Vol. 6 No. 2 (2015)

Group of females of tonina dolphins (Tursiops truncatus) in waters of Bahia de Las Guásimas, Sonora. Dolphins are the most studied cetaceans in the world; this has led to understanding that their behavior is strikingly similar to that of terrestrial mammals. Inter-individual relationships are governed by kinship and herd identity. The different groups in a herd may be dispersed, with subgroups clustered by sex and age categories, as well as females with calves, adult males and juveniles. The subgroups join together to perform collective tasks, include food search and hunting, defense or rest. There are two dolphin morphotypes: the coastal morphotype, which populates coasts, river deltas, estuaries and coastal lagoons. For its part, the open-sea ocean morphotype lives in deep areas, as well as on the continental shelf and slope. These morphotypes differ in morphology, coloration and cranial measurements. Genetic studies of these morphotypes identify several stocks, which are still considered as a single genetic unit worldwide (Cover Photograph ©Janitzio Egido).