Calling in the Cold: Pervasive Acoustic Presence of Humpback Whales (Megaptera novaeangliae) in Antarctic Coastal Waters

Abstract

Humpback whales migrate between relatively unproductive tropical or temperate breeding grounds and productive high latitude feeding areas. However, not all individuals of a population undertake the annual migration to the breeding grounds; instead some are thought to remain on the feeding grounds year-round, presumably to avoid the energetic demands of migration. In the Southern Hemisphere, ice and inclement weather conditions restrict investigations of humpback whale presence on feeding grounds as well as the extent of their southern range. Two years of near-continuous recordings from the PerenniAL Acoustic Observatory in the Antarctic Ocean (PALAOA, Ekström Iceshelf, 70°31’S, 8°13’W) are used to explore the acoustic presence of humpback whales in an Antarctic coastal area. Humpback whale calls were present during nine and eleven months of 2008 and 2009, respectively. In 2008, calls were present in January through April, June through August, November and December, whereas in 2009, calls were present throughout the year, except in September. Calls occurred in un-patterned sequences, representing non-song sound production. Typically, calls occurred in bouts, ranging from 2 to 42 consecutive days with February, March and April having the highest daily occurrence of calls in 2008. In 2009, February, March, April and May had the highest daily occurrence of calls. Whales were estimated to be within a 100 km radius off PALAOA. Calls were also present during austral winter when ice cover within this radius was >90%. These results demonstrate that coastal areas near the Antarctic continent are likely of greater importance to humpback whales than previously assumed, presumably providing food resources year-round and open water in winter where animals can breathe.

Diel and Spatial Dependence of Humpback Song and Non-Song Vocalizations in Fish Spawning Ground

“…The downsweep D-moans recorded here in the Gulf of Maine are similar in frequency band, duration and frequency-time slope to the "P.moan-moan" previously recorded in the vicinity of two humpback whales in Newfoundland Canada [22], (compare D-moans from Gulf of Maine humpbacks in Figure 6A,B with the P.moan-moan in Figure 1 of [57]). The bow-shaped B-moans ( Figure 4E,F) recorded here in the Gulf of Maine with a downsweep followed by an upsweep are similar to other bow-shaped calls recorded from humpbacks in Antarctic coastal waters (compare with Figure 2A of [58]) and in Australian water (compare with Figure 2a of [59]). …”

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

“…com/ articles/ suppl/ n030p239_supp.pdf). Furthermore, rough estimates of distances of ABWs from recording sites were calculated for each Z-call detection, assuming a source level of 189 dB (Širović et al 2007) and using different reported transmission loss models (Širović et al 2007, Breitzke & Bohlen 2010, Van Opzeeland et al 2013b) (see the Supplement for detailed information on amplitude measurements and distance estimation).…”

“…Our study therefore adds to accumulating evidence that annual migration is not obligatory for ABWs and overwintering in the Southern Ocean may occur regularly and over large spatial scales. Local, potentially recurring, polynyas may enable ABWs and other marine mammals to overwinter in otherwise icecovered areas (Ainley et al 2010), but are likely to spatially constrain animal movements to open water areas during winter (see also Van Opzeeland et al 2013b). Decreasing trends in the sea ice extent and the length of the sea ice season (e.g.…”

“…Instead of migrating to lower latitudes after the feeding season, part of the population remains in polar and subpolar waters during winter, indicating partial migration (see also Dingle & Drake 2007) in many species (e.g. Bockstoce et al 2005, Moore et al 2006, Acevedo et al 2011, Van Opzeeland et al 2013b.…”

“…Furthermore, passive acoustic monitoring has the potential to yield seasonally unbiased information on marine mammal acoustic presence, hence being particularly valuable in remote areas which are not accessible year-round for visual surveys (e.g. , Mellinger et al 2007, Rettig et al 2013, Van Opzeeland et al 2013b. ABWs are particularly eligible for passive acoustic studies due to the repetitive production of different types of distinctive low-frequency vocalization (e.g.…”