Research articles NAT. NAT. HIST. BUL L. SIAM Soc. 49: 161-176 ， 2001 THE ECOLOGY AND CONSERVATION OF THE SMALLSCALE CROAKER BOESEMANIA MICROLEPIS (BLEEKER 185 8- 59) IN THE MAINSTREAM MEKONG RIVER ，SOUTHERN LAOS lan lan G. Baird ，Bounpheng Phylavanh ，Bounthong Vongsenesouk ， and Khamsouk Xaiyamanivoni ABSTRACT 百 le smal1scale croaker Boesemania microlepis is a large species in the perciform fami1y Sciaenidae Sciaenidae reaching over a metre in length and at least 18 kg in weigh t. Although drums and croakers croakers from 白is family 訂 e marine main1y ，this freshwater species is found in th 巴 Mekong ， Chao Phraya ，Nan ，M 巴k10ng ，Tachin ， and Bang Pakong River basins. It occurs in the Mekong River River basin in Tb ailand ，Laos ， Cambodia and Vietnam ， and parts of peninsul 釘 Malaysia and Westem Indonesia. In the Mekong River ，the species is known at least as far north as Louang Phrabang Phrabang in northem Laos. This paper reviews the status of mainstream Mekong River populations populations of 出 e smal1sca1e croaker in southem Laos. We have identified seven known spawning spawning grounds in Kh ong Dis 町ict ， Champasak Pr ovince ， southem Laos based on 出e dry- season season occurrence of croaking individua1s in spawning condition in these areas. We discuss habitat habitat usage and 出 e acoustic sounds made by smallscale croakers. Fish Conservation Zo nes have have a1r eady been estab1ished to benefit the species ，加d 由is may be an excellent strategy for protecting protecting populations. Boesemania microlepis be considered should for special IUCN conser- vation vation listing ， based on widespread reports of severely declining of stocks 出is popul 訂 and expensive expensive food fish in southem Laos and northeast Cambodia Key words: Laos; Mekong River; capture fisheries; biological conservation; fish acoustics INTRODUCTION 百le smallscale croaker ， Boesemania microlepis (BLEE 阻 R ，1858-59) ， is a benthopelagic fish fish species found in the Mekong ，Chao Phraya ，Nan ，Meklong ，Tachin and Bang Pakong Rivers and some connecting canals in Thailand (WONGRATANA ，1985). 泊施 speci is found in in parts of the Mekong River basin in Laos ，Cambodia and Vietnam (WONGRATANA ， 1985; BAIRD ET AL. ，1999) ，and has also been reported from Indonesia and West Malaysia (WONGRATANA ， 1985; Ko 廿 ELAT ET AL. ， 1993; M. Kottelat ，personal communication ，May 1999). 1999). In the Mekong River basin in the Lao People's Democratic Republic (Lao PDR or Laos) ， this large drum or croaker (Order Perciformes: Sciaenidae) is res 仕icted to the mainstream Mekong River and large lowland 位ibutaries close to the Mekong. Al though most sciaenid croakers 訂 e marine (DAVIDSON ， 1975; GOULD 町 G ， 1980; WONGRATANA ， 1985; 1985; SASAKI ，1997) ， B. microlepis is one of the very few 出at is a freshwater species. In 町(伺刷l a剖all 制aut 白ho 併rs 吟) P.O. Box 86ω0 ，Pakse 弘， Lao PDR. E-mai1: ian 初nba 剖ir 吋d@lao ∞ne t. net Received Received 20 Ma 訂rch 2001; accept 飽ed 27 Ju1y 200 1. 161 161 162 162 L AN G. BA IRD ET AL ー、，. ー..J ・p ・、， China .... '.... _rli' . '" 、〆 ノ.. )‘司、 a "J f 、r'(" 、， !、 China 、.J '" "::1 "::1 ! 、1 、 、、、 ι〉 Vi etnam ，、 :ノ 、 uR 可 ‘ r dr B 町官官 ¥.-，^'、 ‘ 。叫 yannw) 、、 、，、 .H 岨 oi ‘『、 ~ 、 『‘ f ‘、 ， 、h ー、 L ・. 、 r， Lao co ャ〕¥〆 J~ 』、 ど、 、 w 、 t T 、. 句、 ，J 、 t 生 ( _r 、、 .J 、 、、， 、、 、‘ τbailand τbailand ， ，_'J ~_ 〆 ，戸. Vietnam Fig ure. 1. Lo w 巴r Mekong Basin ECOLOGY AND CONSERVATION OF SMALLSCALE CROAKER 163 the the Mekong River B. microlepis occurs at least as far upriver as Louang Phrabang in northern northern Laos (DAVIDSON ，1975). 百le smallsc a1 e croaker is one of the most desirable and highly highly priced 1釘 'ge food fishes in the Me ¥k ong region (BAIRD ， 1994; BAIRD ET AL. ， 1999). There There has been considerable confusion in the past regarding the taxonomic status of Boesemania Boesemania microlepis. CHEVEY (1 934) ，SERENE (1 951) ，BARDACH (1 959) ，KAWAMOTO ET AL. (1972) ，TAKI (1 974) ，DAVIDSON (1 975) ，YEN ET AL. (1992) ，and others have reported the the species under the names Sciaena soldado ， Nibea soldado ，Otolithoides aenecorpus ， lohnius lohnius soldado and Pseudosciaena soldado. SMITH (1 945) did not list the species as occurring occurring in 百四land. WONGRATANA (1985) finally clarified its true taxonomic identity. RA 町 BOTH (1996) listed the maximum length of B. microlepis as not exceeding 28 cm (SL) ，YEN ET AL. (1992) listed its maximum length as 355 mm ，t北 i (1974) and DAVIDSON (1975) (1975) bo 血 listed maximum length as 45 cm ，and Ko 甘'EL AT ET AL. (1993) listed it as 550 mm. WONGRATANA (1 985) got closer to the truth ，listing maximum weight as at least 6 kg ， with reports from the Menam Noi in Ayutthaya Pr ovince ，τbailand ， of individuals attaining attaining 10 kg. We have seen a number of specimens of 出is species over a me 位e in length ，and in 1993 ， the first author observed at least one that weighed 18 kg from the Mekong River at Ban Hang Kh one ，Kh ong District ，Champasak Province ， southern Laos. SASAKI (1997) also records maximum length for the species as being 1m. DAVIDSON (1975: 95) provides the following description of B. microlepis: It “It is a light brown fish ， with a greenish or grayish tint ， with obscure ripple ripple markings over the upper side of the body 叩 da light underside.τbe fins fins are pa1 e brown to yellow ， but the tail fin is blackish and the spiny dorsal fish fish has a dark edge." The smallsc a1 e croaker is named "pa kouang" in Lao ， "pla ma" 叩 d “pla hang kew" in in Thai ，“ trey promah" or “trey pama" in Khmer ，and “Ca suu" in Vietnamese (WONGRATANA ， 1985; YEN ET A L.， 1992; RA 凹 BOTH ， 1996; BAIRD ET AL. ， 1999). In In recent years ， there have been persistent reports from fishers in southern Laos and northeastern northeastern Cambodia 白紙 smallscale croaker populations have declined. In some 訂 eas where the species was apparently once common ，it is now either very rare or virtually non- existent existent (ROBERTS ， 1993; BAIRD ， 1994; ROBERTS & BAIRD ， 1995; BAIRD ET AL. ， 1999). B. microlepis microlepis is possibly very sensitive to polluted water ， like other euryhaline fishes (WONGRATANA ， 1985). For 出is reason ，WONG 貼 TANA (1 985) reported 伽 t the species is expected expected to be extirpated from many freshwater habitats in Thailand ，especially the lower courses courses of rivers. Th is expectation was based on 白e gradual disappearance of the species from the tidal influent area of the Tachin River since 1980 (WONGRATANA ， 1985). Unlike Unlike most other species of fish in the Mekong River in northeastern Cambodia and southern southern Laos ， the dry season habitat and presumed spawning grounds of the sm a1 1scale croaker croaker c叩 be easily identified. Medium to large sized B. microlepis make loud croaking voc a1 isations in these deep-water areas (BAIRD ET AL. ，1999). 百lI s deep croaking sound ， described described as “oot-oot-oo(" by the Lao ，is often audible even above the surface of the water ， and it makes the croakers vulnerable to directed gillnet fishing during their spaw 凶ng season. season. Th is species may significantly benefit 合om deep-water Fish Conservation Zones (FCZs) (FCZs) in the mainstream Mekong. In creases in populations of this species in and ぽ ound particular particular FCZs in Kh ong District ，Champasak Province ， southern Lao PDR have been reported. reported. Th ese apparent successes may be a result of villagers having protected B. microlepis 164 164 LAN G. BAIRD ET AL. d回:p -water spawning habitat within the boundaries of certain FCZs (BAIRD ， 1996; HOGAN ， 1997; 1997; BAIRD EI AL. ， 1999). 百lis paper reviews the known ecology and conservation status of smallscale croakers 初出eS 増handone We t1 and area in southem Laos. Seven d関 p-water spawning grounds in Kh ongDis 凶 ct are identified ， based on 血eoccu 町'ence of B. microlepis vocalisations d町 ing the the species' spaw 凶ng season. 百le use of villager-m 阻 aged FCZs as a tool for m 釦 aging 佃 d conse 円泊g smallscale croakers is discussed. BACKGROUND TO STUDY AREA 百 e Siphandone We t1 and 紅 ea (which literally means 4000 islands) is 1紅 gely siωated in in Kh ong Dis 住ict ，Champasak Province. It is a complex of channels ，rapids ，waterfalls ， islands islands of various sizes ，seasonally inundated forests ， and deep-water pools included as p釘 t of the mainstream Mekong River in 出e ex 佐eme south of Laos (see figure 1 map of Kh ong 泊 regional setting) (CLARIDGE ， 1996; CES 羽， 1998; ALTOBELLIEI AL. ，1998). 官 lere are are approximately 65 ，000 people 泊Kh ong ， the v出 tmajority of whom are ethnic lowland Lao rural peasant semi-subsistence paddy rice farmers with a long history of inhabitation of of the 紅白. Approximately 94 percent of families in 由.e dis 凶 ct subsist on fishing and many sell fish to generate income. 百le estimated total fish catch for the dis 凶.ct in 1996/ 1997 1997 w 部 4000 metric tonnes ， and US$ 1，000 ，000 worth of fish was reportedly exported from the district during the same year (BAIRD ET AL. ，1998a). 百le wild capture fisheries of of Kh ong may be more important 出m 泊飢y other dis 凶ct in Laos. Of 白e 136 villages 泊Kh ong ，86 are situated on islands ， and most of the rest are located along the e槌 tembank of of the Mekong River (BAIRD EI AL. ， 1998a). Th e aquatic environment of the area is characterised characterised by high diversity and productivity.