A very unusual experiment took place in a chilly Scottish loch 50 years ago. Conducted by an eminent fish scientist who was later honoured by Britain’s Queen Elizabeth II, the results of the experiment were kept secret for many years. But they added to the growing body of scientific knowledge about the harmful impact of man-made underwater sound waves and pressure on our increasingly noisy planet.
The year was 1970. Labour Party leader Harold Wilson was about to make way for Conservative prime minister Ted Heath and the supersonic Concorde passenger jet had just completed its first test flights.
Travelling at more than twice the speed of sound, the Concorde generated sonic booms capable of shattering window panes and cracking building plaster. Understandably, there was some disquiet around what this new form of noise pollution meant, not only for people but also for wildlife and the wider natural environment.
Before getting into the nitty-gritty of the experiments conducted at Loch Torridon off the northwest coast of Scotland five decades ago, by fish bioacoustics expert Anthony “Tony” Hawkins, it’s worth remembering that sound travels nearly 4.5 times faster through water than through air and is also transmitted over greater distances.
Also consider that, unlike elephants and other land animals with big ears, fish do not require outer ears because their bodies have a similar density to water, with sound travelling directly through their bodies to reach their inner ears.
So, while the din of modern cargo and passenger ships churning their way through the world’s shipping lanes might not be a source of disturbance for humanity, try to imagine the amplified sound of giant propellers beneath the sea. Or the sound of pile-driving, seismic blasting by the oil and gas industry. Or underwater vibration from “green” offshore wind farms.
Growing noise levels
Six years ago, as part of Operation Phakisa, former president Jacob Zuma announced plans to drill at least 30 deepwater oil and gas exploration wells as part of a multibillion-rand plan to exploit offshore fossil fuels along the country’s 3 000km coastline.
More recently, Minister of Environment, Forestry and Fisheries Barbara Creecy has cleared the way for energy firm Sasol and Italian oil company Eni to drill up to four deepwater exploration wells off the KwaZulu-Natal coast. The Petroleum Agency of South Africa has also granted exploration rights or cooperation permits to several local and multinational groups (see map), although environmental management plans to limit marine sound disturbance do not appear to be based on research conducted in unique South African conditions.
Why is it increasingly crucial to understand the effects of growing noise levels on fish? For Hawkins and fellow bioacoustics expert Arthur Popper, the answer is simple. “Anything that impairs sound detection can impair the fitness and survival of several fish species,” they told delegates at the Conservation Symposium and African Bioacoustics Community meeting, which was hosted online from South Africa between 3 and 9 November last year.
In a joint keynote address, Popper and Hawkins said research about fish and sound has advanced considerably over recent decades. But there are still “major gaps in our knowledge”, particularly around the more subtle biological impacts, the effects of underwater particle motion and whether current guidelines to regulate noise in different parts of the world’s oceans are still appropriate.
Popper, an emeritus professor in the American University of Maryland’s biology department, said most primitive fish evolved in murky water and needed to detect critical signals in the world around them to hunt other fish or avoid being eaten.
While it is well known that whales and dolphins can sing or transmit clicking noises to communicate with each other, a lesser-known fact is that more than 800 fish species produce a variety of knocking or grunting sounds.
Goldfish, for example, can hear quite well, but they don’t make sounds to communicate with each other. Haddock, however, are quite noisy fish and produce a range of sounds, especially when spawning. The noises are generated by contracting and expanding a band of muscles surrounding their swim bladders.
Hawkins discovered that male haddock emit a “humming” sound while mating
To get a better handle on sound effects, fish researchers conducted a number of behaviour tests in the 1950s, in which fish were trained to respond to various sounds. Later tests involved creating artificial sound barriers in marine tanks to study changes in the breathing and heart rates of fish.
By necessity, most of these experiments were done in laboratory tanks. But there were question marks about the usefulness of some of these tests as it was not possible to replicate sound moving in several different directions in a natural sea environment.
This is one of the reasons Hawkins and some of his colleagues conducted numerous tests in Scottish lochs – lakes or areas of sea surrounded by land – to reflect more natural conditions. While some of the tests were designed to improve catch rates by trawl fisheries, there were other tests to protect fish resources.
This is where we return to Loch Torridon and the secret “Concorde test” of 1970.
Writing in the June 2020 issue of ICES Journal of Marine Science, Hawkins and fellow scientist Colin Chapman recall that a number of experiments on fish, lobsters and shellfish were conducted by British and foreign researchers in the 25km-long loch between the early 1960s and 1993. The Marine Laboratory Aberdeen (MLA), which fell under the Department of Agriculture and Fisheries for Scotland, coordinated the experiments.
Hawkins – who later became the director of the MLA and was honoured as a Commander of the Order of the British Empire in 2000 for his service to education and science – recalls that several nations were reluctant to allow Concorde to fly over their land because of the sonic booms created when the new Anglo-French jet shattered the sound barrier.
Though Concorde air routes would generally be restricted to ocean crossings between London/Paris and New York, some fishers raised objections about the possible impact on fish.
“In 1970, we were asked to measure the underwater sound levels from the sonic booms, and to consider whether they would affect fish behaviour. Concorde’s test flights passed over Loch Torridon and we were able to measure the underwater sounds from the sonic booms.”
Hawkins and Chapman said the sounds reaching the fish were made up of two “double pulses”, one passing through the water and the other generated by substrate, or underground, transmission.
In their recent journal article, they reported a “dramatic slowing of the heart rate” of cod when the Concorde flew over Loch Torridon.
“Anthony was invited to talk to the airlines about the effects of supersonic aircraft upon fishes, and informed them that such aircraft could have detrimental effects upon fishes. Following the crash of an Air France flight [in July 2000], the Concorde was later abandoned.”
Now it has emerged that the results of those tests were suppressed.
A change in heartbeat
“The government that employed me stopped me publishing a paper I had written that described the response of a cod to the Concorde sounds. They were afraid that some countries would prevent Concordes flying over their seas, because the flights might have adverse effects upon fishes and fisheries,” Hawkins replied when asked how British Airways (BA) management responded to the concerns he raised at the time.
“However, I was invited to give a lecture to British Airways pilots on the responses of fish to the Concorde sounds, and they told me that some countries were already objecting to Concorde aircraft flying close to their countries.
“I had been asked originally to observe the effects of the sonic booms from Concorde on fishes, and BA flew one of their Concorde aircraft over Loch Torridon. I recorded the heartbeats of a cod placed in a cage on the seabed, and when the sonic booms arrived as double pulses, one through the water and the other through the substrate, the heartbeats changed.”
Hawkins, now the head of Aberdeen-based private consultancy group Loughine, remains adamant 50 years later that sonic booms “definitely affected the cod adversely. It was especially interesting that the boom transmitted through the seabed, as vibration, was larger in amplitude than the one travelling through the actual water. I think that the boom entered the ground on land and then travelled into the sea as substrate vibration.”
Underwater noise variation
Hawkins and Popper are writing a new paper on the effects of substrate vibration on fish as they say the impact of particle motion on fish and invertebrate creatures is often ignored, although such vibrations could affect them.
Hawkins said modern installations such as offshore wind turbines also generate substrate vibration.
Popper told the symposium that there should not be a uniform, “one size fits all” approach when setting standards to regulate underwater noise from human activity. This is because sound has differing effects on marine species scattered widely around the world, all with significant physiological differences. Noise can also be more harmful at a particular stage in the lifecycle of fish, especially with sensitive eggs and larvae.
At the extreme end of the spectrum, very intense underwater sounds can kill fish. Other noises can result in temporary hearing loss and internal haemorrhage to the eyes and inner organs of fish. Or there can be more subtle effects by “masking” or drowning out vital sound cues or communication signals between marine creatures.
Popper said noise from shipping traffic has roughly doubled in recent decades and this could drive fish from some of their spawning grounds. Pile-driving around coastal settlements, offshore oil rigs, seismic airgun blasting and wind farms have created further disturbances.
He made the point that while additional noise is not “good”, not all human-generated marine noise is necessarily harmful, as fish ignore some of these sounds, become habituated to them or recover quickly from non-mortal injuries.
The real impact
Yet, after many decades of extensive research, Hawkins and Popper say there are still too many unanswered questions and still a long way to go towards properly understanding the real impact of underwater noise on fish.
In a joint review article published last year, the two men with arguably the most experience in this field put it this way: “There are so many information gaps that it is almost impossible to come to clear conclusions on the nature and levels of anthropogenic sound that have potential to cause changes in animal behaviour, or even physical harm.”
There are several reasons for this, including the fact that most laboratory studies have focused on goldfish – and even these studies have produced wide variability by different investigators.
There has also been an undue focus on charismatic sea mammals such as whales and dolphins, rather than the wider ecology.
“Most of the concern by regulators and others has focused upon effects upon marine mammals and other protected species. However, examining the impacts upon the overall ecology of affected habitats is also important as it may be dominated by effects upon the far larger biomasses of fishes and invertebrates, which do not have the same degree of legal protection.”
Another shortcoming is that most research has focused on sound waves rather than particle motion or pressure changes within water bodies, as shown during the suppressed Concorde experiment.
“Sound consists of a travelling energy wave, within which the component particles of the water are alternately forced together and then apart. The to-and-fro motion that constitutes the sound, referred to as the particle motion, is accompanied by an oscillatory change in pressure above and below the local hydrostatic pressure, defined as the sound pressure. Both the sound pressure and the particle motion are important to fishes, although while all fishes detect and use particle motion, only a subset can detect sound pressure.
“A major contribution to this problem is that it is very hard, if not impossible, to accurately predict or even measure the particle motion components of the sound field in tanks … As a consequence, few fish hearing studies have been carried out under acoustic conditions that allow for accurate determination of the sound field.”
Overall, they conclude that: “The vast majority of studies to date have been done in ways, and under conditions, that result in data that may be less than useful in helping to understand what – and how – fishes hear, and the potential effects of anthropogenic sound on fish hearing and behaviour.”