Short- finned pilot whales (Globicephala macrorhynchus) of the Mariana Archipelago: Individual affiliations, movements, and spatial use

Little is known about short-finned pilot whales (Globicephala macro-rhynchus) in the western North Pacific outside of Japanese coastal waters. To expand understanding of short-finned pilot whale ecology in the region, we conducted small-boat surveys in 2010-2016 within the Mariana Archipelago to investigate individual associations, movements, spatial use, and dive behavior of short-finned pilot whales. We collected genetic, photo-identification, and satellite-tag data and identified 191 distinctive individuals. A preliminary social network diagram of photo-cataloged individuals revealed a main cluster that comprised 82% of individuals, representing all five mitochondrial DNA haplotypes identified within the population. Kernel density estimates for tagged short-finned pilot whales (n = 11) during summer were used to identify areas with the highest probability of use (10% probability density contour), core area (50%) and home range (95%). The area with highest probability of use by short-finned pilot whales was off the northwest side of Guam. Satellite tag data also suggest that some individuals are island-associated year-round. Data from five location-dive tags demonstrated that the short-finned pilot whales dove more often to intermediate depths at twilight and night, suggesting they may target prey that forage on the deep scattering layer as it migrates to and from the surface.