OCM Derived Chlorophyll-a Dynamics in the Nearshore Region of the Central West Coast of India: Implications for Fish Catch in the Area

This paper deals with the influence of wind and coastal currents on the distribution and concentration of Chlorophyll-a in the nearshore waters off the northern Karnataka coast (between towns of Karwar and Bhatkal), along the central west coast of India. In general, concentrations of Chlorophyll-a were high (0.6-1.50 mg/l) in this region. High concentrations of Chlorophyll-a in the nearshore waters during the monsoon season were related to local upwelling and river input. During the upwelling, the surface water moved offshore and is replaced by nutrient-rich subsurface water leading to high concentrations of Chlorophyll-a in a narrow zone along the coast, and preventing the dispersion of Chlorophyll-a into the ocean. Higher concentrations of Chlorophyll-a observed in the nearshore water during the winter months (December) were related to vertical mixing due to winter cooling effect. During the pre-monsoon season, high concentration zone was narrow and bordered the coast. These variations corresponded to the wind and the coastal currents in the area. Though the central west coast of India represents a typical tropical coast in terms of cyclicity in wind, waves and river input, the prevailing upwelling and downwelling resulted in the unique dispersion of Chlorophyll-a. There were lower concentrations of Chlorophyll-a beyond the zone of down- and upwelling (corresponding to water depth of 35-40 m), suggesting that fishing-related activities along the coast are more viable within this zone corresponding to water depth less than 35-40 m.