Water resources and freshwater aquaculture development of Yucatan, Mexico
The suitability of aquaculture for inland water bodies in the State of Yucatan, a karstic area of southeast Mexico was investigated. Five types of water bodies distinct in morphometric and hydrological characteristics were identified through land-based surveys. Representative sites for each were selected for further study: a sinkhole, a permanent aguada (clogged sinkhole), a rain-filled seasonal pond, a small <1 ha) gravel quarry and a large (>9 ha) gravel quarry. The water quality in all of the sites had a high pH (range 7.2-9.4) alkalinity (range 130-840 mg/l CaC03) and hardness (range 198-998mg CaC03). Their nutrient status varied from the permanently stratified and hypereutrophic conditions in the permanent aguada, to oligotrophic conditions in gravel quarries. In general, the water quality resulted adequate for fish culture in the gravel quarries, the sinkhole and in the seasonal pond, but ecological considerations prevented sinkholes for aquaculture development. Aquaculture trials involving the stocking of fry of the native cichlid Cichlasoma urophthalmus and O. niloticus in seasonal ponds and a small gravel quarry demonstrated the feasibility of neglected water bodies for small-scale aquaculture. A net yield of 180 Kg/ha/6 months was obtained from a gravel quarry fertilised with grass Panicum virgatum and stocked with C. urophthalmus. Yields from seasonal ponds were 157Kg/ha of O. niloticus from a small (0.010 ha), and 30 kg/ha of C. urophthalmus from a large (1.11 ha) seasonal pond (no fertilisation or feeding. An environmental impact assessment was carried out at an experimental cage site in gravel quarry. An estimated 0.02 kg of phosphorus was wasted per kg fish produced. A socioeconomic survey on attitudes towards aquaculture adoption was carried out in four agricultural villages and a fishing port. This led to the construction and operation of a small pond demonstration unit. Results suggest that farmers are receptive and adoption of aquaculture as a complementary activity may be feasible and beneficial to rural development, especially in areas with existing water bodies. Economic modelling of the different production units involved showed returns to labour higher than the average agricultural wage. A computer-based Geographical Information System identified areas suitable for aquacultural development. Two major areas were identified: the northern Karst plains where gravel quarries are abundant and suitable for intensive cage-culture; and the southern hilly region where small-scale seasonal aquaculture could be developed.