Antarctic-type blue whale calls recorded at low latitudes in the Indian and eastern Pacific Oceans

Description and seasonal detection of two potential whale calls recorded in the Indian Ocean

“…1); Bryde's whales (B. edeni), humpback whales (Megaptera novaengliae), minke whales (B. acutorostrata), blue whales (B. musculus), sei whales (B. borealis), and fin whales (B. physalus) (de Boer et al, 2003). All of these species are known to produce vocalizations , though calls from only blue, fin, and humpback whales have been definitively identified and reported in the Indian Ocean (fin whales, this study; humpback whales, e.g., Murray et al, 2012; blue whales, e.g., Stafford et al, 2004). All six species are known to produce more than one type of vocalization and display intraspecific geographical variation in their repertoires, which may be an acoustic indicator of separate populations (Helweg et al, 1998;Mellinger and Barlow, 2003;McDonald et al, 2006;Delarue et al, 2009;Gedamke, 2009).…”

“…Of the calls recorded on the Diego Garcia hydrophones, Sri Lankan blue whale calls are the most frequently observed blue whale call type (Stafford et al, 2004;Stafford et al, 2011;Harris, 2012;Samaran et al, 2013). The detection peaks in Sri Lanka calls at the northern site showed an increase in the austral winter and a decrease in the austral summer (Stafford et al, 2011;Harris, 2012).…”

“…Recordings from Diego Garcia have been used extensively in previous blue whale acoustic studies (Stafford et al, 2004;Stafford et al, 2011;Harris, 2012). Both unidentified acoustic signals in this study have been frequently opportunistically detected in the Diego Garcia dataset (Harris, 2012) but to date no formal description of these signals has been made.…”

Validating the reliability of passive acoustic localisation: a novel method for encountering rare and remote Antarctic blue whales

“…1). Several studies have since reported detections of such blue whale songs in the Antarctic throughout the austral summer, with an apparent circumpolar distribution (Gedamke et al 2007, Širovi et al 2009, Samaran et al 2013 and with occasional acoustic detections in the tropics in the austral winter (Stafford et al 2004, Samaran et al 2013. Studies have also revealed that individual calls can be localised from distances of 100 to 200 km (Širovi et al 2007(Širovi et al , Samaran et al 2010a, and that the songs of blue whales change but remain recognizable over time scales of at least 50 yr (McDonald et al 2009.…”

“…Alternatively, acoustic tracking and targeting of Antarctic blue whales could also be integrated into lower latitude cetacean surveys in austral winter to target vocalising Antarctic blue whales that have migrated north during these months (Stafford et al 2004, Gavrilov et al 2012. By using a high spectral resolution when viewing spectrograms of whale calls, the 26 Hz tone of Unit A is sufficiently distinguishable from vocalisations produced by blue whales around New Zealand (McDonald 2006, pygmy blue whales in the Indian Ocean (Gavrilov et al 2011, Gavrilov & McCauley 2013, Samaran et al 2013, and those of Chilean blue whales in the southeast Pacific (Buchan et al 2010(Buchan et al , 2014; thus, the risk of misclassification would be minimal.…”