| Summary: | Fin whales (Balaenoptera physalus) producea variety of low-frequency, short-duration, frequencymodulatedcalls. The differences in temporal patterns betweentwo fin whale call types are described from long-termpassive acoustic data collected intermittently between 2005and 2011 at three locations across the eastern North Pacific:the Bering Sea, off Southern California, and in Canal deBallenas in the northern Gulf of California. Fin whale callswere detected at all sites year-round, during all periodswith recordings. At all three locations, 40-Hz calls peakedin June, preceding a peak in 20-Hz calls by 3–5 months.Monitoring both call types may provide a more accurateinsight into the seasonal presence of fin whales across theeastern North Pacific than can be obtained from a singlecall type. The 40-Hz call may be associated with a foragingfunction, and temporal separation between 40- and 20-Hzcalls may indicate the separation between predominatelyfeeding behavior and other social interactions.
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