Visual and passive acoustic observations of blue whale trios from two distincts populations
Blue whale populations from both hemispheres are thought to undertake annual migrations between high latitude
feeding grounds and low latitude breeding grounds (Mackintosh, 1966). For individuals of some populations these
predetermined movements to and from wintering areas where calving occurs have been confirmed through
photo-identification, satellite-tracking, and passive acoustic monitoring (Burtenshaw et al., 2004; Mate, Lagerquist, &
Calambokidis, 1999; Sears & Perrin, 2002; Stafford, Nieukirk, & Fox, 1999a). However, for many blue whale
populations no clear migratory behavior has been reported and locations of respective breeding grounds remain
unclear (e.g., Hucke-Gaete, Osman, Moreno, Findlay, & Ljungblad, 2004; Samaran et al., 2013; Stafford, Chapp,
Bohnenstiel, & Tolstoy, 2011; Thomisch et al., 2016). On feeding grounds in the Gulf of St. Lawrence and along the
coast of California, blue whales have been observed to form female–male pairs during summer, which can remain
stable up to over several weeks, with the number of pairs increasing towards the end of summer (Sears & Perrin,
2002; Calambokidis, unpublished data;1 RS, unpublished data). These pairs are sometimes joined by a second male,
forming a blue whale trio, which often is observed to engage in surface active behaviors lasting several minutes (Sears & Perrin, 2002; RS, unpublished data). The formation of blue whale trios is probably related to reproductive
competition between male escorts and female choice (RS, unpublished data). Blue whale males produce population-specific
songs likely functioning as reproductive advertisement (Edds-Walton, 1997; Oleson et al. 2007a; Stafford, Fox, & Clark,
1998). Several studies have reported song year-round in low-, mid-, and high-latitude waters, frequently with high song
production rates during summer on the feeding grounds (e.g., Barlow et al., 2018; Buchan, Stafford, & Hucke-Gaete,
2015; Samaran, Adam, & Guinett, 2010; Širovic et al., 2004; Stafford, Nieukirk, & Fox, 1999b; Thomisch et al., 2016).
Therefore, breeding activities in blue whales may be more opportunistic, i.e., not restricted to the breeding season or
to a specific habitat.
Elena Schal, Lucia Di Iorio, Catherine Berchok, Diego Filún, Luis Bedriñana-Romano, Susannah J. Buchan, Ilse Van Opzeeland, Richard Sears & Rodrigo Hucke-Gaete. Mar Mam Sci. 2019;1-10.