Energy & environment

Save the porpoise

Offshore wind is widely considered a low-impact form of energy generation. However, the potential damage caused to marine life needs to be addressed. Dr Carol Sparling, Technical Director, SMRU Consulting, University of St Andrews, discusses the issues and explains 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 lower noise pollution and less chance of being termed an eyesore. It may also pose less harm to local ecosystems, with fewer birds and bats killed in turbine collisions.

However, when it comes to the impact on marine life, much remains unknown. Because this is a new and 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, Offshore Windfarm Egmond aan Zee. They found the farm “acts as a new type of habitat”, attracting some types of animal and detracting others.

As the authors explained: “The fish community was highly dynamic both 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.

Lingering worries

As Dr Carol Sparling, technical director of SMRU Consulting Europe at the University of St Andrews, concedes, 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 to before they were built,” she says. “They can function like marine protected areas, with turbine bases attracting fish and encourage 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 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 away 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, as it pertains 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 away 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.”

Unknown impacts

Unfortunately, there is a distinct lack of empirical data underlining the scale of the problem. Scientists don’t know how long the animals will be disturbed for, where else they might go, or what the eventual effect might be on individuals 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 compared to 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 worst affected – because they rely heavily on sound to navigate and communicate, 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 eight decibels, 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, harbor seals, minke whales, bottlenose dolphins and harbour porpoises) and set out a stochastic framework for modeling 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 being 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 the health of individuals. One particular areas of uncertainty is understanding how animals can cope with being disturbed by noise. Does this disrupt their feeding or breeding patterns and does noise effect different animals in different ways – e.g. 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 Assessements (EIAs) and Habitats Regulations Assessments (HRAs) wherever appropriate.

Prior to the closure of the Department of Energy and Climate Change, 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, like bubble curtains, to reduce the noise travelling out from the source.

At SMRU Consulting, Sparling and 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 some 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 rollout, the most ambitious of its kind on the planet, the environmental impacts will no doubt be subjected to ever greater scrutiny. And marine mammals and their wider ecosystem form an essential piece of that puzzle.

This article appears in the 2016 vol 2 edition of World Wind Technology

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