Anthropogenic noise may also interfere with the ability of marine animals to detect biologically relevant sounds – an effect termed masking ( American National Standards Institute, 2008 Erbe et al., 2016b). At lower exposure levels, anthropogenic noise may affect behavioural patterns ( Nowacek et al., 2007 Samson et al., 2016), which can be associated with fitness consequences and eventually population-level effects ( Nabe-Nielsen et al., 2018 New et al., 2014). High-intensity sound sources can have serious consequences including fatal injury or strandings ( Frantzis, 1998 Parsons et al., 2008 Simmonds and Lopez-jurado, 1991) or lead to temporarily or permanently elevated hearing thresholds ( Kastak et al., 2005 Mooney et al., 2009 Smith et al., 2004). The consequence of the limited degree of vocal amplitude compensation is a loss of active space during periods of increased noise, with potential consequences for group cohesion, conspecific encounter rates and mate attraction.Īt present, there is substantial evidence that anthropogenic noise can have detrimental effects on a variety of marine animals ( Slabbekoorn et al., 2010 Weilgart, 2007). We found that signature whistles tended to be louder and with a lower degree of amplitude adjustment to noise compared with non-signature whistles, suggesting that signature whistles may be selected for higher output levels and may have a smaller scope for amplitude adjustment to noise. We present evidence of a Lombard response in the range 0.1–0.3 dB per 1 dB increase in ambient noise, which is similar to that of terrestrial animals, but much lower than the response reported for other cetaceans.
Here, we used sound-recording DTAGs on pairs of free-ranging common bottlenose dolphins ( Tursiops truncatus) to test (i) whether dolphins increase signal amplitude to compensate for increasing ambient noise and (ii) whether adjustments are identical for different signal types. Many terrestrial animals increase the amplitude of their acoustic signals to partially compensate for the masking effect of noise (the Lombard response), but it has been suggested that cetaceans almost fully compensate with amplitude adjustments for increasing noise levels. Anthropogenic underwater noise has increased over the past century, raising concern about the impact on cetaceans that rely on sound for communication, navigation and locating prey and predators.
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