Chamados de orcas (Orcinus orca, L. 1758) e implicações na estruturação de grupos no Oceano Atlântico Sul Ocidental: em águas brasileiras e nas Geórgias do Sul

Abstract

Killer whales (Orcinus orca) have a learned vocal repertoire, allowing the cultural transmission of acoustic traditions and the differentiation of groups based on their calls. However, the acoustic repertoire of this species in the Southwest Atlantic remains poorly understood, limiting our knowledge of their vocal parameters and potential population units. This study analyzed acoustic data collected between 2013 and 2022 using towed array and autonomous moored recording systems in Brazilian waters (north and south) and around South Georgia Island. The aim was to identify killer whale calls, describe their acoustic parameters in the studied regions, and detect potential differences among calls to associate them with distinct groups. Acoustic parameters were extracted using the Real-time Odontocete Call Classification Algorithm (ROCCA) in the PAMGuard software. A total of 230 calls were identified across 21 detections, including two visual-acoustic matches, while the remaining detections were classified through spectrographic inspection and qualitative assessment of call composition. The calls were grouped into six categories: constant, upsweep, downsweep, single modulation, modulated, and multi-component. Cluster analysis revealed two populations of killer whales along the Brazilian coast – north and south – each composed of two distinct groups. In contrast, the absence of clustering in sub-Antarctic waters may suggest the presence of a single group in that region. Most calls were classified as single modulation, with a smaller number associated with echolocation clicks and burst-pulse sounds. This is the first study to describe killer whale calls in the Southwest Atlantic, providing initial evidence of the population structure of this species along the Brazilian coast.