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Fisheries > Culture Fisheries > Mussels

Farming systems

There exist six different types of farming systems that are practiced for mussel culture.

1. Bottom culture

This method is extensively followed in Netherlands. The mussel growing areas have an average depth of 5 m. Seed measuring 10-15 mm in length are dredged from the natural grounds and transplanted usually on muddy grounds. Before marketing the mussels are again laid on firm sandy ground. The entire operations are mechanised with machines for washing, separating clusters and removing the byssus. Bottom culture has not been experimented in India.

2. Stake culture

This method is practiced in France and Philippines. It is suitable where the bottom is muddy and the tidal amplitude is high. In France, poles (called bouchots) of 20 cm diameter and 3-4 m length are driven into the substratum to a depth of 1 m in the intertidal area. The poles are spaced 1 m apart. Mussel seed collected on horizontally placed ropes is removed and placed in plastic net tubing and wrapped spirally around the bouchot. The mussels are harvested in 12-18 months when they grow to 68 cm in length. This method is practised in northern France where the tidal amplitude is about 15 m, exposing extensive areas of mud flats. It is desirable to experiment this method along the Gujarat coast.

In the Philippines, bamboo poles are driven into the bottom where the water depth is 2-5 m. They are spaced 1 m apart. The natural setting of spat on the poles is allowed to grow for 6-8 months to reach the marketable size of about 5 cm. The production is about 15 kg/4 m length of pole and about 50 t/ha. A variation of the single pole method is to form a wigwam wherein about 10 poles are staked in 2 m circle and tied together at the top. It is stated that this structure withstands the wave action better than single poles.

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Stake culture

bouchot

Bouchot culture

 

3. Rack and Bag culture

The strings used in oyster culture are replaced by flexible synthetic mesh tubing of variable mesh size. Mussel seed of 10-15 mm in length are loaded in these tubes and suspended from racks. This type of culture in shallower water, is gaining popularity, and the problem of mussels slipping is overcome by this method.

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Rack and Bag culture

4. Rope culture

Rope culture of mussel is widely adopted in Northern Kerala. Ropes are suspended from rack made of casuarina and bamboo poles. The average area of rack is 400 m2 and length of the ropes used for seeding ranges from 1-1.25 m depending on the depth of the water column. Polypropylene ropes wound with coir ropes are used for seeding. These ropes are hung down from the racks at an interval of 1 feet and nearly 500 - 550 ropes could be suspended from one rack. The seeds collected from wild are being sold in units of one bag and one bag of seed can be used to seed 8-10 ropes. The normal size of the seed ranges from 35-65 mm. Seed collected has to be seeded on the same day and it is estimated that one person can seed around 60-70 ropes in a day. The culture period in Northern Kerala where the activity is taken up fairly on a large scale starts from November and ends in the middle of May before the rains. Once in a fortnight the ropes are lifted for monitoring the growth and removal of fowling organisms. The mussel grows to 80-100 mm size within 6 months of culture period and it is estimated that around 2 lakhs mussels can be harvested from 400 m2.

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Rope culture

5. Raft culture

Spain is the leading producer of mussels in the world by the raft method. In the Galician Bays on the northwest coast of Spain, 20 m x 20 m size rafts made from eucalyptus wood are moored. Seed measuring 10 mm are collected either from the natural grounds or on ropes hung from rafts. About 500 numbers of 10 m long seeded ropes are suspended from a single raft. The ropes have 25 cm long plastic pegs at every 40 cm length to prevent the mussels from sliding down the rope. The mussels grow to the market size of 8-9 cm in 16-18 months. A 10 m long rope yields 100 kg of mussels and the production per raft is 50 t.

This method has been widely experimented at several locations in India and gave highly gratifying results. Rafts are moored in sheltered bays and also in the open sea under favourable conditions in depths of 5 m or more. Rafts made of teakwood or bamboo poles, measuring from 5 m x 5 m to 8 m x 8 m sizes have been used in India.

P. viridis: The size of the seed ranges from 20 mm to 30 mm in length. About 500 to 700 g of seed is used in one metre length of rope. Coir ropes of 20-25 mm diameter and nylon rope of 14 mm diameter are used for growing the mussels. The mussel seed are spread over 25 cm wide knitted cotton clothes and the rope is kept over the mussel seed on the knitted cloth. To prevent the slipping of mussels in the initial stages of growth, wooden pegs are inserted in the rope at fixed intervals. The knitted cloth is wrapped over the rope, securing the mussel seed and both the ends of the knitted cloth are stitched with cotton twine. The seeded part of the rope measures 5 m to 8 m and the ropes are suspended from the raft, 0.5 to 1 m apart. Care is taken to ensure that the end of the rope is about 2 m above sea bottom. The mussels attach to the ropes in 2-3 days and the cloth cover disintegrates in about 10 days.

Farm management involves maintenance of the raft, thinning; the ropes if necessary and removal of the fouling organisms etc. Accumulation of silt and growth of plants over the mussels’ arc found to be negligible at Calicut. The common foulers arc barnacles, tubiculous polychaetes, ascidians, coelenterates and bryozoans. Heavy settlement of the barnacle, Ralanus amphitrite, is common, particularly at the upper 2 m length of the suspended rope. Periodically the foulers are removed manually. Also, exposure of the ropes for a couple of hours to atmosphere helps to kill the larvae of fouling organisms. Crabs, lobsters and fishes are the predators of mussels. The duration of culture is 5 months at Calicut and the ropes seeded in November are harvested in April. The mussels attain 80-88 mm in length (wt 36-40 g) at harvest.

P. indica: Smaller rafts of 6 x 6 m and 5 x 4 m size were used in the Vizhinjam Bay and open sea off Vizhinjam. The average weight of mussel seed per metre length of rope ranged from 1.4 Kg to 2 kg and they have attained 10-15 kg in 7 months in the bay and 15 kg in 5 months in the open sea. With the average production per metre length of rope at 12.5 kg and the seeded portion of rope 5 m, a total of 50 ropes suspended from a 6 x 6 m raft yield 3.1 t of mussels in 7-8 months in the Vizhinjam Bay. The production in the open sea is still higher at 3.75 t/raft/5 months.

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Raft culture

6. Longline culture

The longline system developed for mussel culture in the last 20 years is fast emerging as the most important method throughout the world for mussel culture. It is derived from the Japanese longlines used for culturing oysters, pearl oysters and scallops. The longline method of culture is well developed in China, New Zealand, Korea, Italy and Chile.

The longline system consits of a main line, floats, anchors, marking buoys and connecting ropes. The longlines are made of 16 mm to 20 mm diameter synthetic rope. The main rope (longline) is 150 m long and at every 5 m length, a 220 litre barrel is tied to it and anchored with concrete blocks. Ropes with mussel seed are suspended from the main rope. Spat collection ropes are also hung from the same longline, and often these are directly used for growing the mussels. In the Netherlands the European mussel Mytilus edulis grown on longlines reaches the marketable size of 40-45 mm in 12-14 months and the production is 10 kg/m ropes. Longline method of mussel culture has not been attempted in India.

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Longline culture

(Source: www.photolib.noaa.gov)

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