There are many factors that influence if and how much a sound source affects marine animals. How loud the source is, what frequencies it transmits, where it will be used, and what species might be in the area are all factors that need to be considered. This process is called ecological risk assessment. The first step is to define the problem. This involves determining what might cause ecological effects. The next stage involves two steps, estimating the probability of being exposed to the problem and, based on that exposure, determining the types of ecological effects that are expected. Based on these results, the risk can be estimated.
In order to determine if a specific underwater sound source might affect a particular marine animal species, scientists begin by asking:
- What is the level of sound at different distances and depths as sound travels away from the source?
- Where are marine animals likely to be located relative to the source?
By combining the answers to these questions scientists can make an estimate to answer the following question:
- What are the sound levels to which the animals are likely to be exposed?
Once the sound levels to which the animals might be exposed are known, scientists next ask:
- Can the animal sense these sounds?
If the sounds are within the animals' auditory range, they may have an affect on them. The scientists then ask:
- What effects might these sound levels have on the animals?
Scientists use data on the way in which the animals respond to similar sounds and sound levels to estimate how much the sound might affect their behavior.
For example, in the Animals-Effects section of DOSITS, there is a walkthrough of the analysis that was done to determine how the sound source for the North Pacific Acoustic Laboratory's Acoustic Thermometry of Ocean Climate (ATOC) Project might affect humpback whales around the island of Kauai, Hawaii. This analysis was part of an environmental impact statement that was approved by the National Oceanic and Atmospheric Administration (NOAA) Fisheries Department that oversees environmental regulations. While this example relates to marine mammals, the exact same process could be used to analyze the effects on fish.
- EPA. 1998, "Guidelines for Ecological Risk Assessment." No. EPA/630/R095/002F. U.S. Environmental Protection Agency, Washington, D.C.
- EPA. 1992, "Framework for Ecological Risk Assessment." No. EPA/630/R-92/001. U.S. Environmental Protection Agency, Washington, D.C.
- "North Pacific Acoustic Laboratory (NPAL) Project/Acoustic Thermometry of Ocean Climate Project." (Link)
- Au, W.W.L., Nachtigall, P. and Pawloski, J.L. 1997, "Acoustic effects of the ATOC signal (75 Hz, 195 dB) on dolphins and whales." Journal of the Acoustical Society of America 101(5):2973-2977.
- Costa, D.P., Crocker, D.E., Gedamke, J., Webb, P.M., Houser, D.S., Blackwell, S.B., Waples, D., Hayes, S.A., and Le Boeuf, B. J. 2003, "The effect of a low-frequency sound source (acoustic thermometry of the ocean climate) on the diving behavior of juvenile northern elephant seals, Mirounga angustirostris." Journal of the Acoustical Society of America 113(2):1155-1165.
- Frankel, A.S., and Clark, C.W. 1998, "Results of low-frequency playback of M-sequence noise to humpback whales, Megaptera novaeangliae, in Hawaii." Canadian Journal of Zoology 76:521-535.
- Frankel, A.S., and Clark, C.W. 2000, "Behavioral responses of humpback whales (Megaptera novaeangliae) to full-scale ATOC signals." Journal of the Acoustical Society of America 108(4):1930-1937.
- Frankel, A.S., and Clark, C.W. 2002, "ATOC and other factors affecting the distribution and abundance of humpback whales (Megaptera novaeangliae) off the north shore of Kauai." Marine Mammal Science 18(3): 644-662.
- Klimley, A.P. and Beavers, S.C. 1998, "Playback of acoustic thermometry of ocean climate (ATOC)-like signal to bony fishes to evaluate phonotaxis." Journal of the Acoustical Society of America 104 (4):2506-2510.
- Mobley, J.R., Grotefendt, R.A., Forestell, P.H. and Frankel, A. 1999, "Results of Aerial Surveys of Marine Mammals in the Major Hawaiian Islands (1993-1998): Report to the Acoustic Thermometry of Ocean Climate Marine Mammal Research Program (ATOC MMRP)" Cornell University Bioacoustics Research Program, Ithaca, NY.