Biological Productivity of Coastal Waters of India - From Dabhol to Tuticorin

84-93Biological productivity of coastal waters of India, from Dabhol to Tuticorin was studied during the 17th cruise of RV Gaveshani in March 1977. Within 50 m depth from the coast, data on chlorophyll a, 14C uptake and zooplankton biomass were collected at 55 stations. Larger phytoplankton organisms (microplankton) contributed greater spatial variations in primary productivity than nannoplankton. Maximum primary production was recorded in areas adjoining Karwar and Calicut. production at the primary level of the food chain for the entire coastal area measuring 43x 103 km2 was at the rate of 0•33 gC/m2/day or 122 tonnes C/km2/yr or 5 million tonnes of carbon/yr. Of the 18 major components constituting the zooplankton biomass, copepods formed the dominant group. Caloric value of different components ranged from 0•5 to 6•4 kcal/g dry weight. The average production of zooplankton in the total area was 125 mgC/m2/day which amounted to 2•5 million tonnes of carbon/yr or 60 tonnes of carboni km3/yr. Mean transfer coefficient was found to be 10% and the average tertiary production, calculated from both primary and secondary production rates, was approximately 2 million tonnes of live weight/yr. The average sustainable yield per year has been estimated as 0•8 million tonnes of fish. The annual harvestable yield calculated from the energy budget in terms of calories for the entire coastal area agreed with that estimated from the primary and secondary production rates. The present exploited yield from the coastal waters is of the order of 0.6 million tonnes. The existing yield of pelagic, demersal and crustacean resources from the Kerala region appears to be greater than the annual sustainable yield and hence the stock in this area requires conservation. In the other coastal regions, further increase in the exploitable yield of the order of 0•2 million tonnes seems possible