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Add To Calendar 28/04/2016 14:10:0028/04/2016 14:30:00Africa/JohannesburgAsian-Pacific Aquaculture 2016ZONAL AND FARM-SCALE EFFECTS ON NUTRIENT DISCHARGE FROM NET-CAGE AQUACULTURE IN JATILUHUR RESERVOIR, W. JAVA, INDONESIA Crystal 1The World Aquaculture Societyjohnc@was.orgfalseanrl65yqlzh3g1q0dme13067DD/MM/YYYY

ZONAL AND FARM-SCALE EFFECTS ON NUTRIENT DISCHARGE FROM NET-CAGE AQUACULTURE IN JATILUHUR RESERVOIR, W. JAVA, INDONESIA

Taskov D.*, Murray, F.J., Little, D.C., Bengston, D., Telfer, T., Rice, M., Kamal, M.M., Cut, D.
 
* Institute of Aquaculture, University of Stirling, Stirling, UK, FK9 4LA dimitar.taskov@stir.ac.uk

 

Sited in populous W. Java with an area of 83 km2 Jatiluhur is Indonesia's largest reservoir. Cage aquaculture was introduced as an alternative livelihood option for farmers whose lands were submerged following inundation in 1967. Subsequent unregulated expansion at a range of scales has implicated aquaculture as a major source of phosphorous induced eutrophication contributing to recurrent fish kills and conflicts with other primary water-uses (including electricity-generation, irrigation, urban water supply and tourism). This study aimed to compare total phosphorous (TP) inputs between farm scales and production zones using a mass-balance approach and to assess policy options for improved nutrient management.

Exploratory research incorporated secondary data collection and semi-structured interviews with cage-operators, input suppliers (seed, feed, cages), fish buyers and local-government agencies. This was followed by an in-depth systematic survey of 112 cage operators, with randomised cluster sampling stratified on 'farm-scale' (based on ownership and production indicators) and 'zone' (within and 'external' to Ministry of Fishery 'MoF' designated areas). Data was collected on cage-infrastructure, seed and feed inputs, stock loss and harvests over the last full production cycle. Samples of 18 commercial grower-diets were also collected for TP analysis.

Satellite images (Google Earth) revealed a rapid increase in cage numbers from 2006 to 2014, reflecting increasing local market demand, predominantly for small (<300g) live carps. Of 44,760 cages covering 219ha in 2014, 64% were in 'MoF' and 36% in 'external' zones. Most farmers (78%) deploy multi-net 'dua-lapis' cage systems, a development intervention uniquely adapted to local risk and market conditions. Low densities of tilapia and Pangasius catfish stocked in lower tiers utilise uneaten sinking pellets fed to more densely stocked carps in upper nets (supplemented by 'wet' feeds), resulting in grow-out times of 3 months for carp, 8-12 months for tilapia and 16-24 months for Pangasius. Mean FCRs for carp fed exclusively on commercial diets were significantly higher (p<0.05) in MoF (1.63-1.72) than external zones (1.5-1.52; probably due to superior external water quality associated with lower cage concentration and more lotic siting); and in smaller (7x7m) compared to larger cages (7x14m). TP content of commercial diets ranged from 1.1-2.1% representing feed-losses of 2,003t in 2014; 22%, 31% and 47% from small, medium and large-scale farms respectively and 35% from external farms which also accounted for 35% of cages. Although external farms had superior FCRs, P loss per tonne harvest was higher due to the prevalence higher P content diets i.e. indicating potential for improved feed formulation. Findings also demonstrate that multi-tier 'diaper' cage systems perpetuate use of poorer performing sinking and wet feeds. Demand and supply for less polluting floating extruded pellets remains correspondingly low. Policy recommendations for cage-design, management and feed regulation are discussed in the light of these findings.

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