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Marine Mammal Acoustics

Marine Mammals

The term "marine mammals" (MMs) includes the order Cetacea (whales, dolphins, and porpoises), Sirenia (dugongs and manatees), pinnipeds (seals and sea lions) and certain members of the order Carnivora (the polar bear and otters). Cetaceans can be divided into two orders, Mysticeti (Baleen whales) and Odontoceti (toothed whales).

Baleen whales

Baleen whales are large and feed on plankton and krill. Instead of teeth they have a mesh of comb-like plates which hang from the upper jaw, used to filter the small prey from the water. They can communicate with "thumps", "moans". The humpback whale communicates with complex "songs" that can last over half an hour. Blue whales can weigh up to 160 tons and reach over 33.5 meters in length. It is the largest species to have ever existed on Earth.

Odontoceti

The order Odontoceti covers more species than Mysticetes. With the exception of the sperm whale, they are smaller that the Mysticetes and all have teeth. Odontocete prey includes fish, squid, invertebrates, and even other cetaceans. As with mysticetes, odontocetes have an acoustic modality, using whistles and clicks, for communication and echolocation to find food and navigate. The order includes sperm whales, narwhals, beaked whales, dolphins and porpoises.

Marine Mammal Sounds

Many cetaceans use sound to navigate, communicate and feed. They are, as such, vulnerable to acoustic pollution. Most exploit the excellent sound conductive properties of water, and sound is their main interface with their environment. Sound can be used for con-specific communication and for echo-location - which enables distant objects to be detected well before they are visible.

Click on the links below to hear some cetacean vocalisations.

Marine Mammal Hearing

Audiograms give an indication of the degree to which sound at a particular frequency is detected by an animal. Obtaining audiograms for humans is straightforward, but not so easy for marine mammals in their own environment. They are often based on the auditory thresholds of captive animals. While much work has been carried out on obtaining marine mammal audiograms there are many gaps in our knowledge of marine mammal hearing. The plot below shows audiograms for a variety of marine mammals.

 

 

References:

  1. Johnson C S. Masked tonal thresholds in the bottlenosed porpoise. Journal of the Acoustical Society of America, 44(4) 965-967 (1968).
  2. Hall J D and Johnson C S. Auditory thresholds of a killer whale Orcinus orca Linnaeus. Journal of the Acoustical Society of America 51 515-517 (1972).
  3. Anderson S. Auditory sensitivity of the harbour porpoise (Phocoena phocoena). Investigations on Cetacea, 2 255-259 (1970).
  4. Mohl B. Hearing in seals. In The behaviour and physiology of pinnipeds (eds R.J. Harrison, R.C. Hubbard, R.S. Peterson, C.E. Rice & R.J. Schusterman), 172-195. Appleton-Century-Crofts, New York (1968).
  5. Terhune J M and Ronald K. The Harp seal, Pagophilus groenlandicus (Erxleben, 1777). III. The underwater audiogram, Canadian Journal of Zoology 50 56569 (1972).
  6. Schusterman R. Auditory sensitivity of a California sea lion to airborne sound. Journal of the Acoustical Society of America, 56 91-100 (1974).
  7. Moore P W B and Schusterman R J. Audiometric assessment of northern fur seals, Callorhinus ursinus. Marine Mammal Science, 3 31-53 (1987).