Save the porpoise – minimising acoustic disturbance to marine life9 December 2016
Offshore wind is widely considered a low-impact form of energy generation. However, the potential damage caused to marine life – particularly from acoustic disturbance during piling for the installation of turbines – needs to be addressed. Technical director Dr Carol Sparling of SMRU Consulting discusses the problems and what might be done to mitigate them.
With the UK a world leader in offshore wind, much has been made of the technology’s low environmental impacts. While it is considerably more expensive than onshore wind, it has the edge in various respects, not least the lower noise pollution and smaller chance of being termed an eyesore. It may also pose less harm to local ecosystems, with fewer birds and bats killed in turbine collisions, for example.
Yet, when it comes to the impact on marine life, much remains unknown. Because this is a nascent form of energy generation based on novel technologies and construction processes, it is still difficult to ascertain how certain marine species are affected.
In 2011, a Dutch study found that offshore wind turbines have “hardly any negative effects” on wildlife. The researchers had spent two years monitoring the first offshore wind farm in the Netherlands, Egmond aan Zee. They found that the farm “acts as a new type of habitat”, attracting some types of animals and repelling others.
As the authors explained: “The fish community was highly dynamic in time and space. Some fish species, such as cod, seem to find shelter inside the farm. More porpoise clicks were recorded inside the farm than in the reference areas outside the farm. Several bird species seem to avoid the park while others are indifferent or are even attracted.”Another study, published in 2014, reported that fish and crustaceans tend to cluster on the base of the turbines, creating an artificial reef effect that attracts seals in turn. In other words, the operational stage of wind farms appears to spell good news for marine mammals.
Dr Carol Sparling, technical director of SMRU Consulting, the commercial arm of the Sea Mammal Research Unit at the University of St Andrews, concedes that these positive impacts have been widely noted.
“A few studies have shown that some species are actually found in greater numbers in areas where wind farms have been built compared with before they were built,” she says. “They can function like marine protected areas, with turbine bases attracting fish and encouraging reef formation. The exclusion of fishing within wind farm areas also helps this effect.”
Unfortunately, some concerns remain in place, particularly regarding the construction stage. It is thought that the loud sounds emitted during pile driving could damage animals’ hearing and disorient them, affecting their navigation and leaving them vulnerable to predators. On top of this, marine animals may be injured or disturbed by ships during installation.
“Several studies have shown that several species of marine mammals are displaced from construction areas up to 25km away. Hearing damage is also a concern,” says Sparling.
Sparling has 20 years’ experience as a marine mammals scientist, with a particular interest in how these animals are affected by human activities. She has led multiple projects designed to quantify and interpret the impacts, and currently advises various offshore wind clients on approaches to sustainable development.
Her particular worry with regard to wind farms is displacement. This, she says, can potentially be a major issue if the wind farm is built in an area important for marine mammals – a well-used foraging or transit area, for example.
“We really don’t have a good handle on the consequences,” she explains. “If an animal has to swim around a construction site to reach a foraging area, the effect may be fairly minimal and only result in a short-term increase in energy expenditure, something the animal may be able to compensate for by foraging a bit longer or saving energy by swimming slower.
“But if an animal is displaced from an important area for feeding, it may not be able to find an alternative feeding area and this could result in a decrease in condition and even a decrease in the ability of the animal to breed or survive.”
Unfortunately, there is a distinct lack of empirical data underlining the scale of the problem. Scientists don’t know for how long the animals will be disturbed, where else they might go or what the eventual effect might be on individual animals or populations.
“It is thought that animals that need to eat regularly and have high metabolic costs, such as porpoises, might be more vulnerable to the effects of disturbance than a species that can store energy and undergo fasts, such as seals,” says Sparling. “In terms of hearing impairment, we have absolutely no idea what proportion of the population may have impaired hearing as a result of exposure to underwater noise, and we have absolutely no idea how hearing damage may affect their ability to feed, breed and survive.”
Again, it is porpoises that stand to be the worst affected; they rely heavily on sound to navigate and communicate, so they are likely to be worse off than seals, which use other cues. SMRU Consulting’s most recent study, backed by WWF-UK and published in September 2016, studied the effects of noise reduction on North Sea harbour porpoises. They found that if construction noise levels were lowered by just 8dB, the chances of stemming their population decline nearly doubled.
Along with colleagues at SMRU, Sparling has worked to develop models that might predict the effects of noise disturbance.
In one 2014 report, for instance, the team reviewed the potential threats to five marine mammal species (grey seals, harbour seals, minke whales, bottlenose dolphins and harbour porpoises) and set out a stochastic framework for modelling their population dynamics.
The consultancy has also carried out research concerning seals, specifically. Among other findings, the team has determined that seals forage around turbine bases; that during piling, seals could be exposed to levels of noise high enough to cause injury; and that seals will avoid piling noise.
Because the overall consequences for marine life are so mixed, the offshore wind industry needs to find ways to minimise the negative impacts on ecosystems while doing what it can to enhance the positives. But with research still in its infancy, more work needs to be done on unpicking the subtleties.
“We need to better understand the link between individual effects and if or how they scale up to affect the population,” says Sparling. “For individuals, we are focused on their ability to find food and breed, and their health. One particular area of uncertainty is understanding how animals can cope with being disturbed by noise. Does this disrupt their feeding or breeding patterns and does noise affect different animals in different ways? For example, are juvenile animals or calves and pups more susceptible to being disturbed?
“We need to better understand how noise affects different species as well – which species are most susceptible to noise and which ones are better able to cope and adapt.”
Of course, this is not to say the offshore industry can’t take certain practical steps in the meantime. It goes without saying that location is critical – developers need to site their windfarms away from areas important for marine mammals.
In the UK, developers are required to undertake Environmental Impact Assessments (EIAs) and Habitats Regulations Assessments (HRAs) wherever appropriate.
Prior to the closure of the Department of Energy and Climate Change (DECC), government guidance read: “We recognise that better evidence about the extent of the environmental impacts of offshore wind farms, especially on sensitive receptors such as mobile species, is of prime importance, and DECC continues to fund research to fill these strategic evidence gaps.”
Developers might also consider taking measures to reduce noise. Take suction bucket foundations, for instance, which have been widely praised for their cost-effectiveness. They also benefit from quick, low-noise installation, which leads in turn to lower acoustic disturbance. On a similar note, there is a case to be made for floating wind farms, which don’t require piled foundations. Alternatively, developers might alter their piling schedules or install technology, such as bubble curtains, to reduce the noise travelling out from the source.
At SMRU Consulting, Sparling and her colleagues are working hard to develop their population consequences of disturbance (PCoD) model, with a view to improving its constituent elements.
“We have the overall goal to make it more robust, but also to understand what kinds of models could be used for different species,” she says. “We are also carrying out strategic seal monitoring with a number of offshore wind-farm developers to learn more about the seal populations themselves as well as the direct effect of wind farms.”This kind of work is likely to prove increasingly critical in the years to come. As the UK continues with its offshore wind energy roll-out, the most ambitious of its kind on the planet, the environmental impacts will no doubt be subjected to ever greater scrutiny. Marine mammals and their wider ecosystem form an essential piece of that puzzle.