The River Tweed is home to significant populations of fish-eating birds, including Goosanders and Cormorants. To determine the extent to which bird predation impacts fish populations, we monitor the numbers and behaviour of Goosanders and Cormorants throughout the catchment.
Since 1992, we have been carrying out bird counts on the main stem of the Tweed, counting every Goosander and Cormorant on the river from Ettrickfoot down to the estuary at Berwick. Carrying out several counts throughout each year has enabled us to monitor the changes in their population sizes over time.
In 2017, we started to monitor the numbers of Cormorants, using roost counts. This has also given us the opportunity to trial laser pens on roosting birds as a scaring method, hoping to reduce predation by unsettling the birds enough to get them to feed elsewhere.
We also monitor the movements and diet of both Goosanders and Cormorants.
In 2021 we started tagging and tracking Goosanders to understand their in-river migratory patterns and whether they feed more in certain stretches of the river. Of particular interest is whether some birds concentrate their feeding at caulds (which can act as artificial ‘choke points’) during the smolt run.
The Tweed is also part of a national study looking into the diet of Goosanders and Cormorants. This builds on previous RTC studies of the 1990’s looking at which fish species feature most in their diets. Particular focus is put on the smolt run and on how much of the diet is made up of salmon and trout smolts.
With an Atlantic Salmon “crisis” now recognised by the Scottish government, we hope that the information obtained from our monitoring can help to determine the best management strategies on the river to help minimise the impacts of bird predation.