Fin whale
(Balaenoptera physalus)

In Madeira, fin whales occur mainly in spring, when habitat suitability is highest, and are associated with periods of cooler, more productive ocean conditions (Fernandez et al., 2021). Available behavioural observations and the presence of calves suggest that Madeira may represent an important area for fin whales, as groups were recorded travelling, resting, feeding and socializing, and calves were present in 10% of observed groups (Alves et al., 2018).

Fin whales produce a relatively simple but diverse acoustic repertoire, with fundamental frequencies ranging roughly from 15 to 142 Hz, although the best known and most studied signal is the ‘20-Hz note’ (Watkins, 1981; Hatch and Clark, 2004). This call is a short downswept note of about 1 s, classically described as descending from approximately 23 to 18 Hz, although broader frequency limits have also been reported depending on recording conditions, analytical methods and geographical area (Watkins et al., 1987; Thompson et al., 1992). Fin whales also produce other call types, including 18-Hz backbeats, which are commonly associated with 20-Hz notes but can occasionally occur in independent sequences, as well as less frequent calls around 40 Hz and higher-frequency notes near 100–130 Hz (Watkins et al., 1987; Thompson et al., 1992; Guazzo et al., 2024). The 20-Hz note is typically produced in long, highly stereotyped song sequences that may continue for hours. In the central North Atlantic, fin whale acoustic presence is strongly seasonal, increasing in autumn, peaking in winter, and declining again in spring (Watkins et al., 1987; Romagosa et al., 2020; Guazzo et al., 2024).