Temporal variation in marine mammal species assemblage at South Orkney Islands revealed through passive acoustic data from 2016 and 2017

Abstract

Passive Acoustic Monitoring (PAM) is a non-invasive method providing high- resolution information about marine mammal acoustic presence. Multi-species PAM studies can increase our understanding of temporal changes in species diversity and assemblage and is especially useful in remote areas such as the Southern Ocean. This study was based on 16 months of acoustic data spanning two austral autumns and winters, collected through an autonomous underwater recorder deployed in the Coronation Trough northwest of the South Orkney Islands, Scotia Sea. This region has been recognized as a hotspot for Antarctic krill (Euphausia superba) and is among the most important commercial krill fishing grounds. Acoustic recordings were used to characterize seasonal and inter-annual patterns in the acoustic presence of marine mammals formerly undescribed in this area. Using previously documented species-specific vocalizations, five baleen whale species, two pinniped species, and odontocete spp. were identified. Although there was little change in the level of species diversity over time, there was an almost complete shift in guild composition related to season, reflecting marine mammals’ differential habitat preferences and response to the strong seasonality defining the Southern Ocean. The high degree of seasonality was further evidenced by inter-annual variation in species’ acoustic phenology during one recording period that was defined by the strongest El Niño event on record. This study showed the utility of PAM as a tool in characterizing the distribution and habitat use of these top predators in response to changing environmental conditions.