Sperm whale habitat use and foraging success off northern Chile: Evidence of ecological links between coastal and pelagic systems

Abstract

Cold water upwelling along the coast of Chile drives some of the most productive marine ecosystems in the world; one example is the Mejillones upwelling system at 23° S. We studied the distribution, movements and foraging success of the sperm whale Physeter macrocephalus off the northern coast of Chile (18° 30' S to 25° S) over a 9 mo period. We used a small sailing vessel to survey the area using visual and acoustic methods, and followed any sperm whale groups encountered, col- lecting defecation rate data as an index of foraging success. Both encounter and defecation rates were greater in the southern part of the study area (>22° 30' S) relative to the north, coinciding with the Mejillones upwelling. Movement patterns were also markedly different, with groups in the south- ern part of the area having smaller net 12 h displacements, and less directionality, than those in the north, such that they tended to remain in the area associated with high defecation rates. We suggest that the greater foraging success off Mejillones was due to upwelled water being entrained offshore and southward by local physical oceanography, making productivity from coastal upwelling avail- able offshore to pelagic predators.