Economic Viability of Lake Interventions: A Benefit- Cost Analysis on Mitigating Kanduli (Arius manillensis) Fishkills in Sampaloc Lake, Philippines

The Manila Sea Catfish (Arius manillensis), or Kanduli, an endemic benthopelagic species in Luzon, faces severe threats in Sampaloc Lake, Philippines due to lentic overturn events. In Sampaloc Lake, San Pablo City, the Kanduli’s survival is increasingly compromised by lake turnover events driven by the breakdown of thermal stratification. This study analyzes the economic viability of interventions designed to mitigate the anoxic conditions resulting from the mixing of the oxygen-depleted hypolimnion with the surface epilimnion. A Benefit- Cost Analysis (BCA) was conducted on three distinct intervention scenarios: (i) diffused aeration (reactive), (ii) destratification mixers (preventive), and (iii) lake restoration (nature-based). The economic evaluation reveals that Intervention 2 (destratification mixers) is the dominant strategy, yielding a Benefit-Cost Ratio (BCR) of 5.45 and an Internal Rate of Return (IRR) of 58.4%. This preventive measure addresses the root cause of anoxia, offering Pareto-efficient outcomes that benefit both fishery yields and the tourism sector by mitigating hydrogen sulfide odors. In contrast, diffused aeration proved only marginally viable (BCR 1.18; IRR 7.7%), functioning primarily as a short-term insurance policy against fishkill rather than a sustainable economic driver. Lake restoration demonstrated strong efficiency with a BCR of 2.69. The study recommends a hybrid economic approach framed through Pigovian principles. It proposes that the surplus value generated by the economically strategic destratification mixers be utilized to fund the public goods associated with lake restoration, such as native littoral flora conservation. This creates a closed-loop system where economic utility supports ecological preservation.