The Applecross peninsula is a haven for wild animals, both rare and those more widely recognised. The mix of mountains, rivers, estuary, the calm waters of the Inner Sound, bog and peatland, upland and lowland make the area a breeding ground for all manner of creatures, from golden eagles to sea otters and pine martens. This is also the case for salmon and sea trout. In order to ensure protection of their habitat and to encourage these species to flourish, it is crucial to understand their activities. And this is what Marine Scotland Science has been doing - tracking sea trout and salmon smolts within Loch Torridon – and it has produced some fascinating results. Marine Scotland Science tagged a number of salmon and sea trout smolts from the Shieldaig River, River Balgy and Torridon River with the aim of understanding marine movements, habitat use and potential interactions with aquaculture units. To do this they used individual acoustic transmitters and followed the fish through an array of detectors in the sea and in local rivers.
Jim Raffell, a biologist at Marine Scotland Science based at the Shieldaig Field Station, comments “The work has yielded large amounts of data, which will keep us busy for years to come. We have encountered a mystery behaviour where sea trout smolts tend to disappear from the array at night. We believe the fish either move into shallow water or into river mouths.”
It is the larger-scale movements of the smolts that have been of most interest though. For example, one fish of 17 cm tagged at the Shieldaig fish trap left the river on 28 May and spent the next few days close to the mouth of the Shieldaig River. It then journeyed around Upper Loch Torridon and Loch Shieldaig until mid-July when it was detected in the sea pool in Applecross on 17 July, spending a couple of days there. The following week it returned to Loch Shieldaig, and was last detected at the mouth of the Balgy on 30 July.
“We suspect that the tag ran out of power at this point, but that’s some swimming for a little fish!” says Jim.
Jim – and Marine Scotland Science – will be re-deploying loggers on posts at points in the Applecross River to further monitor the travels of sea trout.