UC San Diego UC San Diego Previously Published Works Title Blue and fin whale call source levels and propagation range in the Southern Ocean Permalink https://escholarship.org/uc/item/8mr3c6vn Journal Journal of the Acoustical Society of America, 122(2) Authors Sirovic, Anna Hildebrand, John A Wiggins, Sean Publication Date 2007 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Blue and fin whale call source levels and propagation range in the Southern Ocean ͒ Ana Širović,a John A. Hildebrand, and Sean M. Wiggins Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92093-0205 ͑Received 20 October 2006; revised 15 May 2007; accepted 21 May 2007͒ Blue ͑Balaenoptera musculus͒ and fin whales ͑B. physalus͒ produce high-intensity, low-frequency calls, which probably function for communication during mating and feeding. The source levels of blue and fin whale calls off the Western Antarctic Peninsula were calculated using recordings made with calibrated, bottom-moored hydrophones. Blue whales were located up to a range of 200 km using hyperbolic localization and time difference of arrival. The distance to fin whales, estimated using multipath arrivals of their calls, was up to 56 km. The error in range measurements was 3.8 km using hyperbolic localization, and 3.4 km using multipath arrivals. Both species produced high-intensity calls; the average blue whale call source level was 189±3 dB re:1 ␮Pa-1 m over 25–29 Hz, and the average fin whale call source level was 189±4 dB re:1 ␮Pa-1 m over 15–28 Hz. Blue and fin whale populations in the Southern Ocean have remained at low numbers for decades since they became protected; using source level and detection range from passive acoustic recordings can help in calculating the relative density of calling whales. © 2007 Acoustical Society of America. ͓DOI: 10.1121/1.2749452͔ PACS number͑s͒: 43.80.Ka, 43.30.Sf ͓WWA͔ Pages: 1208–1215 I. INTRODUCTION Charif et al., 2002͒. Blue and fin whales make distinctive low-frequency, high-intensity calls that vary geographically Blue ͑Balaenoptera musculus͒ and fin whales ͑B. physa- ͑Cummings and Thompson, 1971; Watkins, 1981; Edds, lus͒ were the primary targets of the commercial whaling in- 1982; 1988; Clark, 1995; McDonald et al., 1995; Ljungblad dustry that developed in the Southern Ocean during the et al., 1998; Stafford et al., 1999; McDonald et al., 2006͒, twentieth century. Populations of both species were brought and their source levels have been estimated at several world- to near extinction before their hunt was banned in the 1960’s wide locations. Cummings and Thompson ͑1971͒ estimated and 70’s ͑Clapham and Baker, 2001͒, and their population source level of blue whale moans off Chile in the 14 to recovery has been slow ͑Best, 1993; Branch and Butter- 222-Hz band to be 188 dB re:1 ␮Pa at 1 m. Calls of blue worth, 2001; Branch et al., 2004͒. Both species produce calls whales from the eastern North Pacific Ocean had maximum that are likely to be an important part of the mating and intensity 180–186 dB re:1 ␮Pa at 1 m over the 10–110-Hz feeding behaviors ͑Watkins et al., 1987; McDonald et al., band ͑Thode et al., 2000; McDonald et al., 2001͒. Fin whale 2001; Croll et al., 2002; Oleson et al., 2007͒, and it has been downswept call source levels have been reported at established that certain baleen whale calls can be detected at 160–186 dB re:1 ␮Pa at 1 m in the western North Atlantic ranges of hundreds of kilometers ͑Cummings and Thompson, and between 159 and 184 dB re:1 ␮Pa at 1 m in the eastern 1971; Payne and Webb, 1971; Clark, 1995; Stafford et al., North Pacific Ocean ͑Watkins, 1981; Watkins et al., 1987; 1998͒. Payne and Webb ͑1971͒ postulated that long-range Charif et al., 2002͒. Northrop et al. ͑1968͒ reported fin whale propagation might be important for communication with downsweeps of even higher intensity in the Central Pacific conspecifics over large distances, and the low population Ocean, ranging between 164 and 199 dB re:1 ␮Pa at 1 m, densities resulting from commercial whaling ͑Branch and albeit assuming relatively high transmission loss. Butterworth, 2001͒ could make this type of communication Frequency and temporal characteristics of blue and fin even more important for species survival. whale calls in the Southern Ocean have been described pre- Several methods have been developed for acoustic local- viously ͑Ljungblad et al., 1998; Širović et al., 2004; Rankin ization and source level estimation in the marine environ- et al., 2005͒. Blue whale calls last up to 18 s and generally ment ͑e.g., Frazer and Pecholcs, 1990; Cato, 1998; Jensen et consist of three segments: a 9-s-long, 27-Hz tone, followed al., 2000; Spiesberger, 2001͒. The theory was developed pre- by a 1-s downsweep to 19 Hz and another, longer-lasting dominately for naval and seismic purposes, but similar meth- downsweep to 18 Hz ͑Širović et al., 2004; Rankin et al., ods can be used to determine locations and source levels of 2005͒. Fin whales produce short ͑Ͻ 1s͒ downsweeps from calling cetaceans in the wild ͑Watkins and Schevill, 1972; 28 to 15 Hz ͑Širović et al., 2004, 2006͒. Calls of both spe- McDonald et al., 1995; Stafford et al., 1998; McDonald and cies are usually repeated at regular intervals. No call source Fox, 1999; Clark and Ellison, 2000; Thode et al., 2000; levels from either species have been reported for the South- ern Ocean. ͒ Call intensity may be important for successful intraspe- a Current address: Southwest Fisheries Science Center, NMFS/NOAA, 8604 La Jolla Shores Dr., La Jolla, CA 92037. Electronic mail: cific communication over long distances, and needs to be [email protected] quantified before we can understand the potential impacts of 1208 J. Acoust. Soc. Am. 122 ͑2͒, August 20070001-4966/2007/122͑2͒/1208/8/$23.00 © 2007 Acoustical Society of America FIG. 1. Blue ͑a͒ and fin whale ͑b͒ calls recorded off the Western Antarctic Peninsula, showing multipath arrivals. In both examples, paths shown were first, second, and third bounces ͑marked 1, 2, and 3, respectively͒; di- rect path is not visible. Calculated ranges were 33 km for the blue whale and 40 km for the fin whale. Theoret- ical contributing bounces for the fin whale path arrivals are shown in part ͑c͒, with the thick line representing the first bounce, the medium thickness line for the second bounce, and the thin line for the third bounce. Calling whale location is denoted with a black square and the receiving ARP location is shown by a black circle. anthropogenic noise on these animals. In this paper, we re- analysis because the downswept parts of their calls made it port the average estimated source levels for blue and fin possible to distinguish exact multipath arrival times ͑Fig. 1͒. whale calls recorded off the Antarctic Peninsula and investi- Arrival time for the downsweep was measured in the time- gate the variation in the source levels within the population. frequency domain at the time of the highest frequency for all Also, we calculate the ranges over which these calls can be multipaths, and the differences between the multipath arrival expected to propagate, using the average noise levels for this times were calculated. Spectral parameters were set to 500- region. point FFT and 90% overlap. Calls with multiple arrivals were found only at one instrument at a time and only calls II. METHODS with three or more multipath arrival times and good signal- to-noise ratios were used in the analysis. The error in the Acoustic data were recorded using Acoustic Recording calculation of the arrival time differences was determined by Packages ͑ARPs͒ deployed off the Western Antarctic Penin- taking multiple measurements of the multipath arrival times sula between March 2001 and February 2003. Detailed infor- of an individual whale call. The range to the calling whale mation on ARPs, these deployments, and temporal character- was calculated separately for each measurement and the stan- istics of blue and fin whale calls used in the analyses is given dard deviation of those ranges was reported. in Wiggins ͑2003͒ and Širović et al. ͑2004͒. The ARPs were The following assumptions were made in the multipath not navigated after deployment for precise locations and the arrival model: whale calling occurred near the surface, in- maximum error in the deployment locations is less than struments were located on the bottom, the sound-speed pro- 1 km, given the average ARP sinking speed ͑40 m/min to file was homogeneous ͑c=1480 m/s͒, and the bottom was 3500-m depth͒ and assuming maximum speed of the Antarc- flat. Blue whales are known to make calls at depths of tic Circumpolar Current ͓15 cm/s, Pickard and Emery 20–30 m ͑Thode et al., 2000; Oleson et al., 2007͒, and the ͑1990͔͒. calling depth for fin whales is reported to be around 50 m The goals of the study were to calculate blue and fin ͑Watkins et al., 1987͒. The hydrophone was suspended 10 m whale call source levels and to estimate the maximum range above the ocean floor. Given the water column depth of over which these calls can be heard. Data needed for call around 3000 m, differences in water column depth Ͻ 100 m source level estimation are the instrument response, distance could reasonably be approximated as calling at the surface to the calling whales, and knowledge of the ocean propaga- and receiver on the bottom. All the ARPs used in these tion environment.