By David Leask

IT is the king of fish but its reign is increasingly at risk.

New research suggests that half of young fish do not even make it out of Scottish waters and are dying before they reach the sea.

Atlantic Salmon numbers have been declining for years. For every 100 salmon that leave our rivers, fewer than five return – a decline of nearly 70% in just 25 years.

Everybody has a theory about why this has happened but nobody knows for sure.

This summer scientists began a major project to find out, by tagging smolts – young salmon ready to leave rivers for life at sea – so they can be monitored using acoustic telemetry.

They have now made their first report back.

It is too soon to expect full answers, but early signs show that more fish are being lost in rivers than at sea, which is a major surprise to the researchers. But the team – from the Atlantic Salmon Trust and partners – stressed research is far from over.

They reveal they have deployed receivers rights across the Moray Firth – and also north of Fraserburgh.

Colin Bull, chief investigator, said: "At the same time the teams worked tirelessly travelling thousands of miles up and down seven river systems deploying receivers up and down those rivers." That is 358 receivers in total.

Mr Bull added: "This meticulously planned and laborious exercise was completed in time for the spring migration of smolts."

The teams – which were backed by Glasgow University, fisheries protection organisation Marine Scotland and fisheries boards – then trapped smolts.

He said: "We carefully fitted each smolt with a unique acoustic tag that each radiates a ping out in the water. These fish continued downstream, and as they did so the receivers registered the pings and stored the info."

The scale of data was astonishing. More than 15 million pings were recorded. This mass of information is now being analysed.

Mr Bull said: "The initial results suggest higher than expected losses of smolts before they reach salt water and much lower losses as they move out from the coast.

"We now know that more than half of our salmon are missing in action as they move down the rivers towards the sea.

"The fish that do make it to salt water move rapidly and appear to disperse and take different routes."

Mr Bull said the results were "concerning" but added that they were "exciting" because they offer chances to improve management of stocks. The first year of the project, which cost £1.2 million and saw 151km of receivers stretched out at sea, was to find where the losses were.

Now, for the second stage, scientists have to figure out what is happening in the rivers to cause smolts not to make it to sea. Finally, they will try to figure out ways to reverse trends.

The Atlantic Salmon Trust explained: "There has been a vast amount of research carried out over the years and most of this has been valuable to give us an improved understanding of mortality factors into migrating salmon.

"What it has not done is pursue with determination the process of assigning a value to suspects and therefore prioritising their importance. It is only by using an evidence-based approach that we will win the arguments.

"We all know the major suspects and we can all have an uninformed argument with different groups to suggest what is going wrong. What we have failed to do is collate evidence with a value and then assign it to a suspect.

"It is only in this way that we can challenge the organisations and issues which are impacting on the survival of this iconic fish."

The seven river systems studied, including the Spey, the Ness and the Deveron, account for about a fifth of salmon which leave the UK.

Chris Conroy, director of the Ness District Salmon Fishery Board, earlier this year said: “Last year’s Scottish catches were the lowest on record, causing great concern, and evidence-based management is a key part of the solution."

All sorts of potential reasons have already been given for the decline in salmon.

Some campaigners point to the impact of sea lice originating in fish farms on Scotland’s west coast.

Holyrood’s Rural Economy Committee previously insisted the salmon farming industry, which is worth more than £1 billion to Scotland’s economy, should not be allowed to expand any further without overhauling its environmental standards.

However, it ruled out a moratorium on new development.

In April, official figures showed wild salmon catches had plummeted by 67% on the previous five-year average total. Salmon fishery boards said this was the lowest level since 1952.

If this trend continues, one of the country’s most iconic species will rapidly become endangered.

The Scottish project is not the only one looking at declining salmon numbers. Scientists in Iceland are testing a whole new way of managing salmon in an eco-system in Iceland.

They are able to do so thanks to Sir Jim Ratcliffe, the billionaire and chairman of Ineos, which runs Grangemouth oil refinery.

Ratcliffe has sparked controversy by buying up whole rivers in Iceland – where foreign or absentee ownership is even more controversial than in Scotland. He now holds an estimated 1% of the country.

But the keen angler is eager to show he is not moving in to make a profit. Any surplus he makes from his holdings – land and river – is being ploughed back into salmon conservation.

Iceland is not the same as Scotland. There is less food in those pristine crystal-clear rivers than in Scotland’s more fertile waterways. We have more vegetation and a far more complex eco-system. Icelandic fish take longer to mature and spend longer in the river than Scottish ones. The cold-blooded creatures adjust their biological clocks to temperature.

Salmon researcher Guy Woodward, professor of ecology and deputy head of life sciences at Imperial College, said a salmon in Iceland can spend seven years as a juvenile in a river; an English one can grow in a year.

He is looking carefully at climate change and how rising sea and river temperatures could be interfering with these balances.

Salmon numbers are also in decline in the Pacific, where some species are now regarded as being endangered.