How does anthropogenic or human-generated underwater noise impact marine mammals and the environment? Policymakers and regulators currently have to work on the basis of limited research data. Their hands will be tied until this question can be answered in greater detail. However, more and more useful discoveries are being made all the time. Motivated by a wish to share these discoveries, TNO took the lead role in staging an international conference (ESOMM-2018).
One hundred and seventy people from fifteen different countries attended the 6th International Meeting on the Effects of Sound in the Ocean on Marine Mammals (ESOMM). The conference was held in The Hague ?, in the Netherlands, from 9 to 14 September 2018. The participants included scientists and leading parties from the naval community, plus – for the first time – experts from the oil and gas industry. They, like the navies, are keen to limit any potential impact and damage as much as possible.
The limits of noise pollution
Since the start of the industrial revolution, there has been a huge increase in underwater noise. Ships have become much noisier, and their numbers have increased enormously. Other types of sound have also been added to the mix. In an international setting, TNO is researching the effects of underwater noise pollution caused by the five main sources of human-generated noise. These are shipping, seismic surveys for the oil and gas industry, offshore construction activities (such as pile driving at sea for the construction of offshore wind farms), military sonar systems, and the use of explosives.
“Our concern is that loud noise interferes with marine mammals’ feeding or reproduction. However, it is difficult to obtain hard data on this”
Are marine mammals eating less?
“We originally believed that loud noise was dangerous, and that it could inflict direct physiological injury. We thought this was why the bodies of marine mammals in some cases were being washed up on beaches. But we’ve found that this is rarely the case”, says TNO’s Frans-Peter Lam. “Our current assessment is that loud noise does affect them – by interfering with their feeding or reproduction. However, it is difficult to obtain hard data on this. With issues like noise pollution near airports, you can conduct a survey among local residents or set up a complaints line. This is not an option for the inhabitants of the underwater world.”
Behavioural studies and hearing tests
There are three main lines of research into these animals’ responses to noise. Lam: “We can go along on naval exercises to monitor the movement of animals into and out of the area. That option most closely reflects the real situation, but at the same time it is very difficult to track the movements of every single animal. We can also conduct behavioural studies or hearing tests on animals in captivity, such as rescued seals and porpoises that had become stranded. Indeed, our research efforts in this area do include joint studies of this kind. This method involves quite effective controls and provides a lot of useful information. The snag, of course, is that it is difficult to estimate how the results correspond to real-world situations, in open water.”
“Working from a research ship, we attach transmitter tags to whales by means of suction cups. In this way, we can monitor their responses to sonar or other noises”
Listening in with the whales
Most researchers tend to steer a middle course. “We have been conducting research in Norway for more than ten years, in the context of the 3S project. Our partners include universities and institutes from the United Kingdom, France, Norway and the USA. Working from a research ship, we attach transmitter tags to whales by means of suction cups. These devices record movement and sound, enabling us to ‘listen in’ with the animal. In this way, we can monitor their responses to sonar or other noises. Those experiments still involve reasonable controls, even though the animals are in their normal environment. In this way, we have collected data on the behavioural responses of killer whales, sperm whales, long-finned pilot whales, humpback whales, bottlenose whales, and common minke whales.”
“One discovery that could be of practical use to the oil and gas industry is that low-pitched humming sounds travel further than high-pitched whistling sounds. It would pay out to screen out the high-pitched sounds”
Discoveries for the marine and oil and gas industry
TNO uses the knowledge it has acquired and the discoveries it has made to develop mitigation software for the navy. “Each mammalian species has a different level of sensitivity. So you have to use different sonar settings for each habitat and each season”, Lam explains. “For example, the navy could reduce the volume or duration of its sonar operations, or it could re-schedule the exercise. One discovery that could be of practical use to the oil and gas industry is that low-pitched humming sounds travel further than high-pitched whistling sounds. The equipment this industry uses to survey areas for new reservoirs generates both types of sound, but only the low-pitched sound is actually needed. So it would pay out to screen out the high-pitched sounds.”
New trend in sonar
Traditionally, sonar has used pulses of sound. However, the latest technology uses continuous sound, to deliver a constant stream of data. These new systems have a wider dynamic range, so the navy can transmit signals continuously and simultaneously listen to the echoes. Because the data stream is continuous, modern systems can use much quieter sonar signals. “At the end of the day, however, we still don’t know whether this is better or worse”, warns Lam. “The disturbance impacts a smaller area, yet continuous sound can still be very distressing. What we need is a better understanding of the entire picture. This will enable us to operate these new, promising, continuous sonar systems in a responsible manner.”
Do you want to know more or do you have a question about this TNO research? Please contact Frans-Peter Lam.