Lesions on the jaws of an adult male orca (Orcinus orca) from Punta Norte, Argentina

Abstract

The Punta Norte Patagonia orca (Orcinus orca) population/ ecotype exhibits a unique foraging strategy that involves intentionally stranding onto beaches to capture pinnipeds, primarily Southern sea lions (Otaria byronia, formerly Otaria flavescens). One adult male orca from this population was a prolific hunter. Between 1 February and 30 April, each year from 2006 to 2011, he conducted a total of 319 attacks and 173 successful captures. The highest number of attacks (n = 122) and captures (n = 76) in a single season both occurred in 2008. During that same period, he intermittently presented with multiple bilateral lesions on his maxillae and mandibles. We present milestone images (n = 6) and paired same-day images (n = 16; 8 pairs) documenting the progression of these lesions. Using standardised descriptive criteria, we compared lesion characteristics across time, between left and right sides, and between the maxillae and mandibles. We developed the Lesion- Eye-patch Ratio (LER) to quantify lesion area relative to the corresponding eye patch area using ImageJ software. The highest paired image LER was 2.02 (recorded in 2009), indicating lesions more than twice the size of the eye patch, whilst the lowest was 0.16 (recorded in 2007). This unique dataset provides evidence of what we believe to be the longest documented duration of persistent lesions in a free-ranging orca. We speculate that the most likely contributing factor was temporary mandibular misalignment associated with beach egress during intentional stranding events. Such misalignment may have caused teeth to puncture soft tissues of the mouth, leading to infection and the development of externally visible lesions. A possible genetic predisposition cannot be excluded, as there is evidence (albeit limited) that this adult male’s presumed older brother exhibited smaller but similar lesions. The survival and continued hunting success of this individual demonstrates that orca with significant lesions can forage effectively. These observations support a reassessment of the management framework concerning the rescue and release of injured orca whose lesions might otherwise be considered debilitating, as this male not only hunted for himself, but he also captured prey and provisioned other orca in the population.