Coastal Aquaculture and Mariculture

Unit 7- Molluscan resources

7.2.3. Pearl oyster resource in Gulf of mannar
Hornell (1922) gives the history of the pearl fisheries of the Gulf of Mannar. During the 16th Century', the history of pearl fisheries is intricately connected on the one hand with the ruling power like the Nayakas of Madura, Nawab of Camatic and the Portuguese and on the other hand with the "Paravars" who traditionally exploited the fisheries. The pearl oysters are always found attached to some hard substratum such as rocks, dead coral outcrops or sand grit covered with marine organisms. The areas of occurrence of pearl oysters are known as pearl banks or "Parrs". Hornell divided these Paars into three divisions:
1. Northern (Kilakarai)
2. Central (Thoothukkudi)
3. Southern{Kanyakumari)
Of these, the central division is the most productive one in view of the fact that out of the 40 fisheries that had taken place between 1663 and 1961, 39 fisheries had been in the paars located in this division.
Pearl fishing, which was once historically famous, has been gradually discontinued from 1961. Natural pearls were collected from Pinctada fucata in - the pearl fisheries of Thoothukudi in Gulf of Mannar. There are about 80 pearl banks in this region. These banks vary in depth from 10-20 m. Maximum numbers of pearl banks are along Thoothukudi coast. Among the shellfishes, the pearl oyster - Pinctada fucata is an endangered species in this region. Apart from industrial pollution and intensive bottom trawling, settlement of heavy load of silt and clay from the Tamiraparani has also been identified to adversely affect the habitat and population of pearl oysters. Feeding of pearl oyster flesh by boring molluscs and barnacles are also the reasons for destruction of pearl beds. Presently, all the pearl beds are under the control of State Government.
Utilization
The bivalves are utilized in various forms such as frozen, dried, pickled and canned clam and mussel meat, oyster shell powder and other ornamental shells. Bivalve meat is consumed along the west coast. Smoked and canned oysters are found in big cities. In Kerala ad Andhra Pradesh clams are also used for preparation of artificial shrimp feed or directly as shrimp feed. Shells of bivalves are used for the production of cement, calcium carbide, sand-lime bricks and lime. The lime shell is used as manure, as mortar in building construction, as a pesticide by mixing with copper sulphate, in the effluent treatment and in glass, rayon, polyfibre, paper and sugar industries. Attractive bivalve shells are used and traded for ornamental purpose.
Conservation and management
Bivalves are one of the least managed fishery resources along the Indian coast. There is no proper regulation for effective utilization and conservation of bivalve resources. Sexually mature bivalves with high reproductive potential constitute bivalve fishery. Indiscriminate exploitation of young clams and mussels take place in some states, especially in Kerala and Andhrapradesh. Efforts for fishing bivalves can be enhanced in majority of the states. Pearl oyster spats need to be ranched in the pearl beds to improve the stock of pearl oysters.