Age estimation on long-beaked common dolphins, Delphinus capensis, from the Gulf of California

Introduction: We estimated the age of 41 long-beaked common dolphins, Delphinus capensis, found stranded in Sonora and Baja California beaches in the Gulf of California from 1981 to 2000. The aim of our work was to know the age and if possible the size of stranded dolphins and the possible causes of their stranding. Methods: Dentinal growth layers in teeth were revealed using an acid-etching technique; it involves preparation of half-etched teeth by grinding and polishing with sandpaper (220-600 grit) and demineralization in 5% formic acid. A stereo-microscope was used for counting annual growth layer groups (GLGs). Four different readers of dentinal layers assisted to obtain the estimate of age. Results: Age category estimates were: 17 individuals were adults (12-21 GLGs), 10 individuals were subadults (7-12 GLGs), 10 individuals were juveniles (2-7 GLGs), and 4 individuals were nursing calves (