Marine energy has long carried a paradox at its core: the machines designed to help decarbonize electricity generation operate in one of the planet’s most acoustically sensitive environments. Tidal turbines, wave-energy converters and other devices may produce far less sound than large ships, construction vessels or offshore drilling operations, yet their underwater noise can still raise difficult questions for regulators. A new study by Haxel, Zang, McVey and colleagues examines a problem that has quietly complicated the expansion of the industry: the technical language used to measure marine-energy sounds does not always line up neatly with the environmental rules used to judge them.
Published in Scientific Reports, the research focuses on connecting international technical specifications for acoustic characterization with environmental compliance criteria. That link matters because measuring underwater sound is not simply a matter of placing a microphone in the ocean and recording what happens. Scientists must decide what kind of sound is being measured, where the sensor is positioned, how background noise is removed, which frequencies are analyzed and how the final results are reported. Regulators, meanwhile, may ask a different question: could the sound affect marine mammals, fish, invertebrates or protected habitats? When measurement standards and regulatory requirements speak different technical languages, even carefully collected data can become difficult to interpret.
Underwater sound is commonly measured with hydrophones, instruments designed to detect pressure fluctuations in water. Those fluctuations can be converted into sound-pressure levels, usually expressed in decibels referenced to one micropascal. The figure is not directly interchangeable with the decibel scale used in air, because underwater and airborne acoustic measurements use different reference pressures. A reported underwater level must therefore include its reference and measurement conditions to be meaningful. The distance from the device, the depth of the hydrophone, the orientation of the sensor and the acoustic properties of the seabed can all influence the recorded signal.
Marine-energy devices also generate sounds with highly variable signatures. A tidal turbine may produce continuous or repeating tonal components associated with rotating blades, gears, generators and hydrodynamic flow. A wave-energy converter may create intermittent sounds as it responds to changing wave conditions, while mechanical stops, pumps or hydraulic systems can produce short pulses. These signals can be described through several complementary metrics, including broadband sound-pressure level, frequency spectra, narrowband tones, one-third-octave-band levels and sound-exposure level. Each metric reveals something different, and selecting the wrong one can obscure the features most relevant to an environmental assessment.
The distinction between a device’s acoustic output and the sound experienced by wildlife is especially important. Engineers may estimate a source level, a standardized description of how much acoustic energy a machine emits, while field researchers measure received levels at a particular location. Between those two points, sound can weaken through geometric spreading, absorption and scattering. Low-frequency sound may travel farther underwater than high-frequency sound, while local bathymetry, water depth and sediment type can produce reflections or interference. A compliance assessment therefore needs more than a single number: it requires information about propagation, measurement distance, frequency and the surrounding acoustic environment.
The study addresses the practical consequences of these differences by considering how international technical specifications can be connected to environmental requirements. Technical standards are intended to make measurements repeatable across projects and countries. Environmental regulations, however, are often shaped by local species, habitat conditions and legal definitions of disturbance or harm. One jurisdiction may focus on received sound levels near a protected species, another on cumulative exposure, and another on whether a project changes the existing soundscape. A standardized acoustic description can help provide a common foundation, but it must still be translated into the biological and legal context of a specific location.
That translation is becoming more urgent as governments and companies seek to deploy marine energy at larger scales. Tidal-stream arrays, for example, could place multiple turbines in the same channel, potentially creating a combined acoustic footprint that differs from the signal of a single machine. Repeated operation may also matter differently from a brief construction event. A short, intense impulse and a lower-level, persistent tonal sound can have similar energy under some calculations while posing very different questions for animal behavior. Reliable assessment therefore depends on transparent definitions, consistent sampling plans and reporting methods that allow results from different projects to be compared without disguising their limitations.
For marine biologists, the value of better acoustic reporting lies in connecting physical measurements to biological sensitivity. Different animals hear and respond to different frequency ranges. Some marine mammals are particularly sensitive to low-frequency or mid-frequency sound, while fish and invertebrates may respond through other sensory pathways, including pressure detection or particle motion. Sound-pressure level alone may not capture every biologically relevant aspect of an underwater signal. A technically robust framework can help identify when additional measurements—such as particle motion, behavioral observations or long-term soundscape monitoring—are needed instead of treating one acoustic metric as a universal indicator of risk.
The work by Haxel and colleagues arrives at a moment when public confidence may be as important as engineering performance. Marine-energy developers need predictable rules and measurements that demonstrate whether their equipment complies with environmental requirements. Regulators need evidence that is technically defensible and comparable across applications. Communities and conservation groups need assurance that promises of clean energy do not overlook less visible effects beneath the surface. By linking measurement specifications with compliance criteria, the study highlights a pathway toward assessments that are clearer, more reproducible and more scientifically grounded. The broader message is not that every marine-energy device is either harmless or dangerous, but that credible answers depend on measuring the right sounds in the right way—and explaining precisely what those measurements mean.
Subject of Research: Acoustic characterization of marine energy converter sounds and their connection to environmental compliance criteria.
Article Title: Linking international technical specifications for acoustic characterization of marine energy converter sounds with environmental compliance criteria.
Article References: Haxel, J., Zang, X., McVey, J. et al. Linking international technical specifications for acoustic characterization of marine energy converter sounds with environmental compliance criteria. Sci Rep 16, 25126 (2026). https://doi.org/10.1038/s41598-026-52491-x
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41598-026-52491-x
Keywords: marine energy, underwater acoustics, acoustic characterization, marine renewable energy, environmental compliance, hydrophones, sound measurement, marine ecosystems, regulatory standards, underwater noise
