Underwater acoustic behaviour of leopard seals (Hydrurga leptonyx) and Ross seals (Ommatophoca rossii) in Antarctic coastal and offshore habitats.

Ilse.van.Opzeeland [ at ] awi.de


Geographic variation in the acoustic repertoire has been described for several marine and terrestrial organisms and can be used for the identification of different populations and to allocate individuals to certain populations. Passive acoustic monitoring can be utilized to derive a baseline understanding of the distribution of Antarctic pinnipeds in difficult accessible habitats like the Southern Ocean where harsh weather conditions and limited light availability complicate data collection. Leopard seals (Hydrurga leptonyx) and Ross seals (Ommatophoca rossii) produce underwater sounds during summer in the Southern Ocean. For both species, geographic differences in vocal behavior occur between distant (> 1000 km) locations, but have not been explored over smaller spatial scales. Information on spatial patterns in animal vocal divergence can be used to gain insight in dispersal patterns and the factors that drive geographic variation. Here it is explored if and how vocal behavior of leopard and Ross seals differs over a regional scale (< 1000 km) in the Southern Ocean. The vocal repertoire compositions of leopard and Ross seals were compared between two offshore (68°S 0°E, 66°S 27°W) and one coastal (70°S 8°W) location. The examined records comprised acoustic data from March 2008 to December 2010 and from December 2010 to January 2013 Parameters that were compared between recordings were timing of local vocal activity, repertoire composition and a set of standard acoustic parameters of the various call types, such as duration and frequency of greatest amplitude. Leopard seals were vocally active between October and January, Ross seals from mid-December until January at all recording locations. At all sites, the leopard seal vocal repertoires had equal compositions, consisting of 8 call types, comparably larger than the repertoires recorded elsewhere. Furthermore a new ‘Medium double trill’ subtype with around 1000 Hz was firstly described here in comparison to the already known ‘Medium double trill’ of about 2000 Hz. Call characteristics of leopard seal calls differed mainly between the coastal and offshore areas. An evidence for differences of leopard seal call characteristics in relation to distance is described. It is concluded that young leopard seals leave their original breeding group and join other breeding groups when they become sexual mature, maintaining geographic variations in vocalizations and genetic exchange at the same time. The Ross seal vocal repertoire consisted of 5 call types at all recording locations and did not significantly differ in composition between all locations. The start of high Ross seal vocal activity was temporal consistent over several years and at different locations, suggesting a universal (e.g. cosmic) cue as trigger. Ross seals were observed to have a 2° broader breeding range than previously assumed. It is suggested that Ross seals are able to adapt their call characteristics to specific features of their habitats (e.g. noise).

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Schwenke, T. (2013): Underwater acoustic behaviour of leopard seals (Hydrurga leptonyx) and Ross seals (Ommatophoca rossii) in Antarctic coastal and offshore habitats. , Master thesis, Bremen University.

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