The Commerson’s dolphin, Cephalorhynchus c. commersonii, one of the world’s smallest cetaceans, occurs in the southwestern South Atlantic from about 41°30\u27S to near Cape Horn (56°S), including the central and eastern Strait of Magellan and the Falkland (Malvinas) Islands (Goodall 1978, Goodall et al. 1988). Along the coasts of Patagonia, northern Tierra del Fuego, Argentina, and the eastern Strait of Magellan, Chile, this is the cetacean most often seen near shore, where the animals feed and surf in the breakers. They seldom strand, but are commonly taken incidentally in shore-based gill nets set perpendicular to the coast over the wide tidal flats (Goodall 1978, 1994; Goodall et al. 1994, 2008; Iñíguez et al. 2003). Although there have been few aerial surveys, this is probably the most abundant small cetacean in these waters and is the most affected by bycatch in artisanal fisheries.
Age estimation in marine mammals by counting incremental layers in teeth has been carried out since the 1950s (Scheffer and Myrick 1980). As mentioned in Hohn (2002), the importance of age estimation goes beyond population dynamic studies, and the information on age at sexual maturation and population age structure may help to adopt adequate policies in conservation management (Read and Hohn 1995, Hohn et al. 1996). Additional information can be obtained from teeth, such as life history or environmental events (Klevezal and Myrick 1984, Manzanilla 1989; Lockyer 1993, 1995; Klevezal 1996, Luque et al. 2009). Therefore, the description of a “basic or typical” pattern of a species gives us not only more accurate and precise age estimates, but also allows for the identification of accessory layers (ALs) and other tooth-tissue alterations, which could be correlated with intrinsic or extrinsic factors
