Drones reveal spatial patterning of sympatric Alaskan pinniped species and drivers of their local distributions

Abstract

The Arctic and its adjacent ecosystems are undergoing rapid ecological reorganization in response to the effects of global climate change, and sentinel species provide critical updates as these changes unfold. This study leverages emerging remote sensing techniques to reveal fine-scale drivers of distribution and terrestrial habitat use of two sympatric sentinel species of the central Bering Sea, the Pacific harbor seal (Phoca vitulina richardsi) and the northern fur seal (Callorhinus ursinus), at non-breeding haul-outs in the Pribilof Islands. We surveyed these species using unoccupied aircraft systems with thermal and visible-light photography, and we applied distributional modeling techniques to quantify the relative influence of habitat characteristics and social dynamics on the local distributions of these species. Drone imagery yielded locations and population counts of each species, and spatial data products allowed quantitative characterization of occupied sites, revealing that conspecific attraction is a driver of local site selection for both species, and Pacific harbor seals and northern fur seals are differentially limited by terrain characteristics. These findings represent new applications of species distribution modeling at local scales, made possible by ultra-high resolution drone surveillance and photogrammetric techniques, which add new spatial context to past observations and future scenarios in this changing ecosystem.