Humpback whale calls detected in tropical ocean basin between known Mexico and Hawaii breeding assemblies.

Humpback whales migrate in winter from northern feeding grounds to geographically separate breeding assemblies in near-shore waters of Mexico and Hawaii. Currently assessed as distinct populations warranting separate management, their shared song composition and interchange of photo-identified whales question this paradigm. To investigate a potential connection an autonomous Wave Glider performed a 6965.5 km, 100-day (round trip) acoustic survey from Hawaii toward Mexico circa 20° N, from January 15 to April 25, 2018. The 2272 h of recordings included humpback whale calls to approximately midway from Hawaii to Mexico. Explanations include an undocumented migration route, offshore assembly, or mid-season travel between assemblies.