A really interesting new study from our colleagues at the Sea Mammal Research Unit has predicted the potential for hearing loss from exposure to wind farm construction noise.
The study led by Dr. Gordon Hastie (a former founding member of the SMRU Consulting science team) used special GPS tags to understand how seals move through the environment off the east coast of England – a site of offshore wind farm development:
“Although hearing studies highlight the potential risks to marine mammals from acoustic exposure to pile driving, there is currently no empirical information on the at-sea proximity or the durations of exposure to pile driving, or movements and dive behaviour of seals during pile driving. Such information is critical to understanding the true risk of pile driving sound to seals.”
Crucially the tag data, coupled with information on the piling activity (31 x 5.2 metre diameter monopiles were installed – see video below for example) allowed the researchers to explore how seals moved with respect to the noise and to predict how noisy the piling noise was to the seals as they moved laterally and dived through the water column (for information on SMRU Instrumentation‘s awesome tags and the cool stuff they’ve done elsewhere check out their site). The noise level predictions were validated using recordings made during the installation of one of the piles.
Of the 24 seals they tagged, the closest distance to the piling ranged between 4.7 – 40.5 km from the piling location and the researchers predicted that over half of the individual seals exposed to piling noise were at levels higher than established noise criteria for hearing damage. This means that pile driving noise could be sufficient to cause hearing loss in harbour seals. It should be noted that only 20% of the seals tagged in the study went closer than 10 km to the piling activity. In addition, the authors were keen to point out that this was a prediction exercise and as with every set of predictions, they carry with them uncertainty. Please check out the ‘Discussion’ section of the paper for a details exploration of the factors that should be considered. They include uncertainty in the noise prediction methods, the metrics used to calculate exposure, how quickly seals could recover to exposures and the brief impulsive nature of pile driving sounds.
Of course, it must also be noted that hearing loss does not necessarily mean that the animals become completely deaf. Unfortunately, we don’t know a lot about whether any kind of hearing loss causes a meaningful effect on life history (e.g. reproduction or finding food). Questions also still remain about whether a potentially small number of animals suffering some form of hearing loss has a bigger or smaller impact than a larger number of animals being disturbed or displaced from an area. It’s also unclear from this study whether the tagged seals showed any kind of overt behaviour in response to the piling noise.
The authors also note that:
“Ultimately, information on population-level impacts of exposure to pile driving is required to ensure that offshore industry is developed in an environmentally sustainable manner.”
This could be assessed using frameworks such as the Moray Firth Seal framework developed by the University of Aberdeen, SMRU Consulting, Subacoustech and Natural Power and the interim PCOD framework.
The paper, published in the Journal of Applied Ecology can be (and should be) read here and is cited as: Hastie, GD , Russell, DJF , McConnell, BJ , Moss, S , Thompson, D & Janik, VM 2015, ‘ Sound exposure in harbour seals during the installation of an offshore wind farm: predictions of auditory damage ‘ Journal of Applied Ecology , vol 52, no. 3, pp. 631-640.
Check out a video of a different pile driving activity (in the Gulf of Mexico) below: