How Commercial Ships and Jet Skis Scare Dolphins Away

Noise pollution is a topic of conversation for those in and around large cities. What is not often discussed is the noise pollution that occurs under the sea. While the oceans have never naturally been quiet, over the past several decades, they have become excessively loud. So loud, in fact, that marine mammals have been suffering. Loud sounds below the surface of the ocean can be scary for marine animals. Schools of fish can scatter in a flash. Whales may beach themselves to escape noise. Not surprisingly, there are sounds that scare dolphins, and some of these sounds can have life-altering consequences.

Commercial Ships

Commercial ships have increased exponentially over the last few decades to keep up with the demand of global trade. To make the most of each passage, the ships have gotten larger. This also means that the amount of noise emitted from the ships has gotten louder, scaring marine life, including dolphins, in the process.

A cargo ship on the ocean may not seem like it would make much noise as it cuts through the water to get to its final destination. But these ships emit noise at 180 decibels. This is the equivalent of a jet engine. These loud sounds make it impossible for dolphins to communicate with one another in areas with designated shipping lanes. The noise is so loud that dolphins have even abandoned traditional hunting grounds.

Although technology exists to reduce the noise from the propeller, making it quieter, this process is costly. Consequently, to date, only one shipping company, Maersk, has modified a few of its vessels. While this is a step in the right direction, with over 100,000 commercial ships on the ocean each year, it does not put a dent in the sound that scares the dolphins away from areas they traditionally call home.

Recreational Water Toys

It is not only large ships that scare dolphins away from areas where they traditionally hunted, raised their young, or lived. Smaller, recreational water boats and toys have proven to be frightful to dolphins as well.

While these smaller vessels do cause noise pollution below the surface of the water, the boats and jet skis have proven to separate pods of dolphins. This can be stressful for adult dolphins who are caring for younger ones, where separation from the group could be catastrophic. An April 2023 study found that jet skis are more responsible for this action than ski boats and the like.

During the study, the dolphins tried to get away from the boats and jet skis out of fear, which caused the pod to become dispersed. However, this did not dissuade the boats and jet skis. People who were using them continued to get closer to the dolphins, as seen via photographic evidence. While sound plays a significant role in what can scare a dolphin, so can small vessels captained by those who do not know to give a wide berth to the marine mammals.

Military Sonar

It is a known fact that military sonar can cause harm to marine mammals. Because of this, the U.S. Navy has deemed that the safe level to deploy sonar is at 160 decibels. However, according to a 2024 study published in Royal Society Open Science, the level that is considered safe is still disruptive to dolphins. Both short and long-beaked dolphins were observed from 34 different groups from 2017 to 2021. Because these are the most common dolphins to have consistent run-ins with military sonar, they made the perfect groups to observe.

What scientists discovered is that decibels at “significantly lower levels” scared the dolphins. The dolphins from the short-nosed groups would speed up to get away from the sonar, coming together in larger subgroups than when exposed to the sonar. The long-beaked dolphins would slow down and scatter from the group, coming together in multiple small groups after.

While dolphins have yet to be scared to the point of stranding themselves to exit the water, this has happened with whales. Therefore, scientists are concerned that the more military sonar there is in the ocean, the greater the chances dolphins will swim away from one another in fear and eventually find themselves on beaches or sandbars, unable to return to the water, stranded.

Dredging Off The Coast

Noise pollution is a major issue that marine life lives with daily. One of the causes of this noise is dredging off the coast. Dredging is the process of removing silt, sediment, and debris from bodies of water, including coastal areas. When dredging occurs, it creates loud underwater sounds due to the draghead’s contact with the bottom of the waterway, blasting activities that remove rocks from the bottom of the waterway, and the hydraulic ram, as the force created by it helps to excavate and transport materials from below the water’s surface.

With this type of noise pollution, dolphins have been scared away from foraging grounds and their traditional habitats. Dolphins are incapable of communicating with one another effectively, as the sound is far too loud underwater. When dredging is underway, dolphins swim away at high speed because of the stress they are under.

While dredging has been noted as a process that keeps waterways passable and functional, the impact on marine mammals is not considered. Consequently, animals, like dolphins, are scared away, potentially leaving them without enough food and without their pod to fend for themselves.

Seismic Surveys For Oil And Gas Exploration

As countries around the world participate in oil and gas exploration, much of that exploration is happening below the waves. Seismic surveys are being used to make detailed maps of the ocean floor. This information is then interpreted to determine what geological formations are and where resources could potentially be located.

Unfortunately, to do a proper seismic survey, air guns that create pressurized air are used, blasting for 10 to 12 seconds at a time. These air guns are so loud that only military blasting and cargo ships are louder. The sound of the air guns can be heard up to 2,500 miles away from the blast site. Therefore, dolphins both in the area of the survey and those thousands of miles away can be affected by the air guns.

When dolphins hear sounds this loud, they not only flee the area but also risk damaging their hearing. This is because the noise decibels associated with a seismic survey are around 190 dB. To put this in perspective, this is louder than a rocket launch, which is 180 dB. People would find this sound intolerable. If the dolphins’ hearing is damaged, this interferes with their echolocation and communication skills. This can leave them stranded from their pod and unable to hunt effectively. Therefore, not only is seismic surveying scary, but it can also be detrimental to a dolphin’s health.

Foghorns

While they have become an essential part of maritime safety since the late 1800s, it does not mean that foghorns are a welcome sound to dolphins. In fact, the sound makes it so that dolphins are both scared and have communication difficulties, given the distances the foghorn sound can carry. In some areas where the shoreline was more dangerous than others, an underwater foghorn was used. The goal was to ensure the vibration would reach the ship’s hull long before the ship would be impacted by the rocky terrain. However, this loud blast of noise only worsened the issue for dolphin communication, given that sound travels 4.5 to five times faster through the water.

The goal of foghorns is to be heard two nautical miles away. This makes the horns incredibly loud, to the point where a person would not want to be near the horn when it sounds. Many have wondered if foghorns are still necessary today, given the technology that has advanced since the first one was invented in 1859. The answer is yes, according to those in areas where the terrain can be challenging to maneuver. Therefore, even though the sound pollution affects the ability of dolphins to communicate and forage, the limited use of foghorns used today may make it one of the lesser offenders to dolphins’ sensitivities.

Transient Orcas

Dolphins have been known to be curious about fish-eating orcas. However, transient, mammal-eating orcas are a group that dolphins stay away from so that they do not become a meal. The problem with transient orcas is that they remain relatively silent while they are stalking their prey. A 2005 study published in Animal Behaviour shows that this was likely done to not warn potential prey of the transient orcas’ presence.

However, after a successful kill, the orcas became vocal. It was hypothesized that this was done to signal to other transient orcas that there was food in the area or that there was less of a risk of socialization after mealtime took place. But it is these calls that scare dolphins and keep them out of waters where transient orcas live, so that they do not become the next target of the killer whales.