Towards the definition of the humpback whale population units along the Mexican and Central American coasts in the Pacific Ocean

The SPLASH project (2004-2006) revealed complex population structure and migratory connections, but no regional effort was made along the southern Mexican Pacific coast until dedicated research was initiated in 2010. It is unclear whether humpback whales documented in this region belong to the Mexican or Central American population units. This study aimed to establish the relationship between humpback whales of southern Mexico and those of the surrounding population units. Humpback whale photo-identification images were compared from multiple locations in north, central, and southern Mexico and Central America. Whales' movements among regions were estimated using the Interchange Index (InI) and the Movement Index (MI). The results showed higher movements among the southern sampling areas, suggesting that whales from southern Mexico belong to the "Central American population unit." This population unit migrates north to the feeding areas of the US West Coast using a migratory corridor along mainland Mexico to the mouth of the Gulf of California along the Baja California Peninsula. The degree of interaction with humpback whales from other population units is unknown. More studies are needed to understand population structure and disentangle photographic capture of whales on migration from whales where this is their main wintering area.