Measurements of wild finless porpoise (Neophocaena asiaeorientalis sunameri) on-axis burst-pulse sound

Most small odontocetes utilize burst pulses and whistles as means of communication. However, limited research conducted on burst pulses produced by species that do not produce whistles. This study represents the first to measure on-axis burst pulses emitted by wild finless porpoises (Neophocaena asiaeorientalis sunameri) in Japan, which are classified as a non-whistling species. Passive acoustic monitoring was conducted in the Seto Inland Sea from June to Sepetember 2021 using A-tags and a SoundTrap 300HF. We measured eight parameters of burst pulses: apparent source level, inter-pulse interval, peak frequency, center frequency, -3dB bandwidth, pulse duration, number of pulses, and total duration. Apparent source level of the burst pulses ranged from 150 to 165 dB re 1 μPa, averaging 157 ± 3 dB re 1 μPa. -3dB bandwidth of the burst pulses ranged from 14 to 31 kHz, averaging 22 ± 5. Burst pulses had lower sound pressure levels and wider bandwidths comparing to regular clicks, which are pulsed sounds utilized for echolocation purposes. This observed disparity can be attributed to the fundamental characteristic of burst pulse, their high repetition rate. Notably, the burst pulses of finless porpoise did not exhibit any frequencies below 100 kHz.