Acoustic recordings of finless porpoises visiting Nagoya Port, 2017–2019

Abstract

Echolocation clicks emitted by narrow-ridged finless porpoises (Neophocaena asiaeorientalis sunameri) were recorded using an acoustic data logger at two stations (St.1 and St.2) in Nagoya Port from March 2017 to March 2018 and from July 2018 to July 2019, respectively. A total of 2,553 click trains were observed during the study period, with 1,079 click trains recorded at St.1 and 1,474 at St.2. Click train occurrences were more frequent in winter at St.1 and in spring at St.2. Additionally, click trains were detected more frequently at night than during the day at both stations. The mode value of the mean inter-click intervals within a click train varied between stations, with a peak of 26 ms at St.1 and a range of 12 to 32 ms at St.2. The number of clicks occurring at intervals of 10 ms or less, indicative of feeding effort, was greater at St.2 than at St.1. These differences in inter-click intervals between sites suggest variations in their specific purposes for area use within the same port.