Spatio-temporal patterns in humpback whale (Megaptera novaeangliae) acoustic presence and acoustic behavior in the Atlantic sector of the Southern Ocean

elena.schall [ at ]


Humpback whale males produce songs which are comparable in complexity and behavioral function to bird songs. Humpback whale songs are hierarchically structured, undergo constant change, and are breeding population-specific. These songs and other social vocalizations are produced in various behavioral contexts and along most of the geographic range of humpback whales including winter breeding habitats, summer feeding habitats and on migration routes. In remote areas, such as the Southern Ocean, which humpback whales visit primarily in summer, passive acoustic recordings can provide valuable insights to address open questions including: ‘Where and when are humpback whales present in the Southern Ocean?’, ‘How do they use high latitude habitats?’ or ‘How do they respond to changes in the environment?’. In the scope of this PhD thesis, I analyzed passive acoustic recordings from the Atlantic sector of the Southern Ocean (ASSO) to investigate spatio-temporal patterns in the acoustic presence and behavior of humpback whales and relate these patterns to potential ecological drivers. In the first chapter, spatial and intra-annual patterns of humpback whale acoustic presence were investigated at 12 recording position in the ASSO. The passive acoustic data revealed two humpback whale hotspots at the western and eastern edges of the ASSO with higher acoustic activities towards lower latitudes. At these hotspots, humpback whale acoustic presence was also registered during austral winter, indicating that at least part of the humpback whale population remains in polar waters year-round. In Chapter II, the analysis of a multi-year passive acoustic dataset from the ASSO yielded unique insights into the response of humpback whales to climate oscillations. Considerable humpback whale acoustic presence (i.e., multiple days in different months) was recorded in five out of seven years at different locations. In two years, almost no humpback whale acoustic presence was registered, which coincided with a strong El Niño event and a simultaneously long positive phase of the Southern Annular Mode. These climate oscillations most likely alter baleen whale prey availability in the Southern Hemisphere and thus affect migration routes and destinations of humpback whales. Chapter III describes a new method for the automized and standardized classification of humpback whale vocalizations to circumvent the drawbacks of the common manual parameterization and categorization in the analyses of, for example, humpback whale songs. The combination of standardized and automatically computed acoustic metrics to train a supervised classification model proved useful for the simple, rapid and highly reproducible identification and comparison of vocalization types and shows high potential for broad application purposes in bioacoustics. 6 In Chapter IV, humpback whale singing activity was evaluated for 13 recording positions in the ASSO over seven years. The data show that humpback whale males regularly sing during late summer and autumn on the feeding grounds in the ASSO implying that reproductive activities may be shifted at least partly to areas outside the breeding grounds. Song analyses and preliminary comparisons with song material from breeding populations, additionally, reveal that at least three humpback whale populations share the ASSO feeding area. This discovery illustrates the importance of the ASSO area for the preservation of humpback whale populations from the Atlantic but also the Pacific Ocean. Overall, the findings presented in this thesis highlight the significance of the investigation of long-term and large-scale dataset in order to understand migration patterns, habitat preferences, and the effects of environmental variation on highly mobile marine species. For humpback whales and the ASSO, the results of this thesis present fundamental knowledge that can guide the conservation and management of populations and ecosystems.

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Thesis (PhD)
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Helmholtz Cross Cutting Activity (2021-2027)
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Schall, E. (2021): Spatio-temporal patterns in humpback whale (Megaptera novaeangliae) acoustic presence and acoustic behavior in the Atlantic sector of the Southern Ocean PhD thesis,

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