Coastal Aquaculture and Mariculture

Unit 7- Molluscan resources

7.1.1. Gastropod fishing
Chank Fishing in Gulf of Mannar
Xancus pyrum popularly called, sacred chank forms an important fishery in the Gulf of Mannar. They live in sandy areas preferably under burrows, in search of food such as small polychaete worms and algae. They are abundant in the Paar areas locally known as Sangu nilam where coarse sand and dead corals characterize the bottom areas. About 49 such Paars extending on an average from 4 to 25 km² are present in the GuIf of Mannar. The depth of these grounds ranged from 16 - 24 metres. The chank fishery, which has a long history in Tamilnadu, is solely restricted to Gulf of Mannar for the best quality of chanks viz. X. pyrum var. acuta. Hornell (1915) distinguished five well marked sub-species of T. pyrum in different localities. The varieties distinguished are T. pyrum var. acuta, T. pyrum var. obtusa, T. pyrum var. globosa, T. pyrum var. comorinensis and T. pyrum var. lusus. Their breeding season is during February -March. In Tamilnadu, around Tuticorin, the chank fishing season starts during middle of October and extends to May and moves up the coast to Cuddalore and Rameshwaram until July or August. Over 95% of catch is taken by skin-diving upto 20 m depth, while remaining comes from incidental catches taken in various fishing gears i.e., trawl and bottom set gill nets.
Chank fishery was under the monopoly of State Fisheries Department of Tamilnadu up to 1993. Now the Department has been giving lease of rights of chank fishing to the local chank traders. The chank fishery of Thoothukudi consists of T. pyrum var. acuta, locally known as Jadhi. The chanks collected from this region are very thick and glossy. Hence, they are considered as the most suitable raw material for the bangle industries. Accordingly, they fetch the best price in the market.

During a diving day, on an average 50 to 70 boats are engaged in chank fishing. In a boat about 4 to 6 divers take part and one diver collects about 15 to 20 chanks in a day. Trawlers also land chanks occasionally. Chank production in Gulf of Mannar during 2003-04 was 239 tonnes. The most important chank beds are near Thoothukudi, Tiruchendur and Kilakarai. The estimated chank landings off Thoothukudi, exclusively from traditional skin-diving, were 4.2 lakh numbers during 2003, whereas they drastically decreased to 2.92 lakh numbers during 2005. Comparing the last three years, chank production has fallen considerably. It is a vulnerable shellfish species.
The chank resources are under severe threats all along the coast of Tamilnadu. The factors like intensified bottom trawling, catching of baby chanks and mother chanks during breeding season, dumping industrial effluents etc. are leading to heavy depletion of this valuable resource off Thoothukudi coast. Further, the recent demand for ornaments, making food and medicine led to increased exploitation. Hence, conservation of this resource is of great importance.