THOOTHUKUDI : Over six decades after the fishing of pearl oysters was banned by the State fisheries department, the ICAR-Central Marine Fisheries Research Institute (CMFRI) has sea ranched (released into the sea) over five lakh hatchery-produced Indian pearl oyster spats into the Gulf of Mannar along Thoothukudi coast in order to replenish the pearl oyster population.
Even centuries ago, Thoothukudi was renowned across the world for pearl production, and the region was a leader in the international pearl trade through exports through the port of Korkai. The rich trade had even earned Thoothukudi the sobriquet 'Pearl City. The indigenous species of Indian pearl oyster, Pinctada fucata (Gould) is one of the three valuable species of pearl oyster cultured across the world. The other two are P maxima (Jameson) and P margaritifera (Linnaeus). The Pinctada margaritifera, known as black-lip pearl oyster, is limited to Andaman and Nicobar islands, while Pinctada fucata was largely present in the Gulf of Mannar region.
Pearl fishing activities carried out from time immemorial along the coast of the Gulf of Mannar came to a grinding halt in 1961 after the oyster stocks waned. The 1961 annual report of CMFRI stated, "More than 1,500 divers were engaged in pearl fishery and an average of 3 lakh oysters were fished every day." The next year, the Department of Fisheries also banned pearl oyster fishing citing excessive netting as the reason for the acute drop in the pearl oyster population.
District Collector Dr K Senthil Raj sea ranched the spats at 'Tharaipaar', situated one nautical mile off Tsunami Nagar coast after reaching there in a country craft boat. The district administration will extend all support for the rejuvenation of the Indian pearl oysters and their marine habitats, he assured. Later, spats were also sea-ranched near Chippikulam.
Scientist M Kavitha attached to the Shellfish Fisheries Division said over five lakh Indian pearl oyster spats of 5 mm size (dorsoventral measurement) were produced in the hatchery, and they could be raised as adults and used for pearl culture. The ongoing sea ranching programme is expected to significantly replenish the lost pearl oyster resources at the Gulf of Mannar and result in the development of a commercially viable fishing exercise.
It may be noted that the oyster spat hatching experiment began a year ago following consistent pressure put on the CMFRI by the Union Fisheries Ministry to research and culture pearl oysters at the institute. According to scientists, the Indian pearl oysters grow on underwater rocky surfaces at a depth of 10 to 20 metres, 10 nautical miles off the shore. The sessile organism sticks to the paars using its byssus thread. When a foreign particle enters into a mature oyster, it secretes a solution called "macer" which encapsulates the particle, which gradually develops into pearls, they said.
The oyster spats from the hatchery were arranged into cages and placed at select locations over the paars at Tsunami Nagar coast and Chippikulam. "This being an experimental project, the cages will be cleaned once in 15 days, and the spats will be measured randomly once every month. The areas selected for placing the cages are spots where trawling and other destructive fishing methods are not taken up," Kavitha said.
Referring to previous studies, the scientist said the oysters deployed are expected to grow up to 5 cm in length in 15 months. "At this stage, they become mature and begin spawning. It can grow up to 8 cm in length in two years. The adult pearl oysters will be taken back to the CMFRI laboratory for pearl implantation. In a conditioned lab, a nucleus will be implanted into the adult oyster shell and it will be observed for two days at low temperatures before being left in the sea. The implanted oysters will again be placed undersea for six to nine months to obtain pearls," she added.
Having no proper follow up on the previous studies conducted decades back, the CMFRI scientists hope to generate a baseline study on Indian pearls during this experiment. Dr PS Asha, Principal Scientist & Scientist-in-Charge, Tuticorin Regional Station of CMFRI, told TNIE that though many sea ranching exercises had been conducted before to increase its population in the gulf, they were not monitored properly and their progress was not documented. "This time, we will closely monitor the experiment and evolve a method to produce Indian pearls," she said.
Though pearl fishing was banned in 1962, its population witnessed no surge in the following decades due to destructive fishing methods like trawling, experts said. "The Gulf of Mannar region had as many as 80 pearl banks between Kilakarai and Kanyakumari. Bottom trawling on the seabed by mechanised vessels that are fit with trawlers comprising heavy iron rods destroyed those pearl oyster habitats," they contended. Pearl divers are now enthused following the oyster replenishment experiment. Members of the Mutharaiyar community were largely involved in collecting pearl oysters from the sea bed previously.