Research Finds Tidal Power Turbines Lead to Fewer Porpoises

Research Finds Tidal Power Turbines Lead to Fewer Porpoises

One of the ways to counter the climate change is by utilizing greener, renewably energy source like tidal power. Now, while tidal power enables us to steer away from burning fossil fuels and releasing more carbon dioxide, there’s a side effect.

At a tidal power site in northern Scotland, researchers did an experiment which showed that tidal turbines produce enough noise that leads to fewer harbor porpoises. This species is legally protected; while they’re generally considered “least concern” by the IUCN, populations in Baltic Sea and Western Africa are critically endangered.

Lead author Laura Palmer said, “When the turbines are operating, we’re detecting fewer porpoises.”

Tidal power vs porpoises

As a source of energy that doesn’t rely on fossil fuels, tidal power is one of the more preferred ones because it’s predictable, unlike wind or solar. This type of power employs spinning turbines anchored to the ocean floor to capture the energy from tidal currents.

Even though tidal power industry is relatively new, it’s developing quickly. One report predicted that global wave and tidal energy market, currently worth US $5.8-billion, could almost triple by 2026. But what’s the effect on this species?

In the study, Palmer and her colleagues placed hydrophones on a 1.5-megawatt tidal turbine to record the porpoises’ echolocation clicks. The turbine, one of four at the site, is equipped with 18-meter-diameter blades.

From October 2017 to January 2019, the hydrophones recorded a total of 814 porpoise detections. When the scientists analyzed the clicks, they discovered that the porpoises have been avoiding the turbines, particularly in areas with higher water flow rates.

They also found that the number of porpoise detections within 150 meters of the turbines went down by up to 78% on the flood tide. At the same time, the decrease goes up to 64% on the ebb tide. It remains unknown as to how many different porpoises were making the clicks.

According to the study, the turbines produced noise at a frequency of 20 kilohertz, and that falls in the most sensitive hearing range for harbor porpoises. Hence, they don’t want to go near the turbines.

This can mean two things: first, the porpoises know to stay away from trouble and the possibility of hurting themselves. Second, the turbines have strong impact on the critical habitat of this species that they could be driven to even more state of vulnerability.

 

a tidal power station in Kislaya Guba. Photo by Press-service of RusHydro Wikimedia Commons

 

Is there anything we can do?

Tidal turbines are placed within coastal areas with strong tides because these areas are ideal for generating electrical power. They’re not all bad, since these machines could also serve as artificial reefs and in turn offsetting their physical footprint. However, it potentially attracts foraging marine mammals.

Palmer encouraged further study to see if this effect happens in different places and in tidal power sites with more numbers of turbines as well as different configurations.

“We’ve looked at four turbines, but potentially there could be hundreds if this industry reaches its full potential. We really need to understand how that scale impacts cetacean behavior and risk of collision,” Palmer said.

Another limitation from this study is that it’s only limited to studying porpoises. Andrea Copping, a renewable energy expert (not involved in the research) said that the effect of tidal power turbines on other animals like harbor seals may be different and that it would need a different approach.

Unlike porpoises, harbor seals don’t communicate or vocalize with clicks. Therefore, studying them would need sonar or echo-sounding technology rather than hydrophones.

Copping said, “There’re a lot of these questions that are running around out there and they are very hard to pin down. We’re in new territory here.”

So unfortunately, we still don’t know the future of these harbor porpoises and probably other harbor-dwelling marine animals.

Although, news of noise affecting the marine life (and also land, actually) isn’t exactly new.

Aquatic/marine life and the impacts of noise

Temporary hearing loss as a result of excess underwater noise has previously been recorded in other marine animals like dolphins or whales, squids and fish. On the other hand, reptiles like aquatic turtles haven’t been widely studied nor understood. In this new research, it’s revealed that turtles can in fact experience this as well.

Study coauthor Andria Salas said, “Our study is the first to support that these animals are vulnerable to underwater hearing loss after exposure to intense noise.

“We have assumed that turtles experience hearing loss when exposed to sufficiently intense sounds as observed in other animals, but there hasn’t been any data collected specifically on turtles.”

Aquatic turtles rely on their underwater hearing so that they can navigate around and detect possible predators. Moreover, some species use underwater acoustic communication.

The results of this study bring forth the first evidence of underwater noise-induced hearing loss in turtle species. It also suggests that turtles may be more sensitive to sound than previously understood.

 

an aquatic turtle. Photo by angela n Wikimedia Commons

 

Experimenting on aquatic turtles

Salas and her collaborators conducted experiments on two non-threatened species of freshwater turtles. They used a minimally invasive device, inserted just under the skin above a turtle’s ear, to detect miniscule neurological voltages created by the turtles’ auditory systems when they hear sounds.

Before exposing the turtles to loud white noise (similar to the sound of radio static), they first determined the lower threshold of turtles’ underwater hearing and which tones (frequencies) they heard best.

After giving continuous noise to the turtles and removing turtles from it, the scientists didn’t stop measuring turtle hearing until about an hour to see how they recovered their short-term underwater hearing. Next, they checked back at the turtles to see if they’ve recovered.

The turtles always regained their hearing. However, the hearing loss could last for about 20 minutes to over an hour.

Sometimes, the hearing wouldn’t recover by the end of the testing hour, indicating that they needed more time to fully recover from the noise exposure. One turtle even experienced reduced hearing for multiple days.

Turtles hearing disturbed by low noise

The team didn’t expect that it’s not the type of high noise that impacted the turtles’ hearing. It was surprisingly a relatively low level of noise.

The noise exposure induces what is called a temporary threshold shift (TTS), which is the resulting decrease in the animal’s hearing sensitivity due to the noise.

“If this occurs in nature, turtles would be less able to detect sounds in their environment on these timescales, including sounds used for communication or warning them of approaching predators. Over half of turtle and tortoise species are threatened, and noise pollution is an additional stressor to consider as we work towards protecting these animals,” Salas said.

Associate scientist Aran Mooney added, “It was surprising that we found noise can induce underwater hearing loss in turtles, and then it was surprising that this hearing loss was at much lower levels than was estimated, so lots of surprises all around.”

Interestingly, in spite of the noise being loud enough to lose their hearing temporarily, the turtles either didn’t show a behavioral response or they knew how to keep their composure.

“Notably, this temporary hearing loss is a normal physiological phenomenon in animals. We now see it across the board (mammals, birds, fish, and reptiles). But importantly in this case, it can be a predictor of greater, more deleterious noise impacts such as permanent hearing loss or auditory damage,” Mooney continued.

 

Sources

https://www.smithsonianmag.com/science-nature/for-good-or-ill-porpoises-avoid-tidal-power-turbines-180979491/https://www.sciencedaily.com/releases/2022/03/220302190004.htm

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