Blue whale
(Balaenoptera musculus)

Blue whales are rare in Madeira, with only a small number of records for the archipelago, all involving single animals. This low occurrence has been interpreted as reflecting the fact that Madeira lies outside the main migratory routes of the species in the North Atlantic and the small size of the North Atlantic population (Freitas et al., 2012). Long-term sighting data likewise show that blue whales are among the least frequently recorded cetaceans in Madeira (Alves et al., 2018).

In the North Atlantic, the most common blue whale signals are long, patterned sequences in the 15–20 Hz band, composed of repeated two-part A–B units, with intervals of ~ 73 s, or from repetitions of part A only (Mellinger and Clark, 2003). In a typical A–B unit, part A is a near-constant 18 Hz tone lasting about 8 s, followed by a gap of 5 s and by a descending part B lasting about 11 s and sweeping from ~18.5 to 15.7 Hz (Mellinger and Clark, 2003). Two additional call types have also been described for the North Atlantic: a 2–5 s tone at 9 Hz and an “arch sound” that rises from ~56 Hz to 69 Hz before descending to ~35 Hz over roughly 6 s (Mellinger and Clark, 2003). Blue whales also more variable D calls, which are distinct from the stereotyped A–B song pattern and are generally described as low frequency downsweeps, sometimes beginning with a short upsweep (Berchok et al., 2006). In the central North Atlantic, blue whale acoustic presence shows a broadly similar seasonal pattern to that of fin whales (Romagosa et al., 2020).