Abstract:

Six moored hydrophones have been recording low-frequency sound in the eastern tropical Pacific (ETP) since May, 1996 (sample rate 100 Hz, low-passed at 40 Hz). These hydrophones are spaced widely: they are moored at latitudes 8 N, 0 and 8 S along longitudes 95 W and 110 W. These distances make it very unlikely that two or more hydrophones will simultaneously record sound from one animal. Continuous spectrograms of data from every third day for each hydrophone were examined for whale calls. Calls attributed to eastern north Pacific blue whales (Balaenoptera musculus spp.) were the most commonly recorded recognizable calls. Additionally, western north Pacific blue whale calls were detected as were calls that resemble those recorded in the presence of blue whales off Chile. Pulse series similar to those which have been attributed to minke whales (B. acutorostrata) were also recorded. A number of unidentified ``biologicals'' were recorded. Among these are groups of 1--6 low-frequency pulses with regular interpulse spacing. The data from the eastern hydrophones show more call variability and abundance than do those to the west. This array of hydrophones is semipermanent and should provide years of acoustic data from the ETP.