Many believe salmon farming is an issue exclusive to wild fish in the west Highlands and Hebrides. However, controlling sea lice on farms in Shetland is just as important as our Scottish Director, Andrew Graham-Stewart explains...
The official figures for rod catches of salmon in Scotland during 2018 were published last week. That they were the lowest since official records began was hardly a surprise. There has been a downward trend for several years and last year’s depressing figures were exacerbated and indeed partly explained by extreme conditions; on the majority of rivers most of the summer was unfishable as flows became trickles in the extended drought and temperatures soared. Incidentally it is worth noting that the season was not a universal write-off; despite the conditions, catches on the North Highland rivers were reasonably buoyant (albeit condensed into short periods) and the run registered by the fish counter on the Helmsdale was one of the best for years.
Looking at 'farm by farm' sea lice data
Back in autumn 2017, on the basis of data obtained under FOI (its release by Scottish Government was only forthcoming after our successful appeal to the Information Commissioner), we were able to analyse, for the first time, weekly sea lice numbers on a farm by farm basis; prior to this we only had access to regional monthly averages.
Between November 2016 and August 2017, the period for which the data was forthcoming, the worst performing company in the Scottish Islands and overall worst performing company in Scotland was Grieg Seafood Shetland Ltd. For months on end its Shetland farms’ figures were massively above the industry’s code of good practice trigger threshold for treatment; some of the numbers were eye-watering – in one week on one farm the average number of adult female sea lice per fish was a staggering 29.
I commented at the time:
“Grieg Seafood’s lamentable record exemplifies the very widespread failure to control sea lice in Shetland. It is no wonder that mature wild sea trout have been wiped out in these islands.”
What this means for wild smolts
In the last 18 months there has been little improvement in sea lice control by salmon farms on Shetland, where over 20% of Scotland’s tonnage is concentrated. It remains a hotbed of lice production, with the farms consistently pumping out billions of sea lice larvae into the wider environment. What this means is that any wild salmon smolts passing within 20 miles (studies show that elevated levels of sea lice emanating from a farm may be found up to a distance of 31 km) either side of Shetland are highly vulnerable to picking up lethal infestations of the deadly parasites.
There is scant knowledge of the migration route(s) taken by smolts from Scottish east and north coast rivers. But a cursory glance at a map suggests that it is a reasonable supposition that they will pass close to Shetland as they head north towards the feeding grounds of the North Norwegian Sea.
There is a tendency amongst those who manage and/or fish on these rivers, including the Big Four, to view salmon farming as only being an issue for wild fish in the west Highlands and Hebrides. In numerous conversations with east and north coast river managers over the last two years I have raised the scenario that sea lice from Shetland farms may well be impacting their smolt survival. On reflection (most had not considered the possibility) all have agreed that this could easily be a significant factor.
Indeed, from a wild fish perspective, the control of sea lice on farms may be just as important in Shetland (and indeed Orkney), with the possible implications for east and north coast smolts, as it is in the west Highlands and Hebrides.