How is sound used to study marine mammal distribution?

Each species of whale and dolphin produces distinctive sounds including songs, moans, clicks, sighs, and buzzes (See the Discovery of Sound in the Sea Audio Gallery). For instance, male humpback whales produce a long, patterned song at middle frequencies whereas fin whales produce loud, short, low frequency "pulses."

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Songs can be typically heard in their winter breeding grounds (e.g., Hawaii), but this recording of a humpback whale singing was actually taken in one of their feeding grounds on Cordell Bank Canyon, off the coast of San Francisco, CA. The echoes you hear are from their sounds bouncing off the canyon walls.
Sound ©Thomas R. Kieckhefer. Released under Creative Commons License, non-commercial attribution.

Click either choice below to hear the Fin Whale:
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20 Hz pulses, produced by fin whales, recorded by SOSUS receivers in the eastern North Atlantic. To make this sound audible for humans, it was sped up by a factor of ten. This raises the pitch and compresses the time.
Sound © Cornell Laboratory of Ornithology, Bioacoustics Research Program.

Scientists can listen for these sounds and detect different marine mammal species. Researchers use hydrophone arrays to detect the position of a whale producing a sound. A hydrophone array consists of three or more hydrophones deployed at different locations. Differences in the time of arrival of sounds at each hydrophone are used to calculate the position of the whale. Hydrophone arrays can be towed behind a ship or placed on the seafloor. Passive acoustic tracking methods (towed arrays and fixed horizontal arrays) have been successfully applied to follow individual whales for many days, acoustically observe pods of whales, and describe species- specific seasonal changes in distribution and relative abundance.

Animation showing how a towed hydrophone array can listen to whale calls.
A hydrophone array can be towed behind a ship or placed on the seafloor. It contains at least three hydrophones that pick up sounds in the ocean. Sounds, such as whale calls, are received at different times because the hydrophones are different distances away from the sound source (i.e. whale).

One system used by the U.S. Navy to track submarines in the North Atlantic and North Pacific oceans is called the Sound Surveillance System (SOSUS). SOSUS is a network of hydrophones mounted on the seafloor. Since the end of the Cold War, the Navy has allowed researchers to use SOSUS data to analyze animal sounds in the ocean and to determine marine mammal distribution throughout the year. SOSUS was used to track an individual blue whale for 43 days throughout the North Atlantic Ocean.

Map showing the track of
A blue whale was tracked for 43 days in the north Atlantic Ocean using the US Navy's underwater listening system. Map courtesy of US Naval Research Laboratory.

How is sound used to study right whale distributions? A Case Study

New England waters offer primary feeding grounds for the North Atlantic right whale. Adult right whales traditionally winter in calving grounds off of Georgia and Florida and return to the plankton-rich waters of coastal Massachusetts and Maine in the summer months. Researchers and managers are using sound to monitor the distribution of this critically endangered species (minimum population estimate: 444 animals; NMFS, 2012).

Aerial photo of a North Atlantic right whale mother & calf.
Researchers are looking at the possibility of using sound to protect the endangered North Atlantic right whale. Aerial photo of mother & calf courtesy of New England Aquarium.

Right whales produce a variety of low frequency sounds. The most common are between 10 Hz and 1000 Hz. One typical right whale vocalization used to communicate with other right whales is the “up call”. It is a short “whoop” sound that rises from about 50 Hz to 440 Hz and lasts about 2 seconds. Detection of up calls has been the most common means of determining right whale presence from acoustic data.

Click either choice below to hear the North Atlantic right whale 'up call':
 
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'Up call' or contact call that is most commonly heard when whales are alone or joining with another whale.
North Atlantic right whale sounds recorded by Susan Parks (Syracuse University) and the Woods Hole Oceanographic Institution. Released under Creative Commons License, non-commercial - no derivs.

Passive listening systems called Marine Autonomous Recording Units (MARUs), or “pop-up” buoys, have been deployed along the Atlantic coast to continuously monitor for the presence of cetacean species such as the right whale. The MARUs are deployed for an extended period and record acoustic data to be downloaded upon instrument retrieval. MARUs can be used under weather and light conditions that restrict visual surveys. When weather conditions are good, aerial surveys can be used to complement the acoustic detections. For more information on this passive acoustic technology, and other passive acoustic systems used to monitor marine animals, please see the Observing and Monitoring Marine Animals section in the Technology Gallery: Acoustic Doppler Current Profiler (ADCP).

Archival pop-up buoys have been deployed in the Stellwagen Bank National Marine Sanctuary (SBNMS), off Massachusetts. Scientists use the devices to characterize the marine acoustic environment in the sanctuary, investigate the effects of noise on marine animals, and detect and track vocalizing marine mammals, like the North Atlantic right whale. As a result of increased acoustic monitoring, we now know that right whales occupy the Stellwagen Bank region throughout most of the year. Overall distribution and occurrence of up-calls varies spatially, suggesting the whales use all of Stellwagen Bank while in the area.

Map showing the seasonal distribution of right whale calls in Stellwagen Bankr
Number of North Atlantic right whale upcalls recorded monthly in 2006 on Marine Autonomous Recording Units (MARUs) distributed throughout Stellwagen Bank National Marine Sanctuary. Between six and nine MARUs were recording each month, with the exception of June, in which no MARUs were deployed. The size of the circle indicates the number of upcalls recorded on a specific buoy, and an "x" indicates that no calls were detected. Figure credit: NMFS/NEFSC, SBNMS, Cornell University.

Pop-up acoustic buoys have also been deployed to monitor right whales in areas off the coast of Maine, New York, North Carolina, Georgia and Florida, as well as in the Bay of Fundy, Canada. Scientists are also gathering acoustic data on the seasonal occurrence and distribution of endangered right whales in coastal waters to reduce the risk of ship strike. For more information on how acoustic buoys are being used to reduce the risk of vessel collision and the North Atlantic right whale, please see How is Sound Used to Protect Marine Mammals?

Additional Links on DOSITS

References

  • Clark, C.W. and Clapham, P.J. 2004, "Acoustic monitoring on a humpback whale (Megaptera novaeangliae) feeding ground shows continual singing into late spring." Proceedings of the Royal Society of London B 271: 1051-1057. 
  • Dalton, R. 2008, "Acoustic sensors for rare porpoises." Nature. Vol 456. Pg. 431. 
  • Leeney, R.H., Stamieszkin, K., Jaquet, N., Mayo, C.A., Osterberg, D., and Marx, M.K. 2008, "Surveillance, Monitoring and Management of North Atlantic Right Whales in Cape Cod Bay and Adjacent Waters-2008." Final Report. Provincetown Center for Coastal Studies. 
  • McDonald, M.A., Hildebrand, J.A. and Webb, S.C. 1995, "Blue and fin whales observed on a seafloor array in the Northeast Pacific." Journal of the Acoustical Society of America 98(2): 712-721. 
  • Mellinger, D.K. and Clark, C.W. 2003, "Blue whale (Balaenoptera musculus) sounds from the North Atlantic." Journal of the Acoustical Society of America 114: 1108-1119. 
  • Mellinger, D.K., Stafford, K.M., Moore, S.E., Munger, L. and Fox, C.G. 2004, "Detection of North Pacific right whale (Eubalaena japonica) calls in the Gulf of Alaska." Marine Mammal Science 20: 872-879. 
  • Moore, S.E. et al 2006, "Listening for large whales in the offshore waters of Alaska." BioScience. 56(1): 49-55. 
  • Moore, S.E., Stafford, K.M., Dahlheim, M.E., Fox, C.G., Braham, H.W., Polovina, J.J., and Bain, D.E. 1998, "Seasonal variation in reception of fin whale calls at five geographic areas in the North Pacific." Marine Mammal Science 14(3): 617-627. 
  • Newman, K., and Springer, A.M. 2008, "Nocturnal activity by mammal-eating killer whales at a predation hot spot in the Bering Sea." Marine Mammal Science. 24(4): 990-999. 
  • Nieukirk, S.L., Stafford, K.M., Mellinger, D.K., and Fox, C.G. 2004, "Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean." Journal of the Acoustical Society of America 115(4): 1832-1843. 
  • NOAA/NMFS, "North Atlantic Right Whale Sighting Survey and Sighting Advisory System." (Link)
  • Stafford, K.M., Bohnenstiel, D., Tolstoy, M., Chapp, E., Mellinger, D.K. and Moore, S.E. 2004, "Antarctic-type blue whale calls recorded at low latitudes in two oceans." Deep-Sea Research I 51(10): 1337-1346. 
  • Stafford, K.M., Moore, S.E., and Fox, C.G. 2005, "Diel variation in blue whale calls recorded in the Eastern Tropical Pacific." Animal Behaviour 69(4): 951-958. 
  • Stafford, K.M., Nieukirk, S.L. and Fox, C.G. 1999, "Low-frequency whale sounds recorded on hydrophones moored in the eastern tropical Pacific." Journal of the Acoustical Society of America 106: 3687-3698. 
  • Stafford, K.M., Nieukirk, S.L. and Fox, C.G. 2001, "Geographic and seasonal variation of blue whale calls in the North Pacific." Journal of Cetacean Research and Management 3(1): 65-76. 
  • Stellwagen Bank National Marine Sanctuary, "Noise Mapping." (Link)
  • Waring, G.T., Josephson, E., Maze-Foley, K., and Rosel, P. E. (NMFS) 2012, "U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments." (Link)
  • Watkins, W.A, Tyack, P.L., Moore, K.E. and Bird, J.E. 1987, "The 20-Hz signals of finback whales (Balaenoptera physalus)" Journal of the Acoustical Society of America 82(6): 1901-1912. 
  • Watkins, W.A., Daher, J., George,E., and Rodriguez, D. 2004, "Twelve years of tracking 52-Hz whale calls from a unique source in the North Pacific." Deep-Sea Research I 51:1889-1901. 
  • Watkins, W.A., Daher, M.A., Reppucci, G.M., George, J.E., Martin, D.L., DiMarzio, N.A. and Gannon, D.P. 2000, "Seasonality and distribution of whale calls in the North Pacific." Oceanography 13: 62-67. 
Additional Resources

  • Moore, S.E., Watkins, W.A., Daher, M.A., Davies, J.R. and Dahlheim, M.E. 2002, "Blue Whale Habitat Associations in the Northwest Pacific: analysis of remotely-sensed data using a Geographic Information System." Oceanography 15 (3): 20-25. 
  • Massachusetts Department of Marine Fisheries, "Right Whale Conservation." (Link)
  • NOAA/PMEL, "Whale Acoustics Project." http://www.pmel.noaa.gov/vents/acoustics/whales/projectdesc.html.