Marine mammals live in a world of darkness. Light doesn’t travel very well underwater so they can’t depend on their eyes to explore like we do. Instead, they use their ears, relying on sound for everything from communicating with others to finding food, escaping predators, and navigating their environment. It is essential to their survival.
So, what does this mean for ocean noise? Read on to find out some of the possible effects of noise on marine mammals.
Turning the volume up in the ocean
The ocean is a noisy place and humans are increasing the volume all the time. Just some sources of manmade noise include:
- Shipping and recreational vessels
- Seismic exploration
- Offshore construction work, e.g. drilling and pile driving
- Military sonar
- Acoustic Deterrent Devices (ADD) used to deter animals from fishing nets and fish farms
One source can’t be considered on its own either. In just one area, animals may have to listen to a variety of sounds all at once and it is a very worrying problem.
Possible effects of noise on marine mammals
There is no easy answer to this question. How badly noise effects a marine mammal depends on a variety of factors, such as the environment, the noise, and the species of marine mammal. A noise that negatively effects one species or individual may have less of an impact on another, but here are some of the possible effects of noise on marine mammals.
If you have ever been somewhere with very loud noise, such as near speakers at a concert, you may have noticed that for a while after you can’t hear as well as normal. That is what is called a temporary threshold shift or TTS and it means that noises need to be louder than normal for you to be able to hear them. It is temporary damage to your hearing, and it will recover in time. It is also possible to develop permanent threshold shift or PTS which is a permanent shift in hearing.
Marine mammals can experience the same thing if exposed to loud noises in their environment, though how much TTS impacts them in the long-term is unknown as their hearing recovers. PTS is more serious as a permanent change in hearing will affect how well they can detect sounds in their environment.
Imagine yourself in a busy place with lots of people talking and music playing in the background. Now imagine trying to have a conversation with a friend – can you hear each other? What if you are standing at opposite sides of the room? Probably not. That is masking. The noise is preventing you from talking to each other.
For marine mammals masking reduces the distance over which they can communicate. It can stop them finding a mate, locating food or dodging a predator. They need to be able to detect sounds to carry out essential activities.
Have you ever avoided going somewhere because it was really noisy? Marine mammals can react the same way. Ocean noise can stop them from visiting parts of their habitat and potentially keep them away from crucial breeding and feeding areas. The amount to which this occurs does vary a lot though and will depend on the species, noise and situation. For example, an individual may stay in an area with annoying background noise if the food is good but may leave another if there is less reward.
Changes to behaviour
Again, this is hard to study and varies a lot but there is a possibility that ocean noise can change the behaviour of marine mammals, with scientists reporting effects such as more time spent at the surface, a change in direction to move away from a sound, or an increase, decrease or change in vocalisations. Any change in behaviour could have knock on impacts, for example on feeding or mating.
Changes to prey availability
Marine mammals are not the only animals that rely on and are affected by sound in the ocean, their prey is as well. Any changes to distribution or survival rates of fish and other marine life has the potential to affect the ability of marine mammals to feed.
Marine mammals strand for several reasons, and, while the cause is not always known, mass strandings of deep diving beaked whales in particular have been associated with SONAR.