Spatio-temporal patterns in acoustic presence and distribution of Antarctic blue whales Balaenoptera musculus intermedia in the Weddell Sea

Abstract

Distribution and movement patterns of Antarctic blue whales Balaenoptera musculus intermedia at large temporal and spatial scales are still poorly understood. The objective of this study was to explore spatio-temporal distribution patterns of Antarctic blue whales in the Atlantic sector of the Southern Ocean, using passive acoustic monitoring data. Multi-year data were collected between 2008 and 2013 by 11 recorders deployed in the Weddell Sea and along the Greenwich meridian. Antarctic blue whale Z-calls were detected via spectrogram cross-correlation. A Blue Whale Index was developed to quantify the proportion of time during which acoustic energy from Antarctic blue whales dominated over background noise. Our results show that Antarctic blue whales were acoustically present year-round, with most call detections between January and April. During austral summer, the number of detected calls peaked synchronously throughout the study area in most years, and hence, no directed meridional movement pattern was detectable. During austral winter, vocalizations were recorded at latitudes as high as 69°S, with sea ice cover exceeding 90%, suggesting that some Antarctic blue whales overwinter in Antarctic waters. Polynyas likely serve as an important habitat for baleen whales during austral winter, providing food and reliable access to open water for breathing. Overall, our results support increasing evidence of a complex and non-obligatory migratory behavior of Antarctic blue whales, potentially involving temporally and spatially dynamic migration routes and destinations, as well as variable timing of migration to and from the feeding grounds.

Seasonal and Diel Vocalization Patterns of Antarctic Blue Whale (Balaenoptera musculus intermedia) in the Southern Indian Ocean: A Multi-Year and Multi-Site Study

“…In summer, it is believed that Antarctic blue whales are mainly in the Antarctic feeding grounds [5, 12], where numerous Z-calls are detected [7, 21, 25]. At our northernmost sites, MAD and NEAMS, the number of Z-calls increases from the mid-autumn to reach its maximum during austral winter, then progressively decreases until late spring, meaning that the vocalizing part of the Antarctic blue whale population progressively arrives at these low latitudes, on their way to or settling at wintering grounds, and leaves them in the spring to go south.…”

“…Our data confirm this general picture, however Z-calls are also recorded in the summer at all sites. Conversely, Z-calls are recorded during the winter months off Antarctica [7, 21, 25]. This observation means that parts of the population of whales remain and probably feed in the subtropical to subantarctic latitudes in the summer as well as in the high latitudes during winter.…”

“…However, since this call is likely to be emitted only by males, as noted for other baleen whale and blue whale (sub)species [23, 24], this acoustic indicator would be mainly representative of the presence patterns of the vocally active males. Nevertheless it appears that blue whales emit calls year-round, during reproductive as well as non-reproductive periods [7, 21, 24, 25], allowing for a year-round acoustic monitoring of this species. Unlike previous studies, generally limited in time or in geographic coverage and providing only clues about the long-term presence and distribution of Antarctic blue whales, this study uses a hydrophone network covering a wide range of latitudes and longitudes, spanning the central and south Indian Ocean (4 to 46°S, 53 to 81°E), and deployed for six continuous years from 2010 to 2015.…”

The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges

“…Predator and prey distribution and behavior in the WG are tightly linked: Whales and leopard seals songs show a diel pattern coinciding with zooplankton DVM (Menze et al, ). Baleen whales, feeding on krill, show migratory patterns that are complex and flexible, presumably adapting to food availability (Thomisch et al, ). Leopard seals, inhabiting the pack ice, also consume krill in variable amounts (12–90% of their diet), but they complement their diet with fish, penguins, other seals and cephalopods (Figure ; Botta et al, ).…”

Spatial and seasonal patterns in acoustic detections of sperm whales Physeter macrocephalus along the continental slope in the western North Atlantic Ocean

“…Recently, broad-scale passive acoustic monitoring with fixed recorders has been effectively used to describe seasonal migration patterns of baleen whale species (Risch et al 2014, Thomisch et al 2016 as well as spatiotemporal distributions of odontocetes, such as beaked whales, at locations distributed across an ocean basin (Baumann-Pickering et al 2014).…”