The invisible pollution in our oceans

Written By Lucia Yllan Garcia

Edited By Bobbie Renfro

In the last few decades, ocean pollution has become a major concern internationally. We are all aware of the damaging impacts that the presence of pollutants in the ocean have on marine life and the importance of taking action to protect and ensure the health of our seas. Thinking about ocean pollution, the first image that pops into our minds is plastic residues trapped in the ocean currents. Maybe your mind even goes to the “Great Pacific Garbage Patch”. However, plastic and other material trash are not the only pollutants that threaten our oceans. There is another type of pollution that is invisible to the eye but that affects marine life in all its stages: noise pollution.

But what do we call noise? It’s the unwanted sound product of human activities that interferes with the acoustic signals used by animals [1]. The main sources of noise pollution underwater are: commercial shipping, oil and gas exploration, naval exercises and recreational activities such as cruises or boating [2]. Noise pollution in the oceans is especially problematic as sound travels longer distances and four times faster through water than air and marine animals heavily rely on acoustic communication which makes them more vulnerable to the effects of noise.

Photograph by National Geographic Creative/Alamy Stock Photo.

Since sound transmits effectively through water unlike light and provides information faster, over longer distances and without using large amounts of energy, many marine animals have evolved to use sound to communicate and obtain information about their surroundings [3]. Marine animals use sound to find reproductive partners, find food and stay alert to the presence of predators [4–6]. For example, spinner dolphins (Stenella longirostris) use clicks to coordinate their hunting strategies and male midshipman fish (Porichthys sp.) use ‘hum’ sounds to attract and court females [6,7]. Another example of the importance of sound in the marine realm is the settlement of fish larvae. After hatching from their eggs, the little fish larvae that swim freely in the ocean use the sound of the reef to find the right habitat in which to settle in and become adult fish [8–13]. Thus, the ability to produce and hear sounds is essential for life in the oceans.

At the left, photograph by Paul Vinten of a pod of snipper dolphins. At the right, photograph by roncasual on Flickr of a plainfin midshipman.

However, the presence of noise pollution makes animals unable to hear and understand important sounds in their surroundings making communication impossible. This process is called masking and can have drastic consequences for marine animals [14]. The masking of animal sounds reduces their ability to hunt and feed, find other individuals through their calls, and detect approaching predators, increasing the risk of mortality [15,16]. Scientists have found that noise reduces fish and crab attention span which also reduces their possibilities of detecting a predator and hiding fast [17–19]. In addition, noise pollution can mask reef sounds and prevent fish larvae from locating a good settlement area [20]. Noise can also produce changes in animal behaviour, displacements, strandings, hearing damage and high stress levels which have negative consequences for marine species populations [21,22].  

Photograph by Justin Sullivan of a grey whale stranded in Point Reyes Station, California.
Schematic of the effects of noise pollution on marine animals by Lucia Yllan.

Nowadays, the way noise pollution alters marine life has become more apparent thanks to recent scientific research.  Due to the increasing levels of noise pollution in our oceans, marine animals have started avoiding noisy environments, changed the timing and frequency of their calls, and experienced shifts in their auditory thresholds and even hearing loss [23]. Some examples of these changes can be observed in cetaceans:  humpback whales (Megaptera novaeangliae) decrease the number of dives to feed in the presence of ship noise [24]; right whales (Eubalaena sp.) and blue whales (Balaenoptera musculus) reduce the number of calls emitted when exposed to noise [25,26]; and harbour porpoises (Phocoena phocoena) suffer hearing threshold shifts due to high intensity noise [27]. These changes can either be temporal or permanent depending on the duration and intensity of the noise.

Photograph by Danielle Dion of a mother and calf harbour porpoise in the Bay of Fundy, New Brunswick, Canada. 

Noise has become one of the principal pollutants in our oceans thanks to the increasing ship traffic and the search of new energy sources underwater, jeopardizing the wellbeing of many marine species that rely on acoustic signals to survive and reproduce. However, not everything is lost. The development of international laws and regulations that help modulate the amount of noise in our oceans and new advances in technology which reduce the intensity of these noises [28] can help preserve the ‘acoustic landscape’ of the marine habitats and, therefore, reduce the impact of noise on marine life. 


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