Humpback Whales near Alaska.
Photo Courtesy of EvaDB
Increasing Anthropogenic Noise Drowning out the Whales
Whales are very vocal creatures. From singing Humpback Whales to chirping dolphins, cetaceans are in constant, vocal communication with each other and their surroundings. Baleen Whales, like Blue Whales, Humpback Whales, and Fin Whales, tend to use low-frequency sounds to communicate, usually less than 1kHz. These low-frequency sounds travel great distances under water without losing intensity, which allows these animals to communicate essentially across ocean basins. It is thought that these large whales do actually travel in nontraditional pods. They are not in sight of each other like dolphins or Orcas would be, but they can hear each other and are communicating. Toothed whales like dolphins, Orca, porpoises, etc., tend to use higher frequency sounds, usually between 1-10 kHz. These whales also use echolocation, high-frequency buzzes, clicks, and whistles around 10kHz, to navigate and hunt. These sounds don’t travel as far, but the animals are usually in visual contact with one another so it’s less important. All of these animals depend on sound to navigate, find food, identify themselves and other whales and to attract mates. With sound being so important to these animals, increased noise in the oceans can be extremely detrimental to their survival.
In the last few decades, human-made noise has drastically increased in the oceans. While the number of fishing vessels hasn’t increased significantly, the number of large cargo vessels has increased 8-14% since 2000 and recreational vessels have also significantly increased in number. As a result, the ocean has been growing noisier at an average of three decibels per decade. With most of this new sound being low-frequency shipping noise, it travels very far underwater, and can be heard clearly hundreds of kilometers from the source. Other noise sources are sonar, usually from the navy but also used in other navigation, seismic blasting for oil drilling, pile driving, etc.
When exposed to the loud noise of seismic blasting or high-frequency sonar, whales show disoriented behavior. This often leads to stranding or, in the case of deep diving whales like beaked whales, erratic diving behavior which causes decompression sickness as bubbles form in the blood when they ascend too rapidly. Many stranded whales show signs of cochlear damage or other impact trauma such as hemorrhages in the ear, brain, and kidneys as well. When exposed to chronic noise many whales experience an increase in stress hormones. An increase in stress hormones leads to a depressed immune system, stunted growth, and increased metabolism. These things make it hard for whales to fight off diseases and predators, and to feed themselves. It is thought that the noise in the North Atlantic is what is preventing North Atlantic Right Whale populations from recovering as well as the South Atlantic Right Whale populations have. The Southern Atlantic Ocean is much quieter, those whales have lower levels of stress hormones in their bodies, and their population has recovered much faster than the stress affected North Atlantic Right Whales.
Many whales will leave an area if it becomes too noisy, even if it is a preferred feeding or breeding ground. Many whale species are endangered, so any negative impact on breeding can be detrimental to the species as a whole. If they do stay, many show a disruption in foraging behavior. Humpback Whales, for example will not dive for food as often, or will make fewer attempts to feed at depth when there is a great deal of noise in an area. This of course can lead to malnutrition in whales located in a noisy area if they choose to stay. Many of the big whales, like Humpbacks and North Atlantic Right Whales, will modify their calls, trying to be louder than the outside sound in the environment. They may also change the pitch to try to outcompete the noise in the frequency they normally use. When this fails, they often simply fall silent. This can cause them to lose contact with one another. If these whales are travelling in large, vocally-active pods, this is of particular concern.
Due to the high-intensity and low-frequency sounds caused by commercial traffic, this should be the primary noise concern. Baleen Whales have lost about 80% of their communication space in coastal waters, meaning they have to be 80% closer to hear each other. In some places, it’s closer to 95%. Because Baleen Whales use these low frequency sounds to communicate normally, they are chronically affected by commercial shipping. While toothed whales are affected by it as background noise, they do not experience the same inhibited communication across long distances as the great whales do.
Negative health impacts on the whales due to sound are evident, but they are not the only animals affected. Many species of commercial fish are also being found to use sound to communicate, like Cod and some types of shellfish. As a result, increased ocean noise will not only affect important and charismatic cetacean species, it is also being shown to inhibit human food sources. This of course could lead to an economic food crisis if the ocean is allowed to get too loud.
There are solutions to the noise problem in the ocean. Seismic blasting should be banned offshore, particularly in important feeding and breeding grounds. Turning more towards renewable energy sources will eliminate the noise from drilling and seismic blasting as a result and we will see an increase in cleaner energy overall. Banning sonar testing in important marine habitats, particularly in areas where deep diving whales tend to live since they are the most likely to strand or die of decompression sickness. Regarding shipping, a change in propeller design should be favored. Propellers that create less turbulence in the water will be quieter and, coincidentally, more efficient. The noise level in the ocean has to be lessened, and this is a good place to start.
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