Abstract
Descriptions of seasonal occurrence and behaviour of Antarctic blue and fin whales in the Southern Ocean are of pivotal importance for the effective conservation and management of these endangered species. We used an autonomous acoustic recorder to collect bioacoustic data from January through September 2014 to describe the seasonal occurrence, behaviour and detection ranges of Antarctic blue and fin whale calls off the Maud Rise, Antarctica. From 2479 h of recordings, we detected D- and Z-calls plus the 27 Hz chorus of blue whales, the 20 and 99 Hz pulses of fin whales and the 18-28 Hz chorus of blue and fin whales. Blue whale calls were detected throughout the hydrophone deployment period with a peak occurrence in February, indicating continuous presence of whales in a broad Southern Ocean area (given the modelled detection ranges). Fin whale calls were detected from January through July when sea ice was present on the latter dates. No temporal segregation in peaks of diel calling rates of blue and fin whales was observed in autumn, but a clear temporal segregation was apparent in summer. Acoustic propagation models suggest that blue and fin whale calls can be heard as far as 1700 km from the hydrophone position in spring. Random forest models ranked month of the year as the most important predictor of call occurrence and call rates (i.e. behaviour) for these whales. Our work highlights areas around the Maud Rise as important habitats for blue and fin whales in the Southern Ocean.
Highlights
The Southern Ocean ecosystem is an important habitat for large baleen whales, including Antarctic blue whales Balaenoptera musculus intermedia and fin whales B. physalus, as productivity in this region supports high biomass of the whales’ prey, Antarctic krill Euphausia superba (Everson 2000, Knox 2006)
Blue whale Zcalls were present in 94% of the recorded time (2330 h of audio files), and fin whale 20 Hz pulses were present in 0.7% of the recorded time (17 h of audio files)
The blue whale 27 Hz chorus was present throughout the recorder deployment, and the 18−28 Hz chorus was present from February through September (Fig. 5)
Summary
The Southern Ocean ecosystem is an important habitat for large baleen whales, including Antarctic blue whales Balaenoptera musculus intermedia and fin whales B. physalus, as productivity in this region supports high biomass of the whales’ prey, Antarctic krill Euphausia superba (Everson 2000, Knox 2006). After feeding throughout the austral summer in the Southern Ocean (e.g. Mackintosh 1942, Branch et al 2007), most animals migrate to the low latitudes in winter where they are assumed to mate and calve (Best 1998). The International Union for the Conservation of Nature Red List of Threatened Species classifies Antarctic blue whales as Critically Endangered (Cooke 2018) and fin whales as Endangered (Reilly et al 2013). Low abundances of these species after the extensive whaling pressure means that visual surveys are generally not cost-effective for monitoring population distributions or seasonal abundances, and automated acoustic methodologies are being increasingly used Effects of environmental conditions on the seasonal call occurrence and call rates of Antarctic blue and fin whales in the Southern and Atlantic Oceans have recently been documented (Shabangu et al 2017, 2019)
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