Population structure of humpback whales in the western and central South Pacific Ocean determined by vocal cultural exchange

Abstract

Male humpback whales (Megaptera novaeangliae) produce a continually evolving vocal sexual display, or “song,” which is shared by all males within a population. The rapid cultural transmission of this display between distinct but interconnected populations within the western and central South Pacific region presents a unique opportunity to investigate population connectivity based on a vocal display. Quantitative analyses were conducted on eleven years of data to investigate vocal groupings based on song types shared between populations, to produce an acoustically derived population structure for the region. Four distinct vocal groupings resulted; the western group contained a single population, off eastern Australia, the central group was comprised of whales around New Caledonia, Tonga and American Samoa, and finally the whales of the eastern region were split into two groups, one around the Cook Islands and the other in the waters of French Polynesia. These groupings broadly agree with results obtained using genetic and photo-identification methods, and confirm that humpback whales are likely to form separate breeding populations rather than panmictic subpopulations. This study demonstrates the utility of using culturally transmitted vocal patterns as a way of defining populations, at least in this species.