Fisheries Bioecology at the Khone Falls (Mekong River, Southern Laos)

FISHERIES BIOECOLOGY AT THE KHONE FALLS (MEKONG RIVER, SOUTHERN LAOS)

Eric BARAN Ian G. BAIRD Gregory CANS

FISHERIES BIOECOLOGY AT THE KHONE FALLS ( MEKONG RIVER, SOUTHERN LAOS )

ERIC BARAN, IAN BAIRD, GREGORY CANS

formerly known as “ICLARM - The World Fish Center”

Our Commitment: to contribute to food security and poverty eradication in developing countries.

A Way to Achieve This: through research, partnership, capacity building and policy support, we promote sustainable development and use of living aquatic resources based on environmentally sound management.

We believe this work will be most successful when undertaken in partnership with governments and nongovernment institutions and with the participation of the users of the research results. FISHERIES BIOECOLOGY AT THE KHONE FALLS (MEKONG RIVER, SOUTHERN LAOS)

Eric Baran Ian Baird Gregory Cans

2005

Published by WorldFish Center PO Box 500 GPO, 10670 Penang, Malaysia

Baran E., I.G. Baird and G. Cans. 2005. Fisheries bioecology at the Khone Falls (Mekong River, Southern Laos). WorldFish Center. 84 p.

Perpustakaan Negara Malaysia. Cataloguing-in-Publication Data

Baran, Eric Fisheries bioecology at the Khone Falls (Mekong River, Southern Laos) / Eric Baran, Ian G. Baird, Gregory Cans. Bibliography: P. 56 ISBN 983-2346-47-9 1. Fisheries-Ecology-Laos-Khone Falls. I. Baird, Ian G. II. Cans, Gregory. III. Title. 597.09594

Cover photo: E. Baran Photos: E. Baran and Ian G. Baird

ISBN 983-2346-47-9

WorldFish Center Contribution No. 1765

Design and layout: [email protected] Printed by: JSRC

© WorldFish Center, 2005 All rights reserved. This publication may be reproduced in whole or in part and in any form for educational or non-profit purposes without the permission of the copyright holders provided that acknowledgement of the source is given. This publication may not be copied, or distributed electronically, for resale or other commercial purposes without prior permission, in writing, from the WorldFish Center.

The content of this document has not been peer reviewed. All comments and opinions expressed herein are those of the authors and may not reflect the position of WorldFish Center, its partners or the organizations that provided funding for the project and the publication.

The WorldFish Center is one of the 15 international research centers of the Consultative Group on International Agricultural Research (CGIAR) that has initiated the public awareness campaign, Future Harvest. ACKNOWLEDGEMENTS

Many thanks to the Khong District Agriculture and Forestry Office and the Champasak Province Agriculture and Forestry Division for their support, and particularly Vixay Inthaphaisy, Phongsavaht Kisouvannalath, Bounpheng Phylavanh, Bounthong Vongsenesouk, Khamsouk Xaimanyvong, Bounhong Mounsouphom and Peter Cunningham for assisting in collecting the data. Mr. To Mounsouphom entered much of the data into the computer, with the support of CIDSE - Laos, and Mr. Pierre Dubeau (former CUSO cooperant) helped develop the initial Khone Falls fisheries database. Dr. Mark Flaherty and Ms. Sarah Adams also assisted with the management of the database. Last, but not least, we would especially like to thank all the fishers from Hang Khone and Hang Sadam villages who contributed their time freely to support this project, and who were extremely patient during the period that the data were collected. Without their efforts, this work would certainly not have been possible. Figure 1: The Khone Falls area, including Hang Khone Village, Southern Laos Map prepared by Ole Heggen, Geography Department, University of Victoria, Canada.This map is a generalized illustration only.The representation of political boundaries is not to be used for reference purposes. TABLE OF CONTENTS

1) INTRODUCTION...... 8

2) FISHING GEARS, FISHING OPERATIONS AND FISH CAUGHT...... 10

3) TEMPORAL USE OF KHONE FALLS FISHING GEARS...... 14

3-1) Annual use of fishing gears...... 14 3-2) Monthly use of fishing gears...... 16

4) INTERANNUAL TRENDS: ISSUES AND CONSTRAINTS...... 20

4-1) Interannual trends in overall catches...... 20 4-2) Interannual trends in catches of a migrating species...... 22

5) RELATIONSHIP BETWEEN A LAO AND A CAMBODIAN FISHERY...... 26

6) TEMPORAL ABUNDANCE PATTERNS OF 110 FISH TAXA...... 30

7) HYDROLOGICAL TRIGGER OF MIGRATIONS: THE EXAMPLE OF THE CATFISH PANGASIUS KREMPFI...... 38

8) DOMINANT SPECIES: LIFE HISTORY KEY FACTS, MIGRATIONS AND TRIGGERS...... 42

9) DEEP-WATER POOLS AS FISH REFUGES...... 48

9-1) Comparison between deep-water pools and surface cpues...... 50 9-2) Deep-water pool species versus surface species...... 51 9-3) Size of fishes in deep-water pools...... 52

10) BIBLIOGRAPHY...... 56 ANNEX 1: Dominant species, life history key facts, abundance patterns and response to ischarge...... 62 ANNEX 2: Relationship between abundance and river discharge for dominant species...... 72 EXECUTIVE SUMMARY

GENERAL DESCRIPTION OF THE FISHERY The database that this report is based upon covers six years of monitoring of artisanal fisheries (over 20 nuclear fishing families) in Hang Sadam and especially Hang Khone villages, just below the Khone Falls in Khong District, Champasak Province, Southern Laos. Forty-one fishing methods were monitored. Gill nets with various mesh sizes were the most frequently used gear; they make up to 73% of the number of fishing operations included in the database. A number of categories of gill nets, based on mesh sizes (from 2.5 to 30 cm), were monitored throughout the six years, and seven fishing methods were monitored consecutively for at least five years. There are two main peak periods in fishing activity: from November to March (most intense period), and in June. Fishing intensity is the least between August and October. This trend is driven by the frequent utilization of gill nets during these months. Four main groups of fishing gears can be identified: gears operating all year long; gears targeting migrating fish at the beginning of the rainy season (June-July); gears operating at the end of the rainy season (October to January) and gears operating in the dry season (January to May).

INTERANNUAL TRENDS: ISSUES AND CONSTRAINTS Given the very particular context of these fisheries, which target more than one hundred species of fish, some migratory and others more or less sedentary, with a diversity of gears, an analysis of trends in annual overall catches would face multiple constraints and biases. We detail this point through taking the Probarbus jullieni fishery as an example, and show that such contexts challenge classical fishery science approaches.

COMPARISON OF CAMBODIAN BAG-NET (DAI) FISHERY AND LAO FENCE-FILTER TRAP (TONE) FISHERY It was not possible to draw significant conclusions from an extensive analysis of available data about the correlation between the catch of the tone fishery in the Khone Falls area and the dai fishery in Cambodia. This was due to a limited number of points (n = 5 years).

ABUNDANCE PATTERNS OF 110 SPECIES The abundance patterns of 110 fish taxa (i.e. fish identified at the species level or at least at the genus level) in catches have been analysed; they often indicate migration patterns. Three major groups of fish have been identified: i) species present during the dry season (peak in January), some of them exhibiting a small secondary peak in catches at the beginning of the rainy season (May-June); ii) species present during two equivalent periods (dry and wet season respectively) or being regularly distributed all year long (no evident migrations); and iii)species showing a dominant or exclusive abundance at the beginning of the rainy season (May-June). Among the 110 taxa studied, 90 exhibit strong patterns of sudden abundance in catches. Most of these species are migrating. MIGRATION TRIGGER OF PANGASIUS KREMPFI The catfish Pangasius krempfi provides a clear example of a migration triggered by a water level rise. The migration of this species occurs suddenly at the beginning of the wet season, and lasts in general 40-50 days. There are generally about a dozen days of intense migration peak each year. This points to the likely consequences of building dams that regulate the hydrology of the Mekong River and its tributaries on P. krempfi and on other species responding similarly to hydrological triggers.

DOMINANT SPECIES: LIFE HISTORY KEY FACTS, MIGRATIONS AND MIGRATION TRIGGERS Dominant taxa in catches There are forty-seven taxa for which at least 50 individuals have been caught on average per year over six years

Length of fish caught - 61% of dominant taxa caught have a maximal size greater than 25 cm, but - 85% of fishes actually caught (in terms of biomass) belong to taxa whose maximal size is less than 25 cm. This illustrates the abundance of small species in the catch, despite the diversity of a fish community in which large species are largely represented.

Species migrations Ninety-six percent of dominant taxa are not present all year long, and thus undertake migrations or become impossible to catch at certain periods of time. This figure highlights the importance of migration behavior among dominant species of the Khone Falls fisheries.

Species, discharge and migration triggers The highest biodiversity appears in catches for the lowest discharge levels. This underscores the importance of dry season water levels for fish and fishers, as well as that of rising waters at the end of the dry season. 1) at least 55% of taxa are sensitive to discharge among the dominant taxa of the Khone Falls. 2) Ninety six percent of the fish caught (expressed in terms of biomass) are highly sensitive to discharge in the Khone Falls fisheries. Given this extremely high sensitivity of fishes to discharge and discharge variations, when flows are regularized, a very significant share of the fishery resource will be permanently impacted and might disappear from the catch.

DEEP POOLS AS DRY SEASON REFUGES Catch-per-unit-effort (CPUE) of the gill nets set in deep-water pools in February and March is three to twelve times higher than CPUE of gill nets used in surface during the same period, and with the same mesh sizes.

Among the 30 dominant species caught during this monitoring, only two showed a preference for surface waters. Ten species showed a clear preference for deep-water pools in the dry season; they consisted of seven siluriforms (catfishes) and three cypriniforms (carps).

The average weights of 18 species caught at least five times in each environment were analysed. For ten species, the individuals caught in deep pools are 27 to 78% larger than those caught near the surface; for two species the individuals caught at the surface are larger than those caught in deep-water pools. 1 INTRODUCTION

This study results from a collaboration between the Global Association for People and the Environment (GAPE), which provided the data and the field knowledge used in this report, and the WorldFish Center (formerly ICLARM), which analysed data and developed an interactive interface for data display.

The data were collected as part of the Lao Community Fisheries and Dolphin Protection Project (LCFDPP) and the Environmental Protection and Community Development in Siphandone Wetlands Project (EPCDSWP), with the latter project being implemented by the Italian non-governmental organization CESVI Cooperation and Development, and funded by the European Union. At the WorldFish Center, data analysis and publication result from a project entitled "Conservation of Aquatic Biodiversity / Mekong Initiatives" also funded by the European Union.

In this study, over 20 fishers or fishing families using multiple seasonal gears on the southern end of Khone Island and the adjacent southern Figure 2: Indochina, Mekong River Basin and Khone falls Introduction 8 importance inLaosandtheMekongRiver Basin. management ofinlandfisheriesintheKhoneFalls, azoneofmajorecologicalandlivelihood The overall objective ofthisstudyistocontributebiodiversity conservation andthesustainable for fishinthedryseasonisdemonstrated. are detailed,andthecrucialroleofdeep-water poolsinthemainstreamMekongRiver asrefuges possible migrationpatternsof110 Mekongfishtaxaisprovided, hydrological triggersoffishmigrations The useoftheartisanalfishinggearsinKhoneFalls aredescribed,newinformationaboutthe with Cambodia. 1993 and1999.Bothlocationsarejustbelow theKhoneFalls faultline, andjustnorthoftheborder end ofSadamIsland(mainstreamMekongRiver, SouthernLaoPDR)were monitoredbetween

9 Introduction 10 Fishing gears, fishing operations and fish caught 2 } } } } During theseyears: whose catcheswere onlymonitoredperiodically. were monitoredinHangSadamVillageandespeciallyKhoneVillage, alongwithafewothers season istraditionallyconsideredtostartinOctober).Over 20 fishersandtheirimmediatefamilies May 1999.Thisrepresentsmonitoringofsixfullyears andfive fullseasonsoffishing(a The monitoringoftheKhoneFalls fisheriesstartedon4thMarch1993,andcontinueduntil30th includes abiomassof53metrictons(Table 3). 666,000 individualfishesplusmany bulkweighed fisheswere caught.Overall, thedatabase 138 speciesortaxawere caught; 20,222 fishingoperationswere analyzed(Table 2andFigure3); to overlapping meshsizesamonginitialgillnetcategories;Table 1); Forty-one gearswere initiallymonitored;theywere lumpedforanalyses into32categories(due AND FISHCAUGHT FISHING OPERATIONS FISHING GEARS, al :Names ofthegearsmonitored Table 1: Kha He soi He po Chip meu Chap pakap Chan koung teuksiap Bet khikadeuan teuksiap Bet mengkhinai siap khen Bet mak houn Lai taosiap mak deua Lai taosiap Lao gear name with hands Fish caught Falling-door trap baited withshrimp Pole andline baited withworm Pole andline with molecricket hookbaitedSet trifolia baited with Floating hook baited with Floating hook trap pull basket attractant Branch bundle fish cast-net Small meshed cast-net Large meshed current trap Cylindrical fruit description Gear Gear fruit Crayratia Ficus sp . Lope none Lope gnai Li Lan 4-9 Mong yone 12-18 Mong yone 4-9 Mong 2.5 Mong 18-30 Mong 12-18 Mong Lope tang Lao gear name 4-9 cm setgillnet Deep 12-18 cm setgillnet Deep 4-11 cm gillnet Set 2.5-3 cm gillnet Set 18-30 cm gillnet Set 12-18 cm gillnet Set trap basket standing funnel Hang Sadam Village trap funnel basket Hang Sadam Village trap basket Large funnel (monsoon season) wing trap FallsKhone baited withbran trap Upright basket description Gear Gear Tone na Tone houay Tone Souang pasoi Phiak siap pako Phiak siap mengkhinai Phiak siap mak houn Phiak siap mak deua Phiak siap khikadeuan Phiak siap Lao gear name trap rice fieldfence filter Hang Sadam Village trap stream fence filter Hang Sadam Village season) trap (dry FallsKhone fence filter cone trap Wedge fish cyprinid Longline baited with pennocki Longline baited with molecricket Longline baited Crayratia trifolia Longline baited with with Longline baited with worm Longline baited with description Ficus sp Gyrinocheilus Gear Gear fish .Fruit fruit 11 Fishing gears, fishing operations and fish caught 12 Fishing gears, fishing operations and fish caught al :Abundance andbiomass offishcaught Table 3: Fishers during6years andtheirfishingeffort Figure 3: Fishermen inthedatabase andtheirtotaleffort Table 2: the fishingseasonsfullymonitored arehighlightedabove initalics. fishingseason was monitored; onlyafraction oftheOctober-September In1992-1993and1998-1999, Note: # offishingoperations Fisher code # offishingoperations Fisher code operations # offishing Fishers names Fisher code 1995-1996 1994-1995 1993-1994 1992-1993 Fishing season Nb of fishing operations 1000 2000 3000 0 06789132211 9 8 7 10 5 6 15121623201417182130241925264050 2 4 3 1 0 ia;Bounpheng; Vilay; Nouphai (family) Biomass (kg) Number Biomass (kg) Number Biomass (kg) Number Biomass (kg) Number Sounthone; 3556 1 308 18 13 22 Songma 3196 3 261 21 22 20 18403 15612 9757 8393 8358 6956 9527 1846 1975 Sai 4 255 30 11 10 1871 Keo Fisher code 2 152 24 15 Total biomass(kg) Total Number 1998-1999 1997-1998 1996-1997 6 Fishing season 1408 Sout 5 102 19 12 5 Bounheng 1329 10 25 16 92 5 Biomass (kg) Number Biomass (kg) Number Biomass (kg) Number 1236 Mai 26 23 40 5 6 1011 Tha 40 20 36 5 7 666701 53455 849 50 14 23 Sit 5 8 600737 18640 5318 3070 6870 6668 1713 704 17 22 0 9 13 Fishing gears, fishing operations and fish caught 14 Temporal use of Khone Falls fishing gears 3 the year. period oftime;andii)considering thepresenceandabundanceoffishspeciesat certaintimesof Generally, thedatabaseismostusefulfor i) consideringcertainfisheriesby themselves, andover a not reflectthisrealitywell. tone Tone fishers rosedramaticallyover thecourseofmonitoring,whichisnotillustratedwell by thedata. limited numbersofsmallmeshedgillnetswere initiallyusedandmonitored, buttheiruseby gears operatinginthearea.For example, 2.5cmmeshedgillnetsareunderrepresented;only It shouldbenotedthattheseresultsreflectthegears monitored,andnottheexactnumberof methods isillustratedinFigure4. representing lessthan0.3%ofthetotalfishingeffort).Thegeneralusegearsor Thirteen fishingmethodshave beenmonitoredlessthan70 timesinseven years (arbitraryvalue of catcheswere recorded. of thestudy, butwere notintensively monitoredover alongperiod, althoughsomeobservations years latter gill nets18-30the cm.However, 2.5-3cmmeshed gillnetsgainedpopularityduring g nets were mainlyusedandmonitoredthroughoutthesixyears: gillnets4-11 cm; observations (dataandresultsaredetailedinacompaniontechnicalreport).Threecategories of gill Gill netswere themostfrequentlysampledfishinggears;theymadeupto73%of 3-1) Annualuseoffishinggears for othergearswere notsampledfortheir i) onlyonefishingsiteforeachofthetwo gearswas monitored,andii)fisherswhowere sampled during themonsoonseason)arealsoquiteunderrepresented because, forlogisticalreasons, and traps (fence-filteroperatedduringthedryseason) and li traps aresomeofthemostimportantgearsinKhone Falls area,butthedata does FALLS FISHINGGEARS TEMPORAL USEOF li and tone traps, even thoughmany hadthem.Thus li traps (wingoperated KHONE ill nets12-16cm; iue4 Annual numberofoperation for eachfishingmethodmonitored Figure 4: 2500 2000 1500 1000 500 0

gillnet_set 12-16 gillnet_set 18-30 gillnet_set 4 -11

longline baited_cyprinid fish trap_pull basket and branch bundle trap_falling door trap_wing K. F alls trap_fence filter K.F alls gillnet_set 2.5 - 3 longline baited_mole cricket trap_funnel bas ket H. S adam V. trap_current cylindrical gillnet_deep set 4 - 9 longline baited_worm longline baited_G . pennocki longline baited_Ficus fruit cast-net sml meshed trap_wedge cone gillnet_deep set 12-18 hook_floating baited_F icus fruit hook_set baited_mole cricket trap_upright basket baited_bran longline baited_C . trifolia fruit hook_floating baited_C . trifolia fruit trap_large funnel basket trap_standing funnel basket H. S adam V. cast-net lg. meshed trap_fence filter H. Sadam Village field pole and line baited_worm trap_fence filter H. Sadam Village s hand caught tream 98-99

97-98 pole and line baited_shrimp 96-97 95-96 94-95 93-94 92-93 15 Temporal use of Khone Falls fishing gears 16 Temporal use of Khone Falls fishing gears The resultisgiven inTable 4andtheglobaltemporalpatterninFigure5. 2: 0: according tothefollowing scale: intensity of below aqualitative estimatebasedontheextensive fieldexperienceofthesecond author. Themonthly In ordertogive anideaof theseasonalvariation offishingactivityinthewholearea,we propose fishingactivityinthearea. of the overall monitoring duringsixyears of21 the nuclearfishingfam from dat this Thus due tologisticalconstraints, onlyonesetofthesetrapswas monitored. the monthly variability intheuseoffishinggears. For instance the It isnotpossible, duetosamplingbiasesandothercon 3-2) Monthlyuseoffishinggears gear notusedorset moderate fishing fishing forthe19gearsthatrepresent99.7%oftotalefforthasbeenranked 3: 1: intense fishing few gearssetorlittlecatch straints, tousethedatabase todetermine ilies, butisnotexactlyrepresentative li traps arevery active inMay, but abase results 2: } gears canbeidentified(Figure6): Among thegears, fourmaingroupsoffishing effort andcatches. September istheperiodwithleastfishing are November toMarch,whereasAugust to Overall, themonthswithmostintensefishing 0: Relative intensityoffishingpergearandmonth at BanHang Khone Table 4: Gill net_deepset12-18 Trap_wedge cone Meshed cast netsm. long linebaited_Ficus fruit pennocki long linebaited_G. long linebaited_worm Gill net_deepset4-9 Trap_current cylindrical Sadam V.Trap_funnel basket H. Longline baited_molecricket Gill net_set2.5-3 Falls Trap_fence filterK. Falls Trap_wing K. Trap_falling door Trap_pull basket andbranch bundle fish Longline baited_cyprinid Gill net_set4-11 Gill net_set18-30 Gill net_set12-16 gear notusedorset moderate fishing falling-door traps;andwedge conetraps; funnel baskettraps;cylindrical currenttraps; with molecricket;HangSadamVillage January; thesegearsarelonglinesbaited of thedryseason,between Octoberand Gears operatedmostlyatthebeginning Gear name Gear 3: 1: intense fishing few gearssetorlittlecatch Oct 1 2 1 0 0 2 0 0 1 1 1 0 0 1 0 0 2 0 0 Nov 3 3 1 0 0 3 0 1 2 3 2 0 1 1 0 0 3 0 2 10000 15000 20000 25000 30000 discharge inKhoneFalls area Monthly average intensityoffishingand Figure 5: 5000 Dec 3 2 1 1 0 2 0 0 3 3 2 1 3 1 0 0 1 0 3 0 c oDcJnFbMrArMyu u AugSep Jul MayJun Apr Mar Feb Jan NovDec Oct Jan 1 0 3 3 0 1 0 2 3 2 2 1 1 2 1 1 1 1 1 Fishing intensityindex Monthly averagedischarge Feb 0 0 2 3 0 0 0 2 2 1 1 3 0 3 3 2 1 2 0 Mar 0 0 2 1 0 0 0 2 2 1 1 3 0 3 3 3 0 3 0 Apr 0 0 2 1 1 0 0 1 1 1 1 1 0 3 2 3 0 2 0 May 0 0 3 0 3 0 0 1 1 2 3 0 0 2 1 1 0 0 0 Jun 0 0 2 0 3 0 3 3 2 2 3 0 0 1 0 0 1 0 0 Jul 0 1 1 0 2 1 3 3 1 1 2 0 0 1 0 0 1 0 0 Aug 1 1 1 0 0 1 1 1 1 1 1 0 0 1 0 0 1 0 0 Sep 1 1 1 0 0 2 0 0 1 1 1 0 0 1 1 0 1 0 0 0 5 10 15 20 25 30 17 Temporal use of Khone Falls fishing gears 18 Temporal use of Khone Falls fishing gears iue6 KhoneFalls mainfishinggearsandtheiruseintime Figure 6: } } } 0 1 2 3 0 1 2 3

Oct traps, deep-water gillnets;andlonglinesbaitedwith Gears operatinginthedryseason,mostlyfromJanuarytoMay; theseareKhoneFalls fence-filter Cyprinid fishandcastnets; Gears operatingallyear long; thesegearsaregillnetsofvarious sizes;andlonglinesbaitedwith bundle fishattractantpullbaskettraps); branch Gears targetingmigratingfishinJuneandJuly(inparticular, KhoneFalls wingtrapsand Oct Nov Nov Dec Dec Jan

Gears operatedallyearlong Jan Feb Gears operatedattheendofflood Feb Mar Apr Mar May Apr Jun May Jul Jun Aug Jul Sep Aug

gillnet_set 18-30 Sep gillnet_set 12-16 gillnet_set 4-11 gillnet_set 2.5-3 longline baited_molecricket longline baited_cyprinidfish trap_funnel basketH.SadamV. cast-net sm.meshed trap_current cylindrical trap_falling door trap_wedge cone - 0 1 2 3 0 1 2 3 Oct Oct

Nov Ficus Nov Dec Jan Dec fruit or Feb Jan Mar Gears targetingthesummermigrants Gears operatedinthedryseason Feb Apr Mar May Gyrinocheilus pennocki Jun Apr Jul May Aug Jun Sep Jul trap_fence filterK.Falls

gillnet_deep set12-18 Aug longline baited_Ficusfruit longline baited_G.pennocki gillnet_deep set4-9 Sep branch bundle trap_pull basketand trap_wing K.Falls fish. 19 Temporal use of Khone Falls fishing gears 20 Interannual trends: issues and constraints 4 by lumpingthecatchesofallgearswould notberelevant forseveral reasons: of fishcatchesattheKhoneFalls. However, analysing trendsinoverall catchesover several years Given theavailability ofcatchdataover sixyears, itistemptingtostudythe interannualvariation 4-1) Interannualtrendsinoverall catches lumping allgearstogether would certainlyblurthedetailed trends, asshown inFigure7: shift fromonetargetspeciestoanotherforgiven gearatdifferenttimesofthe year. Thus, methods dependingonthehydrology andonthecorrespondingmigratingspecies, andiii)the 4) coherent groupsoffishonly(e.g. black/whitefishesatleast). 3) might beblurredby changesinthestructureoffishcommunitiesduetofishing itself. 2002, Baird2005d). Therefore, theresponseofcatchestoenvironmentalfactorsover sixyears catches ofsmallopportunistsarelessevident(Van Zalinge&NaoThouk1999,Sverdrup-Jensen years. Theabundanceofsuchlong-lived fishesseemstobedeclining,whilechangesinthe Baran during thesameyear (e.g. smallopportunistslike 2) blur thespecifictrends. species diversity inthefishery(138speciescaught),lumpingthemalltogetherwould only 1) Given i)thevery highselectivityofthedifferentfishinggears;ii)specificchoice The annualabundanceofsomefishspeciesisheavily influencedby thehydrological regime A good(hydrological) year forspeciesAcanbeabadoneB,andgiven the Following previousremarks, interannualtrendsinabundanceshouldbeanalysed for et al ISSUES ANDCONSTRAINTS INTERANNUAL TRENDS: . 2001a), whilethatoflong-lived species(e.g. largecatfishes) isbufferedover several Henicorhynchus spp.; DeapLoeung1999, 5) Comparisons between years should, 0.0300 as pointed out above, be done on the 0.0250 basis of a standardized effort; however standardization (i.e. calculations based 0.0200 on the smallest temporal sequence is 0.0150 common) might force the removal of some months/weeks during which 0.0100 migration peaks occur. Fish abundance gillnet_set 18-30 mm

CPUE (kg/hour) 0.0050 and catches during peak periods can be gillnet_set 4-11 mm 100 times as much as catches during other 0.0000 weeks/months. Therefore, such standardi- 1993 1994 1995 1996 1997 1998 1999 zation would create a major bias. Figure 7: Interannual trends in CPUE for 2 types 6) A quick overview of overall yearly trends of gears (not detailed here) is not consistent with what fishers say about "good" and "bad" years. Fishers, for instance, mightconsider that a year is "good" when catches of a high-valued species like Probarbus are good, while catching the same biomass of small low value fish, such as Henicorhynchus, might not indicate "a good year".

Incidentally, these arguments outline the need for an in-depth and systematic analysis of the Khone Falls fisheries at the species level. Interannual trends:Interannual issues and constraints 21 22 Interannual trends: issues and constraints (Figure 9): of The databaseindicatesthedailytotalcatches for detailsregardingthisspecies(www.fishbase.org). and fisheryhasbeenextensively describedinBaird(2005d). FishBaseshouldalsobeconsulted decline throughoutitsrangeandisnow classifiedasendangeredby IUCN(Baird2005d). Itsecology gill netsduringitsspawning season.Formerly abundant,ithasbeensubjecttoseriouslong-term This excellenttastingandhigh-pricedfoodfishcanreach150 cmandismainlycaughtinlarge-meshed 1997-1998 and1998-1999 fishingseasons). durations, even whendailycatchesremaininthesamerange(Figure10; detailsofdataforthe it becameapparentthatfishingseasonssignificantly vary intermsoftheirbeginnings, endsand Before addressingtheabove issue, we examineddataatasmallertimescale, onadailybasis, and terms ofkilogramsfishperhoursfishingwitha standard net. kilograms offishperhoursquaremeternet,or, ifthesurfaceareaisnotexactlyknown, in prior tomakinginterannualcomparisons. Inthecaseofgillnets, CPUEisexpressedintermsof Mahon 1995)would supportstandardizingthesedataandexpressingtheminterms ofCPUElevels Standard aswell asrevisedfisheryscienceapproaches(e.g. HoldenandRaitt 1974,Caddyand the catchesofthisendangeredspecies? other words, canadeclinebeidentifiedin trend incatchesof following question:whatisthelong-term period ofyears, dataavailability raisesthe in November-December every year. Over a sudden highabundancelevels beginning The dataexhibitclearseasonalpatterns, with Figure 8: jullieni Probarbus might beirrelevant due to very specificconstraintsandbiasesinh cla species, river In thecaseoffisheriestargetingmigratory 4-2) Interannualtrendsincatchesofamigratingspecies P. jullieni Probarbus jullieni during sixyears atHangKhone fishery provides anexample ofsuchinadequacies. Probarbus jullieni ? In iue9 temporal pattern of Figure 9: 70 kg 10 20 30 40 50 60 0 short migrations(Singhanouvong Mekong River, itisbelieved toundertake rivers inmainlandSoutheast Asia.Inthe in themainstreamsofanumberlarge Probarbus jullieni 10/30/93 short distances(MFD2002). that undertakemigrationsover relatively it mightconsistinaseriesdiscretestocks species have resultedinthehypothesis that 2000). Observations ofthe Valbo-Jørgensen migrations (Pantulu 1986, Poulsen and been reportedby someto conductlonger 1996a, Baird2005d), althoughithasalso ssical approachesin

10/30/94 1/30/95 4/30/95 erent tofloodingrivers. The

10/30/95 is alargeCyprinidfound 1/30/96 Probarbus jullieni

10/30/96

1/30/97 fisheries science

10/30/97 1/30/98 et al catches

10/30/98 . al :Catch of Table 5: Comparison of2fishingseasons Figure 10: The conclusionsarethat: caught intheseason,tolastday). also integratedthenumberofdays ofcatches(startingfromthefirstday whenProbarbusjullieniis The standardizedcomparisonofCPUEsbetween 97-98and98-99isincludedinTable 5.We have (A/B)xC A/B which resultsinlargercatchesoverall. seasons, fishcanbecaughtatthesamerate(i.e. sameCPUE)butover alonger periodoftime, 2) as lessfishwere caughtperhouroffishing. 1) A B C Catch per day (kg) Standard CPUEanalysis leadstotheconclusionthatfishwere scarcerin97-98than96-97, 30kg The fishingperiodwas muchshorterin96-97than97-98.Duringyears withlongfishing 10 15 20 25 0 5 Probarbus jullieni CPUE integrating peakabundance duration Nb ofdays ofpeakabundance CPUE (kg/hourofnet) Total (hoursofnet) effort Total catches (kg)

Season

v em

corresponding andCPUE effort ,

ra tion o tion

Probarbus jullieni

f t f

97-9

a ura

509.21 93-94 so 0.345 1476

22.4

65 D

tion o tion

ec em

552.65

94-95 t f 0.162 ber 3420 12.0

74 e96-9 he 95-96 0.319

1728 19.5 7 552

so n 96-97 0.228 139.3 612

5.5

u a 97-98

0.178 247.8

1392 r

7.1 40 y 96-97 97-98 98-99 0.230 154.3 11.0 672 48 23 Interannual trends: issues and constraints 24 Interannual trends: issues and constraints jullieni Interannual trend inthecatch of Figure 12: 2 different approaches Interannual trends asconcluded from Figure 11: iue1:Possible biasesintheanalysis ofinterannual trends for migrant species Figure 13: analysis focusing on biom on focusing analysis standardized analysis focusingonCPUEsonlyleadstoerroneousconclusions. Conversely an An importantlessonfromthisanalysis isthatintermsofecologyandinterannualtrends, a kg/hour

(kg/hour) x nbof days of migration 0.0 0.1 0.2 0.3 0.4 10 15 20 25 0 5 were greaterin97-98.This illustratesahigherabundanceof 3) in 96-97. in KhoneFalls Fishes were available muchlongerin97-98than96-97,andthereforeoverall catches 39 49 59 69 79 98-99 97-98 96-97 95-96 94-95 93-94 erCthEfr CPUE Effort Catch Year 69 97-98 96-97 x2 2x/2y=z 2y 2x B x/y=z y x A Cthi igri erB butthenfishingis (Catch isbiggerinyear B, also twice more intensive) is variable effort bias:

CATCH ANALYSIS ass onlyass would also be bi

2 0 5 10 15 20 25 = 0.4601 =

(kg/hour) x nb of days of migration Probarbus duration migration integrating CPUE CPUE on CPUEs based solely Trend duration the migration integrating Trend ased, asillustratedbelow. and Baird1995, able aboutthebehavior offishes(Roberts fishers, whoareparticularlyknowledge- catches. Thisisthecaseof KhoneFalls space andtimeinaway thatmaximizes are skilled,andthattheysettheirnetsin possible undertheassumptionthatfishers the numberofdays offishing.Thisis this problemistomultiplytheCPUEby 5) irrelevant, atleastinthisparticular case based solelyonCPUEisproven tobe facts (points2and3above), theapproach (Figure 11). However whentestedversus that integratepeakcatchdurationdata CPUE analysis contradict conclusions 4) of only0.46. very significant,witharegressioncoefficient P. jullieni that therewas adeclineinthecatchesof variability infishingeffort,thedataindicate with lessknowledge orconsiderationof who probablyfocusonbiomasscaught, catches ishigh.Despitetheclaimsoffishers of monitoringshow thatthevariability in in Table 5andinFigure12.Thesesixyears the in catches for Thus theinterannualtrends 2005a). A possibleway topartiallyovercome Conclusions drawn from standard rbru ju Probarbus (CPUE remains thesamefrom year to year, even whencatch increases two fold) bias: catch and effort correlation catch andeffort bias: over time, butthistrendisnot Probarbus jullieni CPUE ANALYSIS llieni fishery areillustrated et al . 1999a,Baird in 97-98than of thestudy. years ascomparedtotheearlieryears marginal fishingperiodsinthelatter to leave gillnetsinthewater during gill nettheft,fisherswere lesswilling individual gillnets. Also,due toincreased later years, reducingtheefficiencyof more filamentousalgaeinthewater in the latteryears. Therewere alsoreportedly willing orabletoinvest in new gillnetsin to beindecline, andfisherswere less This was becausethefishery was believed and lessefficientthaninearlieryears. years ofthestudywere generallyolder For example, gillnetsusedinthelater economic issuesmustalsobeconsidered. as indicatedby Baird(2005d), socio- the fishingseason(Figure14).Inaddition, CPUE, butalsobiomassanddurationof tri-dimensional approachencompassing from year toyear shouldresultfroma every year, anassessmentofproduction harvested over alimitedperiodoftime In thecaseofmigratingriver fishes migrating speciesproduction Parameters inthemonitoring of ofimportance Figure 14: . . . .

u r

a CPUE t

h e B

f o

s m

h i a

n s

g s

o n . . . . . 25 Interannual trends: issues and constraints 26 Relationship between a Lao and a Cambodian fishery 5 (2000), Loeung (1999),HapNavy andNgorPeng Bun(2000), Ngor Peng BunandHemChanthoeun This fisheryhasbeenmonitoredfrom94-95uptonow andisdescribed inLieng and 12%respectively). mainly targetssmallmigratingCyprinids such as the KhoneFalls as et al peaks operates fromDecembertoMarch,with mainstream MekongRiver wherethegeography allows fortheuseofthesetraps. Thefishery weirs andbaskettrapssetinaroundtheKhoneFalls area,theonlypartoflower The 1 The BAG-NET ( COMPARISON OF THE FENCE-FILTER TRAP ( described inRoberts andBaird(1995),(1998)especiallyin Baird (2003). Thisfisherywas monitoredduringfive seasonsfrom94-95to98-99andisextensively Henicorhynchus lobatus Henicorhynchus lobatus . 2003). Thespeciesthataredominant incatchesareallsmallhighlymigratoryCyprinidssuch tone dai and Baran (or bag-net)fisheryinthe Tonle (or fence-filter trap) fishery in Hang Hang in (or fence-filtertrap)fishery (Smith 1945)isreferenced as FISHERY A LAO ANDACAMBODIAN RELATIONSHIP BETWEEN area inSouthernLaoswere comparedby Baird DAI et al . (2001). The catches of the the of . (2001). Thecatches ) FISHERIES 1 , and Cirrhinus lobatus Paralaubuca typus (Smith 1945) in FishBase 2004, based on Roberts (1997). basedonRoberts (Smith 1945)inFishBase 2004, Sap River (Cambodia) operates from October to M to October from Sap River (Cambodia)operates Khone Villageconsistsofavariety ofdifferenttypes strongly associatedwithnewmoonperiods(Baird (51 and33%ofcatchesrespectively; Baird dai Henicorhynchus fishery in Cambodia and the fishery inCambodiaandthe et al spp. and . (2003). TONE et al Paralaubuca typus et al . (2003). ) AND tone . (1995),Deap fishery in arch; it et al (37 . } } } two fisheries isimportant: The differenceofscalebetween these fishery towherethey fish takingabout20 days onaverage tomigrate up Baird around thesametimeofyear. thetarget both same species at as they two fisheries arev Despite theirdifferenceinscale, these Cambodia (alltheunitsinuse). Falls area),63unitsmonitored in 200 inusethroughouttheKhone 1 unitmonitoredinLaos(ofabout per gearinCambodia. gear inLaos, andabout200 tonnes tonnes peryear foronefishing Annual average yieldsofabout3 in Cambodia. Limited unitsizeinLaos, largegear et al . (2003) reported that both probablytarget many ofthesamefish,withthose fisheries ery similarinnature, are targetedby thetone

Drawing from Claridge et al. 1997 Figure 15: fishery stream from where they are targeted by the dai the by fromwheretheyaretargeted stream Henicorhynchus "Tone" fishing gear. p.and spp. Paralaubuca typus , the 27 Relationship between a Lao and a Cambodian fishery two dominant taxa in the catches of both fisheries, migrate between October and March from the Tonle Sap Great Lake (through the Tonle Sap River where the dai fishery operates) to the Khone Falls, where the tone fishery operates. When the water recedes in the Tonle Sap, Henicorhynchus spp. migrate down to the Mekong (Lieng et al. 1995) and from October to February the fish continue their journey up the Mekong, past the Khone Falls (Baird et al. 2003; Poulsen and Valbo-Jørgensen 2000).

Lao fishers operating the tone fishery

believe that at this time of year a (Photo E. Baran) good fishing season in Cambodia Figure 16: One dai unit in the Tonle Sap River corresponds (in relative terms) to a poor fishing season in Laos. They also believe that catches of the tone fishery in Laos reached historical record highs in 1975-1979, when the Khmer Rouge interrupted large-scale fishing operations. These claims have never been substantiated, and call for a more detailed comparison of the two fisheries. Baird et al. (2003) show that between 1995 and 1999 good dai fishing years tend to result in relatively poor catches in the tone fishery, but there are not enough years of data to significantly represent this negative correlation statistically.

An extensive analysis of available data has been undertaken by the authors in order to determine if the tone fishery catches were positively or negatively correlated to those of the dai fishery and to the hydrological level in each zone. However, the limited number of points (n = 5 years) led to contradictory or spurious correlations (e.g. catch of year y with water level of year y+1). Subsequently, it was impossible to provide, based on existing monitoring data, clear-cut conclusions about the relationship between the two fisheries.

In both cases, catches are dominated by Henicorhynchus spp. and Paralaubuca typus (between 50 and 80%), whose similar migrating behavior is well known; however 30 to 50% of catches are due to other species exhibiting various migratory patterns (see section on migrations), and these species might blur a trend noticed by fishers, and due to only a few species. It is therefore recommended that, beyond the scope of this exploratory report, comparisons between tone and dai fisheries should be deepened at the species level. The following section standardizes taxonomic categories for such an analysis.

The analysis of the tone and dai data sets highlighted

Thailand several discrepancies between the fish taxonomy used Lao PDR in Southern Laos and in Cambodia. The intricacies of the taxonomy of Mekong fishes have already been pointed Cambodia out elsewhere (Rainboth 1996, MRC Mekong Fish Database), and the resulting confusions have been highlighted (Baird et al. 1999a, Baran et al. 2001b, Baran and Chheng 2003).

In view of a detailed comparison of catches in the two Figure 17: October-March migrations of fisheries for which different Latin names were used, it dominant species caught in Tone and Dai was necessary to adopt a common taxonomic system, fisheries detailed in Table 6. Relationship between a Lao and a Cambodian fishery a Lao and Cambodian Relationship between 28 al :TaxonomicTable standardization for speciescaught in 6: ( Cyclocheilichthys Botia Barbodes gonionotus Barbichthys thynnoides Achiroides leucorhynchos Acantopsis sp./ Dermogenys Xenentodon Puntioplites proctozysron Probarbus jullieni Polynemus multifilis Parambassis wolffi Pangasius hypophthalmus Mystus nemurus Mystus Morulius chrysophekadion Henicorhynchus siamensis non (dai fisherydatabase) enoplos) sp. spp. Latin name sp. sp. spp. /sp. Lumped Latinname(Khone Xenentodon cancila Puntioplites falcifer Probarbus jullieni/labeamajor (valid name= Polynemus longipectoralis Parambassis wolffi hypophthalmus Pangasianodon mysticetus/ singaringan/ multiradius/Mystus + Hemibagrus wycki/wyckioides/ Hemibagrus nemurus phekadion/spp. Morulius chryso- H.siamensis andlineatus Henicorhychus lobatus, non Cyclocheilichthys spp. Botia modesta/Botia Hypsibarbus wetmorei Hypsibarbus lagleri/ Thynnichthys thynnoides Achiroides Acantopsis Falls fisheriesdatabase) enoplos spp. sp.or sp .dubius P. /spp. spp ) spp. Pangasius hypophthalmus Mystus Hemibagrus nemurus Labeo chrysophekadion Henicorhynchus enoplos Cyclocheilichthys Botia sp.or sp Barbodes/Hypsibarbus Thynnichthys thynnoides Achiroides Acantopsis Xenentodon cancila Puntioplites Probarbus Polynemus Parambassis dai Latin nameused spp. and p.non spp. spp. spp. sp. sp. spp. tone spp. spp. nemurus spp.non fisheries /spp. .nemurus H. except related species, Lumping ofclosely (reference FishBase 2004) nemurus H. FishBase 2004) Valid name(reference related species Lumping ofclosely Sevral possiblespecies Dispute overidentification not exist Barbichthys thynnoides (2 closespecies) Uncertain identification uncertain identification Species unknownOR to becaught only species)istoo small (pusilla, Dermogenys Dispute over identification related species Lumping oftwo closely Dispute over identification (reference FishBase 2004) Pangasius =valid genus Reason = valid name does 29 Relationship between a Lao and a Cambodian fishery 30 Temporal abundance patterns of 110 fish taxa 6 Several authorshave describedthemigrationpatternsofMekongfishes(reviewinBaran which implicitlyfollows atbesttheabundanceoffishin river. Analysis ofCPUEdataisnot performed onraw biomasses, asgearsaregenerallychosenby fisherstobeasefficientpossible, conditions (sixannualcycles, 32distinctfishinggearssampled; 666,000fishcaught).Analysis is migration survey covering adiversity ofspecies, ofgearselectivity, andofhydrological fishing All fishingmethodsareindistinctlylumped,asthisisconsidered tobeacomprehensive multi-gear month, thefractionorpercentageoftotalannual catches foragiven species isprovided. The analysis isbasedontherelative monthlyabundanceofspeciesincatches;thusforeach all ofthoseareimportantinfisheries(Baird2001). not but species, have beenrecordedfromthemainstream MekongRiver justbelow theKhoneFalls, basis ofKhoneFalls fisherymonitoringover sixyears. Sofar, 201 fishspecies, including196native Here, we detailtheseasonalappearanceof fishesincatchesfor110 taxainSouthernLaos, onthe of smallCyprinidaecarpsandPangasiidae catfishesbasedmainlyonquantitative fielddata. 2004), Hogan In SouthernLaos, Singhanouvong (2005) andBaird(2005a) have reliedheavily onlocalknowledge provided by fishers. and HengKong (2002) have beenuseful,andinLaos, Baird Peng Bun(2000), ChhuonKim Chhea (2 Cam In knowledge. partially onfishers' those ofPoulsen andValbo-Jørgensen (2000), Bao River fishmigrations. Amongthe mostcomprehensive publicationsonregionalmigrationsare In thepastfewyears aconsiderableamountofprogresshasbeenmadeintheknowledge ofMekong et al PATTERNS OF110FISH TAXA TEMPORAL ABUNDANCE . (2004) andBairdFlaherty(2004) have alsodetailedthemigrationpatterns et al . (1996aandb),Warren bodia, recent insightsrecent bodia, providedNgor and by Srun Phallavan 0) hn ohn (2 000), ChanhSokheng et al . (2001) andMRC (2001), allbasedatleast et al et al . (1998),Baird 000); ChanhSokheng . (1999a),BairdandFlaherty et al . (2001a, 2003, et al et al . 2001b). . (2000) on theCD-ROM companiontothisdocument. Correspondence Analysis. Interactive distributionanalyses forindividualspeciescanbeperformed For improved readability, specieshave beenorderedingroupsoftenfollowing theirscoresina Figure 18andits11 graphsdetailthetemporaldistributionoffishspeciesinKhone Falls fisheries. from site-specificcatchestomigrationsisappropriate for mostspecies. that theKhongfisheriesareprincipallybasedonfishmigratory behavior. Inany case, theinference Mekong fishes, andfieldexperience(e.g. Roberts andBaird1995; However, thestudiescitedabove have largelydemonstratedthat migrationsareamajorfeatureof variation inKhoneFalls catches, andisnotastudyoffishmigrationsbetween differentlocations. microlepis at certaintimesoftheyear becomemoreeasilycatchablethen(e.g. fish. TheKhoneFalls fisheriesaredependent onboth,aseven fishmigratingover shortdistances to constituteany kindoflong-distanceorshort-distance systematic movement by apopulationof The appearanceoffishincatchesoftenimpliesmigratorybehavior. Here, migrationsareunderstood ii) becauseofthebiasesdetailedinsection3-2-1). possible i)becausethediversity ofgears, whichwere notallmonitoredconsistentlyeachyear; and , Baird et al . 2001b; Baird2005d). Formally speaking,thisstudyonlyreflectstheabundance Probarbus jullieni et al . 2003; 2004) confirms , Boesemania 31 Temporal abundance patterns of 110 fish taxa 32 Temporal abundance patterns of 110 fish taxa

% of annual abundance % of annual abundance % of annual abundance 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 0 0 0 0 c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct Graph 3 Graph 2 2 Graph 1 Botia spp Crossocheilus siamensis Boesemania microlepis Bangana behri Paralaubuca typus Mystus multiradius/mysticetus/spp. Garra fasciacauda Botia modesta Cyclocheilichthys spp. Cynoglossus microlepis Parambassis wolffi/spp. Mekongina erythrospila Mystacoleucus spp. Mystus singaringan/spp. Arius stormi Hemipimelodus borneensis Cirrhinus jullieni Channa marulius/spp. Glyptothorax spp. Achiroides spp. Euryglossa panoides Cirrhinus molitorella Rhinogobius spp. Polynemus longipectoralis Pseudomystus siamensis Amphotistius laosensis Tetraodon spp. Probarbus jullieni Chonerhinus nefastus Tor tambroides Probarbus labeamajor % of annual abundance

100 % of annual abundance % of annual abundance 100 10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 10 20 30 40 50 60 70 80 90 0 0 0 c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct Graph 6 Graph 4 Graph 5 Osteochilus microcephalus/spp. Cirrhinus microlepis Chitala blanci Hypsibarbus malcolmi Macrognathus siamensis/spp. Poropuntius deauratus Henicorhynchus spp. Bagrichthys spp. Chitala ornata Clarias batrachus/spp. Sikukia gudgeri Acantopsis sp.orspp. Coius undecimradiatus Aaptosyax grypus Labeo erythropterus Barbodes altus Hemibagrus wycki Labiobarbus leptocheilus Onychostoma cf.elongatum Luciosoma bleekeri Bagarius yarrelli/spp. Pangasius polyuranodon Gyrinocheilus pennocki Rasbora spp. Kryptopterus spp Scaphognathops stejnegeri Crossocheilus reticulatus Thynnichthys thynnoides Toxotes microlepis Catlocarpio siamensis 33 Temporal abundance patterns of 110 fish taxa 34 Temporal abundance patterns of 110 fish taxa

% of annual abundance % of annual abundance % of annual abundance 10.0 20.0 30.0 40.0 50.0 60.0 10 20 30 40 50 60 70 10.0 20.0 30.0 40.0 50.0 60.0 0.0 0 0.0 c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct Graph 7 Graph 9 rp 8 Graph Pangasius sanitwongsei Raiamas guttatus Laides hexanema/spp. Notopterus notopterus Channa striata Amblyrhynchichthys truncatus Systomus orphoides Micronema apogon-micronema Cosmochilus harmandi Glossogobius koragensis Hypsibarbus wetmorei Puntioplites falcifer Wallago leeri Hemibagrus wyckioides Hemibagrus nemurus Opsarius spp. Belodontichthys dinema Leptobarbus hoeveni Hampala macrolepidota Labeo chrysophekadion/spp. Lobocheilos melanotaenia Ompok bimaculatus Pangasius pleurotaenia Helicophagus waandersi Osteochilus melanopleurus Hemisilurus mekongensis Osteochilus spp Scaphognathops bandanensis Mastacemblus armatus/spp. Hypsibarbus lagleri Graph 2to5: Graph 1: Four clearpatternscanbeisolated: Conclusions: Temporal distributionoffishspeciesintheKhoneFallsFigure fisheries 18:

% of annual abundance 100 % of annual abundance 10 20 30 40 50 60 70 80 90 10.0 20.0 30.0 40.0 50.0 60.0 70.0 0 0.0 c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct c o e a e a p a u u u Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct Mystacoleucus spp.,Mekonginaerythrospila, Parambassis wolffi/spp.,Euryglossapanoides, (May-June). themexhibitingasmallsecondarypeakatthe beginningoftherainy season of having adominantpresenceduringthedryseason(peakinJanuary);withsome Rhinogobius spp., Tetraodon spp.,Amphotistiuslaosensis, Pseudomystussiamensis, Polynemus longipectoralis, Probarbus labeamajor, Tor tambroides, Chonerhinusnefastus, Probarbus jullieni, precocious speciesarrivingatthebeginningofnewhydrological year (Oct-Nov). spp., Botiamodesta,Garra fasciacauda, Mystus multiradius/mysticetus/spp., Paralaubuca borneensis, Ariusstormi,Mystus singaringan/spp.,Cynoglossusmicrolepis, Cyclocheilichthys Achiroides spp.,Glyptothorax spp.,Channa marulius/spp.,Cirrhinusjullieni,Hemipimelodus Cirrhinus molitorella. Graph 10 Graph 11 Hampala dispar Pangasius bocourti Tenualosa thibaudeaui Pangasianodon hypophthalmus Osphronemus exodon Cyclocheilichthys enoplos Xenentodon cancila Cirrhinus mrigala Hypsibarbus pierrei Pristolepis fasciata Pangasius krempfi Cyprinus carpio Pangasius macronema Pangasius conchophilus Pangasius larnaudiei Wallago attu Macrochirichthys macrochirus Micronema bleekeri Setipinna melanochir 35 Temporal abundance patterns of 110 fish taxa 36 Temporal abundance patterns of 110 fish taxa Graph 6to8: species consideredinboth studies: spawningabove resultswith theMRC "Fishmigrations andhabits"the surveyof (Poulsen and Valbo-Jørgensencomparison 2001) gives thefollowing resultsfor28 detailed a Furthermore, during thedryseason. fishers oftenhave morefreetimeforfishing to catchwhenwater levels arelow, and season. Moreover, fisharegenerallyeasier when water levels riseduringtherainy drop. Theyenterthetributariesagain end oftherainy season,whenwater levels into themainstreamMekongRiver atthe number ofspeciesmigratefromtributaries largely beexplainedby thefactthatalarge and Poulsen 2000). Thesepatternscan are somedifferences(Bouakhamvongsa River Commission(MRC), althoughthere Mekong River conductedby theMekong with theinterviews offishersalongthe These patternsareingeneralagreement Graph 9to11: deauratus, Macrognathus siamensis/spp.,Hypsibarbusmalcolmi,Chitalablanci,Cirrhinus Clarias batrachus/spp., Chitala ornata,Bagrichthysspp.,HenicorhynchusPoropuntius beingregularlydistributedallyear long. or species having two equivalent abundanceperiods(dryandwet seasonrespectively) undecimradiatus. Hemibagrus wycki,Barbodesaltus, Labeoerythropterus, Aaptosyaxgrypus, Coius gudgeri, Luciosomableekeri,Onychostomacf.elongatum,Labiobarbusleptocheilus, pennocki, Pangasius polyuranodon, Bagariusyarrelli/spp., Acantopsis sp.orspp.,Sikukia reticulatus, Scaphognathopsstejnegeri,Kryptopterusspp.,Rasbora spp.,Gyrinocheilus Catlocarpio typus, Banganabehri,Boesemaniamicrolepis, Crossocheilus siamensis, Botiaspp, conchophilus, Pangasius macronema, Cyprinus carpio,Pangasius krempfi. macronema, Pangasius conchophilus, Macrochirichthys macrochirus, Wallago attu,Pangasius larnaudiei,Pangasius Pangasius bocourti,Hampaladispar, Setipinnamelanochir, Micronema bleekeri, Osphronemus exodon,Pangasianodonhypophthalmus,Tenualosathibaudeaui, Hypsibarbus pierrei, Cirrhinusmrigala,Xenentodon cancila,Cyclocheilichthysenoplos, Wallago leeri,Puntioplitesfalcifer, Hypsibarbuswetmorei, Pristolepisfasciata, Belodontichthys dinema,Opsariusspp.,Hemibagrusnemurus, Hemibagruswyckioides, Labeo (May-June). species showing adominantorexclusive peakatthebeginningofrainy season mekongensis, Osteochilusmelanopleurus, Helicophaguswaandersi, Pangasius pleurotaenia. Mastacemblus armatus/spp.,Scaphognathopsbandanensis, Osteochilusspp.,Hemisilurus sanitwongsei, Ompokbimaculatus, Lobocheilosmelanotaenia,Hypsibarbuslagleri, Channa striata,Notopterusnotopterus, Laideshexanema/spp.,Raiamas guttatus, Pangasius Micronema apogon-micronema, S microlepis, Osteochilusmicrocephalus/spp., Glossogobiuskoragensis, Cosmochilusharmandi, chrysophekadion/spp., Hampalamacrolepidota,Leptobarbushoeveni, siamensis, Toxotes microlepis, Thynnichthysthynnoides, Crossocheilus mainstream, after Bouakhamvongsea after andPoulsen (2000) mainstream, Majormigration patterns intheMekong Figure 19: 100 150 200 250 300 350 400 450 50 0 123456789101112 ystomus orphoides, Amblyrhynchichthystruncatus, (m3/second/100) Water Discharge reports) Migration (#of } } } } } The two studiescomparedherearehighlycomplementary, as: } Cirrhinus microlepis Aaptosyax grypus Pangasius polyuranodon Paralaubuca typus Pangasius hypophthalmus Botia modesta Mekongina erythrospilla Pangasius krempfi Wallago attu Hypsibarbus malcolmi 3 disagreements: database, asdoesBaird provide muchinformationofthisnatureforallthespeciesrecordedinKhone Falls fisheries indication ofthedirection,amplitudeorpurpose migrations, butBaird As opposedtoPoulsen andValbo-Jørgensen (2001), thepresentstudydoes notprovide any species, including information foronly50 species. Thelatterstudyfailedtosomeofthemostimportantfish above allencompasses110 taxa,whenthatofPoulsen andValbo-Jørgensen (2001) provides The presentstudyprovides thedetailsofmigrationpatternsover allthemonthsofyear and this lattermethodaredetailedinPoizat and Baran1997). on by Poulsen andValbo-Jørgensen (2001) isbasedoninterviews offishers(thedrawbacks of The presentstudyisbasedonactualcatchdataover asix-year period,whilethestudyreported 7 caseswithminimalvariation: 18 specieshaving essentiallythesameresults Migration Migration pattern pattern Scaphognathops bandenensis et al. (2001a; 2003; 2004), andRoberts andBaird(1995). Peak inJuly Peak inJune Unclear patterns Unclear pattern above falls Khone No mentionofasecond migration Onset ofthefloodseason Two migrations peryear Nov.-Dec. peak inKhong peak Nov.-Dec. Peak inJune-JulyKhong March-May Poulsen and Valbo-Jørgensen Poulsen and Valbo-Jørgensen (2001) (2001) . Peak inJune Peak inMay Two peaksinDecemberandMay Peak inJanuary migrationSecond inJune Unclear pattern migrationSecond non-visible Peak inMay-June Peak inFebruary Clear peakinJanuary Present Present et al. study study (1999a) does 37 Temporal abundance patterns of 110 fish taxa 38 Hydrological trigger of migrations: 7 affected downstream hydrology forhundredsofkilometres inCambodia(BairdandDearden2003). river istheYali Falls dam ontheSesanRiver in theCentralHighlandsofVietNam,whichhas example ofalargedamthathashadmassive impactonthedownstream hydrology ofalarge of thisspecies, aswell asonother speciesrespondingsimilarlytohydrological triggers. One serious one itstributarieswould likelyhave very seriousnegative impacts onthebehavior and migrations These resultsindicatethatdamsregulatingthedownstream hydrology oftheMekongRiver or soon aswater levels riseagain(examplesin1997and1998). should thewater recedeafterafirstrise, themigrationcorrespondingly slows down. Itre-startsas necessary fortriggeringmigrations(see, also,Hogan construction couldnegatively impactfishpopulationsthroughchanginghydrological conditions species towater level rises, andwarns usofhow changesinwater levels causedby largedam of within 10 days in1993). Thisphenomenoniswell known by fisherswhobelieve thatmigrations starts risingafterthedriestperiodofyear (e.g. evolution ofthecatchfrom0to270 kgper day However thereareingeneral adozendays eachyear whenmigrations peak,justwhenthewater and risingwater levels. ThemigrationoccurssuddenlyatKhone, andlastsaround40-50 days. recorded inPakse (Figure20) shows thecloserelationshipbetween themigrationsofthisspecies The analysis ofthedailycatches The catfish discharge, andthisstudyconfirmstherelationshipbetween migrationsandhydrological changes. Various factorsareknown totriggerfishmigrations, includingrisesinwater levels andchangesin P. krempfi Pangasius krempfi THE CATFISH OF THEEXAMPLE MIGRATIONS: HYDROLOGICAL TRIGGERSOF are triggeredby thefirstseasonalincreasesincurrentspeeds. Graphsalsoshow that provides aremarkableexampleofthesensitivityhighlymigratory Pangasius krempfi PANGASIUS KREMPFI et al . 2005). . in 12-16cmgillnetsvs. water level as a graphicapproach,asdetailedinthefollowing section. The impossibilityofaddressingthemigrationtriggerswith standardstatisticalmethodsledtoprefer detailed herebecause: The statisticalquantificationoftherelationshipsbetween fishabundanceandwater levels isnot statistical approachbasedoncorrelationswould beirrelevant. from water levels. Inthatsensethesewould beevents ofstochasticnatureforwhichaclassical initiates migrations, butthatonceinitiated,themigrations occur relatively independently 4) 3) normalized by adisputableLn(x+1)transformation; between catches(whichvary alot)andwater levels (whichvary alittle),unlesscatchdatais 2) 1) The catchesonday Dmightdependonwater levels onday D-n,butnremainsundetermined; The relationshipisgraphicallyclearanddoesnotrequirefurthertesting; Beyond thatparticularcaseitcanbeconsideredtheriseofwater levels isatriggerthat The day-to-day variability ofcatchesisamajorimpedimenttocalculatingthecorrelation 39 Hydrological trigger of migrations: 40 Hydrological trigger of migrations: iue2:Relationships between water level increases and Figure 20:

Daily catch (kg) 100 150 200 50 0 1993 1994

May 1995 1996 Pangasius krempfi

June 1997 July Pangasius krempfi Daily catch(kg) in Pakse(S.Laos) Water level(m) 1998

catches inKhoneFalls fisheries Aug. 0 2 4 6 8 10 12 14

Water level (m) 41 Hydrological trigger of migrations: 42 Life history, migrations and triggers 8 from otherexistingparameters (detailsaregiven below). IntheKhoneFalls fisheriesdatabase, combines originalvalues fromtheliterature (inparticularmaximumlength)andvalues calculated of allecologicalkeyfactsforagiven listofspecies(matrixSpeciesxKey facts).This matrix our requestby theFishBaseteamtoautomaticallyproducea"Speciesecologymatrix",i.e. atable FishBase gives lifehistoryfactsforeachspecies. Herewe usedanewproceduredeveloped upon Life historyfacts Falls database, butupdatedvalid namesaccordingtoFishBase2004 arealsogiven. according toFishBase2004 have beenlisted.Theoriginaltaxonomy usedcomesfromtheKhone to 47taxa.Whenonlythegenuswas known, allpossiblespeciesofthisgenuspresentinLaos Khong between 1993and1999(i.e. atleast50 individualsperyear onaverage); thiscorresponds This analysis hasbeenperformedontaxaforwhichmorethan750 individualswere caughtin Dominant species Method patterns, inparticularrelationtoriver discharge, andsensitivitytoflow modifications. (e.g. maximumlength,sizeatmaturity, approximate lifespan,mainfood,etc),seasonalabundance overview oftheecologicaltraitsdominantspecies, includingmajorlifehistorykeyfacts and ii)fromFishBasewithhydrological datafromtheMRC. Theobjective istoprovide an This sectioncombinesbiologicalinformationoriginatingi)fromtheKhoneFalls fisheriesdatabase MIGRATIONS AND TRIGGERS LIFE HISTORY FACTS, KEY DOMINANT SPECIES: pattern basedonfiguresfromsectionIII-3. This matrixissupplemented,foreachtaxon,by abriefdescriptionoftheseasonalabundance Main food items: infinity Thematrixofspeciesandcorrespondinglifehistory keyfactsisdetailedinAnnexA. given theirsizeandabundance. Thisparameterisestimatedfromgrowth studiesorfromlengthat Length for maximumyield: maximum length(FroeseandBinohlan2000). are available, frommaximumlengthusinganempiricalrelationshipbetween lengthatinfinityand from thelengthatinfinity, thatisitselfcalculatedfromgrowth studies, orwhennogrowth studies Approximate lifespan: for thespeciesinquestion. Maximum length: values foundfortheLaospeciesofgenus. when fisheswere notknown atthespecieslevel butonlyatthegenuslevel, we gave therangeof from theliteraturereviewed inFishBase. The defaultvalue usedhereisthemaximumlengthever reportedintheliterature This isthemaximumagethatafishofspecieswould reach.Itiscalculated This isthesizeoffishthatwould resultinthemaximumpossibleyield 43 Life history, migrations and triggers 44 Life history,migrations and triggers higher thepercentageoflargespecies,healthierfisheryisassumedtobe. of fishcaught(eitherlargeorsmallspecies),whichisanindicatorthehealthfishery: of auniquevalueforeachspecies,orrangealuesgenu.Thisanalysishighlightsthekind For eachofthedominanttaxa,FishBasematrixgivesmaximallengthknown;thisconsists 2) Lengthoffishcaught six yearsare: The forty-seventaxaforwhichatleast50individualshaebeencaughtonerageperyearoer 1) Dominanttaxaincatches Results nil, mediumorhigh. on thesegraphs,thesensitivitytodischargeof47taxahydrologicaltriggershasbeencodedas details forspeciesofagivengenuswheneerailable);thesegraphsaredetailedinAnnexB.Based catch data.Graphsshowingabundancevs.dischargehaebeengeneratedforeachtaxon(with data. DailywaterdischargedatainPakseoriginatingfromtheMRChavebeenjuxtaposedtodaily Daily overallcatcheshaebeencalculatedforeachtaxon,basedonthesumofallgear-specific Abundance patternsanddischarge iue2:Maximum size pertaxon Figure 21: Maximum length (cm) 100 150 200 250 50 0 Bagarius Hemipimelodus borneensis;Hemisilurusmekongensis;Henicorhynchus enoplos; Garrafasciacauda;Glyptothoax microlepis; Cosmochilusharmandi;Cossocheiluseticulatus;siamensis;Cyclocheilichthys Thynnichthys thynnoides. Puntioplites falcifer;Rasbora typus; Parambassiswolffi/ larnaudii; Pangasiusmacronema;pleuotaenia;polyuanodon;aalaubuca spp melanotaenia; Mekonginaerythrospila;Labeo chrysophekadion/spp.;Mystacoleucus Kryptopterus

Bagarius spp. Bagrichthys spp. .; Osteochilus Bangana behri

Barbodes altus spp Botia modesta spp Cirrhinus microlepis .; Bagrichthys Botia spp

Cosmochilus harmandi .; Labeoerythropterus;Labiobarbusleptocheilus;Laideshexanema/spp.;Lobocheilos Crossocheilus reticulatus spp Crossocheilus siamensis .; Pangasiusbocourti;conchophilus;krempfi; Cyclocheilichthys enoplos Garra fasciacauda spp spp Glyptothorax spp. spp Gyrinocheilus pennocki .; Pristolepisfasciata;Probarbusjullieni;Pseudomystussiamensis; .; Scaphognathopsbandanensis;Sikukiagudgeri;Tenualosathibaudeaui; Hemibagrus nemurus .; Banganabehri;Barbodesaltus;Botiamodesta;spp;Cirrhinus Hemipimelodus borneensis Hemisilurus mekongensis Henicorhynchus spp. Hypsibarbus malcolmi Kryptopterus spp.

Labeo erythropterus spp Labiobarbus leptocheilus

Lobocheilos melanotaenia .; Gyrinocheiluspennocki;Hemibagrusnemurus; Laides spp. Mekongina erythrospila Labeo chrysophekadion Mystacoleucus spp. Opsarius spp. Osteochilus spp. Pangasius bocourti Pangasius conchophilus Pangasius krempfi Pangasius larnaudiei

Pangasius macronema spp Pangasius pleurotaenia

Pangasius polyuranodon .; Hypsibarbusmalcolmi; Paralaubuca typus Parambassis wolffi/spp. Pristolepis fasciata Pseudomystus siamensis spp.; Opsarius Probarbus jullieni Puntioplites falcifer Scaphognathops bandanensis Rasbora spp. Sikukia gudgeri Tenualosa thibaudeaui Thynnichthys thynnoides The distribution of maximum sizes per taxon is given in Figure 21. The number of taxa and the biomass caught per class of maximum size are expressed below in terms of relative frequencies (this analysis is based on 43 species sensu stricto for which the maximum length range is well defined):

126-150cm 101-125cm 26-50 cm 7% 5% 12% 76-100cm 0-25 cm 9% 39%

51-75cm 0-25 cm 26-50 cm 12% 85% 28%

Figure 22: Maximum size distribution Figure 23: Maximum size distributionin the among the dominant taxa total biomass caught

These figures show that:

} 61% of dominant taxa caught have a maximum size superior to 25 cm, but

} 85% of fishes actually caught (in terms of biomass) belong to taxa whose maximum sizes are inferior to 25 cm.

This illustrates the abundance of small species in the catch, despite the diversity of a fish community in which large species are largely represented.

3) Species migrations Each of the 47 dominant taxa is characterized by its relative abundance during a year (see section 3). This abundance pattern has been coded according to five possible classes: i) caught all year long; ii) dominant in dry season; iii) dominant between the rainy and dry seasons; iv) dominant in rainy season; v) peaks during both dry and in rainy seasons.

The figure below shows the relative distribution of dominant taxa in terms of temporal abundance.

Peaks during both dry and in rainy Seasons: 11% These figures lead to the conclusion that 96% of Dominant in Rainy season 28% Caught all year long: 4% dominant taxa are not present all year long, and thus undertake migrations or become impossible to catch at certain periods of time (selectivity and operation mode of a gear depending upon hydrology). Given the diversity of fishing methods in the Khone Falls area (see section 2 and 3) aimed at catching fishes whenever they are present, Dominant between Dominant in this figure mostly highlights the importance of rainy and dry seasons 9% dry season 48% migrating behavior among dominant species of Figure 24: Temporal abundance patterns of 47 the Khone Falls fisheries. dominant species Life history,Life and triggers migrations 45 4) Species, discharge and migration triggers The relationship between discharge and abundance is illustrated for each of the 47 dominant taxa in Annex B. Figure 25, resulting from an analysis based on all catches over six years and including all the 110 taxa, shows clearly that the highest biodiversity appears in catches during times with the lowest discharge levels. This underscores the importance of dry season water levels for fish and fishers, as well as the importance of rising waters at the end of the dry season. These rising water levels actually act as triggers for several taxa, as illustrated by Pangasius krempfi in section III-4.

50 45 40 35 30 25 20 15 Trend Number of taxa 10 5 0 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

Discharge (m3/s)

Figure 25: Number of taxa caught versus Discharge

The sensitivity of taxa, to discharge variations has been analysed further with the 47 dominant taxa of the Khone Falls database. For each taxon, the sensitivity to discharge has been coded; this sensitivity is expressed by the nature of the relationship between abundance and discharge in the figures of Appendix B, and is coded as nil, medium, high or unknown. The abundance of each taxon in overall catches has also been integrated.

Nil 17% Other Medium 19% Unknown 9% sensitivity 4%

High High 55% sensitivity 96%

Figure 26: Percentage of each class of sensitivity to Figure 27: Percentage of taxa sensitive to discharge among the dominant taxa. discharge in the total biomass caught Life history,Life and triggers migrations 46 These resultsshow: most intensive inlandfisheryworldwide. results inanoverall loss. Thislosscanbevery significantwhentheriver concernedishometothe range ofspeciesarepermanentlyimpactedanddisappearfromthecatch,whichinlongterm certain catch,madeofvariable species, islikelyyear afteryear. Butwhenflows areregularized,a flooding makessomehydrological years goodforcertainfishspeciesandbadothers;overall a As aconclusion,onecannotethatwhenflows vary naturally, thediversity ofspecificresponsesto the KhoneFalls fisheries. 2) 1) The highpercentageoftaxasensitive todischargeamongthedominanttaxaofKhoneFalls The extremelyhighpercentageofspecieshighlysensitive todischargeintheoverall catchof 47 Life history, migrations and triggers 48 Deep-water pools as fish refuges 9 (2001a andb),Poulsen andValbo-Jørgensen (2001), Poulsen 1991, Roberts andBaird1995). outlined inseveral studiesorpublications(Blanc1959,Nguyen XuanTan andNguyen Van Hao The importanceofdeep-water poolsinthe mainstream totheecologyofMekongfisheshasbeen Northeastern Cambodia(Roberts andBaird, 1995;Baird of HangKhoneVillage, KhongDistrict,justbelow theKhoneFalls, rightontheborderwith c), andmorespecifically, someimportant deep-water water poolshave beenmonitoredinfront identified (Baird In partofthemainstreamMekongRiver inKhongDistrict,several deep-water poolshave been inhabited by largenumbersoffish,albeit,withoutbeingabletoidentifyspecies. Khong Districthave indicatedthatdeep-water poolsinthemainstreamMekongRiver areinfact Mekong Basin,althoughKolding However, beyond fishers'reports, thereisnobiologicaldatatoconfirmthesehypotheses inthe establishment ofFishConservation Zonesforprotectingdeep-water poolsfrombeingfished. (Champasak Province, SouthernLaos)reportedthat51 specieshaddirectlybenefitedfrom the Baird (2005c) wrotethatfishersfrommainstreamMekongRiver villagesinKhongDistrict Poulsen spawning areasforseveral species(see, forexample, Baird It appearsthatdeeppoolssheltermany species duringthedryseason;theyarealsothoughttobe Baird andFlaherty(2005) andBaird(2005a andc)have recentlyaddressedthistopicagain. et al . (2002) give alistof39speciesreportedtousedeeppoolsasdryseasonhabitat;and FISH REFUGES DEEP-WATER et al . 1999aandb;Baird et al et al. . (2002) reportedthathydro-acoustic methodspilotedin (1999a), CheaVannaren andSienKin(2000), Baird et al . 2001b, BairdandFlaherty2005, Baird2005a and POOLS AS et al et al ., 2001b; Baird2005c). et al. . 2001b; BairdandFlaherty2005). (2002), Kolding et al. (2002), et al. are very similartothoseofsurfacegillnets. the assumption(confirmedby fieldobservations) thattheaverage surfaceareasofdepthgillnets The exactsurfaceofeachindividualgillnetwas unknown, sothefishingunitwas "onenet",under monitored, timespentfishingwas recorded,and2153 fishbelongingto68specieswere caught. 1998. Duringthesemonths150 deepfishingoperationsand218 surfacefishing operationswere Subsequently bottomandsurfacecatcheswere comparedinFebruary andMarch1994,1997 season monthsduringwhichfishconcentrateindeep pools. nets areusedalmostexclusively inFebruary andMarch(98%ofannualuse),asthesearethedry gill netsareusedallyear long(withapeakbetween Decemberand February) whiledeep-set gill from 1993to1998,butdeep-setgillnetswere monitoredonlyin1994,1997and1998.Surface 2 fordetailsaboutthisgear).Surfacegillnetswere monitored,asadominantgear, every year The gearsstudiedaremonofilamentgillnetswithmeshsizesrangingfrom4to9cm(seesection difference between inCPUEsandcatchcompositions forbothfisheries. (approximately 20 mdeep)infrontofHang KhoneVillage, andtoassessifthereisasignificant in relatively shallow areasoutsideofdeep-water poolsornearthebottomofdeep-water pools Our objective inthisstudyistocomparethecatchesofsamegearseteitheratsurfaceor 49 Deep-water pools as fish refuges 9-1) Comparison between deep-water pools and surface CPUEs

Deep-water and surface 4-9 cm meshed gill nets are compared below during the same period and in the same general areas, in order to determine whether the CPUE of gill nets used in deep-water pools is different from those of the same gear used near the surface or in relatively shallow areas. The CPUE for surface and depth gill nets are given in Table 7.

Table 7:Catches per unit effort (CPUE) of surface and deep gill nets at Hang Khone village

CPUE Hours spent fishing Catch (kg) (grams per hour per net)

Depth gill Surface gill Depth gill net Surface gill Depth gill Surface gill net set 4-9 mm net set 4-9mm set 4-9 mm net set 4-9 mm net set 4-9 mm net set 4-9 mm

March 1994 1284 660 193.7 7.9 151 12

February 1997 12 1665 2.5 60.4 206 36

February 1998 504 948 66.4 34.0 132 36

This analysis shows that the CPUEs of gill nets set in deep-water pools in February and March are three to twelve times higher than the CPUEs of surface nets during the same months (see, also, Baird 2005c). This demonstrates the concentration of fishes in deep-water pools during the dry season. Fishers are well aware of this high concentration of fishes, but their fishing effort is tempered by the frequent loss of gears and reduced lifespan of nylon gill nets in rocky deep-water areas.

25 DECREASING TOTAL ABUNDANCE 20

15 CPUE Pools (g/h)

10 CPUE Surface (g/h)

0 Arius stormi Chitala blanci Bangana behri Bagrichthys spp. Hemibagrus wycki Puntioplites falcifer Pangasius bocourti Euryglossa panoides Labeo erythropterus Hemibagrus nemurus Hypsibarbus malcolmi Cosmochilus harmandi Coius undecimradiatus Boesemania microlepis Notopterus notopterus Parambassis wolffi/spp. Gyrinocheilus pennocki Mekongina erythrospila Hemibagrus wyckioides Pangasius conchophilus Helicophagus waandersi Pangasius polyuranodon Hemisilurus mekongensis Cyclocheilichthys enoplos Polynemus longipectoralis Hemipimelodus borneensis Scaphognathops bandanensis Amblyrhynchichthys truncatus Labeo chrysophekadion/spp. Micronema apogon - micronema

Figure 28: Biomass in surface and pools of the 30 most abundant species D eep-wa t er pools as fish r efuges 50 catfish), being For allthesespecies, CPUEishigherindeeppoolsthanatthesurface, withtheonly exceptions large Cyprinid).Thislatterlistgives prominencetospeciesabundantbutalsooflargesizes. in depthandatthesurface. Thenabi-plotofspecieswas created(Figure29). the differencebetween abundanceindepthand atthesurface, aswell asthedifferencebetween biomass In ordertomaketheseresultsmorereadableandintegrative, we calculatedforeachofthe30 species common upperMekongCyprinid), (a suctorialalgaefeeder), The mostabundantspeciesincatches(numberofindividualscaught)are dominant species. ordered accordingtotheirdecreasingabundance. Results arepresentedinFigure28forthethirty The catchofeachspeciesinFebruary andMarchhasbeendividedby theuniteffort,andspecies in thecatchesof4-9cmmesheddeep-water andsurfacegillnets. The following analysis, basedonthesamedatasetusedabove, focusesonthespeciescomposition 9-2) Deep-water poolspeciesversus surfacespecies iue2:Dmnneo ims n bnac nec aia,for the30dominant species Dominance ofbiomassandabundance ineachhabitat, Figure 29: species are Mekongina erythrospila B P C P N H M H S E C P B A H C P H u a a c u a o o m y o o e e e h y i Mekongina erythrospila c a n n n e l c r r p t m i l m i y b u t i o a r y p c l g g t s a s o n o i g s l p m i i o o h e y i a a l b b n Cosmochilus harmandi e c b a l t p r o p m u o n s a a e b e h m a h h g l i b n s a g g r a m e u i r a Pangasius conchophilus, Gyrinocheiluspennocki,Hemisilurusmekongensis y u t u a s n d l b r r s e i s a n n b u u l s a a g s a e u s i s n c i c e s s p u a t c i s n p l a h c h s h h f o o s i w n o a a m p i i m t m o r n c l w h e i y t l w n o y p c h o g r i y a u m o o c g c a s i a t p i s f l r p h l r k i o c e d f a u a t d o b f e y i e e o n r i i o n r n e a l a / s c r n e u l s i d m o s u - t n d t o p s u p t o e d s d m r (a MekongendemicCyprinid).However intermsoftotalbiomass, thedominant e i p i s p r u r s o a s a s l . i n o n c n i l i c s r e s Hemipimelodus borneensis o a n n t s u e i s s m and a and Labeo erythropterus S Morulius U R Pangasius conchophilus F M ABUNDANCE A e k C o L w H n E a spp. (or g e y b i c m n e k a o i i b (an Aridaecatfish), e e a M r r C g A y y o r , forwhichCPUEishigheratthesurface. o t r t r u h h i u s u s r r B Labeo l m s o o i P u a s p H HIGHER INPOOLS o s a s g p t t c n e e o r i c h l g i m r a r c h i u m a l h r u i s s y s t c P spp., including i s h i s i o u l a u y o h (a largecatfishreaching1.2m),and n s n s r p a c u g b h r s h s a m o e p o s c m k p a p i o a u . n h e u H d s d i k Cosmochilus harmandi l r i e u G i o t o i m s n n y / g r i s p i e n p i n m o p s c . e i h s l o e Labeo chrysophekadion d i l u u Gyrinocheilus pennocki s s P p b (a Mekongendemic O e o n r O n n e o L e c n k S s i i s (a relatively

BIOMASS HIGHER IN POOLS , a 51 Deep-water pools as fish refuges 52 Deep-water pools as fish refuges } } } This analysisshowsthat: individual weight offishatthesurfaceandinbottomdeeppoolsisgiven inTable 8. the smallest,andinparticularlargest,individualscannot becaught.Thecomparisonofaverage range (here, 4to9cm)cannotbeconsideredassuitableforlengthfrequencyorcohortanalysis, since therefore hadthesameselectivity(nosamplingbias). However, the useofarestrictedmeshsize and surfacegillnets).Thisanalysis was performedongillnetswiththesamemeshsizes, andthey individuals were caught,andatleast5individualswere caughtby eachfishingmethod(deep-water For thisanalysis, thesame datasetasabove was used,butwe selected18species, forwhichatleast10 analyze thedifferencesinweights ofindividualscaughtindeep-water poolsandatthesurface. pools fromoverfishing (Baird adults thatcontributesignificantlytospawning, hencetheimportanceofprotectingdeep-water dry season;itisassumedthatthese"largefishes"(largeindividualsofcommonspecies)areold Fishers claimthatdeep-water poolsareplaceswherelargefishesoftencaught,especiallyinthe 9-3) Sizeoffishesindeep-water pools } at mid-depth.ItispossiblethatG. and Cosmochilus harmandi,Ariusstormii, pools: Some specieslistedherehave notbeenidentifiedby Poulsen Hemibagrus wyckii, Baird 1995).andFlaherty(2005) wrotethatfishersinKhongreported result indifferentcatchcompositions(BairdandFlaherty2005, Baird2005c). deep-water pools, even withinKhongDistrict,andespeciallyabove theKhoneFalls, willcertainly of fish,even inarelatively restrictedarea,suchasthroughoutKhongDistrict.Therefore, studiesinother do notrepresentasinglehabitat,butrathermultitudeofhabitatsthatsupportdifferentcommunities It isimportant,however, torecognizethatdeep-water poolsinthemainstreamMekongRiver certainly of therocksadjacenttodeepareas. the fishingarea,andthesealgaeeatingfishareprobablystaying insideholesandaroundtheedges In fact,G. Mekongina erythrospila dominant intermsofabundance. spp. aredominantintermsofbiomass,whereas At thebottomofdeep-waterpools chrysophekadion/spp; Cosmochilusharmandi;Ariusstormii;Bagrichthysspp. Hemisilurus mekongensis,HemipimelodusborneensiHemibagruswycki,Gyrinocheiluspennocki;Labeo preference forthebottomsofdeep-waterpoolsindryseason;theyare Ten speciesamongthethirtydominantcaughtduringthismonitoringexpressaclear fishery; theymakeupto46%ofthecatch(with16%for and Gyrinocheilus pennocki,Hemipimelodusborneensis,Cosmochilusharmandi,Pangasiusconchophilus Arius stormi, Hemisilurus mekongensis, Hemipimelodusborneensis, Hemibagruswyckii,Gyrinocheiluspennocki, Mekongina erythrospila pennocki are Ariidaecatfishesnotfoundabove theKhoneFalls (Roberts, 1993;Roberts and and are foundinrockyareas, andaregenerallynotfoundinthedeepestareasbut Cosmocheilus harmandi and Labeo erythropterus are thefivedominantspeciesin4-9mmgillnetpeakdryseason et al and pennocki Pangasius conchophilus,Hemibagruswycki . 1999a;BairdandFlaherty2005; Baird2005c). Below, we Bagrichthys was particularlycaughtbecausetherearesteepcliffsin as inhabitantsofcertaintypesdeep-water habitats. are amongthefewspeciesdominantatsurface; spp. Two ofthesespecies, Gyrinocheilus pennocki Gyrinocheilus pennocki et al . (2002) asmakinguseofdeep orLabeo and Hemipimelodus borneensis and Hemisilurus mekongensis, Pangasius conchophilus, Pangasius bocourti Pangasius bocourti. chrysophekadion alone). are Table 8: Comparison of average individual weight in surface and in deep-water pools

Sample:nb in pools vs. Species name % heavier in pools nb in surface

Parambassis wolffi/spp. 9/11 78

Amblyrhynchichthys truncatus 8/8 63

Pangasius conchophilus 147/11 53

Chitala blanci 5/5 50

Scaphognathops bandanensis 29/66 48

Hemibagrus nemurus 26/14 48 Individuals larger in pools Hemipimelodus borneensis 167/6 43

Mekongina erythrospila 7/144 42

Cosmochilus harmandi 87/75 42

Puntioplites falcifer 49/32 41

Cyclocheilichthys enoplos 15/9 27

Euryglossa panoides 32/5 0

Notopterus notopterus 14/8 -4

Hypsibarbus malcolmi 20/32 -5

Labeo chrysophekadion/spp. 48/21 -7

Polynemus longipectoralis 45/11 -8

Micronema apogon - micronema 14/14 -16 Individuals larger at surface Gyrinocheilus pennocki 256/89 -25

Thus, among the 18 species caught at least five times in each environment:

} For eleven species the individuals caught in deep-water pools are 27 to 78% larger than those caught at the surface; these species are Parambassis wolffi/spp.; Amblyrhynchichthys truncatus; Pangasius conchophilus, Chilata blanci; Scaphognathops bandanensis; Hemibagrus nemurus; Hemipimelodus borneensis; Mekongina erythrospila; Cosmochilus harmandi; Puntioplites falcifer; and Cyclocheilichthys enoplos.

} For two species (Micronema apogon/micronema and Gyrinocheilus pennocki) the individuals caught at the surface were larger than those caught in deep-water pools. However, it is important to recognize that only juvenile Micronema spp. appeared in those results due to the relatively small mesh-size of the gill nets used. It is very rare to catch large individuals of these species in shallow waters, and adults are widely associated with deep-water pools (Baird et al. 1999a and b). No analysis could be made on the reproductive status of these species. D eep-wa t er pools as fish r efuges 53 54 Deep-water pools as fish refuges } } } } important roleofthesehabitatsasrefugesinthedryseason.Duringthosemonths: This briefanalysis offish catches atthesurfaceandbottomofdeep-water pools confirmsthe Baird 2005c). Baird fishing andtoprotectfisheries importance ofdeep-water poolstofish,andhave usedthisknowledge tobothassistthemin pools. FisherslivingalongtheMekongRiver inSouthernLaoshave longrecognized the ecological the KhoneFalls), have createdalargenumberofFishConservation Zones(FCZs)indeep-water the mainstreamMekongRiver inKhongDistrict,ChampasakProvince (bothabove andbelow pools becomeactualfreshwater protectedareas. Italsoshows thereason why fisherslivingalong Overall theseresultshighlighttheimportanceofdeveloping measuressothatMekongdeep-water breeders contributinglargelytostockreplenishment. hypothesis accordingtowhichdeep-water poolsplay arefugeroleforlargeold individuals, i.e. at thebottom,whileonlytwo have largerindividualsatthesurface. Thisindirectlyconfirmsthe Within aspecies, among18 speciesstudied,individualsof11 aremuchlarger(27to78%larger) surface. species, tenareclearlymoreabundantatthebottom,whiletwo onlyaremoreabundantatthe Species exhibitvarious degrees ofpreferencefordeep-water pools;however among30 dominant CPUEs fromthebottomofdeep-water poolsarethreetotwelve timeshigherthanatthesurface. resources (see, also,Bairdetal.2001b, BairdandFlaherty2005, 55 Deep-water pools as fish refuges 56 Bibliography 10 Baird, I.G.andP. Dearden2003. Baird, I.G.2005d Baird, I.G.2005c Baird I.G.1998. Baird, I.G.2005b. Baird I.G.2005a. Baird, I.G.2001. 1 h ouainadDvlpetDtbs,http://www.alsagerschool.co.uk/subjects/sub_content/geography/Gpop/HTMLENH/country/kh.h The populationandDevelopment Database, study fromNortheastCambodia. Freshwater andMarineEcosystems of two ofthelargestfishspeciesinMekongRiver inSouthernLaos. 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The main The main MRC ), , 61 Bibliography 62 Annex 1 ANNEX 1: DOMINANT SPECIES, LIFE HISTORY KEY FACTS, ABUNDANCE PATTERNS AND RESPONSE TO DISCHARGE

Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity % of total the Khone species and valid Family length life span max. yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Species caught Abundant in Oct.-Dec. + between 1,000 and Bagarius bagarius 70-200 2.2-8.3 46.1-135.3 mainly animals secondary peak in rainy Medium 13,000 m3.s-1, rather season (May-June) around 5,000 m3.s-1 Bagarius spp. 0.06 Sisoridae Bagarius rutilus Bagarius suchus mainly animals Bagarius yarrelli mainly animals Sharp and dense peak Bagrichthys plants/detritus + Dry season + rainy 24.9-30 6-6.2 16-19.4 between 1,500 and High macracanthus animals season peaks 3,000 m3.s-1 Bagrichthys spp. 0.07 Bagridae Bagrichthys zoobenthos macropterus mainly animals Bagrichthys obscurus Dry season peak + small mainly Peak between 2,000 Bangana behri 0.06 Bangana behri Cyprinidae 60 20.4 39.4 secondary peak at first High plants/detritus and 4,500 m3.s-1 rains Species caught Dry season peak + small between 2,000 and plants mainly Barbodes altus 0.17 Barbonymus altus Cyprinidae 20 8.8 12.8 secondary peak at first 8,000 m3.s-1,with a High plants/detritus rains peak between 2,000 and 3,000 m3.s-1 Dry season peak + small Very sharp and dense Botia caudipunctata 5.5-30 3.2-15.7 3.4-19.4 secondary peak at first peak between 2,000 High rains and 3,000 m3.s-1 Botia eos mainly animals zoobenthos Botia helodes mainly animals zoobenthos Botia lecontei mainly animals Botia spp. 0.17 Botia longidorsalis Cobitidae plants plants/ Botia longiventralis detritus + animals Botia morleti mainly animals Botia nigrolineata zoobenthos Botia sidthimunki mainly animals Botia splendida Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity the Khone % of total species and valid Family length life span max. yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Very sharp and dense zoobenthos Botia modesta 14.55 Botia modesta Cobitidae 25 13.5 16.1 Dry season peak peak between 2,000 High mainly animals and 3,000 m3.s-1 Species caught between Dry season peak + small plants mainly 1,500 and 7,000 m3.s-1, Cirrhinus microlepis 0.13 Cirrhinus microlepis Cyprinidae 65 26 42.7 secondary peak at first High plants/detritus concentrated between rains 2,000 and 4,000 m3.s-1 Two peaks, one at Species caught between decreasing flows Cosmochilus plants mainly 1,500 and 13,000 m3.s-1, Cosmochilus harmandi 0.40 Cyprinidae 100 32 66.5 (November-December) Medium harmandi concentrated between plants/detritus and one at first rains 1,500 and 6,000 m3.s-1 (May-June) Species caught between 1,500 and Crossocheilus Crossocheilus plants/detritus + 3.47 Cyprinidae 17 7.6 10.8 Dry season peak 19,000 m3.s-1, with a High reticulatus reticulatus animals sharp peak between 1,500 and 2,500 m3.s-1 Species caught between 1,500 and 10,000 m3.s-1, Crossocheilus Crossocheilus mainly with a sharp and intense 0.07 Cyprinidae 16 7.2 10.1 Dry season peak High siamensis siamensis plants/detritus peak between 1,500 and 2,500 m3.s-1 (but 10 data points only) Species caught Dominant peak at first between 1,500 and Cyclocheilichthys Cyclocheilichthys zooplankton 0.10 Cyprinidae 74 28.7 48.8 rains, but also caught in 20,000 m3.s-1, with a High enoplos enoplos mainly animals the dry season sharp peak around 3,000 m3.s-1 Sharp peak between plants/detritus + Garra fasciacauda 1.62 Garra fasciacauda Cyprinidae 11 5 6.9 Dry season peak 2,000 and 3,000 m3.s-1, High animals but few data points 63 Annex 1 64 Annex 1

3 Complex group of poorly identified species and controversial taxonomy, including also Cirrhinus spp., in particular Henicorhynchus/Cirrhinus lobatus, dominant in catches and coming from Cambodia where it is not recorded. Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity the Khone % of total species and valid Family length life span max. yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Species caught between 1,500 and Poropuntius 2 equal peaks, in dry Hypsibarbus malcolmi 0.37 Cyprinidae 50 20.4 32.7 mainly animals 11,000 m3.s-1, with a High malcolmi season and wet season peak between 3,000 and 5,000 m3.s-1 Peak in December + nekton mainly Kryptopterus apogon 12-130 2.9-7.6 7.6-87 small secondary peak No pattern Nil animals at first rains (May) Kryptopterus bicirrhis mainly animals Kryptopterus cheveyi mainly animals Kryptopterus nekton mainly cryptopterus animals Kryptopterus dissitus Kryptopterus Kryptopterus spp. 0.18 Siluridae geminus Kryptopterus mainly animals hexapterus Kryptopterus limpok mainly animals Kryptopterus mainly animals micronema Kryptopterus moorei mainly animals Kryptopterus mainly animals schilbeides Species caught between Peak in December + mainly 1,500 and 33,000 m3.s-1, Labeo erythropterus 0.09 Labeo erythropterus Cyprinidae 70 28.6 46.1 secondary peak at first High plants/detritus concentrated between rains (June) 2,000 and 4,500 m3.s-1 Species caught Dry season dominant between 1,500 and Labiobarbus Labiobarbus plants mainly 6.35 Cyprinidae 30 12.9 19.4 peak + small secondary 21,000 m3.s-1, with a High leptocheilus leptocheila plants/detritus peak in rainy season concentration between 1,500 and 3,000 m3.s-1 Almost two equal peaks Species caught Laides hexanema 14.2-16.5 4.5-4.8 9-10.5 in dry and early rainy between 2,000 and High Laides hexanema/spp. 0.06 Schilbeidae season 5,500 m3.s-1 Laides longibarbis mainly animals 65 Annex 1 66 Annex 1

Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity the Khone % of total species and valid Family length life span max.yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Dry season peak + small Species caught between Lobocheilos Lobocheilos plants mainly 1.25 Cyprinidae 20 8.8 12.8 secondary peak in early 1,500 and 24,000 m3.s-1; Nil melanotaenia melanotaenia plants/detritus rainy season no clear pattern Very sharp and dense Mekongina Mekongina mainly Dry season peak peak between 1,500 and 0.57 Cyprinidae 45 19 29.3 High erythrospila erythrospila plants/detritus (January) 3,500 m3.s-1,in particular around 2,000 m3.s-1 Species caught between Dominant peak at first Labeo Labeo plants mainly 1,500 and 26,000 m3.s-1, 0.06 Cyprinidae 90 28.7 59.7 rains, secondary peak in Medium chrysophekadion/spp. chrysophekadion plants/detritus concentrated between the dry season 1,500 and 5,000 m3.s-1 Dominant dry season Mystacoleucus plants/detritus + Peak between 2,000 7.3-20 3.4-7.4 4.5-12.8 peak + small secondary High atridorsalis animals and 5,000 m3.s-1 peak at first rains Mystacoleucus chilopterus Mystacoleucus Mystacoleucus spp. 0.11 ectypus Cyprinidae Mystacoleucus greenwayi Mystacoleucus lepturus Mystacoleucus plants/detritus + marginatus animals Dominant peak at first zoobenthos Opsarius spp. 0.06 Opsarius koratensis Cyprinidae 10 4.6 6.3 rains, secondary peak in Insufficient data Unknown mainly animals the dry season Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity the Khone % of total species and valid Family length life span max. yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Caught almost all year Osteochilus enn mainly long (except in April 8.2-60 2.5-23.8 5.1-39.4 Pattern species-specific Unknown eaporus plants/detritus and Sept.) but species- specific variability zoobenthos Osteochilus hasseltii plants/detritus + animals mainly Osteochilus lini plants/detritus Osteochilus spp. 0.08 Osteochilus Cyprinidae plants mainly melanopleurus plants/detritus Osteochilus mainly microcephalus plants/detritus Osteochilus salsburyi Osteochilus striatus Osteochilus vittatus Osteochilus mainly waandersii plants/detritus Dominant peak in early Species caught between plants/detritus + Pangasius bocourti 0.14 Pangasius bocourti Pangasiidae 120 17.5 80.2 rainy season, secondary 2,00 and 31,000 m3.s-1; Medium animals peak in Nov. no clear pattern Species caught between Pangasius Pangasius Exclusive peak in early 1,500 and 25,000 m3.s-1, 0.59 Pangasiidae 120 24 80.2 mainly animals Medium conchophilus conchophilus rainy season concentrated between 3,000 and 6,000 m3.s-1 Species caught between Exclusive peak in early 1,500 and 20,000 m3.s-1, Pangasius krempfi 0.25 Pangasius krempfi Pangasiidae 120 2.6 80.2 High rainy season concentrated between 2,000 and 9,500 m3.s-1 Species caught between zoobenthos Exclusive peak in early 1,500 and 22,000 m3.s-1, Pangasius larnaudiei 0.07 Pangasius larnaudii Pangasiidae 130 2.7 87 Medium mainly animals rainy season concentrated between 2,500 and 10,000 m3.s-1 Species caught between 1,500 and 26,000 m3.s-1, Pangasius zoobenthos Exclusive peak at first Pangasius macronema 0.26 Pangasiidae 30 2.6 19.4 with a sharp and High macronema mainly animals rains intense peak between 3,000 and 4,000 m3.s-1 Dominant peak at first Pangasius Pangasius plants/detritus + 0.17 Pangasiidae 35 2.4 22.7 rains, secondary peak in No pattern Nil pleurotaenia pleurotaenia animals the dry season 67 Annex 1 68 Annex 1

4 Present in the Khone species list, but not in Laos according to FishBase 2004 Taxon in List of possible Max. Approx. Length for Seasonal Abundance in relation Sensitivity the Khone % of total species and valid Family length life span max. yield Main food abundance to to Falls fisheries catch database names (cm) (years) (cm) patterns discharge discharge Almost exclusive peak Unclear response, Rasbora amplistriga 2.6-17 1.3-7.6 1.6-10.8 Unknown in the dry season probably species-specific Rasbora atridorsalis zoobenthos Rasbora aurotaenia plants/detritus + animals Rasbora zoobenthos borapetensis mainly animals zoobenthos Rasbora daniconius mainly animals Rasbora dorsinotata zoobenthos Rasbora dusonensis mainly animals zoobenthos Rasbora hobelmani mainly animals plants/detritus + Rasbora myersi Rasbora spp. 0.16 Cyprinidae animals zoobenthos Rasbora paucisqualis mainly animals zoobenthos Rasbora paviei mainly animals Rasbora rubrodorsalis Rasbora septentrionalis zooplankton Rasbora spilocerca mainly animals Rasbora steineri Rasbora sumatrana zoobenthos Rasbora tornieri mainly animals zoobenthos Rasbora trilineata mainly animals 69 Annex 1 70 Annex 1

Biomass (grams) Biomass (grams) Biomass (grams) 20000 25000 400 200 300 10000 15000 100 400 200 600 300 500 700 100 5000 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 Species: Bagrichthysmacracanthus 5 5 Species: Botiacaudipunctata/spp. 5 Species: Cosmochilusharmandi 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 Discharge (1,000m3/s) 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 RIVER DISCHARGEFORDOMINANTSPECIES Biomass (grams) Biomass (grams) Biomass (grams) 4000 2000 3000 5000 1000 400 200 300 100 150 100 200 250 300 50 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 Species: Crossocheilusreticulatus Species: Bagrichthysmacropterus 5 6 6 6 7 7 7 Species: Botiahelodes 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29

Biomass (grams) Biomass (grams) Biomass (grams) 4000 2000 20000 25000 6000 8000 10000 15000 200 100 150 5000 50 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 Species: Crossocheilussiamensis 5 5 6 6 6 7 7 7 Species: Botiamodesta Species: Banganabehri 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 Discharge (1,000m3/s) 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 73 Annex 2 74 Annex 2

Biomass (grams) Biomass (grams) Biomass (grams) 40000 20000 30000 50000 100000 10000 10000 12000 14000 40000 20000 60000 80000 2000 6000 8000 4000 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 Species: Cyclocheilichthysenoplos Species: Henicorhynchussiamensis 4 5 5 6 5 6 Species: Hemibagrusnemurus 7 7 6 8 8 7 9 9 8 10 10 9 11 11 10 Discharge (1,000m3/s) 12 12 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 13 13 12 14 14 15 13 15 16 16 14 17 17 15 18 18 16 19 19 17 20 20 18 21 21 19 22 22 20 23 23 24 21 24 25 22 25 26 26 23 27 27 24 28 28 25 29 29 26 30 30 27 31 31 32 28 32 33 29 33

Biomass (grams) Biomass (grams) Biomass (grams) 2000 4000 2000 6000 3000 5000 1000 1500 1000 4000 2000 6000 3000 5000 1000 500 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 Species: Hemipimelodusborneensis 5 5 6 Species: Hypsibarbusmalcolmi 7 6 6 Species: Garrafasciacauda 8 7 7 9 8 8 10 9 11 9 12 10 10 Discharge (1,000m3/s) 13 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 14 12 12 15 13 13 16 17 14 14 18 15 15 19 16 16 20 17 17 21 22 18 18 23 19 19 24 20 20 25 21 21 26 27 22 22 28 23 23 29 24 24 30 25 25 31 32 26 26 33 27 27 34 28 28 35 29 29 36 Biomass (grams) Biomass (grams) Biomass (grams) 100 4000 2000 6000 3000 5000 1000 400 200 300 100 40 20 60 80 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 Species: Hemisilurusmekongensis 6 6 6 7 7 Species: Glyptothoraxspp. Species: Kryptopterusspp. 7 8 8 9 8 9 10 10 9 11 11 10 12 Discharge (1,000m3/s) 12 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 13 13 12 14 14 13 15 15 14 16 16 17 17 15 18 18 16 19 19 17 20 20 18 21 21 19 22 22 20 23 23 24 21 24 25 25 22 26 26 23 27 27 24 28 28 25 29 29 26 30 30 31 27 31 32 28 32 33 33 29 34

Biomass (grams) Biomass (grams) Biomass (grams) 100000 4000 2000 6000 3000 5000 7000 1000 2000 40000 20000 60000 80000 1000 1500 500 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 Species: Henicorhynchuslobatus 6 Species: Gyrinocheiluspennocki 5 Species: Labeoerythropterus 6 7 6 7 8 7 9 8 8 10 9 9 11 10 10 12 Discharge (1,000m3/s) Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 13 12 12 14 13 15 13 16 14 14 17 15 15 18 16 16 19 17 17 20 18 18 21 19 19 22 20 23 20 24 21 21 25 22 22 26 23 23 27 24 24 28 25 25 29 26 26 30 27 31 27 32 28 28 33 29 29 75 Annex 2 76 Annex 2

Biomass (grams) Biomass (grams) Biomass (grams) 100 40000 20000 30000 50000 10000 4000 2000 6000 3000 5000 7000 1000 40 20 60 80 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 Species: Labeochrysophekadion/spp. 4 4 5 Species: Labiobarbusleptocheilus 5 5 6 Species: Osteochilushasselti 6 6 7 7 7 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) 11 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29

Biomass (grams) Biomass (grams) Biomass (grams) 100 120 140 1000 1200 1400 40 20 60 80 400 200 600 800 40 20 60 0 80 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 Species: Osteochilusmelanopleurus Species: Mystacoleucusatridorsalis 5 5 Species: Laideshexanema/spp. 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 Discharge (1,000m3/s) 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29 Biomass (grams) Biomass (grams) Biomass (grams) 4000 100 150 2000 6000 3000 5000 7000 1000 200 250 300 100 150 50 50 0 0 0 0 0 0 1 1 1 2 2 2 Species: Osteochilusmicrocephalus/waandersii 3 3 3 4 4 4 5 Species: Mystacoleucusmarginatus Species: Lobocheilosmelanotaenia 5 5 6 6 6 7 7 7 8 8 9 8 10 9 9 11 10 10 Discharge (1,000m3/s) 12 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 13 12 12 14 13 15 13 14 16 14 17 15 15 18 16 16 19 17 17 20 18 18 21 19 22 19 20 23 20 24 21 21 25 22 22 26 23 23 27 24 28 24 25 29 25 30 26 26 31 27 27 32 28 28 33 29 29 34

Biomass (grams) Biomass (grams) Biomass (grams) 12000 15000 12000 10000 40 20 30 10 6000 9000 3000 4000 2000 6000 8000 0 0 0 0 0 1 0 1 1 2 2 2 3 3 3 4 4 4 5 5 5 Species: Mekonginaerythrospila 6 6 Species: Opsariuspulchellus Species: Pangasiusbocourti 6 7 7 8 7 8 9 8 9 10 9 10 11 10 Discharge (1,000m3/s) 11 12 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 13 12 12 14 13 13 15 14 16 14 15 17 15 16 18 16 19 17 17 20 18 18 21 19 19 22 20 20 23 21 24 21 25 22 22 26 23 23 27 24 24 28 25 25 29 26 26 30 27 31 27 32 28 28 33 29 29 77 Annex 2 78 Annex 2

Biomass (grams) Biomass (grams) Biomass (grams) 400000 200000 300000 1000 1200 1400 100000 40 20 60 30 50 10 400 200 600 800 0 0 0 0 0 1 0 1 2 1 2 3 2 3 4 3 4 5 4 5 Species: Pangasiusconchophilus Species: Pangasiuspleurotaenia 6 5 6 Species: Pristolepisfasciata 7 6 7 8 7 8 9 8 9 10 9 10 Discharge (1,000m3/s) 11 10 Discharge (1,000m3/s) 11 Discharge (1,000m3/s) 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29

Biomass (grams) Biomass (grams) Biomass (grams) 100000 120000 20000 15000 10000 4000 2000 6000 8000 40000 20000 60000 80000 5000 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 Species: Pangasiuspolyuranodon 5 6 6 6 Species: Pangasiuskrempfi Species: Probarbusjullieni 7 7 7 8 8 8 9 9 10 9 10 11 10 Discharge (1,000m3/s) Discharge (1,000m3/s) Discharge (1,000m3/s) 12 11 11 13 12 12 14 13 13 15 14 14 16 15 15 17 18 16 16 19 17 17 20 18 18 21 19 19 22 20 20 23 21 21 24 25 22 22 26 23 23 27 24 24 28 25 25 29 26 26 30 27 31 27 32 28 28 33 29 29 Biomass (grams) Biomass (grams) Biomass (grams) 200 100000 150000 100 150 4000 2000 6000 3000 5000 7000 1000 50 50000 0 0 0 0 0 1 0 1 2 1 2 3 2 3 4 3 4 5 4 Species: Pseudomystussiamensis 5 6 5 Species: Pangasiuslarnaudiei 6 Species: Paralaubucatypus 6 7 7 7 8 8 8 9 9 10 9 10 Discharge (1,000m3/s) 10 11 Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29

Biomass (grams) Biomass (grams) Biomass (grams) 40000 20000 30000 50000 10000 200 250 300 100 150 400000 200000 600000 800000 50 0 0 0 0 0 1 0 1 2 1 2 2 3 3 3 4 4 4 5 5 Species: Parambassiswolffi/spp. 5 6 Species: Pangasiusmacronema 6 6 Species: Puntioplitesfalcifer 7 7 7 8 8 8 9 9 9 10 10 10 11 Discharge (1,000m3/s) 11 11 Discharge (1,000m3/s) 12 Discharge (1,000m3/s) 12 12 13 13 14 13 14 15 14 15 16 15 16 17 17 16 18 18 17 19 19 18 20 20 21 19 21 22 20 22 23 21 23 24 22 24 25 25 23 26 26 24 27 27 25 28 28 29 26 29 30 27 30 31 28 31 32 32 29 33 79 Annex 2 80 Annex 2

Biomass (grams) Biomass (grams) Biomass (grams) 10000 1200 1500 1000 1200 1400 600 300 900 4000 600 800 2000 6000 8000 400 200 0 0 0 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 Species: Thynnichthysthynnoides 5 6 6 6 7 7 Species: Sikukiagudgeri 7 Species: Rasboraspp. 8 8 8 9 9 9 10 10 10 Discharge (1,000m3/s) Discharge (1,000m3/s) Discharge (1,000m3/s) 11 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 16 17 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 24 25 25 25 26 26 26 27 27 27 28 28 28 29 29 29

Biomass (grams) Biomass (grams) 2000 1000 1500 10000 40000 20000 60000 30000 50000 500 0 0 0 0 1 1 2 2 3 3 Species: Scaphognathopsbandanensis 4 4 5 Species: Tenualosathibaudeaui 5 6 6 7 7 8 8 9 9 10 10 Discharge (1,000m3/s) 11 Discharge (1,000m3/s) 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 26 27 27 28 28 29 29 81 Annex 2