A Marine Scotland Science study investigating the coastal movement of Scottish salmon deployed a number of satellite tags on fish in 2013 to 2014. This work was aimed at determining the potential for marine renewable energy to affect migrating salmon.
The satellite tags detach from the salmon at a pre-determined time and transmit their location, together with swimming depth and water temperature data they have recorded during deployment, to the satellite network. This information is then relayed to the scientists conducting the study.
However, the battery life of the tags is limited, and only a small portion of the data recorded by the tag can be uploaded via satellite. It is therefore very useful if the tags can be physically recovered. While the battery lasts, radio-signals can guide scientists to the tags, and many were recovered in this way. Once the battery fails though, it is only good luck and the sharp-eyes of beachcombers that can locate the tags; and only their goodwill that makes them contact the e-mail address printed on the tag (although Marine Scotland does offer a small reward).
Marine Scotland has had 14 tags returned to it from Scottish locations, often found by tourists or dog-walkers; these tags were generally recovered only a month or two after they had detached from fish. However, the prevailing winds of the north Atlantic, as well as ocean currents, will tend to carry tags eastward toward Scandinavia. To date, five tags were returned to Marine Scotland from this region, four from Norway and one from Denmark. These were found a year or two after having detached from the fish.