cCMB FUTURE SCIENCE BRIEF 
4.3 Mitigating the effects of 
underwater noise 
Unlike other forms of pollution, noise is temporary and once 
the sound generating operation stops, the pollution stops too. 
Although some of the effects on species may last longer than the 
duration of the sound (see Chapter 3), the temporary nature of 
noise renders this pressure potentially easier to manage than many 
athers (e.g. chemical pollutants). In line with the precautionary 
principle, and given the uncertainties regarding the effects of 
noise, mitigation measures need to be employed when there is 
a risk of population- or ecosystem-level consequences or harm 
to individuals arising from anthropogenic noise (Thomsen et al, 
2019). Some examples of the latest developments in mitigation 
for shipping noise and other marine industrial activities, as well 
as a summary of potentially quieter alternatives to current marine 
operations in a European context are provided in this section. 
Mitigation strategies for shipping noise 
Beside the IMO guidelines mentioned in Section 4.1.1, the largest 
set of potential solutions for the mitigation of ship-generated noise 
can be found in the joint final report of the multidisciplinary EU- 
Funded projects SONIC® and AQUO* (Baudin & Mumm, 2015). 
These include both long-term and temporary noise reduction 
solutions, whose effectiveness depends on energy efficiency, 
cost, and effect on marine organisms. Long-term solutions 
are focused on the reduction of the main noise source Le. 
propeller noise, and other sources such as machinery vibrations 
transmitted by hull structures into the water (Huang et al., 2016; 
Young et al., 2016). However, these solutions can be expensive 
because of the high material and maintenance costs and are 
usually applicable for new construction only. A revolution in 
ship design is underway to reduce greenhouse gas emissions 
and move towards decarbonization, providing an opportunity 
within the next few years to include noise emissions as one 
of the variables in design optimisation. Temporary solutions 
can be achieved by adjusting vessel operational conditions 
(e.g. reducing ship speed), managing traffic, and better and 
regular vessel maintenance (see IMO, 2014). Traffic control 
strategies, such as prescribed shipping routes, avoiding marine 
life 'hot spots', and speed limits in vulnerable areas (Audoly et 
al., 2017), can be customised to take into account ship traffic 
characteristics, ambient sound patterns and information on 
ocal marine organisms. The aforementioned SATURN® project 
will further assess the effectiveness and feasibility of mitigation 
measures to reduce shipping noise effects from a policy, legal 
and commercial perspective. 
Figure 8. Traffic control strategies such as nrescribed shipping routes and speed limits can he used in vulnerabhle areas 
3 www. sonic-project.eu 
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