Anthropogenic (man-made) sounds may affect the behavior of marine mammals. The occurrence and significance of a behavioral change varies by individual, species, and circumstances. Some sounds may not cause any response, while others may result in minor to significant changes in a variety of behaviors, such as diving, surfacing, vocalizing, feeding, and/or mating. For example, sperm whale and pilot whale stopped vocalizing during transmissions of the Heard Island Feasibility Study sound source. Based on research of behavioral responses of Blainville’s beaked whales to Navy sonar, scientists developed a risk function that predicts that half of the individuals in the Blaineville's beaked whale population would stop foraging at received level of 150 underwater dB, but that the other half of the population would continue feeding. Marine mammals have also been shown to learn to use anthropogenic signals for their benefit, as grey seal learned that the sound produced by acoustic fish tags indicated the location of a food source.
To best understand how anthropogenic sounds may impact marine life, observations of normal behavior, "control" or "baseline" data, are needed to determine the range of natural variability as well as whether any changes occurred during or after sound exposure. (see How do you determine if a sound source might affect a marine animal?)
Behavioral responses depend on a number of factors, including an individual animal's hearing sensitivity, tolerance to noise, exposure to the same noise in the past, behavior at the time of exposure, age, sex, and group composition.
Not all changes in behavior are cause for concern. Some marine animal responses are momentary inconsequential reactions, such as the turn of a head. Other responses are within natural variation. In response to Acoustic Thermometry of Ocean Climate (ATOC) sounds, humpback whale slightly increased their average dive time and underwater travel distance as the received level was increased. However, these changes were well within the range of dive times and distances observed in the absence of ATOC transmissions. Further, there was no difference in humpback whale sighting rate (number of animals seen per kilometer searched) or distributions between a year when the source was off and two years when the source was on.
In another example, sounds of the Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) sonar were played to singing humpback whales off Hawaii. The whale songs were 29% longer during transmissions and remained 10% longer up to two hours after exposure. Even though the songs were longer on average, the two graphs look similar and show that there is considerable variation in the length of humpback whale songs.
In other cases, more significant changes in behavior have been observed. For example, beluga whale stopped feeding and swam rapidly away from approaching ice-breaking vessels. The whales traveled up to 80 km away from productive feeding areas and remained there for 1-2 days before returning . Some of the strongest reactions occur when the sounds are similar to those made by predators. Harbor seal responded to playbacks of mammal-eating killer whale and unfamiliar fish-eating killer whales , but did not respond to familiar calls of fish-eating killer whales. (For more information on killer whale calls see group-specific vocalizations). This also suggests that animals can become accustomed to sounds that appear harmless by learning from previous experiences and stop responding to them or habituate.
Sometimes it is difficult to know whether observed changes in behavior are due to sound or to other causes. Manatee reduced their use ofspecific areas when continually disturbed by boats . Similarly, gray whale left a breeding lagoon in Baja California during extensive industrial activity and returned to the lagoon when the shipping decreased . It is not known whether these disturbances were related to increased anthropogenic sound levels or to the physical presence of increased numbers of boats.
How these short-term, individual effects may result in population-level effects is also being studied. The Population Consequences of Acoustic Disturbance (PCAD) model is a conceptual framework to structure future studies to investigate if and when measurable short term responses of marine mammals result in 'biologically significant'or meaningful effects on individuals and/or populations. This framework demonstrates how behavioral responses to sound (e.g., diving, resting, orientation, changes in vocalizations) may affect life functions (e.g., feeding, breeding, migrating), how these are linked to vital rates (e.g., adult survival, reproduction), and how that may result in population changes (e.g., through growth rate, population structure, or extirpation).
The content on DOSITS is based on well-understood scientific principles, peer-reviewed literature, and high quality sources of scientific data. Independent experts who specialize in underwater acoustics have reviewed the material in this section.
- Anthropogenic Sounds
- Beluga Whale
- Gray Whale
- Group-specific Vocalizations
- Harbor Seal
- Humpback Whale
- Killer Whale
- Pilot Whale
- Potential effects of sound on marine mammals
- Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) Sonar
- Bowles, A.E., Smultea, M., Würsig, B., DeMaster, D.P. and Palka, D. 1994, "Relative abundance and behavior of marine mammals exposed to transmissions from the Heard Island Feasibility Test." Journal of the Acoustical Society of America 96(4): 2469-2484.
- Moretti, D., L. Thomas, T. Marques, J. Harwood, A. Dilley, B. Neales, J. Shaffer, E. McCarthy, L. New, S. Jarvis, and R. Morrissey. 2014., "A Risk Function for Behavioral Disruption of Blainville's Beaked Whales (Mesoplodon densirostris) from Mid-Frequency Active Sonar." PLoS ONE 9:e85064.
- Stansbury, A. L., Götz, T., Deecke, V. B., & Janik, V. M. 2015, "Grey seals use anthropogenic signals from acoustic tags to locate fish: evidence from a simulated foraging task." Proceedings of the Royal Society B: Biological Sciences, 282(1798), 20141595.
- National Research Council. 2003, "Ocean Noise and Marine Mammals." The National Academies Press, Washington, D.C.
- 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.
- 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. 1998, "Results of low-frequency playback of M-sequence noise to humpback whales, Megaptera novaeangliae, in Hawaii." Canadian Journal of Zoology 76:521-535.
- Mobley, J. R., Jr. 2005, "Assessing responses of humpback whales to NPAL transmissions: Results of 2001-2003 aerial surveys north of Kauai." Journal of the Acoustical Society of America 117: 1666-1673.
- Fristrup, K.M., Hatch, L.T. and Clark, C.W. 2003, "Variation in humpback whale (Megaptera novaeangliae) song length in relation to low-frequency sound broadcasts." Journal of the Acoustical Society of America 113(6): 3411-3424.
- Finley, K.J., Miller, G.W., Davis, R.A. and Greene, C.R. 1990, "Reactions of belugas and narwhals to ice breaking ships in the Canadian high arctic." Canadian Bulletin of Fisheries and Aquatic Science 224: 97-117.
- Deecke, V.B., Slater, P.J.B. and Ford, J.K.B. 2002, "Selective habituation shapes acoustic predator recognition in harbour seals." Nature 420(Nov.14 2002): 171-173.
- Provancha, J.A. and Provancha, M.J. 1988, "Long-term trends in abundance and distribution of manatees in the northern Banana River, Brevard County, FL." Marine Mammal Science 4: 323-338.
- Gard, R. 1974, "Aerial census of gray whales in Baja California lagoons, 1970 and 1973, with notes on behavior, mortality and conservation." California Fish and Game 60(3): 132-143.
- Ljungblad, D.K., Würsig, B., Swartz, S.L. and Keene, J.M. 1988, "Observations on the behavioral responses of bowhead whales to active geophysical vessels in the Alaskan Beaufort Sea." Arctic 41: 183-19.
- Miller, P.J.O., Biassoni, N., Samuels, A. and Tyack, P.L. 2000, "Whale songs lengthen in response to sonar." Nature 405(22 June 2000): 903.
- 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.
- Moulton, V. D., Richardson, W. J., Elliott, R. E., McDonald, T. L., Nations, C. and Williams, M. T. 2005, "Effects of an offshore oil development on local abundance and distribution of ringed seals (Phoca hispida) of the Alaskan Beaufort Sea." Marine Mammal Science 21(2): 217-242.
- Moulton, V.D., Richardson, W.J. and Williams, M.T. 2003, "Ringed seal densities and noise near an icebound artificial island with construction and drilling." Acoustics Research Letters Online 4(4):112-117.