Fisheries and cage culture of three reservoirs in west Java']Java, Indonesia; a case study of ambitious development and resulting interactions

The interactions between cage culture and wild fishery activities in three Indonesian reservoirs, Saguling, Cirata and Jatiluhur, of the greater Ciratum watershed, West Java, were evaluated using historical data and interviews with cage culture operators. In all three reservoirs, cage culture of common carp, Cyprinus carpio L., and later of common carp and Nile tilapia, Oreochromis niloticus (L.), were encouraged as an alternative livelihood for persons displaced by the impoundment. Currently, a two-net culture system, locally known as 'lapis dua', in which in the inner cage (7 x 7 x 3 m) is used for common carp culture and the outer cage (7 x 7 x 5/7 m) is stocked with Nile tilapia, is practised. On average each cage is stocked with approximately 100 kg fingerlings each of common carp and Nile tilapia. The numbers of cages and production of cultured fish has increased in the reservoirs, but total and per cage production began to decline from about 1995 in Saguling from 2200 kg cage(-1) in 1989 to < 500 kg cage(-1) in 2002, and in Cirata from a peak of approximately 2300 kg cage(-1) in 1995 to approximately 400 kg cage(-1) in 2002. In Jatiluhur, which has a considerably lower cage density, total fish production and production per cage has increased since 2000, and currently is approximately 4000 kg cage(-1), close to production in the early years of cage culture activities. The cage culture operations also resulted in substantial nutrient loading, estimated at 3.2, 15.2 and 3.1 t of nitrogen and 134, 636 and 128 kg of phosphorous per year in the maximum years of production for Saguling, Cirata and Jatiluhur reservoirs, respectively. In later years, when cage culture production was high, fish kills occurred in the cages, and in Jatiluhur reservoir coincided with a dramatic decline in wild fishery catches. An attempt is made to determine the maximum number of cages for each of the reservoirs that will bring long-term sustainability of cage culture operations and the wild fisheries in the three reservoirs.