Low-frequency whale sounds recorded on hydrophones moored in the eastern tropical Pacific

An array of autonomous hydrophones moored in the eastern tropical Pacific w as monitored for one year to examine the occurrence of whale calls in this region. Six hydrophones which recorded from 0-40 Hz were placed at 8 degree s N, 0 degrees, and 8 degrees S along longitudes 95 degrees W and 110 degre es W. Seven types of sounds believed to be produced by large whales were de tected. These sound types were categorized as either moan-type (4) or pulse -type (3) calls. Three of the moan-type calls, and probably the fourth, may be attributed to blue whales. The source(s) of the remaining calls is unkn own. All of the call types studied showed seasonal and geographical variati on. There appeared to be segregation between northern and southern hemisphe res, such that call types were recorded primarily on the northern hydrophon es in the northern winter and others recorded primarily on the southern hem isphere hydrophones in the southern winter. More calls and more call types were recorded on the eastern hydrophones than on the western hydrophones. [ S0001-4966(99)06012-9].