Blue whales off the southern coast of Sri Lanka during the southwest monsoon season

Abstract

Observations of 37 individual blue whales were recorded off the southern coast of Sri Lanka during the southwest monsoon season. Sightings were made during a scientific geophysical survey campaign conducted in July and August 2017. Whilst blue whales are regularly recorded on the continental slope of southern Sri Lanka during the northeast monsoon season (NEM) (December-March) and during the two inter-monsoonal periods (March-April and September-October), limited data are available for the SWM (May-September) mostly due to unfavourable weather conditions and a lack of survey effort. In the Northern Hemisphere, blue whales generally undertake seasonal migrations from higher latitude feeding grounds to lower latitude breeding and wintering areas. However, it has been suggested that a population of blue whales in the northern Indian Ocean (NIO) remains in lower latitudes year-round, taking advantage of the rich upwelling areas off Somalia, southwest Arabia and western Sri Lanka. Data from this study support a hypothesis that a certain number of individuals remain off the southern coast of Sri Lanka during the SWM, suggesting that the productivity in this region is sufficient to support their year-round presence. This study fills a knowledge gap on the presence and movement of blue whales in the NIO, highlighting the importance of data that can be obtained from platforms of opportunity.