Fish migrations of the Lower Mekong River Basin: implications for development, planning and environmental management - Mekong River Commission

Mekong River Commission

    Fish migrations of the
 Lower Mekong River Basin:
implications for development,
 planning and environmental
         management

          MRC Technical Paper

                 No. 8

             October 2002

Published in Phnom Penh in October 2002 by the
                                  Mekong River Commission

This document should be cited as:

Poulsen A.F. , Ouch Poeu, Sintavong Viravong, Ubolratana Suntornratana and Nguyen Thanh Tung.
2002. Fish migrations of the Lower Mekong River Basin: implications for development, planning
and environmental management. MRC Technical Paper No. 8, Mekong River Commission, Phnom
Penh. 62 pp. ISSN: 1683-1489

           The opinions and interpretations expressed within are those of the authors
           and do not necessarily reflect the views of the Mekong River Commission.

Editor: Ann Bishop
Layout: Boonruang Song-ngam

                               © Mekong River Commission
                     P.O. Box 1112, 364 M.V. Preah Monivong Boulevard
                                  Phnom Penh, Cambodia
                     Telephone: (855-23) 720-979 Fax: (855-23) 720-972
                               E-mail: mrcs@mrcmekong.org
                               Website: www.mrcmekong.org

Acknowledgements

This report was prepared with financial assistance from the government of Denmark (through
Danida), under the auspices of the Assessment of Mekong Fisheries Component (AMFC)
of the MRC Fisheries Programme.

The authors wish to thank staff at the Department of Fisheries (Cambodia), LARReC (Lao
PDR, Department of Fisheries (Thailand) and the Research Institute for Aquaculture number
2 (RIA2) in Ho Chi Minh City (Viet Nam) for their contribution in compiling the ecological
information, on which much of this report is based.

The authors also wish to thank Dr. Chris Barlow and Kent Hortle from the MRC Fisheries
Programme, and Dr. Ian Campbell from the MRC Environment Programme, for reviewing
early drafts of the report.

Table of Contents

    Summary - English............................................................................................... 1
    Summary - Khmer................................................................................................. 5
    Summary - Lao................................................................................................... 9
    Summary - Thai.................................................................................................. 13
    Summary - Vietnamese......................................................................................... 17

1. INTRODUCTION........................................................................................... 21
   1.1 Background............................................................................................21
   1.2 The purpose of this report................................................................................ 22

2   ANIMAL MIGRATIONS...................................................................................... 23
    2.1 Fish migrations and life cycles..........................................................................24

3. FISH MIGRATION IN THE MEKONG RIVER.......................................................25
   3.1 Important fish habitats in the Mekong Basin.........................................................26
   3.2. Fish migrations and hydrology in the Mekong Basin................................................31
   3.3. Major migration systems of the Mekong ..........................................................32

4. MANAGING MIGRATORY FISHES....................................................................... 41
   4.1. Key issues for the maintenance of ecological functioning of
        the Mekong ecosystem, with reference to migratory fishes........................................42

5. POTENTIAL IMPACTS OF DEVELOPMENT ACTIVITIES......................................... 47
   5.1 Human impacts on the Mekong fisheries ..........................................................47

REFERENCES..................................................................................................... 59

Fish migrations of the Lower Mekong River Basin

Summary

In the Mekong River Basin, most fishes are migratory. Many of them migrate long distances, often
across international borders during their seasonal movements. People throughout the basin depend,
directly or indirectly, upon the migrating fish for food and livelihood. Water management projects
such as hydroelectric dams could adversely impact those migrations and thus negatively effect the
livelihoods of a large number of people.

This report identifies some key features of the Mekong River ecosystem that are important for the
maintenance of migratory fishes and their habitats. The report further discusses ways in which
available information about migratory fishes can be incorporated in planning and environmental
assessments.

Three distinct, but inter-connected, migration systems have been identified in the lower Mekong
River Basin, each involving multiple species. These are respectively the lower (LMS), the middle
(MMS) and the upper (UMS) Mekong migration systems. These migration systems have evolved as
a response to the hydrological and morphological shape of the Mekong in its lower, middle and
upper sections.

In a complex, multi-species ecosystem, such as the Mekong River Basin, single-species management
is not feasible. Instead, a more holistic ecosystem approach is suggested for management and planning.
The migration systems mentioned above could be used as the initial, large-scale framework under
which ecosystem attributes can be identified and, in turn, transboundary management and basin
development planning can be implemented.

The important ecological, or ecosystem, attributes of migratory fishes are identified for each migration
system. The emphasis is on maintaining critical habitats, the connectivity between them and the
annual hydrological pattern responsible for the creation of seasonal floodplain habitats.

The Lower Mekong Migration System (LMS)

    Dry season refuge habitats: Deep pools, particularly in the Kratie-Stung Treng stretch of the
    Mekong mainstream.

    Flood-season feeding and rearing habitats: Floodplains in the Mekong Delta in Viet Nam, in
    southern Cambodia, and in the Tonle Sap system.

    Spawning habitats: Rapids and deep pool systems in Kratie -Khone Falls, and in the Sesan
    catchment. Floodplain habitats in the south (e.g. flooded forests associated with the Tonle Sap
    Great Lake).

                                                    1

Fish migrations of the Lower Mekong River Basin

    Migration routes: The whole Mekong mainstream from the Mekong Delta to the Khone Falls,
    including the Tonle Sap River (longitudinal connectivity). Between floodplain habitats and river
    channels (lateral connectivity). Between the Mekong mainstream and the Sesan
    sub-catchment (including the Sekong and Srepok Rivers).

    Hydrology: The annual floods that inundate large areas of southern Cambodia (including the
    Tonle Sap system) and the Mekong Delta, and the annual reversal of the Tonle Sap River, are
    essential for fisheries productivity.

The Middle Mekong Migration System (MMS)

    Dry season refuge habitats: Deep pool stretches of the Mekong mainstream and within major
    tributaries.

    Flood-season feeding and rearing habitats: Floodplains of this system that are mainly associated
    with major tributaries.

    Spawning habitats: Rapids and deep pool systems in the Mekong mainstream. Floodplain
    spawning habitats associated with tributaries.

    Migration routes: Connections between the Mekong River (dry season habitats) and major
    tributaries (flood season habitats).

    Hydrology: The annual flood pattern that causes inundation of floodplain areas along major
    tributaries.

The Upper Mekong Migration System (UMS)

    Dry Season refuge habitats: Occur throughout the extent of the Upper Mekong Migration
    System, but are most common in the downstream stretch from the mouth of Loei River to Louang
    Prabang.

    Flood-season feeding and rearing habitats:Floodplain habitats are restricted to the floodplains
    that border the main river, as well as smaller floodplains along some of the tributaries.

    Spawning habitats: Spawning habitats that are situated mainly in stretches where rapids alternate
    with deep pools.

    Migration routes: Migration corridors between downstream dry-season refuge habitats and
    upstream spawning habitats.

    Hydrology: The annual flood pattern that triggers fish migrations and causes inundation of
    floodplains.

These ecosystem attributes should be taken into account when assessing impacts of development
activities. A pre-requisite for impact assessments is a valuation of the impacted resource (e.g. migratory
fishes) from a fishery perspective. Undertaking such a valuation of migratory fishes is extremely
difficult because they are targeted throughout their distribution range in many different ways, and

                                                    2

Fish migrations of the Lower Mekong River Basin

with many different fishing gears and operations. Given the scale and complexity of such an
undertaking in the Mekong River, it is probably not possible to fully assess the economic value of
migratory fishes.

However, a partial assessment of value, together with an assessment of information gaps is in many
cases sufficient for planning and assessment purposes. It is also important to emphasise that in the
decision-making process, qualitative information and knowledge from various sources should be
included on equal terms with quantitative data. Furthermore, along with the direct value of fishery
resources, the Mekong River ecosystem provides numerous intrinsic, non-quantifiable goods and
services.

To ensure that the Mekong River Basin can continue to provide these important goods and services,
we propose that development planning and environmental assessment should be based on an ecosystem
approach within which the ecological functioning, productivity and resilience of the ecosystem are
maintained. Experiences from other river basins suggest that from an economic, social and
environmental point of view, this is best way to utilise a river.

                                                  3

Fish migrations of the Lower Mekong River Basin

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                                             5

Fish migrations of the Lower Mekong River Basin

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Fish migrations of the Lower Mekong River Basin

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                                                7

Fish migrations of the Lower Mekong River Basin

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                                                    8

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¹ìÒÁ¹ì´, ꆴó¡¾−À¦‡º´ªÒ ì½¹¸È¾¤ ꆺ¾Ä¦−˜− ¡ñ® 콩ñ®º÷êö¡¡½¦¾©¯½¥¿¯ó ꆴ󣸾´
¦¿²ñ−Ã−¡¾−¡ÒùÉÀ¡ó© ꆵøȺ¾Ä¦¢œ−Ã−À¢©−իɸ´¯½¥¿¯ó.

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Œê†µøȺ¾Ä¦ ìšÄ²Ã−콩øÁìɤ: ¸ñ¤Àìò¡, ©¨¦½À²¾½Ã−À¢© ¡½Á¥½ ¹¾ §¼¤Áª¤ (¡¿¯øÀ¥¼)
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(Tonle Sap System) ¢º¤¡¿¯øÀ¥¼.
Œ®Èº−¯½¦ö´²ñ− ¸¾¤Ä¢È: À¢©À¯ñ−Á¡É¤ Á콸ñ¤Àìò¡ ÁªÈ ¡½Á¥½ ¹¾ −Õªö¡£º−²½À²ñ¤, Áì½
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Lake) ¢º¤¡¿¯øÀ¥¼).
ŒÀ¦˜−꾤À£‡º−¨É¾¨¢º¤¯¾: Ã−ì¿Á´È−Õ¢º¤ ¥¾¡À¢© Mekong Delta ¹¾ −Õªö¡£º−²½ À²ñ¤
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บทคัดยอ

ในลุมน้ําโขง สัตวน้ําสวนใหญมีการอพยพยายถิ่น สัตวน้ําเหลานี้หลายชนิดเดินทางเปนระยะทาง
ไกลและมักผานขามพรมแดนระหวางประเทศในชวงการอพยพตามฤดูกาล ประชาชนที่อยูอาศัย
ทั่วทั้งลุมน้ําพึ่งพาสัตวน้ําที่มีการอพยพยายถิ่นเหลานี้เปนแหลงอาหารและการดํารงชีพไมทางตรง
ก็ทางออม โครงการบริหารจัดการทรัพยากรน้ําตาง ๆ เชน โครงการเขื่อนผลิตไฟฟาพลังน้ํา สงผล
กระทบเสียหายตอการอพยพยายถิน่ ของสัตวนํ้าดังกลาว ซึ่งสงผลเสียหายตอเนื่องถึงความเปนอยู
ของประชาชนจํานวนมาก

รายงานฉบับนี้ระบุคุณ ลักษณะหลักของระบบนิเวศแมน้ําโขงที่มีความสําคัญตอการบํารุงรักษา
สัตวน้ําที่มีการอพยพยายถิ่นตลอดจนแหลงที่อยูอาศัยชนิดตาง ๆ ของสัตวน้ําเหลานั้น นอกจาก
นั้น ยังมีการระบุแนวทางในการผนวกสารสนเทศเกี่ยวกับการอพยพยายถิ่นของสัตวน้ําที่มีอยูแลว
เขาในกระบวนการวางแผนงานและการประเมินผลกระทบสิง่ แวดลอม

ระบบการอพยพยายถิ่นของสัตวน้ําในลุมน้ําโขงตอนลางจําแนกไดเปนสามระบบที่มีการเชื่อมตอ
ระหวางกัน ทุกระบบเกี่ยวของกับสัตวน้ําหลายชนิด ระบบเหลานี้ ไดแก ระบบการอพยพยายถิ่น
ของสัตว น้ําในแม น้ําโขงตอนลาง (Lower Mekong migration system; LMS), ระบบการอพยพ
ย า ยถิ่ น ของสั ต ว น้ํ า ในแม น้ํ า โขงตอนกลาง (Middle Mekong migration system; MMS) และ
ระบบการอพยพย ายถิ่น ของสัต วน้ํ าในแม น้ําโขงตอนบน (Upper Mekong migration system;
UMS) ระบบการอพยพย า ยถิ่ น เหล านี้ มี วิ วัฒ นาการมาจากการปรั บ ตั วของสั ต ว น้ํ า ให เข ากั บ
ลักษณะทางอุทกวิทยาและลักษณะสัณฐานของแมนาํ้ โขงตอนลาง ตอนกลางและตอนบน

ในระบบนิเวศที่ซับซอนและหลากหลายทางชีวภาพเชนลุมน้ําโขง ไมเหมาะสมที่จะบริหารจัดการ
สัตวน้ําเพียงชนิดหนึ่งชนิดใด ในทางตรงกันขาม การพิจารณาระบบนิเวศทั้งระบบเปนแนวทางที่
สมควรใช สํ าหรับการบริห ารจั ด การและการวางแผน ระบบการอพยพย ายถิ่ นดั ง กล าวข างต น
สามารถใชเปนกรอบเบื้องตน เพราะสามารถใชเปนแนวทางในการจําแนกระบบนิเวศออกจากกัน
ซึง่ จะสามารถดําเนินการบริหารจัดการประเด็นขามพรมแดนรวมทั้งวางแผนการพัฒนาลุม น้ําไดใน
ขณะเดียวกัน

ลักษณะทางนิเวศวิทยาหรือระบบนิเวศที่สําคัญสําหรับสัตวน้ําที่มีการอพยพยายถิ่นหลายชนิดได
รับการจําแนกในทุกระบบการอพยพยายถิ่น สิ่งที่ตองตระหนัก ไดแก การรักษาสภาพที่อยูอาศัยที่
สําคัญและการเชื่อมตอระหวางแหลงที่อยูอาศัยตาง ๆ เหลานั้น รวมถึงรูปแบบการเปลี่ยนแปลง
ทางอุทกวิทยาในรอบปทม่ี ผี ลตอการเกิดพืน้ ทีน่ าํ้ ทวมตามฤดูกาล