Commerson's dolphins (Cephalorhynchus commersonii) inhabit coastal waters of Southern South America and Kerguelen Islands. Limited information exists about the acoustic repertoire of this species in the wild. Here, echolocation signals from free-ranging Commerson's dolphins were recorded in Bahía San Julián, Argentina. Signal parameters were calculated and a cluster analysis was made on 3180 regular clicks. Three clusters were obtained based on peak frequency (129, 137, and 173 kHz) and 3 dB bandwidth (8, 6, and 5 kHz). The 428 buzz clicks were analyzed separately. They consisted of clicks emitted with a median inter-click interval of 3.5 ms, peak frequency at 131 kHz, 3 dB bandwidth of 9 kHz, 10 dB bandwidth of 18 kHz, and duration of 56 μs. Buzz clicks were significantly shorter and with a lower peak frequency and a broader bandwidth than most of the regular clicks. This study provided the first description of different echolocation signals, including on- and off-axis signals, recorded from Commerson's dolphins in the wild, most likely as a result of animals at several distances and orientations to the recording device. This information could be useful while doing passive acoustic monitoring.

Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.