What the Rules Actually Protect
The Marine Mammal Protection Act defines two levels of harassment. Level A is physical injury — permanent threshold shift in hearing. Level B is behavioral disruption — defined as exposure above 160 dB re 1 μPa.
The Incidental Harassment Authorization (IHA) sets a shutdown zone — approximately 5.7 km radius with standard 6 dB attenuation — where pile driving must cease if a right whale is detected. Within this zone, the received level exceeds the Level B threshold. Outside it, the whale is considered unaffected.
This framework protects whales from direct acoustic injury. It does not ask whether they can still communicate.
The Sound That Fills the Gap
North Atlantic right whales produce upcalls — frequency-modulated contact calls between 50 and 500 Hz — at a source level of approximately 160 dB re 1 μPa at 1 m. These calls are how mothers find calves, how individuals maintain group cohesion, and how the population coordinates during migration.
Pile driving produces broadband noise in the same 50–500 Hz frequency band. For a whale to detect another whale’s call, the call must arrive at least 8 dB above the ambient noise floor — the signal-to-noise ratio (SNR) required for auditory detection.
Pile driving raises the noise floor. When the noise floor rises above the received level of an incoming whale call minus 8 dB, the call is masked. The whale is not injured. It simply cannot hear the other whale.
Two Zones from the Same Model
The shutdown zone and the masking zone come from the same RAM PE propagation model. The physics is identical. The only difference is the question.
The 80 km masking zone is computed at the baseline (pre-inversion) bottom parameters. Investigation 08 (Bayesian inversion) suggests the actual zone may be ~60 km with data-constrained bottom properties. The qualitative finding (masking zone >> shutdown zone) is robust to this uncertainty.
A whale at 50 km from the pile — ten times outside the shutdown zone, safe by every regulatory standard — cannot hear another whale calling. The call arrives below the noise floor. The whale is not harassed. It is acoustically isolated.
RAM PE propagation · CUDEM bathymetry (31m res) · WOA2023 sound speed profiles · 10 dB bubble curtain mitigation assumed · Masking threshold derivation: ambient noise ~105 dB re 1 μPa in the 50–500 Hz band (typical shallow continental shelf; see Wenz, 1962) + 8–10 dB SNR required for upcall detection (Clark et al., 2009; Parks et al., 2011) = masking above ~115 dB received level
Ambient noise uncertainty. The masking zone is at least as uncertain as the shutdown zone: it depends on both propagation uncertainty and ambient noise uncertainty. Ambient noise on the US East Coast continental shelf varies 10–15 dB with shipping density, wind state, and biological noise. The 105 dB baseline represents moderate conditions; busy shipping lanes or calm conditions could shift the masking threshold — and thus the masking zone — by ±30%.
RAM PE Confirms the Estimate
The masking zone was computed by running the RAM PE parabolic equation solver to 100 km at the Vineyard Wind site using real CUDEM bathymetry and WOA2023 sound speed profiles. The RAM PE model shows that shallow-water propagation on the continental shelf maintains higher noise levels at long range than simple spreading laws predict — sound energy is trapped between the surface and the bottom, creating a waveguide effect. At 80 km, the received pile driving noise still exceeds the threshold for masking whale communication.
Actual RAM PE broadband output (azimuth 0, October SSP, CUDEM bathymetry). The oscillatory pattern is real multipath interference from shallow-water propagation — sound bouncing between the surface and seafloor creates constructive and destructive interference at different ranges. Source level: 210 dB SPLrms re 1 μPa (10–12 dB bubble curtain from ~222 dB unmitigated per Rand Acoustics).
Red shaded band: masking threshold uncertainty due to ambient noise variability (±10 dB per Wenz 1962). Quiet conditions (~95 dB ambient) shift the masking threshold down to ~105 dB, extending the masking zone beyond 100 km. Heavy shipping (~115 dB ambient) raises it to ~125 dB, shrinking the zone to ~55 km. The 80 km estimate uses moderate-condition ambient of ~105 dB.
11 Projects Tile the Entire Corridor
Each project creates a masking zone of approximately 80 km radius. The US East Coast has 11 active or permitted offshore wind projects spanning from Virginia to Massachusetts. The NARW migration corridor along this coast is approximately 660 km.
If even a fraction of these projects conduct pile driving simultaneously — which current schedules allow, since each IHA is reviewed independently — their masking zones overlap. With simultaneous construction at five or more projects, 100% of the 660 km migration corridor falls within at least one masking zone.
There is no quiet path. A right whale migrating from Cape Cod to Cape Hatteras would travel through continuous noise for the entire journey. It could not hear another whale at any point along the route.
How Much Quiet Shelf Remains?
With all 11 projects piling simultaneously, only 30% of the continental shelf between Virginia and Massachusetts falls below the masking threshold. The remaining 70% is acoustically compromised — whales in those areas cannot maintain the 8 dB SNR needed for call detection.
The 30% that remains quiet is concentrated in the deepest offshore areas and the far northern and southern ends of the shelf — regions where right whale density is lowest. The high-density habitat areas are the first to be masked because they overlap directly with the wind energy lease areas.
The per-project IHA evaluates whether one project’s shutdown zone overlaps with another’s. At 5.7 km, it never does — adjacent lease areas are 30+ km apart. At 80 km, every project overlaps with its neighbors. The regulatory unit of analysis is too small to see the cumulative impact.
This is not an argument against offshore wind. It is an argument for managing construction acoustics at the corridor scale, not the project scale. The transition to clean energy and marine mammal conservation are both essential. They can coexist — but only if the regulatory process looks beyond individual project boundaries.
RAM PE propagation · CUDEM bathymetry (31m res) · WOA2023 sound speed profiles · NARW upcall source level 160 dB · 50–500 Hz band · 8 dB SNR detection threshold · 11 active/permitted lease areas · Masking zone = 80 km radius per RAM PE