Name of Fishery Clam Fishery (Black Clam)-(Gear –Hand pick & Dredge)
Target Species Villorita cyprinoides
Location India-South west coast (Vembanad Lake)
Fishing Area FAO 51
Fishery History Study reveals that fishery has been in operation for the past 61 years. Many fishermen have harvested black clams all their working lives and most have harvested for at least 25 years (Suja and Mohamed, 2010). During 1991-2000 period the annual black clam production varied from 28,806 t in 1998 to 38,456t in 2000 (Average 33,633t) (Laxmilatha and Appukuttan, 2002). During 2008-09, the black clam, Villorita cyprinoides (Family, Corbiculidae) contributes 45,000 t, or about two-thirds of total (66,000 t) production in India. (CMFRI Annual Report, 2009). Production of black clams fluctuated from 30,178 t to 40,299 t during 2012-2016. (CMFRI, 2017-unpublished)
Stock Biology Biological Informations such as habitat, size at maturity, Age and growth, Reproduction, spawning, condition index population density, etc. are available. The black clams are located just below the surface of the soft bottom sediments. The black shows preference to sediments containing 70% sand, 0-6% silt and 0-12 % clay (Kizhakudan and Narasimham, 1995). The black clam attains sexual maturity at a length of 11 to 15 mm. It spawns twice a year, from May to August, and from January to late March (Nair, 1975). Peak spawning period is during May – June (Kizhakudan and Narasimham, 1995). Males are dominant throughout the year with a sex ratio of 1: 0.25 (M: F) (Laxmilatha and Appukuttan, 2002). A change in salinity is the most important factor that triggers spawning. The optimum salinity for spawning is about 10- 12 ppt.
Data on Target
Species population Landing data of past 15 years are available. Data are collected from clam societies by CMFRI. The clam fishermen are organized into professional societies. The black clam attains a length of 30 mm by the end of its first year, and during its second year it grows an additional 11 mm (Nair, 1975). The estimated von Bertalanffy growth equation parameters are: L∞ = 58mm, K =0.56 (annual basis) and t0 = 0 (Kizhakudan and Narasimham, 1995). Rasalam and Sebastian, (1976) studied the population density of Veluthully Kayal (4,620 clams/m2) and Vayalar (2,860 clams/m2) of Vembanad Lake.
Fishing Activities Fishing is done by three methods (Narasimham, 2005). 1) Handpicking by women and children in shallow waters below 0.5 m depth at low tide (Catch/day = 6-16 kg). 2) In slightly deeper waters of < 1.15 m depth, women feel and detect the presence of clams by their feet, remove the clay over the buried clams by their feet, accumulate the clams at a particular spat and collect them in bamboo basket or aluminium containers. About 18-32 kg of clams are collected by women per day. 3) Fishing is carried mostly by men from a canoe with hand operated dredge. Harvesting of the black clams continues throughout the year (Kripa et al., 2004). Each fisherman harvests black clams about 20 days a month. Sundays are an off-day, fishermen cannot harvest in stormy days during the June to July monsoon months, and some days are taken to rest. The principal harvesting method is by diving under water and collecting the clams by hand. Most fishermen own their canoes, while others rent them at a rate of about Rs.20. Their harvesting gear also consists of a bamboo pole, about 15 ft long, and one of two types of cylindrical baskets (“koodu”). The harvesting sites with abundant clams vary somewhat among years according to spat settlement (Laxmilatha and Appukuttan, 2002; Ravindran et al., 2006). Fishermen harvest in a different site almost every day, and it often takes them about 1.5 hr to paddle each way.
In some harvesting location, the fishermen-divers do not use their fingers to gather the clams. Instead, they use an iron frame with a net.
Another harvesting method is using a hand rake with a pole attached (“kolli” or “varandi”) while standing in the canoe. Each fisherman and his family produce about 14 kg of meat and 130– 140 kg of shells on his best harvesting days
Large scale dredging for the white clam shells is practiced in Vaikom and Allappuzha. The subsoil deposit of white clams in the lake is estimated at about 4.5 million tons. The shells are taken at a rate of 41,000 to 69,000t/yr. Dredges are used where waters are about 3 m (8–9 ft) deep. The white clam shells are also harvested by individual fishermen, who use hand rakes from their canoes. Each fisherman collects 250–300 kg of white clam shells/day (Ravindran et al., 2006).
Ecosystem Impacts Kerala has a tropical climate with two rainy seasons, the heavy southwest monsoon from June to September and the lighter northeast monsoon from October to November. The lake has both brackish and nearly freshwater environments. They are separated from each other by a man-made bund or barrier, the Thanneermukkom, which runs across the middle of the lake. The government keeps it open to allow brackish water to flow to the southern part of the lake for six months, but then closes it for six months, December to May, each year. Black clams cannot reproduce well in low salinity and large areas in this southern region, otherwise suitable for the clams, cannot support them now. The average size of the black clams has diminished also. In the northern region, salinities from 8 to 18 ppt are usual in March to May but the water salinity can be as low as 0 ppt during the monsoon. Especially in the southern section of the lake, live black clams in some habitats have been buried by the sediments. Over the centuries, this annual process has led to the accumulation of large deposits of black clam shells.
Threats to Sustainability Catch of under sized clam or juvenile catch in some parts of Vembanad Lake is the major threat to sustainability in long run.
Fishers About 6,500 people are involved in the black clam fishery, 3,658 of these are fishermen and the remainders are their wives, children, and grandparents (Kripa et al, 2004; Sathiadhas et al., 2004). This fishery is their main source of income; some have other part-time jobs. Fishermen families are permanent residents of their villages.
Management Agencies The clam fishermen are organized into professional societies. There are eight black clam societies distributed around the lake in the Kottayam and Alappuzha districts. Fishing rights and licenses for harvesting in the lake are issued by the State Department of Mining and Geology. They in turn issue licenses for harvesting to their members. The total harvesting area leased out to the societies comprises about 4,582 acres (7.2 sq mi) (Laxmilatha and Appukuttan, 2002).
The taking of the fossil shell deposits is controlled by the government. Dredges are used where waters are about 3 m (8–9 ft) deep.
Processing and marketing Processing of the clams is usually done in the fishermen’s yards at home on the same afternoon. The clams are boiled in Aluminum tub for about 45 minutes with a fire fueled by wood and dry coconut leaves. While being cooked, the clam meats become loose from their shells. The cooked clams are separated through sieve. The mesh size of the sieve is chosen to hold the shells but it allows the meats to fall through to the ground. The ratio of meat to shell weight is 1 to 10; the wet meat percentage varies from 9 to 14% (Laxmilatha and Appukuttan, 2002). Each fisherman and his family produce about 14 kg of meat and 130–140 kg of shells on his best harvesting days. Fishermen’s wives usually sell the meat. Most is sold in the local village door-to-door. The black clam shells are in high demand because the occurrence of lime- stone is scarce. The shell is used by industries that make cement, calcium carbide, and lime (for use on rice farms). The gross and net returns from marketing of black clam at Alapuzha were Rs. 82,720/- and Rs. 58,220/- respectively per family per year (Nikita et al., 2014).
Management Regime CMFRI provide the state level policy details which includes management plan for fisheries as a whole. Recently CMFRI included black clam in Minimum Legal Size (MLS) list and is adopted in KMFR Act.
Management Compliance Yes fishers comply with management regime
Community Participation in Management Yes, Community is involved in the management of the fishery. No strict enforcement
Interest in Certification Fishery interest in certification will be decided based on stake holder meeting shortly
Stake holders Key stakeholders are fishers, buyers and processors/exporters
Issues Requiring Special Attention
CMFRI, 2009. Annual Report 2008-09. Central Marine Fisheries Research Institute, Cochin.
CMFRI, 2017 (unpublished). Annual Report 2016-17. Central Marine Fisheries Research Institute, Cochin.
Kizhakudan, J.K. and Narasimham, K.A. 1995. Observations on the population characteristics of the corbiculid clam Villorita cyprinoides (Gray) in the Citrapuzha portion of the Vembanad Lake. CMFRI Spl. Publ., 61:83-87.
Kripa, V., T. S. Velayudhan, J. Shoji, P. S. Alloycious, P. Radhakrishnan, and J. Sharma. 2004. Clam fisheries in Vembanad Lake, Kerala, with observations on the socioeconomic conditions of the clam fishers. Mar. Fish. Info. Serv. T and E Series No. 178:14 -16.
Laxmilatha, P and Appukuttan, K K. 2002. A review of the black clam (Villorita cyprinoides) fishery of the Vembanad Lake. Indian Journal of Fisheries, 49 (1):85-92.
Nair, G. S. 1975. Studies on the rate of growth of Villorita cyprinoides var. cochinensis (Hanley) from the Cochin backwaters. Bull. Dep. Mar. Sci. Univ. Cochin 7(4):919–929.
Narasimham, K.A. (2005). Molluscan fisheries of India. BR Publications, New Delhi, 348p
Rasalam, E. J., and Sebastian M. J. 1976. The lime-shell fisheries of the Vembanad Lake, Kerala. J. Mar. Biol. Assn. India 18(2):323-355.
Ravindran, K., Appukuttan, K. K., Sivasankara Pillai, V. N., and Boopendranath, M. R. 2006. Report on the committee of experts on ecological and environmental impact of dredging at Vaduthala Kayal and Vaikam Kayal. Unpubl. rep. submitted to the Government of Kerala, Thiruvananthapuram. Sept., 2006, 45 p.
Sathiadhas, R., F. Hassan, and Y. J. Raj. 2004. Empowerment of women involved in clam fisheries of Kerala—a case study. Indian J. Soc. Res. 46(1):39-48.
Suja, N and Mohamed, K. S. 2010. The black clam, Villorita cyprinoides, fishery in the State of Kerala, India. Marine Fisheries Review, 72 (3): 48-61.