The acoustic calls of blue whales off California are described with visual observations of behavior and with acoustic tracking. Acoustic call data with corresponding position tracks are analyzed for five calling blue whales during one 100-min time period. Three of the five animals produced type A-B calls while two produced another call type which we refer to as type D. One of the animals producing the A-B call type was identified as male. Pauses in call production corresponded to visually observed breathing intervals. There was no apparent coordination between the calling whales. The average call source level was calculated to be 186 dB re: 1 μPa at 1 m over the 10–110-Hz band for the type B calls. On two separate days, female blue whales were observed to be silent during respective monitoring periods of 20 min and 1 h.

Preliminary results are presented from a combined acoustic and visual study of blue whales in the Channel Islands National Marine Sanctuary off the California coast, conducted during four 3-day expeditions in July 1996. Acoustic recordings were collected using GPS positioned sonobouys arrays, with up to five sonobuoys deployed at approximately 1-km spacing. Visual observations were made to estimate the number of blue whales in the vicinity of the arrays, and to record whale behaviors. Significant numbers of blue whales (5–15) were sighted each day, and as many as 100 blue whale calls per hour were recorded. About one-third of the time, large ships transited through this area, providing loud low-frequency sound sources to examine blue whale sensitivity to noise. Low-frequency blue whale calls, similar to those previously designated ‘‘A’’ and ‘‘B’’ in the literature, were recorded. Additional blue whale calls include an approximately 4-s duration frequency downswept tone between 30 and 80 Hz, often heard at about the same intensity as the more typical ‘‘A’’ and ‘‘B’’ calls. Cross correlation of signals received by sonobuoys provides information to localize calling whales. The location accuracy relative to the different call types will be discussed.

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