Coherence between 19th century sperm whale distributions and satellite-derived pigments in the tropical Pacific

Abstract

It has often been suggested that, given their large food requirements, sperm whale Physeter macrocephalus distributions should reflect the distribution of productive ocean environments, and it seems therefore that chlorophyll concentration might be a good indicator of sperm whale distribution. To examine the existence of such a relationship, and to determine over which scales it occurs, sperm whale density was correlated with phytoplankton pigment concentration over a range of spatial and temporal scales. Sperm whale distribution was determined using records of kills from 19th century Yankee whaling, and the distribution of pigment concentration from satellite colour observations averaged over an 8 yr interval. These measures were coniparecl over scales of 220 k m square to 1780 km square. The distribution of sperm whales in the temperate and tropical Pacific Ocean was associated with distributions of phytoplankton pigment over every spatial scale considered, and the coefficient of correlation increased with increasing spatial scale. However, a few exceptions to this scheme were found, implying that other factors could be of importance in some regions. This study confirmed the existence of a space lag and a time lag between a peak in chlorophyll concentration and a peak in sperm whale density. It also demonstrated that over large spatial scales, and when the data are averaged over large temporal scales, chlorophyll concentration is a good indicator of sperm whale distribution, and that over these scales ocean colour recorded from space could help predict areas of high or low sperm whale density.