Frozen verses: Antarctic minke whales (Balaenoptera bonaerensis) call predominantly during austral winter

Abstract

The recent identification of the bio-duck call as Antarctic minke whale (AMW) vocalization allows the use of passive acoustic monitoring to retrospectively investigate year-round spatial-temporal patterns in minke whale occurrence in ice-covered areas. Here, we present an analysis of AMW occurrence patterns based on a 9-year passive acoustic dataset (2008–2016) from 21 locations throughout the Atlantic sector of the Southern Ocean (Weddell Sea). AMWs were detected acoustically at all mooring locations from May to December, with the highest presence between August and November (bio-duck calls present at more than 80% of days). At the southernmost recording locations, the bio-duck call was present up to 10 months of the year. Substantial inter-annual variation in the seasonality of vocal activity correlated to variation in local ice concentration. Our analysis indicates that part of the AMW population stays in the Weddell Sea during austral winter. The period with the highest acoustic presence in the Weddell Sea (September–October) coincides with the timing of the breeding season of AMW in lower latitudes. The bio-duck call could therefore play a role in mating, although other behavioural functions of the call cannot be excluded to date.

Static species distribution models in the marine realm: The case of baleen whales in the Southern Ocean

“…(2012) showed a consistent positive effect of sea ice cover on AMW suitability, and similarly, Filun et al. (2020) found a strong positive correlation between SIC and AMW acoustic presence in the Weddell Sea, with the highest acoustic activity occurring at SIC >75%. Distance to SIE was also important in other SDM studies with highest suitability close to it (Beekmans et al., 2010; Bombosch et al., 2014; Friedlaender et al., 2011; Herr et al., 2019; Kasamatsu, Ensor, et al., 2000; Murase et al., 2013; Williams et al., 2014).…”

“…Highest AMW density was estimated in the Western Antarctic Peninsula and the Weddell and Ross Seas (Dominello & Širović, 2016; Risch et al., 2019). The AMW is a year‐round resident in the SO and occurs throughout a wide range of SIC (Filun et al., 2020; Friedlaender et al., 2011; Herr et al., 2019; Thiele et al., 2004), preferring the SIE area (Dominello & Širović, 2016; Herr et al., 2019; Kasamatsu, Ensor, et al., 2000; Scheidat et al., 2011; Williams et al., 2014). It has been observed both within the pack ice region and in open water (although in lower numbers) (Beekmans et al., 2010; Ensor, 1989; Friedlaender et al., 2006; Herr et al., 2019; Thiele & Gill, 2004; Williams et al., 2014).…”

“…Highest AMW density was estimated in the Western Antarctic Peninsula and the Weddell and Ross Seas (Dominello & Širović, 2016;Risch et al, 2019). The AMW is a year-round resident in the SO and occurs throughout a wide range of SIC (Filun et al, 2020;Friedlaender et al, 2011;Herr et al, 2019;, preferring the SIE area (Dominello & Širović, 2016;Herr et al, 2019;Kasamatsu, Ensor, et al, 2000;Scheidat et al, 2011;Williams et al, 2014).…”

“…Filun et al (2020) reported very little acoustic activity near the SIE area in the Weddell Sea during December and January. Some studies discussed the important role of the Antarctic ice shelf break:…”

“…The Southern Ocean (SO) is a biodiversity hotspot area, showing distinctive biogeographic features and high environmental variability (Convey et al, 2014;De Broyer et al, 2014;Fabri-Ruiz et al, 2019;Guillaumot et al, 2020). The SO's sea ice environment represents a critical habitat for many threatened migratory and resident species, particularly for baleen whales (Filun et al, 2020;Thomisch et al, 2016;Van Opzeeland et al, 2013). Nevertheless, research efforts in the SO were limited because of its remoteness, vastness and sea ice coverage, posing considerable financial and logistical constraints (Bombosch et al, 2014;Scheidat et al, 2011).…”