* Population data isn't perfect: Accurate population counts are challenging for marine animals, especially those with wide ranges.
* Definitions of "least common" vary: Some might consider rarity based on total population, others might look at geographic range or specific threats.
However, some contenders for the title of least common dolphin include:
* Vaquita (Phocoena sinus): Critically endangered with an estimated population of less than 10 individuals. They live only in the northern Gulf of California, Mexico.
* Maui's Dolphin (Cephalorhynchus hectori maui): Critically endangered with an estimated population of less than 50. Found only in the waters around New Zealand.
* Yangtze Finless Porpoise (Neophocaena asiaeorientalis asiaeorientalis): Critically endangered with an estimated population of fewer than 1,000 individuals. Found only in the Yangtze River in China.
Important note: These populations are rapidly declining due to human activities like fishing bycatch, habitat destruction, and pollution. Conservation efforts are crucial for the survival of these rare dolphins.