Remote sensing based observation of ocean conditions and their influence on the sei whale [Balaenoptera borealis] distribution in the Western South Pacific

Like other baleen whales, the Sei Whales of the southern hemisphere undertake seasonal migration toward high-latitude feeding grounds in the summer and toward low-latitude breeding grounds in the winter. They are highly migratory with wide oceanic distribution; hence spatial and temporal scale observations are necessary to understand their distribution pattern. Under this investigation we used satellite derived ocean parameters and the whale sighting location data collected under the Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) in order to elucidate prevalent ocean condition where whale sighting was undertaken, and to understand its influence on the distribution of the Sei Whales. The Sei Whales mostly feed on the low level zooplankton such as copepods and copepods feed on the phytoplankton. Due to such trophic relationship the Sei Whales are closely associated with the pelagic ocean environment which can be advantageously monitored by remote sensing observation. The present study was carried out using the whale sighting location data in the western South Pacific (20 deg-60 deg S, 170 deg E-160 deg W) in 2000 and 2002 along with the satellite derived ocean parameters such as sea surface temperature (SST), SST gradient, chlorophyll-a concentration as well as the sea bottom topography to understand the relative impact of the ocean parameters on the distribution of the Sei Whales. The whale sighting locations were found to coincide mostly with the ocean areas with high chlorophyll-a concentration as well as the high topography gradient. We coined an index for the characteristic SST of the whale sighting locations and named as favorable temperature index (FTI). Statistically strongest relationship was noticed between the FTI and the whale sighting locations. Our FTI coincided with that of the SST of sub-tropical frontal waters. Such results clearly indicate major influence of the sub-tropical front on the distribution of the Sei Whales in the western South Pacific.