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. 2021 Apr 8;16(4):e0249904. doi: 10.1371/journal.pone.0249904

Aquatic invasive alien rodents in Western France: Where do we stand today after decades of control?

Manon Bonnet 1,2, Gérald Guédon 3,*, Marc Pondaven 3, Sandro Bertolino 4, Damien Padiolleau 5, Vanessa Pénisson 6, Francine Gastinel 7, Fabien Angot 8, Pierre-Cyril Renaud 1, Antonin Frémy 9, Olivier Pays 1,2,*
Editor: Bi-Song Yue10
PMCID: PMC8031452  PMID: 33831091

Abstract

Two aquatic invasive alien rodents, the coypu (Myocastor coypus) and muskrat (Ondatra zibethicus), have taken over a significant amount of wetlands in France. Pays de la Loire is an administrative region of about 32 000 km2 in the Western France with 6.3% of its area in wetlands (excluding the Loire River). Populations of coypus and muskrats are established and a permanent control programme has been set to reduce their impacts. The control plan is based on few professional trappers and many volunteers which makes this programme unique compared to other programme relying on professionals only. The aim of this study is to analyse the temporal and spatial dynamics of coypu and muskrat captures during the last 10 years to evaluate their effectiveness. The number of rodents removed per year increased by 50% in 10 years and reached about 288 000 individuals in 2016 with about 80% of them being coypus. During the same time length, the number of trappers involved in the programme also increased by 50% to reach 3 000 people in 2016. Although the raise of coypus and muskrats trapped can possibly be explained by an increase of the number of trappers, the number of coypus removed per trapper per year increased by 22%. Despite the outstanding number of individuals removed per year, our results suggest that the programme does not limit the population dynamics of coypus. Finally, since 2017, the number of data gathered from municipalities decreased, as did the total number of individuals trapped. Indeed, although rewards are crucial to recruit new volunteers, subsidies from local and regional authorities are declining. Decision makers and financers should be encouraged to fund this programme from the perspectives of the direct or indirect costs related to the presence of aquatic invasive alien rodents in wetlands.

Introduction

Invasive alien species (IAS) are considered as one of the main threats to native biodiversity [1–3]. They trigger important losses of native species and habitats and alter ecosystem functioning [4]. They can also carry infectious diseases threatening native species and human health [5]. Freshwater ecosystems are particularly impacted by invasive species [6] and the effective management of invasion is a priority. Even though global management frameworks exist and can be applied to tackle some biological invasions [7–10], the lack of solutions to limit their spatial expansion and associated costs makes management decisions against IAS very challenging [11].

According to the stage of the invasion process, a hierarchical strategy has been proposed to mitigate the negative impacts of invasive species, ranging from prevention of new introductions, eradication of newly established species, to spatial containment and/or population control programme [1, 12]. In several cases, eradication has been proved to be an effective conservation action, both on islands and on the mainland [13, 14]. However, when a species is widespread and the complete removal of individuals is not considered practical anymore, a permanent control programme promoting actions to mitigate its negative impacts could be considered as a possible alternative approach [15]. Though, control activities are very complex to implement in the field and maintain them for long-term as well can become very expensive [16–18].

In Europe, two semi-aquatic rodents, the coypu (Myocastor coypus) and muskrat (Ondatra zibethicus), have been included in the list of Invasive Alien Species of Union Concern (EU Regulation No 1143/2014). These two aquatic invasive alien rodents (AIAR) are widespread in Europe [19–21] and have been found across many wetlands in France [22, 23]. On top of this, they are important carriers of diseases contagious to humans, including leptospirosis [24], toxoplasmosis [25] and alveolar echinococcosis [26], and livestock and pets, including leptospirosis, giant liver fluke and salmonellosis [24, 27]. Both species dig burrows to shelter from climatic conditions and breed. The number of burrows is a significant siltation factor, and thus contribute to reduce drastically the water flow in some areas [28]. Moreover, burrows make riverbanks unstable and sometimes may collapse [28]. Although the real costs of AIAR on agricultural damages are largely unknown, several studies have reported that crops consumption close to streams and marshes may be high [16, 29]. Finally, it has been documented that coypus and muskrats may affect waterbirds in Italy [30], bivalve molluscs in USA [31] and France [32] and a large range of invertebrate species in Finland [33]. Studies have also proved that these species could impact native vegetation [34–37]. To sum up, it is commonly assumed that coypus and muskrats could negatively impact wetlands although more studies are needed to quantify their impacts on biodiversity and ecosystem services.

In France, despite the establishment of coypus’ and muskrats’ populations [24, 38], few studies reporting the current management strategies for these species and their results at the national or regional level have been published, particularly since the 1990s [39]. Indeed, there is no national data on the number of coypus and muskrats that are trapped each year although a study in 2016 indicated that around 350 000 coypus and 70 000 muskrats were shot during the 2013–2014 game season in France [40]. Unpublished data of captures exist but mainly at local levels as for instance in some municipalities, protected/conservation areas, or departments. Data are mostly sketchy, fragmented, sometimes non-standardised and their scientific robustness is largely questioned. It is therefore a big challenge to obtain data of removed animals to examine the temporal dynamics of control activities during the last decades, particularly at a scale larger than protected areas or departments. However, such analyses are crucial (1) to evaluate whether captures affect coypu and muskrat populations, (2) to examine the spatial dynamics of trapping efforts, and (3) to define areas where trapping efforts should be intensified or 4) whether control strategy should be revised.

The aim of this study is to analyse the temporal and spatial dynamics of AIAR removed by trappers in Pays de la Loire Region during the last 10 years in France. From the data that have been gathered by a network of trappers, we report an estimate of the number of individuals that have been removed per year at the regional level and test whether temporal trends exist in each department during the last decade. We use this data to discuss whether populations of coypu and muskrat are limited or not by the permanent control programme.

Methods

Ethics statement

This study analyses data that have been collected by Polleniz. Polleniz is the regional entity recognised by the French Ministry of Agriculture and Fisheries and French Ministry of Ecology and Sustainable Development, decree of the 06/4/2007, as a health organisation in charge of managing the permanent control programme of alien rodents and to collect data from the network of professional actors and local volunteers. Public and private landowners gave permission to trappers to remove AIAR from their property and to conduct this study. The 2924 trappers of the network have obtained an official permit with an individual number or an official agreement to trap from a decree of the local authority including the Prefecture of the five departments Loire-Atlantique, Maine-et-Loire, Mayenne, Sarthe and Vendée (Decrees n°2019/SEE/2194, n°DAPI-BCC 2007–1179, n°2019308-001C of the 04/2/2019, n°07/DDAF/263 of the 16/07/2007 or decree of the 17/2/2016). The trapping procedure compiled with the current laws in France (Decree of the French Ministry of Ecology and Sustainable Development of the 29/1/2007 pursuant to the Article L. 427–8 and 2/9/2016 pursuant to the Article R. 427–6 from the French Environmental Code) and has been fully described in “Trapping procedure” in Methods. Individuals were legally killed and methods used by trappers compiled with the current laws of the French Penal Code pursuant Article 521–1 et R. 654–1. Although an ethical approval from an Ethical Committee is not needed, all procedures for population control of AIAR complied with the ethical standards of the relevant national and European regulations on the care and use of animals (French authority Decision 2007/04/06 and Directive 2010/63/EC). Field studies did not involve endangered or protected species.

Study area

The study area is Pays de la Loire Region (Fig 1). With a typical oceanic climate, the average annual temperature is 11.5°C and rainfall is 750mm. Pays de la Loire is an administrative region of about 32 000 km2 in Western France with 6.3% of its area in wetlands (excluding the Loire River) and hosts 8.7% of the largest wetlands in France. The study area comprises a dense network of rivers and wetlands. It hosts 63 Natura 2000 sites including 16 which are marshes, ponds and lakes of major interest. The Atlantic Ocean borders the region, creating coastal landscapes and marshes with wetlands of major importance (e.g., Lac de Grand-Lieu, Marais Poitevin, La Brière, Le Marais Breton). The relief is rather flat mainly composed of plains and few steep valleys. The average altitude is 78 m with the highest point 417m. The first economic activity is agriculture with 2.2 million hectares of cultivated lands (i.e. 70% of the region). Thus, the landscape is mainly a hedged farmland, meadows, and crops separated by lines of hedges and ditches. The region is divided into five jurisdictional areas called “departments”: Loire-Atlantique, Maine-et-Loire, Mayenne, Sarthe, and Vendée (Fig 1) and is composed by 1 238 municipalities with a human density of about 117 residents/km2. The department is the administrative scale at which coypu and muskrat are managed from departmental federations for pest control.

Fig 1. Location of Pays de la Loire Region in France divided into 5 departments.

Fig 1

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LoA is Loire-Atlantique, MaL: Maine-et-Loire, Ma: Mayenne, Sa: Sarthe, and Ve: Vendée. Source of the background map: IGN GEOFLA®.

Control activities

Control activities are coordinated by a regional consortium for invasive species control which involve different types of actors: i.e. trappers, managers, and financers. Trappers could be employed or volunteer, managers are involved in wetland management and conservation, and financers are the local authorities subsidizing control programmes. Polleniz is a regional entity recognised as a health organisation in charge of managing the permanent control programme and to collect data from the network of professional actors and local volunteers.

Trapping procedure

Coypus and muskrats were captured mainly using one-door cage traps (45 × 45 × 90 cm), X, Conibear trap or two-door cage traps, baited with apples or carrots. The number of cages per volunteer trappers ranged from one to ten but could be higher for professional trappers. All traps have to be checked before noon by law. This is a main factor that limited the number of cages set on the field per trapper. Traps were mainly deployed on the obvious active tracks used by animals near banks of rivers, channels, ponds, ditches, marshes, lakes, collinear restraints, and dams. When banks were abrupt and did not allow traps to be set, they could be set on rafts linked to the banks. Different periods of trapping are commonly used in the programme. Trappers could set traps over (1) several weeks to target a particular area and period, (2) several months to cover their zones moving their traps to different areas particularly when trapper is the sole one in the municipality, (3) one or two seasons that trappers found appropriate to capture during, and (4) the whole year. The summer period (July and August) was not the optimal period of trapping because of vacations and the recreational activities of visiting tourists. Trappers are mostly volunteers although some of them are professional (as is the case in Vendée). The number of volunteer and/or professional trappers varied between municipalities and departments (S1 Table). The number of trappers per municipalities can vary from one to tens depending mostly on the budget allocated to control the species and the level of damage they triggered. The trapping procedure compiled with the current laws in France (Decree of the French Ministry of Ecology and Sustainable Development of the 29/1/2007 pursuant to the Article L. 427–8 and 2/9/2016 pursuant to the Article R. 427–6 from the French Environmental Code).

Data collection

Trappers, regardless if they are professionals or volunteers, are mandated to complete a notebook of captures, reporting the number of coypus and muskrats removed per day and municipality. Twice a year, local meetings allowed trappers to communicate their data to their contact in each departmental federation for pest control. We asked the five departmental contacts to communicate their data and we created a regional database containing all captures at the municipality level from 2008 to 2019.

In Sarthe, the total number of AIAR removed did not discriminate between coypus and muskrats, and the number of trappers was not reported (S1 Table). The permanent control programme did not cover all municipalities in Pays de la Loire Region. Over the last 10 years, the percentage of municipalities with available data was on average 68% in Loire-Atlantique, 64% in Maine-et-Loire, 65% in Mayenne, 55% in Vendée, and 32% in Sarthe (S1 Table). The percentages of municipalities with data varied within and between department and year. During the last three years (from 2017 to 2019) the number of data collected by the permanent control programme decreased (S1 Table).

The trapping effort is an important component of any control programme. Unfortunately, local authorities did not initially mandate trappers to record when and how many traps were active in the field. The only available data to evaluate the trapping effort was the number of trappers active per municipality and the number of animals individually removed. Trappers who removed many animals in a municipality might indicate that their trapping effort was high and/or the local population density of AIAR was high. As most trappers did not change their practices (i.e. trapping procedure and effort) between year (personal communication from the contacts of the programme in each departmental federation), we thus believed that the overall number of animals removed per trapper per year was an acceptable index to examine variation in captures between year.

Data analysis

We fitted a Generalized Least Squares (GLS) model to test for the effect of time (i.e. year) on the total number of coypus and muskrats that had been removed. A common application of GLS estimation is a time-series regression, in which it is generally implausible to assume that errors are independent [41]. We also included the quadratic effect of time (i.e. time2) to investigate a potential curvilinear relationship. To handle autocorrelation in our time series, we ran an autocorrelation function to identify the time lag after which the autocorrelation estimates was confined into the 95% confidence intervals assuming no serial autocorrelation [42]. Then, we implemented in a GLS model an autoregressive moving average (ARMA) term in which the moving average (MA) errors were accounted for using the maximum time lag determined in the previous step [43]. We paid special attention to check the normality of residuals, the distribution of these residuals against fitted values and the lack of sequential autocorrelation in residuals. The same procedure was applied to the total number of coypus, the total number of trappers, the total number of animals of both species, and coypus removed per trapper. Finally, we used the same procedure to analyse the effect of the number of trappers on the total number of animals of both species as well as coypus only. We ran each model in each department separately. Analyses were not performed at a municipality level as spatial autocorrelation existed in our data set (see S1 Fig).

We used QGIS [44] to perform maps and statistical analyses were performed using R 3.6.1 [45], using the nlme package [46].

Results

First, we investigated the number of AIAR removed per year over the study period (2008–2019). The total number of individuals removed per year increased with time in the Pays de la Loire Region, ranging from 186 438 individuals in 2008 to 287 763 in 2016 (Fig 2A, S1 Table). Although about 80% of AIAR removed were coypus (S1 Table), analyses showed that the number of AIAR and coypus only removed increased by 50% in the region (Fig 2A) and in each department (about 108% increase in Loire-Atlantique, 54% in Mayenne, 52% in Sarthe, 39% in Maine-et-Loire, and 35% in Vendée, Figs 3 and 4) with a nonlinear way (S2 Table), although data were available only for two departments beyond 2016.

Fig 2. Temporal dynamics of captures of aquatic invasive alien rodents (AIAR) in the region Pays de la Loire.

Fig 2

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Variation over time in (a) the number of AIAR (full blue square) and coypus only (open square) trapped, (b) the number of trappers, and (c) the number of AIAR (full green dot) and coypus only (open dot) removed per trappers. Variation in (d) of the number of AIAR (full golden square) and coypus only (open square) trapped with the number of trappers. Curved lines represent significant trends from generalized least squares (GLS) models with an autoregressive moving average term (see S2 and S3 Tables for statistical details).

Fig 3. Number of aquatic invasive alien rodents (AIAR) removed per municipality in the region Pays de la Loire.

Fig 3

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In (a) 2008, (b) 2012, (c) 2016 and (d) 2018 with no data available at a municipality level in Sarthe in the three former periods (see S1 Table for details). Source of the background map: IGN GEOFLA®.

Fig 4. Variation over time of the number of aquatic invasive alien rodents (AIAR) in the 5 departments of the region Pays de la Loire.

Fig 4

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AIAR (full square) and coypus only (open square) removed in (a) Loire-Atlantique, (b) Mayenne, (c) Sarthe, (d) Vendée, (e) Maine-et-Loire. Curved lines represent significant trends from generalized least squares (GLS) models with an autoregressive moving average term (see S2 Table for statistical details). Source of the background map: IGN GEOFLA®.

During the same time period, the number of trappers increased from 1 994 in 2008 to 2 924 in 2016 (i.e. 50% increase) in the Pays de la Loire Region (Sarthe not considered because of missing data, see S1 Table) (Fig 2B). The number of trappers increased linearly in Mayenne (Fig 5B) and in a curvilinear trend in Loire-Atlantique (Fig 5A) and Maine-et-Loire (Fig 5D) although it remained constant in Vendée (Fig 5C, S2 Table). Apart from Vendée (Fig 6C), the number of captures increased with the rise in the number of trappers in the Pays de la Loire Region (Fig 2B), in Loire-Atlantique (Fig 6A), Mayenne (Fig 6B), and Maine-et-Loire (Fig 6D, S3 Table).

Fig 5. Variation over time in the number of trappers in 4 departments of the region Pays de la Loire.

Fig 5

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In (a) Loire-Atlantique, (b) Mayenne, (c) Vendée, and (d) Maine-et-Loire. Data in Sarthe were not available. Curved lines represent significant trends from generalized least squares (GLS) models with an autoregressive moving average term (see S2 Table for statistical details). Source of the background map: IGN GEOFLA®.

Fig 6. Variation of the number of aquatic invasive alien rodents (AIAR) with the number of trappers in the 5 departments of the region Pays de la Loire.

Fig 6

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AIAR (full square) and coypus only (open square) removed in (a) Loire-Atlantique, (b) Mayenne, (c) Vendée, and (d) Maine-et-Loire. Data in Sarthe were not available. Curved lines represent significant trends from generalized least squares (GLS) models with an autoregressive moving average term (see S3 Table for statistical details). Source of the background map: IGN GEOFLA®.

Since the increase of AIAR trapped over time could be explained by an increase in the number of trappers, we examined how the number of animals removed per trapper changed with time. Discarding Sarthe due to missing data (S1 Table), the ratio between the total number of AIAR removed and the number of trappers indicated that each trapper removed about 92 individuals per year in the region Pays de la Loire. In regards to the departments, the same assessment in 2016 (except Sarthe) highlighted that the number of AIAR (and coypus in brackets) removed per trapper reached about 280 (226) in Vendée, 102 (90) in Loire-Atlantique, 35 (32) in Maine-et-Loire, and 30 (24) in Mayenne (S1 Table). Although we did not detect a significant change over time in the total number of AIAR removed per trapper at the regional level, the number of coypus removed per trapper increased by 22% over time (Fig 2C, S2 Table). Analyses showed that the number of AIAR or coypus only removed per trapper increased with time in at least 3 departments (Mayenne (Fig 7B), Vendée (Fig 7C) and Loire-Atlantique (Fig 7A) with the two former showing a curvilinear trend, see S2 Table). Although we detected a curvilinear variation in the number of trappers over time in Maine-et-Loire (Fig 7D, S2 Table), analyses showed that the number individuals removed per trapper remained similar in 2008 and 2016.

Fig 7.

Fig 7

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Discussion

Although the database from the permanent control programme was sometimes heterogeneous across municipalities and departments, our study is unique. The total number of AIAR removed per year in Pays de la Loire Region (32 000 km2 with 6.3% of wetlands) reached an outstanding amount of about 288 000 individuals (about 20% muskrats and 80% coypus) in 2016. To make a comparison, the programme covering 23 384 km2 in South Korea managed to trap 27 487 coypus in 5 years-period (2014–2018) [18], while in Italy in an area of 41 515 km2 more than 64 000 coypus were removed in a year [16]. In East Anglia (UK) 34 822 coypu were removed from 5 379 km2 to eradicate the species [47]. The number of AIAR removed by the programme here would represent about 70% (424 907) of the total AIAR shot during the game season at the national level in France [40].

In 10 years, the total number of AIAR removed per year increased by 50% in the region. During the same time length, the number of trappers involved in the programme each year increased also by 50%. Thus, the strength in the increase of AIAR trapped over time might be explained by the increase in the number of active trappers and it might explain why we did not detect any significant change with time in the total number of AIAR removed per trapper at the regional level. However, the number of coypus removed per trapper increased by 22%, and the number of AIAR or coypus only removed per trapper increased at least in 3 departments including Mayenne, Vendée, and Loire-Atlantique. Thus, these increases of both the (1) AIAR and coypus only removed in these departments and (2) the number of coypus removed in the region did not seem to support the hypothesis that the increase of captures was mainly explained by the increase of the trapping effort with time. Although we acknowledged that variation of captures with time should be evaluated, controlling for the number of trap-days [48]–information that the programme did not collect–the increase in the total number of AIAR removed per trapper per year over time suggest that population of coypus is still not limited by control activities; on the contrary, it is probably increasing.

Over the last decade, the spatial dynamics of captures was heterogeneous although the number of municipalities involved in the programme varied across department. The number of AIAR removed per department increased from 35% in Vendée to 108% in Loire-Atlantique. This difference between departments might be explained by several factors including variation in the local density of AIAR, the amount of suitable habitats, the number of trappers (volunteers and professionals), and the local management plan of municipalities to encourage AIAR trapping (including rewards). Future studies should thus investigate factors influencing temporal dynamics of captures at a municipality level.

The permanent control programme in Pays de la Loire Region is mainly based on trappers who are mainly volunteers and thus makes this programme unique. One of the strategies that has been used to promote recruitment of volunteer trappers was to reward them for their AIAR captures. Rewards are locally defined (municipalities/departments) and are not the same across all municipalities in the region. Studies have questioned whether rewards might not alter the performance of trappers when they are perceived as an extra salary [49]. The reward in Pays de la Loire is on average 1.5 euro/animal and though there are several trappers which caught hundreds of individuals per year, the overall reward is still limited. Although the reward is an important (but not unique) argument to recruit new volunteers and to maintain the ones who are involved in the programme, it might also adversely lead trappers to maintain a population of coypus when it is a significant bonus per year. We believe that future studies should (1) test the efficiency and sustainability of such strategy in a permanent control programme and (2) examine motivations of trappers to be part of the programme.

The number of data gathered from the programme decreased since 2017. Several explanations can be proposed here: (1) Several municipalities have decreased their funds and withdrew from AIAR control. For instance, some municipalities have stopped rewarding trappers and the number of trappers declined in some areas (apart from Vendée). (2) Subsidies from departments towards AIAR control declined, affecting the consortium to manage the permanent control programme. This is for instance the case when 20% of municipalities gave up the programme in Loire-Atlantique in 2017 and 2018 (S1 Table, Fig 3D) or when the programme lost its departmental contact in Sarthe. (3) The cost of the permanent control programme is very expensive [17, 18] and the programme has to deal with a local decline in annual willingness to pay for AIAR control. (4) during the last few years, all data were not inserted in the regional database by departmental federations.

A strategy that should encourage decision makers and financers to fund the permanent control programme is to assess the direct or indirect costs related to the presence of AIAR in ecosystems [50, 51]. One of the decisive arguments to convince local, federal, or national governmental authority is that AIAR are healthy carriers of significant diseases which are contagious to humans including leptospirosis, toxoplasmosis, and alveolar echinococcosis [24]. In France, about 600 cases of leptospirosis were confirmed in humans in 2014 for which 75% of cases were due to the use of wetlands through recreational-based water activities [52]. For instance, a cluster of seven kayakers on the river Vilaine in Britany (France) with clinical symptoms of leptospirosis was reported to French health authorities in 2016 [53]. Although we did not find any study assessing costs of medical care, we predict that they would be significantly high if the number of contagious events increases. Whilst digging their burrows, coypus and muskrats make riverbanks unstable and sometimes may collapse. Costs associated with hydraulic damages related to the need to clean streams have been documented to be important [16, 28]. Indirect damages on hydraulic structures including dams may cause flooding, leading to other local costly damages. Agricultural damages on crops near streams and marshes in which AIAR have established have been documented [28, 54]. Although studies are rare, refunding farmers due to agricultural damages of AIAR might be very costly [55]. Furthermore, it has been documented that AIAR affect native species in different taxa, for instance plants [35, 37], birds [30], or molluscs [31], their direct and indirect effects on population dynamics of native species and more generally on ecosystem functions have rarely been studied. Despite the fact that it is commonly accepted that alien species contribute to the transformation and downgrading of ecosystems, more studies are needed to assess the costs of habitat restoration and more generally on the loss of ecosystem services provided by wetlands where AIAR have established communities. Finally, although it is not common in our studied area, other initiatives of fundraising/sponsoring potential partnerships with private companies should be explored to strengthen the permanent control programme against AIAR.

To conclude, the permanent control programme has managed 1) to remove an outstanding number of AIAR per year in the region Pays de la Loire and 2) to recruit new volunteer trappers during the last decades. Despite these successes, our analyses suggest that control activities did not limit the population of AIAR and the number of data gathered decreased since 2017. Our study pleads for a discussion between all stakeholders including actors involved in this programme, local, and regional authorities and decision makers, scientists, and citizens to decide collectively objectives of captures and priority zones and to encourage financers to fund this permanent control programme. Finally, the permanent control programme would benefit from a scientific study monitoring population dynamics and crucial biological parameters of AIAR including, survival, reproduction, and migratory rates.

Supporting information

S1 Fig. Correlogram of the variation of the Moran’s I index assessed from the number of captures per municipalities.

Open dot indicates that Moran’s I index is not significant. Red full dot indicates a significant Moran’s index with a value being outside the 95% CI assessed from 1000 simulations. This analysis has been run from all data of AIAR captures in 2016 using pgirmess package in R. This figure shows that the number of captures in a municipality is indisputably spatially correlated with captures in neighbouring municipalities distant up to 40 km and in a lesser extent up to 90 km.

(DOCX)

Click here for additional data file. (585.9KB, docx)
S1 Table. Data that were available per year and department in the permanent control programme on the Alien Invasive Aquatic Rodents (AIAR) in the region Pays de la Loire.

(DOCX)

Click here for additional data file. (21.7KB, docx)
S2 Table. Statistics from the generalized least squares models with Auto Regressive Moving Average term (ARMA (q = 1)) of the effect of time on the number of Alien Invasive Aquatic Rodents (AIAR) removed (coypus and muskrats), coypus only, number of trappers, AIAR removed per trapper and number of municipalities that encountered positive value of inter-annual captures rates of animals (both coypu and muskrat and coypu only).

Each GLS run is presented with the F-value, the numDF, the p-value and the Pseudo-R2.

(DOCX)

Click here for additional data file. (25.2KB, docx)
S3 Table. Statistics from the generalized least squares models with Auto Regressive Moving Average term (ARMA (q = 1)) of the effect of the number of trappers on the number of Alien Invasive Aquatic Rodents (AIAR) removed (coypus and muskrats) and coypus only, number of trappers, AIAR removed per trapper, and number of municipalities that encountered positive value of inter-annual captures rates of animals (both coypu and muskrat and coypu only).

Each GLS run is presented with the F-value, the numDF, the p-value and the Pseudo-R2.

(DOCX)

Click here for additional data file. (17.8KB, docx)

Acknowledgments

We would like to thank all regional and local partners including volunteers who contribute to make this study possible. Finally, we thank Franck Courchamp for his helpful references on the economic costs on alien species and Marie-Alice Budniok, Jürgen Tack, and Martin Fox from European Landowners’ Organization for their helpful comments and English editing.

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

“Polleniz” provided support in the form of salaries for GG, MP, DP, VP, FG, FA and “FDGDON49” for AF. Each departmental federation for pest control (“Polleniz 44”, “Polleniz 85”, “Polleniz 72”, “Polleniz 53”, and “FDGDON49”) has communicated all captures from trappers from 2008 to 2019. “Polleniz” and “FDGDON49” did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.

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Decision Letter 0

Bi-Song Yue

25 Jan 2021

PONE-D-20-36473

Aquatic invasive alien rodents in western France: where do we stand today after decades of control?

PLOS ONE

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Reviewers' comments:

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Comments to the Author

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Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: General comment

The manuscript presents a very interesting work about the difficult field management of two invasive mammal species in a large area in northwest France. It was quite impressive the amount of data (individuals captured and traps) and the time period analyzed (10 years), in addition to the people working in the field to make the captures. The results reach the proposed objectives, which was to analyze the temporal and spatial dynamics of captures by trappers involved in this program during the last 10 years to evaluate its effectiveness. The analyses seemed appropriate to the proposal of the work and in fact support the conclusions. However, some points caught my attention and I explain them in sections, as follows.

Abstract

Concise and very informative, the summary makes the work and its results very clear. However, I think that the end of the abstract can be used to list some final points of the conclusions, because the way it is written does not make it clear what are the 'several explanations'.

Introduction

The introduction is relatively short, but very objective, citing key articles in the literature on species invasion and control of invasive species. The chain of ideas presented allows readers to understand the context of the problem situation, especially in relation to specific citations of invasions of these species in France. However, I do not know if there is a lack of literature, but I have not seen results on the impacts of these invasions in the study region, so, I think it is very interesting to have one more paragraph before the objectives, to add information about other invasions or even work related to the invasions of these two species in the specific region of Pays de la Loire Region.

Methods

The methods are very well written and detailed. However, I suggest changing the subtitle only to 'Methods'. The subsection 'Study area' is very well written, and in Figure 1, I suggest adding a scale bar to the central map, I know that this is not a rule either, but adding a compass with the north can be interesting. Nothing to add in the subsections 'Control activities', 'Trapping procedure', and 'Data collection'. In the subsection 'Data analysis' I have some points to list:

1. Why did the authors not use a GLMM (with Poisson family), with the fixed part of the model being the temporal relationship to analyze the data, in addiction with model selection?

2. It would also be interesting to analyze the number of Trappers as a predictor for Number of AIAR removed and Number of coypus removed, analyzing the years as a fixed factor, to answer whether in fact the reduction of the traps influences the Number of AIAR and coypus

3. The authors present a very interesting result in figure 3, which are the catches by municipalities over time. Suggest doing a spatial analysis (Moran's I index global and local) to analyze the spatial structuring of the catches and to know if the populations are grouped over time

4. If there are annual municipal data, it would be very interesting to do these regressions by municipalities. Sometimes patterns can arise from the grouping of data, which are often not observed for the ungrouped data

5. Lastly, the authors also mention the effects of AIAR on several points: public health (leptospirosis), damages on hydraulic structures and affect native species in different taxa. A very interesting analysis would be to compile this information at the municipal level: cases of leptospirosis, drainage density and occurrences of native species affected by AIAR and to make the spatial relationship to assess the relationship of the number of AIAR with these factors. Thus, since resources are scarce to control these species, this analysis could indicate priority locations for mobilizing more effective control

6. These analyze could be combined with a study of payment for environmental services, to translate in a monetized way, how much the control program reduced the impacts and how much it benefited in the reduction of losses caused by invasive species.

Results

The results are concise and very written and explained. However, I suggest improving the appearance of the regressions. One possibility is to use different colors to discriminate the number of AIAR and coypus only, in addition to increasing the formats that represent the data and the regression lines.

Discussion

The discussion focuses on analyzing the results in order to compare them with similar results from other works.

On lines 275-276 "Studies have questioned whether rewards might not alter the performance of trappers when they are perceived as an extra salary", I missed the references to support this statement.

In the penultimate paragraph, the authors cite the decline in data collection since 2017, attributing mainly to the lack of resources for the control program. However, I missed possible partnerships with private sources to increase fundraising for this purpose. I don't know how these initiatives work in France, and especially in the region, but it can be a way out of the lack of resources.

Finally, the authors show that a strategy to obtain resources from decision makers is the impacts on public health (leptospirosis), damages on hydraulic structures and affect native species, ending with the question of more studies to evaluate the costs and ecosystem services, but here I missed a conclusion for the proposed objectives: "where do we stand today after decades of control" and "We use this data to discuss whether populations of coypu and muskrat are limited or not by the permanent control program.", or that is, did the analyses in fact make it possible to analyze the state of these regions in relation to the control program? And the populations were actually limited by the control program?

Reviewer #2: This study is to analyse the temporal and spatial dynamics of AIAR removed by trappers in Pays de la Loire Region during the last 10 years in France. From the data that have been gathered by a network of trappers, researchers report an estimate of the number of individuals that have been removed per year at the regional level and test whether temporal trends exist in each department during the last decade. They use this data to discuss whether populations of coypu and muskrat are limited or not by the permanent control programme.

However, there still are some concerns need to be clarified

1.In some areas, the total number of AIAR removed did not discriminate between coypus and muskrats, and the number of trappers was not reported. I suggested to improve relevant data.

2.The experimental design is too simple. Is the number of AIAR removed by trappers affected by other factors? For example, some natural factors.

3.The total number of AIAR in the area each year and the number of AIAR migrated into this area are not considered. These data are also very important for the evaluation of removal efficiency.

**********

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Reviewer #2: No

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PLoS One. 2021 Apr 8;16(4):e0249904. doi: 10.1371/journal.pone.0249904.r002

Author response to Decision Letter 0

24 Mar 2021

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

5. Review Comments to the Author

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Referee #1

The manuscript presents a very interesting work about the difficult field management of two invasive mammal species in a large area in northwest France. It was quite impressive the amount of data (individuals captured and traps) and the time period analyzed (10 years), in addition to the people working in the field to make the captures. The results reach the proposed objectives, which was to analyze the temporal and spatial dynamics of captures by trappers involved in this program during the last 10 years to evaluate its effectiveness. The analyses seemed appropriate to the proposal of the work and in fact support the conclusions. However, some points caught my attention and I explain them in sections, as follows.

RESPONSE: Many thanks for the positive comments. Please find below the responses to your comments.

Abstract

Concise and very informative, the summary makes the work and its results very clear. However, I think that the end of the abstract can be used to list some final points of the conclusions, because the way it is written does not make it clear what are the 'several explanations'.

RESPONSE: As suggested, we have tried to revise the last two sentences of the abstract considering the words limit. We have now changed “We addressed here several explanations including the decline of subsidies allocated towards collective fights against alien aquatic rodents” mentioning “Indeed, although rewards are crucial to recruit new volunteers, subsidies from local and regional authorities are declining. Decision makers and financers should be encouraged to fund this programme from the perspectives of the direct or indirect costs related to the presence of aquatic invasive alien rodents in wetlands.” This is now lines L40-44.

Introduction

The introduction is relatively short, but very objective, citing key articles in the literature on species invasion and control of invasive species. The chain of ideas presented allows readers to understand the context of the problem situation, especially in relation to specific citations of invasions of these species in France. However, I do not know if there is a lack of literature, but I have not seen results on the impacts of these invasions in the study region, so, I think it is very interesting to have one more paragraph before the objectives, to add information about other invasions or even work related to the invasions of these two species in the specific region of Pays de la Loire Region.

RESPONSE: This is a good point but unfortunately there is a lack of literature. As we mentioned in the introduction, there are few published studies reporting the current management strategies for these species and their results at the national or regional level. We cited the study from Aubry et al. (2016) reporting in 2016 that around 350 000 coypus and 70 000 muskrats were shot during the 2013-2014 game season in France. We did not find any other articles documenting the number of captures or the impacts of these species in the region Pays de la Loire or at the national level. Few studies that have been published in France in the last decades on the effect of AIAR. This is clearly stated in our article.

As we mentioned in the text, unpublished data of captures exist but they are mostly sketchy, fragmented, sometimes non-standardised, and their scientific robustness is largely questioned. Thus, in this article, we wanted to refer to studies that have been peer reviewed by the scientific experts.

However, to consider referee’s suggestion, we have now included these new references to the article:

Bos D, Kentie R, La Haye M, Ydenberg RC. Evidence for the effectiveness of controlling muskrat (Ondatra zibethicus L.) populations by trapping. Eur J Wildl Res. 2019;65: 45. (L69)

Gethöffer F, Siebert U. Current knowledge of the Neozoa Nutria and Muskrat in Europe and their environmental impacts. J Wildl Biodivers. 2020;4: 1-12. (L69)

Guillois Y, Bourhy P, Ayral F, Pivette M, Decors A, Aranda Grau JH, et al. An outbreak of leptospirosis among kayakers in Brittany, North-West France, 2016. Euro Surveill. 2018;23: 1700848. (L338)

Jouventin P, Micol T, Verheyden C, Guédon G. Le Ragondin. Biologie et méthodes de limitation des populations. Paris: Editions ACTA, France. 1996. (L85)

Methods

The methods are very well written and detailed. However, I suggest changing the subtitle only to 'Methods'.

RESPONSE: Corrected as suggested (L104)

The subsection 'Study area' is very well written, and in Figure 1, I suggest adding a scale bar to the central map, I know that this is not a rule either, but adding a compass with the north can be interesting. Nothing to add in the subsections 'Control activities', 'Trapping procedure', and 'Data collection'.

RESPONSE: Fig 1 has been revised as suggested (L142)

In the subsection 'Data analysis' I have some points to list:

1. Why did the authors not use a GLMM (with Poisson family), with the fixed part of the model being the temporal relationship to analyze the data, in addiction with model selection?

RESPONSE: Variation of the number of captures or trappers over time was investigated using statistical procedure to analyse time series, which was our main concern. A common application of generalized least-squares (GLS) estimation is a time-series regression, in which it is generally implausible to assume that errors are independent (Cryer JD, Chan KS. Time series analysis: With applications in R. New York, NY: Springer. 2008.r). This method is for instance commonly used to analyse precipitation data (Pearson & Carroll 1998 Conservation Biology 12: 809–821). As we stated in the methods section, to control for the time-dependence of regression errors, we fitted a first-order auto-regressive model using ‘correlation=corAR1’ function (Zuur AF, Leno EN, Walker NJ, Saveliev AA, Smith GM. Mixed effects models and extensions in ecology with R. New York, NY: Springer. 2009.). As we checked the normality of residuals, the distribution of these residuals against fitted values and the lack of sequential autocorrelation in residuals, we believe that our procedure is fully robust here.

To consider the referee’s concern, we now state (L200-201) that “A common application of GLS estimation is a time-series regression, in which it is generally implausible to assume that errors are independent (Cryer & Chan 2008)” refer to Zuur et al. 2009 and add these two new references to our references list. We hope that these details in the existing paragraph give enough evidence that our procedure is robust.

2. It would also be interesting to analyze the number of Trappers as a predictor for Number of AIAR removed and Number of coypus removed, analyzing the years as a fixed factor, to answer whether in fact the reduction of the traps influences the Number of AIAR and coypus

RESPONSE: This is a really good point. Using the same procedure as described above (i.e. considering time-dependence of regression errors), we ran models testing for the effect of the number of trappers (including also the quadratic term) on the number of AIAR and coypus. Results are presented in a supplementary material S3 Table. Our analyses show that the number of captures increased with the number of trappers at the regional level (Fig 2d). This is also true for 3 departments except in Vendée (Fig 6). Thus, our analyses show that when the trapping effort increases, the number of captures increases.

We have revised the text to include these new analyses (L248-250). We now mention in the results section “Apart from Vendée (Fig 6c), the number of captures increased with the rise in the number of trappers in the Pays de la Loire Region (Fig 2b), in Loire-Atlantique (Fig 6a), Mayenne (Fig 6b), and Maine-et-Loire (Fig 6d, S3 Table)”.

3. The authors present a very interesting result in figure 3, which are the catches by municipalities over time. Suggest doing a spatial analysis (Moran's I index global and local) to analyze the spatial structuring of the catches and to know if the populations are grouped over time.

RESPONSE: The aim of this article was to analyse temporal trends of the number of captures and trappers at a regional level and for each department as it is the spatial level at which the permanent control programme against AIAR is organised in our studied area. Moreover, analysing captures at a municipality level requires performing statistical analyses that cope with spatial autocorrelation.

As suggested by the referee, we analyse the spatial structures of captures using Moran’s I index in 2016 as it is the year for which the permanent control programme has gathered the maximum amount of data. Analyses show that the number of captures in a municipality is indisputably spatially correlated with captures in neighbouring municipalities distant up to 40 km and in a lesser extend up to 90 km. This is not so surprising as AIAR are established all over the region Pays de la Loire.

S1 Fig. Correlogram of the variation of the Moran’s I index assessed from the number of captures per municipalities.

Open dot indicates that Moran’s I index is not significant. Red full dot indicates a significant Moran’s index with a value being outside the 95% CI assessed from 1000 simulations. This analysis has been run from all data of AIAR captures in 2016 using pgirmess package in R. This figure shows that the number of captures in a municipality is indisputably spatially correlated with captures in neighbouring municipalities distant up to 40 km and in a lesser extend up to 90 km.

We have added this analysis in supplementary material S1 Fig. This analysis was cited in methods (L213-214) “Analyses were not performed at a municipality level as spatial autocorrelation existed in our data set (see S1 Fig)”.

4. If there are annual municipal data, it would be very interesting to do these regressions by municipalities. Sometimes patterns can arise from the grouping of data, which are often not observed for the ungrouped data.

RESPONSE. Data of captures have been collected from more than 1500 municipalities in our studied area. As we said in the previous comment, the aim of this article was to analyse the dynamics of captures at the scale from which the permanent control programme operates. Analysing temporal trend for the 1500 municipalities is tedious. Moreover, analysing temporal trends for a given municipality requires to consider the captures of neighbouring municipalities (see previous comment on the spatial autocorrelation existing in the data set). Thus, we think that this interesting idea should be considered in another article. This is now mentioned in discussion “Future studies should thus investigate factors influencing temporal dynamics of captures at a municipality level” (L306-307).

5. Lastly, the authors also mention the effects of AIAR on several points: public health (leptospirosis), damages on hydraulic structures and affect native species in different taxa. A very interesting analysis would be to compile this information at the municipal level: cases of leptospirosis, drainage density and occurrences of native species affected by AIAR and to make the spatial relationship to assess the relationship of the number of AIAR with these factors. Thus, since resources are scarce to control these species, this analysis could indicate priority locations for mobilizing more effective control.

RESPONSE. This is a very interesting idea. Unfortunately, to our knowledge, such data set does not exist, and we cannot perform this analysis.

6. These analyze could be combined with a study of payment for environmental services, to translate in a monetized way, how much the control program reduced the impacts and how much it benefited in the reduction of losses caused by invasive species.

RESPONSE: We agree with the referee, it would be a fascinating project. However, from the data that are available, it is not possible to run this analysis. As we mentioned in the discussion section, the direct or indirect costs related to the presence of AIAR in our ecosystems are hard to assess. Here again, we think that it should be the focus of another article.

Results

The results are concise and very written and explained. However, I suggest improving the appearance of the regressions. One possibility is to use different colors to discriminate the number of AIAR and coypus only, in addition to increasing the formats that represent the data and the regression lines.

RESPONSE: Corrected as suggested (L227-233, L238-243, L251-255, and L256-261)

Discussion

The discussion focuses on analyzing the results in order to compare them with similar results from other works.

On lines 275-276 "Studies have questioned whether rewards might not alter the performance of trappers when they are perceived as an extra salary", I missed the references to support this statement.

RESPONSE: We have added this new reference (L313).

Sheail, J. The grey squirrel (Sciurus carolinensis)—a UK historical perspective on a vertebrate pest species. J Environ Manage, 1999;55: 145-156.

In the penultimate paragraph, the authors cite the decline in data collection since 2017, attributing mainly to the lack of resources for the control program. However, I missed possible partnerships with private sources to increase fundraising for this purpose. I don't know how these initiatives work in France, and especially in the region, but it can be a way out of the lack of resources.

RESPONSE: In France, most of the funds allocated to the permanent control programme of AIAR comes from the departments or other local authorities such as groups of municipalities or local watershed unions. Local hunting associations, municipalities, or other local public administrations that have an interest in rivers or artificial water damming on their territories can also contribute financially to this programme. However, as we mention in the text, the programme exists because it manages to recruit volunteer trappers. To respond to the referee’s suggestion, private companies do not contribute to this programme for different reasons: 1) It is an initiative that has not been fully explored by the programme, 2) private companies might have ethical concerns to be involved in such programme, 3) it is commonly assumed that captures should be managed by local authorities.

To consider the referee’s thinking, we mention this potential initiative in the discussion (L351-353): “Finally, although it is not common in our studied area, other initiatives of fundraising sponsoring potential partnerships with private companies should be explored to strengthen the permanent control programme against AIAR.”

Finally, the authors show that a strategy to obtain resources from decision makers is the impacts on public health (leptospirosis), damages on hydraulic structures and affect native species, ending with the question of more studies to evaluate the costs and ecosystem services, but here I missed a conclusion for the proposed objectives: "where do we stand today after decades of control" and "We use this data to discuss whether populations of coypu and muskrat are limited or not by the permanent control program.", or that is, did the analyses in fact make it possible to analyze the state of these regions in relation to the control program? And the populations were actually limited by the control program?

RESPONSE: A suggested, we added a last paragraph of conclusion in the discussion. We now mention (L354-362): “To conclude, the permanent control programme has managed 1) to remove an outstanding number of AIAR per year in the region Pays de la Loire and 2) to recruit new volunteer trappers during the last decades. Despite these successes, our analyses suggest that control activities did not limit the population of AIAR and the number of data gathered decreased since 2017. Our study pleads for a discussion between all stakeholders including actors involved in this programme, local, and regional authorities and decision makers, scientists, and citizens to decide collectively objectives of captures and priority zones and to encourage financers to fund this permanent control programme. Finally, the permanent control programme would benefit from a scientific study monitoring population dynamics and crucial biological parameters of AIAR including, survival, reproduction, and migratory rates.”

Referee #2:

This study is to analyse the temporal and spatial dynamics of AIAR removed by trappers in Pays de la Loire Region during the last 10 years in France. From the data that have been gathered by a network of trappers, researchers report an estimate of the number of individuals that have been removed per year at the regional level and test whether temporal trends exist in each department during the last decade. They use this data to discuss whether populations of coypu and muskrat are limited or not by the permanent control programme.

However, there still are some concerns need to be clarified

1.In some areas, the total number of AIAR removed did not discriminate between coypus and muskrats, and the number of trappers was not reported. I suggested to improve relevant data.

RESPONSE: Yes, it is true, and this lack of data exists for trappers operating in the Sarthe (one of the 5th department). However, we found a successful way to analyse the temporal trends of captures of AIAR in this department and at a regional scale. Thus, to respond to the referee’s concern, we cannot improve the data set when data do not exist.

2.The experimental design is too simple. Is the number of AIAR removed by trappers affected by other factors? For example, some natural factors.

RESPONSE: As we mentioned in the text, this study investigating temporal trends of captures and trappers at a regional scale is unique in France. Indeed, there is no other comparable study in France. The aim of this study is the analysis temporal trends during the last decades to provide an assessment of the permanent control programme operating mostly with volunteer trappers. Thus, the effect of the natural factors on the captures is beyond the scope of our article.

With that said, we agree that lots of factors might influence the number of AIAIR removed by trappers including environmental factors. For instance, figure 3 shows that reservoirs of AIAR in our studied areas are mainly located in the Western part of the region. Indeed, these two departments, Loire-Atlantique and Vendée, host the largest wetlands, marshes, and lakes of Pays de la Loire region. Although it was mentioned in Methods, we have revised our text to make this clearer. We now mention (L132-133): “The Atlantic Ocean borders the region, creating coastal landscapes and marshes with wetlands of major importance (e.g., Lac de Grand-Lieu, Marais Poitevin, La Brière, Le Marais Breton)”.

3.The total number of AIAR in the area each year and the number of AIAR migrated into this area are not considered. These data are also very important for the evaluation of removal efficiency.

RESPONSE. Yes, we agree that such data are important. More broadly, a scientific project investigating population dynamics would be useful in the permanent control programme to assess crucial biological parameters of survival and reproduction. However, there is no such ongoing project in the Pays de la Loire region and in its surrounding. In France, data on biological performance of AIAR are old (they are over 30 years old, see Jouventin et al. 1996 cited in our article (L85)) and should be updated. To consider the referee’s thinking, we have now mentioned in the Discussion (L351-353): “Finally, the permanent control programme would benefit from a scientific study monitoring population dynamics and crucial biological parameters of AIAR including, survival, reproduction, and migratory rates.”

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Reviewer #1: No

Reviewer #2: No

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Decision Letter 1

Bi-Song Yue

29 Mar 2021

Aquatic invasive alien rodents in western France: where do we stand today after decades of control?

PONE-D-20-36473R1

Dear Dr. Pays,

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Acceptance letter

Bi-Song Yue

31 Mar 2021

PONE-D-20-36473R1

Aquatic invasive alien rodents in western France: where do we stand today after decades of control?

Dear Dr. Pays:

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Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Fig. Correlogram of the variation of the Moran’s I index assessed from the number of captures per municipalities.

    Open dot indicates that Moran’s I index is not significant. Red full dot indicates a significant Moran’s index with a value being outside the 95% CI assessed from 1000 simulations. This analysis has been run from all data of AIAR captures in 2016 using pgirmess package in R. This figure shows that the number of captures in a municipality is indisputably spatially correlated with captures in neighbouring municipalities distant up to 40 km and in a lesser extent up to 90 km.

    (DOCX)

    Click here for additional data file. (585.9KB, docx)
    S1 Table. Data that were available per year and department in the permanent control programme on the Alien Invasive Aquatic Rodents (AIAR) in the region Pays de la Loire.

    (DOCX)

    Click here for additional data file. (21.7KB, docx)
    S2 Table. Statistics from the generalized least squares models with Auto Regressive Moving Average term (ARMA (q = 1)) of the effect of time on the number of Alien Invasive Aquatic Rodents (AIAR) removed (coypus and muskrats), coypus only, number of trappers, AIAR removed per trapper and number of municipalities that encountered positive value of inter-annual captures rates of animals (both coypu and muskrat and coypu only).

    Each GLS run is presented with the F-value, the numDF, the p-value and the Pseudo-R2.

    (DOCX)

    Click here for additional data file. (25.2KB, docx)
    S3 Table. Statistics from the generalized least squares models with Auto Regressive Moving Average term (ARMA (q = 1)) of the effect of the number of trappers on the number of Alien Invasive Aquatic Rodents (AIAR) removed (coypus and muskrats) and coypus only, number of trappers, AIAR removed per trapper, and number of municipalities that encountered positive value of inter-annual captures rates of animals (both coypu and muskrat and coypu only).

    Each GLS run is presented with the F-value, the numDF, the p-value and the Pseudo-R2.

    (DOCX)

    Click here for additional data file. (17.8KB, docx)

    Data Availability Statement

    All relevant data are within the manuscript and its Supporting Information files.

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