The decline of Scotland’s wild salmon is spiralling despite measures to save the “king of fish”, a report has warned.
Closing coastal netting fisheries and encouraging anglers to release fish they have caught briefly stopped the fall in numbers but it has not brought a permanent revival.
Salmon stocks have continued to plummet over the past decade with sea trout in even steeper decline, according to an assessment by NatureScot, a government agency.
The Marine Assessment 2020, billed as the most comprehensive assessment of Scotland’s seas to date, said there was some evidence that sea health was improving but warned of a “mixed picture” for many fish species.
It will add to concerns that wild salmon will become extinct in the next 20 to 30 years, mainly because of climate and habitat change in their north Atlantic feeding grounds and their home rivers.
Salmon live in fresh water as juveniles before migrating thousands of miles to feed and grow in the north Atlantic. As adults they return to the rivers in which they were born, and spawn to begin the next generation.
The report said there had been no decline in young salmon being produced in Scottish rivers but a steep fall in those returning to spawn over the past half century. Stocks are now failing to reach the level that would ensure long-term survival of the species.
Although the decline had been slowed by closing coastal netting stations and catch-and-release policies introduced in individual rivers, these measures had failed to stop the trend.
“The decline in salmon populations has occurred despite significant reductions in exploitation,” the report said. Studies suggest that this is the result of “marked increase in the natural mortality of salmon at sea”, it added, with return rates of fish now at their lowest levels, even after the closure of marine fisheries.
Warming waters in the north Atlantic feeding grounds are believed to be a significant factor affecting the supply of food that salmon need for long journeys as well as their growth rates.
“A reduction in the size of returning salmon, and therefore egg production, has further exacerbated these declines,” the report said.
One example is the North Esk river in Angus where in 2018 approximately 125 hen fish were needed to produce the same number of eggs produced by 100 hen fish in 1970.
Stocks of sea trout, which also spawn in rivers, are in freefall across the country, the report added, with the best available evidence suggesting that the stock is at its lowest level since 1952. Stocks of cod, whiting and herring are in poor condition.
Mark Bilsby, chief executive of the Atlantic Salmon Trust, said: “It is a complex problem and there are major issues in both the salmon’s freshwater and ocean environments. But there are a range of actions we can still take to save the Atlantic salmon. The biggest threat is apathy.”
The report added that “disturbance of seafloor habitats from towed, bottom-contacting fishing activity is predicted to be widespread”.
It said that climate change was the most critical factor affecting Scotland’s marine environment, with impacts already being observed across the ecosystem on species such as fish, birds and plankton at the bottom of the ocean food chain.
Climate change is leading to a rise in sea levels, with the largest effects on Scotland in the past 30 years observed at Stornoway, Kinlochbervie and Lerwick. This increases the threat of coastal flooding and erosion.