Description: The ocean is crowded with human uses, many of which also introduce underwater sound in the ocean environment. To understand if and how these underwater sound sources impact marine mammals and eventually mitigate against the potential consequences, information on distribution patterns is crucial. Passive acoustic monitoring techniques offer a versatile tool to study marine mammals, particularly in polar ocean environments where ship access is often limited and visual sighting conditions can be compromised by light availability and weather. In this talk I will provide an introduction on passive acoustic techniques, how they can be applied and what type of data they generate. Three case studies serve to illustrate how passive acoustic techniques have contributed to fundamentally improve the knowledge status on cetacean and pinniped species in Antarctic waters.

Description: Antarctic minke whales (Baleanoptera bonaerensis) occur in open as well as ice-covered waters throughout the Southern Ocean. Their low visual detectability and ice-associated habitat makes the species difficult to study using traditional visual methods. The recent identification of vocalizations produced by Antarctic minke whales now allows the use of passive acoustic records to investigate spatio-temporal patterns in occurrence, also in areas that are (seasonally) inaccessible to ships due to extensive ice cover. Here we present preliminary results on Antarctic minke whale occurrence patterns based on part of a multi-year passive acoustic data set collected from 6 locations throughout the Atlantic sector of the Southern Ocean. These comprised four autonomous passive acoustic recorders which collected data along the Greenwich meridian between 2008 and 2011, one passive acoustic recorder in the Weddell Sea that collected data between 2010 and 2012 and long-term recordings from the PALAOA observatory on the Eckström Iceshelf off the Antarctic continent (2006-2016). Analyses were based on daily presence of Antarctic minke whale pulse trains, also referred to as the bio-duck call. The bio-duck signal is characterized by its repetitive nature, consisting of regular down-sweeped pulses, with most energy located in the 50-300 Hz band. Antarctic minke whales were present at all six Antarctic recording locations from June to December, with highest presence occurring between August and November (〉80% of days with bioduck calls present). At the southernmost recording locations and the location in the Weddell Sea, the bioduck call was present throughout nine and ten months of the year, respectively. Substantial variation in the seasonal on- and offset period of vocal activity of Antarctic minke whales was observed between years at the different recording positions, possibly corresponding to variation in local ice conditions. Ongoing work aims to further quantify this relationship to better understand year-round Antarctic minke whale habitat preferences. Furthermore, further work will comprise more fine-scale analyses to unravel diel patterns in vocal activity and explore if variation in the acoustic signature of the bioduck call can potentially be attributed to regional differences in Antarctic minke whale vocal behavior, possibly representing subpopulations of the species.

Description: Cetacean density can be estimated from passively-collected acoustic data via received calls attributed to the species of interest. Acoustic equipment can be used to gather data continuously for long periods, at high sampling rates, and over multiple channels, resulting in vast datasets. Humans are assumed to be the gold-standard for extracting features of interest from acoustic data, but automatic detection and classification software is necessary for large datasets where human auditing is not feasible. Here, we compare the abilities of two freely-available software (PAMGuard and the Low Frequency Detection and Classification System (LFDCS)) to detect and classify Argentinian southern right whale (Eubalaena australis) upcalls based on 4417 human ground-truthed calls. The number of detected calls varied substantially between the two software (PAMGuard recorded approximately the same number of true positives as LFDCS, but up to ten times as many false positives), and between separate runs of LFDCS with different parameter values (the results of which varied by up to a factor of four). The resulting differences between detected and truly-present calls can significantly impact subsequent density estimates. While it is possible to apply correction multipliers to outputs obtained from automated software, the aim is to minimise the amount of extrapolation required in order to maintain robust results. When using automatic detection algorithms, it is therefore essential that a rigorous, data-based detector performance analysis is conducted.

Description: Spatio-temporal patterns in Antarctic minke whale (Balaenoptera bonaerensis) vocal behaviour in the Weddell Sea. Antarctic minke whales (Baleanoptera bonaerensis) occur in open as well as ice-covered waters throughout the Southern Ocean. Their low visual detectability and ice-associated habitat makes the species difficult to study using traditional visual methods. The recent identification of Antarctic minke whale vocalizations now allows the use of passive acoustic monitoring to investigate year-round spatio-temporal patterns in occurrence in ice-covered areas. Here we present preliminary results on Antarctic minke whale occurrence patterns based on a multi-year passive acoustic data set from 6 locations throughout the Atlantic sector of the Southern Ocean. Analyses were based on daily presence of the bio-duck call, which is characterized by its repetitive nature, consisting of regular down-sweeped pulses with most energy located in the 50-300 Hz band. Antarctic minke whales were present at all six Antarctic recording locations from June to December, with highest presence occurring between August and November (〉80% of days with bioduck calls present). At the southernmost recording locations, the bioduck call was present up to ten months of the year. Substantial inter-annual variation in the seasonal on- and offset period of vocal activity was observed at the different recording positions, possibly corresponding to variation in local ice conditions.