Quest to solve mystery of the missing Atlantic salmon begins as wildlife organisations team up to save 'king of fish'

A quest to solve one of Britain’s most haunting natural mysteries is to get underway next week when an alliance is launched to save the wild Atlantic salmon.

The fish, which famously overcome fearsome currents and obstacles to spawn in the rivers where they were born, have seen numbers collapse by 70 per cent in a quarter of a century.

But their extraordinary life cycle, which sees them spend the first years of life in fresh water before disappearing into the vast open ocean, has made tracing the cause of their decline all but impossible.

“We’ve got a pile of possibilities a foot high,” says Mark Bilsby, CEO of the Atlantic Salmon Trust (AST). “Is it obstacles to migration, water quality, predation? Then there’s climate change, which really does change everything, from food availability to water temperature.”

Warming waters around coastal Britain, for example, have seen species like bass, which predate on smolts (as adolescent salmon are known) migrate northwards towards traditional salmon waters off Scotland. “That’s one theory, but everyone has a theory, and we need to move away from pet issues. We need the science, the data.”

To compile that data, that AST has banded together with three other major campaigning organisations - the Angling Trust, Game and Wildlife Conservation Trust and Salmon and Trout Conservation - to launch The Missing Salmon Alliance.

The Alliance, which will be unveiled next Tuesday, will unveil a “Likely Suspects Framework”, listing possible culprits for the salmon population collapse. These include agricultural pesticides, run-off from commercial forestry, poor water quality, fish farming, netting and avian and inshore seal predation, among others.

The aim now is to collect data in order to eliminate those suspects from the Alliance’s enquiries, or select them for further questioning.

“You have to have the evidence,” says David Mayhew, a city grandee who was chairman of JP Morgan Cazenove until 2011, and has spent the last three years convening the Alliance. “Everyone who has ever held a rod has a theory. But it’s the science that matters. I believe it will transform our understanding of salmon which, as things stand, is on its way to extinction.

“That’s how serious the trend is.”

The data-rich, scientific modelling on which the Missing Salmon Project is based is a fruit of Mayhew’s experience as chairman of Alzheimer's Research UK, where he helped ensure that academic work on drug discovery was translated as far as possible into practical action.

In an echo of that governing structure, researchers aiming to gather information which may identify the guilty party in the salmon’s decline will report to a steering committee at the Alliance which will coordinate a policy response.

“We had four separate salmon preservation bodies and many more internationally not working as one group,” says Mayhew, who himself fishes the Islamouth beat on the Tay near Perth. “Three years ago, I said it would be better for us and the fish if we banded together. Now we have, and in a meaningful way.”

The “Likely Suspects” framework is inspired in part by work done to help save stocks of cod in the Irish sea. “It’s about separating potential causes into bite-size chunks” says Bilsby. He notes that the complexity of factors affecting an animal which can roam from the White Sea off Arkhangelsk, northwest Russia, to the coast of Canada, and as far south as Spain, means it is always currently possible to point the finger of blame elsewhere.

Key to the project is pioneering work tracking salmon and identifying the threats they face on their journeys out into the Atlantic. This year the Atlantic Salmon Trust used acoustic tags to track 850 smolts as they swam out from the headwaters of seven rivers in the Moray Firth. The results were startling. “Two thirds were being lost before they really got out to sea, in the first 60 miles of their journey,” Bilsby says. “Now we know where they died. Next year we want to find out what caused that?”

For the fish, making it well out into the ocean is crucial. Many smolts are just 6in long when they leave, but those that do survive can be more than 4ft long when they return after two or three winters away.

The tracking project, which Bilsby describes as “by far Europe’s largest” was complemented by similar scheme run by the Game and Wildlife Conservation Trust, which followed salmon further south, as they moved out into  the Channel from rivers in England and France.

“The issue is more than local or national,” he says. “It’s a global problem. Even in the Pacific they’ve seen similar problems with their salmon.”

Campaigners around the world are particularly concerned because they see the salmon as a bellwether species which, almost uniquely, indicates the health of both freshwater and marine ecosystems.

“We had between eight and 10 million swimming around the Atlantic in the mid-1980s and between 2-3 million now,” says Bilsby. “That is a crisis. “The salmon is such a canary of the sea and the rivers. And the song it’s singing is that we now have a major problem.”

The plan to solve that is essentially three-fold, of which convening the Alliance is the first part. Identifying the cause of the decline is part two, and doing something about it is part three. All concerned acknowledge it will be a long game.

“There aren’t going to be quick wins,” says Mayhew. “It will outlive me.” But he insists that rapid recent strides in data collection and analysis techniques will eventually solve the mystery of the missing salmon. “It can be done with modern technology.”

He knows as well as anyone the effects of the salmon population collapse. “The autumn run this year was remarkably diminished,” he recalls. At first he describes the salmon numbers as “very disappointing”. Then he pauses and offers an even gloomier assessment. “It’s frightening really. It’s absolutely evident there’s something wrong. This is a lot to do with the environment, with mankind. It’s not that different to so many other species.”