American mink control on inland rivers in southern England: An experimental test of a model strategy

Invasive species are an important driver of global biodiversity loss. Under international legislation, the UK has an obligation to eradicate or to control the alien, invasive American mink. Using a large-scale field experiment, we tested the effectiveness of a specified mink removal strategy, identified through earlier modelling work, in reducing the relative abundance of mink. We found that mink removal could be effective in reducing mink populations with four months or less of trapping per year, over only 2-3 years, but that for small sites (c. 20 km) a flexible, reactive approach, coupled with continual monitoring for mink presence is necessary. Survival of reintroduced water voles at four sub-sites within our mink removal sites suggest that the reactive mink removal strategy adopted in this study was sufficient for water vole protection. We discuss the use of an adaptive management approach in local mink management, and consider the wider implications of our results for invasive species control on mainlands.     

Trapping for mink control and water vole survival: Identifying key criteria using a spatially explicit individual based model

Introduced alien species are the second most important threat to global biodiversity after habitat loss. The American mink Mustela vison has been introduced to several countries and is threatening a number of native species worldwide. We developed a spatially explicit and individual based model as a planning tool to identify key criteria for the implementation of trapping campaigns as a way to control open American mink populations. We first predicted the minimum effort required to reduce populations of mink below a certain threshold and the best time of year in which to trap mink to minimise their numbers. We then employed this methodology to predict the best trapping strategy to ensure the long-term survival of the water vole Arvicola terrestris, one of the species most endangered by the spread of the mink in the UK. We also applied the mink and water vole population models to rationalise a set of observed data in an area of 50 × 30 km in the Upper Thames (UK). The model predicted that it is necessary to remove mink for at least 3 months every year and that a mixed strategy of trapping during the mating, late dispersal and winter seasons is best for keeping mink at low densities. Concentrating trapping during the late dispersal and winter seasons is instead best for ensuring the long-term survival of water voles. Targeting immigrating juvenile mink as well as reproductive adults is important. The model also showed that trapping efficiency might be an important factor to consider when choosing periods in which to trap.     

The American mink in Europe: Status, impacts, and control

We examine the distribution of American mink Mustela vison in 28 European countries, and we review the impacts of this invasive species and the efforts made so far in controlling it. Our study reveals that, although mink farms are mostly concentrated in northern countries, mink are widely distributed across Europe, and that in some countries mink are apparently declining, although in most cases the causes are unknown. Countries for which the impact of mink on native species has been studied show that mink can have a significant effect on ground-nesting birds, rodents, amphibians and mustelids. The overall economic impact of feral mink seems to be relatively small but can be significant in specific regions. Recently, a number of eradication and local control projects have been carried out throughout Europe, indicating that these actions could be effective to protect native species. A consistent body of knowledge is starting to accumulate on issues concerning the American mink as an invasive alien species, but, as this review highlights, for most European countries there is currently a limited knowledge about its distribution or impacts. Taking all these observations together, we present some of the actions that have recently emerged as effective for dealing with this species and discuss which considerations may further encourage competent European authorities to take action to prevent and mitigate impacts of American mink.     

Effects of feral mink removal on seabirds, waders and passerines on small islands in the Baltic Sea

We studied the effects of removing introduced American mink (Mustela vison) on the number of birds breeding on small islands in the Baltic Sea. During autumn 1992-2001 mink were removed from a 72 km² area, while mink were not removed from a 35 km² control area. Second removal (125 km²) and control areas (130 km²) were established during 1998-2001. The breeding densities of ringed plover (Charadrius hiaticula), arctic skua (Stercorarius parasiticus), arctic tern (Sterna paradisaea) and rock pipit (Anthus petrosus) increased markedly in the removal areas in comparison to the control areas. Turnstone (Arenaria interpres), common gull (Larus canus) and wheatear (Oenanthe oenanthe) also appeared to increase. Two species already extinct in one of the removal areas, razorbill (Alca torda) and black guillemot (Cepphus grylle), returned to breed in the area. Breeding densities of great black-backed gull (Larus marinus), oystercatcher (Haematopus ostralegus) and white wagtail (Motacilla alba) were unaffected. We conclude that it is possible to remove feral mink from large archipelagos with many small islands, and that mink removal increases the breeding densities of many bird species in this habitat.     

Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile

Biological invasions constitute one of the most important threats to biodiversity. This is especially true for “naïve” birds that have evolved in the absence of terrestrial predators in island ecosystems. The American mink (Mustela vison) has recently established a feral population on Navarino Island (55°S), southern Chile, where it represents a new guild of terrestrial mammal predators. We investigated the impact of mink on ground-nesting coastal waterbirds with the aim of deriving a vulnerability profile for birds as a function of different breeding strategies, habitat, and nest characteristics. We compared rates of nest survival and mink predation on 102 nests of solitary nesting species (Chloephaga picta, Tachyeres pteneres), on 361 nests of colonial birds (Larus dominicanus, Larus scoresbii, Sterna hirundinacea), and on 558 artificial nests. We calculated relative mink and bird densities at all nest sites. Nests of colonial species showed the highest nest survival probabilities (67-84%) and no predation by mink. Nest survival rates for solitary nesting species were lower (5-20%) and mink predation rates higher (10-44%). Discriminant analyses revealed that mink preyed upon artificial nests mainly at shores with rocky outcroppings where mink were abundant. High nest concealment increased the probability for predation by mink. Conservation planning should consider that invasive mink might severely affect the reproduction success of bird species with the following characteristics: solitary nesting, nesting habitat at rocky outcrop shores, and concealed nests. We recommend that work starts immediately to control the mink population with a priority in the nesting habitats of vulnerable endemic waterbirds.     

Using prey densities to estimate the potential size of reintroduced populations of Eurasian lynx

In previous centuries human activities had a profound effect on the distribution of Eurasian lynx (Lynx lynx) in Europe. The species has since been reintroduced to several areas but still much former range remains unoccupied. A relatively poor coloniser, it is likely that further reintroductions will be required to restore the species to potentially suitable areas. However, in the human-modified landscapes of Europe, where extensive wooded habitats are often fragmented, it is important to assess the potential lynx population size that could be supported in the available habitat. A previous study identified two networks of potential lynx habitat in Scotland. The present study further explores the feasibility of reintroducing lynx to Scotland by estimating the potential population size for the identified habitat by considering the availability of prey. An examination of lynx and wild ungulate densities from four areas in Europe, revealed a highly significant relationship between lynx density and the density of ungulate biomass. Based on the biomass represented by the densities of roe, red, sika and fallow deer occurring in two potential lynx habitat networks in Scotland, it was predicted that habitat in the Highlands could support 2.63 lynx 100 km⁻², while the Southern Uplands could support 0.83 lynx 100 km⁻². Applied to the amount of identified habitat, it is estimated that a Highlands habitat network could support around 400 lynx, and a Southern Uplands network, around 50. Scotland could support a large population of Eurasian lynx, which at current estimates, would be the fourth largest in Europe.     

Why are there fewer signs of mink in England? Considering multiple hypotheses

Understanding the causes that determine the spread and subsequent population trends of invasive species is important as it can help predict and manage their impact, as well as advance the theory of invasion. The American mink Mustela vison is a riparian mustelid and an invasive species in several countries. Mink have been introduced to England in the early decades of the last century and have been expanding their range until the mid-eighties. Since then, however, the number of sites occupied by mink has been declining. We investigated three possible causes of such a decline: (1) A downtrend of the fur farming industry; (2) An increase of European polecats Mustela putorius; (3) An increase of Eurasian otters Lutra lutra. Mink trends were derived from data collected by the National Otter Survey, a large-scale long-term survey of the whole of England from 1977 to 2002. We discuss how the observed decline in the number of sites occupied by mink may be due to a combination of an actual decrease in the distribution and density of mink and to a change in the focus of mink activities away from water, rather than to a change in their marking behaviour. Taken together, our results suggest that the decline of mink is related to an increase in the native otter population through interspecific competition, although at a local level also other factors may be important. As the otter population is still increasing, it is likely that the number of sites occupied by mink will continue to decline, a process that may be beneficial to aquatic and semi-aquatic species suffering from mink predation.     

The value of marine ecological data collected by volunteers

Volunteers are potentially a huge scientific resource but there is scepticism among some scientists about the reliability of data collected by inexperienced people. An assessment was therefore made of the ability of a group of 13 volunteers, recruited by the Earthwatch Institute, to collect valid data in a project that aimed to map the distribution and abundance of common littoral organisms on shores of the Isle of Cumbrae, Scotland. The volunteers ranged considerably in age, educational background, knowledge and experience. They were capable of performing straight-forward tasks, such as learning to identify species, recording their occurrence on specific parts of the shore and making length measurements of samples of some gastropods. They made some recording errors during the fieldwork but similar errors were also made by experienced scientists and it is recommended therefore that all ecological studies should include quality control of data whether or not they involve volunteers. The assessment of abundance was problematic. Volunteers’ assessments for some species were inconsistent and there is evidence that individuals interpreted the scale in different ways. It is suggested that these problems stemmed from: (1) a lack of field experience in the volunteers; (2) inadequate guidelines on the use of the abundance scale; and (3) insufficient training before field surveys commenced. However, projects themselves may benefit in unexpected ways from the input of volunteers. They contributed taxonomic and computing skills to the current project. Members of the group also offered new insights by developing hypotheses relating to populations of gastropods during their fieldwork. These were tested and could have formed the basis of longer-term research programmes. There were also educational benefits for the volunteers who were involved in the project. These included increased knowledge of marine issues and clearer understanding of the ways in which scientific studies are undertaken.     

Modifying And Evaluating a P Index For Denmark

The European Union recently adopted the Water Framework Directive aiming at protecting and enhancing the status of aquatic ecosystems. The Water Framework Directive mandates EU member states to develop river basin management plans for each river basin. Consequently, water district managers need tools for identifying critical source areas within a catchment in order to target cost-effective remedial measures. The P Index could be well suited for screening large areas because of its low demand for input data and manpower compared to mechanistic, process based models. The P Index needs to be modified to local or regional conditions in order to incorporate all potential P loss pathways. In Denmark tile drains and leaching are considered major P loss pathways. We modified the Pennsylvania P Index to reflect Danish conditions. The Pennsylvania P Index and the modified Danish P Index were applied on a 1000 km² catchment. In order to test the P Indices we examined their capability to correctly rank measured annual diffuse total P losses from twelve sub-catchments within the 1000 km² catchment. Both P Indices, calculated on a sub-catchment basis, correlated with total P losses. The Danish P Index, however, performed distinctly better than the Pennsylvania P Index and explained 85% of the variation in measured diffuse total P losses.     

Squirrel poxvirus: Landscape scale strategies for managing disease threat

Squirrel poxvirus (SQPV) is a well-documented example of pathogen-mediated competition between an invasive species, the grey squirrel (Sciurus carolinensis), and a native species, the Eurasian red squirrel (Sciurus vulgaris). SQPV causes disease with high mortality in red squirrels but appears non-pathogenic in grey squirrels. Not all populations of introduced grey squirrels carry the virus, notably those in Scotland and Italy, and the rate of red squirrel replacement by grey squirrels is some twenty times faster in those areas where grey squirrels carry the virus. Here we develop strategies to manage the SQPV disease threat to red squirrels by reference to the largest, designated red squirrel refuge site in England, Kielder Forest (50 000 ha). Using modelling techniques, we identify four main corridors within the buffer zone by which grey squirrels will reach Kielder, initially within two years and in large numbers within 10 years. Assuming that greys will not settle within Kielder because of the unfavourable nature of the spruce habitat, we predict that SQPV disease will burn out at the edges of the forest, although many red squirrels will die. This burn-out is unlikely to be the scenario in other refuge areas where the habitat is more favourable to greys. We conclude that the conservation of red squirrels will depend on minimising contact between red and grey squirrel populations, and we advocate monitoring grey squirrels in corridors within buffer zones around refuge areas, and removing them when detected.     

Numerical and behavioral responses of waterfowl to the invasive American mink: A conservation paradox

A behavioral response is usually the first adaptation of animals to environmental changes such as the introduction of an alien invasive species, and it seems to be the most important factor in reducing the negative impact of new predators on naive prey. This study examined changes in the abundance and behavior of breeding coots (Fulica atra) and great crested grebes (Podiceps cristatus) in response to invasion of the Mazurian Lakeland (NE Poland) by American mink (Neovison vison), first recorded here in 1984. Feral mink densities varied from 1.0 to 14.6 individuals per 10 km of shoreline. Mink were responsible for the losses of 17–58% of experimental clutches (artificial nests containing chicken eggs) that were deployed. Mink destroyed more experimental clutches than other predators; the effects of mink predation were similar in reeds and on the bank. Radio-tracking showed that mink avoided lake banks near human settlements. Mink have markedly affected the breeding distribution of both species and caused a greater than 20-fold decline in coot numbers. For coots and grebes breeding distribution and nesting success were positively associated with built-up areas along lake shores and also with whether the birds were breeding in colonies. Increased brood survival of coots and grebes near human settlements is a paradox in the sense that a man-made habitat change has provided refuge from an alien predator.     

Development of population control strategies for mink Mustela vison, using floating rafts as monitors and trap sites

We describe a raft designed to act both as a monitoring device and as a trap site for American mink, Mustela vison. The raft uses a wet tracking medium to record footprints. It was evaluated during summer in a chalk-stream river catchment in central southern England. The raft detected mink at significantly more sites (55%) than did either owners and managers relying on field observation and trapping (19%), or established biological survey techniques (33%).

The primary value of the raft is seen to be in experimental field research to determine appropriate policies for mink management. In the pilot application described, rafts were used to derive a minimum mink population estimate for the catchment, and to determine the benefit of a commercially available scent attractant for mink. The raft also has immediate value in management to improve several aspects of trapping for mink population control: efficiency, non-target involvement, and post-removal monitoring.     

Monitoring rare or elusive large mammals using effort-corrected voluntary observers

Populations of rare or elusive large mammals are difficult to monitor, because they usually are secretive, solitary, occur at low densities, and have large home ranges. The global trend of generally decreasing large carnivore populations necessitates new, feasible, reliable, and cost-effective monitoring methods. We evaluate an index method developed for monitoring populations of moose (Alces alces) based on voluntarily and systematically collected observations from hunters, corrected for effort, for use in monitoring populations of large carnivores in Sweden. For our evaluation, we used independent estimates of minimum brown bear (Ursus arctos) densities from DNA-based scat surveys and brown bear distribution from mandatory reports from successful bear hunters. We verified that the index correctly reflected bear distribution. We also found strong linear relationships between the indices and the independent density estimates for bears at the scale of local management units (about 1000-2000 km²) in all three regional study areas (adjusted R² = 0.88-0.60). Our results suggest that systematic, effort-corrected reports of observed animals can be an alternative and accurate monitoring method for the conservation and management of large mammals occurring over large areas when large numbers of willing volunteers are available (effort >30,000 h).     

Regional and local scale variations in soil organic carbon stocks in West Greenland

The soil organic carbon (SOC) pool of the Northern Hemisphere contains about half of the global SOC stored in soils. As the Arctic is exceptionally sensitive to global warming, temperature rise and prolonged summer lead to deeper thawing of permafrost‐affected soils and might contribute to increasing greenhouse gas emissions progressively. To assess the overall feedback of soil organic carbon stocks (SOCS) to global warming in permafrost‐affected regions the spatial variation in SOCS at different environmental scales is of great interest. However, sparse and unequally distributed soil data sets at various scales in such regions result in highly uncertain estimations of SOCS of the Northern Hemisphere and here particularly in Greenland. The objectives of this study are to compare and evaluate three controlling factors for SOCS distribution (vegetation, landscape, aspect) at two different scales (local, regional). The regional scale reflects the different environmental conditions between the two study areas at the coast and the ice margin. On the local scale, characteristics of each controlling factor in form of defined units (vegetation units, landscape units, aspect units) are used to describe the variation in the SOCS over short distances within each study area, where the variation in SOCS is high. On a regional scale, we investigate the variation in SOCS by comparing the same units between the study areas. The results show for both study areas that SOCS are with 8 kg m^?2 in the uppermost 25 cm and 16 kg m^?2 in the first 100 cm of the soil, i.e., 3 to 6 kg m^?2 (37.5%) higher than existing large scale estimations of SOCS in West Greenland. Our approach allows to rank the scale‐dependent importance of the controlling factors within and between the study areas. However, vegetation and aspect better explain variations in SOCS than landscape units. Therefore, we recommend vegetation and aspect for determining the variation in SOCS in West Greenland on both scales.     

A New Assessment of Soil Loss Due to Wind Erosion in European Agricultural Soils Using a Quantitative Spatially Distributed Modelling Approach

Field measurements and observations have shown that wind erosion is a threat for numerous arable lands in the European Union (EU). Wind erosion affects both the semi‐arid areas of the Mediterranean region as well as the temperate climate areas of the northern European countries. Yet, there is still a lack of knowledge, which limits the understanding about where, when and how heavily wind erosion is affecting European arable lands. Currently, the challenge is to integrate the insights gained by recent pan‐European assessments, local measurements, observations and field‐scale model exercises into a new generation of regional‐scale wind erosion models. This is an important step to make the complex matter of wind erosion dynamics more tangible for decision‐makers and to support further research on a field‐scale level. A geographic information system version of the Revised Wind Erosion Equation was developed to (i) move a step forward into the large‐scale wind erosion modelling; (ii) evaluate the soil loss potential due to wind erosion in the arable land of the EU; and (iii) provide a tool useful to support field‐based observations of wind erosion. The model was designed to predict the daily soil loss potential at a ca. 1 km² spatial resolution. The average annual soil loss predicted by geographic information system Revised Wind Erosion Equation in the EU arable land totalled 0·53 Mg ha⁻¹ y⁻¹, with the second quantile and the fourth quantile equal to 0·3 and 1·9 Mg ha⁻¹ y⁻¹, respectively. The cross‐validation shows a high consistency with local measurements reported in literature. © 2016 The Authors. Land Degradation and Development published by John Wiley & Sons, Ltd.     

Designing a transfrontier conservation landscape for the Maputaland centre of endemism using biodiversity, economic and threat data

A number of global priority region schemes have been developed, but local assessments are needed to identify priority areas for conservation within these regions. Here, we describe results from a conservation assessment for Maputaland, part of a biodiversity hotspot in southern Africa that is also the focus of the Lubombo Transfrontier Conservation Area (TFCA) initiative between South Africa, Mozambique and Swaziland. The TFCA seeks to establish new state-, private- and communally-managed conservation areas to boost economic development through nature-based tourism and game ranching. The assessment will guide the TFCA process and used a systematic conservation planning approach to design a landscape to conserve 44 landcover types, 53 species and 14 ecological processes. The assessment also included data on modelled risk of agricultural transformation, of which low-risk areas were selected where possible. The current PA systems in the three countries cover 3830 km², which represents 21.2% of the region, and meet the representation targets for 46% of the conservation features. The proposed conservation landscape adds 4291 km² of new core areas and 480 km² of linkages and, if appropriate, could provide potential revenues of US$18.8 million from game ranching, based on modelled large ungulate density, life history and game auction data. We also discuss the benefits of including data on widely distributed, better known conservation features together with less-well studied, range-restricted species and the advantages of using agricultural transformation risk data in conservation assessments.     

Spatial and temporal assessment of linear erosion in catchments under sloping lands of northern Laos

Linear erosion (LE), including rilling and gullying, has been identified as the major problem for sustainable agriculture in steepland areas. It causes severe environmental, economic, and social impacts. This issue is even more crucial in those areas undergoing rapid changes in land use, as for example northern Laos, and may dramatically affect soil conservation. Despite an increasing interest in the sloping lands of tropical areas, field evaluations of LE are still infrequent. Furthermore, the controlling environmental factors of topography, land use, climate and soils at the catchment level are seldom analysed. Our main objective was to quantify the spatial and temporal variations of LE at the catchment level and at a yearly basis. The study was conducted in a 0.62 km² watershed of Laos (Luang Prabang province) representative of the slash and burn systems of sloping lands. Linear erosion was monitored from 2001 to 2003 within 9 sub-catchments of differing surface areas, topographic characteristics and land use. The length, depth and width of the linear erosion features were recorded every 5-m from their headcuts to their outlets in order to estimate the total catchment LE. 52 linear features, mainly rills, were formed or developed within the study area with a mean erosion rate of 1.3 Mg ha^{− 1} y^{− 1}. LE rates ranged between 0.1 Mg ha^{− 1} y^{− 1} in 2003 to 2.4 Mg ha^{− 1} y^{− 1} in 2001. LE features mostly occurred within croplands where erosion rates reached 18 Mg ha^{− 1} y^{− 1}. In 2001 and 2002 there was a significant correlation between LE and the proportion of the catchment area under crops (r = 0.88 and r = 0.69, respectively). However this was not the case in 2003 when few rills developed. In 2002 only, LE correlated well with the catchment surface area, the mean slope gradient and the sub-catchment perimeter confirming the non-constancy of LE landscape relation under varying rainstorm conditions. A linear regression model for LE prediction at the catchment level, generated from 2001 data, was able to explain 78% of LE variance for the 9 sub-catchments. However, this model was unable to predict accurately LE for 2002 and 2003 (ME > 5 Mg ha^{− 1} y^{− 1}). This method for quantifying the linear erosion at the catchment level and some of its controlling factors can also be used for prediction over larger areas since topography and land use data, closely correlated with LE, are easily accessible.     

Quantifying the fine scale (1km × 1km) exposure and effects of ozone. Part 1. Methodology and application for effects on forests

Surface ozone concentrations show very large local variability. This, in rural areas, is largely a consequence of the degree to which the surface air is decoupled from the bulk of the atmosphere by nocturnal and winter stability effects and of the aerodynamic roughness and topography of the countryside. Procedures have been developed to simulate these effects and have been used with O₃ data from a regional monitoring network to quantify exposure of vegetation to mean and peak O₃ concentrations. The index of exposure to potentially phytotoxic O₃ concentrations is the AOT40 (accumulated exposure over a threshold of 40 ppb) expressed in ppb.h. The accumulated exposure of crop and forest surfaces to ozone is shown to increase approximately linearly with altitude and along a gradient from 3000 ppb.h in north west Scotland to 7000 ppb.h in the south of England. The area of UK forest which exceeds the critical level for ozone effects (10⁴ ppb.h above 40 ppb) totals 2.0 × 10⁴ km² and represents 47% of afforested land. The areas affected include most of southern and central England and Wales and large plantation forests of Northumberland and the Scottish borders.     

The effects of persecution on age of breeding and territory occupation in golden eagles in Scotland

Several studies have documented negative effects of persecution by humans on the population dynamics of large birds of prey. Several areas have seen a reduction in persecution in modern times, but the demography of large raptors still makes these birds vulnerable to such effects. In a GIS analysis, utilising data collected during two national censuses of the golden eagle Aquila chrysaetos in Scotland and contemporary data on the distribution of poisoning incidents (a common method of raptor persecution in Scotland), we show that persecution was associated with a reduction in the age of first breeding, territory vacancies, and the use of territories by non-breeding immatures. Persecution was therefore reducing adult survival and distribution and was probably creating ecological traps that attract mobile immatures, increasing subadult mortality in birds that may originate from persecution-free areas. Mapping a form of land management unique to moors managed for red grouse Lagopus lagopus scoticus shooting, where most poisoning occurs, we also show similar associations between golden eagle demography and grouse moor management. As such, persecution may be having a major impact on the golden eagle population of Scotland, since it occurs over a wide area and at least in some areas has continued unchecked over many decades.     

Public and professional views on invasive non-native species – A qualitative social scientific investigation

The potential of invasive non-native species to modify ecosystems is well established. Yet, the resulting visibility of the field of invasion biology and its growing influence on policy decisions has led to the development of persistent critique. In addition, public opposition to the removal of non-native species has repeatedly delayed interventions, sometimes to the point where eradication has become impossible. Understanding the views of the lay-public is thus of crucial importance. Our study investigated views on invasive non-native species as held by both the general public and ecologists. We chose an in-depth qualitative social scientific approach to identify species attributes that people draw on to evaluate biological invasions and potential management options. Interviews and focus group discussions (n = 79 participants) were conducted in the North-east of Scotland, and included members of the public from a wide range of backgrounds, as well as research ecologists and professionals dealing with invasive non-native species. Two key arguments, namely (i) harmfulness of a species and (ii) human responsibility for its spread, shaped both ecologists’ and lay-people’s discussions. Non-nativeness was understood by our participants in various ways and did not necessarily raise concerns about a species. Our results indicate that for information campaigns on species management to be effective, values inherent to the debate about invasive non-native species need addressing in a more explicit and transparent manner. Arguments such as human responsibility that are currently neglected in the scientific discourse, but that were important criteria for a wide range of participants, should be made explicit.