Imagine, for a moment, driving a car along a winding road in the dead of night, while your passenger shines a torch into your eyes. Difficult? Dangerous? Life-threatening?
As humans, we are used to finding our way with our eyes, but in the depths of the ocean eyes can take one only so far. For a multitude of marine life, it is sound and the ability to hear that are critical. As human activity across the oceans has grown so has the noise we produce, and there is compelling and growing evidence that suggests that some of this noise, particularly that produced by seismic surveys and active sonar devices, has been directly responsible for a number of disastrous events including whale and dolphin strandings. For marine creatures who navigate by sound, our activities are, in extreme circumstances, resulting in deaths.
Research has shown that many dozens of species of fish communicate using sound and studies have found that whales can communicate over hundreds of miles using low frequency calls. These fascinating insights help to highlight the importance of acoustics in the oceans and force us to consider how our activities affect the wealth of ocean life that depends on sound to navigate and communicate, to find prey and avoid predators.
As I write this, many questions remain unanswered but, day by day, we are building up a far more detailed picture of how noise affects these complex ecosystems. A recently published study that brings together a large amount of primary research into the impacts on anthropogenic noise has shown that marine life at every scale can be adversely affected by increased noise levels. From dolphins and squid down to the smallest zooplankton, we are only just beginning to properly understand how important sound is to marine life.
Over the past few decades, the huge increase in shipping and other human activities in the oceans has given rise to noise levels that threaten much of its ecosystem. Vibrations from engines, generators and propulsion systems all produce noise which is transmitted into the ocean through the hull. Propellers are a major contributor to the overall acoustic signature produced by a ship, and research is ongoing to better understand the mechanisms behind noise generation and how to design quieter propellers.
There is already a wide range of proven technologies that could, and should, be applied far more routinely by ship builders and operators. A simple example is the mounting of engines and other machinery on vibration damping mounts that can significantly reduce the amount of noise that is transmitted through the hull and into the surrounding ocean. However, such technologies increase both purchase and maintenance costs and there are few incentives for ship operators to adopt this technology.
The concept of noise exclusion zones (NEZ) and mandatory acoustic limits for vessels operating in certain waters is gaining traction in numerous regions around the world. For a vessel to operate in a noise exclusion zone, it would have to limit its acoustic signature over particular frequency ranges. In the Author’s view, these limits should be determined by the ecosystems that the NEZs are designed to protect. This will require ecologists, classification societies and ship builders to work more closely together to better understand how we can design ships and other vessels to meet the needs of the environment without unnecessarily impeding global trade and the local economies that rely on the oceans through tourism and other activities.
