To date little is known about the distribution, abundance, and migratory patterns of marine mammals within the Southern Ocean due to climatic conditions and ice cover seasonally restricting access to the area. As climatic trends are rapidly altering the polar environment, it is vital to improve our knowledge of marine mammals to understand the effects that changes in habitat might have on their behaviour and ecology. Given that marine mammals produce sound in many different behavioural contexts (e.g. communication, orientation), passive acoustic monitoring (PAM) techniques have become an essential tool to study these species. This thesis is about a specific type of PAM unit: PALAOA-S (PerenniAL Acoustic Observatory in the Antarctic Ocean satellite station) and how it can be used to monitor marine mammals. The focus of this thesis is twofold: 1) The first part is about the analyses of the acoustic data collected with PALAOA-S in December 2008 in the Antarctic Ocean. The acoustic data are analysed manually using spectrograms and additionally inspected with an automatic detection tool. The following research questions are addressed: (a) Which marine mammals could be detected in the PALAOA-S recordings? (b) How does vocal behaviour of marine mammals change in the presence of ship noise? (c) How effective is the automatic detection tool in comparison with the manual detection? (d) How does the acoustic PALAOA-S dataset compare to visual observation data in terms of species detected? 2) The second part is concerned with the hardware of PALAOA-S and how the system can be improved for future applications. The questions that addressed here are: (a) How can the self-noise of the recording device be minimized? (b) How can the recording duration be extended? The results of part 1 show that PALAOA-S can successfully be used as an acoustic monitoring unit for marine mammals. Calls of four pinniped and three cetacean species were detected in the PALAOA-S recordings. Based on the PALAOA-S data it is not possible to determine how vocal behaviour changed due to ship noise as it is not possible to differentiate if the ship noise masks the animal calls, or if the animals showed an actual change in (vocal) behaviour. The comparison of the two data-analysis techniques shows that the automatic detection tool could effectively be used to assess the acoustic presence of pinnipeds. The comparison between acoustic and visual monitoring techniques furthermore illustrates that PALAOA-S recorded calls of marine mammals which could not be observed during visual censuses. This is likely due to the fact that acoustic monitoring tools can detect marine mammals over greater distances. The results of part 2 show that the self-noise of the recording device could be minimized by changing the way the signal is transmitted to the acoustic recorder. The recording duration could either be extended by an electrical modification of the recording instrument or by the use of a new type of recording device.