Modelling the effects of environmental conditions on the acoustic occurrence and behaviour of Antarctic blue whale

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Distribution and migration of Antarctic blue whales

Blue whales are generally cosmopolitan in range, although generally not frequenting coastal waters (Mackintosh and Wheeler, 1929; Best, 2007a). Antarctic blue whales feed predominantly on small zooplankton, primarily the Antarctic krill Euphausia superba in  Antarctica (Bannister, 2002; Branch et al. 2007a) and on megalopa larvae when in the southern African region which qualifies them to be strict carnivores (Best, 1967). Feeding on low trophic level prey makes blue whales an important ecological component of the marine ecosystem as they therefore transfer nutrients within and between various elements and levels of the ecosystem (Leaper and Miller, 2011). Antarctic blue whale distribution during the austral summer is largely determined by food or prey availability and distribution (Mackintosh and Wheeler, 1929; Bannister, 2002; Branch et al. 2007a); and factors determining the winter distribution blue whales are currently poorly understood. A comprehensive and detailed analysis of the distribution of Antarctic blue whales was undertaken by Branch et al. (2007a), where they used multi-disciplinary data from catches, sightings, strandings, Discovery marking and recoveries, and acoustic recordings.
Antarctic blue whales are commonly distributed throughout the Antarctic (high latitude) in austral summer and migrate to southern African region, Australia and South America (low latitude) in winter while a small proportion of the population spend their winter in the Antarctic (e.g. Rice and Scheffer, 1968; Mizroch et al. 1984; Jefferson et al. 1993; Branch et al. 2007a; Samaran et al. 2013, Širović et al. 2009, Thomisch et al. 2016). The distribution of Antarctic blue whales on the high latitude feeding grounds is fairly-well understood due to the extent of the modern whaling of blue whales that occurred in the region last century (Mizroch et al. 1984; Branch et al. 2007a). The distribution of the majority of blue whales in the Antarctic is in the ice edge region in close correspondence to the dense concentrations of krill (Branch et al. 2007a). However, the migration routes and distribution of this species off South-western and South-eastern African regions are still not well established (Branch et al. 2007a; Figueiredo and Weir, 2014; Leroy et al. 2016).
An understanding of the behaviour and movement of Antarctic blue whales on their calving and wintering regions will fill a large information gap in the ecology of this species. Based on the extensive land based catch histories, Best (1998) suggested from catch records that the west coast of South Africa and Namibia are potential overwintering grounds and migration route of the Antarctic blue whale. Catches of large pregnant females close to term or recently pregnant or ovulating whales are suggestive that the southern African region is important for this species as the calving and mating ground (Best and Ross, 1989; Best, 1998). Recent acoustic recordings also confirm the west coast of South Africa as overwintering ground of Antarctic blue whales (This Study – Chapter Five).

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Chapter 1: General introduction and thesis structure
1.1 Taxonomy and nomenclature of blue whales
1.2 Distribution and migration of Antarctic blue whales
1.3 Population history and status
1.4 Vocalizations of Antarctic blue whales
1.5 Objectives and aims of this study
1.6 Thesis structure
1.7 References
Chapter 2: Passive acoustic monitoring of marine mammals in South Africa, with special reference to Antarctic blue whales
2.1 Introduction
2.2 Sound in the sea
2.3 Acoustic research of marine mammals
2.3.1 Applications of passive acoustic monitoring
2.3.2 Factors determining the detectability of marine mammal sounds
2.3.3 Antarctic blue whale density estimation
2.3.4 Antarctic blue whale calls
2.3.5 Passive acoustic monitoring research on large baleen whales in South Africa – the South African Blue Whale Project
2.4 Challenges and the way forward
2.5 Conclusion
2.6 Acknowledgements
2.7 References
Chapter 3: Overview of the IWC SOWER cruise circumpolar acoustic survey data and analyses of Antarctic blue whale calls within the dataset
3.1 Introduction
3.2 Materials and methods
3.2.1 Field recordings
3.2.2 Database compilation
3.2.3 Database analyses
3.3 Results
3.3.1 Available recordings – new analyses of the compiled database
3.3.2 Antarctic blue whale call detections
3.3.3 Data comparison
3.3.4 Other sounds and vocalisations detected
3.4 Discussion
3.4.1 Distribution and occurrence of Antarctic blue whale call types
3.4.2 IWC SOWER data mining potential
3.4.3 Other species
3.5 Acknowledgements
3.6 References
Chapter 4: Modelling the effects of environmental conditions on the acoustic occurrence and behaviour of Antarctic blue whale
4.1 Introduction
4.2 Materials and Methods
4.2.1 Developing and testing detector
4.2.2 Outcomes of detectors
4.2.3 Detector caveats
4.2.4 Whale numbers and groups
4.2.5 Call rate calculation
4.2.6 Environmental data used
4.2.7 Model choice
4.3 Results
4.3.1 Southern Ocean environmental conditions
4.3.2 Blue whale call rates
4.3.3 Acoustically detected whale occurrence modelling output
4.3.4 Acoustic behaviour modelling outputs
4.4 Discussion
4.5 Conclusions
4.6 Acknowledgements
4.7 References
Chapter 5: Seasonal occurrence and diel calling behaviour of Antarctic blue whales and fin whales in relation to environmental conditions off the west coast of South Africa
5.1 Introduction
5.2 Materials and Methods
5.3 Results
5.4 Discussion
5.5 Conclusion
5.6 Acknowledgements
5.7 References
5.8. Supplementary material
Chapter 6: Acoustic seasonality and behaviour of Antarctic blue and fin whales off the Maud Rise, eastern Weddell Sea
Chapter 7: General conclusions

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