Photo: Chris Johnson
September 6, 2002
"Noise Pollution: Part II"
This is Roger Payne continuing with comments on ocean noise and whales
Various interest groups hotly dispute whether noise pollution is having a serious negative impact on marine mammals. Unfortunately all we can say with confidence at the moment is that we don't know. However, it is thought that the potential effects may range from minor behavioral disturbance to severe injury-perhaps even death. The possible seriousness of these threats to marine mammals has sparked deep public concern and debate.
At present this issue is caught up in an unfortunate 'catch 22'. If we would protect marine mammals that are threatened by noise pollution, we need to hold ships to noise standards. However these standards must be based on established scientific facts about the acoustic systems that marine mammals like whales, have, and currently there are too few such facts. That means that standards for ships cannot be put into place yet.
Sound levels are measured by the decibel (dB) scale. This is logarithmic scale, meaning that the difference between 160 and, say, 170 decibels is a ten fold increase in loudness of the sound (not merely an increase of 10 arithmetical-i.e. linear-units). Recent U.S Navy sonar testing in the Bahamas reached sound levels of 235 decibels above the human threshold of sound (as measured a yard from the source). Underwater, a sound intensity of 180 decibels on this same scale visibly affects human lung tissue as bruising. However, such human references are not necessarily helpful as a guide. For example, a blue whale call is very loud: approximately 190 - 195 decibels-an intensity that would be harmful to humans but apparently has no deleterious effect on the whales that make these sounds. There is little doubt however, that if manmade sonar is intense enough it can harm any mammal in its path.
Darlene Ketten, who holds a joint appointment at Woods Hole Oceanographic Institute and Harvard University Medical School, studies ear anatomy of whales and porpoises. She investigated a high profile U.S. Navy sonar testing case a couple of years ago where 16 whales-mostly beaked whales-beached themselves. Six died, and the rest were pushed back into the sea-their fate unknown. These whale deaths and the possibility that sonar may be responsible triggered a storm of controversy that has yet to be settled. Ketten became frustrated when she was pressured by government agencies and conservation groups to come up with definitive answers.
Although she did find hemorrhages in the ears, and in the acoustic fats of five of the dead whales, Ketten refused to jump to conclusions. Instead, she stuck to her valid claim that more work needs to be done before the cause of death in this case could be known. She would not state conclusively that the sonar testing was responsible. Instead, she emphasized that although the injuries were consistent with acoustic or impulse trauma, which probably did cause the animals to strand, the ear injuries did not kill the whales.
Together with the Navy, the National Marine Fisheries Service and the National Oceanic and Atmospheric Administration, Ketten put out a joint report recommending further research to prevent such incidents in the future. Everyone hates to wait around while further research is done, but if we are to base our actions on rational causes, it is absolutely necessary that we be patient in cases such as this one
It is encouraging to see that following this event, other countries such as Australia are now taking precautionary measures in relation to Navy sonar testing. The willingness of the military and of governments to recognize that this problem may be serious is a giant leap forward. However as Ketten points out, determining whether humans indirectly cause the death of any sea creature is an enormously difficult task and can be expected to take a long time.
Although it has been largely ignored to date it seems likely that increasing ships' traffic should probably be of great concern. Shipping lanes across the globe are crowded with tankers that generate low-frequency noise which may be harming marine mammals, and doing so on a daily basis. However, from watching the way marine mammals act in the presence of such sounds, scientists are unable to ascertain whether the sounds pose a significant harm. For example dolphins have been known to ride the bow waves of military vessels while the sonars on those vessels were operating at high intensities. Could this be comparable to the effects of industrial noise on humans? Countless people work in noise environments that may be harmful, they also voluntarily attend rock concerts which are so loud they may cause permanent hearing loss (and sometimes do). It is still to be determined whether marine mammals are sustaining hearing damage without displaying behavioural reactions that we can recognize as being indicative of that fact.
"Masking", the covering up of one sound by another, is probably one of the most serious effects of loud sounds in the environment. Masking by ships' traffic noise must shorten the distance over which animals can communicate, and may therefore jeopardize their ability to locate one another to mate.
The problem with all of these concerns is that even when we can accurately describe some potentially destructive loud sound, it is seldom possible to know whether it is, in fact, a significant problem to a whale. The ears of all mammals have an enormous dynamic range. They can survive such insults as violent blows to the ear during a fight, yet also be able to detect sounds so faint they move the eardrum only half the diameter of a hydrogen molecule-a single Angstrom unit. This underlines the fact that one of the most important characteristics of an ear is its resilience-indeed, as we should expect it to be. For it is inevitable that mammalian ears have always been exposed, at least occasionally, to stupefyingly loud sounds-not just direct blows to the ear, but roars, shrieks or shouts from a few inches away; earthquakes (particularly underwater), close lightning strikes, etc. If each of these acoustic insults resulted in a significant hearing loss, the majority of animal species that live longer than a few years should have impaired hearing. However, the evidence does not support this scenario. Which makes it difficult to know whether things that seem self-evidently to be major threats to the hearing of mammals like whales really are. That means that just as it is important to invoke the Precautionary Principle on behalf of safeguarding whales from the loud sounds we make, we must also invoke the Precautionary Principle when faced with the temptation of jumping to the conclusion that all loud noises are a problem to marine mammals such as whales.
This is Roger Payne wishing you, once more, a quiet and peaceful world, far from industrial noise.
The effects of manmade noise on marine mammals
Edited by: Roger Gentry, (NOAA) Fisheries Marine Acoustic Program.
"Do we kill whales with sound?"
Susan McCarthy, Discover magazine, April 2002.
© 2002 Written by Roger Payne
Research by Genevieve Johnson