Paper presented at the Annual Meeting of the Society for Conservation Biology, Victoria, B.C., Canada, June 1997.
L.S. Weilgart and H. Whitehead
The noise that humans have been adding to the oceans has increased substantially since the industrial age. Mainly, this noise comes from shipping and boating, drilling for oil, seismic surveys, sonars, and ocean science studies. Because sound propagates so well underwater and light relatively poorly, many marine animals, particularly cetaceans, rely heavily on sound for all aspects of their life. As you know, cetaceans use sound for communication, prey and predator detection, and navigation. Recently, two new, very loud sources of noise have been added to the already noisy marine environment. These projects are problematic because they operate over vast scales of space and time, and because they have been launched with little justification.
One is the ATOC program which is an oceanographic project to measure ocean temperature using sound, and the other is the LFA sonar program which has recently been developed by the U.S. Navy to detect newer, quieter enemy submarines. ATOC, which stands for "Acoustic Thermometry of Ocean Climate", is a US$ 43 million project funded by the Pentagon, run by Scripps Institute of Oceanography. ATOC hopes to measure global ocean climate changes by making use of the fact that sound travels faster in warmer water. A global network of underwater speakers and receivers is proposed to measure the speed of sound (and thus ocean temperature) across whole ocean basins. ATOC sounds travel some 11,000 km across the Pacific, from California to N.Z. So far, two ATOC speakers have been placed on the ocean floor and have been given permits to operate for 2 years. The speakers are located off Kauai, Hawaii, and Monterey, California. The one off Monterey, California, has been operating from November 1995 until March 1997, when the undersea cable broke for unknown reasons. Long-range plans call for 12 additional speakers in all oceans of the world broadcasting for at least a decade.
The U.S. Navy's Low Frequency Active, or LFA, sonar program sends out very loud, low-pitched sound pulses from naval vessels and listens for echoes from enemy submarines. These 72-ton sonar systems are to be used in deep and shallow water world-wide, but perhaps especially near the edges of continental shelves. LFA sonar has been extensively field tested since 1992, mostly off the West Coast of North America.
How loud are these sounds? Well, if we compare them to the level that several species of whales and fish so consistently avoid, which is 120 dB re 1 microPa re 1 m, the ATOC signal at 195 dB is 10 million times louder, and LFA sonar at around 235 dB, 10 trillion times louder. (The decibel scale is logarithmic.) LFA sonar could place the hearing of marine life at risk over a radius of 25 km, and could alter the behavior of whales within a 500 km radius. This translates to an area greater than that of Texas. ATOC, which is quieter than LFA sonar, can still be heard above background noise in the deep sound channel over 1/4 of the whole Pacific Ocean. What are the effects on marine life? We don't really know. The U.S. National Research Council's Committee on Low-Frequency Sound and Marine Mammals concluded that the effects may "...range between potential hearing damage and gradual deafness for the entire species--and eventual extinction--or practically no discernible impact". However, we do know that a pilot study for ATOC found unequivocal evidence of behavioral effects on several whale species, including sperm whales, southern bottlenose whales, and pilot whales. These effects sometimes lasted days. We know that major studies on migrating grey and bowhead whales showed that these whales clearly changed the course of their migrations to avoid noise levels of about 120 dB. Grey whales, especially mothers and calves, cleared out of a breeding and calving lagoon for one month after being exposed to certain types of underwater noise. Belugas consistently avoided approaching icebreakers at ranges of up to 60 km, and took as long as 2 days to resume normal activities. The most serious effects of noise on biological populations are those which affect growth, reproduction, mortality, and other population parameters. Fish species exposed to noise showed lower growth rates and reduced egg viability; shrimp showed reduced growth and reproduction, and increased mortality as well. The Marine Mammal Research Program (MMRP) is an over $5 million program funded directly by ATOC, indeed is a part of ATOC, and it is charged with determining whether marine mammals are affected by the ATOC noise.
Unfortunately, the MMRP is structurally unable to detect any changes to any cetacean population parameters, even though these variables are ones likely to be affected by noise. These population-level variables such as birth rates and survival rates are the most essential indicators of the welfare of a population. ATOC's MMRP can only study short-term (over seconds-hours) changes in behavior or medium-term (over days-months) changes in distribution of only a few species of marine mammals. Short-term effects may or may not be detectable, and even if detectable, are not necessarily linked to the more important long-term consequences on populations. Thus determining whether ATOC is "safe" or not is an impossible task. Yet what action does one take in the face of this scientific uncertainty? Usually, there are calls for more research. However, when a science is as inexact as most studies of cetaceans, more research often just produces more complexity and ambiguity. Research on the effects of noise pollution is worthwhile, but it cannot provide us with the answers needed to safeguard marine life.
Instead, we propose a step-by-step process to consider projects that may provide benefits yet pose large-scale environmental risks:
1). Justify project. Strong justification for the need and benefit should be required for any project that is potentially devastating to the environment. From the outset, proponents should make a convincing case that there are no adequate, more benign alternatives. This is part of the U.S. Environmental Impact Statement process. Only if this can be done, should one proceed to:
2). Design the project to minimize potential harm. This can be done for projects like ATOC or LFA sonar by:
a) placing the sound source in areas of minimal ocean life, like the center of an oceanic gyre away from large oceanic islands. Productive areas rich in marine life should be avoided, especially coastal regions. As this Coastal Zone Color Scanner photograph shows, the vast majority of the ocean regions are deserts, with the principal exception being coastal waters. Whales also generally migrate close to shore. Unfortunately, both ATOC and LFA sonar are mostly being used in near-shore waters. At least in the case of ATOC, there is no ostensible need for a coastal location. Unbelievably, one of ATOC's underwater speakers was intended to be located in a National Marine Sanctuary before public opposition forced its relocation.
b) keeping sound sources deep, over 600 m, and steering them initially downwards. This avoids the most productive zones of the ocean. When feasible, the deep sound channel should also be avoided.
c) reducing the impact of the sound source to as small as possible, both over space and time. Obviously, one way of achieving this is by making the sound level as quiet as possible.
d) avoiding spatial and temporal marine mammal concentrations like migration routes, feeding aggregations, and especially, calving or mating grounds.
e) avoiding the use of mid-range frequencies like 1-10 kHz, preferably using extremely low frequencies (1-2 Hz or below) or extremely high frequencies (over 200 kHz).
f) turning sounds off when animals are detected (using high- frequency sonar or hydrophones) near the sound source.
After designing a project to minimize potential harm, one should: 3) Sponsor independent research on the effects of such sounds on marine life. We will be talking more about this topic of funding after the coffee break in another presentation. The project should provide a sum to an independent agency to fund peer- reviewed independent research into the effects of the sounds on marine life. An independent committee which has power should establish priorities for the research, commission it, review the results, and regulate the original project. MMRP scientists for ATOC sometimes found that their actual or perceived close ties to their paymasters, the ATOC oceanographers controlling the project, weakened their credibility. Finally, in deciding whether such environmentally-risky projects should proceed, the more prudent course of action follows the Precautionary Principle, where measures are taken to prevent harm even in the absence of conclusive scientific evidence. Perhaps in this way we can prevent marine life from being enveloped in an "acoustic smog" and minimize tinkering on such a grand scale with the world's oceans.
|
|
Last Updated April, 1998 by Sascha Hooker |