OS72B-0356 Blue-Whale Calls Detected at the Pioneer Seamount

Underwater ObservatoryMichael D. Hoffman,1 Carl O. Vuosalo,1 Newell Garfield,2

and Roger Bland1

1. Physics and Astronomy Department and Romberg Tiburon Center for Environmental Studies, San Francisco State University

2. Department of Geosciences and Romberg Tiburon Center for Environmental Studies, San Francisco State University

In August 2001 a vertical linear array (VLA) of four hydrophones was installed by NOAA-PMEL at Pioneer Seamount, 95 km off the California coast and 930 m below the surface. The four channels, digitized at 1000 Hz with 16-bit precision, are available in near real time. We used this array to monitor sounds from marine mammals. Sounds from blue whales (Baleinoptera musculus) were quite prominent for much of the time. Data were collected over a 13-month period (8 months active time). (The observatory is currently off the air due to a cable problem.) We have found the “B” call of the blue whale to be lower in frequency and less variable than previously reported. Further work is planned to investigate the possibility of identifying individual whales from their calls.

Help and advice is gratefully acknowledged from: Dave Mellinger, Chris Fox, Jonathan Klay, Andy Lau, and Haru Matsumoto, NOAA-PMEL Jim Mercer and Lyle Gullings, APL, University of Washington; Ching-Sang Chiu, Monterey Naval Postgraduate School; and John Bourg and Jim Lockhart, San Francisco State University

Underwater topography near Pioneer Seamount. (Graphics courtesy of PMEL/NOAA)

Map of the Monterey Bay National Marine Sanctuary, showing the location of Pioneer Seamount and the underwater cable.

Pioneer Seamount Observatory

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Blue-Whale Calling Sequence, day 285 of 2001. This A-B calling sequence is the standard modality of vocalization for North-Eastern Pacific Blue Whales. The arrows indicate a feature sometimes referred to as the “D” call, a precursor to the “B” call with components, in this instance at about 260 and 325 Hz, coming about 6 seconds before the start of the “B” call.

Fitted frequency and sweep rate for this sequence of very loud calls (red points) compared to a larger sample of calls from the entire year’s data. The tighter grouping of this sample probably reflects the smaller errors associated with the larger signals. The distribution of red points is centered at (f0,) = (16.03 Hz, 0.06 Hz/sec), with widths of ( f0, ) = (0.04 Hz, 0.01 Hz/sec).

Blue-Whale Calling Sequence of 24 “B” calls (day 285 of 2001). This sequence starts with “B” calls only, a common modality. The average separation of “B” calls (excluding the longer breathing intervals, is 130 sec.

Fitted frequency and sweep rate for the “B”-only sequence. The distribution is looser than for the main sample of (louder) calls.

Blue-Whale Calling Sequence, “B” calls only (2001 day 284) . This type of call sequence, without “A” calls, is less frequent than the “A_B” pattern. This long sequence of calls started at 5:40 UT (9:30 PM local time) and continued throughout the night and up to almost noon (local time) the next day. The calls are more closely spaced than in the “A_B” calling pattern, with an inter-call interval, excluding breathing intervals, of 35 sec (standard deviation 2 sec).

AB AB AB AB AB AB ABAB AB AB AB AB AB AB

Fitted frequency and sweep rate for the shorter call sequence above, showing a shift in frequency for this sub-sample. This is an illustration of the type of characteristic which might be used to distinguish individuals.

A short A-B” calling sequence (10:40 to 11:35 UT, day 255 of 2001).

ARE BLUE WHALES SINGING A DIFFERENT SONG?

Published descriptions [Stafford 1998; Stafford 1999] of the blue whale “B” call indicate a fundamental frequency decreasing from 18.9 Hz to 17.3 Hz over the course of a 16-second call (whale calls recordedfrom shipboard in August-September 1993 within 100 miles of Pioneer Seamount) or from 17.7 to 16.1 Hz over 18.7 sec (moored hydrophones in the Eastern tropical Pacific). Our results indicate an entirely different call, lower and more constant in pitch. The Stafford 1998 results are based on. This change is especially striking given the very precisely defined central frequency of our whale calls. It seems quite remarkable that a sample of animals presumably including a range of physical sizes should all vocalize at the same frequency to within one part in 400. Such a difference in pitch would not be discernable to a trained human ear.

Stafford, Fox and Clark [1998], “Long-range acoustic detectin and localization of blue whale calls in the northeast Pacific Ocean,” J. Acoust. Soc. Am. 104, 6.Stafford, Nieukirk and Fox [1999], “Low-frequency whale sounds recorded on hydrophones moored in the eastern tropical Pacific,” J. Acoust. Soc. Am. 106, 6.

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5000 detections in 2001-2002

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Peak height of 2.0

800 whale calls

Least-squares fit to 6-second linear sweep

Measured sweep rate and central frequency

Data analysis. Signals from the four hydrophones of the Pioneer Seamount linear vertical array were digitized at 1000 Hz and transmitted over the internet to the NOOA Pacific Marine Environmental Lab in Newport, Oregon for archiving. We downloaded data from the Newport ftp site and searched the time series for blue-whale “B” calls, using a linear-sweep matched filter. A sample of such detections were further processed by fitting to a linear sweep with variable central frequency and sweep rate.

Scatter plot of whale-call sound intensity (peak output from matched filter) versus day detected. The line at an intensity of 2.0 (arbitrary logarithmic units) is the threshold for the sub-sample chosen for waveform fitting. The cable was out of operation for about five months due to a failure of the submarine electronics module, coming back into operation on day 104 of 2002. The relative absence of points from April 14 to July 1 2002 (days 104-182), however, represents a real absence of whale calls during this period. The whale calls around day 260 (mid September) were louder and more numerous in 2001 than in 2002.

Frequency range of callsobserved by Stafford et al.

Distributions for f0 (the central frequency) and alpha (the sweep rate) from least-squares fits to waveforms for 800 blue-whale “B” calls. A cut on a goodness-of-fit parameter restricts the sample to the dense dot in the middle of the diagram. This sub-sample is shown in more detail in the figures to the left. The average values and standard deviations obtained from this sub-sample are: (f0,) = (15.99 Hz, 0.04 Hz/sec), with widths of ( f0, ) = (0.04 Hz, 0.03 Hz/sec).

An “A-B” blue-whale calling sequence and spectrogram.

Blowup of “B” call and its spectrogram.Precursor, down an interval of a

fifth from the “B” fundamental.

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