Efficacy and Animal Welfare Impacts of Novel Capture Methods for Two Species of Invasive Wild Mammals in New Zealand

Abstract

All capture methods impose animal welfare impacts, but these impacts are rarely quantified or reported. We present data from two wildlife capture studies that trialled new methods for capturing Bennett’s wallabies (Notamacropus rufogriseus) and red deer (Cervus elaphus) in New Zealand. We used helicopter net-gunning for both species, and compared this method with ground-based netting for wallabies and helicopter darting for red deer, using, for the first time in New Zealand, the fast-acting opioid thiafentanil. Efficacy and animal welfare parameters quantified were duration of handling and recovery, and frequency of adverse events, including escape, injury, and mortality. Cost-effectiveness was quantified for each method. Capture mortalities occurred for all methods for both species. For red deer, chemical immobilisation led to fewer traumatic injuries and fewer mortalities, while for wallabies, net-gunning led to fewer mortalities. Net-gunning was an efficient capture method for deer in open habitat, but led to the escape of 54% of wallabies and one wallaby mortality (4%). Ground-based netting resulted in the mortality of 17% of wallabies at the time of capture, and the capture of non-target species. The cost per captured wallaby was 40% more expensive for net-gunning (NZ$1045) than for ground-based netting (NZ$745), but, once corrected for mortalities at the time of capture and suitability of individuals for GPS-collar deployment, this was reduced to 29% and 12% more expensive, respectively. Net-gunning for red deer resulted in the escape of 13% of animals and mortality of 10% of animals at the time of capture. Helicopter-based darting for red deer using thiafentanil (c. 0.03–0.06 mg/kg) had high capture efficacy (zero escapes), rapid induction times (mean of 3 min), and a low mortality rate at 14 days post-capture (3%), but it was more expensive per deer captured and collared than aerial netting (NZ$2677 and NZ$2234, respectively). We recommend reporting of adverse event data for all wildlife capture techniques to permit continual refinement of field methods.

Evaluation of helicopter net-gunning to capture wild fallow deer (

“…Another important advantage of helicopter net-gunning over these capture methods was that it avoided the animal health risks, expenses and logistical constraints associated with chemical immobilisation, such as long handling times and the requirement for veterinary assistance (e.g. DelGiudice et al 2005;Hampton et al 2021), although chemical capture and immobilisation may be safer in some situations (Latham et al 2020). The short average handling times in our study (,7 min, cf.…”

“…Animals are captured using a weighted net fired by a shooter in a helicopter and are usually physically restrained and handled without chemical immobilisation. Helicopter netgunning is now established as standard practice for capturing several ungulate species in North America (Ortega et al 2020;Van de Kerk et al 2020), and it has also been used to capture deer for research in New Zealand (Nugent and Yockney 2004;Latham et al 2020) and South America (Flueck et al 2005). It can provide an efficient and selective method for capturing many animals in a short time over a large geographic area (Webb et al 2008).…”

“…However, mortality rates $8% have been reported in some species and landscapes that have subsequently been associated with inherently high risk of injury (e.g. Firchow et al 1986;Jacques et al 2009;Latham et al 2020). Helicopter net-gunning has scarcely been used in Australia and its use in Australian conditions, which are generally much warmer than those in which net-gunning is common practice for capturing deer (e.g.…”

A comparison of fragmenting lead-based and lead-free bullets for aerial shooting of wild pigs

“…We were unable to collect ante-mortem (before death) data from wild pigs that were shot. This was due to inherent difficulties associated with examining animals soon after shooting when using an aerial platform [ 7 , 8 ] and procedural protocols precluding having an observer in the shooting helicopter or the use of worn cameras to collect ante-mortem data [ 42 ]. This also precluded quantifying the frequency of adverse animal welfare events such as non-fatal wounding [ 6 ].…”

Animal welfare testing for shooting and darting free-ranging wildlife: a review and recommendations

“…However, there have been far fewer animal welfare studies of wildlife shooting (firing bullets or shot at animals with an intention to kill), with a general exception for studies of wounding/crippling in game birds (Pierce et al 2015). Darting (firing hollow syringes at animals with an intention to inject liquid) is used to capture and mark wildlife and has also been subjected to few animal welfare studies until recently (Jung et al 2019;Latham et al 2020;Hampton et al 2020a). Shooting and darting are examples of wildlife management techniques that rely on ballistics, the behaviour of projectiles (Caudell 2013).…”