Smolt migration through the River Dee and Aberdeen Harbour

April 06, 2020

Acoustic tagging and tracking have been used to investigate the migration of salmon smolts in the River Dee and harbour. Between the years 2016-2019, we trapped thousands of smolts to help us better understand smolt production and to find out more about the perils they face in the early stages of their migration to the sea.

In 2019, the fourth and final year project, 134 smolts were tagged. Some were tagged as pre-smolts but the majority were tagged as smolts. The aims of the 2019 study were to 1) identify effect of tagging time on losses; 2) identify differences in migration timing between the two tagged groups; 3) assess losses between areas of intensive and background piscivorous bird control; 4) compare timing of smolt presence in Aberdeen Harbour between 2016 and 2019; and 5) make a comparison of fish tagged at the Baddoch smolt trap between the years 2017 and 2019.

A summary of the findings can be viewed on pages 13 & 14 of the report, which can be viewed here.

River Director, Dr Lorraine Hawkins explains what it all means for the Dee and its precious smolts.

What does it all mean for the river?

“Firstly, we’ve shown that losses of smolts in the harbour can be substantial in some years. Knowing this, we have been able to challenge working practices and get conditions added to the licensing of dredging operations. This should help ensure smolts now get safely through the harbour every year.

Secondly, the tracking has shown substantial losses of smolts in the river, with predation considered the primary cause of these losses. This has been highlighted to Scottish Government and as a result we were pleased to note the Cabinet Secretary for the Environment state that fish-eating birds are a big issue and create pressure locally on fish stocks.

What action will we take as a result?

“We will continue to press the Scottish Government, directly and through our representative body Fisheries Management Scotland (FMS), on the need for management options to tackle predation when it impacts on fish stocks. Having evidence helps us present a stronger case. We will continue examine the scale of the predation problem in 2020 and 2021 and plan to work with other impacted rivers and Marine Scotland Science to deliver this.”

What is the take-home message from this work?

“Smolts are more precious than ever before and they need protection. Previously, it’s been assumed that if there are lots of juvenile salmon then there would be big smolt runs going to sea, but we can now see that this is not necessarily the case. As a Fishery Board and Trust, we have two duties – to produce as many healthy, wild smolts as possible, and to ensure these smolts transition safely into the ocean.”

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