Estimating the welfare impacts of differing projectile types utilised for stranded cetacean euthanasia

Euthanasia may be necessary for stranded cetaceans to alleviate suffering, achievable through properly applied ballistics causing rapid insensibility and death. Despite widespread use, understanding of appropriate equipment relative to anatomical variation remains limited. We conducted experimental ballistics trials using cetacean cadavers to examine cranial trauma from five projectile types. A .308 calibre rifle with two deforming and three non-deforming projectiles was tested on 30 cadavers across four odontocete species (six per projectile type). Post-mortem computed tomography (PMCT) and dissection evaluated ballistics trauma. PMCT analysis assessed calvarium damage across 8 quadrants, summarized into four sectors. Marked caudoventral (brainstem) fractures were used as a conservative proxy indicator for likely instant insensibility. Generalized linear mixed models evaluated projectile type, brain sector, and species effects on fracture severity and fragmentation. Only 17 (56.7%) cadavers exhibited marked brainstem fractures. Non-deforming full metal jacket and hydrostatic projectiles caused significantly less severe fractures than other projectiles. Deforming and non-deforming monolithic projectiles produced brainstem-disrupting fractures in common, striped, and dusky dolphins. Monolithic projectiles appear more effective for bottlenose dolphins. Preliminary findings indicate deforming or monolithic projectiles were associated with a higher frequency of brainstem-associated osseous fractures in the cadavers studied. However, increased sample sizes with the addition of soft tissue damage quantification, are required to better elucidate species-specific equipment selection.