Small dolphins in a small sea: age, growth and life‑history aspects of the Black Sea common bottlenose dolphin Tursiops truncatus

Abstract

We provide first data on the life span, growth and seasonal aspects of the life history of Black Sea bottlenose dolphins Tursiops truncatus in the wild and compare these with historical data and conspecific populations in other geographical regions. Average life span is 20 to 32 yr; the oldest record is 41 yr. The reproductive season lasts at least from February to September or October and includes the coldest months of the year (February and March). Average adult body lengths are 240 ± 14 cm for females and 255 ± 10 cm for males. Rapid early body growth ceases by 3 to 4 yr. Two morphs, one large (offshore) and one small (coastal), possibly co-exist in the Black Sea. The larger morph may include winter-breeding migrants or immigrants from the Mediterranean Sea. The small coastal form is similar in body size and growth patterns to coastal populations in the eastern Mediterranean region and the Gulf of Mexico, but is characterized by early growth to maturity and small asymptotic body size. Small-sized dolphin populations in enclosed water bodies can be treated as an example of the ‘island rule’, and their dwarfism may hypothetically be explained as an effect of smaller prey size.