Using remote sensing to study phytoplankton biomass and its influence on herbivore fishery in the South-Eastern Arabian Sea

Abstract

In this chapter, satellite remote sensing data are analysed to study the physical forcing that favors coastal upwelling and the variability in phytoplankton biomass in the South-Eastern Arabian Sea for a time period of 14 years. Analysis of monthly binned measurements of Sea Surface Temperature (SST) coupled with reanalysis wind data clearly demonstrate the dominating influence of the strong southwest monsoon in cooling the SST, breaking down the surface water warm pool, and the subsequent development of wind induced upwelling off the southwest coast of India. During southwest monsoon (June-September), the depth of the 20 °C isotherm shoals from typically 140 m to about 80 m. The development of negative Sea Level Anomaly (SLA) along with cyclonic eddies during summer monsoon season prove the occurrence of divergence and upwelling. Ekman mass transport computed using the monthly reanalysis wind data show strong negative values during the southwest monsoon, which indicate strong upwelling along the coastal regions of southwest India, also discernible from the high chlorophyll-a (Chl-a) concentrations (≥1 mg m-3) during southwest monsoon season, which decrease to about 0.2-0.5 mg m-3in non-monsoon months. Increased primary production triggers higher catches of Indian oil sardine (Sardinella longiceps Valenciennes), and the analysis of fish landing data for the State of Kerala, India show that the sardine catch follows Chl-a peaks with a lag of one season with significant positive correlation.