An economic analysis of the impact of removing organic waste from small scale cage aquaculture systems in irrigation dams in the Western Cape

[摘要] ENGLISH ABSTRACT: The rising demand of fish due to population growth coupled by stagnation of fish supply fromnatural capture has led the world to turn to aquaculture to fill in the gap between fish supply anddemand. Aquaculture has emerged as the only sustainable way of supplying the rising populationwith fish. However the rapid expansion of aquaculture has been met with growing concerns over itsenvironmental effects especially waste produced from aquaculture. The net cage system that iscurrently being used by small scale trout farmers in the Western Cape is an open water basedsystem where release of waste into the water bodies is inevitable and this put into question the longterm sustainability of trout farming using net cages in irrigation dams in the Western Cape.This study sought to compare identified production techniques that can be used by aquaculturefarmers to reduce accumulation of organic waste in irrigation dams. The proposed 'clean'production techniques include use of net cages fitted with Lift-up system, semi intensive floatingtank system (SIFTS) and intergrated aquaculture systems. The study revealed that the intergratedaquaculture system is the most effective way of recovering waste that shows great potential ofmoving aquaculture towards long term sustainability as it fullfills sustainability dimensions such as'zero emission', nutrient recycling and integrated production. Mechanical methods of recoveringwaste such as Lift-up system and SIFTS are also effective in recovering particulate waste buthowever dissolved nutrients are lost into the environment.The study went on further to investigate if economic, environmental and social benefits ofrecovering waste from irrigation dams outweigh the costs of recovering waste using differentproduction techniques. Models of small scale aquaculture farms using the three identifiedproduction techniques were developed and compared with a modelled small scale net cage farmwhere there was no waste recovery. A comparative financial analysis of the modelled small scaletrout farms using alternative production techniques carried out showed that trout production usingany of the three alternative 'clean' production techniques is financially viable with the SIFTSproduction technique giving the farmer the highest returns, followed by the intergrated system, thenthe net cage with a Lift-up system and lastly the net cage system without waste recovery.The second part of the study used the contingent valuation method to estimate the environmentaland social benefits of removing waste from dams. Households revealed that they were willing topay (WTP) R40 on average annually to improve water quality from a state where eutrophicationhad occurred to a state suitable for irrigation and aquaculture. To improve water quality from a statesuitable for irrigation to a state suitable for swimming, households were willing to pay R16.67annually. If water was to be improved from a state suitable for irrigation to a level suitable fordomestic purposes, average willingness to pay (WTP) was R26.17 annually. WTP indicate thatbesides financial benefits associated with using 'clean' production techniques there areenvironmental and social benefits that will arise to the farm community using water from theirrigation dams.

[发布机构] Stellenbosch University