3.3.2. Intertidal and shallow water culture
This is an off-bottom type of mussel culture. Rack culture is predominantly practiced in the Philippines and Italy where sea bottom is usually soft and muddy, and tidal range is narrow. The process involves setting of artificial collectors on poles or horizontal structures built over or near natural spawning grounds of the shellfish. In the Philippines, this is called the hanging method of mussel farming. The different variations used are as follows:
Hanging method. The process starts with the preparation of the spat collectors or cultches. Nylon ropes or strings, No. 4, are threaded with coco fibre supported by bamboo pegs or empty oyster shells at 10 cm intervals. These collectors are hung on horizontal bamboo poles at 0.5 m apart. A piece of steel or stone is attached at the end of the rope to prevent the collector to float to the surface. Setting of collectors is timed with the spawning season of the mussels. Spats collected are allowed to grow on the collectors until marketable size.
Stake (tulos) method. The stake method is midway between the rack and bottom methods. Bamboo poles, 4-6 m in length are staked firmly at the bottom in rows, 0.5-1 m apart during low tide in areas about 3.0 m deep and above (Fig. 3). In areas where water current is strong, bamboo poles are kept in place by nailing long horizontal bamboo supports between rows. Since mussels need to be submerged at all times, it is not necessary that the tip of the poles protrude above the low water level after staking. However, boundary poles should extend above the high water level. In staking, enough space between plots is allowed for the passage of the farmer’s banca during maintenance.
Collected spats are allowed to grow in-situ until marketable size, 5-10 cm after 6-10 months. It has been observed, that about 2,000-3,000 seeds attach on 1 metre of stake, 1-2 m below low water level.
Tray culture. Tray culture of mussels is limited to detached clusters of mussels. Bamboo or metal trays, 1.5 m x 1 m x 15 cm sidings are used. The tray is either hang between poles of the hanging or stake methods or suspended on four bamboo posts.
Wig-wam culture. The wig-wam method requires a central bamboo pole serving as the pivot from which 8 full-length bamboo poles are made to radiate by firmly staking the butt ends into the bottom and nailing the ends to the central pole, in a wigwam fashion. The stakes are driven 1.5 m apart and 2 m away from the pivot. To further support the structure, horizontal bamboo braces are nailed to the outside frame above the low tide mark. Spats settle on the bamboos and are allowed to grow to the marketable size in 8-10 months.
Rope-web culture. The rope-web method of mussel culture was first tried in Sapian Bay, Capiz, in 1975 by a private company. It is an expensive type of culture utilizing synthetic nylon ropes, 12 mm in diameter. The ropes are made into webs tied vertically to bamboo poles. A web consists of two parallel ropes with a length of 5 m each and positioned 2 m apart. They are connected to each other by a 40 m long rope tied or fastened in a zigzag fashion at an interval of 40 cm between knots along each of the parallel ropes (Fig. 6). Bamboo pegs, 20 cm in length and 1 cm width are inserted into the rope at 40 cm interval to prevent sliding of the crop as it grows bigger.
4.0 Mussel transplantation to new site
Transplantation of young mussels from natural spawning grounds to sites with favorable conditions for growth is practiced in numerous countries as mentioned earlier. In the Philippines, however, mussel transplantation to new sites is being encouraged to develop new areas for mussel culture, due to various reasons. Major reasons are: rampant pollution of some existing mussel areas, urbanization growth near mussel farms and competitive use of lands.
Mussels to be transplanted could be breeders or young adults. Important points to be considered are: Conditions from natural spawning areas must be almost similar to the new area, mussels on original collectors showed better survival than those detached, and in transporting the mussel avoid being exposed to heat and freshwater.
5.0 Harvesting procedure
Harvesters should be aware of the stress caused during the harvesting process. In harvesting mussels special care is needed. Pulling them or using a dull scraper may tear the byssal thread. This will result in loss of moisture after harvest or cause physical damage causing early death of the bivalve. The right procedure is to cut the byssal thread and leave it intact to the body. Exposure to sun, bagging and transport also increases the stress of the mussels.
7.0 Economic aspects (the figures and amounts below maybe outdated and just an estimated value)
TABLE 1. Project costs, income from mussel farming at Samar by long-line, rope-web and stake culture systems.
TABLE 2. Cost-benefit ratio for a 300 sq. m. area of mussel stake culture.
The term primary processing is applied to the component of mussel production to make it ready to the live, fresh market. Secondary processing is applied to frozen, canned or cooked mussels.
Depending on the goals and focus of the growers, those who get involved in the promotion of their crops enjoy a much greater return for their product than those who don’t.
It is important to remember that until somebody consumes what you grow, you are just spinning your wheels. As the production of cultured mussels continues to expand, consumption must increase also. Controlling quality is one key to that growth.
Mussel growers have a number of options for which to choose when deciding on socking material and methods. It’s important to consider the region and specifics of the site when making the choice, with an eye toward achieving a profitable seed conversion ratio.
For complete instructions with illustrations read here