Fin whale (Balaenoptera physalus) migration in Australian waters using passive acoustic monitoring

Abstract

The fin whale is a globally endangered species and is listed as threatened in Australia, however no peer-reviewed studies are available to indicate the migratory movements of the species in Australian waters. This study uses passive acoustic monitoring as a tool to identify the migratory movements of fin whales in Australian waters. Sampling was conducted from eight locations around Australia between 2009 and 2017, providing a total of 37 annual migratory records. Taken together, our observations provide evidence of fin whale migration through Australian waters, with earliest arrival of the animals recorded on the Western Australian coast, at Cape Leeuwin in April. The whales travel through Cape Leeuwin, migrating northward along the Western Australian coast to the Perth Canyon (May to October), which likely acts as a way-station for feeding. Some whales continue migrating as far north as Dampier (19°S). On Australia's east coast, at Tuncurry, fin whale seasonal presence each year occurred later, from June to late September/October. A total of only 8,024 fin whale pulses were recorded on the east coast, compared to 177,328 pulses recorded at the Perth Canyon. We suggest these differences, as well as the spatial separation between coasts, provide preliminary evidence that the fin whales present on the east and west coasts constitute separate sub-populations.

Figure 1

(a) Map of the locations of the passive acoustic Underwater Sound Recorders (USR) of the Australian Integrated Marine Observing System (IMOS) and Curtin University, and the Comprehensive Test Ban Treaty Organization (CTBTO) hydroacoustic array around Australian waters. And temporal pattern of fin whale presence around Australia, (b) off the Western Australian coast at Cape Leeuwin, the Perth Canyon and Dampier, (c) off the east coast at Tuncurry, NSW and (d) at Portland, Victoria. Bars represent the percentage of calling days for each month, all data sampling periods for each location were grouped.

Figure 2

Spectrograms of an example of the three different pulse displays recorded by IMOS or Curtin USR’s: (a) the repeated pattern 20 Hz classic pulses (pygmy blue whale signals in the background), (b) the doublet train pulse display, and (c) the back-beat pulse display.

Figure 3

Mean number of fin whale pulses counted in every normalised 5 min sample averaged over 24 h (a) at the Perth Canyon, WA, (b) Tuncurry, NSW, (c) Dampier, WA. And the number of fin whale pulses recorded in every 1 h sample averaged over 24 h at (d) Cape Leeuwin, WA. Red horizontal lines indicate when recorders were deployed; no recordings were obtained during months without red lines. Note that the Y axis is different for each sampled location.

Figure 4

Mean number of fin whale pulses counted in every 5 min sample averaged over 24 h at Portland, VIC. Only sample years with detected fin whale signals are presented. Red horizontal lines indicate when recorders were deployed; no recordings were obtained during months without red lines.

Figure 5

Image of template used in spectrogram cross correlation in the first algorithm. The white line is the frequency trend of a high SNR call, the black values are the padded spectrogram template area and the grey areas are the locations used for comparing noise levels above and below the fin whale pulse frequency band (14.6 Hz, to 29.3 Hz).