CUMMINGS ET AL.: SOUND FROM BRYDE AND FINBACK WHALES 



preamplifier (Wilcoxon, 5 Type M-H90-A) suspended 

 at depths of 6 to 53 m below the surface Up to 800 

 m of floating cable carried the signals to the ship, 

 allowing the hydrophone to be stationary until the 

 ship drifted out to this distance The hydrophone was 

 suspended from an inflatable 8 m spar buoy which 

 provided effective acoustic isolation from low-fre- 

 quency acceleration caused by surface waves. The 

 hydrophone's response was attenuated at low fre- 

 quencies (beginning with 3 dB down at 12 Hz) to fur- 

 ther reduce low-frequency noise and to prevent most 

 of the preamplifier blockage from any drag motion 

 that remained. Without these or similar measures, 

 we have found that hydrophone and sea noise below 

 100 Hz, even in relatively smooth seas, usually 

 prevents satisfactory recordings of low-frequency 

 mysticete sounds with suspended systems. 



One track of a magnetic tape recorder (Magnecord 

 1020), powered by a DC-AC converter, carried a run- 

 ning commentary and airborne whale sounds from 

 a radio microphone (Vega Telemike). The other track 

 recorded signals from the hydrophone. Continuous 

 visible records were made on station with a level 

 recorder (Briiel & Kjaer, Type 2301), also powered 

 by the converter which was acoustically isolated. A 

 sound analyzer (General Radio, Type 1558) was used 

 to monitor incoming signals and their absolute levels 

 and to provide power to the hydrophone-preamplifier. 

 Calibration was by means of a 1,000-Hz tone and 

 pink or white noise which were inserted through the 

 system and recorded at frequent intervals. Overall 

 response of the recording system was +5 dB from 

 25 Hz to 18 kHz. 



Without a hydrophone array we could not precisely 

 localize sound sources. However, correlations be- 

 tween whale movements and changes in received 

 sound level provided evidence that those sounds 

 came from the whales observed. 



At sea we find it difficult to distinguish the Bryde 



B Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



whale from other balaenopterids, especially the sei 

 whale, B. borealis. An exception was the circum- 

 stance noted here, involving long contacts and good 

 visibility above and below water, so that identifying 

 features of behavior and form were revealed. Most 

 useful of these field characteristics were 1) the pres- 

 ence of ridges on top of the head of Bryde whales, 

 2) the asymmetrical coloration of finbacks, usually 

 a yellowish white on the lower right jaw and baleen 

 that is contrasted with the darker appearance of the 

 left area, and 3) the peculiar surfacing of sei whales 

 whereby head and fin appear nearly simultaneous- 

 ly, without arching. 



Received overall sound levels are reported in dB 

 re 1 jiPa, and source levels are referenced to 1 m. 

 Analysis was accomplished using graphic level 

 recorders, oscilloscopes, a sound spectrographic 

 recorder, and a RTA (real time analyzer). 



RESULTS 



Sightings and Recordings 



The locations of whale sightings associated with 

 recordings of whale sounds are listed (Table 1). Un- 

 identified balaenopterid whales were sighted off La 

 Paz, where two low-level whale sounds were recorded 

 during Contact 1. 



We spotted two Bryde whales, about 11 m long, 

 southeast of Loreto (Contact 2). The sea was calm 

 and the surface water temperature was 24 °C. The 

 two animals separated as the ship approached. One 

 swam away and remained mostly out of sight. The 

 other began passing back and forth under the ship's 

 keel. It dove about 10 m and surfaced every 1 to 6 

 min. W C. Cummings dove on the whale and photo- 

 graphed it underwater for identification. 



We recorded 288 low-frequency moans in 50 min 

 from the Bryde whales during Contact 2. Some of 

 these sounds were of very low signal-noise ratio 

 (down into the ambient level of the sea noise) and 

 presumably originated from the more distant of the 



Table 1.— Contacts with sound producing whales in the Gulf of California. 



Contact Date Time 



Location 



Subjects (No.) 



5'N, 110°36'W, 2 km S of Isla San Francisco 



5'N, 110°19'W, 8 km SSE of Loreto 



N, 111°42'W, 14.8 km SE of Pta. Concepcion 



N,111°46'W, midway, Guaymas to Isla San Esteban 



N, 112°9.5'W, 18.5 km ENE of San Pedro Martir Island 



N, 112°53.5'W, 24.1 km ESE of Isla Angel de la Guarda 



N, 113°31'W, 3.7 km ENE of Puerto Refugio 



5'N, 113°27'W, 17.6 km NE of Puerto Refugio 



N, 113°33'W, N. end of Ballenas Channel 



5'N, 113°30'W, N. end of Ballenas Channel 



Balaenoptera sp. (1) 

 B. edeni (2) 

 B. edeni (1) 

 Large whale (1) 

 Balaenoptera sp. (1) 

 B. physalus (3) 

 B. physalus (about 35) 

 B. physalus (2) 

 Balaenoptera sp. (1) 

 Balaenoptera sp. (1) 



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