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

Abstract

In response to the health threats posed by toxic lead to humans, scavenging wildlife and the environment, there is currently a focus on transitioning from lead-based to lead-free bullets for shooting of wild animals. We compared efficiency metrics and terminal ballistic performance for lead-based and lead-free (non-lead) bullets for aerial shooting of wild pigs (Sus scrofa) in eastern Australia. Ballistic testing revealed that lead-based and lead-free bullets achieved similar performance in precision and muzzle kinetic energy (E0) levels (3337.2 J and 3345.7 J, respectively). An aerial shooting trial was conducted with wild pigs shot with one type of lead-based and one type of lead-free bullets under identical conditions. Observations were made from 859 shooting events (n = 430 and 429 respectively), with a sub-set of pigs examined via gross post-mortem (n = 100 and 108 respectively), and a further sub-set examined via radiography (n = 94 and 101 respectively). The mean number of bullets fired per pig killed did not differ greatly between lead-based and lead-free bullets respectively (4.09 vs 3.91), nor did the mean number of bullet wound tracts in each animal via post-mortem inspection (3.29 vs 2.98). However, radiography revealed a higher average number of fragments per animal (median >300 vs median = 55) and a broader distribution of fragments with lead-based bullets. Our results suggest that lead-based and lead-free bullets are similarly effective for aerial shooting of wild pigs, but that the bullet types behave differently, with lead-based bullets displaying a higher degree of fragmentation. These results suggest that aerial shooting may be a particularly important contributor to scavenging wildlife being exposed to lead and that investigation of lead-free bullets for this use should continue.

Thermal-assisted aerial culling (TAAC) for the improved control of vertebrate pest animal populations

“…The difference arises because the thermal-assisted approach specifically targets densely vegetated areas (particularly during the deer program), rather than the more open areas that are typically targeted during visual aerial culling. Welfare assessments for visual helicopter-based aerial culling have not been done for pigs, but the number of impact shots per pig in a visual aerial culling study assessing ammunition were similar (3, SD = 1.3 versus 2.98-3.29) (Hampton, Eccles et al 2021). Shooters involved in the TAAC programs also indicated improved welfare outcomes (see Supporting Information) and the TAAC crew configuration appears to be an integral part of the improved welfare outcomes.…”

Lead ammunition residues in a hunted Australian grassland bird, the stubble quail (Coturnix pectoralis): Implications for human and wildlife health

“…Harvested birds were immediately labelled with unique numbered metal tags ( Fig 2 ), placed in zip-lock plastic bags and frozen at -20°C. Birds were thawed and radiographed in a lateral position using a portable veterinary radiography unit (Cuattro, Golden, US) [ 34 ] set at 68 kVp and 1.0 mAs. From radiographs, the number of embedded pellets, their anatomical distribution, and the number and size of fragments [ 35 ] and their anatomical distribution were recorded ( Fig 2 ).…”

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

“…The New South Wales National Parks and Wildlife Service (NSW NPWS) in Australia has developed a standardised process for non-animal ballistic testing for any previously unused shooting methods (Hampton et al 2021). The process consists of conducting extensive trials on a shooting range before commencing testing on animals.…”

“…Several projectile variables in shooting influence animal welfare outcomes, including bullet material, design and yaw (Caudell 2013). Traditional lead-based bullets used for wildlife shooting typically fragment to maximise the size of the temporal cavity they create, whereas most lead-free bullets achieve similar results through deforming (mushrooming) rather than fragmenting (Stokke et al 2017), noting that some newer lead-free bullets are designed to fragment (Thomas et al 2016;Hampton et al 2021). Bullet behaviour (including fragmentation) can be more important than E K for determining animal welfare outcomes in many contexts.…”

“…setting a maximum shooting distance ,100 m). The E K levels used for boat-based adult harp seal shooting were less than half of those used for helicopter shooting of wild pigs/boar (,3300 J; Hampton et al 2021), an animal of similar size also shot from moving platforms. This may be influenced by a difference in intended shot placement, with thoracic shots used for wild pigs compared with cranial shots for seals.…”