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Project Laxford – Spring 2024 Update

The past few weeks and months have been action-packed for our team working on Project Laxford, a catchment-scale restoration partnership between the Atlantic Salmon Trust and Grosvenor’s Reay Forest Estate. The project is now advancing, both in terms of its habitat restoration activity and its important salmon population and environmental monitoring.

Over the past two years since the project launched, 2,000 autumn salmon parr per season have been PIT tagged (Passive Integrated Transponder) by the team, in order to allow us to build a picture of the catchment’s salmon population dynamics, marine survival and adult salmon return rates, and importantly how restoration action on the river and surrounding landscape will affect the salmon population over time. This relationship is at the core of Project Laxford.

Another important task to help build this understanding is to capture downstream migrating smolts (juvenile salmon on their way out to sea) with a technique known as ‘mark-recapture’, and this has been one of our team’s focus activities this spring.

Temporarily capturing smolts and counting them allows us to estimate the current total freshwater smolt production or ‘smolt escapement’ level in the catchment, while other sampling also allows us to determine the age, condition, timing, and genetic characteristics of the fish. After being sampled, the smolts are then released to continue their journey to sea.

All this information will allow us to better understand the link between the habitat restoration action taking place, and its impact on the salmon population.

Salmon smolts caught for ‘mark-recapture’ on the Laxford in Spring 2024

The team deployed a rotary screw trap on the River Laxford to safely capture smolts and a proportion of the fish were then given a small dye mark before being released. Later, further sets of smolts are captured below the release site, and the marked individuals within the samples are counted. Since the number of marked smolts represents a proportion of the whole population, calculations can be made to estimate the catchment’s total smolt escapement figure.

Salmon parr PIT tagging and recording in Autumn 2023

The downstream movements of the juvenile salmon PIT tagged as autumn parr over the last two years are also being closely monitored using strategically located instream PIT detection arrays. These record unique tag IDs as fish pass over antennae located in the riverbed. This provides information relating to the timing of the migration, transit times between arrays, together with freshwater survival and eventually marine survival. The upstream movements of returning adult spring salmon are also being actively monitored using a state-of-the-art ARIS scope (multibeam sonar fish counter system). We expect the first PIT tagged grilse (one sea winter adult salmon tagged as a salmon parr in autumn 2022 and smolted in spring 2023) to return this year too which will be exciting to see.

While Project Laxford’s key focus is on wild Atlantic salmon, the project takes an ‘ecosystem approach’ to catchment restoration, and so other environmental monitoring is also underway. Again, this is to build an understanding of the link between restoration action and the environment which supports salmon and other plants and animals. The team is therefore now delivering an ambitious, catchment-wide sampling programme to monitor aquatic invertebrates such as stonefly, mayfly, caddisfly and others. This will allow us to monitor changes in the abundance and species of stenotherms (only capable of living or surviving within a narrow temperature range) and certain functional feeding groups over time and in response to our restoration efforts.

Last but not least, the team has recovered, downloaded data from, and replaced a network of 14 strategically positioned temperature loggers which record river temperature every 15 minutes. River temperature can have a significant impact on the health of freshwater ecosystems, controlling species distribution and abundance. For example, juvenile Atlantic salmon experience optimum growth when temperatures are in the mid-teens, and struggle where temperatures extend much beyond 20°C.  At 23°C juvenile salmon experience thermal stress and behavioural/condition change, ultimately negatively affecting their ability to survive at sea. This level of understanding will allow us to target further restoration efforts such as riverside woodland restoration, measure success over time, and see how the salmon population responds.

The partnership now continues to work hard on all fronts, and we look forward to providing a further update this summer.

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