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. 2015 Nov 24;96(6):1184-1193.
doi: 10.1093/jmammal/gyv126. Epub 2015 Aug 18.

Calls reveal population structure of blue whales across the southeast Indian Ocean and the southwest Pacific Ocean

Naysa E Balcazar  1 , Joy S Tripovich  1 , Holger Klinck  1 , Sharon L Nieukirk  1 , David K Mellinger  1 , Robert P Dziak  1 , Tracey L Rogers  1
Affiliations

Calls reveal population structure of blue whales across the southeast Indian Ocean and the southwest Pacific Ocean

Naysa E Balcazar et al. J Mammal. .

Abstract

For effective species management, understanding population structure and distribution is critical. However, quantifying population structure is not always straightforward. Within the Southern Hemisphere, the blue whale (Balaenoptera musculus) complex is extremely diverse but difficult to study. Using automated detector methods, we identified "acoustic populations" of whales producing region-specific call types. We examined blue whale call types in passive acoustic data at sites spanning over 7,370 km across the southeast Indian Ocean and southwest Pacific Ocean (SWPO) from 2009 to 2012. In the absence of genetic resolution, these acoustic populations offer unique information about the blue whale population complex. We found that the Australian continent acts as a geographic boundary, separating Australia and New Zealand blue whale acoustic populations at the junction of the Indian and Pacific Ocean basins. We located blue whales in previously undocumented locations, including the far SWPO, in the Tasman Sea off the east coast of Australia, and along the Lau Basin near Tonga. Our understanding of population dynamics across this broad scale has significant implications to recovery and conservation management for this endangered species, at a regional and global scale.

Keywords: Australia; Lau Basin; New Zealand; bioacoustics; marine mammal; passive acoustic monitoring; pygmy blue whale; vocalization.

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Figures

Fig. 1.
Fig. 1.
A) Proportion (%) of total number of calls found for AUSB (grey) and NZB (black) calls at each site (PC = Perth Canyon, BS = Bass Strait, TS = Tasman Sea, TN = Tonga, SA = Samoa; no calls were detected off Samoa). B) Spatial distribution and movement known for AUSB (grey), NZB (black), and predicted spatial distribution and movement of NZB (dashed black). C) AUSB and D) NZB calls, grey box shows the part of the call used in the detector. Spectrogram parameters: 1,024 points Fast Fourier Transform, 93.75% overlap, Hanning window.
Fig. 2.
Fig. 2.
Box plots represent the median (with 0.25 and 0.75 quantile) number of calls detected per month (February to September) for AUSB at the PC = Perth Canyon and BS = Bass Strait and NZB at the TS = Tasman Sea and TN = Tonga. No AUSB or NZB whale calls were detected off SA = Samoa. Bars indicate maximum and minimum values and outliers are plotted as individual points.
Fig. 3.
Fig. 3.
Box plots represent the median (with 0.25 and 0.75 quantile) number of AUSB calls per month (January to December) between 2009 and 2012 in the Perth Canyon and Bass Strait. Bars indicate maximum and minimum values and outliers are plotted as individual points. Grayed out months indicate when data were not available.
Fig. 4.
Fig. 4.
The distribution of individual NZB calls per month (January to December) between 2010 and 2011 in the Tasman Sea. Grayed out months indicate where data were not available.
See this image and copyright information in PMC

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