Directional hydrophone clusters reveal evasive responses of small cetaceans to disturbance during construction at offshore windfarms

Abstract

Mitigation measures to disperse marine mammals prior to pile-driving include acoustic deterrent devices and piling soft starts, but their efficacy remains uncertain. We developed a self-contained portable hydrophone cluster to detect small cetacean movements from the distributions of bearings to detections. Using an array of clusters within 10 km of foundation pile installations, we tested the hypothesis that harbour porpoises ( Phocoena phocoena ) respond to mitigation measures at offshore windfarm sites by moving away. During baseline periods, porpoise movements were evenly distributed in all directions. By contrast, animals showed significant directional movement away from sound sources during acoustic deterrent device use and piling soft starts. We demonstrate that porpoises respond to measures aimed to mitigate the most severe impacts of construction at offshore windfarms by swimming directly away from these sound sources. Portable directional hydrophone clusters now provide opportunities to characterize responses to disturbance sources across a broad suite of habitats and contexts.

Characterising Underwater Noise and Changes in Harbour Porpoise Behaviour During the Decommissioning of an Oil and Gas Platform

“…4 provides an average response over the entire five-day event. In future studies, fine-scale responses to these and similar activities could be explored using alternative methods, either by logging techniques applied to individual marine mammals (Wisniewska et al, 2018), or finer scale passive acoustic monitoring methods (Graham et al, 2023).…”

Automated Detection and Tracking of Marine Mammals in the Vicinity of Tidal Turbines Using Multibeam Sonar

“…As increasing numbers of structures associated with marine renewable energy are installed in our oceans, it is important to understand how animals behave in these changed environments. Noise disturbance during the construction phase is clearly a cause for concern [1][2][3] and is known to cause temporary displacement from construction areas [2,4,5]. Conversely, there is compelling evidence that some structures may be creating artificial reefs, which can make a preferential foraging ground for some marine mammals [6].…”