Use of fin whale (Balaenoptera physalus) vocalizations to determine stock identity and structure; a comparative study of two North Atlantic feeding grounds
Fin whale stock structure in the North Atlantic remains poorly understood. The International Whaling Commission currently recognizes seven broad stocks but their definition is obscured by potential overlap in the distribution and movements of fin whales. Acoustics is increasingly mentioned as a potential alternative to investigate the population structure of pelagic, farranging species such as blue and fin whales. In the latter, there is evidence of geographic variations in songs, in particular in areas where singers are sympatric either acoustically or physically. However, due to a lack of systematic description of vocalizations—specifically those produced on feeding grounds—it is not known whether other types of non-singing calls can be used to evaluate population structure. This study compared the vocal repertoire of two adjacent feeding aggregations in the Gulf of St. Lawrence (GSL) and Gulf of Maine (GoM) in order to examine their potential degree of segregation. Fin whales belonging to these aggregations exhibit high site fidelity although they are genetically undifferentiated and occasionally move between both areas. Acoustic data were obtained using autonomous recording units (pop-ups) that recorded continuously during 75 days in the GoM (Summer 2006) and intermittently for 11 months in the GSL, starting mid-July 2005. Additional recordings were obtained using modified DIFAR sonobuoys and conventional hydrophones in the vicinity of fin whales in summer 2006 and 2007 in the GSL. Results indicate that the internote spacing of 20-Hz pulse sequences differs significantly between the two areas (p<0.001); thus songs may be characterized as feeding aggregation-specific. Other non-singing calls recorded included several types of constant and frequency-modulated sounds between 30 and 150 Hz. Four out of 5 call types showed some variation between areas suggesting regional differences and/or potentially an impact of recording conditions.
Delarue, J., S. Todd, R. Sears and L. Di Lorio. 2007. Use of fin whale (Balaenoptera physalus) vocalizations to determine stock identity and structure; a comparative study of two North Atlantic feeding grounds. Poster presented at the Seventeenth Biennial Conference on the Biology of Marine Mammals, Cape Town, South Africa.
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