#OctopusStory and Noise Pollution in the Marine Environment

_{By Rowena Cowton, Marine Champion for the Hampshire and Isle of Wight Wildlife Trust.}

Noise is very important in the underwater world; sound travels more efficiently through water than it does air, and after 200m there is not a lot of sunlight available to see by. Marine mammals, like whales and dolphins, use sound to both communicate with each other and to navigate through deeper, darker waters. With a rise in the number of ships and boats in the sea over the last century, the background noise beneath the surface has also increased, and this has an impact on marine life.

Understanding how important sound is to these animals is key to mitigating these harmful effects. Whales, dolphins and porpoises belong to a group called cetaceans, which are further divided into two main groups: baleen whales (mysticetes) and toothed whales (odontocetes). Baleen whales are well known for ‘singing’, like humpbacks and blue whales, and they can be heard from hundreds of miles away across the ocean. These vocalisations allow individuals to locate other members of their species over vast distances, and with the right microphone, a human can tell which species are in the area from the different frequencies being heard.

Toothed whales have special adaptations that allow them to use echolocation, which helps them to hunt. Studies have shown that dolphins can recognise and respond to 3D objects that are invisible to the eye underwater. This is possible because of an organ called the melon, which consists of a fatty substance that conducts sound very efficiently. Dolphins create sound waves at a frequency that human ears cannot detect and use the melon to focus the direction of the waves. These then bounce off of objects in the environment, and return to the dolphin. Instead of external ears, toothed whales

have a hollow jawbone, which is filled with the same substance as the melon; returning sound waves are picked up and conducted along the bone to the inner ear. This information about the environment around them allows toothed whales to navigate areas where visibility is poor. Sperm whales can hunt squid in the Mariana Trench, and river dolphins can chase fish through muddy waters, because of the advantages of echolocation.

With sound being so important to marine mammals, underwater noise pollution can pose serious dangers. If a whale is unable to distinguish one vessel’s engine from another in a busy shipping lane, or to gauge the distance between them, there is a greater chance of a collision occurring. Ship strikes result in severe injury and often death, like the fin whale that arrived in Portsmouth on the bow of a cargo ship in 2019. For toothed whales that rely on echolocation, all this noise can seriously affect their ability to navigate. Imagine sitting in the middle of road works on a busy road without ear defenders – it would be very hard to concentrate and stay focused with all the noise around you. A disorientated dolphin is unable to hunt or navigate effectively, and far more likely to collide with vessels or become stranded on land.

Studies have also shown that over time, whales have changed the frequencies of their songs in order to be heard over the increased background noise from shipping traffic. Many migration routes have been established over tens of thousands of years, while industrial shipping is only a couple of centuries old. For creatures that can live as long as humans, and potentially longer, a lot of things have changed in their environment very rapidly in just a few generations.

Research is being conducted to find ways to reduce marine noise pollution. Insulating engines, designing propellors to be quieter and encouraging ships to travel at lower speeds through areas of high whale activity all help to decrease noise levels. Slower speeds also help whales to evade ship strikes by detecting vessels earlier and reducing the likelihood of lethal injuries if a collision occurs.

Sources

Handbook of Whales, Dolphins and Porpoises by Mark Carwardine

The Sound Aquatic Podcast, Episode 5

Whales and Dolphins: Cognition, Culture, Conservation and Human Perception; Chapter 12 by Lori Marino; Chapter 13 by Paul Spong

https://www.bbc.co.uk/news/uk‐england‐hampshire‐51017001

https://www.bbc.co.uk/news/uk‐england‐hampshire‐50956780

By Rowena Cowton, Marine Champion for the Hampshire and Isle of Wight Wildlife Trust.