Fishery managers are calling for an end to dredging in Aberdeen harbour when young salmon are migrating to the sea. They say a quarter of all tagged smolts were lost in the harbour last year when dredge boats were active.

Salmon numbers in many rivers have been experiencing long-term decline and millions is being spent trying to establish the reasons. Aberdeen Harbour Board has insisted a link between mortality and dredging is “improbable and speculative.”

Scientists have been tracking young salmon and trout on the River Dee since 2016 by inserting radio devices into the fish while they are upstream.