Geographic variation and acoustic structure of the underwater vocalization of harbor seal (Phoca vitulina) in Norway, Sweden and Scotland

Abstract

The male harbor seal ͑Phoca vitulina͒ produces broadband nonharmonic vocalizations underwater during the breeding season. In total, 120 vocalizations from six colonies were analyzed to provide a description of the acoustic structure and for the presence of geographic variation. The complex harbor seal vocalizations may be described by how the frequency bandwidth varies over time. An algorithm that identifies the boundaries between noise and signal from digital spectrograms was developed in order to extract a frequency bandwidth contour. The contours were used as inputs for multivariate analysis. The vocalizations' sound types ͑e.g., pulsed sound, whistle, and broadband nonharmonic sound͒ were determined by comparing the vocalizations' spectrographic representations with sound waves produced by known sound sources. Comparison between colonies revealed differences in the frequency contours, as well as some geographical variation in use of sound types. The vocal differences may reflect a limited exchange of individuals between the six colonies due to long distances and strong site fidelity. Geographically different vocal repertoires have potential for identifying discrete breeding colonies of harbor seals, but more information is needed on the nature and extent of early movements of young, the degree of learning, and the stability of the vocal repertoire. A characteristic feature of many vocalizations in this study was the presence of tonal-like introductory phrases that fit into the categories pulsed sound and whistles. The functions of these phrases are unknown but may be important in distance perception and localization of the sound source. The potential behavioral consequences of the observed variability may be indicative of adaptations to different environmental properties influencing determination of distance and direction and plausible different male mating tactics.

Year-round acoustic detection of bearded seals (Erignathus barbatus) in the Beaufort Sea relative to changing environmental conditions, 2008–2010

“…Expanding the study to the Bering and Chukchi Seas will cover much of the range of Alaskan bearded seals and provide a broader picture of their seasonal occurrence under the different ice conditions they experience over this range. Finally, detailed analysis of call types can be used to determine whether or not geographic variation exists among the three seas as has been shown in other regions and with other species (Van Parijs et al 1999;Bjørgesaeter et al 2004;Risch et al 2007;Van Opzeeland et al 2009). There are potential subpopulations that reside in each region throughout the year that may be determined by comparing call types present throughout the year at each location.…”

Integrating genetic data and population viability analyses for the identification of harbour seal (Phoca vitulina) populations and management units

“…) and acoustics (Bjorgesaeter et al . ; Delarue et al . ), but such approaches to population identification are typically time‐ and resource‐consuming and may be logistically and technically complex.…”

“…whales and seals) where assessments may be further hampered by their large body sizes, low densities and/or complex life histories, as well as ethical issues. Valuable insights can be obtained from tagging and tracking (Block et al 2011), photo-ID (Katona & Whitehead 1981;Smith et al 1999), trace element analyses (Kelly 2000), morphometrics (Galatius et al 2012) and acoustics (Bjorgesaeter et al 2004;Delarue et al 2009), but such approaches to population identification are typically time-and resource-consuming and may be logistically and technically complex.…”

Vocal learning in seals, sea lions, and walruses

“…Geographic differences in call types or repertoires have been described for underwater rutting vocalizations of Weddell seals [35-37], leopard seals [38], harbor seals [39,40], harp seals [41], and bearded seals [42], raising the possibility that social learning alters sound production in these species [43,44]. With respect to the social transmission of more complex sounds, there is also evidence that male walruses can modify their patterned underwater songs and adopt new song variants over the course of a few breeding seasons [45 ].…”