A “13-Hz” short call recorded off Elephant Island, Antarctica – By which species is it emitted?

Over the last years passive acoustic recording devices were used frequently to observe baleen whales acoustic presence in the Southern Ocean. During previous analyses a low frequency call was detected that had not been observed before in recordings from the passive acoustic recording device at 61°00.88’ S and 55°58.53’ W off Elephant Island, Antarctica, further referred to as “13-Hz” short call. The name was chosen on the basis of the frequency and duration of the call. Due to signal characteristics of the sound and known acoustic presence from previous studies, fin and blue whales were considered as potential producers of this call. Previous analysis detected the “13-Hz” short call in Austral fall, therefore, data from March to June of 2014 were analysed to associate the hourly presence of the “13-Hz” short call with the presence of either ’20-Hz’ fin whale pulses or Antarctic blue whale z-calls. Additionally, the “13-Hz” short call characteristics were investigated (n = 75). Furthermore, temporal distances between single “13-Hz” short calls to vocalizations of fin and blue whales were investigated (n = 518). The “13-Hz” short call had a frequency range of 11 ± 1 Hz to 14 ± 1 Hz and a mean duration of 2 ± 1 seconds. The temporal distribution analysis showed a positive correlation between the occurrence of fin whale pulses and “13-Hz” short calls and a negative correlation of blue whale z-calls and the “13-Hz” short call. The investigation of the temporal distances between the “13-Hz” short call and fin and blue whale calls showed a non-normal distribution of the data for both species, but a more normal distribution of the data for blue whale z-calls, suggesting an association with fin whale pulses. Overall, the results indicate that fin whales could be the producers of the “13-Hz” short call, but further investigation is necessary to confirm this hypothesis. Further investigation could include analysis of more data as well as the use of a continuous passive acoustic recording, or the use of different methods such as tagging, simultaneous visual surveys and the comparison with vocalizations of other fin whale populations in different regions