On the Biology of the Coastal Spotted Dolphin Stenella attenuata graffmani (Lönnberg, 1934) in Pacific South America

Knowledge on the biology of the coastal spotted dolphin Stenella attenuata graffmani from western South America, one of the least studied delphinid taxa, is summarized for the first time. Information was obtained largely opportunistically during field research targeting other species or during whale watching. Life history is discussed including distribution (Colombia, Ecuador, Peru, Chile), external morphology and pigmentation, cranial characteristics, reproduction and growth, feeding, behavioral ecology, parasites and pathology, but also genetic diversity, population structure and fisheries interactions. As a (sub)tropical dolphin its habitual austral range is the Piura Department, northern Peru, but under El Niño conditions it can reach Lima Province (Cerro Azul at 13°02’S). No evidence was found for Chile. The coastal subspecies is heavily spotted and substantially bigger, as reflected in body length and all cranial measurements. Condylobasal length, mandibular ramus length and height do not even overlap with the offshore S. a. attenuata morph. Phylogenetic analysis of the hypervariable part of mtDNA control region, revealed Ecuadorian coastal spotted dolphins to be distributed across seven different clades, with most belonging to the three largest clades, while only one haplotype was found in each of the remaining four. This pattern suggests a complex evolutionary history, possibly indicating substructures within the population or an ongoing evolutionary process. The presence of haplotypes in multiple clades may reflect high genetic diversity, likely influenced by dolphin migration between nearby geographic areas, facilitating haplotype exchange and contributing to the observed distribution.