The effects of vessel noise on the communication network of humpback whales

Abstract

Humpback whales rely on acoustic communication to mediate social interactions. The distance to which these social signals propagate from the signaller defines its communication space, and therefore communication network (number of potential receivers). As humpback whales migrate along populated coastlines, they are likely to encounter noise from vessel traffic which will mask their social signals. Since no empirical data exist on baleen whale hearing, the consequences of this are usually assumed, being the modelled reduction in their communication space. Here, the communication space and network of migrating humpback whales was compared in increasing wind-dominated and vessel-dominated noise. Behavioural data on their social interactions were then used to inform these models. In typical wind noise, a signaller's communication space was estimated to extend to 4 km, which agreed with the maximum separation distance between groups that socially interacted. An increase in vessel noise reduced the modelled communication area, along with a significant reduction in group social interactions, probably due to a reduction in their communication network. However, signal masking did not fully explain this change in social behaviour, implying there was also an additional effect of the physical presence of the vessel on signaller and receiver behaviour. Though these observed changes in communication space and social behaviour were likely to be short term and localized, an increase in vessel activity due to tourism and coastal population growth may cause more sustained changes along the humpback whale migration paths.

Use of Ecoacoustics to Characterize the Marine Acoustic Environment off the North Atlantic French Saint-Pierre-et-Miquelon Archipelago

“…Some sound units of this are repeated and organized in the same order in the reproduction phrase. The humpback whale sounds are typical of those used in social and foraging activities [57].…”

The effects of noise on the vocal behaviour of singing humpback whales (Megaptera novaeangliae)

“…Despite overall similarities in the spectral content of vessel and wind noise, wind-generated noise is homogeneous over broad areas, while vessel noise is produced by a (moving) point source. A possible explanation for the lack of a Lombard response to increasing level of vessel noise in humpback whales was mentioned by Dunlop (2016a), and later further discussed by Dunlop (2019), when studying the effect of vessel noise on the social sounds of this species. The author suggested that humpback whales may be responding to the presence of vessels instead of noise; and that vessels may be perceived as a threat.…”

“…By comparing interactions observed in the presence and absence of the noise vessel, we could assess the effect of this type of noise on the receivers of the song. As mentioned above, if the response of the receivers to the song playback is the same in the presence or absence of vessel noise, then the whales may be using spatial masking release (Dunlop, 2019). This hypothesis may be further tested by changing the relative bearing of the two vessels in relationship to the receivers.…”

“…However, results of Dunlop (2019) on social sounds do not support the hypothesis that humpback whales use spatial and/or comodulation masking release. Dunlop (2019) investigated the effect of noise on humpback whale communication networks by analysing interactions between groups producing social sounds and nearby conspecifics under different noise conditions. She found that in the presence of vessel noise, neighbouring whales are less likely to interact with the signalling group.…”

“…whales (Williams et al, 2014), North Atlantic right whales (Eubalaena glacialis; Clark et al, 2009;Cunningham and Mountain, 2014), fin whales (Balaenoptera physalus; Clark et al, 2009) and humpback whales (Megaptera novaeangliae; Clark et al, 2009;Dunlop, 2019). This growing body of evidence is raising concerns about the consequences of increasing shipping activities on the ability of marine animals to communicate (Erbe, 2002).…”