Crabeater Seal
(Lobodon carcinophaga)

Image of two crabeater seals on an ice floe in Antarctica.
Crabeater seals resting on an ice floe in the Western Antarctic Peninsula. The rake-like scars seen on the body of the far seal are most likely from leopard seals, their main predator. Image credit: Dan Costa, UC Santa Cruz.
Photograph of crabeater seal teeth.
Crabeater seals have very specialized teeth. Multilobed teeth interlock to strain prey as the seal gulps seawater. Despite its name, the crabeater seal feeds mainly on krill, small, shrimp-like crustaceans. Image credit: Dan Costa, UC Santa Cruz.

Click either choice below to hear a crabeater seal:
 
Click this button use any media player
Crabeater seal high moan vocalization recorded with the Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA), located at 70°31' S, 8°13' W on the Ekstroem Ice Shelf, Antarctica in November 2007.
Sound credit: Alfred Wegener Institute for Polar and Marine Research. Sound file released under Creative Commons license, Non-Commercial attribution.
Click either choice below to hear a crabeater seal:
 
Click this button use any media player
Crabeater seal low moan vocalization recorded with the Perennial Acoustic Observatory in the Antarctic Ocean (PALAOA), located at 70°31' S, 8°13' W on the Ekstroem Ice Shelf, Antarctica in November 2007.
Sound credit: Alfred Wegener Institute for Polar and Marine Research. Sound file released under Creative Commons license, Non-Commercial attribution.
Description
Crabeater seals are the most numerous of the world's seals and are widely distributed along the pack ice that surrounds Antarctica. Their fur ranges from dark brown to silver. They often have linear, rake-like scars on their bodies caused by leopard seals, their main predator. Adult crabeater seals are about 2.6 m (8.53 ft) long and can weigh up to 225 kg (496 lb).

Despite its name, the crabeater seal feeds mainly on krill, small, shrimp-like crustaceans. Their specialized teeth are used to strain prey as the seal gulps seawater. They forage primarily at night, resting on ice floes during the day. Crabeater seals are unique among the phocid seals in that they form “family” groups consisting of an adult female, her pup, and an adult male. Females give birth to a single pup. A male usually joins a pregnant female shortly before or after the pup's birth. He remains with the female on the ice until after the pup is weaned, at which time mating occurs. The seals breed on the ice from early October to mid-November. During the time a family group is together, the adult male defends the female and pup from other adult males and predators.

Male crabeater seals are especially vocal during the breeding season, producing two types of calls, the groan-like “low moan” call, and the “high moan” call. The low moan lasts about 2.5 s with a frequency range of 260-2500 Hz. It rises to a constant frequency and decreases at the end. The high moan call is characterized by a brief down sweep followed by a series of short pulses. This call lasts about 2.6 s with a frequency range of 1000-4900 Hz.

As males remain with females and their pups during the breeding season, it is thought that they do not need to vocalize to attract a mate. However, they may need to communicate their status, and possibly compete, with rival males. Crabeater seals appear to respond to distant groans with their own low moans.

Crabeater seals have been found to produce sounds outside the breeding season. These sounds include groans, whistles, screeches, and grunts. The function of these sounds remains unknown.
 
References

  • "Crabeater Seal." In: Guide to Marine Mammals of the World. Randall R. Reeves, Brent S. Steward, Phillip J. Clapham, and James A. Powell. Alfred A. Knopf. New York. 2002. Pp 170-171. 
  • "Crabeater Seal." In: Encyclopedia of Marine Mammals (Second Edition). Editors: William F. Perrin, Brend Wursig, J.G.M. Academic Press. Amsterdam. 2009. Pp 290-29. 
  • Australian Antarctic Division, "Crabeater Seals." (Link)
  • Klinck, H., D.K. Mellinger, K. Klinck, and J. Hager 2010, "Long-range underwater vocalizations of the crabeater seal (Lobodon carcinophaga)" Journal of the Acoustical Society of America. 128(1): 474-479. 
  • McCreery, L. and J.A. Thomas. 2009, "Acoustic analysis of underwater vocalizations from crabeater seals (Lobodon carcinophagus): Not so monotonous." Aquatic Mammals. 35(4): 490-501. 
  • National Marine Mammal Laboratory, "Crabeater Seals." (Link)
  • NOAA Fisheries Service, "Crabeater seal fact sheet." (Link)
  • Sea World Animal Bytes, "Crabeater Seal." (Link)
  • Van Opzeeland, I., S. Van Parijs, H. Bornemann, S. Frickenhaus, L. Kindermann, H. Klinck, J. Plotz, and O. Boebel. 2010, "Acoustic ecology of Antarctic pinnipeds." Marine Ecology Progress Series. 414: 267-291.