A key to quieter seas: half of ship noise comes from 15% of the fleet

How can ports act to reduce underwater noise from shipping? Identifying effective management frameworks

“…If ships of a similar type and size are compared, the noisiest ships are likely to be among those which are less efficient (Leaper et al, 2014). Moreover, there is evidence that half of the total power radiated by modern vessels comes from 15% of the fleet (Veirs et al, 2017). However, the relationship between energy efficiency and underwater noise emissions needs to be analysed for each technology (Vakili, 2018).…”

Small reductions in cargo vessel speed substantially reduce noise impacts to marine mammals

“…A moderate reduction in speed is, therefore, an effective, immediate, and readily implemented approach for reducing the source levels of fixed pitch propeller cargo vessels, with positive economic and climatic synergies (45,46). However, given that slower vessels take longer to pass an animal, do reductions in speed translate unequivocally in reduced impacts on marine mammals or is it a zero-sum game (25,26,30,31)?…”

“…Slowdowns have the added benefit of reducing fatal ship strikes (29,51). However, concerns have been raised that slowdowns, by prolonging the period over which animals are exposed to vessel noise, could end up being a "zero-sum game" (30,31); animals are exposed less but for longer durations, potentially weakening the benefit of this mitigation strategy. However, our results show that this is not the case: Vessel slowdown also reduces the overall exposure time during which an animal may be affected by noise.…”

“…However, a potential concern with technologically quietened vessels operated at high speeds is that animals may respond too late to close approaching vessels, thereby increasing the risk of collision. Some vessels, even when slowed down, can remain loud due to older technology and poor maintenance, resulting in excess cavitation (31). To illustrate this, we modeled a vessel traveling at a slow steaming speed (10 knots) but with 18-dB higher source level from excess cavitation compared to our reference vessel at the same speed.…”

“…We examine how the area and thereby, on average, the number of animals exposed to vessel noise changes as a function of vessel speed and noise-reducing technological improvements and how increasing the distance to animals affects the proxies for impact. We also test the frequently invoked concern about slowdowns that the resulting reduction in source level is offset by the longer time the ship spends within the habitat (30,31).…”