Unusual seal behavior occurred in 15 of 216 elevated pile-driving noise encounters
There is nothing quiet about inserting steel monopiles into the seabed. When constructing offshore wind farms, large hydraulic hammers pound steel every few seconds for hours on end. This produces intense acoustic pulses that travel far through the water. Scientists have known for years that marine mammals move away from the sound, but one critical question still lingered: what do the individual animals do when the pounding starts?
Scientists discovered the answer by studying the movements of harbor seals while navigating near a construction zone, matching up to more than 10,000 hammer strikes beneath the water.
Twenty-four seals were moving around a construction site
In January 2012, scientists tagged 24 harbor seals in the Wash and North Norfolk Coast protected area, England’s primary hub for the species. GPS tags tracked the animals for 12 to 114 days, recording their location roughly every 10 minutes while at sea.
Considering the density of the animals locally, it was estimated that about 180 seals could modify their behavior in response to pile-driving at the 5.4-mile radius.
Crews were laying foundations for the Lincs offshore wind farm. From January 28 until May 11, 27 monopiles were installed, producing 77,968 hammer strikes across 64 operations with an average duration of one hour. Acoustic modeling showed that twenty of the tagged seals had encountered pile driving sounds in excess of the ambient level, producing 216 such sound encounters.
An encounter did not necessarily turn into an unusual movement
These sound encounters occurred when the seals were situated at distances ranging from 2.6 to 28 miles from the piling operation location.
Each seal’s movement in response to acoustic encounters was compared to the baseline behavior for this particular animal. Out of 216 sound encounters, 15 of them met statistical criteria to be recognized as an unusual movement response. These 15 responses came down to nine individual seals.
Underwater construction noise detection did not cause any immediate drastic changes in the horizontal path of seals’ movement, highlighting an important difference between hearing a sound and escaping from it.
The 15 responses fell into three groups
There were three distinct types of behavioral responses:
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Accelerated flight: In six encounters, seals traveled at unusually high speeds, either speeding up along their existing path or turning before sprinting away from the wind farm.
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Abrupt stoppage: In six other encounters, seals did the exact opposite—abruptly slowing down and drastically reducing their horizontal movement while piling occurred.
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Delayed departure: The remaining three seals stayed nearly stationary for 3 to 12 hours before suddenly initiating fast, highly directed travel away from the area.
Halting could mean that the seal is assessing the noise.
More sound meant a greater chance of a response
The factors of distance and volume determined the chance of a response. Fifteen responses were recorded at distances ranging from 3 miles to 18 miles from the piling location.
In dose-response analysis, it was shown that the mean population response threshold was 186 decibels and the 50% response rate was at 175 decibels. Within the construction area, this meant that the median response radius was 5.4 miles around active piling sites. Considering the density of the animals locally, it was estimated that about 180 seals could modify their behavior in response to pile-driving at the 5.4-mile radius.
Fifteen is not the same as no impact
These 15 instances don’t signify the noise had no impact. The use of GPS technology helps detect only dramatic alterations in horizontal displacement; it cannot reveal temporary responses, modified diving patterns, or stress reactions.
However, it’s precisely these tracks that help reveal one crucial thing: the reaction of marine species to offshore wind piling is not a panicking herd movement. In fact, the overall process of their relocation from construction sites happens through the creation of a quilt made up of individual behaviors: some seals flee, some freeze, while others wait.
The full study can be read here: Whyte, K. F., Hastie, G. D., Sparling, C. E., Binnerts, B., & Russell, D. J. (2026). Movement Responses of Seals During Pile Driving for Offshore Wind Farm Construction. Animal Conservation.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
