Repetitive rates of harp seal underwater vocalizations

Underwater recordings of harp seal (Phoca groenlandica) vocalizations, obtained within the breeding herd during March, were examined with respect to calling rate and repetition of calls. Vocalizations typically overlapped one another. Calling rates ranged from 32 to 88 calls/min. Repetition rates averaged between 1.9 and 4.7 sound pulses/call (maximum repetition 24 times). Approximately 30% of the calls were not repeated and 40% were repeated twice. We found no significant relationships between calling rates and repetition rates. There were no variations in these factors throughout the day or month. An automatic level control on the recorder and the overlapping of the calls may have compromised the counts by altering the effective sampling area. The use of vocalization indexes in association with population estimations may be possible only when calls do not overlap.