1 



55 



24 



19 



SECONDS 



FIGURE 2. — Lengths of 120 sweep sounds from Histriophoca 

 separate all but one (at 2.75 s) into three categories. 



(19 measured) because of the higher frequency 

 ending. Harmonics (up to 6 or more) were consis- 

 tently present in the spectrographic analyses of 

 even low-level sweep sounds, and appear to be a 

 result of the pulsed character of the seal sounds 

 (Watkins 1967). 



Since we never knew the distance to calling 

 seals, we did not have accurate acoustic source 

 levels for these sounds. Some sweeps overloaded 

 the recording system at the usual gain settings 

 and therefore were received at levels estimated in 

 excess of 40 dB (re 1 volt/dyne cm 2 ). Assuming a 

 60-65 dB source level at 1 m and spherical spread- 

 ing losses, these very loud sounds were sometimes 

 from animals that were only 15 to 20 m from the 

 hydrophone. Sounds of each type and length cate- 

 gory were heard from distant as well as nearby 

 seals so that none of these sounds were character- 

 istic of a particular seal. 



A second type of underwater sound which we 

 associate with Histriophoca was a broadband 



puffing sound with frequencies below 5 kHz and 

 lasting a little less than 1 s (Figure 3). This was 

 somewhat reminiscent of some seal respiratory 

 sounds, but it was not audible in air and we could 

 not correlate them with respiratory activity. The 

 puff sounds were 20 to 25 dB lower level than the 

 sweeps. 



Discussion 



The downward sweeping frequency and pulsed 

 quality of the sounds is characteristic of many 

 underwater calls of other seals: Erignathus bar- 

 batus (Ray et al. 1969), Leptonychotes weddelli 

 (Ray 1967; Schevill and Watkins 1965, 1971), 

 Pagophilus groenlandica (Watkins and Schevill in 

 prep.), Pusa hispida (Stirling 1973), Arcto- 

 cephalus philippii (Norris and Watkins 1971). 

 Coincident with spring reproductive activities, 

 most of these pinnipeds produce striking under- 

 water acoustic signals and greatly increase their 

 calling. Ovulation normally occurs from mid- 

 April to mid-May in Histriophoca and adult males 

 remain sexually potent through early June 

 (Burns 3 ). Analogy to these other pinnipeds 

 suggests similar social functions for the under- 

 water sounds of Histriophoca, in reproductive 

 and/or territorial behavior. 



3 Burns, J. J. 1969. Seal biology and harvest. Marine Mammal 

 Investigations. Fed. Aid Completion Rep., Alaska Dep. Fish 

 Game 10:1-25. 



4- 



r 



2- 







FIGURE 3, 



Seconds 



-The "puffing" sound of Histriophoca is not related to any respiratory activity but is an underwater sound with broadband 

 characteristics that are quite variable. Analyzing filter was 45 Hz. 



452 



