Passive acoustic monitoring of the distribution patterns of Irrawaddy dolphins (Orcaella brevirostris) in the middle reaches of the Ayeyarwady River, Myanmar
Zhi‐Tao Wang, Peng‐Xiang Duan, Tomonari Akamatsu, Ke‐Xiong Wang, Ding Wan
The Irrawaddy dolphin (Orcaella brevirostris) is an endangered species and its distribution in the middle reaches of the Ayeyarwady River, Myanmar, was investigated Using a towed passive acoustic monitoring device to survey between Mingun and Katha. Sixteen echolocation encounters, with a series of click trains separated by less than eight min and 26 dolphin acoustic trajectories were recorded. The mean dolphin detection rate (animals/km) progressively increased from upstream to downstream. The average interclick intervals of each click train varied significantly among river segments, indicating that the dolphins in some segments use shorter‐ranged biosonar. Future surveys with a systematic sampling track design that incorporates other factors and covering the whole distribution range along the Ayeyarwady River and at varied water levels are needed.
Occurrence, site fidelity, and associations of oceanic common bottlenose dolphins (Tursiops truncatus) off northeastern New Zealand
Jochen R. Zaeschmar, Gabriela Tezanos‐Pinto, Sarah L. Dwyer, Catherine H. Peters, Jo Berghan, David Donnelly, Anna M. Meissner, Ingrid N. Visser, Jody S. Weir, Alastair G. Judkins, Tom Brough, Marta Guerra, Lily Kozmian‐Ledward, Karen A. Stockin
Two types of bottlenose dolphin occur in New Zealand: a nationally endangered coastal type and a little-known oceanic type. This study investigated the occurrence of oceanic bottlenose dolphins using photographic records of individuals collected off the northeastern coast of North Island between 2005 and 2016. Home ranges of the two types overlap more than previously assumed yet there is little contact between them. Additionally, unlike the coastal type, oceanic bottlenose dolphins frequently associate with false killer and pilot whales and usually occur in larger groups. These findings suggest that they form two distinct populations that should be managed separately for conservation purposes.
Blowhole anomaly in pantropical spotted dolphin (Delphinidae: Stenella attenuata)
Carolina Iozzi Relvas, Michael Moore, Lucas Milmann
Herein we document through photos a blowhole anomaly in pantropical spotted dolphin (Stenella attenuata) in offshore waters of south eastern Brazil. It appears that two functional blowholes are present. This may be an ontogenetic anomaly since fetal development, as an opening of a second blowhole after full development of that apparatus would likely undermine its functionality. Although the modification may influence individual’s vocalization, the dolphin seemed healthy adult, and with control over the closure of the vestibular bag. We believe this is the first record of this type of anomaly in the respiratory tract of a functional odontocete.
Respiration cycle duration and seawater flux through open blowholes of humpback (Megaptera novaeangliae) and North Atlantic right (Eubalaena glacialis) whales
Maria Clara Iruzun Martins, Carolyn Miller, Phillip Hamilton, Jooke Robbins, Daniel P. Zitterbart, Michael Moore
Little is known about whale respiratory cycles, especially how blowholes function and if they interact with seawater. In this study, we described the duration of respiration cycles (exhalation/inhalation events) for North Atlantic right whales (NARWs) and humpback whales (HWs) using unoccupied aerial systems (UAS, drones). The NARWs had a mean duration of 3.07 seconds, slightly higher than HWs, 2.85 seconds. We also found seawater covering an open blowhole, potentially entering the respiratory system, in 20% of NARWs and 90% of HWs. This observation has not been described before and has implications for other fields within marine mammal science.
Gray whales hear and respond to signals from a 21–25 kHz active sonar
Adam S. Frankel and Peter J. Stein
Southbound gray whales off California were presented with 21-25 kHz sound sweeps. A research vessel moored in the migration path, transmitted the sweeps half the time, and was silent the other half. Whales had no overt or obvious response to the sound. However later statistical analyses showed that the whales slightly avoided the sound. This response demonstrates that gray whales can hear sounds in the 21-25 kHz range. These findings extend our understanding of baleen whale hearing.
Maximizing surveillance through spatial characterization of marine mammal stranding hot spots
Jennifer K. Olson, John Aschoff, Alice Goble Shawn Larson, Joseph K. Gaydos
Spatial analyses of marine mammal stranding data can be critical for improving surveillance and monitoring. We analyzed 12 years (2002-2014) of stranding data to identify carcass deposition “hot spots” for harbor seals (Phoca vitulina) in San Juan County, Washington. Carcass deposition showed a strong relationship with beaches having high proximity to public access points, suggesting increased reporting effort in those areas. Stranding frequency was also higher on beaches with longer fetch and gentle slopes. Beaches with these geomorphic characteristics would be ideal locations to actively survey to improve carcass collection during times of high expected mortality and limited resources.
Mating patterns of dusky dolphins (Lagenorhynchus obscurus) explored using an unmanned aerial vehicle
Dara N. Orbach, Jordan Eaton, Lorenzo Fiori, Sarah Piwetz, Jody S. Weir, Melany Würsig, Bernd Würsig
We used drones to film free-swimming dusky dolphins and to characterize their mating patterns at the surface of the water. We compared patterns between dolphins that mated in isolated subgroups and those that mated within large pods to explore potential distinctions between social and procreative functions of mating. We found few differences between dolphins that mated in these two group types.
Vocal repertoires and insights into social structure of sperm whales (Physeter macrocephalus) in Mauritius, southwestern Indian Ocean
Léonie A. E. Huijser, Vanessa Estrade, Imogen Webster, Laurent Mouysset, Adèle Cadinouche, Violaine Dulau-Drouot
Female and juvenile sperm whales live in social units, communicating using codas, i.e., stereotyped click sequences. Units with similar coda repertoires share vocal clan membership. Clans may exhibit differences in their social structure. To investigate vocal clan presence and social structure among sperm whales in Mauritius, we analyzed 4,767 recorded codas and investigated associations between 22 resighted individuals (out of 101 different photo-identified individuals). Differential use of about 24 detected coda types distinguished two sympatric vocal clans and social analysis revealed four candidate social units. However, more resightings are needed to confirm our results and allow for comparisons with other populations.