Description: The eastern Atlantic Ocean is considered to provide important breeding and wintering habitats for several migratory cetacean species. The spatio-temporal distributions and migratory behaviors of cetaceans off southern Africa are nevertheless still poorly understood. This study investigated the temporal patterns of acoustic occurrence of baleen whales in a presumed baleen whale breeding area off Namibia using passive acoustic recordings collected between November 2011 and May 2013. Our results show seasonal acoustic presence of humpback whales Megaptera novaeangliae, fin whales Balaenoptera physalus and Antarctic minke whales B. bonaerensis from November to January and from June to August. Their acoustic absence from February to May possibly indicates that most animals migrated to other areas (presumably in higher latitudes) in austral summer to feed. By contrast, Antarctic blue whales B. musculus intermedia were acoustically present throughout the recording period, indicating that part of the population remains at lower latitudes year-round. Our findings support the presumed ecological importance of the oceanic area off Namibia, providing (part of) a suitable cetacean wintering and, possibly, breeding range or migratory corridor. Furthermore, the occurrence of Antarctic blue and minke whales off Namibia, concurrent with their reported acoustic presence in high-latitude feeding areas, adds to growing evidence that baleen whale migration is not obligate but much more dynamic than has long been assumed.

Description: Although the Fram Strait presumably provides an important habitat for several marine mammals, including several baleen whale, toothed whale and seal species, the migratory behavior and both the spatial and temporal distribution of marine mammals in Arctic waters remain poorly under-stood. While some of the marine mammals inhabit Fram Strait year-round, others are only pre-sent for some months when migrating towards high-latitude waters during summer. This study presents baseline data of the spatial and temporal distribution of marine mammals in Arctic Fram Strait. As marine mammals are known to produce various vocalizations in different behavioral contexts, acoustic presence of marine mammals in Fram Strait was studied. Between 01 July and 30 November 2012 passive acoustic data were collected at 78° 49, 76’ N to 0° 25, 77’ E. During the recording period blue whales (Balaenoptera musculus), fin whales (Balaenoptera physalus), bowhead whales (Balaena mysticetus), narwhals (Monodon monoceros), sperm whales (Physeter macrocephalus) and harp seals (Pagophilus groenlandicus) were acoustically present. Further-more, the vocalizations of detected marine species are presented in this study. Variations of pre-viously classified call types of bowhead whales, harp seals and sperm whales were recorded. Additionally, a presumably unknown call type of narwhals was found. The results show temporal acoustic presence of bowhead whales and narwhals in October and November and acoustic ab-sence from July - September. Their presence in fall may indicate that they either overwinter or remain longer in central Fram Strait. Furthermore, fin whale calls were heard from July until October and were absent in November. Blue whales and harp seals were acoustically present throughout the recording period. Sperm whales were acoustically present in July and September and acoustically absent in June, August, October and November. Therefore, it can be assumed that Fram Strait may serve as a feeding ground for fin whales, blue whales, harp seals and sperm whales. Since many of the marine mammals are listed as critically endangered, it is important to know where they are distributed. The results of this study will help to better understand the dis-tribution patterns of marine mammals in Arctic Fram Strait.

Description: Passive acoustic monitoring enables data collection on marine mammals over large temporal and spatial scales and in remote areas such as the Arctic Ocean. Passive acoustic data are collected at different recording sites in eastern and central Fram Strait since 2012, contributing to the Arctic Observatory FRAM (FRontiers in Arctic Marine Monitoring). Here, data recorded at 78°50 N, 0°E from July to November 2012 were analyzed for the daily acoustic presence of marine mammals. Bowhead whales (Balaena mysticetus) were acoustically present during 12 days in October and during 16 days in November, but acoustically absent from July to September. Downsweep song (three types) was present both in October and November, while upsweep song (one type) was only present in October. Besides bowhead whales, blue whales (Balaenoptera musculus), fin whales (B. physalus), narwhals (Monodon monoceros), sperm whales (Physeter macrocephalus) and harp seals (Pagophilus groenlandicus) were recorded. Acoustic species interactions regarding the overlap of species-specific sounds in time and frequency range were explored. In this context, temporal and spectral overlap of biophonic (blue and fin whale vocalizations) and anthrophonic (airgun) signals were detected in the low-frequency (〈100 Hz) spectrum. Our results emphasize the importance of Fram Strait as marine mammal habitat, possibly providing (summer) feeding opportunities for blue and fin whales and an overwintering ground for bowhead whales and narwhals. Understanding the spatio-temporal patterns in the distribution and acoustic behavior of marine mammals considerably benefits the development of effective conservation and management strategies for critical habitats in the Arctic Ocean.