Saturday, August 6, 2011

Life of Commerson's Dolphin

Life of Sea | Commerson's Dolphin (Cephalorhynchus commersonii)Commerson's dolphins can be found in shallow waters along the southernmost tip of South America and around the Kerguelen Islands in the Indian Ocean. Those found around the Kerguelen Islands are larger than the South American variety, and may be a subspecies. Commerson's dolphins are found in cold inshore waters near open coasts, sheltered fjords, bays, harbors and river mouths. They are occasionally found in rivers. In South Africa, there is a little knowledge about the migratory patterns of these dolphins, however fishermen report that they disappear from their common areas during the winter. They may follow fish such as róbalo and merluza that migrate offshore in winter.

Commerson's dolphins have small stocky bodies with with rounded, paddle-like flippers. Juveniles are gray-black and lighten into their adult white coloring of the anterior body and black head. The dorsal area from the fin back is also black with a black patch on the lighter ventral side. Commerson's dolphins range in size from 1.2-1.7 m, and can reach up to 86 kg. The Kerguélen population in the southern Indian Ocean, east-southeast of South Africa, differ markedly from those in South America. They are larger and are black, gray, and white in color unlike the black/white coloration of the South American population. These dolphins tend to be found in small groups of 1-3, although aggregations of 100 or more have been observed. Like other dolphin species, they are quick and agile, and enjoy leaping and riding bow waves. They have also been observed swimming upside down.
Commerson's dolphins is very active. It is often seen swimming rapidly on the surface and leaping from the water. It also spins and twists as it swims and may surf on breaking waves when very close to the shore. It will bow-ride and swim behind fast-moving boats. They are also known to enjoy swimming upside-down, which is thought to improve the visibility of its prey. This dolphin feeds on a mix of coastal and pelagic fish and squid. Those in the South American sub-population supplement their diet with crustaceans. Commerson's dolphins are typically found alone or in small groups of two to three animals and occasionally spotted in larger groups of 20-30 or more dolphins. They often hunt cooperatively either encircling fish and taking turns passing through to feed on the clustered fish or even driving fish onshore and temporarily stranding themselves to snatch up the fish.

Commerson's dolphins typically eat 3.5-6 kg of food per day. This is proportionally a much greater amount than either killer whales or bottlenose dolphins ingest each day, and is due to Commerson's having a metabolic rate that is two to three times higher than many other whale or dolphin species. Commerson's dolphins are fast and highly maneuverable cetaceans regularly swimming at speeds of 11-13 kph (7-8 mph). These dolphins are commonly seen wave-riding in the bows or wakes of high-speed boats, shoreline breakers or groundswells.
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