Wildlife Iceland

Recordings of Blue Whales sound with single hydrophone and Ecological Acoustic Recorders (EARs)

In courtesy of  Iversen, M.,  Rasmussen, M. H., Magnúsdóttir, E. E. and Lammers, M. O.
2011

Abstract

Blue whale calls were recorded from the 21st to 23rd of June 2009 with a single hydrophone and Ecological Acoustical Recorders (EARs). Fifteen (144 min.) out of 94 recordings made with the single hydrophone and 21 recordings (31.2 min.) with EARs contained blue whale sound. These recordings were analyzed both aurally and with BatSound Pro software and all files were amplified and filtered. Spectrograms of blue whale calls were done using a 1024-point FFT, 85% overlap, and Hanning window. A total of 163 blue whale sounds were analysed and revealed 11 different sounds types, most in the audible range. Both the single hydrophone and the EARs captured four of the more common sound types; however, the single hydrophone recorded two other common sounds and one only with the EARs. Unfortunately, we had no recordings were the two recording methods were used simultaneously. All blue whale sound frequencies were comparable to previously reported frequencies on the species and several sound types were directly comparable to sounds recorded in the St. Lawrence estuary by Berchok et al. (2006).

Introduction

Blue whales have a large geographical distribution and previous studies have found that at least 10 distinct regional calls remain stable over decades. As a result, sound has been suggested to be a good indicator of subdivisions of the species(5). Blue whales have been observed feeding in June and July in Skjálfandí Bay, Iceland since 2004(2, 4). We aim to compare blue whale sounds recorded with two different methods, single hydrophone and Ecological Acoustic Recorders, to see if those two methods could be combined in future analysis on blue whale sound production and occurrence in Skjálfandi Bay.

Materials & Methods

Table 1: Methods and recordings

Table 1: Methods and recordings

The recordings were done with a single hydrophone and with Ecological Acoustic Recorders (EARs) in Skjálfandí Bay (65°57’18”N, 017°25’31”W) in Iceland during the 21st to 23rd of June 2009. The single hydrophone recordings were supported by visual observations and photo-identification. Table 1 summarizes the methods.

All files were amplified, low-pas and analyzed both aurally and using BatSound Pro software. Spectrograms of blue whale calls were done using a 1024-point FFT, 85% overlap, and Hanning window. Spectrogram correlation algorithm was used for finding blue whale downswept sounds on the EARs whereas the sound files from the single hydrophone were all manually scanned.

Results

A total of 163 blue whale sounds were analysed and revealed 11 different sounds types, most in the audible range (table 2). Nine of these sound types were recorded by the single hydrophone and six by the EARs.

Table 2: Results, type of sound, numbers, frequencies range and durations ± standard deviations.

Table 2: Results, type of sound, numbers, frequencies range and durations ± standard deviations.

Discussion

To analyze the occurrence and sound production of blue whales in a new area, it is very practical to combine these two methods. The recordings from a single hydrophone can reveal the variety of sound types produced by the whales as well as collecting greater quality of recordings due to closer proximity to the animals. This information creates basis for the construction of detection algorithms used for finding sound of interest in a long-term recordings within the same area. The blue whale sounds recorded in the Bay contained mainly frequencies between 19 to 261 Hz. These frequency ranges are comparable to blue whale frequencies worldwide (e.g. 9) and the moderate downswept calls, grunts, bubbling and blurps observed in this study corresponds roughly to the previously reported calls in the Northeast Atlantic by Berchok et al. (2006). However, the downswept calls are seen more or less worldwide (e.g. 6; 8 & 10).

Figure 1: An example of four down swept calls in a phrase with the amplitude of the calls

Figure 1: An example of four down swept calls in a phrase with the amplitude of the calls

Figure 2: An example of one of the small constant call which often follow a downswept call.

Figure 2: An example of one of the small constant call which often follow a downswept call.

Figure 3: An example of a grunt

Figure 3: An example of a grunt

1) Húsavík Research Center, University of Iceland, Hafnarstrett 3 , 640 Húsavík, Iceland, 2) Danish Institute for Study Abroad, Science & Health department, Vestergade 4.7, 1456 Copenhagen K, Denmark,) Hawaii Institute of Marine Biology, University of Hawaii at Manao, P. O. Box 1106, Kailua, HI 96834, US

References

(1)Berchok, C. L., Bradley, D.L. & Gabrielson, T. B. (2006): St. Lawrence blue whale vocalizations revisited: Characterization of calls detected from 1998 to 2001. J. Acoust. Soc. Am. 120: 2340–2354.

(2)Iversen, M., Rasmussen, M. H., Cecchetti, A., Sigurðardóttur, V., Wald, E. & G.A. Vikingsson: Seasonal occurrence and potential movement of feeding area of blue whales (Balaenoptera musculus) around Iceland – Preliminary studies. European Research Cetacean 23. Poster at ECS conference, Turkey.

(3)Lammers, M. O, Brainard, R.E., Au, W.W.L., Mooney, A.T. & Wong, K.B (2008): An ecological acoustic recorder (ear) for long-term monitoring of biological and anthropogenic sounds on coral reefs and other marine habitats J. Acoust. Soc. Am. 123 (3): 1-10.

(4)Magnúsdóttir, E. E., Rasmussen, M. H., and Lammers, M. O. Combining visual and fixed passive acoustic methods to measure the variability of cetacean occurrence at the NE-coast of Iceland. Lecture at the 159th Meeting of the Acoustical Society of America, Baltimore, Maryland, 19. – 23. April 2010.

(5)McDonald, M.A., Hildebrand, J.A. & Mesnick, S. (2009): Worldwide decline in tonal frequencies of blue whale songs. Endang Species Res. 9: 13–21.

(6)McDonald, M. A., Calambokidis, J., Teranishi, A. M. & Hildebrand, J. A. (2001): The acoustic calls of blue whales off California with gender data, J. Acoust. Soc. Am. 109: 1728–1735.

(7)Mellinger, D.K. & Clark, C.W. (2003): Blue whale (Balaenoptera musculus) sounds from the North Atlantic. J. Acoust. Soc. Am. 114(2): 1108-19.

(8)Oleson, E. M., Calambokidis, J., Burgess, W.C., McDonald, M.A., LeDuc, C. A. & Hildebrand, J. A. (2007): Behavioral context of call production by eastern North Pacific blue whales. Mar Ecol Prog Ser 330: 269–284.

(9)Stafford, K.M., Nieukirk, S.L. & Fox, C.G. (2001): Geographic and seasonal variation of blue whale calls in the North Pacific. J. Cetacean Res. Manage. 3(1): 65-76.

(10)Thompson, P. O., Findley, L. T., Vidal, O. & Cummings, W. C. (1996): Underwater sounds of blue whales, Balaenoptera musculus, in the Gulf of California, Mexico. Marine Mammal Sci. 12: 288–293.

Acknowledgements

Dansk-Islands fond, DIS, Oticon, Peter Teglberg Madsen, Gísli A. Víkingsson, Tryggvi Finnsson, Viola Palvona , Lee Millerand and Line Reinstrup,

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