cCMB FUTURE SCIENCE BRIEF 
ittle cuttlefish caught during 
scientific campaign of FishConnect 
3n RV Simon Stevin 
To summarise, despite much progress in the past decade, our 
knowledge of patterns in hearing across taxa is still incomplete as 
hearing has been investigated for only a few fish and invertebrate 
species. Knowledge has improved for marine mammals but there are 
gaps too, especially concerning the hearing abilities of baleen whales. 
3.2 Effects of noise 
As we have mentioned in the introduction, the ‘zones of noise 
influence’ (masking, behavioural response, impaired hearing, and 
physical and physiological effects) in Figure 2 provide a conceptual 
Framework for the possible effects of underwater noise on marine 
organisms. While this simplified 2D framework has proven useful 
For a systematic approach when assessing the effects of noise and 
describing its spatial reach, it also has considerable limitations 
because the reality is a lot more complex. For example, sound 
propagates from the source in all directions, both horizontally and 
vertically through 3D space. Also, factors such as depth or bottom 
:ype etc. affect sound transmission and will influence the extent 
and magnitude of effects. In addition, physiological effects and 
hearing damage are related to the dose of exposure, which is 
defined by both the received sound pressure level and the duration 
of exposure (Southall et al., 2019). Exposure over a long period can 
lead to physical and physiological effects even if sound levels are 
low and would not trigger a behavioural reaction. This may lead to 
a larger zone of influence for hearing impairment than behavioural 
effects. Physiological effects can also arise from behavioural 
responses to noise, such as in the case of beaked whale strandings, 
where rapid surfacing may have led to various decompression 
sickness manifestations (see review in Bernaldo de Quirös et al, 
2019). Thus, the zone of behavioural response can become the 
zone of physiological and physical effects, and even death. Finally, 
there is no clear-cut answer as to whether masking or behavioural 
response zones are larger. However, despite these limitations, the 
zones of noise influence’ is a practical model when defining and 
broadly categorizing noise impacts. 
According to Boyd et al., (2008) the degree of uncertainty on noise 
mpacts on marine mammal individuals was ‘high’ for all effects 
except hearing impairment (TTS, PTS). Subsequent research has 
improved our knowledge on mammals and fish especially on TTS 
(Popper et al., 2014; Finneran et al., 2015; Southall et al., 2019), 
although many open questions remain. 
Masking 
Broadly speaking, masking can affect communication, navigation 
and predator detection in marine animals. Masking potentially 
has an important impact on marine taxa because, (i) it can be 
‚ong-lasting (chronic), and (ii) it affects the ‘acoustic habitat’ of 
an animal which can impair both the active and passive usage of 
sound over considerable ranges (Clark et al., 2009; Slabbekoorn et 
al., 2010). Focussing on marine mammals, Erbe et al., (2016) review 
a variety of studies from the past decade which have improved our 
understanding of masking. These relate tothe sources of underwater 
noise (see Chapter 2) and the role of the acoustic environment in