Smolt Migration through the River Dee and harbour

January 22, 2018

Smolt tagging and tracking has been taking place on the Dee since 2016. The recent decline in salmon stocks prompted the Dee management to take a new focus to investigate the estuarine and coastal environment, where the risk to smolts was believed to be greatest.

Over the course of 2016-2017, the evidence tells us that our original belief -that smolt mortality was more pronounced in the lower river and harbour area- was not reflected in the information we gathered.  One of the key findings from the 2017 study is that in river mortality can be as high as 70% for smolts migrating from the Baddoch burn on the upper Dee. 

A total of 101 smolts were tagged: 40 from the Baddoch burn, 30 from the Beltie burn and 31 from the Sheeoch burn. They were monitored by 19 receivers in the river and harbour.

River Dee Trust Manager, Lorraine Hawkins said, “ Our findings suggest that smolt mortality is due to predation. The greatest losses occurred in the middle and the lower river, where predator densities are greatest. In 2016, the first year we carried out this work, we were unsure just to what extent tagging/handling contributed the 26% mortality rate. In 2017 the timing and location of smolt losses showed that, on average, the smolts survived for at least 12 days. That said, while tagged fish may have survived the tagging process, it is possible they were made more vulnerable to predation and that mortality maybe greater than in the untagged population. The results, specifically the timing and location of the highest losses, suggest that predators are the cause of smolt mortalities, although the final figure may be inflated by the tagging process. The work will continue in 2018 and we will repeat what we did in 2017. Given what we found in 2017, we will be adding five extra receivers to give us greater insight into in river predation.”

Read the study here- Smolt Tracking 2017