We’d like to let you know about a new publication, authored by researchers from SMRU Consulting, the Sea Mammal Research Unit, and a couple of PAMGuard programmers. Our paper presents findings from the first in-situ passive acoustic monitoring array for marine mammals at an operational tidal turbine in Ramsey Sound, Wales, UK. This post reviews our findings, and then provides a link to providing some sample code for underwater noise analysis.
Ambitious renewable energy targets to reduce carbon emissions have prompted the progression of the marine renewables industry. Energy from tidal turbines (akin to an underwater wind turbine, Figure 1) is seen as attractive because it’s a predictable and sustainable form of energy; the sun doesn’t always shine and the wind doesn’t always blow, but the tide always flows. Many tidal energy projects around the world are in their early stages.
However, we should monitor how such devices could impact marine life; it’s awesome if it’s a carbon-free, green energy option, but harder to view as ‘green’ if it operates at the expense of harming marine life. Some conservation concerns have been raised because animals could collide with turbine blades, or perhaps any noise generated by the device could drive animals outside of these areas (or maybe not). Since only a handful of turbines are actually in the water, and even fewer have been monitored regarding these effects, there are a lot of unknowns.
So how do we address these uncertainties? By using state-of-the-art monitoring equipment (both passive and active acoustics) to check out how animals are moving and behaving in the vicinity of the tidal turbine. This was a challenging task, whose development and analysis built upon methods developed for the fine-scale tracking of echolocating animals in 3D using passive acoustics, and trialling these methods on a multi-channel static array in a tidal rapid site.
Our publication focused on the passive acoustic monitoring component of this environmental monitoring. This included the installation of a PAM array, comprising 4 clusters of groups of 3 hydrophones, atop the base of the seabed-mounted turbine (Tidal Energy Ltd.’s DeltaStream turbine). These were all connected to a data acquisition system installed inside the turbine, which was in turn connected to a PC back ashore via a 3 km long optical fibre. This PC ran the opensource PAMGuard software to process the data in real time to detect, classify, and localise echolocating porpoises and dolphins.
We found examples of porpoises closely approaching the turbine and then veering sharply left/right of the turbine. In these instances, the porpoise likely detected the turbine both actively with its biosonar, and passively from the low-frequency clanging sounds that the turbine made. Since the porpoise would have been able to detect the turbine with its echolocation from father away, these close approaches (<15 m) could be an example of investigatory but cautious behaviour. We also recorded a dolphin directly buzzing on one of the hydrophones, potentially actively inspecting this foreign structure.
We then examined patterns in porpoise presence at the tidal energy site using GAM-GEE models and found that porpoises were most likely to be acoustically detected during the night, when low-frequency noise levels in the environment were low, when the moon was nearly full, and during ebb tide (at least at our study site in Ramsey Sound, Wales – *caution* in extrapolating this to other sites). Sadly, the turbine wasn’t rotating very often, so we were not able to adequately assess and compare the movements and behaviours of porpoises/dolphins around the turbine when it was rotating vs. not rotating.
The story doesn’t end just yet: SMRU Consulting alongside colleagues at the Sea Mammal Research Unit, have been building upon the lessons learned from this project to inform the environmental monitoring (currently underway) at the MeyGen tidal energy project in the Pentland Firth.
Read our publication here:
Malinka CE, Gillespie DM, Macaulay JDJ, Joy R, & CE Sparling (2018). First in-situ passive acoustic monitoring for marine mammals during operation of a tidal turbine in Ramsey Sound, Wales. Marine Ecology Progress Series 590: 245-266. (DOI: https://doi.org/10.3354/meps12467).
Check out this complementary post:
Check out the Coding for Conservation blog about how we used PAMGuard’s MATLAB library to conduct our noise analysis.
Feel free to get in touch with her here:
chloe.e.malinka -at- gmail.com