Empirical development of strategy for the control of invasive American mink by trapping

Abstract

American mink (Neovison vison) are an ecologically damaging invasive species in Europe and Iceland where attempts to control them typically rely on trapping. The focus and efficiency of trapping can be improved by using track-recording mink rafts to identify where mink are present before traps are deployed. This paper describes development of operating strategy for the use of mink rafts with traps, to optimise capture efficiency against costs. We worked sequentially on two unconnected chalk streams in central southern England. On 17 km of the River Itchen, we operated a very high density of rafts (5.9 per km) through spring and summer to generate multiple detections of each mink present. All rafts recording mink tracks were armed with traps, and captured mink were euthanased. After removal of mink until no further detections were made, we calculated that each mink was detected 5.3 times at 5.1 raft sites, and on this basis, rationalised raft density to a standard one per kilometer of river. We set a trap deployment time (10 days) that encompassed the longest observed lapse from detection to capture (7 days), and extended the check interval for rafts in monitoring mode from 1 week to 2 weeks to further reduce costs. These operating rules were then deployed for 12 months on the 44-km River Wylye beginning in autumn. Rafts indicated that the river was cleared of mink through the capture of seven individuals, each of which was detected 3.6 times at 2.7 raft sites, on average, and was trapped within 6 days of detection giving a response time of less than 20 days. Although these operating rules may need refinement for other environments, we believe this is a sound basis for effective mink control.

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

“…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).…”

“…Following a capture, other traps already set in response to tracks left by the same mink at other raft sites were potentially redundant if no other mink was present. This situation could not be recognized during use; hence, our protocol was to terminate all trap deployments after 10 days and return the raft to monitoring mode (Porteus et al 2012). In a few exceptional circumstances (e.g., following an escape from a trap), we continued trap deployments beyond 10 days.…”

“…In previous work, we found that track‐recording mink rafts, which accumulated tracks on a clay‐and‐sand substrate over periods of 7–14 days, were a more sensitive detector of mink presence than were either field sign surveys or incidental sightings and, if rafts were used systematically, the probability of detecting each mink present was high, even at low population density (Reynolds et al 2004, 2009; Porteus et al 2012). This suggested a targeted control strategy in which traps were deployed only where mink were recently detected, economizing on daily trap‐checking effort (Porteus et al 2012). Because evidence of mink occupancy was obtained even when traps were not in use, any control effort organized in this way could potentially document its impact on mink occupancy.…”

“…After 2004, the raft‐guided approach to mink control was adopted in several contemporary conservation projects throughout Britain, some of which included research elements already reported elsewhere (Harrington et al 2009, Moorhouse et al 2009, Bryce et al 2010, Porteus et al 2012). Across all such projects, control of trapping effort and documentation of outcomes has tended to be impaired as spatial scale increased because of increased dependence on a volunteer workforce and less systematic methods (Reynolds 2009).…”