Passive acoustic monitoring (PAM) has become a common means of investigating vocal species in a variety of habitats. This is especially true in cetacean research, where acoustic surveys have become commonplace in most of the world'sPAM's effectiveness depends upon a comprehensive understanding of the vocal repertoire of the species being studied. Cetaceans make a wide variety ofanimal-mounted recorders and localization via a towed hydrophone or sonobuoy array, coupled with visual survey data, have confirmed theof many biological signals (e.g., minke whale bio-duck). Despite these advances, many “unknown” biologicalare still recorded, especially in areas that are remote and have not been extensively monitored. Here we report a new, complex call likely produced by a baleen whale, which was recorded via passive acousticgliders in an area east of Guam that includes the Mariana Trench Marine National Monument (MTMNM).

The FLAC files were decoded to standard WAV audio file format at 194 kHz sampling rate. Two datasets with reduced sampling rates of 10 kHz and 1 kHz were generated for baleen whale call occurrenceLong-term spectral average (LTSA) plots were calculated using the TritonPackage (version 1.81, Scripps Whale Acoustic Lab, Scripps Institution of Oceanography, La Jolla, CA). LTSA parameters were Δt of 2 s and Δf of 10 Hz (for 10 kHz data) and Δt of 1 s and Δf of 1 Hz (for 1 kHz data). The 10 and 1 kHz data were then time-aligned in thepackage Raven Pro (version 1.5 beta, Bioacoustics Research Program, Cornell University, Ithaca, NY), and calls were logged for both datasets simultaneously.used the MATLAB basedOsprey () to measure calls. Calls selected for measurements (n = 20 calls) had a high (>20 dB) signal-to-noise ratio (SNR), did not overlap other calls, and were at least a few hours apart to maximize the chance that measured calls represented more than one animal.

In 2014, a glider was deployed on 29 September 2014 off the west coast of Guam (13° 30.79′ N, 144° 35.04′ E). The glider was recovered about 24 nautical miles southwest of the deployment location (13° 10.81′ N, 144° 31.22′ E) on 14 November 2014. In March 2015, two gliders successfully surveyed this area again. Both gliders were recovered on 27 April 2015 (Fig.).

Three passive-acoustic surveys in offshore waters east of Guam and Saipan were conducted using a Seaglider ™ (Kongsberg Inc., Lynwood, WA). The glider was equipped with a custom-designed and -built passive acoustic recording system (Applied Physics Laboratory, University of Washington, Seattle, WA). Acoustic signals were received by a single omnidirectional hydrophone (type: HTI-99-HF, High Tech Inc., Gulfport, MS; sensitivity: −164 dB re 1 V/μPa), amplified by 36 dB, and recorded at 194 kHz sample rate and 16-bit resolution. The acoustic system was optimized for continuously collecting data in the frequency range 15 Hz to 97 kHz, and thus was well suited for the recording of both baleen and toothed whales. The glider repeatedly dove in a saw tooth pattern to 1000 m depth and back to the surface at a typical horizontal speed of 25 cm/s. Dive durations were usually on the order of 4–6 h.

In 2009, a 246 000 kmarea east of the Mariana Archipelago (Fig.) was designated as the Mariana Trench Marine National Monument (). This area also includes the Mariana Islands Range Complex (MIRC), which is the primary Western Pacific range for U.S. military training activities. Glider surveys were conducted east of the islands in support of the U.S. Navy monitoring program for cetacean species occurrence within the MIRC.

Between 14 October and 6 November 2014, 326 of these WPB calls were recorded during 38 glider dives (Fig.). Calls were typically 5–6 min apart and often occurred in long sequences. In data from March–April 2015,identified 29 WPB calls during seven glider dives in the northern survey and 81 calls during nine dives in the southern survey (Fig.). Calls were recorded during both nearshore and offshore portions of the survey, in shallow and deep water and during all portions of a dive.

On numerous occasions,observed a multi-part Western Pacific “Biotwang” (WPB) call, so named because of its unusual syntheticWPB calls were complex and difficult to measure, lasting 2.5–3.5 s overall (Fig.). The call began with a brief 0.4 ± 0.3 s long tone (Part A) centered at 60.1 ± 6.0 Hz, followed by a 1.6 ± 0.1 s low-frequency moan (Part B) that swept from 44.5 ± 3.5 Hz down to 30.8 ± 2.7 Hz. The moan appeared to have both amplitude modulation and strong harmonics; the harmonic at ∼410 Hz was typically one of the stronger components of the call, often appearing above the background noise level in the LTSA, making it useful for finding WPB calls in long recordings. The moan was followed by two ∼60–150 Hz upsweeps lasting 0.5 ± 0.1 s (Part C) that often had diffuse energy up to 1000 Hz. Part D of the call started with a ∼0.2 s long noisy burst ofwith energy up to 7.5 kHz. The call ended with metallic-sounding upsweeps (Part E) with most energy between 700 and 800 Hz, but up to 7.5 kHz, and lasting 0.66 ± 0.03 s. In calls with low SNR, Parts A, C, D and E were often not visible or audible.

4. Discussion Section: Choose Top of page ABSTRACT 1.Introduction 2.Methods 3.Results 4.Discussion << References and links CITING ARTICLES

ocean soundscape, sounds originate from anthropogenic, geophysical, and biological sources ( Pijanowski et al., 2011 Soundscape ecology: The science of sound in the landscape ,” Bioscience 61, 203– 216 . https://doi.org/10.1525/bio.2011.61.3.6 13. Pijanowski, B. C., Villanueva-Rivera, L. J., Dumyahn, S. L., Farina, A., Krause, B. L., Napoletano, B. M., Gage, S. H., and Pieretti, N. (2011). “,” Bioscience, 203– sounds reported here are not similar to known anthropogenic sources such as noise produced by ships or seismic airguns. They also do not resemble geophysical sources such as the very low-frequency sounds produced by earthquakes and ice, nor the sounds produced by wind or rain ( Hildebrand, 2009 Anthropogenic and natural sources of ambient noise in the ocean ,” Mar. Ecol. Prog. Ser. 395, 5– 20 . https://doi.org/10.3354/meps08353 4. Hildebrand, J. A. (2009). “,” Mar. Ecol. Prog. Ser., 5– Stafford et al., 1999 Low-frequency whale sounds recorded on hydrophones moored in the eastern tropical Pacific ,” J. Acoust. Soc. Am. 106, 3687– 3698 . https://doi.org/10.1121/1.428220 21. Stafford, K. M., Nieukirk, S. L., and Fox, C. G. (1999). “,” J. Acoust. Soc. Am., 3687– sounds were produced by a biological source. In anoriginate from anthropogenic, geophysical, and biological). Thereported here are not similar to known anthropogenicsuch as noise produced by ships orairguns. They also do not resemble geophysicalsuch as the very low-frequencyproduced by earthquakes and ice, nor theproduced by wind or rain (). Using the spectral and temporal criteria long established in the bioacoustics community (), the authors hypothesize that these complexwere produced by a biological

sounds from Bryde's whales. In the Pacific, at least six low-frequency calls have been attributed to Bryde's whales ( Heimlich et al., 2005 Types, distribution, and seasonal occurrence of sounds attributed to Bryde's whales (Balaenoptera edeni) recorded in the eastern tropical Pacific, 1999-2001 ,” J. Acoust. Soc. Am. 118, 1830– 1837 . https://doi.org/10.1121/1.1992674 3. Heimlich, S., Mellinger, D., Nieukirk, S., and Fox, C. G. (2005). “,” J. Acoust. Soc. Am., 1830– Oleson et al., 2003 Low frequency calls of Bryde's whales ,” Mar. Mammal Sci. 19, 407– 419 . https://doi.org/10.1111/j.1748-7692.2003.tb01119.x 8. Oleson, E. M., Barlow, J., Gordon, J., Rankin, S., and Hildebrand, J. A. (2003). “,” Mar. Mammal Sci., 407– Hill et al. (2015 5. Hill, M. C., Oleson, E. M., Ligon, A. D., Martien, K. K., Archer, F. I., Baumann-Pickering, S., Bendlin, A. R., Dolar, L., Merkens, K. P. B., Milette-Winfree, A., Morin, P. A., Rice, A., Robertson, K. M., Trickey, J. S., Adam, C. Ü., Van Cise, A. M., and Woodman, S. M. (2015). “ Cetacean monitoring in the Mariana Islands range complex, 2014 ,” PIFSC Data Report DR-15-003, 61 pp. Oleson et al. (2015) 10. Oleson, E. M., Baumann-Pickering, S., Širović, A., Merkens, K. P. B., Munger, L. M., Trickey, J. S., and Fisher-Pool, P. (2015). “ Analysis of long-term acoustic datasets for baleen whales and beaked whales within the Mariana Islands Range Complex (MIRC) for 2010 to 2013 ,” PIFSC Data Report DR-15-003, 19 pp. sounds similar to the lower parts (Part A and B) of the WPB vocalization in their acoustic data recorded in the Mariana Islands and conclude their sound is similar to a Bryde's whale Be3 call ( Oleson et al., 2003 Low frequency calls of Bryde's whales ,” Mar. Mammal Sci. 19, 407– 419 . https://doi.org/10.1111/j.1748-7692.2003.tb01119.x 8. Oleson, E. M., Barlow, J., Gordon, J., Rankin, S., and Hildebrand, J. A. (2003). “,” Mar. Mammal Sci., 407– vocalization. The low-frequency (<200 Hz) components of this call superficially resemble the short and variablefrom Bryde's whales. In the Pacific, at least six low-frequency calls have been attributed to Bryde's whales ()., Fig. 16, p. 57) andreport findingsimilar to the lower parts (Part A and B) of the WPBin their acoustic data recorded in the Mariana Islands and conclude theiris similar to a Bryde's whale Be3 call (). However, the call we report here contains components above 200 Hz, including some components exceeding 7 kHz, and to date there are no published accounts of Bryde's whale calls with anything like the Part D and E components of the WPB

sound most closely resembles the “Star Wars” (SW) sound produced by dwarf minke whales on the Great Barrier Reef ( Gedamke et al., 2001 Localization and visual verification of a complex minke whale vocalization ,” J. Acoust. Soc. Am. 109, 3038– 3047 . https://doi.org/10.1121/1.1371763 2. Gedamke, J., Costa, D. P., and Dunstan, A. (2001). “,” J. Acoust. Soc. Am., 3038– sound, the frequency sweep, and the metallic nature of the final part of this call are all very similar to characteristics of dwarf minke whale SW calls. When all five parts of the call reported here are examined, including frequencies up to 8 kHz, thismost closely resembles the “Star Wars” (SW)produced by dwarf minke whales on the Great Barrier Reef (). The complex structure of the WPBthe frequency sweep, and the metallic nature of the final part of this call are all very similar toof dwarf minke whale SW calls.

oceans and produce a wide variety of regionally specific calls, including the SW call in northeastern Australian waters, low-frequency pulse trains in the Atlantic ( Winn and Perkins, 1976 28. Winn, H. E., and Perkins, P. J. (1976). “ Distribution and sounds of the minke whale, with a review of mysticete sounds ,” Cetology 19, 1– 12 . Rankin and Barlow, 2005 Source of the North Pacific ‘boing’ sound attributed to minke whales ,” J. Acoust. Soc. Am. 118, 3346– 3351 . https://doi.org/10.1121/1.2046747 14. Rankin, S., and Barlow, J. (2005). “,” J. Acoust. Soc. Am., 3346– 1 Balaenoptera acutorostrata) across the North Pacific ( Rankin and Barlow, 2005 Source of the North Pacific ‘boing’ sound attributed to minke whales ,” J. Acoust. Soc. Am. 118, 3346– 3351 . https://doi.org/10.1121/1.2046747 14. Rankin, S., and Barlow, J. (2005). “,” J. Acoust. Soc. Am., 3346– vocalizations are produced by dwarf minke whales, a conspecific of B. acutorostrata occurring in the southern hemisphere close to the equator ( International Whaling Commission, 2001 6. International Whaling Commission (2001). “Report of the scientific committee,” J. Cetacean Res. Manag. 3 (SUPPL.). Pastene et al., 1994 11. Pastene, L. A., Fujise, Y., and Numachi, K. (1994). “ Differentiation of mitochondrial DNA between ordinary and dwarf forms of southern minke whale ,” Reports Int. Whal. Comm. 4, 277– 282 . Wada et al., 1991 26. Wada, S., Kobayashi, T., and Numachi, K. (1991). “ Genetic variability and differentiation of mitochondrial DNA in minke whales ,” Reports Int. Whal. Comm. 13, 203– 215 . Sea, East China Sea and the Sea of Japan, and the “O stock” found in the Sea of Okhotsk ( Reilly et al., 2008 Balaenoptera acutorostrata ,” The IUCN Red List of Threatened Species, 16. Reilly, S. B., Bannister, J. L., Best, P. B., Brown, M., Brownell, R. L., Jr., Butterworth, D. S., Clapham, P. J., Cooke, J., Donovan, G. P., Urbán, J., and Zerbini, A. N. (2008). “,” The IUCN Red List of Threatened Species, http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T2474A9444043.en (Last viewed September 1, 2016). Reilly et al., 2008 Balaenoptera acutorostrata ,” The IUCN Red List of Threatened Species, 16. Reilly, S. B., Bannister, J. L., Best, P. B., Brown, M., Brownell, R. L., Jr., Butterworth, D. S., Clapham, P. J., Cooke, J., Donovan, G. P., Urbán, J., and Zerbini, A. N. (2008). “,” The IUCN Red List of Threatened Species, http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T2474A9444043.en (Last viewed September 1, 2016). sea states make sighting this species difficult. Given that there are several types of minke whales with unknown vocal behavior in close proximity to our survey area, and that many species of baleen whales, including minke whales, produce regionally distinct calls, the WPB could have been produced by a minke whale. Minke whales are found in most of the world'sand produce a wide variety of regionally specific calls, including the SW call in northeastern Australian waters, low-frequency pulse trains in the Atlantic () and boings in the North Pacific (). Coincidentally, minke whale boing calls were also recorded during our southern survey in March 2015 (Fig.). Boings are produced by the common minke whale () across the North Pacific (), while SWare produced by dwarf minke whales, a conspecific ofoccurring in the southern hemisphere close to the equator (). Two additional stocks of common minke whales are known in the western North Pacific, the “J stock,” found in the YellowEast Chinaand theof Japan, and the “O stock” found in theof Okhotsk (); calls produced by these whales have not been identified. Very little is known of minke whale and dwarf minke whale distribution at low latitudes in the Pacific (), primarily because the species is the smallest of the baleen whales, produces an inconspicuous blow, spends little time at the surface, and often occurs in areas where highstates make sighting this species difficult. Given that there are several types of minke whales with unknown vocal behavior in close proximity to our survey area, and that many species of baleen whales, including minke whales, produce regionally distinct calls, the WPB could have been produced by a minke whale.

source of the call (e.g., Oleson et al., 2007 Temporal separation of blue whale call types on a southern California feeding ground ,” Anim. Behav. 74(4), 881– 894 . https://doi.org/10.1016/j.anbehav.2007.01.022 9. Oleson, E. M., Wiggins, S. M., and Hildebrand, J. A. (2007). “,” Anim. Behav.(4), 881– Hill et al. (2015) 5. Hill, M. C., Oleson, E. M., Ligon, A. D., Martien, K. K., Archer, F. I., Baumann-Pickering, S., Bendlin, A. R., Dolar, L., Merkens, K. P. B., Milette-Winfree, A., Morin, P. A., Rice, A., Robertson, K. M., Trickey, J. S., Adam, C. Ü., Van Cise, A. M., and Woodman, S. M. (2015). “ Cetacean monitoring in the Mariana Islands range complex, 2014 ,” PIFSC Data Report DR-15-003, 61 pp. Stafford, 2016 20. Stafford, K. M. (2016). “A review of blue whale studies from HARUphones in the Pacific,” in Listening in the Ocean, edited by W. W. L. Au and M. O. Lammers ( Springer , New York ), pp. 21– 34 . Risch et al., 2014 Mysterious bio-duck sound attributed to the Antarctic minke whale (Balaenoptera bonaerensis) ,” Biol. Lett. 10, 20140175. 18. Risch, D., Gales, N. J., Gedamke, J., Kindermann, L., Nowacek, D. P., Read, A. J., Siebert, U., Van Opzeeland, I. C., Van Parijs, S. M., and Friedlaender, A. S. (2014). “,” Biol. Lett., 20140175. https://doi.org/10.1098/rsbl.2014.0175 Reilly et al., 2008 Balaenoptera acutorostrata ,” The IUCN Red List of Threatened Species, 16. Reilly, S. B., Bannister, J. L., Best, P. B., Brown, M., Brownell, R. L., Jr., Butterworth, D. S., Clapham, P. J., Cooke, J., Donovan, G. P., Urbán, J., and Zerbini, A. N. (2008). “,” The IUCN Red List of Threatened Species, http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T2474A9444043.en (Last viewed September 1, 2016). sound. Seasonal patterns in calling behavior are often used to infer the function of a baleen whale call and the potentialof the call (e.g.,). In this study, WPB calls were recorded during glider surveys in September–November 2014 and March–April 2015, indicating the presence of this species during fall, winter, and early spring. This is similar to the pattern reported by, in which their “unidentified whale - tonal calls” were recorded off Tinian in most months of the year. Thus, the species making the WPB call is vocalizing and in the area during both the breeding and feeding season for most baleen whales, indicating that this call may have a complex function similar to blue whale vocal behavior in the Eastern Tropical Pacific (reviewed in) or the bio-duck calls recorded in Antarctica (). Interestingly, the J stock of minke whales breeds in fall, which is different from other North Pacific minkes and most other baleen whales that breed in the winter (). The year-round presence of this call in MTMNM and surrounding waters may facilitate the identification of the species making this