Paul Castle, High Life Highland Ranger, April 2025

Paul Castle is the dedicated Countryside Ranger for North Sutherland and North Caithness with High Life Highland. He has been volunteering with the Scottish Invasive Species Initiative for several years and has written about American mink and the challenges of monitoring for this invasive non-native species in the far north of Scotland.

The American mink (Neovison vison or Mustela vison) is a small member of the Mustelid family of mammals, related to otters, stoats, weasels, and pine martin and an invasive species in the UK.

My journey with mink monitoring began in north Sutherland several years ago, where I took on the role of monitoring a mink raft. For years, I faithfully checked the raft for footprints, and while I never confirmed mink presence, I was often greeted by the tracks of otters and, occasionally, rats. These experiences gave me an insight into the lives of our native wildlife and the ever-present need for vigilance against invasive species.

The Mink may look harmless given their size (smaller than an otter) but their presence has had devastating effects on native species. Introduced to the UK in 1929 for fur farming, for the once desirable fur industry (mink coats etc), mink have slowly escaped either accidentally or through deliberate releases over many years. They were eventually confirmed breeding in the wild in 1956.

In Scotland, the first mink farm opened in 1938, and by the 1980s, wild mink had spread north of the Great Glen, though they are yet to reach the far north of Scotland and some of the Scottish islands.

Mink are highly effective predators and once established they can have significant adverse impacts on local species. Prey includes birds and their eggs (native and domestic), small mammals, fish, amphibians, shellfish, and crustaceans, but their effect on water voles is particularly alarming.

Water voles (Arvicola amphibius), the UK’s fastest-declining mammal, have suffered a 95% loss of range in the past century, partly due to habitat loss but increasingly because of mink.

Water voles of course have native predators, such as herons, owls, pike, and foxes but their defence against these natural predators was to retreat inside their bankside burrows. Unlike native predators, female mink can enter water vole burrows, wiping out entire colonies.

Mink are quick to colonise areas and easily cross waterbodies such as lochs, rivers and even sea channels to reach islands, this makes monitoring essential part of conservation efforts.

Currently, I’m responsible for the only mink raft in Caithness. It’s positioned along a small burn that flows from an important loch, home to a variety of wild bird species. The burn provides a lifeline for wildlife, but it’s also a potential corridor for mink, which makes the raft’s presence vital.

What is a Mink Raft?

For those unfamiliar, a mink raft is a simple yet effective tool used to monitor mink activity.

These anchored rafts float on the water surface and house a container of moist clay. This surface layer is positioned in the centre of the tunnel. Mustelids are very inquisitive mammals and mink are no exception. They will naturally investigate any unusual objects found around water courses and tunnels seem irresistible to them. Passing through one of these raft tunnels, they they leave their prints on the clay, which can then be identified by volunteers. Regular monitoring of these clay surfaces may indicate any presence of mink in an area.

Over time, my Caithness raft took a battering from the elements. When I discovered it recently, it was in quite a sorry state and needed replacing. The tunnel was completely missing, it is anyone’s guess where that finally ended up, after the wind carried it away! The plywood boards were also split and damaged yet amazingly the clay lined container was still there, complete with faint otter prints.

Thankfully, the West Sutherland Fisheries Trust, as part of the Scottish Invasive Species Initiative (SISI), stepped in to replace the damaged raft. This initiative is another great example of cooperative conservation, bringing together ten fishery trusts and over 350 volunteers to monitor invasive mink across 43 river catchments in northern Scotland. It’s an extraordinary effort, with around 650 rafts and traps regularly checked by dedicated volunteers.

So, with a new raft in place, fresh clay and tunnel attached – back into the burn it went and I have resumed monitoring. The replacement Caithness raft has so far, only produced otter prints – and long may that continue. If mink tracks were to be identified, following careful consideration and approval, live trapping may be introduced. Live traps are also monitored by volunteers but any handling and dispatch of captured mink is only undertaken by fully trained and licensed individuals.

How You Can Help

I’m proud to be part of this collective effort. Several of my colleagues in the High Life Highland Ranger service also monitor mink rafts in their areas. Every set of otter prints we find and every mink footprint we don’t find feels like a small victory. Volunteers are always needed to help with raft monitoring. Together, we can protect Scotland’s native wildlife. Conservation is a team effort, and together we aim to keep the Highlands a haven for native species.

If you spot an American mink in the Highlands, please report it to the Scottish Invasive Species Initiative.

Paul Castle has devoted over two decades to the ranger service of North Sutherland and North Caithness. His commitment reflects his love for the area, marked by its breathtaking landscapes, diverse wildlife, friendly communities and rich natural heritage. Paul’s work plays a pivotal role in promoting and protecting the wildlife, flora, and fauna that make this part of Scotland so extraordinary.

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Visit Nature Unveiled for more blogs by Paul and the Highlife Highland Rangers and Am Baile for more on Highland History and Culture.

Greg Miller, Mink Monitoring and Control Officer, SISI Project, February 2025

The Isle of Martin is part of the Summer Isles archipelago in Wester Ross, located about 3 miles north of Ullapool. The island is owned and maintained by The Isle Martin Trust and is uninhabited but seasonally accessible by a small ferry. Isle Martin is a recognised bird sanctuary but unfortunately also visited by the invasive non-native American mink, which prey on the vulnerable native birds which live there. Greg Miller, Mink Monitoring and Control Officer with the Scottish Invasive Species Initiative, has been monitoring live-capture traps with the help of the local community and recently has had to visit the island on short notice when the traps have been triggered. Find out more from Greg about how he travelled over to the island on cold January day with the help of the Ullapool Sea Savers, followed by another trip just a few weeks later.

I was preparing for a day on the water, skippering the Ullapool Sea Savers boat for the Native Oyster Restoration project, when I got the ping from the remoti located on the Isle of Martin. Isle Martin is a community owned island which is at the entrance of Loch Broom; I’ve had two mink traps on the island for a number of months but this was the first time that one had been triggered. The custodians of the island had approached me to see if it would be possible to place traps on the island as they had noticed a steep decline in bird life over the years, with the occasional mink spotted. Mink are not the only pressures causing the sea birds (and birds in general) to decline but they sure don’t help – and it would be a step in the right direction to alleviate this added pressure.

It was going to be a cold one with the mercury hovering around freezing in the day and nose-diving at night, making for a picture postcard day, but one for wrapping up warm. I had a few jobs to do on the water before I could get to the trap. When I got to the boat the mooring ropes were frozen solid after continuous days of cold weather and the boat was full of snow that needed to be moved – deep snow can dangerously unbalance a boat. With the jobs on the water done it was time to head to the island, with Ullapool Sea Savers accompanying me for the trip. The island is a quiet place at the best of times but with snow and the light fading it felt even quieter. The snow was pristine apart from some geese prints and scat and I was wondering if the trap was triggered at all – maybe the cold had got to the remoti?

The trap was located in the centre of the island at the back of the old abandoned settlement that used to house the mill and old herring curing station. When this island was bustling with life, they tried to make a paddock by draining the few flat areas and walling them in. Where the drain met the wall and ran underneath, this I thought, made the ideal place to intercept a mink if they were to travel across the island. As I approached it became clear that I was correct as in the silence I could hear the snow and the vegetation I had used to cover the trap rustling – indicating that something had indeed been captured.  I slowly approached and confirmed that it was a mink. Once I had humanely dispatched the animal I took measurements and photos of its teeth, which can help to estimate age. Then it was time to head back to the mainland as the sun had already disappeared below the hill and the temperature was dropping quickly.

As it happens I was back to the island in February, only a few weeks later, to dispatch another mink that triggered the very same trap behind the settlement. As I was not skippering the Ullapool Sea Savers boat this time I accessed the island via The Isle Martin Trust work boat located at Ardmair jetty, where the ferry to the island departs from in season. It’s always good when working in these remote locations that there are a number of volunteers who can assist – with the help of John McIntyre and the rest of the Isle Martin Trust members monitoring the traps, this makes control work on the island a viable option. 

Greg will continue to monitor traps on the Isle of Martin with the help of the local community. Trapping on an uninhabited island is no easy feat, and we are grateful to everyone who has helped in these efforts including The Isle Martin Trust and Ullapool Sea Savers. Thank you for helping us to keep mink populations under control and protect native wildlife!

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The Scottish Invasive Species Initiative has tackled invasive plants along rivers and watercourses in northern Scotland since 2018. Working across 43 major river catchments and over a third of mainland Scotland, it is the largest invasive non-native species management and control project in the British Isles. The project operates on a landscape scale and targets key invasive plants species including: giant hogweed, Japanese knotweed, Himalayan knotweed, Himalayan balsam and American skunk cabbage.

To operate successfully on this scale we must be systematic and organised in our approach to plant control. Most obviously we need to identify the uppermost source (or sources) of each species in the river catchment and begin from there. Invasive plants in the wider environment, often introduced via escapees from ornamental gardens or in discarded plant materials, can readily spread downstream by seeds or rhizome fragments carried in the water flow. In this way, they can become widespread in a catchment using the river as their distribution highway and have detrimental impacts on biodiversity, local communities and economies. Starting control at the upstream sources and moving downstream from that point helps prevent reinfestation of cleared sites and enables us to work toward eradication.

This all sounds fantastic in theory – but how do we put it into practice? The realities of implementing this basic strategy can seem overwhelming when faced with multiple species infestations in multiple tributaries – and when accumulations of species in lower rivers are very visible and scream for attention. To get the job done successfully we need to harness and coordinate input from a wide variety of people. This year for Invasive Species Week we thought that, rather than talk about the invasive plants themselves, it would be useful to work through our approach to harnessing the most important asset we have in the battle against these species – people!

Here’s how we approach things….

1. Our partners: the fishery boards and trusts

We are a partnership project led by NatureScot but with 10 different fishery and rivers trusts as delivery partners (and not forgetting the University of Aberdeen as our academic partner). The trusts employ our team of Project Officers and provide essential local support and knowledge of the catchments in which we operate – and of the people who live and work there too. Some partner trusts have controlled invasive plants in predecessor projects and made good progress in identifying the sources and controlling the upper infestations. Partner staff assist with our hands on control work and provide invaluable support at the height of the plant control season.

So, first things first, we have established and reliable local partners with local connections and knowledge of the catchments we work in.

2. The project team

The next step is to add a team of dedicated Project Officers. Our team identify and confirm sources of infestations; develop a management strategy and plan of action for each catchment; collaborate effectively with relevant stakeholders; organise training courses for volunteers and landowners; ensure all intended control work is completed and, essentially, be the eyes, ears and mouth (!) of the project on the ground!

Our Officers coordinate and carry out much of the practical control work themselves or alongside other individuals and organisations, and ensure our work is strategic and effective. They keep records of chemical use, time spent on control work and survey for abundance of invasive plant species at control sites – all of which allow us to monitor progress over time and, crucially, demonstrate progress across years and by species.

Step two then – hire a great team and add to your local partners!

3. Contractors

Each year our Project Officers identify the worst infestations and any sites where specialist skills are required before we can move towards community-based control. In these areas, we bring in the contractors.

Contractors are often the go-to option for invasive plant control, for private landowners, organisations and projects. However, we use the contractor option sparingly. There are a number of reasons for this including:

• The need to stretch our budget as far as possible and make each £ work hard. Contractor skills cost money and so if grant funding were to run out we have no fall back option if all work is completed using these groups.
  
• There often aren’t enough contractors around to do the work needed! Therefore, we use contractors tactically and sparingly on the worst of sites in initial control years.
  
• Our desire to build capacity in communities and with volunteers (local individuals and landowners and managers) so that we have a sustainable control programme delivered by those most invested in each area and catchment. We can do this when the worst of sites have been initially tackled by expert contractors.

We also use contractors when access to a site is difficult or dangerous. For example, we have several control sites on the Rivers North, South Esk and Findhorn where giant hogweed has managed to establish itself on cliff sides, which are only accessible by top roping. Our fantastic top-roping contractors (‘Bloke’s on Ropes!’) are deployed on these sites to ensure nowhere on the river is left untreated.

Next ingredient in the mix then is expert contractors deployed to the worst or most technically challenging of sites.

4. Collaborate with other organisations

Our catchments cover large areas and within each are different landowners and stakeholders to collaborate with. By working with organisations such as the Scottish Wildlife Trust, National Trust for Scotland, Abernethy Trust, the RSPB, Forestry and Land, NatureScot and local councils, we are able to make progress more rapidly than we would do on our own.

Organisations such as these own and manage land and are invaluable allies in the fight against invasive species. Our team works with local organisation staff to carry out control work annually and, once the problem has improved, look to them to maintain and take responsibility for on-going management. To support this handover process we can, for example, provide training which enables staff to carry out control work independently of the project or lend equipment or supply chemicals to remove barriers to participation.

In recent years, we have also collaborated with Perth and Kinross Council and Moray Council to tackle infestations of invasive plants on the Almond, Findhorn, Lossie and Spey rivers. For example, the River Almond control project, which began in 2023, is funded by Perth and Kinross Council and jointly managed by the Council and Scottish Invasive Species Initiative staff. There has been a fantastic response within the local community with many enthusiastic volunteers joining to help with control work – you can find out more about this project here.

So, after partners, staff and contractors we add local organisation collaboration to the mix – and then add communities!

5. Work with communities

Community groups are an integral part of the Initiative, helping to control invasive plant species in their local area. Such groups do not normally own the land they help to manage but take ownership of their local environment and give their time, passion and enthusiasm to the cause.

Similarly to land-owning organisations, we provide training, advice, practical support and, where possible, look to hand over responsibility of sites for groups to manage independently. Some of the groups we work with include Green Hive in Nairn, the Upper Tay Paths Group and the Fearnan community group in Perthshire, various local angling clubs, the educational charity Wild Things, and the ‘Beauly Balsam Bashers’ and ‘Bolland’s Balsam Bashers’ on the River Dee. The enthusiasm and commitment for local places within such groups, we believe, exists in many communities and groups and so our role is to support such groups and to translate and harness their goodwill and passion to contributions within a wider control programme.

So having now added community groups we turn to individuals committed to making a difference – volunteers.

6. Volunteers

We consider anyone giving up their time for the project to be a volunteer. However, we give special recognition here to everyone who has signed up with the project and given up their time to help tackle invasive plants. Hundreds of people from across the project area join us every season to help with plant control – their contributions allow us to control larger areas than would otherwise be possible and help us to push control operations further downstream and work towards eradication.

Volunteers come in all forms – students and early stage careerists looking for experience to enhance employment prospects, people with time on their hands wishing to make a difference in their local area, retirees giving something back locally or enjoying the social interactions of volunteering – and many more besides. We look to provide safe and enjoyable volunteering activities with a purpose and are happy to have supported many to gain employment (with the project and elsewhere) and secure formal qualifications and skills for use in the future.

The final people ingredient to our plant control programme mix is that of landowners and land managers.

7. Landowners

Last but certainly not least – landowners. We work with landowners all the time as we need their permission to undertake any work but they are also integral to our long-term sustainable control strategy.

We aim to identify problem areas in a catchment then control infestations with a mix of staff, contractor and volunteer contributions (see all of the above) to improve the sites sufficiently to handover responsibility for future management back to landowners. By providing training, equipment, advice and practical support in the early years, we provide landowners with the tools they need to control and, ultimately, eradicate invasive species on and from their land.

There is no legal obligation on a landowner to remove invasive plants from their land – only to prevent the spread elsewhere. The reality is that often infestations are large and expensive to control and landowners may simply have neither the resources nor technical expertise or skills to complete control. By reducing the scale of the problem, removing barriers to action and simply asking landowners to participate and contribute, we have made significant progress.

We already have a number of landowners contributing to the project – including estates, organisations, farmers and businesses. Currently, over 60 voluntary landowner agreements are in place where landowners have agreed to take on responsibility for ongoing management of invasive plants on their land after initial support from the project. This approach has already allowed the project to move resources to new (downstream) sites with future management on early control locations delegated to landowners.

The key to success

And that’s our approach to people engagement within our landscape scale invasive plant control project. Identify the key elements, groups and individuals and look to bring them into a coordinated overall programme where they can see that their contributions are valuable and valued.

Controlling invasive plants at this scale can seem an impossible and overwhelming task but we know that real progress is possible when you have clear goals, priorities, a proper plan and, most importantly, a collaborative effort. There are many different stakeholders involved in the project and this collective effort is what allows us to make progress.

Volunteers, in all their different forms, have contributed an incredible 23,750 hours to our plant control project so far – the equivalent of >16 staff working with us for one year! However, it’s not simply just about the time – it’s important to recognise what that time is achieving in terms of invasive plant control. This collective effort has helped us to bring 1,580km of riverbank under management for our target invasive species – the large majority of this total on an annual basis. To give some context, Edinburgh to London (in a straight line by air) is 534km – so, each year, we are managing a riverbank length equivalent to three trips between Edinburgh and London!

Thank you to everyone who has helped us so far – we hope you will continue to be involved in the future.

The American mink control project run by the Scottish Invasive Species Initiative has been operating for 6 years and so far has captured 673 mink across the north of Scotland. Each year over 300 volunteers monitor an extensive network of rafts and traps, collectively contributing over 103,000 hours since the project began. After 6 years of co-ordinated control, it is important to look back and ask how effective the mink control programme has been so that we can continue to reduce mink numbers and the impact this invasive species has on Scotland’s ecosystems and native biodiversity. My ongoing research at the University of Aberdeen, in collaboration with the Initiative, is helping to answer these questions by investigating how the past and current mink control efforts have helped native species recover.

Going forward, we have two new opportunities available for existing and new volunteers: Mink ‘super-volunteers’ and the ‘Volenteers’. These opportunities will, respectively, help understand: (1) how effective we are in reducing mink numbers in Scotland and, (2) how these efforts have contributed to the recovery of one of the UK’s most affected species by mink predation: the water vole.

Mink ‘super-volunteers’

Mink super-volunteers will be the project’s eyes on the river and this role is suited for those interested in helping improve our ability to detect and remove invasive mink. Mink super-volunteers’ will provide key information to assess how invasive mink populations are changing year-to-year.

As with current mink volunteers, ‘super-volunteers’ would oversee monitoring rafts and traps but also collect additional data on when and where these checks occur – and whether a mink has been detected and/or captured and, equally as important, when it has not. No mink news is good news! Knowing how often mink are not detected or captured will help us understand where and why we have successfully reduced mink populations and to what extent.

To sign up please get in touch with your local Scottish Invasive Species Initiative officer. Once we have you set up with a mink raft, data will be recorded with your smartphone (or pencil and paper) and submitted through an on-line form or via email. Your monitoring rafts would be placed in a suitable spot within the project area .

Finally, super-volunteers will not exclusively be ‘mink-watchers’. As a super-volunteer you can also choose to develop your naturalist skills and learn how to identify signs of other amazing riparian species like the otter or water vole that might leave marks on or near your rafts. Do not hesitate to report any interesting signs you find!

To be a mink super-volunteer you do not require any previous expertise in mink raft monitoring or species identification as we will provide training opportunities and material – absolutely anyone can join!

‘Volenteers’

The ‘Volenteers’ opportunity will be for those of you who are interested in looking beyond the ‘mink horizon’ of the project and want to help figure out how water voles and other species may have recovered following mink control. Water voles are the UK’s second largest native rodent (second only to the beaver!) and their populations experienced a decline of over 90% during the 20^th century – largely due to predation by the American mink. They serve as ecosystem engineers, cycling the nutrients in the soil when they burrow and promoting vegetation growth. What’s not to like? Since mink control programmes started in the 21^st century, water voles seem to have recovered in different locations, but we still do not know exactly by how much or why that is.

Volenteers will be the extra eyes (and legs) on the ground to help monitor where water voles are in Scotland. Volenteers will participate in periodic water vole surveys (monthly for the summer months or twice a year, for example), which consist of walking alongside a strip of waterway in search of signs indicating water vole presence – such as dropping latrines which they use to mark their territories. Surveys would take place in late-spring and throughout the summer and so gives a perfect reason to go on a nice hike in the warm Scottish weather looking for water vole signs (or see the beasts if you’re lucky!) with friends and family.

You can choose to survey locations near your patch or mink monitoring rafts (if you are a mink volunteer), or even choose to do one-off surveys further away when you go hiking in the summer. Unlike mink raft locations, water vole surveys can be within or outside the Initiative’s area, just make sure you let us know where and when you would be interested in surveying beforehand as it may be necessary to get permission from landowners.

These surveys are a fantastic way to develop field and species identification skills, help an iconic Scottish species and spend time in nature. As with Mink super-volunteers, there is no need to have previous experience with these kinds of surveys. We will provide the training and guidance necessary to make sure you excel in the art of voling. If you are interested in water vole survey training, going out on practice surveys, or wanted to try it out before signing up let us know and we can arrange something for you.

How to sign up?

If you are looking to sign up or have any questions, do not hesitate to get in touch with me (Albert) or any other wonderful member of the Scottish Invasive Species Initiative using the contact details below. Or, if you know of someone who would be interested in participating, please send them this post (add some cute vole pictures, works a treat) and get them signed up too!

You can choose whether to be Mink super-volunteer, a Volenteer, or both, which by my naming convention would make you a Super-volenteer (now we’re talking)! If you have any doubts then do consider just giving it a go – you won’t know how rewarding this can be until you try!

We hope that these opportunities will help bring you and communities feel closer to nature and, together, help us better understand and protect our biodiversity.

Together we can help safeguard Scottish fauna and flora against invasive species in a rapidly changing climate. And who knows, maybe we can find the answer to the overarching question: how many mink is too many mink?

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Contact details

Water vole surveys: To sign up as a volunteer for water vole surveys, contact Albert Bonet Bigata: a.bonetbigata.22@abdn.ac.uk

Mink volunteers: To sign up as a mink volunteer, contact your local Scottish Invasive Species Initiative Project Officer. All contact details are available on our website – if you are unsure who to speak to you can email us at: sisi@nature.scot

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For more information on Albert’s PhD project you can read his first blog – ‘The big question: how many mink is too many mink?’

In 2023 the Scottish Invasive Species Initiative received support from Moray Council and the Ian and Clare Mattioli Charitable Trust to tackle invasive species in the Spey, Findhorn and Lossie catchments. This allowed us to trial a new method of chemical application and make rapid progress on significant giant hogweed and Japanese knotweed infestations, which would otherwise have taken several years to tackle. Find out more about these innovative methods in the blog below, written by Project Officers Karen and Elise.

Here on the rivers Findhorn, Lossie and Spey we are no strangers to large infestations of giant hogweed and Japanese knotweed, especially in lower areas of the catchments.  As we work towards bringing many of our sites under control, we cannot help but cast nervous glances at the strongholds of invasive plants further downstream.  Towering, dense forests of giant hogweed and tangled, impassable walls of Japanese knotweed await, daring us to even look in their direction with a knapsack.  The thought of beginning to tackle these bastions for the first time is a daunting one.  

But worry not dear friends, ‘tankfully’ there is a solution!  In the expansive flowering fields of invasive plants, the peace and quiet was about to be broken by the sounds of ‘engine-uity’. Armed with determination, herbicide, a pressurised sprayer and, in some areas, a tractor-mounted cage, we embarked on a mission to reclaim the land for native species. Join us in this green adventure, where we turned the tide against an ocean of invasives! 

Sprouting the Plan
In many places, we face expansive areas of dense interlocking Japanese knotweed and giant hogweed plants, often towering over our heads, smothering native biodiversity, and making access for effective control difficult. Traditional control methods via knapsack or stem injectors would require significant people power, time and would often mean that our control efforts would be limited to the outskirts of the densest stands, requiring a few years before we were finally able to meet in the middle.

We are left pondering how many hours will be spent bashing a path through the undergrowth with a fully laden knapsack? How many dauntless volunteers will disappear into the fray and will the biscuits we offer be enough to tempt them out again? And perhaps most importantly, how effective will our efforts be against such mature and overwhelmingly huge stands?

While there are many factors against us, there are also some crucial advantages on these sites, namely good track access, large areas of invasive non-native plants growing away from the river, and land managers who are supportive of new and innovative strategies. So, we hatched a plan that was as ambitious as it was ‘engine-ious’.

We turned to the newest weapon in our armoury; a motorised spray tank normally used by a local estate for controlling hill fires, with a capacity of 400 litres, a 50-metre hose and a lance that can spray up to 10 metres! With the tank safely loaded into our trailer and filled with the standard glyphosate and water mixture we’d use in our knapsacks (Roundup ProVantage at 2% concentration), we set off down the aforementioned access tracks to introduce the invasive plants of Moray to our formidable new weapon.

We quickly settled on a strategy and established that a team of three was optimal; with one team member staying in the trailer to keep an eye on the engine and to feed the hose out to the operators on the ground; another team member managing the hose between the trailer and the lance, ensuring it didn’t get snagged or tangled; and the last team member handling the business end and operating the lance.  Working together we were able to achieve a very fine level of control with the sprayer to minimise off-target application.  Using this approach our staff, volunteers, and groundskeepers were able to operate the power sprayer safely.  

Rivers Lossie and Findhorn

We started the season by tackling infestations of giant hogweed on the lower Lossie and Findhorn.  These areas were dominated by mature plants that were well on the way to flowering – if not flowering already.  On top of that, there was also a heatwave to deal with, which would have further ‘sapped’ operators’ energy and could have proved limiting if using heavy knapsack sprayers.  However, armed with the tank, we were able to travel light, with operators only carrying saws to cut their way into thickets to reach flowering heads before spraying their way out with the tank’s powerful lance.  The increased range of this lance meant large areas were covered quickly and efficiently.  It also meant that plants growing in areas that would be hard to access with a knapsack were given no respite as we were able to find safe vantage points and use our new-found range to sufficiently douse them with spray.  Seeing the amount of ground that three or four of us were able to cover in a day was incredible – but we were hardly complaining!

Later in the year the tank had another chance to shine in the fight against previously untreated Japanese knotweed.  Well-established knotweed tends to grow in large, dense stands which form thick canopies of leaves, making them ideal targets for the tank.  Using the same techniques we had perfected during our days treating giant hogweed, we marched into battle against the Japanese knotweed on the Lossie.  In some areas we were faced with solid walls of knotweed as well as smaller isolated clumps.  To use the tank on these small sections would have been irresponsible as it would run the risk of off-target application.  However, rather than just leaving these sections untreated, we instead turned to a hybrid method of treatment and tackled it the old-fashioned way, with team members working with knapsacks in tandem with the tank. 

This goes to show that every site is different, and varying abundance and distribution of invasive plants require different combinations of treatment methods, as we were about to find out on the Spey.

River Spey

In the lower Spey catchment, this year’s focus with the tank was solely on untouched Japanese knotweed stands. After identifying suitable sites, we approached it in the same way as on the Findhorn and Lossie in the first instance – on foot. This was the best approach where Japanese knotweed was growing in dense but narrow stands along both sides of an estate track.

In stark contrast, the next site was 220 meters in width and featured towering knotweed wall to wall, broken only by a couple of tracks and natural breaks between the mature stands that were increasingly merging together after years of unchecked growth. We looked to elevate our approach – literally – with a tractor mounted cage to provide us with the advantage of height to spray beyond the initial wall of knotweed without having to enter it on foot. Luckily, we had a supportive land manager with a skilled groundskeeper and his tractor who came to our aid.

This came with a new level of safety considerations but armed with a helmet and fall arrester for the person manning the cage, high visibility clothing and a thorough risk briefing for everyone involved, as well as experienced operators, we took our control to new heights.

The trailer was hooked up to the tractor where the tank was manned by a team member, the hose was secured over the cab and fed into the cage where a member of staff was utilising the pressurised lance to spray as far across the top of the knotweed expanse as possible. Some of the natural breaks between Japanese knotweed stands meant that these could be tackled from a number of angles, although the centre of some of the largest expanses remained out of reach even from the cage. In just one treatment season, this approach allowed us to nearly eliminate smaller, isolated stands and greatly reduced the extent of the larger, merging areas of growth.  This was particularly important in mixed sites, where the reduction of Japanese knotweed will improve the efficiency of giant hogweed control in following years.

Last but knot least

The humble knapsack will always have a place in the battle against invasive plants, but we cannot be afraid to think outside the box when faced with challenging sites.  Collaboration often provides new opportunities to explore innovative control methods and bring together the different skillsets necessary to make them a reality. 

The support we received from Moray Council and the Ian and Clare Mattioli Charitable Trust has made this work possible and enabled us to hire the specialized equipment required for this new method. This has allowed us to make rapid progress on really badly infested sites by covering significantly more ground, saving countless hours and ultimately being more efficient than would ever have been possible using only traditional spraying strategies. It is tricky to give exact figures as spraying on foot can be so variable, but we would estimate that using the spray tank we were able to cover 10-15 times more ground than one person could cover using a backpack sprayer in the same time period.

Having visited the sites a few weeks after treatment we are delighted with the results so far. When faced with infestations this significant the problem can often seem overwhelming, even hopeless – but take heart that there is always a solution, even on the most difficult sites!

A special thanks goes to Moray Council and the Ian and Clare Mattioli Charitable Trust for supporting the funding of this control work. Thank you also to Kellas Estate for access to the spray tank, Gordon Castle Estate for providing the tractor and their groundskeeper – and in particular for their support and confidence in us.

As always, we couldn’t have done this without our stalwart volunteers, committed partner staff and David Mitchell with his tireless skill navigating the tractor through the knotweed jungles.

The Scottish Invasive Species Initiative is a partnership project funded by The National Lottery Heritage Fund & NatureScot (2017-2023) and the Scottish Government’s Nature Restoration Fund, managed by NatureScot (2023-2026).

NatureScot employees are allocated one day per year to spend on a volunteering opportunity or activity of their choosing. In August 2023, Liz Colmer and a group from the Inverness office chose to spend their day with us and joined Project Officer Trudi on the banks of the River Beauly to tackle Himalayan balsam – an invasive non-native species. The gang cleared a woodland area, helping to preserve the native flora found there and prevent this highly invasive plant from reinfesting the riverbanks.

On Wednesday 9 August, myself and some NatureScot colleagues; Megan, Cat, Lucie, Kat and Susi and Susi’s daughter Lucy met at the Beauly Fisheries Office to meet with Trudi Clarke, Scottish Invasive Species Initiative Project Officer – Cromarty, Ness & Beauly catchments.

We were meeting to go Himalayan balsam bashing.  This opportunity was organised by Susi Hodgson and advertised on the NatureScot intranet.  I have often wondered what I would do with a volunteer day and so when this opportunity to help in my local area appeared, I couldn’t pass it up.

A short way from the Lovat Bridge, in some riparian woodland by the River Beauly, was our location.  As we were walking in, we spotted a roe deer bounding across the field and Trudi spotted a kingfisher a bit later.

We started with a brief introduction from Trudi; Himalayan balsam is an invasive species, it spreads fast, dominating and blocking the light of other native plants and its shallow roots do not help to prevent soil erosion along the banks of the river.  She explained that the plant is non-toxic and the technique for pulling it out by the root and placing it in piles, or over the branches of trees, so that the roots dry out and it can no longer spread. It is best to pull it at this time of year before it goes to seed, as the seed pods can scatter quite explosively and are responsible for the invasive element of this annual plant.

At first inspection, there didn’t look to be much Himalayan balsam by the river (due to success of previous years’ bashing efforts) but it wasn’t long before we found vast areas of it deeper into the woodland.  The plant is easy to pull out, however, it was growing at all different heights so involved stooping.  It was hard work but immensely satisfying seeing the areas we had cleared and the space and light it created for the other plants. 

It was great to be outside, working alongside colleagues and I enjoyed the smell of water mint, which was growing alongside the Himalayan balsam in places, and will no-doubt now flourish without being shaded out by the invasive invader we’d spent the day removing.

Would you be interested in joining us for a balsam bashing volunteer day in 2024? Get in touch! These volunteer days are held all across our project area (including Highland/Eastern Perthshire, Angus, Aberdeenshire, Moray and northern Highlands) in July and August. Contact: sisi@nature.scot for more information.

The Scottish Invasive Species Initiative was delighted to have Tony Martin of the Waterlife Recovery Trust attend and present at our recent project conference in Aviemore.  Tony leads work which controls and is close to eradicating the American mink from a sizeable chunk of East Anglia using volunteers and an extensive network of smart traps.  In this blog he tells us about this work and offers his thoughts and ambitions for a “mink free GB”.  The Waterlife Recovery Trust approach to things is in some ways very different to ours in the north of Scotland but there are, of course, many similarities.  We share the same objective of delivering American mink control at landscape scale working with volunteers and communities – and it’s always good to hear of different tactics and to share knowledge and experience to learn and improve as we go along. We look forward to seeing how the project progresses over the coming years.

Despite decades of trapping costing millions of pounds, American mink remain firmly established in Britain’s countryside from the south coast of England to the north of Scotland. It’s hardly surprising, therefore, that few people would give any credence to the idea that mink could be entirely eradicated from this rather large island of ours. It’s a completely barking mad concept, obviously.

I had the privilege of leading the rodent eradication project on the sub-Antarctic island of South Georgia – an equally preposterous concept. Who in their right mind would believe it possible to eliminate every single one of the millions of rodents on this huge, mountainous, glacier-riven island, a thousand miles from anywhere, with no roads or access by air? But we did it, and in so doing I learned an important lesson – that it’s foolish to dismiss even the daftest idea without giving it proper consideration. Might mink eradication in Britain be possible, after all? Would it not be worth carrying out a trial to discover if it might be feasible?

Pest eradications can only work if the area to be ‘treated’ cannot be readily re-invaded. Usually the barrier to re-invasion is the sea, which is why small islands lend themselves to this process. But a meaningful trial of mink eradication would need to cover a very large area (5,000 sq km, say), and there are no islands of a suitable size with mink on them in Britain. Even Lewis is less than 2,000 sq km in extent. The next best thing might be a large peninsula, with effort put in place to stop re-invasion from its landward side. I live in East Anglia, which happens to be a large peninsula, sort of…..

The first part was easy – increasing collaboration and cooperation. A Steering Group of key stakeholders was set up and has continued to meet quarterly. The Steering Group discusses and agrees matters such as methodology, Best Practices, fund raising and strategy, ensuring a consistent, effective, safe and humane way of removing mink across the region. The second part was establishing the scientific basis for the strategy. To be successful, the project would need to be adaptive – continuously learning and improving as evidence dictated. That evidence would come from close examination of the mink caught, and from keeping a close eye on changes in the Catch Per Unit Effort (CPUE), a proxy for mink abundance – number of mink caught per thousand trap nights, to aid targeting of traps and volunteer effort. To that end, every mink caught would need to be measured, weighed, DNA sampled (the tip of an ear is sufficient) and teeth taken to determine age.

The third and fourth factors were to do with the practical process of mink removal. Aerial spreading of toxic bait, as used in many pest eradication campaigns worldwide (including on South Georgia) was not practical for many reasons, and trapping was the next best option. The question was whether we could find ways to improve the efficacy of trapping to the extent that literally every mink could be captured, while at the same time avoiding harming the good guys – the native wildlife we seek to protect. The two elements we focused on were (a) making trapping far less labour intensive than hitherto, and (b) increasing the probability that a mink near a trap would be enticed to enter it.

We tackled the first problem by taking advantage of electronic boxes that alert the trapper when a trap door closes; we call them Remote Monitoring Devices (RMDs). These boxes (one per trap, turning it into a ‘smart’ trap) use the cellular phone system to send alerts by email and text message with 100% reliability, and their use means that a trap visit need only be made when there’s a high probability of an animal being in the trap, rather than daily. This reduces labour (and often fuel) by up to 98%. These huge efficiency gains mean that traps can be active 24/7/365 at every site, other than when temporary retreat is demanded by flash flooding, and that’s crucial. Trapping effort per location is far greater than is normally achieved with a traditional raft fitted with a clay pad to detect mink footprints. We detect mink by catching them, rather than by looking for their footprints.

The second issue was approached by recognising what every mink trapper knows – that a second mink will often follow a first mink into a trap, within days or even hours. They do so because of the scent left by the first animal, and that eye-watering scent mostly comes from glands either side of the anus. We now harvest that eau de mink from every animal captured, carefully expressing it, drop by noxious drop, onto roll-your-own cigarette filters. The filters are then stored in a freezer until used as scent bait in our traps, suspended above the treadle inside a hollow practice golf ball. And they work – there’s now plenty of evidence to show that mink are drawn into traps by following this scent to its source.

So far, so good, but back to the eradication trial – how could the test area (termed the ‘Core Area’) be isolated from the rest of Britain, stopping mink immigration from untrapped areas? The answer was to use East Anglia’s natural defence – the sea – to prevent incursion from the north and east, and to establish a 60 km-wide ‘Buffer Zone’ of traps to stop inward movement from the west and south (see Map 1). The Core Area comprises a large number of contiguous river catchments covering the central and eastern portions of Norfolk and Suffolk, totalling 5,853 sq km, while the Buffer Zone covers 10,423 sq km. Together, they amount to 12.5% of England.

Another question was how we would define trial success. Would an absence of mink in the area for a day suffice? Or for a week or a year? And how would we know if that had been achieved? We can’t expect to mobilise East Anglia’s entire population to look for mink on a particular night, let alone every night for a year. Furthermore, perhaps it’s not necessary to remove every mink – eradication would inevitably ensue if mink remained, but all of one gender, or if reproduction stopped. In the end, the decision was made to define trial success as the lack of evidence of reproduction over a 12-month period despite substantial search effort. We could never expect to prove that no reproducton had occurred, no more than we can prove that the Loch Ness Monster is a myth. But we would expect even one mink family to come to our attention, either through a report from a member of the public (as frequently happens from far and wide – a live sighting or a roadkill) or by way of the capture of a very young mink or a lactating female.

With funding from Natural England, water companies, Internal Drainage Boards (IDB) and private donors, and the participation of many hundreds of volunteers, reserve wardens, IDB staff etc, a comprehensive network of electronically-monitored traps was set up across East Anglia during 2020 and 2021, in both the Core Area and Buffer Zone. The average trap density across the Core Area was just one per 18 sq km. Catches were high initially, as was catch per unit effort (CPUE), but both rapidly diminished (see Figures 1 and 2). We found that, on average, CPUE dropped by some 70% each year, which means that fewer than 1% would remain after just 4 years.

So,the big question: is mink eradication feasible on a landscape scale in England? Remarkably, the tentative answer is ‘Yes, it is’. We almost reached the point of zero reproduction in the Core Area in 2022, before belatedly hearing of an unconfirmed but persuasive sighting of a single mink family in eastern Norfolk. The 2023 breeding season has, though, come and gone with no evidence of mink reproduction despite many thousands of hours of sighting effort, and over 106,000 trap nights of catch effort. We’re not quite ready to declare the trial to be over, but that will happen if no evidence of breeding in 2023 comes to light very soon. The occasional mink does turn up in a trap, but the genetic evidence indicates these are probably immigrants that have found their way in to the Core Area along the coast. We are now in little doubt that the eradication of American mink is entirely feasible in England, and almost certainly in Wales, too. What’s more, this could be achieved within no more than five years of setting up a smart trap network, and substantially through the efforts of trained volunteers.

So, what about Scotland? Is mink eradication feasible here? Although there are certainly greater challenges (lower density of people to visit traps, poor to no mobile coverage in some areas, access difficulties in winter, waterways in spate after heavy rains among them), and costs would be greater per unit area in consequence, I suspect that Scottish ingenuity and determination would win through in most mainland regions. The west coast and western isles do pose huge difficulties, though, and I’m unsure whether all mink could be removed from this vast and complex area with existing technology and methodology. There are two new tools on the horizon that may help in even these remote and windswept places, though. Firstly, a satellite-linked RMD is likely to be available within a year, so traps in even the most remote spots can then be electronically monitored. Secondly, a synthetic version of mink lure should soon be available, closely mimicking the real thing, but dispensed from handy containers which every trapper can carry in their kit. Together, these two innovations should bring a mink-free Scotland that bit closer.

I sign off from a train to Oban. I have been invited to Lismore and Mull this week, with a view to seeing if smart traps can enhance the efficiency of trapping mink in western Scotland, as they have in England. Mink are threatening to force the closure of an organic, free-range poultry business on Lismore, so the stakes are high. I very much look forward to what I’m sure will be an educational and enjoyable visit for this resident of the flat Fenlands of Cambridgeshire.

For more information on the Waterlife Recovery Trust you can visit their website at: https://www.waterliferecoverytrust.org.uk/