhilarating! 961 01:11:50,460 --> 01:11:52,980 Beyond the sanctuary of the reedbeds, 962 01:11:52,980 --> 01:11:54,780 our human presence dominates. 963 01:11:58,180 --> 01:12:00,420 Downstream lies Dundee, 964 01:12:00,420 --> 01:12:02,660 Scotland's fourth largest city. 965 01:12:04,820 --> 01:12:08,540 Like many of Britain's great cities, it owes its fortune to the river 966 01:12:08,540 --> 01:12:10,140 that flows through it. 967 01:12:15,860 --> 01:12:20,300 150 years ago, Dundee's docks bustled with cargo boats 968 01:12:20,300 --> 01:12:23,460 supplying textile mills that dominated the city's skyline. 969 01:12:28,180 --> 01:12:31,420 But, as industries moved elsewhere, the city had less need 970 01:12:31,420 --> 01:12:36,660 for the river and the 1960s Road Bridge blocked large ships 971 01:12:36,660 --> 01:12:38,380 from travelling upstream. 972 01:12:44,540 --> 01:12:47,140 There's rain and mist on the far side of the river here 973 01:12:47,140 --> 01:12:49,500 and I can see the lights of all the cars coming into Dundee 974 01:12:49,500 --> 01:12:50,740 over the bridge. 975 01:12:52,180 --> 01:12:54,500 And the waters here are unchanging, they've looked like this for 976 01:12:54,500 --> 01:12:56,020 thousands of years. 977 01:12:56,020 --> 01:12:58,900 But the city has changed around them. 978 01:13:01,540 --> 01:13:04,780 The city has undergone a rebirth in recent years. 979 01:13:06,220 --> 01:13:09,260 Video games companies have clustered here 980 01:13:09,260 --> 01:13:12,540 and this new temple to art and design has risen 981 01:13:12,540 --> 01:13:15,100 from the very spot where ships once docked. 982 01:13:17,340 --> 01:13:20,780 I'm standing underneath the extraordinarily stacked eaves 983 01:13:20,780 --> 01:13:22,620 of the V&A building here. 984 01:13:22,620 --> 01:13:24,940 What's going on is this wonderful regeneration, 985 01:13:24,940 --> 01:13:29,300 the sense that the river, that was once an industrial highway, 986 01:13:29,300 --> 01:13:32,780 has become an inspirational highway for the city. 987 01:13:35,060 --> 01:13:37,500 And the river flows past, as it always has done, 988 01:13:37,500 --> 01:13:39,620 completely unchanged 989 01:13:39,620 --> 01:13:42,740 as culture ebbs and flows along its banks. 990 01:13:51,700 --> 01:13:56,140 Beyond Dundee, river and sea become ever harder to separate. 991 01:13:59,060 --> 01:14:01,700 And, with the coast just a few miles away, 992 01:14:01,700 --> 01:14:04,180 the Tay's famous fish are already homing in 993 01:14:04,180 --> 01:14:05,980 on their route back upstream. 994 01:14:07,740 --> 01:14:11,660 The waters that are flowing past me into the ocean are carrying 995 01:14:11,660 --> 01:14:16,020 with them the particular chemical signature of this one river. 996 01:14:17,940 --> 01:14:20,100 And, somewhere out there, salmon are going to smell them, 997 01:14:20,100 --> 01:14:22,460 they're going to make their way home, they're going to follow 998 01:14:22,460 --> 01:14:24,580 those signatures until they get stronger and stronger 999 01:14:24,580 --> 01:14:27,060 and they're going to end up in the river in which they were 1000 01:14:27,060 --> 01:14:29,940 hatched. And I guess it's that... 1001 01:14:29,940 --> 01:14:32,820 It's just a really moving thought! 1002 01:14:32,820 --> 01:14:35,820 That you can find your way home through the smell of water. 1003 01:14:38,980 --> 01:14:43,420 But one insistent question has followed me this whole journey... 1004 01:14:43,420 --> 01:14:45,980 ..why are there fewer fish in the river? 1005 01:14:45,980 --> 01:14:49,300 Despite all that's done to boost their numbers? 1006 01:14:49,300 --> 01:14:51,660 We'll just go ahead and have a look at one of these. 1007 01:14:51,660 --> 01:14:54,260 Hints to an answer could be locked in the bodies 1008 01:14:54,260 --> 01:14:55,860 of the salmon themselves. 1009 01:14:58,580 --> 01:15:02,180 Doctor Nora Hanson studies salmon at Marine Scotland's lab 1010 01:15:02,180 --> 01:15:03,940 near the Tay. 1011 01:15:03,940 --> 01:15:06,900 She's interested in what's happening to fish beyond the bounds 1012 01:15:06,900 --> 01:15:08,580 of their birth rivers. 1013 01:15:08,580 --> 01:15:10,300 Growth has slowed down. 1014 01:15:11,380 --> 01:15:13,140 We know an awful lot about salmon 1015 01:15:13,140 --> 01:15:14,740 and we know especially 1016 01:15:14,740 --> 01:15:16,420 about their lives in freshwater 1017 01:15:16,420 --> 01:15:17,620 but their lives at sea 1018 01:15:17,620 --> 01:15:20,260 are still quite a bit of a mystery. 1019 01:15:20,260 --> 01:15:24,060 One thing we've been interested in doing is using what I like 1020 01:15:24,060 --> 01:15:27,620 to consider the natural data storage tag of salmon 1021 01:15:27,620 --> 01:15:29,420 which are their ear bones, 1022 01:15:29,420 --> 01:15:30,860 called otoliths. 1023 01:15:30,860 --> 01:15:35,900 These are little structures that sit in the inner ear of all bony fish. 1024 01:15:35,900 --> 01:15:38,260 Oh, it's exquisitely tiny! 1025 01:15:38,260 --> 01:15:41,420 They're quite small in this species and they can be quite 1026 01:15:41,420 --> 01:15:43,100 large in other species. 1027 01:15:43,100 --> 01:15:46,660 And, as it's growing and layering up, it's actually 1028 01:15:46,660 --> 01:15:50,900 incorporating information about the chemical properties 1029 01:15:50,900 --> 01:15:53,700 of the water in which it's bathed 1030 01:15:53,700 --> 01:15:57,940 and then we know from satellites and other measurements in the sea 1031 01:15:57,940 --> 01:16:02,020 quite a lot about sea surface temperature in the North Atlantic. 1032 01:16:02,020 --> 01:16:04,980 So, using those pieces of information, 1033 01:16:04,980 --> 01:16:09,380 we can recreate possible migratory paths taken by fish 1034 01:16:09,380 --> 01:16:12,060 just by looking at the pattern of temperature within the otolith. 1035 01:16:12,060 --> 01:16:14,740 This is an example of... 1036 01:16:16,380 --> 01:16:17,660 ..an output. 1037 01:16:17,660 --> 01:16:22,340 This is a fish that emigrated to sea from the north coast of Scotland. 1038 01:16:24,020 --> 01:16:27,460 The red areas of the map indicate the most likely location 1039 01:16:27,460 --> 01:16:29,300 of the salmon as the months pass. 1040 01:16:31,660 --> 01:16:35,940 Pursuing its prey, it migrates to waters beyond Iceland 1041 01:16:35,940 --> 01:16:38,580 then moves east to the Norwegian Sea... 1042 01:16:40,420 --> 01:16:41,740 ..then returns home. 1043 01:16:43,540 --> 01:16:46,620 One suggestion is that, as ocean waters warm 1044 01:16:46,620 --> 01:16:50,300 and currents shift, salmon are being pushed further 1045 01:16:50,300 --> 01:16:52,140 and further to find enough food. 1046 01:16:54,740 --> 01:16:57,660 So, there are problems that they're facing at sea. 1047 01:16:57,660 --> 01:17:01,620 Perhaps they're needing to travel further north in order to encounter 1048 01:17:01,620 --> 01:17:05,100 enough prey and enough resources in order to make it back. 1049 01:17:05,100 --> 01:17:07,300 Perhaps they need to travel to different parts 1050 01:17:07,300 --> 01:17:09,060 of the North Atlantic. 1051 01:17:09,060 --> 01:17:14,300 But only by being able to study where fish are migrating to at sea 1052 01:17:14,300 --> 01:17:17,260 will we really be able to start to unpick why it might be happening 1053 01:17:17,260 --> 01:17:18,740 to them there. 1054 01:17:22,620 --> 01:17:25,060 The implications are obvious. 1055 01:17:25,060 --> 01:17:28,260 Preserving salmon isn't limited to the length of the river. 1056 01:17:30,740 --> 01:17:34,300 The Tay's fate is intertwined with events in deep 1057 01:17:34,300 --> 01:17:35,660 and distant oceans. 1058 01:17:40,260 --> 01:17:43,780 But I've not quite reached the last gasp of our greatest river. 1059 01:17:47,140 --> 01:17:49,780 Three miles from the North Sea coast, the fast, 1060 01:17:49,780 --> 01:17:53,020 falling tide is exposing the bare estuary beneath. 1061 01:17:57,740 --> 01:18:02,180 And, in this desolate seeming place, flocks of winged visitors 1062 01:18:02,180 --> 01:18:06,380 are gathering to feast on life forms buried beneath the mud's surface. 1063 01:18:10,180 --> 01:18:11,220 Oh! 1064 01:18:11,220 --> 01:18:12,380 Those are redshanks! 1065 01:18:14,260 --> 01:18:16,140 Fast-beating, sharp wings. 1066 01:18:16,140 --> 01:18:19,140 There are hundreds and hundreds of birds assembling. 1067 01:18:19,140 --> 01:18:21,020 It's really thrilling! 1068 01:18:27,500 --> 01:18:30,260 Wading birds that have been breeding in the Arctic will stay 1069 01:18:30,260 --> 01:18:32,140 here for a few days, or a day or so, 1070 01:18:32,140 --> 01:18:33,860 and then they'll head south. 1071 01:18:33,860 --> 01:18:38,140 What I love about that is it makes me feel that the River Tay has, 1072 01:18:38,140 --> 01:18:41,900 sort of, tendrils, dots on the map, that extend way further than simply 1073 01:18:41,900 --> 01:18:43,580 the British Isles. 1074 01:18:47,780 --> 01:18:53,780 There are birds currently in Africa whose bodies are built of atoms 1075 01:18:53,780 --> 01:18:56,140 that have been drawn, molecules that have been drawn 1076 01:18:56,140 --> 01:18:58,260 from the mud of the River Tay. 1077 01:19:05,380 --> 01:19:09,020 As the river slows and hits the incoming salt, 1078 01:19:09,020 --> 01:19:12,860 much of its rich cargo of minerals and organic matter simply falls 1079 01:19:12,860 --> 01:19:14,660 to the floor, 1080 01:19:14,660 --> 01:19:18,060 fuelling huge populations of hidden invertebrate life. 1081 01:19:25,260 --> 01:19:28,220 To see these tiny creatures that are feeding a profusion 1082 01:19:28,220 --> 01:19:31,780 of birds, I team up with biologists Doctor Rachel Hale 1083 01:19:31,780 --> 01:19:33,580 and Doctor Andy Blight. 1084 01:19:36,380 --> 01:19:38,020 Oh, it's proper sand castles 1085 01:19:38,020 --> 01:19:39,580 but with mud rather than sand. 1086 01:19:43,380 --> 01:19:46,180 Oh, wow! It doesn't look like there's anything here 1087 01:19:46,180 --> 01:19:48,500 but you turn over a piece of sediment and you can see 1088 01:19:48,500 --> 01:19:50,780 all these U-shaped burrows 1089 01:19:50,780 --> 01:19:53,100 that loads of shrimps that live within the burrows have made. 1090 01:19:53,100 --> 01:19:56,340 They look a bit as if someone's pressed a hair pin into the mud. 1091 01:19:56,340 --> 01:19:58,300 So, what's made these burrows? 1092 01:19:58,300 --> 01:20:01,940 So, these have been made by a small amphipod called Corophium. 1093 01:20:01,940 --> 01:20:05,020 The thing I like about these guys is they look a bit 1094 01:20:05,020 --> 01:20:06,500 like a big sci-fi monster. 1095 01:20:06,500 --> 01:20:07,700 They've got huge antennae. 1096 01:20:07,700 --> 01:20:09,740 They've got these antennae! 1097 01:20:09,740 --> 01:20:12,300 So, there aren't very many species in this mud, 1098 01:20:12,300 --> 01:20:15,860 but there are lots of those species, lots of them, lots of individuals? 1099 01:20:15,860 --> 01:20:18,060 Basically because it's nutrient-rich and there's lots 1100 01:20:18,060 --> 01:20:19,620 and lots of organic matter. 1101 01:20:19,620 --> 01:20:21,140 So, there's loads of food! 1102 01:20:21,140 --> 01:20:23,500 But because it's quite a harsh environment to live in, 1103 01:20:23,500 --> 01:20:26,140 there are only a few species that adapted to live here. 1104 01:20:26,140 --> 01:20:28,420 But those that do live here are hugely abundant. 1105 01:20:28,420 --> 01:20:31,340 So, birds, basically, have a feast when they come here. 1106 01:20:37,980 --> 01:20:43,180 The river's final act is to feed vast numbers of buried shrimp, 1107 01:20:43,180 --> 01:20:44,540 worms and snails. 1108 01:20:48,860 --> 01:20:52,820 It can be hard to comprehend the sheer amount of life squeezed 1109 01:20:52,820 --> 01:20:55,580 into the top few inches of the estuary. 1110 01:21:01,220 --> 01:21:04,300 Rachel studies the living arrangements of these creatures. 1111 01:21:06,860 --> 01:21:09,180 In the lab at St Andrews University, 1112 01:21:09,180 --> 01:21:11,100 she gave me a glimpse into the incredible 1113 01:21:11,100 --> 01:21:13,020 complexity she's uncovering. 1114 01:21:17,740 --> 01:21:20,260 We've been using computer tomography scanning, 1115 01:21:20,260 --> 01:21:23,380 CT scanning, exactly the same as you would get in a hospital 1116 01:21:23,380 --> 01:21:26,380 but we use a scientifically dedicated machine. 1117 01:21:26,380 --> 01:21:30,180 And you can actually see these burrows within the sediment. 1118 01:21:30,180 --> 01:21:31,940 So, this is just of a single species 1119 01:21:31,940 --> 01:21:34,340 and, you can see, here's the sediment surface. Oh, wow! 1120 01:21:34,340 --> 01:21:38,020 And they create these huge networks of burrows underneath. 1121 01:21:38,020 --> 01:21:41,180 So, this is essentially making the sediment see through. 1122 01:21:41,180 --> 01:21:42,980 So, what organism is this? 1123 01:21:42,980 --> 01:21:45,180 So, this is the ragworm. 1124 01:21:45,180 --> 01:21:47,860 It's really complex! It is, yeah. 1125 01:21:47,860 --> 01:21:50,300 You can see it's using up pretty much all the space available 1126 01:21:50,300 --> 01:21:52,980 in that particular column of mud. 1127 01:22:00,060 --> 01:22:01,620 You know what? 1128 01:22:01,620 --> 01:22:04,540 I know this is going to sound really, really ridiculous, 1129 01:22:04,540 --> 01:22:07,220 but this is making me quite emotional! 1130 01:22:07,220 --> 01:22:12,540 I had no idea that this, sort of, complex beauty was hidden 1131 01:22:12,540 --> 01:22:17,940 beneath the featureless mud of an estuary or a salt marsh flat. 1132 01:22:17,940 --> 01:22:19,700 It's just... 1133 01:22:19,700 --> 01:22:21,020 It's just a thing of... 1134 01:22:21,020 --> 01:22:22,180 A thing to marvel at! 1135 01:22:32,540 --> 01:22:37,700 Those beautiful, branching patterns that Rachel has shown with ragworm 1136 01:22:37,700 --> 01:22:42,220 burrows remind me so much of other patterns 1137 01:22:42,220 --> 01:22:44,540 that I've seen on this journey down the Tay. 1138 01:22:44,540 --> 01:22:48,100 There's the patterns of winter branches. 1139 01:22:48,100 --> 01:22:52,620 The patterns in rock, of veins in rock. 1140 01:22:52,620 --> 01:22:59,740 The patterns, indeed, of the river and its tributaries itself. 1141 01:22:59,740 --> 01:23:02,620 This kind of branching pattern has been seen everywhere in nature 1142 01:23:02,620 --> 01:23:05,660 and people have recognised it ever since there have been people! 1143 01:23:07,220 --> 01:23:10,740 But it took a long time for us to answer the question... 1144 01:23:10,740 --> 01:23:14,980 ..why this pattern is everywhere. 1145 01:23:29,140 --> 01:23:33,020 100 years ago, a man who lived and worked alongside the River Tay 1146 01:23:33,020 --> 01:23:37,340 for his entire life decided to explore why the same 1147 01:23:37,340 --> 01:23:40,860 shapes and patterns often repeat themselves in the living 1148 01:23:40,860 --> 01:23:42,700 and nonliving world. 1149 01:23:52,820 --> 01:23:56,580 Mr D'Arcy Thompson, a really fascinating figure 1150 01:23:56,580 --> 01:23:58,780 in the history of British science. 1151 01:23:58,780 --> 01:24:02,940 He was a polymath, he worked as a lecturer in biology 1152 01:24:02,940 --> 01:24:06,140 in both Dundee and St Andrews universities 1153 01:24:06,140 --> 01:24:09,180 and he was also quite eccentric. 1154 01:24:09,180 --> 01:24:13,140 I have a pet parrot at home, kind of renowned for it, 1155 01:24:13,140 --> 01:24:16,340 and he was well-known also for wandering around St Andrews 1156 01:24:16,340 --> 01:24:18,780 with his pet African grey on his shoulder. 1157 01:24:18,780 --> 01:24:20,420 There's a kind of kinship there. 1158 01:24:24,620 --> 01:24:28,820 D'Arcy Thompson's great quest was to find simple mathematical 1159 01:24:28,820 --> 01:24:31,900 and physical laws that guide the shapes and patterns 1160 01:24:31,900 --> 01:24:33,980 we see across nature. 1161 01:24:36,340 --> 01:24:39,340 He wanted to show that life isn't just sculpted by Darwin's 1162 01:24:39,340 --> 01:24:41,100 theory of evolution. 1163 01:24:42,900 --> 01:24:47,220 That other powerful forces also influence how organisms take shape. 1164 01:24:52,020 --> 01:24:55,060 D'Arcy Thompson's great work was this book, 1165 01:24:55,060 --> 01:24:59,420 On Growth And Form from 1917. Along with Darwin's On The Origin 1166 01:24:59,420 --> 01:25:02,540 Of Species, one of the most influential books ever written 1167 01:25:02,540 --> 01:25:04,580 on the natural world. 1168 01:25:04,580 --> 01:25:07,580 It's still an enormous inspiration for artists, 1169 01:25:07,580 --> 01:25:10,660 architects, engineers, anyone who's concerned 1170 01:25:10,660 --> 01:25:12,620 with natural form 1171 01:25:12,620 --> 01:25:16,260 and it's full of the most exquisite illustrations that connect 1172 01:25:16,260 --> 01:25:18,820 the mathematical with the biological 1173 01:25:18,820 --> 01:25:21,460 and nonbiological parts of the world. 1174 01:25:25,260 --> 01:25:28,700 His great revelation was that, even though the world 1175 01:25:28,700 --> 01:25:31,500 around us can appear incredibly complex, 1176 01:25:31,500 --> 01:25:36,580 nature's marvels often boil down to fundamentally simple laws. 1177 01:25:41,500 --> 01:25:43,260 It's why railway bridges bear 1178 01:25:43,260 --> 01:25:46,140 similarities to dinosaur skeletons. 1179 01:25:49,700 --> 01:25:54,460 And how the forces that shaped soap bubbles and water droplets 1180 01:25:54,460 --> 01:25:58,100 are the same as those sculpting tiny ocean plankton. 1181 01:26:01,140 --> 01:26:04,100 Architects and engineers have since been inspired 1182 01:26:04,100 --> 01:26:08,580 by his insights, creating structures that mimic natural forms. 1183 01:26:12,540 --> 01:26:14,820 And D'Arcy Thompson also explored 1184 01:26:14,820 --> 01:26:17,100 why objects branch in certain ways 1185 01:26:17,100 --> 01:26:18,260 as they grow. 1186 01:26:20,220 --> 01:26:22,540 Using simple mathematical formulae, 1187 01:26:22,540 --> 01:26:24,060 he showed it's possible 1188 01:26:24,060 --> 01:26:25,740 to replicate natural patterns. 1189 01:26:29,020 --> 01:26:32,060 They are simply the most efficient way to fill a space 1190 01:26:32,060 --> 01:26:33,380 with minimal material. 1191 01:26:37,260 --> 01:26:41,180 And this natural engineering that shapes trees, 1192 01:26:41,180 --> 01:26:45,860 lichens and bacteria also governs entire river systems. 1193 01:26:48,940 --> 01:26:53,780 A reminder that our greatest river isn't just one watercourse, 1194 01:26:53,780 --> 01:26:55,660 it's formed from thousands. 1195 01:27:01,740 --> 01:27:05,940 And here, at the end of its journey, the river's final moment 1196 01:27:05,940 --> 01:27:10,580 is just as complex and fuzzy to define as it was at its start. 1197 01:27:17,540 --> 01:27:20,980 This is such a strange, eerie place. 1198 01:27:20,980 --> 01:27:23,980 It seems halfway between the land and the sea. 1199 01:27:23,980 --> 01:27:25,860 It's not quite a river any more. 1200 01:27:25,860 --> 01:27:28,500 The sky's reflected in the water on the sand. 1201 01:27:28,500 --> 01:27:30,860 It's a kind of place that really seems like no place 1202 01:27:30,860 --> 01:27:32,380 and like every place 1203 01:27:32,380 --> 01:27:34,620 and it makes me think a lot about the journey that I've taken 1204 01:27:34,620 --> 01:27:37,100 and what I've learned in this year. 1205 01:27:37,100 --> 01:27:41,300 It's taught me about the complexity of the systems that surround us, 1206 01:27:41,300 --> 01:27:44,340 how a river is not just a discrete river in Scotland, 1207 01:27:44,340 --> 01:27:48,980 it also spans the migratory routes of birds and it spans the travels 1208 01:27:48,980 --> 01:27:50,980 of salmon right out to the Arctic seas and back. 1209 01:27:50,980 --> 01:27:52,740 A river is not just here, 1210 01:27:52,740 --> 01:27:54,420 it stretches all over. 1211 01:27:58,540 --> 01:28:02,220 D'Arcy Thompson showed us that inherent simplicity often 1212 01:28:02,220 --> 01:28:05,900 underlies the shapes and forms of the natural world. 1213 01:28:07,900 --> 01:28:12,060 But the key to preserving the future of our wild places is to understand 1214 01:28:12,060 --> 01:28:15,820 the complexity and interdependence that allows so many 1215 01:28:15,820 --> 01:28:17,420 creatures to flourish. 1216 01:28:20,460 --> 01:28:23,740 There's hope for the Tay, our most magnificent river. 1217 01:28:25,180 --> 01:28:27,940 Long may it flow and thrive.