Fish tagging study – an update

In July and September we conducted some further fish tagging work in the upper Teign catchment. Tagging fish allows us to uniquely identify juvenile salmon and brown trout, that can be then monitored throughout their life in the Teign.

Tiny electronic tags are attached to each fish. Each tag has a unique number and it is recorded when fish travel close to antennae which have been placed on the river bed. This helps us to study the migration patterns of fish in the river, record their growth and test the importance of their specific environmental and physical conditions. Tagging exercises are undertaken by a team of colleagues from the River Teign Restoration Project, Bournemouth University, and the Westcountry Rivers Trust. Across all survey days, over 600 juveniles were tagged and safely returned to the river.

The fish were captured via electrofishing, more about this effective and safe method can be learned by reading last years post ‘annual fish surveys are underway’ August 24th 2022. For further detail on this tagging study, PhD student Bertie Warren writes “We were pleased to note a number of salmon fry recruits had emerged since spawning last December/January, despite the low number of redd observations over winter. Fry are typically too small to tag, as we focus on individuals greater than 70 mm a threshold shown to maximise survivorship. Any fish that are recaptured from the previous year can be identified by a clipped adipose fin or from scanning for a tag during processing. Recaptured fish are recorded and measured, from which we can determine their growth and any potential movements. In total we recaptured 9 brown trout, one of which had grown 3.5 cm since last recapture. Non-tagged fish are also measured, scales are taken for ageing purposes and then depending on the fish’s length, can be tagged using either a 12- or 23-mm long tag. Due to their small size the tags have little impact on the fish and are similar to the chips used in pet dogs and cats. This is inserted under aesthetic to minimise harm and stress to the fish. A fin clip may also be taken to provide insight into the diet of the fish in another aspect of the study. Finally, the fish are returned to the same locations from which they were caught and are observed to ensure full recovery”

The days were a great success, and all fish were released without complication. These fish will now be monitored over the next 2 years and, with luck be detected on their migratory journeys both to and from their ocean phase. We will be repeating this process every year to maximise our insight into this population and ultimately identify possible limitations within the catchment. This project is unique in scale and detail compared to other rivers in the Southwest and will provide insight into the complex lives of these threatened fish. Many thanks to all involved ensuring another successful field session for the project.