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SE Asian freshwater fish population and networks: the impacts of climatic
and environmental change on a vital resource
Rita Santos1*, Ian Cowx2 and Daniel Parsons1
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
*[email protected]
Introduction
Study site
The Mekong River is the 10th 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 km2.
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.
Tonle Sap Lake - Cambodia
Methodology
A series of data from a range of sources are being used:
Fisheries data
Hydrology data
Sediment Flux 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.
• 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 discharge in monitored stations across the
Lower Mekong Basin;
• Water discharge (m3 s-1) vs suspended sediment
concentration (SSC) (mg l-1) from new SSC rating
curve calibrations.
Results
Outcomes
Viet Nam
7
Water level (WL)
50
30
20
10
11.50
6
11.00
5
4
10.50
3
10.00
2
9.50
1
0
2003
2004
2005
2007
2008
2009
0
2010
9.00
2003
Fishing Season
Fig.1 – Fishing production from 5 provinces of Cambodia and Viet Nam represented by fishing
season (2003 – 2010).
Mekong River
Kampong Cham
Kandal
Kratie
Ratanakiri
17.9
9.1
22.9
0.0
0.0
0.0
0.0
0.0
Sesan
River
Srepork
River
Tonle
Sap
0.0
0.0
0.0
5.5
0.0
0.0
0.0
20.4
0.0
21.4
0.0
0.0
17.9
30.4
22.9
25.9
2005
2007
2008
Fishing season
60000
50000
40000
30000
20000
10000
0
19.9
69.9
5.7
5.7
0.0
5.5
2.9
23.3
0.0
21.4
28.6
125.9
Stung Treng (2009 - 2014)
Mekong
River
Vam Nao canal
Total Catch
(tonnes)
An Giang
51.3
9.1
21.1
81.4
Dong Thap
0.0
113.7
0.0
113.7
Tien Giang
0.0
2.7
0.0
2.7
Tra Vinh
34.6
0.8
0.0
35.5
Vinh Long
3.2
17.4
0.0
20.6
Total
89.1
143.8
21046
253.9
* No official fisheries data was recorded in 2006 for both countries under analysis
Discharge (Q)
Province
Bassac
River
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
800
700
600
500
400
300
200
100
0
Q (m3/s)
•
•
•
 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.
SSC (mg/l)
Fig. 4 – Annual fluctuation of water discharge (Q) and suspended sediment concentration (SSC),
measured in Stung Treng (Cambodia) station.
References
•
 The total fishing production from Viet Nam is double the
fisheries production from Cambodia;
SSC (mg/l)
Fig. 3 – Annual fluctuation of water discharge (Q) and suspended sediment concentration (SSC),
measured in Kratie (Cambodia) station.
Table II – Total catch (tonnes) from the 5 provinces of Viet Nam by location, during the 7 years
fishing season (2003 – 2010).
Catch (tonnes)
2010
600
500
400
300
200
100
0
Q (m3/s)
Stung Treng
Total
2009
Kratie (2009-2014)
Discharge (Q)
Provinces
Sekong
River
Total
Catch
(tonnes)
2004
Fig. 1 – Annual fluctuation in fishing production from Kratie (Cambodia) in relation to flood water
levels, according to the 7 years fishing season.
Table I – Total catch (tonnes) from the 5 provinces of Cambodia by location, during the 7 years
fishing season (2003 – 2010).
Catch (tonnes)
12.00
Suspended Sediment
concentration (SSC)
40
WL (m)
Suspended Sediment
concentration (SSC)
Cambodia
Total catch (tonnes)
Catch (tonnes)
8
Catch (tonnes)
60
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), 11-14 February 2003.
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: 252-263.
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.
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).