Acoustic analysis of social sounds in humpback whales (“Megaptera novaeangliae”) in Skjálfandi Bay: effects of decreasing daylight and underwater anthropogenic noise.

Humpback whales (Megaptera novaeangliae) produce a wide range of social sounds that differ from their well-known songs; however, these vocalizations remain understudied due to the absence of a standardized classification system. This study aims to catalogue these sounds and explore their significance within Skjálfandi Bay (Iceland), a highly productive feeding ground that attracts several whale species each year during summer. Located just 30 km south of the Arctic Circle, the bay undergoes a rapid and substantial decrease in daylight from summer to autumn. Additionally, the area is exposed to significant anthropogenic noise generated by tourism-related activities such as cruise ships, whale-watching excursions, and fishing operations. Acoustic data were collected through passive acoustic monitoring using a fixed hydrophone, with recordings made daily from July to September 2023, between 3:30 and 7:00 AM. The study investigates the relationship between acoustic activity and diminishing daylight, as well as the influence of vessel presence on vocal behavior. All sounds were amplified, visualized using Raven Pro software, and manually analyzed through spectrographic methods. Signals that were heavily masked by noise or resulted faded were excluded. The findings contribute to the classification of humpback whale social sounds repertoire and try to enhance understanding of their function, variability, and the combined effects of environmental and anthropogenic factors on whale communication within this context.