14 Jan 2025

Habitat improved to protect rare aquatic insects

Written by Paul Williams

A walking trail next to a pond with trees on the left-hand side.

The Alton Brae trail at Castle Fraser’s Flight Pond has been improved following work carried out to protect the habitat for rare insects

Work has been carried out to protect the habitat of rare dragonfly and damselfly species at Castle Fraser.

The Trust has completed important work to help conserve the habitats of aquatic invertebrates, ensure they are suitable for the species to thrive in, and safeguard their future at Castle Fraser, one of the few habitats in northern Scotland that supports the rare northern damselfly and azure damselfly, the former being one of the Trust’s priority species.

The work includes repairing a sinkhole and leaks at the castle’s Flight Pond, a popular attraction within the castle’s grounds and home to a variety of Odonata, the collective name for dragon and damselfly species. Alongside these repairs, the Trust also surveyed the fish stock within the pond and identified a critically endangered eel estimated to be between 30–60 years old that was re-released back into the pond. Non-native species were also observed and removed, minimising risk to Odonata larvae, a common food source for the fish.

A yellow and black digger sits at the end of a newly excavated trench in the ground next to a pond with brown trees and grey sky in the background

A yellow and black digger sits at the end of a trench in the ground covered in a white material next to a pond with brown trees and blue sky in the background

A newly constructed path with fresh brown top soil in the foreground with a pond and trees on the left and felled trees on the right

The project, supported by funds raised by People’s Postcode Lottery players through its Postcode Earth Trust, follows the publication of the Trust’s Plan for Nature, which sets out its ambitions to conserve nature in its care. The northern damselfly has been identified as one of 26 priority species within the plan, for which the Trust is responsible. The plan outlines the focus of further research to understand their conservation status and ecological requirements and improve conditions for the species.

The work was required following the appearance of a sinkhole next to the pond’s boundary at the end of 2023, caused by heavy rainfall and flooding. This caused the closure of the neighbouring Alton Brae trail to visitors due to health and safety concerns.

Vivian Bisset, the Trust’s Ranger in the North East who has been leading the project, said: ’It is really satisfying to see the pond back in action after work to fix the sinkhole took place earlier in the year. We used over 18.5 tonnes of clay to reinforce the side of the pond. A 17-metre stretch of path along the Alton Brae trail was dug out in sections to form a trench that was filled with high-density clay, and a Terram membrane was installed by our contractor to hold it in place. During the work, additional underground leaks were identified that would have caused a similar issue on the opposite side of the pond over time, so we decided to address these during the work to help prevent future leakages from occurring.

’By doing this, we have helped protect the integrity of the pond and improved its longevity while also protecting the habitat of our Odonata assemblages. We are pleased that we’ve addressed a health and safety concern caused by the sinkhole while also making improvements. We’ve widened a 20-metre stretch of the Alton Brae trail to two metres, level it out and re-surface it to improve accessibility. We’re enhancing the visitor experience further by installing new information boards and way markers around the Flight Pond to improve engagement, which will be installed in early 2025.

’Alongside the pond repair, we also carried out a fish stock survey to assess the different types of fish present. We excitingly discovered a critically endangered European Eel (Anguilla anguilla), a protected species, which was re-released back into the pond. It was around 70cm in length and the team estimated it to be between 30-60 years old. Eels can travel upstream and across the land, so it is very exciting that it has found their way from the Sargasso Sea to Castle Fraser as a part of their epic migration journey. Based on its advanced age, the eel may eventually leave to return to the Sargasso Sea to breed. We also removed some non-native fish from within the pond, thought to have been released by a member of the public without our knowledge.’

A pair of hands in black rubber gloves hold a black eel on a wide white plastic measuring instrument

A critically endangered European Eel, a protected species, was discovered during the fish survey and re-released back into the pond.

The Castle Fraser team has been brainstorming ways to enhance the habitat even more. One concept under consideration is the establishment of a new wetland area. They have conducted topographic, soil, and peat surveys to assess its potential and suitability as a new home for the local Odonata. Additional survey work will be needed in spring 2025 to determine if this idea can be successfully implemented.

Vivian continued: ’We’ve been collaborating closely with the British Dragonfly Society on the potential new wetlands to create a mosaic of habitats for the dragon and damselfly species to thrive in. We’re exploring the feasibility of the proposed wetlands, which are subject to the necessary surveys and planning permissions, that will help to bolster Odonata in the area and offer increased protection for nationally scarce species, such as the northern damselfly. Thanks to the continued generosity of our members and supporters, including players of People’s Postcode Lottery, we can continue our vital work to care for and protect Scotland’s natural heritage at this special place for everyone to enjoy, now and into the future.’

A man in waterproofs sits on a small boat in a pond with a net to carry out fish stock survey with trees in the background and blue sky with the sun on the right hand side

Players have supported the Trust’s Love Our Nature project since 2022, which benefited from £900k last year. Further funding will support conservation work at Castle Fraser and across various habitats, including coastal and marine areas, peatlands, wetlands, woodland, and eight National Nature Reserves cared for by the Trust.

Head of Charities at People’s Postcode Lottery, Laura Chow, said: ’It is rewarding to know that funds raised by players of People's Postcode Lottery are supporting vital nature conservation work at some of our country’s most impressive heritage properties cared for by the National Trust for Scotland. Protecting rare Odonata is necessary to promote the health of our landscapes and the natural ecosystems in our waterways and the creation of new habitats is paramount in addressing biodiversity loss as a result of climate change.’

Two blue Northern Damselflies sit on a leaf with green vegetation in the background

Northern damselflies are one of the priority species highlighted in the Trust’s Plan for Nature

Players of People’s Postcode Lottery have now raised over £3.4m since 2014 to support the National Trust for Scotland. The funds are awarded through Postcode Earth Trust.

The Love Our Nature project supports the National Trust for Scotland’s vision to care for, protect and share Scotland’s nature, beauty and heritage for everyone, as outlined in its 10-year strategy, launched in 2022.