Detectability of American Mink Using Rafts to Solicit Field Signs in a Population Control Context

Abstract

American mink (Neovison vison) are an ecologically damaging invasive species where they have been introduced in Europe.Effectiveness of mink population control by trapping has been difficult to assess, without knowing how efficiently mink are caught by traps or detected by other methods. Use of track-recording rafts to detect mink and guide trapping effort has proved efficient and leads to a supposition that no detection indicates absence of mink. To draw this conclusion with any confidence requires a measure of detectability. We applied occupancy models to data from an earlier study to estimate detectability of individual American mink on track-recording rafts. Estimated detectability of individual mink, per raft, and 2-week check period varied between 0.4 in late summer and 0.6 in late autumn. By inference, risk of failing to detect a mink that was present would be ,5% given 4-6 independent opportunities to detect it. These opportunities could be created either by using a raft spacing that ensured multiple detections of each mink or by monitoring rafts through a succession of check intervals. Within certain simple constraints, raft location did not contribute substantially to detection probability. These findings will allow field operators, strategists, and funders to assess with confidence the success of efforts to control mink density. We expect the estimation of individual detectability to be similarly valuable in population control or eradication of other species.

Matching the Strategy to the Scenario; Case Studies of MinkNeovison visonManagement

“…The eradication of invasive Mustelids in general can be difficult due to their elusiveness, neophobia to objects such as traps, and low encounter rates with control mechanisms due to their wideranging behaviour (King et al 2009). Most mink management projects in Europe are longterm con trol operations or eradications that are quite restricted in range at local river catchment level scales (Bonesi and Palazon 2007) or at a local catchment level in England (Reynolds et al 2010). The increasing use of volunteers to reduce operating costs has allowed removal over in creasingly large areas as seen in Scotland (Bryce et al 2011;Robertson et al 2017).…”

“…In addition to these approaches, a further method developed for use on slow flowing lowland waterwaysthe mink raft (Reynolds et al 2010), -was also consid ered. This combines detection (through footprint tracking media) followed by subsequent trap operation to ensure the traps are only open when and where animals are detected, making largescale trapping operations more economic.…”

“…• Developing methods to detect animals that do not require their capture or daily checking. This is one of the fundamental aspects of the use of mink rafts (Reynolds et al 2010). Here tracking systems associ ated with traps first detect the presence or absence of mink, and the traps are only opened once an animal is known to be frequenting the area.…”

Management decisions and knowledge gaps: learning by doing in a case of a declining population of slavonian grebe Podiceps auritus

“…Six mink raft stations consisting of a fl oating monitoring footprint plate and removable trap were deployed at each lake (Reynolds et al 2004, Anonymous 2007, Bryce et al 2011. Distance between each trap was 1 km allowing multiple detection possibilities within active mink territories at each checking period (Gerell 1970, Birks and Linn 1982, Reynolds et al 2010. Stations were monitored every seven days to comply with the wildlife laws and to be a suffi cient time interval to both remove individuals from a treatment area and record activity in control areas (Moore et al 2003, Asakskogen 2010.…”

Comparison of Two Methods for Detecting Atlantic Salt Marsh Mink

“…Atlantic salt marsh mink appear dependent on salt marsh habitat that has highly fluctuating water levels (Gorga 2012); therefore, survey methods are needed that can effectively detect them in those conditions. Traditional survey methods for mink, including walking surveys for signs (both track and scat), track plates, and mink raft surveys (Humphrey and Zinn 1982, Bonesi and Macdonald 2004, Reynolds et al 2004, Reynolds et al 2010, Schooley et al 2012) are ineffective in a tidally-influenced salt marsh. Sign surveys fail because the high tide removes tracks and scat from the environment, and track stations, even on rafts, experience high levels of disturbance to the track surface from fiddler crabs (Uca pugilator) and blue crabs (Callinectes sapidus; Boulerice and Tucker 2012).…”