44 DECEMBER 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Requirements for pond aquaculture include land for pond construction, soil with suitable properties for constructing stable embankments, sufficient water availability and an enabling socioeconomic environment (Giap et al. 2005). Data reported by national aquaculture agencies to the FAO Fisheries and Aquaculture Department for compiling country-level aquaculture production statistics1 are based on pond water surface area. However, additional land on farms is necessary to support the pond culture system, including embankments, canals, roads, storage areas, buildings and parking lots, as illustrated in the image of a farm in Figure 1. This land is needed for farms to operate and usually cannot be used for other purposes. Since the middle of the 20th century, aquaculture production has increased sharply in response to increasing demand for foodfish. Farmers reacted by establishing more farms and by intensifying production on existing farms to meet this demand. This phenomenon is continuing in the 21st century. Intensifying a system requires a greater stocking density; use of feeds, antibiotics, pesticides and disinfectants; and a greater amount of mechanical aeration (Sapkota et al. 2008). On intensive farms, ponds tend to be smaller than on extensive and semi-intensive farms, and this means a relatively greater area for roads and canals on intensive farms. The intensity of pond aquaculture has been increasing as better management practices were developed and implemented. For example, channel catfish production in the southern USA averaged Land to Water Surface Area Ratio in Pond Aquaculture Lauren N. Jescovitch, Philip Chaney and Claude E. Boyd less than 2 t/ha in the late 1960s, but is over 5 t/ha today (Boyd et al. 2013). Measuring the Area of Aquaculture Ponds Based on 2005 data, there were about 11.1 million ha of water surface area of ponds in the world, including freshwater and saltwater areas (Verdegem and Bosma 2009). This number possibly has increased to around 16.7 million ha, based on 2011 aquaculture production data from FAO, assuming no increase in production intensity during the intervening 6 years. This area is very likely an underestimate of the total amount of land dedicated to aquaculture use. The most accurate way of measuring water and land areas is with conventional surveying and mapping techniques (Boyd and Shelton 1984). This technique requires surveying instruments and knowledge of their use and is time-consuming and tedious. Considering the alternatives, estimation of areas using satellite imagery was considered appropriate for the objectives of this study. Remote sensing and GIS allow the acquisition of a series of synoptic data for large geographic areas, uniformly in space and time, and without the need for exhaustive field surveys (Green et al. 1996). This permits prediction of impacts to the local environment of food production around the globe. Aquaculture competes for resources with other economic activities, and should be evaluated for the sustainability of land management (Alonso-Perez et al. 2003). The satellite imaging approach requires current and accurate thematic information to TOP, FIGURE 1. A typical farm, located in Malaysia, that was evaluated in this study. Screenshot by Lauren Jescovitch. BOTTOM, FIGURE 2. Natural breaks in the distribution of land to water surface area ratios were determined from a sample of 100 farms by Jenks Optimization. The average ratio of total land area to pond water surface area was 1.48, with a range of 1.08 to 4.02. Most farms had land to water ratios less than 1.89. As average pond size increased, the ratio decreased, stabilizing at about 1.25 beyond a pond water surface area of 3 ha. A ratio <1.29 can be recommended as a standard for improved land use efficiency in pond aquaculture.
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