The wild salmon is telling us something and we refuse to listen. It is, as the Prince of Wales once put it, “an aquatic canary” in the coalmine. This is a fish whose life journey takes it through fresh and marine water environments, and provides a barometer for what we are doing in both those spaces. As Mark Kurlansky, author of Salmon: A Fish, the Earth and the History of Their Common Fate, has put it, “Our greatest assaults on the environment are visible in salmon”.

The latest data shows that 35,693 Atlantic salmon were caught by anglers on Scottish rivers last year, the lowest number since records began in 1952 and just 75 percent of the average over the last five years..

Two years ago, just before the first lockdown of the pandemic, I went out for a morning of salmon-fishing on the River Tay, with ghillie Bob White, as part of a story about why wild North Atlantic salmon numbers are in freefall, not just on his then beat, but across Scotland and the world.

He observed then, “If you look at the chart of salmon numbers, 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 story, in those two years, has only got worse, and the decline in Scotland is echoed in other parts of the species’ native range. The North Atlantic salmon is in trouble everywhere. The International Council for the Exploration of the Sea estimates the number of eggs it takes to produce one adult surviving its first year at sea has doubled from 1000 eggs prior to 1990 to 2000 eggs in recent years.

The reasons for this are the subject of much research – some of it by the Missing Salmon Alliance – but it still seems we are nowhere near an easy answer. And that, perhaps, is because the actual answer is the most difficult one. I suspect those who seek to point the finger at a sole cause miss key elements of the story. The salmon are missing because of everything – a perfect storm of human impacts, from greenhouse gas emissions to other pollutions. It’s missing because, as Kurlansky has put it, “it’s destroyed by everything we do to the oceans and everything we do to the land.”

We learn, for instance, from the Moray Firth tracking project that 50 percent of smolts (young salmon) were lost before they even reached the sea. The Scottish Government, meanwhile, has identified 12 pressures impacting on salmon. Among them are exploitation, predation, sea lice transferral from farmed fish, water pollution from agriculture, changing temperatures. Some of these are being tackled through innovative projects – the removal of weirs and barriers, the planting of trees along rivers to provide shade and cooling. But we need to tackle all.

I spoke to Bob again, following the recent figures. He marvelled at the fact that “despite the lack of fish there is still a real thirst to get out there on the rivers”, but he questioned how long that would last given the reduction in numbers. “How many times are you going to keep coming back if you don’t see a fish or catch one?” he said.

READ MORE: Rivers of no return: What's happened to Scotland's salmon?

I asked him why he thought it was happening. “There’s a long, long list of reasons,” he said, “but one that stands out is global warming. It looks like the sea is warming and the food source is moving away. Look at the fact that there has been an explosion in the mackerel fishery, and that, once based in Lowestoft, it has moved north to the Hebrides, and some say the young salmon migrating there are getting caught as by-catch, as well as predated on by mackerel.””

Bob also expressed his fortune at working on a river on the east coast, rather than the west. “There’s no doubt that salmon farming has ruined the west coast rivers. At least we don’t have salmon farms on the east coast.”

We know that salmon farms, whose production the Scottish Government plans to double (by 2030), are having some impact. One Scottish Government study revealed that many wild salmon populations in the west Highlands and Islands are severely compromised with farmed salmon genes introduced by escaped fish – leading to serious implications for their survival. Sea lice from farms transfer to these wild fish.

The catastrophic collapse of the salmon run in the River Awe, which was reported in 2017, led to Roger Brook, chairman of the Argyll District Salmon Fishery Board, describing the decline in wild fish "in salmon farming's southern heartland" as critical. He called on the Scottish government to review its policy of facilitating the continued "expansion of the salmon aquaculture industry without first addressing the negative impacts".

But rivers like the Tay, on which Bob works, are also suffering astonishing decline. An advocate for the stocking of rivers from hatcheries, Bob sounded despondent. “You wonder if there’s a will at the top to do anything about it,” he said.

Meanwhile, global warming impacts the salmon in burns and rivers as well as sea. The average temperature of such waterways in Scotland rose by 0.22C between 2000 and 2009, and is set to climb. At 23C, juvenile salmon experience thermal stress and behavioural change; above 32C, they die in minutes. During the summer of 2018, it is estimated that around 70 percent of Scotland’s rivers experienced temperatures that exceeded this threshold for thermal stress.

Saving the salmon would be so much easier if there was just one simple reason – but that’s not the case. The plight of this iconic species is caught in the Venn diagram of our various footprints. There are probably multiple species that could tell us parts of this story. The reason it has become our canary, is because it is an animal we closely watch, the king of fish, a tourist draw and sporting trophy.

We look for the salmon. Too often now we don’t see it. And whenever it’s not there, we should see a reminder of how much we must change.