NAT. NAT. HIST. BULL. SIAM Soc. 51 (1): 5-36 ，2003 RHYTHMS OF THE RIVER: LUNAR PHASES AND MIGRATIONS OF SMALL CARPS (CYPRINIDAE) IN THE MEKONG RIVER Ian ιBa かI1 'd 1ヘMark S. Flahe 同'1， and Bounpheng Phylavanh 1 ABSTRA Cf τ'hro ughout history ，many differ 耳目 tcultures have associa 胞d lunar cycles with changes in variety a variety of human and animal behaviors. In the southem-most part of La os ，血血 .e area known 鼠“Siphandone" or 血.e 4，0∞islands ，rur 百 1 fishers living on islands 泊 the middle of the mains 悦 am Mekong River are especially conscious of the influence of lunar cycles on aquatic life. life. They associate upriver migrations of large quantities of small cyprinid fishes from Cambodia Cambodia to La os at the beginning of each year with lunar ph 舗 es. 百 is article examines the fishery fishery for small cyprinids in 血e Kh one Falls area ，Kh ong District ， Champasak Pr ovince ， southem southem La o PDR ，飢da five-year time series of catch -e ffort fisheries da 旬 for a single fence- fJl ter 釘ap are presented. 百lese da 筒 are then compared with catch da 組合om the bag-net fishery fishery in the Tonle Sap River 泊 C 釘 nbodia. It is shown 白紙 the migrations of small cyprinids ， particul 釘'i y Henicorhynchus lobatus and Paralaubuca 砂'P us ，眠 highly correlated with new moon periods at 血e Kh one Falls. Many small cyprinids migrate hundr 哲也 of km up the Mekong River River to Kh one Falls 台。 m 血eTo 叫巴 Sap River and probably 血.e Great Lak e in Cam bodia. Th e evolutionary evolutionary conditions 白紙 have led to the behavior of these fish are discussed ， and manage- ment ment implications are conside 陀 d. Key words: Cambodia ，La os ，Mekong River ，副 isanal cap 加 re fisheries ，Cyprinidae ， lunar cycles ，migrations 別 TRODUCTION As the moon follows its natural phases ， orbiting the e紅白 once per mon 出， our view of it dramatically changes. It begins as a new moon ，hidden from E 紅白's view ，and over 血e course of 29.5 days becomes fully visible and brigh t. Thr oughout history ，many di 丘'erent cultures cultures have associated the cyclic lunar transformations wi 白 predictable changes in a variety variety of human and animal behaviors. 百 e scientific evidence for the existence of these relationships relationships is mixed. In vestigations 加to the behavioral e釘ects of lunar phases on fish 釘 e often often inconclusive (e.g. ，ROBERTSON EJ AL. ，1990; ROOKER & DENNIS ， 1991). Ne 河川leless ， 抑 ong associations between lunar ph 酪 es and some behaviours of p制 icul 紅 fish and crustacean species have been documented; In particul 紅， spawning cycles (e.g. ，CRABτ 'RE E ， 1995;JERL 町 GANDW ∞LDRIDGE ，1992; JOHANNES ， 1981). Fishers around the world have long believed that 血e most successful fishing times are associated with particul 紅 looar Ip.O. Ip.O. Box 860 ，Pakse ，La o PDR ，[email protected] 2Ge ography De partment ，University of Victoria ，Victoria ，B.C ・， Canada Received Received 30 May 2002; ぉ cepted 8 November 2002. 5 6 IAN G. BAIRO ，MARK S. FLAHERTY ANO BOUNPHENG PHYLAVANH periods. periods. Wh ile this body of knowledge based on personal experiences m ak: es up fishing folklore ，scientific evidence also supports the association between fish catch and lunar cycle cycle (e.g. ，0 叩 BUS 町， 1990). In In the Lao People's Democratic Republic (L ao PDR or Laos) rural ethnic Lao people still still predominantly use a lunar calendar. Th ey are well aw 紅 'e of how lunar cycles affect natural natural and human processes. In th 巴 southem-most part of Laos ， in an area known as “Siphandone" ，or 出e4 ，000 islands ，rural fishers living on islands in the middle of the mainstream mainstream Mekong River are especially conscious of the lunar cycles influence have on aquatic aquatic life. They associate upriver migrations of large quantities of small cyprinid fishes from Cambodia to Laos at the beginning of each year with lunar phases (BAIRD ， 1998; SINGHANOUVONG ET AL. ， 1996; ROBERTS & BAIRD ， 1995; ROBERTS & WARREN ， 1994; ROBERTS ， 1993). Highly Highly migratory populations of small cyprinids are extremely important to 血e people of of the lower Mekong River basin in several ways (BAIRD ET AL. ， 1998; ROBERTS ， 1997; JENSEN ， 1996; ROBERTS & BAIRD ， 1995; LIENG ET AL. ， 1995; ROBERTS ， 1993; BARDACH ， 1959). 1959). Ecologically ， they are important primary consumers of phytoplankton in the mainstream mainstream Mekong River during the dry season (SINGHANOUVONG ET AL. ， 1996; ROBERTS & BAIRD ， 1995; ROBERTS & WARREN ， 1994). Th ey produce the 1釘 gest proportion of animal animal protein consumed by people in the lower Mekong River basin (BAIRD ET AL. ， 1998; ROBERTS ， 1997; LIENG ET AL. ， 1995). Socially and culωrally ， they support ways of life based based around the m 叩 y artisanal fisheries 血at tぽ get them over their long joumey. In In Cambodia ， the bulk of the bag-net fishery (，ぬ i in Kh mer) catch in the Tonle Sap River ，one of the largest inland commercial fisheries in the world ，is dominated by small cyprinids. cyprinids. Th e most import 加 t are the labeoin cyprinids Henicorhynchus lobatus 佃 d， to a lesser lesser extent ， Henicorhynchus siamensis (LIENG ET AL. ， 1995). Th ese species and many others ， migrate out of the Great L ak: e and other seasonally inundated areas in central Cambodia at the end of the monsoon rainy season between November and March of each year ，and move into and up the Mekong River via the Tonle Sap River (VAN ZAL 町 GEET L.， AL.， 1999; BAIRD ， 1998; DIEP ET AL.， 1998; ROBERTS ， 1997; LIENG ET AL. ， 1995). ROBERTS & BAIRD (1 995) note that H. lobatus (referred to by them as Cirrhinus lobatus) is an ecologically ecologically significant species in the lower Mekong River in southem Laos due to its large large biomass ，and it may be the single most important species in the Mekong River below 出e Kh one Falls (ROBERTS ， 1997). Important Important fisheries artisanal in the Kh one Falls area 紅 e also based on migrations of Henicorhynchus spp. ，Paralaubuca typus ，Labiobarbus leptocheilus ， Lobocheilus melanotaenia ， Botia modesta and a number of other species (BAIRD ， 1998; ROBERTS & BAIRD ， 1995; ROBERTS & WARREN ， 1994; ROBERTS ， 1993). Th ese fish migrations 訂 e similarly similarly significant for fishers living in other parts of Siphandone above the Kh one Falls. BAIRD ET AL. (1998) found that approximately 40 percent of the families in Kh ong District ， Champas ak: Pr ovince (Siphandone 紅 ea) reported 血at Henicorhynchus spp. were 白e most abundant abundant fish species caugh t. Despite the small size of individual fish ， the to ta1 catch su 甲assed all other groups in terms of weight. BAIRD (1 998) proposed that the small cyprinid fence-filter trap (tone in Lao) fishery at at the Kh one Falls targets largely the s創 ne populations of fish that 訂 e caught in 血e bag-net bag-net fishery in central Cambodia. Moreover ，it is believed 出at some of these small cyprinids cyprinids migrate past 出e Khone Falls to the border between Laos and 百四land ，組d RHYTHMS OF THE RIVER: LUNAR PHASES AND MIGRA TIONS 7 possibly possibly as far upriver as Vientiane or beyond. The migration of important fish stocks 100s or or possibly over 1，000 km between three countries ，highlights the need for the nations in the the Mekong basin to cooperate in improving their understanding of the biology and socio- economic significance of Henicorhynchus lobatus and other migratory small cypri 凶 d fishes. Joint Joint research and management efforts are warranted to ensure the long-term sustainability of of the fisheries based on such species. Th is paper examines the fishery for small cyprinids in the Khone Falls area ，Khong District ，Champasak Province ，southem Lao PDR. The nature of the fishery is reviewed and a time series of catch-effort fisheries data for a single fence-filter trap are presented. These data are then compared with catch data from the bag-net fishery in the Tonle Sap River River in Cambodia. STUDY AREA Th e Mekong River basin supports one of the most diverse fish faunas in the world ， and probably the most fish species for a single river basin in Asia. Approximately 1，200 species species of fish occur in the Mekong basin ，including brackish water areas ， although many have not yet been taxonomically described (VAN ZALINGE ET AL. ， 2000; RAINBOTH ， 1996). As of 2000 ，201 fish species in 109 genera and 39 families had been identified from the Mekong River and adjacent tributaries below the Khone Falls 泊Kh ong District (BAIRD ， 200 1). Many species seasonally migrate long distances up the Mekong River from as f;釘 away as the Great Lake in Cambodia and the South China Sea in Vietnam (BAIRD ET AL. ， 1999; 1999; BA ，IRD ， 1998; VAN ZALINGE ET AL. ， 2000; LIENG ET AL. ， 1995; ROBERTS & BAIRD ， 1995). 1995). Other species are relatively sedentary (BAIRD ET A L.， 2001b; BAIRD ET AL. ， 1999). The Siphandone Wetland 訂 ea is a complex ecosystem found in the mainstream of the Mekong River in the extreme south of Laos. is It made up of large and small inhabited and uninhabited uninhabited islands ，channels ，seasonally inundated forests ， deep-water pools ， rapids and waterfalls waterfalls (DACONTO ， 2001; ALTOBELLI ET A L.， 1998; CLARIDGE ， 1996). Th e Siphandone Wetland area is largely situated in Khong District ，which is in the southem-most part of Champasak Pr ovince (Fig.