Types, distribution, and seasonal occurrence of sounds attributed to Bryde's whales (Balaenoptera edeni) recorded in the eastern tropical Pacific, 1999-2001

Vocalizations resembling known Bryde's whale sounds were recorded on autonomous hydrophones at seven sites in the eastern tropical Pacific. Five short (< 3 s) low-frequency (< 80 Hz) -phrase types were observed. Swept alternating tonal phrases included a 37-Hz tone and often a 25-16-Hz downswept tone, while nonswept alternating tonal phrases had a predominant tone at 29 Hz and often additional tones at 16 and 47 Hz, Alternating tonal phrases were found in 79% of the total hours in which phrases were detected, and occurred primarily at the eastern hydrophone sites. Burst-tonal phrases included tones that were often preceded by a wideband burst of noise. The low burst tonal Phrase contained tones at 19 and 30 Hz, and was detected at five of the hydrophone sites. The high burst-tonal phrase included a 42-Hz tone and was observed only on the northwestern hydrophones. A single harmonic tone phrase type was observed that included a fundamental tone at 26 Hz and at least two harmonics, this phrase was observed exclusively at the eastern hydrophone stations. This opportunistic survey has shown that acoustics is an effective means of studying this poorly understood, pelagic balaenopterid,