A BROAD grin stretches across Robert White’s face when I come in from the frost at the Catholes hut, a wooden cabin, perched on a dramatic bend on the river Tay. He had woken up to a clear sky. After weeks of Storm Ciara’s dirt, wind and torrents, of river heights always above 9ft, it happens that today has brought a window of bright clarity – perfect salmon-fishing weather.

In fact, he says, he’s already been down to the water and hooked himself a 16lb-er. “When I got up,” he says. “I looked out the window and thought, ‘We’re in with a shout today.’”

Not long after 9am he got in the boat, and started casting furiously. But the time ticked by and there was nothing. Then he cast out, and recalls, “Suddenly the line just went tight. I thought, 'Christ, what the hell’s that?' I could feel there was a bit of weight to it. I thought, this is no kelt [salmon that has already spawned], because a kelt is spent and they come like a dog. This thing meant it.”

The salmon fought so strongly that in the end, he had to call a friend who was further down the river and ask him for a hand. He pulls a photograph up on his phone of silver-white form being held in a net at the river's edge. “We didn’t weigh it. I wanted just to release it. We know pretty much by looking at it that it was about 16 lbs.”

This comes as a surprise to me because the story I have come to tell is of the disappearance of salmon from Scottish rivers – yet even before I’ve arrived one has been netted. However, it becomes rapidly clear that White's excitement is all the more because salmon catches these days are increasingly rare. In fact, he is so frustrated at seeing the populations drop, that he launched a petition asking that the Scottish Government commit to a full consultation on stocking the rivers – an idea that had been rejected in Marine Scotland's recently published stocking policy.

“If you look at the chart of salmon numbers,” White says, “there’s a distinct line that is going down, but the last few years it has really crashed, to the point where it’s commercially just about unviable. I’ve got four beats that I look after and we’re making a whacking loss. The thing I always tell people when they come here is that there was a time when I would have been able to say to you, ‘We’re going to go out and you’re going to get a chance of catching a fish today.’ I can’t say that any more. It’s more of a lottery now.”

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The story of the decline of salmon isn’t just a Scottish one. It’s happening in all the countries around the Atlantic where the fish once swum in vast numbers. Mark Bilsby, of the Atlantic Salmon Trust, a driving force behind a coalition of groups investigating and campaigning around the crisis, called the Missing Salmon Alliance, tells me, “In the mid-1980s there were between 8 and 10 million salmon swimming around the Atlantic. That number has dropped to 2-3 million. It really is a dramatic decline and it’s not showing any signs of levelling out. ”

Wild Atlantic salmon is now being discussed with increasing urgency – at a meeting in January in the Scottish parliament, the Government’s lead scientist, John Armstrong, warned that unless we act, it could be extinct within 20 or 30 years – and Bilsby, like many, believes that the problem is part of a much larger environmental crisis. The salmon, he says, is the “canary in the coalmine”.

“These fish,” he says, “are pretty uniquely placed. They tell you about the quality of the rivers they are living in for the first few years of their life, and also what’s happening at sea – and they’re telling us that something’s really wrong with both our rivers and our sea. That’s why salmon are important.”

The Missing Salmon Alliance plans to work its way through what Bilsby calls the “likely suspects” or causes of the collapse, collating and bringing together the best international research, as well as doing its own. “It sounds really simple but it’s not been done before, this look at what’s causing the problems and where to focus energy on resolving them.”

One of the questions the trust has already started looking into is where the majority of fish were being lost. It was always assumed that this was mostly at sea, but their research, in the Moray Firth tracking project, revealed that many of the fish were disappearing in freshwater. “We found that large numbers of fish went missing in freshwater. That’s worrying because it’s telling us about the state of our rivers.”

The Scottish Government, meanwhile, has identified 12 pressures impacting on salmon. Among them are exploitation, predation, “genetic introgression” (escaped farmed fish interbreeding with wild, causing a change in genetic make-up), sea lice transferral from farmed fish, water pollution from agriculture, changing temperatures. Many of these are the result of human impacts. They are a litany of the sort we find in any list of causes of biodiversity loss.

Among the many suspects, Bilsby says, is climate change. “The rivers are getting warmer on average over the course of a year. ” Another is pollution from agriculture. “We know that pesticides in very high dosages kill fish. But there’s also much more sub lethal impacts at lower levels. ”

Another significant impact on wild salmon populations is believed to be the salmon farming industry – through a combination of escaped farm fish breeding with wild and the rise in sea lice infection picked up by wild fish when they pass farms. Director of Scottish Salmon Watch, Don Staniford, observes, "Peer-reviewed science has reported how lice-infested feedlots are killing off wild fish. Genetic pollution via escapees also precipitate an 'extinction vortex' in wild salmon."

Andrew Graham-Stewart, director of Salmon and Trout Conservation Scotland, recalls that he started voicing his concerns over the impact of salmon farming on wild salmon populations over 20 years ago. He says, “successive Scottish governments have prevaricated and procrastinated.” Last week, the Salmon and Trout Conservation Trust, along with other NGOs, declared that given Scottish Ministers' "lamentable failure to regulate salmon farming to protect wild fish”, their next step would be to call for a boycott of Scottish farmed salmon.

Graham-Stewart observes that the curve of decline of salmon population has been far greater in the west coast rivers than those in the east – and that this is where the salmon farms are located. “Numbers have declined drastically in the west,” he says. “In particular most of the smaller West Highland and island rivers have seen their salmon populations severely depleted, if not wiped out .” The long term solution for salmon farming, he believes, is entirely separating farmed and wild fish by farming in “closed-containment systems, whether tanks in the sea or tanks on the land.”

He learnt to fish, he says, at the age of four and has been salmon fishing for over 50 years. “I can remember tremendous runs of wild salmon and sea trout in the West Highlands and islands in the early 1980s. Then salmon farming took off from the late eighties, and the decline coincided with that.”

The fish farming industry, which contributed £620 million to the Scottish economy last year, and supports thousands of jobs, denies being at the root of the problem.

Like many who love the fish, Graham-Stewart waxes lyrical. “Salmon are an incredibly important part of the ecosystem of rivers. These are astonishing creatures, travelling thousands of miles, coming back to spawn within a few yards of where they were born. Few creatures can match their natural history.”

He notes that the rivers where he lives, in Sutherland, in the far north of Scotland, are bucking the trend towards rapid decline. “We haven’t seen the same level of collapse that has been seen elsewhere. There are several possibilities. One is that human populations here are minimal compared to further south. If you look at the northern rivers, from the Findhorn round to Cape Wrath, any towns or villages are all concentrated in the lower reaches if not right on the coast where the river goes into the sea. Once you get inland, there’s just no population, no pollution, very little agriculture.”

On the Tay, however, where Robert White has been ghillie on a series of four beats since 2001, the populations have been in freefall. On average, he recalls, the catch there used to be around 450 in a good year, and over 300 in a more regular year, but last year, saw them catch only 89 salmon. “To qualify that though,” he says, “there aren’t as many people fishing because there are less salmon, so people aren’t coming.”

Of course, you can still catch a salmon on the Tay, but you need to be in the right place, on the right day, with the right guide, like White, to take you to the perfect spot. That wasn’t how it used to be, he observes, “In the past there would be salmon jumping all over the place. People knew where to go because they saw the fish jumping.”

I’ve seen salmon jump before but I’ve never even tried to catch one. We stand on White’s rowing boat, floating in the calm just upstream of a series of white-frothed torrents, secured by a rope to the river’s edge. White explains why this a good time to fish. “The salmon coming into the river are moving very slowly because they haven't got much energy because of the cold and they’ll only go in short stages up the river. They’ll climb up into these rapids and they’ll come to a quieter bit of the water for a rest.”

He coaches me on using the spinner and I flick the rod through the air. I cast erratically, sometimes dropping too short, others arching the line out far and wide. “Going back to the late 1970s and early 1980s," he says, "the catches here were mindboggling – more than I would get in about five seasons now. In 1978 they had 600 spring salmon recorded.”

While I get into the rhythm of the cast, he stands behind me, swiping away at his phone, putting the image of the morning’s catch on all his social media platforms, so people out there can see there are fish here. White is a reminder that what we’re losing along with salmon is way of life, a tourist draw, and a huge contribution to rural economies. Angler-spend from wild fisheries in Scotland is reportedly around £135m annually. “I think the powers that be have sat on their backsides for years,” he says. “We’ve been going on about it for ages. But suddenly, of course, everyone is starting to wonder what are they are doing about it. It feels like Marine Scotland are sitting up in the cloud there looking down on us, saying, 'We don’t think you should stock the rivers. We want it to happen naturally.' But they’re not at the coal face. They’re not seeing people not coming, people’s jobs being lost, the hotelier moaning like hell because nobody is coming to the hotel. They don’t seem to realise how vital it is.”

The current Marine Scotland stocking policy, published last year, advised that there were “only a limited number of situations where hatchery and stocking strategies may benefit individual populations”. "Increasingly," it said, “scientific studies are concluding that there are risks of negative effects of stocking wild Atlantic salmon.”

The use of stocking and hatcheries is, of course, not a new idea. The earliest recorded effort to incubate eggs to restock rivers in Scotland, took place in 1838, and by 1890 there were 18 hatcheries across the country. However, the method, in its bluntest form, is now controversial. Last year, a documentary, Artifishal, made by the clothing brand, Patagonia, examined the impact of fish farms and hatcheries on the wild populations and argued that human "hubris", our belief in technology as solution, is only causing further decline.

Yet, many still believe that technology – hatcheries and stocking – could still have a place in helping us bring back our wild salmon. Not far from White’s beats on the river Tay is a state-of-the-art hatchery that shows how it may still be useful. At Almondbank, a team, led by Mike Brown, operations manager at the Tay District Salmon Fisheries Board, are using hatchery eggs to stock areas on the River Garry, which was recently rewatered after a seventy-year dry period following hydro abstraction for the Tummel hydropower project.

They are using a pioneering process in which kelts, which would normally die after one spawning, are reconditioned so that they can spawn repeatedly, providing more eggs. What’s striking about this project is that it’s not about adding extra stock into a declining river, but about recolonising a river that was recently brought back to flow. They are helping the Garry, which otherwise would take a long time to be colonised, get its salmon back. Last year they saw many adults return to the river and spawn.

“Wild fish would eventually colonise it but it could take a long time," says Brown. "By using the hatchery we’ve quickened the whole process up. The idea is to try to kickstart the area.” He sees hatcheries as a useful tool in rivers where a barrier has been removed and there is no wild population yet at all. “Crucial,” he says, “for a hatchery to be effective is to be very specific about what you’re trying to achieve. The 'pro hatchery' or 'against hatchery' argument it usually for them all or against them all. People don’t tend to look at hatcheries on their individual merits. Ours is a very carefully thought out thing backed up by science.”

One big question, however, is if we do stock rivers, what do we gain, unless we tackle all the other issues that are causing salmon decline?

Mark Bilsby of the Atlantic Salmon Trust believes that stocking can have a place in the restoration of salmon. “But,” he says, “it’s like any tool – you use a specific tool for a specific purpose.” He points out that what is most important is to “work out what’s really going wrong with our salmon and then deal with it with great energy, focus and clarity.”

The state of our salmon represents a wake-up call. Global collaboration is what’s needed in this search for answers – and that is what the Atlantic Salmon Trust is trying to achieve. Bilsby recalls how he was recently interviewed by Mark Kurlansky, author of Cod: A Biography Of The Fish That Changed The World, for a new book due out this year on salmon. Kurlansky has described salmon as “a natural barometer for the health of the planet”.

“Mark,” says Bilsby, “is a North American and he’s seeing the same problems. But we’re actually seeing the same problems in the Pacific salmon population. They’re a bit further behind us in their decline. And it’s because of climate change, habitat loss, urbanisation. All of these different pressures that we’re seeing in Scotland.”

The challenge may seem huge, but Bilbsy is optimistic. He believes it is possible to halt the decline and bring the populations back – but that the biggest thing we have to fight is our own apathy. “We’ve seen how other species can come back, such as the red kite, or the cod in the Irish sea. We can do this. We can look after and protect a species. We just need to have the will to do it. Collectively, everyone needs to pull together.”