Fish farms had no impact on falling wild salmon stocks, study finds

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The decline of Scotland’s wild salmon is a battle line drawn in the pro- vs anti-fish farm debate, as governments and scientists try to identify the multiple causes to bring numbers back up.

‘Independent peer-reviewed scientific evidence is unequivocal that salmon farming is lethal to wild salmon populations,’ says Salmon & Trout Conservation Scotland, a charity campaigning for wild fish and their environment.

The group’s study, published in December, concluded: ‘Open net salmon farming has introduced acute and chronic threats to wild Atlantic salmon populations.’

These threats included hybridisation caused by farmed salmon escapes, sea lice, and diseases.

To help tackle the decline, last year Scotland’s salmon farm companies, through their representative body the Scottish Salmon Producers Organisation, launched the Wild Salmonid Support Fund for organisations, such as Argyll Fisheries Trust, working to protect wild salmon populations.

Then, last month, the Scottish Enviroment Protection Agency (SEPA) proposed tighter rules for fish farmers, including wild salmon protection zones and a sea lice exposure threshold, arguing ‘sea lice from open-net pen finfish farms in Scotland can pose a significant risk to wild salmon populations.

‘Whilst the causes of the poor conservation status of wild salmon stocks are complex and believed to be due to a range of different factors rather than a single cause, we know that sea lice from marine finfish farms can be a significant hazard.’

Now, a new report published in the independent journal Aquaculture & Fisheries Studies has found no impact on wild fish stocks from Scottish salmon farms.

The peer-reviewed study, written by an expert in the interaction between wild and farmed fish, Dr Martin Jaffa, a consultant at Callander McDowell, which carries out strategic planning and marketing for the aquaculture industry, said the research should end the ‘scapegoating of 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, 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 usually combined these types of wild salmon, showing differences in trends between salmon in east and west coast rivers – which some campaigners attributed to the presence of salmon farms on the west coast of Scotland.

However, 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.

Further evidence in the paper shows 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 Martin Jaffa 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 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.’

In response to the Dr Jaffa’s report, a SEPA spokesperson said: ‘The Scottish Government has identified 12 groups of high-level pressures on the status of salmon stocks, one of which includes sea lice from marine finfish farms.’