Spatial modelling for optimisation of bivalve culture: A case study for Green Mussel (Perna viridis) and Blood Cockle (Anadara granosa) culture in Pattani Bay, Thailand
Supat Khongpuang: Ph.D.
Pattani Bay (right) is a relatively small bay, around 58 km2, in the southern most part of Thailand. It is used intensively for many purposes; fish processing plants, urban and community settlement, coastal aquaculture (shrimp farms, cockle, mussel, sea bass and seaweed culture), communal/industrial waste water treatment area, fishing grounds, and a mangrove reserved area.
Focusing on marine molluscs, the bay has at least 90 species and 10 of them are of economic importance. Among the various uses, some conflicts are inevitable. GIS–based modeling is one of the possible technologies that can be used as a part of the Pattani bay sustainable fishery resources management. This study project develops a “GIS-Based Model for Economic Marine Molluscs Production and Management in Pattani Bay”. The study focuses mainly on green mussel (P. viridis) and bloody cockle (A. granosa), which are considered as the dominant economic species of the bay, as well as in Thailand and many Asian countries.
The main input data are classified into 3 different groups, (1) water and sediment quality parameters, (2) empirical mussel growth and (3) secondary data. Twelve water parameters were collected during June 2009-February 2010 at 1-2 times a month while the mussel growth was done during June-September 2009. The important secondary data are sattelite image of study area, and biology and ecology of the two species mentioned previousely. The different combination of data group are combined for different purposes. The main output models of the study are (1) mussel growth determination models, (2) suitable mussel culture and harvestable areas models and (3) optimization for suitable cockle culture area models.
For mussel growth determination, Principal Component Analysis (PCA) and Multiple Linear Regression (MLR) are employed and the study found that the main determinants for mussel growth are particulate organic matter (POM), chlorophyll-a and salinity. All three together can predict mussel growth for 85% while that of the last two and salinity show the prediction success of 84.92 and 83.43%, respectively. The spatial growth of mussel predicted by salinity is shown at right (above). The suitable area of mussel culture is around 13.275 km2 and the rest area of the bay is limited by salinity, water depth and ship route. Based on the empirical growth of mussel by length, the harvestable areas of mussel in the bay can be calculated (right, below).
The area suitable fro cockle culture is estiomated by Multi-Criteria Evaluation (MCE) and fuzzy suitability scores based mainly on water and sediment qualities. The most suitable area is found in the middle part of the bay (see right). When compared to existing farm areas (blue line), it can concluded that some parts of existing farms are in vulnerable low salinity and low pH areas. However, farm relocation is technically feasible.