CARRYING CAPACITY OF TROPICAL RESERVOIRS FOR TILAPIA CAGE CULTURE: CASE STUDIES AT UPPER PARANÁ RIVER BASIN, SOUTHEASTERN BRAZIL.David, G. S.*, Carvalho, Vivanco,A, Gerardo D., Dallaglio- Sobrinho, M., Silveira, A. N. GIANMARCO SILVA DAVID GERARDO VIVANCO A.Proc. no. 07/58246-4 and 08/52139-4
Carrying capacity: concepts (Beveridge, 2004)Cage aquaculture production needs to be sustained by surroundingenvironment, considering:• What determines the productivity of the environment – in this case, totalPhosphorus in water.• What the farmed fish consume/produce, in terms of wastes – here, we considerP loads.• How the environment responds to waste loadings – such a good question!• How much charge is permissible – in this case, Brazilian environmentalregulation states the limit for water total P of 30mg/m 3 in reservoirs to farmaquatic animals (this is the limit of total P for a lake be classified as eutrophic(Vollenweider, 1975). Environmental carrying capacity for cage aquaculture for freshwater lakescan be defined as the maximum amount of P that can be loaded keeping total Pbelow the levels assumed to indicate eutrophication
upper Paraná river basin Brazil Sites considered in this studyCage culture of tilapia in large reservoirs is an emergent aquaculturepractice in Brazil. Due to the availability of large amounts of suitablequality waters in hydroelectric dams at Grande, Paranapanema andTietê rivers, there is a large but still undetermined potential for cageaquaculture in the upper Paraná river basin.
South American major river basinsParana river basin
In this work, are presentedevaluations of two among 18suitable sites at Ilha Solteirareservoir, one of the biggest atBrazil (1200 km2) and oneamong at least 12 at Xavantesreservoir.Only 1% of the reservoirs area isallowed to be occupied byaquaculture.Brazilian government will assignpart of the Ilha Solteira studiedsites to receive small scale,familiar aquaculturists. Distribution of hydroelectric power plants in Brazil
Multiple uses for reservoirs Eletric Power generation Aquaculture Tourism Irrigation Artisanal fisheries
Today, fisheries are scarce, resulting on low incomes for fishers.Former fisheries collapsed afterinstallation of hydroelectricdams, due to ecologicalconstrains for fish production.
After many attempts of stock enhancement,tilapia cage culture have became the firstecologically and economically feasible optionfor fish production in southeastern Brazilhydroelectric dams, since impoundment ofrivers in the 60’s.
Model used for tilapia cage aquaculture at upper Paraná river basin.
• Nile tilapia (Oreochromis niloticus) is reared in intensive system• 8-16 m3 cages made of synthetic materials• up to100 kg fish/m3 at the end of cycle• fish weights 500-800 g at the end of cycle• one or two cycles of 4-8 months per year, depending on water temperature.
METHODSHydrodynamics - in reservoirs with linear morphology, water exchange rate canbe obtained from flow measurements of power plants and bathymetry.
Ilha Solteira reservoirRio Grandinho Sao Jose dos Dourados
For dentritic reservoirs, water flow must be obtained for each portion by means fromcurrent measurements and hydro dynamic modeling for the site named Can CanNumerical solutiongrid Bathymetry Winds ADCP current profile
BathymetryLand use Waves modelingWater circulation pattern
Carrying capacity was estimated based on the Dillon& Rigler (1975) mass balance model, consideringlimnological data to evaluate area-specificPhosphorus loads from tilapia cage culture that canbe assimilated in each selected site.
Limit for environmental carrying capacity for P assimilation (L, in grams of Phosphorus/m2/year) L = (∆P*Z*θ) / (1-R),∆P - is the allowable phosphorus increase, in mg/m 3; is the difference oftotal P from analysis of water samples collected with van Dorn bottles, andthe limit stated by environmental agencies (30 mg/m3) and by Vollenweider(1975) as an indicator of eutrophicationZ - is the mean depth obtained from acoustic bathymetry, in meters;θ - is the rate of water exchange, i.e., how many times the water is totallyexchanged in a year. (this is calculated as 1/residence time); and R - is the sedimentation coefficient, obtained from direct measurementswith sediment traps (desirable), or from numerical modeling based onhydro dynamics data.
Estimation of P loads per ton of tilapia produced Pe= (Pf x FCR) – Pa Pe= Phosphorus loads, in kg P/ton tilapia produced Pf= mean feed Phosphorus content (%), obtained from chemical analysis of samples (N=15) of fish feed used in farms in the study area. (= 27 kg ton-1) FCR= Food Conversion Rate, obtained from average field farming data for the upper Paraná river basin (= 1,6 ± 1) Pa= whole fish Phosphorus content (%), specific for Nile tilapia (Dantas & Athayde, 2007) (= 9 kg ton-1) Pe= 37 kg P ton-1
Parameters used for the estimation of carrying capacity for tilapia cage culture inselected sites on tropical hydroelectric reservoirs at southeastern Brazil. Rio S.J. Grandinho Parameter unit Dourados IpaussuWater renovation rate years -1 31,52 9,38 7,80Area km² 9,62 69,49 25,49Mean depth m 8,00 11,11 28,89P water concentration mg m-3 5,34 12,36 16,6Limit P concentration mg m-3 30,0 30,0 30,0Sedimentationcoefficient - 0,230 0,352 0,373Area loading rate g m-2 year -1 8,080 2,835 4,814Total allowableproduction for the site ton year -1 2106 5340 3326Area specific production ton km-²year -1 219 77 131
Tilapia Control farm area 25 450 400 20 350 Total P (mg/m 3) Total N (mg/m3) 300 15 250 200 10 150 5 100 50Ipaussu: 0 Apr Jun Aug Oct Dec Feb 0 Apr Jun Aug Oct Dec Febcomparative control cages control cageslimnological 5,0 4,5 70 60data 4,0 conductivity (µS cm-1) 3,5 50 a clorophill (µg/L) 3,0 40 2,5 2,0 30 1,5 20 1,0 10 0,5 0,0 0 Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec Feb control cages control cages
• Modeling provided evidence for the importance offeed phosphorus content and availability fordetermination of total allowable production• Proper inputs of limnological field data areexpansive and demands sophisticated hydrographicstudies.•The availability of sites with similar features forcage culture in southeastern Brazil reservoirsindicates a significant potential for tilapia productionat global scale.