Scallop Farming Techniques
Collection of Larval Stage
Information Gathering
With the information obtained earlier in the bio-oceanographic stage, we proceed to the installation of manifolds. This stage requires very specific dates to maximize the peak spawning. Otherwise, the deposits will be poor.
Spawning Season
Although scallops spawn almost throughout the year, major spawning occurs in the spring and summer months. The first larvae for the period referred to above begin to appear in November, with a peak incidence between December and January, decreasing gradually until April.
Collector Placement
The area inside the bay where the collectors are installed must ensure the widest possible uptake. It is useful to study pre-currents, as the place of greatest concentration of larvae usually corresponds to areas of convergence of currents or eddies. The depth at which the collectors are placed is determined by plankton analysis and with the help of a test collector.
Collectors
Collectors, based on Japanese technology, consist of mesh bags suspended from a “long-line” forming a curtain or barrier to the passage of larvae swimming in the water column. The lock period is very brief and occurs, depending on temperature, between 15 to 20 days after spawning, hence the importance of the precise date on which to place the collector.
Seed Growth
The seed captured by collectors is grown in them for periods ranging from two to four months, depending on the experience of the growers. Some growers prefer to cultivate the seed early to minimize mortalities, but in no case should the seed be left in the collector for more than four months due to the increased mortality rate from predators. At the end of this period, the seed has reached sizes ranging from 6 to 30 mm long.
Intermediate Stage of Crop or Pre-culture
Seed Harvest and Selection
This stage begins with the harvest of the seed collected on the collectors, which is then selected and transferred to culture trays called “pearl-nets”, where they remain for a period ranging from three to six months.
Density in Trays
In trays, scallop densities vary inversely with growth, as they are species that do not tolerate overcrowding. Initially, densities of 100 to 200 scallops per “pearl-net” are used, ending with a density of 20 scallops per “pearl-net” before being transferred to the final crop structures or “headlights”.
“Stretcher” Use
Some growers who harvest the seed from the collector early, before moving them to “pearl-nets”, and because they are still small, use a structure called a “stretcher”, consisting of a wooden frame covered with a fine mesh to retain scallops of 2 to 4 mm. Apparently, this system minimizes the loss of juveniles by detachment and predation.
Final Stage of Crop or Fattening
Transfer to Final Structures
This stage begins with the movement of scallops from the “pearl-nets” to headlights or other cultivation systems to achieve market size growth of 65 mm. Scallops from the “pearl-nets” can, at this point, follow three paths:
- Transfer of the “pearl-nets” to headlights
- Keeping the “pearl-nets” until market size, for which the density should be further reduced (10 to 15 scallops in each)
- Dropping directly to the bottom of the marina concession.
Growth Period
Whichever way is used, scallop juveniles remain in the chosen culture system until they reach marketable size, which is achieved between 14 to 18 months from the moment of fertilization.
Ear Suspension Culture
Apart from the system suspended in mesh trays, such as “flashlights” and “pearl-nets”, the “ear suspension culture” system (ear hole) is also used. In this system, the scallop’s ear is pierced, and it is suspended from a rope. This growth system is as good as the flashlight system but requires more labor. The shedding of scallops due to the rupture of the ear in severe sea conditions is high. However, if appropriate materials are used, the cost of materials in this type of culture is much lower than the tray system, but there are further losses and more manpower required.
Suspension Culture in Bags
Another system different from the previous crop is the “suspension culture in bags”. This is a technology developed locally due to the high cost of traditional culture elements. It consists of placing the scallops in a plastic mesh sleeve, crossing the suspension cape at each end of the sleeve, introducing two or three scallops, and then closing the ends. The sleeves are interspersed every 30 cm. This experimental system is working well because it is very low cost, and similar growth is said to be even higher than in headlights. It also decreases the action of polychaetes that pierce the shell. However, the leaflets grow deformed, which is a problem when selling the scallops in their shells. It requires more labor, and in farming centers that handle millions of scallops, this is a factor limiting its use.