SALMON STUDY: Fish farms “no impact” on wild stocks, research claims

Fish farming has attracted opposition in recent years. Pic, Willie Urquhart

A new research paper controversially claims there has been no impact on wild fish stocks from Scottish salmon farms.

The study, published in the Aquaculture and Fisheries Studies journal, is written by Dr Martin Jaffa who says he has analysed decades of data on wild salmon numbers.

Dr Jaffa, an aquaculture expert who now specialises in the interaction between wild and farmed fish, believes the research should end the “scapegoating of the salmon farming industry as the cause of population declines in wild salmon”.

However this week, wild salmon and trout conservationists dismissed the paper and said numerous reputable studies had found wild stocks are severely impacted by salmon farming.  

Dr Jaffa said his paper analyses rod catch data from as far back as 1952, separating this into larger Atlantic salmon which spend up to four years at sea before returning to rivers, and the smaller “grilse” salmon that spend just one winter at sea.

Previous research has usually combined these types of wild salmon, showing differences in trends between salmon in east and west coast rivers, which some campaigners have attributed to the presence of salmon farms on the west coast of Scotland.

However, Dr Jaffa claims the new data shows that overall numbers of larger salmon have declined in the east coast, where there are no farms, whereas there has been an increase in grilse catches on both coasts.

The report suggests that “cyclical patterns” resulting from changing sea temperatures and variations in marine growth rates therefore explain the fluctuations in wild salmon stocks – not the presence of farms.

The paper says that these cyclical patterns can be documented as far back as 1740, with trends showing that both larger salmon and grilse numbers go through peaks and troughs lasting over 50-year periods – and the recent proportional increase in grilse on the east coast is similarly matched on the west coast.

Dr Jaffa, who also writes the ReLAKSation blog, said: “This analysis shows that between 1952 and 2010, catches of grilse have steadily increased.

“Increasing numbers of grilse returning to Scotland’s rivers means that they cannot have succumbed to sea lice after making their way out to sea as some anglers claim, and thus salmon farms are not having a negative impact on wild stocks at all.

“Catches of large salmon may have declined, but they have declined across all of Scotland even in areas where there is no salmon farming.

“Those concerned about safeguarding the future of wild salmon should start to address the real issues affecting wild salmon rather than scapegoating the salmon farming industry as the cause of population declines in wild salmon.”

The paper, titled Merged Data Hides Differences in the Catch Trends of Scottish Salmon, concludes that more detailed analysis of Scottish salmon catch data is required to ascertain the true underlying trends of salmon catches in Scottish rivers.

However Andrew Graham Stewart, director of Salmon and Trout Conservation Scotland, told the Free Press: “Marine Scotland have acknowledged that there’s a risk of negative impact in Scotland and numerous studies across the northern hemisphere, including in Norway and Canada, have found that wild stocks are severely impacted by salmon farming, particularly the impact from sea lice.

“These studies have been written and put together by experts in the field and have real credibility. Dr Jaffa is essentially a spokesman and an apologist for the salmon farming industry.

“It’s no coincidence that wild salmon stocks have collapsed in all areas of the northern hemisphere where open net salmon farming has developed.”

Peter Cunningham, biologist with the Wester Ross Fisheries Trust, said: “It is the salmon farming industry’s inability to manage parasitic sea lice that is the major threat to wild salmon. It is a natural parasite but they multiply and become much higher in number on open cage salmon farms.

“Sampling by the WRFT in the spring of 2021 supports contention that cumulative levels of infective sea lice were again much too high between Skye and the mainland of Scotland to protect migrating post-smolt salmon within these waters in the next spring.

“Salmon populations in rivers Applecross, Ling, Sheil, Glenmore, Glen Beag, Arnisdale, Broadford, Sligachan and many others around Skye are particularly vulnerable.”