Baleen whale acoustic ecology with focus on minke whales (Balaenopteraacutorostrata) and reference to anthropogenic noise

Passive acoustic approaches for studying marine mammals have developed substantially over the past decade. Advances in technology now allow data collection in remote areas and over extended timescales. The first two chapters of this thesis focused on the application of passive acoustics for monitoring migratory baleen whales in the Northwest Atlantic Ocean. The development and application of new localization algorithms showed how small-scale arrays can be used to obtain baseline data about the acoustic behavior of individuals, which will help to improve interpretation of longterm acoustic data sets. Acoustic monitoring in the Stellwagen Bank National Marine Sanctuary (SBNMS) revealed seasonal peaks of acoustic abundance for right (Eubalaena glacialis) and sei whales (Balaenoptera borealis) in spring and fall, respectively. Both species are primarily present during these two seasons and to a lesser extent in winter and summer, indicating the importance of this area as part of their migration route. Fin whales (Balaenoptera physalus) were acoustically present year-round, although song production was reduced during summer. While recorded on only a few days of the entire period, blue whale (Balaenoptera musculus) song was detected near SBNMS in three separate years. There is considerable uncertainty concerning migration routes, winter calving habitats and thus population structure of North Atlantic minke whales (Balaenoptera acutorostrata). Given that this species is still being hunted across its summer range, this uncertainty has important conservation and management implications. In chapters III-V I used 3.5 years of acoustic array data from the Gulf of Maine to describe the species' vocal repertoire, examine individual calling behavior and provide first source level estimates. Based on these data, an automatic detector was developed and applied to year-round data from several sites along the US East coast and beyond to track minke whale migration. Minke whales produced three call categories at a mean source level of 165 ± 4 dB rms re 1 μPa. Individual whales combined calls in non-random order, leading to two distinct calling patterns. Unlike other baleen whales, animals sharing the same acoustic space used different patterns simultaneously, without switching. Analysis of seasonal occurrence patterns revealed peak acoustic presence in higher latitudes during summer and fall and in lower latitudes during winter. Migration appears to follow the general direction and location of the Gulf stream in the spring and occurs in more open waters in the fall. A higher abundance of calls at offshore recording sites, suggests that there is a winter habitat located in deeper waters off the Southeastern US. Antarctic minke whales (Balaenoptera bonaerensis) have long been suggested as the likely source for the mysterious 'bioduck' signal, which is the predominant underwater sound in the Souther Ocean during austral winter. I analyzed data from the first two multi-sensor acoustic tags attached to Antarctic minke whales and was able to confirm the production of the bioduck by this species. This finding will allow the interpretation of a wealth of existing recordings, and thereby substantially improve our understanding of the distribution, abundance, and behavior of Antarctic minke whales. This is critical information for a species that lives in a rapidly changing polar environment and is subject of ongoing lethal sampling efforts. The effects of widespread anthropogenic noise in the marine environment is of increasing concern. Most discussions have centered on highly visible and regulated activities, such as seismic airguns and naval sonar. In this last chapter we showed, that humpback whale (Megaptera novaeangliae) song was reduced, concurrent with transmissions of an Ocean Acoustic Waveguide Remote Sensing (OAWRS) experiment approximately 200 km distant. This is the first time that active sonar used in fisheries science has been shown to have this effect, highlighting the importance to study and regulate the impact of all anthropogenic noise sources, including research applications. In conclusion, this thesis highlighted the suitability of passive acoustic monitoring for an increased understanding of the spatio-temporal distribution patterns and behavior of highly mobile and little studied baleen whales. In particular, it considerably improved current knowledge about the acoustic ecology and spatio-temporal distribution of minke whales.