Noise travels below the waves. The rumble of ships, the quest for hydrocarbons, and the installation of offshore wind farms all create a piercing sound that unsettles the seabed and its inhabitants. This isn’t a minor nuisance; it disrupts the breeding and feeding routines of many fish and marine mammals, sometimes driving them away or pushing them toward decline. Scientists warn about the scale of the issue and point to practical solutions that could ease the burden on ocean life.
Researchers say that with the right instruments, ships are audible from New York Harbor to Europe, showing how sound travels underwater. A key recommendation is to reduce ship speeds by about 11 percent. “Ships are the main source of underwater noise, but this small change can make a big difference,” notes José Antonio Díaz, a participant in the Saturn consortium and a technician at the Canary Islands Ocean Platform (Plocan). Plocan is among twenty centers involved in the European Saturn project (Developing Solutions to Underwater Radiated Noise), which spent three years exploring strategies to cut acoustic impacts beneath the waves.
Led by the Science Foundation of Ireland and coordinated by University College Cork, the project gathers a broad EU coalition with twenty partners across ten countries. An interdisciplinary team of acoustic scientists, marine biologists, and marine engineers collaborates to map out effective methods to reduce underwater noise.
Most ships operate at speeds between 20 and 24 knots, so trimming speed by 11 percent translates to about 18–21 knots. That slowdown can substantially ease the acoustic load. “Contrary to what some might expect, it is the propellers that generate most of the noise, not the engines,” Díaz explains.
Specifically, when propellers turn, they create bubbles that burst and produce a persistent, problematic sound for marine life. While slowing down is a practical short-term fix, Saturn researchers also believe changing the propeller design to produce fewer bubbles can further reduce noise without sacrificing performance, as one researcher emphasizes.
Cutting speed also brings additional benefits. A 2019 assessment by Reynolds Environmental Sustainability Consultants (RESC) indicated that a 20 percent reduction in speed could lower fuel use by more than 24 percent. Beyond cutting greenhouse gas emissions, such reductions could slash underwater noise by about 67 percent and lower cetacean fatalities from ship collisions by roughly 78 percent, according to the RESC study.
One of the major threats to species like sperm whales and pilot whales is collision with moving vessels. When ships strike, the harm can range from minor injuries to severe trauma or death, often occurring gradually and painfully.
“Permanent or temporary deafness”
Ocean noise varies widely. Díaz emphasizes a comparison between pristine, quiet regions and zones with heavy economic activity and shipping. The disparity can be staggering, sometimes exceeding ten thousand to one. “That contrast is unacceptable,” the Saturn project researcher remarks.
To illustrate, imagine moving from a field where natural sounds prevail to parking beside an airplane ready for takeoff. In Spain, the Strait of Gibraltar stands out as especially noisy, with about 300 ships passing daily, roughly every five minutes.
“Underwater noise affects all species,” Díaz notes. Historically, the focus has been on large mammals such as whales and dolphins because they rely on sound to communicate. There are two potential effects: a physical one causing permanent or temporary deafness, and a communication one where noise interferes with their vocal exchanges. This can prevent social listening, causing individuals to drift away from their groups, which disrupts ecosystems and human activities like fishing.
“Noise is a relatively underappreciated problem, and now is the moment to propose viable solutions,” Díaz asserts. Clear measures and practical steps are needed to move the issue forward.
Txema Brotons: “The problem is we treat the sea like a highway”
From a vessel length of about 90 meters and a slow pace of 10 knots, the risk to cetaceans increases dramatically.
Underwater noise can directly harm marine mammals, but it often creates chronic stress that makes them more susceptible to other threats. Tursiops is a group researching these effects.
Question: How does underwater noise affect marine mammals?
Answer: The noise concentrated in low frequencies travels far and affects certain species more than others. For instance, a fin whale emits at very low frequencies, while a dolphin operates at higher ones. Chronic noise may not trigger a single fatal blow, but it raises stress levels and lowers resilience to other shocks, much like a wound that becomes prone to infection when stress spikes.
Q: Could this noise ever directly cause death?
A: A seismic survey for hydrocarbons can involve powerful underwater detonations that may be lethal if an animal is caught nearby. Military sonar can provoke avoidance behaviors that lead to death in deep-diving species.
Q: Can slowing the browse speed help?
A: Slower speeds reduce noise and also lower collision risk with cetaceans. As new vessels enter service, the industry may be asked to design more efficient ships. In fact, a ship that makes a lot of noise can indicate a malfunction. There are many large ships that still sail on our seas. The core issue remains: the ocean is being treated like a highway.
Q: The other major problem is collisions with cetaceans…
A: Large ships account for the highest fatality toll. A collision with a 12-foot sailboat at six miles per hour is not the same as a collision with a 25-meter yacht at 30 miles per hour or a 120-meter ferry at 24 miles per hour. Survival chances rise with speed and length thresholds, which researchers have identified as meaningful breaks in the survival curve at about 10 nautical miles and 90 meters in length. That does not mean slower boats cannot still cause harm. On the latest expedition, two sperm whales showed collision marks within a week.