Climate proofing aquaculture: a case study on pangasius farming in the Mekong

<strong>Abstract</strong> Vietnam is among the top five countries that will be most affected by sea level rise. This study aimed to assess the subsequent impacts of flooding and salinity intrusion on, and to evaluate suitable adaptation strategies for the Mekong Delta's pangasius farming sector. Water level rise and salt water intrusion for three sea level rise (SLR) scenarios (i.e. +30cm, +50cm and +75cm) were simulated by using the MIKE11 model. The results showed that at SLR+50, the 3m flood level would spread downstream and threaten farms located in upstream and midstream regions. Rising salinity for SLR+75 would reduce the appropriate time-window for the culture in coastal areas. A Chi-Square test and a logit regression model were employed to examine factors which influence pangasius farmers’ perception of and adaptation to climate change impacts. Less than half of the respondents were concerned about climate change and actively sought suitable adaptation measures to alleviate its impacts. The adaptive capacity of pangasius farmers can be improved by increasing the information on climate change and introducing early warning systems. The technical efficiency (TE) of randomly sampled pangasius farms was estimated using Data Envelopment Analysis, and factors affecting technical and scale efficiency were examined with bootstrap truncated regression. The mean TE score assuming constant return to scale was 0.66, and under variable return to scale it was 0.84. TE of downstream farms was higher compared to the upstream and midstream farms due to lower energy costs and stocking once a year at a lower density, but these reduced the scale efficiency of farms affected by salinity intrusion. Upstream and midstream farms needed to pump water and stocked at least three times in two years. Regression analysis showed a positive effect on TE of the farmer’s education level, and of having experienced climate change impact through flooding or salinity intrusion in the past. Using a decision tree framework, this study analyzed possible options for adapting pangasius farming to the projected climate-change impacts. Options to adapt to salinity intrusion are: modify the pangasius farming practice by using e.g. water recirculation systems, stock other species, or stock saline-tolerant pangasius with support from research and extension. A breeding program for saline-tolerant striped catfish requires long-term investments (0.4 % of the present production costs). To adapt to worse flooding, pangasius farms not located within the upgraded government dyke-protected areas could raise the height of the dyke around their pangasius farm, which would increase the total variable costs per ha for one harvest by about 0.34% in the upstream and midstream regions, and by 0.25% in the downstream region.