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The Crinan Canal – APEM to the fish rescue!
In 2020 the specialist team at APEM were commissioned by SSE Renewables to investigate the movement and behaviour of Atlantic salmon (Salmo salar) smolts at Invergarry Power Station.
Glen Garry Viewpoint, Invergarry
Invergarry Hydroelectric Power (HEP) Station is located on the beautiful River Garry in the Scottish Highlands and was built as part of the Great Glen hydroelectric scheme, one of the major post-war hydroelectric developments.
This area is a habitat for Atlantic salmon (Salmo salar) who live in freshwater as juveniles but migrate to sea as smolts before returning up river to spawn.[1] They are listed on Schedule 3 of the Conservation (Natural Habitats, &c.) Regulations 1994, and therefore appropriate measures must be in place.
Water taken from Loch Garry is transferred via a buried intake tunnel to the powerhouse. Smolts emigrating from the Upper Garry catchment must therefore pass downstream via Invergarry Dam using the fish pass or the intake tunnel. Migration of smolts from the Ness system occurs from late March to end of May, typically peaking in mid to late April. It was believed that smolts were encountering difficulties when attempting to escape from the loch. Therefore, SSE Renewables commissioned APEM to investigate the movement and behaviour of Atlantic salmon smolts passing through the intake to the HEP station.
APEM’s approach was to monitor the intake of water to the HEP for a period of 40 days towards the end of the migration season.
The monitoring was achieved using two sonar cameras placed on the angled wing walls of the intake structure. The orientation and positioning of the cameras was chosen to maximise coverage of the central area of the intake bay, immediately in front of the entrance to the power station intake tunnel, which represents the main attraction route for downstream migrating smolts.
Following the monitoring period, the footage was then thoroughly analysed. Once fish were located on the echograms, raw footage was then reviewed on a frame-by-frame basis allowing for the most accurate size measurements, the direction of movement and behaviour to be recorded.
The behaviour of each individual fish was apportioned to running, hanging or milling. Generalised linear mixed effects models (GLME) were used to investigate drivers of variation in the number of smolts observed around the Invergarry HEP intake against multiple predictors, including rainfall and rate of abstraction.
Example of ARIS footage output showing a small shoal of smolts (circled)
Examples of echogram outputs showing the movement path of a shoal of smolts (left) and a single smolt (right)
A total of 857 smolts were recorded across the two cameras over the 40 day monitoring period.
The experts at APEM analysed the entire 40 day block of footage from both cameras, providing the client with a detailed report which covered:
APEM made recommendations for future monitoring requirements, including analysis of risk from migratory smolts utilising the compensation flow for passage through the dam, which was subsequently commissioned and completed by the APEM experts in 2021.
Andy Jacobs, SSER Hydro Operations Environment Manager said:
SSER is committed to using innovative techniques and equipment to gather suitable data and information to allow informed decision making in relation to our operations and environmental impacts.
[1] https://www.nature.scot/plants-animals-and-fungi/fish/freshwater-fish/atlantic-salmon
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