Climate change casts a shadow over Britain’s biggest food export

Spend time on the west coast of Scotland and it won’t be long before you spot them. Dotting the region’s lochs and bays, salmon farms are big business. Tourists and locals grumble that they spoil the views. But according to the Scottish government, the industry is worth more than £1bn ($1.3bn) annually and supports around 12,000 jobs. Last year salmon—almost all of it reared in Scotland—was Britain’s biggest food export, well ahead of cheddar and lamb.

Sir James Maitland, the eccentric owner of a Victorian hatchery in Stirlingshire, was probably the first Scot to breed the fish in captivity. (His recommended diet for salmon fry—horse meat and eggs—did not catch on.) But the industry took off only in recent decades. Technology from Norway, where the business was pioneered, combined with investment from Unilever, a consumer-goods firm, to yield Scotland’s first salmon harvest in 1971. Production has exploded. In 2016 Scotland produced twice as much salmon as it did in 1996; the brand has cachet worldwide.

A shadow lies across the industry, however. Data from Scotland’s Fish Health Inspectorate show a sharp increase in the number of premature salmon deaths in saltwater farms in recent years. More than 10m farmed salmon died offshore in both 2022 and 2023, well above the average for the previous six years. (Include freshwater farms, where vulnerable juveniles are reared, and the figure is higher.) Figures from Salmon Scotland, a trade body, show that the mortality rate roughly doubled between 2018 and 2023, from 1.18% to 2.35%. Mass die-offs, in which many salmon perish in a short period, play a big role in boosting these numbers; last autumn one farm near the Isle of Colonsay reported more than 200,000 deaths in a week.