ORIGINAL ARTICLE Fisheries

Data mining and stock assessment of fisheries resourcesin Tonle Sap Lake, Cambodia

Kazuhiro Enomoto • Satoshi Ishikawa •

Mina Hori • Hort Sitha • Srun Lim Song •

Nao Thuok • Hisashi Kurokura

Received: 17 January 2011 / Accepted: 25 May 2011 / Published online: 25 June 2011

� The Japanese Society of Fisheries Science 2011

Abstract The potential of catch per unit effort (CPUE)

analysis based on statistics of local fisheries in Tonle Sap

Lake in Cambodia was evaluated. The fishery statistics

system was improved through a cooperative project con-

ducted by the Department of Fisheries and the Mekong River

Commission between 1994 and 2000, especially in the seven

provinces adjacent to Tonle Sap Lake. However, the fisheries

statistics were not effectively utilized for sustainable stock

management. After the cooperative project, fish catch data

sorted by species or species group were collected at the

province level in the seven provinces. Another recent project

also revealed the numbers of fishing gears that operated in the

seven provinces. The CPUEs of ten species in Kampong

Thom Province—including Channa micropeltes and Cir-

rhinus spp.—could be calculated from 1994 to 2007, because

these are caught solely using bamboo fence systems or bar-

rages. CPUE analysis clarified that stocks of high-price

fishes such as Ch. micropeltes, Hampala spp., and

Pangasius spp. have deteriorated while those of relatively

low-price fishes such as Cirrhinus spp., Cirrhinus microl-

epis, Cyclocheilichthys enoplos, and Channa striata have

increased in recent decades.

Keywords Cambodian inland fisheries � CPUE �Stock assessment � Tonle Sap Lake

Introduction

Inland fishes are vital as both food and income resources

for Cambodians. More than 81.5% of per-capita animal

protein intake in Cambodia is supplied from fishery prod-

ucts [1], and approximately 85% of total fish catch comes

from inland fisheries [2]. In addition, a recent study

revealed that small-scale fishing in Cambodia is quite an

important income source for rural people [3]. Almost all

people have some fishery-related activities, especially

around Tonle Sap Lake [4]. Recently, several reports

speculated about the possibility of exhaustion of fishery

resources in the lake, and a relationship between stock

of fishery resource and hydrological fluctuations in the

Mekong water system was insinuated [5]. However, those

reports and discussions were not based on fluctuations of

fishery resources but depended only on the trend of total

fish catch or correlation analysis between total fish catch by

several fishing methods and hydrological records [6]. The

Cambodian fisheries authorities recognized the importance

of stock assessment, and in order to obtain an accurate

status of the fish stock, the government, the Food and

Agriculture Organization (FAO), and the Mekong River

Commission (MRC) conducted a fisheries statistics

improvement program in the seven provinces adjacent to

Tonle Sap Lake from 1994 to 2000. Although the FAO

K. Enomoto � H. Kurokura (&)

Graduate School of Agricultural and Life Sciences,

The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku,

Tokyo 113-8657, Japan

e-mail: akrkrh@mail.ecc.u-tokyo.ac.jp

S. Ishikawa

School of Marine Science and Technology,

Tokai University, 3-20-1 Orido, Shimizu-ku,

Shizuoka, Shizuoka 424-8610, Japan

M. Hori

Graduate School of Kuroshio Science, Kochi University,

2-5-1 Akebono, Kochi 780-8520, Japan

H. Sitha � S. L. Song � N. Thuok

Fisheries Adminisitration, Ministry of Agriculture Forestry

and Fisheries, 186 Preah Norodom Blvd, 582 Phnom Penh,

Kingdom of Cambodia

123

Fish Sci (2011) 77:713–722

DOI 10.1007/s12562-011-0378-z

statistics database, named ‘‘FAO Fish STAT,’’ reflected the

improvements after the project, all fish catch data were

summed up as a total in the database, and records of fishing

effort were not available. Catch data sorted by species or

species groups might have been collected under the project

at the local level [7–9], but these detailed data were not

utilized. Even as the statistics improvement project was

underway, the government and the MRC implemented

another project to collect information on Cambodia’s

fishing gear [10]. This project revealed the existence of a

strong link between the type of fishing gear and the target

species. Therefore, stock assessment using the catch per

unit effort (CPUE) method is possible for the species for

which records of both catch volume and fishing effort are

available from several local fisheries management organi-

zations. The survey reported in this paper comprises two

steps: data mining of fishing records in provinces around

Tonle Sap Lake, and CPUE analysis and evaluation of the

present stock of each species.

Materials and methods

Data mining

Domestic fisheries statistics data were officially collected

by the Department of Fisheries of the Government of

Cambodia [DOF, currently called the Fisheries Adminis-

tration (FiA)] and compiled as Fisheries Statistics Year

Books. We collected as many yearbooks as possible from

the headquarters of the DOF in Phnom Penh in February

2005. In addition, we gathered information from the cur-

rent fisheries statistics data collection system through

interviews with government officers in charge at the DOF.

We conducted field surveys in the five provinces directly

connecting with Tonle Sap Lake, namely Siem Reap,

Kampong Thom, Kampong Chhnang, Pursat, and Battan-

bang (Fig. 1) from February to April 2005. In the collab-

orative project by the DOF and MRC [7–9], the provincial

government had collected monthly catch and effort data on

large-scale fishing, i.e., commercially operated fisheries, in

demarcated areas called fishing ‘‘lots.’’ We tried to gather

the actual primary records of fish catch and effort data for

each fishing lot, which had been collected by the provincial

governments. Simultaneously, we also asked the provincial

governments about the current data collection systems

conducted by them, including the person who reported the

catch amount of each species, the person who described the

record, and how the accuracy of the reports was confirmed.

Simultaneously, the relationship between the local classi-

fication of fish and scientific classification was confirmed

by direct interview using picture books and fish samples.

Then, taxonomic group classifications written in Khmer

were translated to species or species groups according to

the contemporary system on the basis of published field

guides and biological reviews [11–13]. The species com-

position of each fishing gear’s yield was examined on the

basis of outcomes of the MRC project compiled in the

Information of Major Fishing Gears in Cambodia [14]. As

the large-scale fishing season extends from the previous

October to May of the current year, all annual data were

calculated by summing up the monthly data for the same

period.

CPUE analysis and evaluation of present stock

of each species

Before CPUE analyses, the correlation between percent-

ages of catch volume in a lot to the total catch volume in

the province in a year and number of fishing gears, size of

the gears, and duration of season of the fishing method in

the year in the lot were analyzed, and the catch effort data

with the highest correlation to the contribution of each

species were selected as parameters of fishing effort. We

selected Kampong Thom Province as the target area for

CPUE analysis because of the existence of reliable raw

data. CPUEs of Barbodes gonionotus, Channa micropeltes,

Channa striata, Cirrhinus microlepis, Cirrhinus spp.,

Cyclocheilichthys enoplos, Hampala spp., Osteochilus

melanopleurus, and Pangasius spp., in lots no. 3, 4, and 5,

were calculated by dividing the catch volume of each

fishing year (ton) by the total length of the bamboo fence

systems (km) in the lot as an index of fishing effort. The

bamboo fence system is a huge barrier made from bamboo

along the fringe of flooding forest. For migratory fish

Fig. 1 Five provinces around Tonle Sap Lake and location of fishing

lots. B Battanbang, C Kampong Chhnang, P Pursat, S Siem Reap,

T Kampong Thom

714 Fish Sci (2011) 77:713–722

123

species such as Cirrhinus spp. and Trichogaster microlepis,

additional CPUEs were performed in lots 1, 2, and 7 using

the maximum width of the water current (m) where the

barrages (set nets) were set in the river. A barrage is a

setting net with a bag net and wing net, being set across the

flow of the river or canal between both shores. The target

species for each fishing gear were selected on the basis of

catch amount. The species caught in analyzable amounts

by each gear were selected for CPUE analysis. Among

them, Cirrhinus spp. is a target species for both bamboo

fence and barrage. This is because analyzable amounts of

Cirrhinus spp. are also caught by bamboo fence due to their

huge biomass, although they are migratory species mainly

caught by barrage.

Statistical analysis

The distribution pattern of the species among the lots in

Kampong Thom Province were categorized by cluster

analysis. In the analysis, the Bray–Curtis similarity coef-

ficient was used as the similarity index, and the neighbor-

joining method was used for clustering of species. The fish

groups were divided at 85% similarity level. In the corre-

lation analysis for clarification of CPUE trends, fishes were

divided at 0.05 risk level without Bonferroni correction.

Results

Data mining

Although the raw data were not compiled in provincial

offices, species-wise annual fish catch data from each

fishing lot in five provinces around Tonle Sap Lake were

reported in the annual year books from 1995 to 1997, and

the records of total catch of each species in all fishing lots

in 1998 existed in all provinces. Among them, only

Kampong Thom and Battanbang Provinces maintained

primary fish catch records. We could obtain further fish

catch data for 2000–2007 in Kampong Thom Province

from records kept in the provincial office. The data

recorded catch volumes of each fish species in each fishing

lot. Subsequently, we could collect catch data for each

species in each of five provinces from 1995 to 1998. Thus,

we had catch data for each species in different fishing lots

in Kampong Thom Province from 1995 to 2007 except

1999. The precise numbers of fishing gears used for large-

scale fishing in the fishing lots were also described in the

domestic fisheries statistics for more than 10 years. No

consistent increase or decrease in catch volumes of any

species and fixed ratio among catch volume of species

throughout the recorded period were noticed in any fishing

record of the five provinces. We selected ten species for

which multiyear catch records were obtainable in the five

provinces. The species names were written in Khmer, and

we estimated the scientific name of each species based on

interview surveys referring to several previous field guides

[11, 12]. Their scientific names and local names in Khmer

are shown in Table 1. Among them, the fish called trey riel

was mainly Cirrhinus siamensis, and other species in the

genera Cirrhinus and Henicorhynchus were included in

trey riel. However, among Cirrhinus, Ci. microlepis was

classified as other species and called trey pruol by local

people. Therefore, we classified trey riel as Cirrhinus spp.

and trey pruol as Ci. microlepis. Hampala spp. (trey

khmann in Khmer) mainly consisted of H. dispar, although

small amounts of H. macrolepidota were included.

Pangasius spp. (trey pra in Khmer) included P. hypoph-

thalmus, P. djambal, and other species in Pangasius. Trey

raws included several species in the genus Channa, such as

Table 1 Local and scientific

names of fish groupsKhmer name Latin name

Trey chhipin Barbodes gonionotus

Trey chhdaur (diep: juvenile) Channa micropeltes

Trey raws (ptuok: juvenile) Channa striata

Trey pruol (kralang: juvenile) Cirrhinus microlepis

Trey riel Cirrhinus spp.

(Ci. siamensis, other species in Cirrhius

and Henicorhynchus except Ci. microlepis)

Trey chhukok Cyclocheilichthys enoplos

Trey khmann Hampala spp.

H. dispar, H. macrolepidota)

Trey krum Osteochilus melanopleurus

Trey pra Pangasius spp.

(P. hypophthalms, P. djambal, others)

Trey kamphleanh Trichogaster microlepis

Fish Sci (2011) 77:713–722 715

123

Ch. marulia and Ch. striata. It was mentioned in the field

guide [12] that the most common snakehead in Cambodia

was Ch. striata, and a review [11] reported that Ch. striata

was distributed mainly in the lake. We also confirmed the

scientific name of trey raws in Tonle Sap Lake as

Ch. striata through interviews with DOF staff. For these

reasons, we assumed that trey raw in the statistics records

of these provinces mainly included Ch. striata. Figure 2

presents the interannual fluctuation in catch from 1995 to

2007 in five provinces. The figure shows the sum of catch

amount of the above-mentioned ten species, and the catch

amount of Cirrhinus spp., Channa micropeltes, Chana

striata, and Trichogaster microlepis. The total catch weight

in Kampong Chhnang Province was several times higher

than that in other provinces. The catch volumes of Cir-

rhinus spp. were prominently higher than those of other

species, especially in Kampong Chhnang and Kampong

Thom Provinces. The catch volume of Ch. micropeltes was

high before 1998 and decreasing after 1999. Chana striata

and Trichogaster microlepis were distributed mainly in

Battanbang Province.

In Kampong Thom Province, there are seven fishing

lots. The geographical features of the lots are different

from each other (Fig. 3). The lots could be roughly divided

into two types according to their geographical features.

Lots no. 1, 2, and 7 are located in large rivers or near the

river mouth. We categorized this type as river-type lots. On

the contrary, lots no. 3, 4, and 5 are located not in rivers but

in flooding areas in the high-water season. We categorized

this type as lake-type lots. Lot no. 6 is of intermediate type,

located in both river and flooding areas. Two types of

fishing gear were used in these fishing lots, namely bamboo

fence and barrage. Bamboo fence is a long barrier made

with bamboo along the flooding area, and fish are caught

inside the barrier when water depth decreases. Barrage is a

set net used in the river with a bag net and wings across the

flow. Bamboo fences were used in fishing lots 3, 4, 5, and

6, and barrages were used in lots 1, 2, 6, and 7. Therefore,

fish in lots 3, 4, and 5 were caught solely by bamboo

fences, and in lots 1, 2, and 7 they were solely caught by

barrages.

The annual catch of the seven fishing lots had been

approximately stable for 10 years from 1995, fluctuating

from 2437 to 4434 tons; significantly increasing or

decreasing trends were not observed. However, the main fish

species caught showed significant variation. In particular,

the catch of Cirrhinus spp. (before 1997 this genus was

categorized as Henicorhynchus [15]) had increased during

the period, with several fluctuations, whereas that of

Ch. micropeltes constantly diminished, except in 1999. The

catch volumes of the seven fishing lots showed different

fluctuation patterns. Fishing lot no. 2 had the highest catch

for the 10 years except 1995. The catches of lots 1 and 3

Fig. 2 Interannual fluctuation of catch amount in Battanbang (solidsquares), Kampong Chhmang (open triangles), Pursat (solid trian-gles), Siem Reap (solid circle), and Kampong Thom Provinces (opencircles). The fluctuation is expressed as the sum of the catch amount

of 10 species and the catch amount of Cirrhinus spp., Channamicropeltes, Channa striata, and Trichogaster microlepis

Fig. 3 Location of lots in Kampong Thom Province. The numbers in

the figure indicate lots

716 Fish Sci (2011) 77:713–722

123

gradually declined during the 10 years. For the 10 years

from 1994, the main fishing grounds for Cirrhinus spp.

and Ch. micropeltes had not changed. Figure 4 shows

the average share of each lot in the total catch volume of

each species in the province. For statistical confirmation of

species categorization, we performed cluster analysis using

a similarity index (Bray–Curtis similarity coefficient),

including the result in the figure. Based on cluster analysis,

fishes could be divided into three groups. Group A

included O. melanopleurs, Cy. enoplos, Pangasius spp.,

and Ci. microlepis, and group B included B. gonionotus,

Hampala spp., Ch. striata, and Ch. micropeltes. Cirrhinus

spp. and T. microlepis formed a clear cluster independent of

the other species (group C). The fishes in group A were

mainly caught in lake lots (lots 3, 4, and 5), and the fishes

in group C were mainly caught in river lots (lots 1, 2, and 7).

A large portion of group B fishes were caught in lot 6

(an intermediate-type lot).

CPUE analysis

Tables 2 and 3 present the results of correlation analysis

between the ratio of each lot to the total annual catch of

each species and several annual catch effort records. Sig-

nificant correlations (p \ 0.01) were observed between the

total length of bamboo fence in the lots and the share of the

lots in the annual catch volume of B. gonionotus, Ch. mi-

cropeltes, Cirrhinus spp., Hampala spp., and Pangasius

spp. in lake lots. For river lots, the contribution of each lot

to the total catch volume of Ci. microlepis, Cirrhinus spp.,

Cy. enoplos, and Pangasius spp. had significant correla-

tions with maximum river width at the site of barrage

fisheries. We calculated CPUEs for stocks of 9 species

except T. microlepis, namely B. gonionotus, Ch. micropeltes,

Ch. striata, Ci. microlepiss, Cirrhinus spp., Cy. enoplos,

Hampala spp., Pangasius spp., and O. melanopleurus in

lake lots using the total length of bamboo fence in the lot as

the unit of catch effort, and implemented CPUE analysis for

stock of Cirrhinus spp. and T. microlepis in river lots using

the maximum river width as the unit of fishing effort. CPUE

analysis showed different patterns of fluctuations among

the species. As the result of correlation analysis between

year and CPUE, four species (Ch. striata, Ci. microlepis,

Cirrhinus spp., and B. gonionotus) increased, two (Cy.

enoplos and O. melanopleurus) were stable, and three

(Ch. micropeltes, Hampala spp., and Pangasius spp.)

decreased in lake lots. Two species analyzed in river lots

increased in CPUE at the risk rate of 5%.

Discussion

Fisheries statistics in Cambodia

In general, as fisheries statistics data for developing

countries contain ‘‘gray’’ data, they cannot be used for

practical stock assessment [16, 17]. However, a coopera-

tive project intended to improve fisheries statistics was

implemented from 1994 to 1996 by the MRC and Cam-

bodian DOF in the seven provinces around Tonle Sap Lake

Fig. 4 Share of fishing lots in

Kampong Thom Province:

average shares of lots by catch

amount of each species (%C)

from 1995 to 2007 except 1999

in Kampong Thom Province

(right) and the result of cluster

analysis of similarity of catch

amount distribution of the

species (left). Bray–Curtis

similarity coefficient was used

as the similarity index. The

component bar chart (right) and

diagram (left) are formed from

the share of lots in the total

amount of each species (%C) by

the Clark and Warwick method,

in which fish species can be

divided into three groups at 85%

similarity level. Numbers in the

bar chart indicate lots

Fish Sci (2011) 77:713–722 717

123

[10]. We did not find any suspicious trend in the data on ten

species in five provinces from 1995 to 1998. Kampong

Chhnang Province is located at the outlet of Tonle Sap

Lake to Tonle Sap River. Battanbang Province is located

on the west coast of the lake and has broad flooding forest

areas. All fish migrating to the Mekong River should pass

through Kampong Chhnang Province when the lake water

recedes. The habitats of C. striata are in sluggish or

standing water, such as in flooding forest areas [12].

Lamberts [18] reported that habitats with a lot of vegetation

cover that are not completely submerged during flooding

offer specific protection for T. microlepis. The significantly

highest total catch volume in Kampong Chhnang Province

and the inhomogeneous distribution of Ch. striata and

T. microlepis in Battanbang Province correspond to pre-

vious knowledge of fish behavior in this area. We could not

find any conclusive evidence to discredit the data as bogus.

The distribution pattern of catch volume was convincing,

and we can conclude that the project succeeded in making

some progress in improving the quality of the statistics.

After the project terminated, the Kampong Thom and

Battanbang Province offices continued to collect fisheries

statistics using the same system. In Kampong Thom

Province, in particular, reliable catch data of large-scale

fishing were collected until 2007, although 1999 data were

missing. Fishery data of Kampong Thom Province were

recorded by fishing lot and sorted by species. There were

seven lots in Kampong Thom Province: three in flooding

areas (lake lots), three in water channels (river lots), and

one of intermediate type. Among the ten species analyzed,

Cirrhinus spp. and T. microlepis were mainly caught in

river lots. We concluded that O. melanopleurs, Cy. enop-

los, Pangasius spp., and Ci. microlepis could be classified

as lake-type species and Cirrhinus spp. and T. microlepis

as river-type species. The local name of Cirrhinus spp. is

trey riel; the local people distinguish this fish from

Table 2 Catch volume records of ten species in five provinces around Tonle Sap Lake in 1995 (t)

Species Province Total

Siem Reap Kampong Thom Battanbang Pursat Kampong Chhnang

Barbodes gonionotus 145 163 50 87 184 629

Channa micropeltes 1207 864 796 771 973 4610

Channa striata 116 46 985 126 164 1437

Cirrhinus microlepis 5 – 2 27 498 532

Cirrhinus spp. 10 243 118 181 801 1353

Cyclocheilichthys enoplos 133 258 50 161 1249 1851

Hampala spp. 53 180 81 57 – 371

Osteochilus melanopleurus 19 – 29 19 191 258

Pangasius spp. 87 143 76 556 232 1093

Trichogaster microlepis 3 1 391 – 33 429

Total 1778 1898 2578 1985 4325 12563

Table 3 Catch volume records of ten species in five provinces around Tonle Sap Lake in 1998 (t)

Species Province Total

Siem Reap Kampong Thom Battanbang Pursat Kampong Chhnang

Barbodes gonionotus 91 152 85 182 125 635

Channa micropeltes 425 350 792 841 557 2965

Channa striata 82 31 850 122 15 1100

Cirrhinus microlepis 19 147 14 13 315 508

Cirrhinus spp. 46 79 165 258 1170 1718

Cyclocheilichthys Enoplos 150 239 144 473 144 1150

Hampala spp. 63 86 66 50 183 448

Osteochilus melanopleurus 32 87 39 47 205 410

Pangasius spp. 147 162 32 367 550 1258

Trichogaster microlepis 48 25 373 129 1 576

Total 1103 1358 2560 2482 3265 10768

718 Fish Sci (2011) 77:713–722

123

Ci. microlepis by calling the latter trey pruol. The fish trey

riel includes several fish species in the genus Cirrhinus,

though the greater part is Ci. siamensis. Ci. siamensis is

well known for its migration between the floodplains

around Tonle Sap Lake and Mekong River. They migrate

to Mekong River in the dry season. T. microlepis is not a

migratory species. However, they migrate to flooding areas

in the early stage of flooding and return to the lakes with

the receding lake water [18]. Cirrhinus spp. and T. mi-

crolepis were supposed to be caught during migration to

Mekong River by barrage when they return to the lake from

tributary flow.

In the lake lots of Kampong Thom Province, the cor-

relation between total length of bamboo fence in a lot and

its contribution to the annual total catch volume in the

province was higher for B. gonionotus, Ch. micropeltes,

Cirrhinus spp., Hampala spp., and Pangasius spp

(Table 4). Bamboo fences are set along fringes of flooding

forests in a lot, and fish are caught in the latter half of the

fishing season after the flooding water recedes. Bamboo

fence is a traditional fishing gear, and little improvement in

its methods and fishing efficiency has been carried out.

There has also been little change in the total length of

bamboo fencing in recent decades, although the number of

systems in a lot has changed as a result of fragmentation.

Therefore, the total length of bamboo fencing in a lot

expresses the total fishing ground area covered by the

systems in the lot. The possible duration of this fishing

method is determined by the time the flooding water takes

to recede, and the fishing period cannot be used an index of

fishing effort.

In river lots, significantly higher correlations exist

between the maximum width of the river at the site where

the barrage fishery systems were set in the lot and the

contribution of each lot to the total catch volume of Cir-

rhinus spp. and Ci. microlepis in a year (Table 5). Gener-

ally, a number of barrages are set in a river or channel. The

river and channel function as catchment systems of flood-

ing water while the water recedes. Large portions of water

are thus filtered through the barrage in the river or channel

more than once. The depths of rivers and channels do not

differ from each other significantly, while the river width

increases due to the confluence of water from the flood-

plain. As a result, the river downstream is wider than

upstream. The maximum river width of the river at the

barrage site at the lowest position of the river can be used

as an index of the total volume of water filtered by all

barrages in the river. Barrage is also a traditional fishing

Table 4 Correlations between

the ratio of each lot to the total

annual catch weight of each

species and several indexes of

fishing effort in a year in lake

lots of Kampong Thom

Province

* Significant at p \ 0.01

Species Total length of

bamboo fence

Number of

bamboo fences

Duration of

fishing period

n

Barbodes gonionotus 0.70* 0.42 -0.13 21

Channa micropeltes 0.80* 0.52 -0.25 21

Channa striata 0.38 0.04 0.24 18

Cirrhinus microlepis 0.01 -0.27 0.31 21

Cirrhinus spp. 0.58* 0.56* -0.51 21

Cyclocheilichthys enoplos 0.18 0.03 0.08 21

Hampala spp. 0.55* 0.06 0.28 21

Osteochilus melanopleurus -0.40 -0.62* 0.28 21

Pangasius spp. 0.56* 0.55* -0.30 21

Trichogaster microlepis 0.40 0.65 -0.27 12

Table 5 Correlations between

the ratio of each lot to the total

annual catch weight of each

species and several indexes of

fishing effort in a year in river

lots of Kampong Thom

Province

* Significant at p \ 0.01

Species Maximum

river width

Total length

of fence

Number of

gears

Duration of

fishing period

n

Barbodes gonionotus -0.24 -0.32 -0.42 0.33 21

Channa micropeltes -0.40 -0.70* -0.79* 0.37 21

Channa striata -0.43 -0.51 -0.68 0.59 9

Cirrhinus microlepis 0.90* -0.06 0.33 -0.89* 21

Cirrhinus spp. 0.98* 0.07 0.47 -0.92* 21

Cyclocheilichthys enoplos 0.60* -0.25 -0.01 -0.45 21

Hampala spp. -0.22 -0.11 -0.15 0.06 21

Osteochilus melanopleurus 0.43 -0.19 0.02 -0.45 21

Pangasius spp. 0.67* 0.00 0.25 -0.53 18

Trichogaster microlepis -0.55* 0.15 -0.01 0.61* 15

Fish Sci (2011) 77:713–722 719

123

gear in Cambodia, and little improvement to this fishing

method has been carried out in recent history. Therefore,

significant correlations existed in the maximum river width

and catch of widely and densely distributed fish species

such as Cirrhinus spp. and Ci. microlepis. The catch vol-

umes of these species had negative correlations with the

duration of fishing period. It would be very interesting to

clarify the mechanism or background of this negative

correlation, though we do not have any reliable information

to explain the background. We presume that the following

two explanations could be possible: First, barrage fishery is

performed mainly during the first half of the fishing season

when the lake water level decreases rapidly with the

recession of water. Fish are caught more efficiently when

the water level decreases in a shorter period. Larger vol-

umes of fish can be caught in shorter fishing periods.

Second, fishers close the fishing period earlier when the

catch is better. However, we need more detailed field

observations of barrage fisheries to clarify the background.

The results of CPUE analysis indicate that major fish

species had been replaced and resource conditions had

deteriorated qualitatively, though there was little change in

the total fish resources in Tonle Sap Lake. When we

compared the species that decreased and increased in

CPUE, we found that all the species that decreased were

large-size carnivorous fish with higher market value.

Among them, Ch. micropeltes and Pangasius spp. are

cultured species. Large amounts of Ch. micropeltes and

Pangasius spp. fingerlings had been caught and sold as

seed for aquaculture before aquaculture was regulated in

2004. The slight increases in CPUE after 2004 of both

species may possibly be attributed to the effect of regula-

tion, and the increase of CPUE in these species will be

shown by future surveys. Most of the species that increased

in CPUE are omnivorous fish, being good prey for Channa

and Pangasius (Figs. 5, 6).

From these characteristics of fish species, we presume

that the possible mechanisms of species replacement are

overfishing of valuable fish for direct consumption,

Fig. 5 CPUE analysis of fish species in lake lots, namely lot number 3 (diamonds), lot number 4 (squares), and lot number 5 (triangles), in

Kampong Thom Province

720 Fish Sci (2011) 77:713–722

123

aquaculture, and reduction of predators and competitors.

We cannot conclude the relevancy of this presumption only

from the present data. Further research to estimate the

predation pressure of Channa and Pangasius and to

understand competition among fish species is urgently

required to establish adequate fish resource management in

Tonle Sap Lake.

One of the most urgent issues relating to fish resources

in Tonle Sap Lake is the hydrological impacts caused by

water resource management of Mekong River. Tonle Sap

Lake is a unique lake, whose area fluctuates depending on

the flow volume of Mekong River. Tonle Sap Lake accepts

large amounts of water from the Mekong River in rainy

season through Tonle Sap River as a natural control basin,

and discharges water to Mekong River in dry season. It is

said that hydropower is fundamental for regional devel-

opment of the Mekong Basin. Every country around the

Mekong River and some international and regional orga-

nizations have agreed on the construction of new dams for

hydropower on the Mekong River. Currently, a total of

fourteen plants are under construction or are ongoing [19,

20]. Flood control and irrigation are also important for

improving agricultural production and human life. How-

ever, these artificial alterations of the river system will lead

to huge changes in the hydrologic circumstances of the

Mekong River System and area of floodplain around Tonle

Sap Lake. These changes would cause further damage to

fishery resources, because many fish adjust their biological

features to the unique hydrologic circumstances of the

Mekong River System [21–23]. Unfortunately we could

not find any catch volume data for 1999 on any species in

any province. The year was an extremely dry year. We

cannot conclude from the present study whether the water

level of the lake has a strong impact on all fish species in

Tonle Sap Lake. It is expected that future studies of fish

stock conditions in Tonle Sap Lake will clarify the

hydrological impact on each fish species.

Acknowledgments We are grateful to the staffs of Fisheries

Administration of Cambodia and Inland Fisheries Research and

Development Institute of Cambodia, Phnom Penh who participated in

the field survey for data collection. We thank I. McTaggart for

proofreading the manuscript of the earlier version of this paper. This

study was supported in part by the research project ‘‘Water man-

agement system of the Mekong River’’ under the Core Research for

Evolutional Science and Technology by the Japan Science and

Technology Agency and the 21st Century COE Program ‘‘Biodiver-

sity and Ecosystem Restoration Research Project’’ from the Ministry

of Education, Culture, Sports, Science, and Technology.

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