SE Asian freshwater fish population and networks: the impacts of climatic and environmental change on a vital resource Rita Santos 1*, Ian Cowx 2 and Daniel Parsons 1 1 GEES – Geography, Environmental and Earth Sciences Department, University of Hull – Cottingham Road, HU6 7RX, Hull, UK 2 HIFI - Hull International Fisheries Institute, University of Hull – Cottingham Road, HU6 7RX, Hull, UK References Acknowledgements This PhD project started in September 2014 and has received funding for 3 years from the University of Hull scholarship and additional funding from MRC (Mekong River Commission). The Mekong River Commission is a joint non-profit organization of the 4 countries that composed the Mekong River (Thailand, Lao PDR, Viet Nam and Cambodia). The Mekong River is the 10 th largest freshwater river in the world, with the second highest biodiversity wealth globally, only behind the much larger Amazon basin. The fisheries activity in the Lower Mekong countries produces 2.7 million tonnes of fish per year, with an estimated value up to $US 7 billion. For many of the 60 million people living in the basin, fish represent their primary source of economic income and protein intake, with an average per capita consumption estimated at 45.4 Kg. Proposed hydropower development in the basin is threatening its sustainability and resilience. Such developments affect fish migration patterns, hydrograph flood duration and magnitudes and sediment flux. Climate change is also likely to impact the basin, exacerbating the issues created by development. As a monsoonal system, the Mekong River’s pronounced annual flood pulse cycle is important in creating variable habitat for fish productivity. Moreover, the annual flood also triggers fish migration and provides vital nutrients carried by the sediment flux. This interdisciplinary project examines the interactions between both dam development and climate change scenarios on fish habitat and habitat connectivity, with the aim of predicting how these changes will affect fish species composition and fisheries catch. The project is using environmental DNA (eDNA) to quantify and understand the species composition and distribution across this complex and large freshwater system. By applying molecular analysis, it is possible to trace species abundance and migration patterns of fish and evaluate the ecological networks across this complex freshwater system. The aim of this work is to estimate, using process-informed models, the impacts of the proposed dam development and climate change scenarios on the hydrological and hydraulic conditions of habitat availability for fish. Furthermore, it will evaluate the connectivity along the Mekong and its tributaries, and the importance of maintaining these migration pathways, used by a great diversity of fish species. The Mekong River rises from the Tibetan plateau and flows for approximately 4800 km through China, Myanmar, Lao PDR, Thailand, Cambodia and Viet Nam, where it forms a large delta in the South China Sea. The river drains a total catchment area of 795,000 km 2. The impact of present and future dams on fish productivity, and changes in the water flow cycle and sediment flux, will be analysed and predicted along the Lower Mekong Basin, with special focus on the highly productive Tonle Sap Lake, that is a hotspot of biodiversity. van Zalinge, N., Loeung, D., Pengbun, N., Sarkkula, J., Koponen, J. (2003) Mekong flood levels and Tonle Sap fish catches. Contributions to the Second International Symposium on the Management of Large Rivers for Fisheries, Phnom Penh (Cambodia), February Baran, E. (2010) Mekong fisheries and mainstream dams. Fisheries section in: ICEM 2010: Mekong River Commission Strategic Environmental Assessment of hydropower on the Mekong mainstream, International Centre for Environmental Management, Hanoi, Vietnam. 145 pp. Arias, M.E., Cochrane, T.A., Kummu, M., Lauri, H., Holtgrieve, G.W., Koponen, J., Piman, T. (2014) Impacts of hydropower and climate change on drivers of ecological productivity of Southeast Asia’s most important wetland. Ecological Modelling, 272: Baran, E., Guerin, E., Nasielski, J. (2015) Fish, sediment and dams in the Mekong. Penang, Malaysia: WorldFish, and CGIAR Research Program on Water, Land and Ecosystems (WLE). 108 pp. Fisheries data Cambodian Official Fisheries Statistics (2003 – 2010); Vietnamese Official Fisheries Statistics (2003 – 2010); Fisheries production; Catch on the different provinces by river basin; New eDNA data. Hydrology data Water level duration, extension and amplitude, according to monitored discharge stations across the Lower Mekong Basin; Historical flooded area extents via Landsat TM; Fisheries production vs Water level (m). Sediment Flux data Sediment discharge in monitored stations across the Lower Mekong Basin; Water discharge (m 3 s -1 ) vs suspended sediment concentration (SSC) (mg l -1 ) from new SSC rating curve calibrations. Fig.1 – Fishing production from 5 provinces of Cambodia and Viet Nam represented by fishing season (2003 – 2010). Introduction Study site Methodology Table II – Total catch (tonnes) from the 5 provinces of Viet Nam by location, during the 7 years fishing season (2003 – 2010). * No official fisheries data was recorded in 2006 for both countries under analysis Table I – Total catch (tonnes) from the 5 provinces of Cambodia by location, during the 7 years fishing season (2003 – 2010). The total fishing production from Viet Nam is double the fisheries production from Cambodia; The declines observed in 2007 are likely due to changes in the policy of collecting fisheries data observed in both countries; Declines observed from 2007 have been associated with the already constructed dams on the mainstream river; The Mekong River and Bassac River are important pathways for migrating fish with high economic importance; The fisheries production in Kratie can be seen to map pulses in the floods over the fishing season, where increase in water level led to increase in total catch. This is being associated with triggers on fish migration patterns and habitat connectivity between floodplains and mainstream river; A close relationship was observed between discharge levels and suspended sediment concentration in Kratie. How this will affect fisheries will be evaluated in future work; Ongoing eDNA analysis will allow for the connectivity of the system’s dynamics in fish migration to be effectively coupled to the hydrology; Future work will be carried out to predict future scenarios of dam development effects on the Lower Mekong Basin and how climate change will likely affect fish habitats and its connectivity along the basin. Catch (tonnes) Province Bassac River Mekong RiverVam Nao canal Total Catch (tonnes) An Giang Dong Thap Tien Giang Tra Vinh Vinh Long Total Catch (tonnes) ProvincesMekong River Sekong River Sesan River Srepork River Tonle Sap Total Catch (tonnes) Kampong Cham Kandal Kratie Ratanakiri Stung Treng Total ResultsOutcomes Suspended Sediment concentration (SSC) Fig. 3 – Annual fluctuation of water discharge (Q) and suspended sediment concentration (SSC), measured in Kratie (Cambodia) station. Suspended Sediment concentration (SSC) Fig. 4 – Annual fluctuation of water discharge (Q) and suspended sediment concentration (SSC), measured in Stung Treng (Cambodia) station. Fig. 1 – Annual fluctuation in fishing production from Kratie (Cambodia) in relation to flood water levels, according to the 7 years fishing season. Catch (tonnes) A series of data from a range of sources are being used: Tonle Sap Lake - Cambodia