Ecotechnology and ecosystem based management tools as alterative solutions to reduce risks of ecosystem disaster and fish kills in Lake Maninjau

Overexploited by floating cage fishery and extreme wether condition due to global climate-change has caused ecosystem disater including massive fish kills, decrease in local/ endemic fish-population and deteriorated water quality in Lake Maninjau. Decrease in water quality including-eutrophication problems due to high input of organic matter and nutrient concentrations from the-excess feeding of floating cage fishery (FCF) has led the ecosystem of Lake Maninjau are susceptible-to climate change. The fact that Lake Maninjau is a tectono-vulcanic type of lake, the sulfide-production can cause oxygen defisit in the lower water column and with the extreme weather this-anoxic water column can be overturn to the surface and trigger even bigger disaster of fish kills. Fish-kills disaster in Lake Maninjau has occured more often since 1997 up to 2014 and has caused more-than thousands of tons fish dead and the farmer has lost billions of IDR (Indonesian rupiah) over the-years. The catch of local fish production hasl also been decreasing. Although floating cage fishery is-considered non-ecosystem based fishery for lake ecosystem, to get the cage fishery completely out-from the lake is impossible because it is considered the main economy for the people. The complexity-of the problems faced in Lake Maninjau requires a comprehensive management tools and inovative-ecosystem based technology to reduce disaster risk and to advance climate change adaptation. Ecosystem based management tools proposed include determination of the numbers of FCF units-according to lake carrying capacity and the placing, determination of the fish loadings in one cage-using high nutritious efficient fish pellets, practice of lake resting (no fish loadings) during extreme-weather months (e.g. December – February), and application of layered fish cage fishery. Development ecosystem based technology such as Attracting Fish Device Floating Wetland (AFDFW) to serve as nursery ground and habitat protection for local/endemic fish and to reduce-nutrient and organic matter concentration in the lake to advance the climate change adaptation. In-addition, develop an early warning system tools such as determining the key parameters in critical-time (e.g. threshold dissolved oxygen concentration and water transparency) also help in disaster risk-reduction. Fundamental requirement is that developed ecosystem based management tools can be-incorporated into decision making in order to not only effective in reducing disaster risk in Lake-Maninjau but also effective in maintaining the stability of lake ecosystem to advance climate chage-adaptation and to enhance ecosystem services in lake.