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.

Effective control of non‐native American mink by strategic trapping in a river catchment in mainland Britain

“…During the 4‐year study, we did not detect mink on any raft in the treatment area during 42/166 check periods (25%), forming long periods without detections during both spring and summer (up to 9 consecutive weeks with no mink detected in year 4) and winter (up to 5 consecutive weeks). Given the detectability implied by earlier work with rafts (Reynolds et al 2010, Porteus et al 2012) and by capture rates as calculated in this study, the probability of detection failure for such extended periods would be very small indeed. The probability of failing to detect 1 mink for 5 weeks given even 1 raft within its activity range would be expected to be around (1 − 0.059) 5×7 = 0.12.…”

“…Rafts are located along a linear habitat which is known to be strongly favored by mink. Raft spacing has been pre‐determined to promote multiple detections of each mink present (Reynolds et al 2010, Porteus et al 2012). Rafts do not carry prominent scent cues because the clay‐and‐sand medium is a natural material, and no bait or scent lure is used.…”

“…We used mink rafts to guide trapping, following previously established protocols (Reynolds et al 2004, 2009, 2010; Porteus et al 2012). We deployed rafts at a spacing of approximately 1 per km (average 1.1 km, range 0.14–3.79 km).…”

The large-scale removal of mammalian invasive alien species in Northern Europe

“…New technologies also offer the prospect of more labour‐efficient approaches. Examples include self‐reporting or self‐resetting traps, the use of camera or footprint traps to record presence without the need for daily checking, the optimisation of trap use and the use of contraception in place of, or as an adjunct to, lethal control in specific circumstances …”

Nest predation in declining populations of common eiders Somateria mollissima: an experimental evaluation of the role of hooded crows Corvus cornix

“…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.…”