Baleen whale presence in northern Mariana islands in 2015–2017

Many baleen whale vocalizations are species, and in some cases, population−specific. Although baleen whale occurrence has been studied in different parts of the ocean, little is known about the seasonal distribution of baleen whales in the Western Pacific. Since 2010, more concerted visual and acoustic survey effort has been occurred around a very remote region of the western Pacific Ocean, the Northern Mariana Islands. Passive acoustic data were collected at two locations in the Northern Mariana Islands, Tinian and Saipan, from 2015–2017 and they were analyzed for call characteristics and occurrence of different baleen whale call types from blue whales, fin whales, and Bryde’s whales. There was a clear seasonal pattern in fin whale calls, with peak call detections during winter and spring. Low levels of blue whale calls were detected year-round with peaks in winter (December) and summer (June). Bryde’s whales were detected sporadically at both locations. Moreover, two low-frequency sounds with currently unknown origin were detected, one tonal and one pulsed sound. The former was more common at Tinian and the latter at Saipan. This work enhances our understanding of the species’ vocal repertoire and population structure.