Mussel farming depends entirely on onenatural phenomenon: spatfall. This is the periodwhen mussel larvae are developed enoughto cease their floating existence, settle, andattach themselves to solid surfaces.
Successful collection of these spats is essential formussel farming. While the technology to artificially produce the spats in controlled conditionsis available, it is not yet economicallyviable and is probably not necessary consideringthe abundance of natural spats. Themussels need not be grown in the same areawhere the spats are collected, and in somecases it is actually more desirable to have aseparate growing area.
Here in the Philippines,however, all successful mussel farmingventures have been conducted in the spatfallareas. Thus, at the moment, the presence ofnatural mussel spatfall should be considered aprimary criterion in determining the viability ofa potential mussel farming project.
The following parameters must be considered in site selection:
1. Sufficient breeding stock and spatfall.
2. Protection from strong winds and waves. Area must be sufficiently enclosed to retain larvae.
3. Enough tidal range to change watercompletely and frequently; strong tidalcurrent (>2 cm/s); and depth of at least2 m at low tide.
4. Sufficient food in the water. (Generally,clear waters do not contain enough foodto sustain optimum growth. Greenishwater is one indication of food availability.)
5. Distance from river mouth as abrupt salinity changes is possible.
6. Proximity to market.
7. Absence of sources of pollutants.
Selection of suitable collector materials
Mussel farming depends largely onplacing the right type of collector in the rightplace at the right time or season to collectyoung mussels or spats. The material whichwas proven most effective is coconut huskbecause of its hairy, fibrous nature that is veryattractive for mussel larvae to settle on. Furthermore,coconut husks are readily availablein the Philippines and are easy to prepare. Thehusk is stripped from the coconut shell andshredded. The only difficulty with coconuthusk, however, is that it does not last long inthe water, so that usually the mussels will haveto be “re-laid” or transplanted.Other suitable materials as collectorsare cabo negro, old frayed ropes, etc.
1. Cultures should always be underwater even at low tide. Mussels that attach and survive above the lowest tide level are generally stunted or deformed.
2. Cultures should always be in an off bottom position to prevent potential predators such as starfish, crabs, snails, and other organisms from crawling up the culture ropes.
3. Materials used should be durable enough to last at least until the mussels are harvestable.
4. Clusters of mussels on a rope should be adequately spaced to avoid contact with each other through wave action.
5. Structures must always be positioned so as not to obstruct navigation.
6. Cultures should be laid perpendicular to wave action and lined up in the direction of current flow.
7. The environment of a mussel farm degrades with continued use. It is advisable to have an area 2-3 times larger than actual culture site to allow the farm to be moved from one section to another.
Materials and design. Raft or suspension culture of mussels consists of growing mussels on ropes hung from rafts or other similar floating structures.
Spat collectors (coconut husk) are inserted in the lay of ropes to collect mussel spats. These spats are allowed to grow for 4-5 months and are harvested when they reach37-60 mm in length.
Spat fall period can be predicted with a fair degree of accuracy after a few years of observation. Thus in Baco or Bay, farmers generally lay their stakes before April and in November. In Sapian Bay, the periods of highest spat fall intensity are from February to March and again from September to October.
In Himamaylan River, the spatfall occurs inMarch with a lower-intensity spatting inOctober. Generally, for greater chances ofspat settlement, the collectors or ropes shouldbe installed not earlier than February and notlater than March to catch the first spatfall which is usually the heavier one. For the secondaryspatfall, ropes should be laid not earlier than September and not later than November.