Changes are taking place in the runs of Atlantic Salmon: recent Autumn catches are declining, Summer catches are generally increasing but with considerable annual variation, and Spring catches are staying much the same. While overall both Salmon (fish that have stayed at sea for more than one winter) and Grilse (fish that have been at sea for just one winter and have hitherto been particularly numerous) are declining, it is only Summer Salmon that are increasing; Summer Grilse are not. Not only that, but sizes are changing with fish caught in Summer getting bigger, while those caught in Autumn are getting smaller.
The key points about these changes are:
(1) they are also happening on other rivers and so are not peculiar to Tweed and
(2) they have happened before
The main theory of the cause is that the temperature of the northern Atlantic is rising: when it is warmer the fish can go further north and so stay longer at sea, and so Salmon outnumber Grilse. Warmer temperatures also make the feeding in the Grilse feeding areas, (which are more to the East and South in the Atlantic) poorer, compared to the feeding in the Salmon areas, (which are more to the West and the North), so the size and condition of the Grilse also decline.
At a public meeting held in Kelso by the Tweed Foundation, the changes were shown in a talk by the Foundation’s biologist, Dr Ronald Campbell, which was followed by a talk from Dr Jens Christian Holst, a Norwegian marine biologist, who showed how the food supply in the East Atlantic had declined and may be the root of the problem.
A summary of The Tweed Foundation’s paper can be read in the Resources section of its website, Click here
The Tweed Foundation, a company with charitable status, aims to protect and enhance the economic and social value of the fishes of the Tweed and the Eye through the study, maintenance and restoration of their populations, ecosystems and habitats and the encouragement of wider participation in angling. Further information on the work of the Tweed Foundation can be found at: www.tweedfoundation.org.uk