Tidal flow can mask porpoise clicks by 29 dB

Estimated reading time: 4 minutes · Last updated: 11 September 2026

Tidal flow noise can swamp the echolocation clicks used to detect harbour porpoises, Veneruso et al. (2025) report: flow-related sound levels shifted by up to 29 decibels over a 12-hour tidal cycle and varied across distances under 1,640 feet. That degree of masking skews passive acoustic monitoring, the standard method for tracking porpoises, and risks undercounting animals where tidal turbines are planned. The study appears in Journal of the Acoustical Society of America (vol. 158, no. 4, pp. 2883–2891; DOI 10.1121/10.0039560) and recommends adaptive detection thresholds and closer microphone spacing to restore data accuracy.

Why tidal monitoring matters for marine renewables

Offshore renewables are expanding because onshore options are constrained. The material notes a prospective clean power capacity of almost 5 terawatts available from coastal waters and says global offshore wind capacity has exceeded 92 gigawatts, with modern turbines averaging over 10 megawatts each. That surge is driven in part by rapid electrification: the source text reports data-centre power needs rise by nearly 20 percent each year. Tidal turbines sit beneath the surface and tap predictable currents, but their deployment intersects habitats used by cetaceans. Accurate monitoring of where and when animals are present is therefore a prerequisite for credible environmental impact assessments and permit decisions.

How tidal flow noise hides porpoise clicks

Veneruso et al. measured underwater sound across tidal cycles and found the movement of fast currents stirs sediment and generates flow noise (turbulence) that interferes with biological signals. In their high-energy site, background levels shifted by as much as 29 decibels over a 12-hour cycle. That variation was not uniform: it changed with distance, with differences detected across ranges under 1,640 feet, and the elevated flow noise overlapped the frequency and amplitude of harbour porpoise echolocation clicks. The practical result is that passive acoustic detectors register fewer clicks at times or locations where porpoises may in fact be present, producing spatial and temporal blind spots in datasets used for impact assessment.

What this means for impact assessments and permitting

When passive acoustic monitoring undercounts animals, environmental assessments can understate site usage and risk. The authors warn that data which do not account for intense flow noise will misrepresent where and when marine mammals use an area, a consequence that could affect mitigation measures and regulatory decisions for tidal projects. Because tidal energy is still emerging, the baseline understanding of its ecological effects remains limited; the study highlights a methodological gap rather than documenting a direct turbine impact. Until monitoring protocols incorporate flow-noise effects, comparisons between sites or between high- and low-flow periods will risk systematic bias.

Practical fixes and next research steps

Veneruso et al. offer two concrete adjustments that can reduce the masking problem: use dynamic detection thresholds that adapt to changing local currents, and place passive acoustic microphones closer together to capture spatial differences in sound. These changes lower the chance that a temporary rise in flow noise will drop click detections below a fixed threshold. The paper is explicit that implementing adaptive thresholds and tighter sensor spacing will improve data accuracy in high-energy tidal zones; it stops short of claiming a single universal configuration, indicating instead that deployment should be tailored to local current regimes and sediment conditions.

Outlook: the case for and against rapid methodological change

The bottom line

Tidal flow noise is not an abstract measurement problem: in a high-energy site Veneruso et al. observed changes up to 29 decibels over a 12-hour cycle, enough to mask harbour porpoise clicks across ranges under 1,640 feet. That masking undermines passive acoustic monitoring unless surveys adjust thresholds and sensor layouts to local currents. For developers, regulators and conservationists the takeaway is procedural: build monitoring that detects animals under realistic noise conditions rather than assuming a fixed background. Doing so will make impact assessments for tidal turbines more defensible and better aligned with marine life protection.

What to watch

• Watch for follow-up field studies that test adaptive detection thresholds at multiple high-energy tidal sites; no date has been set.
• Watch for monitoring protocols from regulators or consortia that specify microphone spacing and adaptive processing to account for tidal flow noise; no date has been set.