A mysterious disease has been killing dolphins for decades and in 2005, after Hurricane Katrina,…
Sound is the way of life in the ocean. It travels faster and farther in the water than in the air and many ocean species from the tiniest invertebrate to the largest whale rely on sound for survival. Sound is key for locating prey, avoiding predators, finding a mate or home and communication in general. If you ever had the opportunity to snorkel or SCUBA dive you will have realized that the ocean is not silent. From the snapping of crustaceans like crabs and lobsters as they snap their claws shut, the grunts and clicks of fish, the songs of whales far off, to the depths of the abyss the ocean is far from a silent world.
We are changing that soundscape and it is having adverse effects on marine life. Human activities such as energy exploration, shipping, recreational boating, construction, active sonar and seismic surveys are just a few forms of the loud and prevalent noise pollution that is wreaking havoc. Underwater anthropogenic noise pollution is drowning out the natural sounds of the ocean ecosystem disrupting the daily lives of all species. Comparison of sound on land to underwater is not a straightforward conversion due to a variety of factors including pressure. A normal conversation between humans on land (air) is about 60 db would register at 86 db one meter below the ocean surface.
For toothed whales and dolphins sound via echolocation is the main way they locate their prey in the ocean waters. Echolocation is a type of sonar in which a species emits a click that bounces off and object and when received back is processed as a picture – like seeing with sound. Deep diving whales use echolocation at a lower frequency which travels further getting a fuzzy picture whereas dolphins hunt in shallow waters closer to closure where more light penetrates and use a high frequency getting back a clearer picture of their prey. Studies have shown that in shallower waters where dolphins are frequently found, the sound frequency at which boats are travelling interrupts the ability of the dolphins to communicate. Scientific studies have shown that anthropogenic noises decrease the ability of marine mammals to communicate and become disorientated which has been linked to beach strandings through the world. One example of this is the use of seismic air guns used by companies surveying the deep sea emit sound pulses that reach 250 decibels (db) underwater – the human eardrum threshold for pain is 166 db under water. These loud blasts damage marine mammals hearing and is also believed to be a cause of behavioral changes in whales and dolphins.
Other species are affected by noise pollution. Larval fish and other juveniles listen for the sounds of “home” and hone in on sounds from the open ocean in order to return to or find suitable home habitat. In many places around the globe, this call from home is being drowned out by human activities. Noise pollution disrupts all aspects of marine life from reductions in reproduction rates, changes in behavior and physiological damage such as hearing loss, hemorrhaging and internal injuries.
We live in a technically advance world and have developed advancements in the medical field that allows those suffering from hearing and vision loss to see and hear the world in new ways. Marine species are not as lucky. They cannot simply put on headphones or earplugs to drown out loud painful noises or rely on other senses for survival. As fewer ships, exploration vessels and recreational boats were on the waters over the past year due to the COVID-19 pandemic, the response by marine life was quick with species returning to areas they previously had left due to increased anthropogenic noise. Through regulations of noise thresholds, more efficient and quieter propulsions technology as well as the possibility of deploying temporary acoustic barriers are options we can and need to undertake. We have the capacity and responsibility to develop alternatives to reduce anthropogenic noise pollution.