In Scotland, there is frequent conflict between salmon rod fisheries and seals, which is often managed by the shooting of seals in rivers, with potential negative impacts on protected populations of seals. Non-lethal devices have not been tested extensively in rivers as an alternative to shooting. Trials were carried out between January and May 2006 on the River North Esk and between October 2007 and February 2008 on the River Conon in northeast Scotland to examine the effectiveness of an acoustic deterrent device (ADD) at deterring seals from a specific area of river and as a barrier to the upstream movement of seals. The ADD was switched on and off alternately for periods of several days, and surveys were carried out to estimate the number of seals present within each river. The ADD had no significant effect on the absolute abundance of seals in the survey area in either river, but it did reduce seal movement upstream significantly, by ∼50% in both rivers. This reduction was constant over the 4-month period of both trials. The results suggest that ADDs might be a useful conservation tool in the management of seal–salmon conflicts, particularly in estuaries and rivers where the potential for adversely impacting cetaceans is limited.