Stock assessment and ﬁshery management of Henicorhynchus spp., Cyclocheilichthys enoplos and Channa micropeltes in Tonle Sap Great Lake, Cambodia Nguyen T. Hai Yen a, ⁎, Kengo Sunada a , Satoru Oishi a , Kou Ikejima b,1 , Tomaya Iwata a a Department of Civil and Environmental Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi, Japan b Japan Society for the Promotion of Science (JSPS),159 Sukumvit Soi 21, Bangkok 10110, Thailand abstract article info Article history: Received 20 December 2007 Accepted 26 November 2008 Communicated by Tim Johnson Index words: Tonle Sap Great Lake Fishing effort Catch-per-unit-effort Schaefer model Henicorhynchus spp. Cyclocheilichthys enoplos Channa microplestes Tonle Sap Great Lake, in the lower Mekong River basin, contributes 60% of Cambodia's inland ﬁsheries catch. There are four types of ﬁsheries, including the middle-scale ﬁshery. The major species comprising the middle-scale ﬁshery are Henicorhynchus spp. (16%), a small-bodied ﬁsh caught mainly with small-mesh nets, and Cyclocheilichthys enoplos (13%), and Channa micropeltes (7%) which are caught with a variety of gear. Here we apply the Schaefer surplus production model to the middle-scale ﬁsheries using monitoring data collected between 1995 and 1999. Model simulations determined that the maximum sustainable yield (F MSY ) for Henicorhynchus spp., was obtained with the use of 47,206 gillnets (mesh size b 50 mm) and 4269 and 1605 ﬁshing boats for C. enoplos and C. microplestes, respectively. Over 1995–1999, there was a strong trend of increase in ﬁshing effort and decrease of catch-per-unit-effort in the waters of Pursat, Siem Riep and Kampong Chnnang provinces. These provinces have large population centres located close to the ﬁshing grounds; ﬁshing in these areas should be more strictly regulated. © 2009 Published by Elsevier Inc. Introduction Tonle Sap (TS) Great Lake of Cambodia is situated in the lower part of the Mekong River Basin (MRB) (Fig. 1). The lake has a catchment area of 81,456 km 2 (Hak and Piseth 1999, MRC 2003); during the wet season (June to October) the lake has a surface area of over 10,000 km 2 while in the dry season the lake recedes to 2500 km 2 (Hak and Piseth 1999, MRC 2003). The TS ecosystem comprises the largest wetland in Southeast Asia. Biodiversity is high with at least 179 ﬁsh species caught between 1995 and 2002 (Campbell et al. 2006). It also supports the fourth most productive capture ﬁshery in the world (Rainboth 1996) with the total annual catch estimated to range between 177,000 and 400,000 tonnes (IFReDI 2001, Sverdrup-Jensen 2002, Van Zalinge et al. 2003). TS contributes approximately 60% of the total inland catch of Cambodia (Ahmed et al. 1998), contributes 16% to Cambodia's GDP and is the source of 60 to 80% of Cambodian's consumable animal protein (Ahmed et al. 1998, Baird et al. 2003). There is strong evidence that ﬁshing pressures are adversely affecting TS ﬁsh communities. Fish catches increased from 125,000 tonnes in the 1940s to 235,000 tonnes in 1995–1996 (IFReDI 2001) while the individual ﬁsh catch declined from 347 kg/ﬁsherman in the 1940s to 196 kg/ﬁsherman in 1995–1996. At the same time, the contribution of large ﬁsh species to total catch decreased (Van Zalinge et al. 2001) as did the average size of smaller ﬁsh in the catch (Hortle et al. 2004). Water level in TS Lake is highly variable, ranging from 1 m deep in the dry season (November to May) to 14 m deep in the wet season (June to October). This change in depth is strongly inﬂuenced by seasonal water outﬂow and inﬂow from the Mekong River throughout the 100 km long TS River (Hak and Piseth 1999, MRC 2003). In recent years, river and ﬂoodplain ﬁsh habitats have been lost, modiﬁed or fragmented because of changes in hydrological regimes caused by demands of water resource uses (MRC 2003). Changes in catchment land use, increases in agro-chemical usage for agriculture, and increases in urban and industrial waste are believed to be adversely affecting ﬁsh quality and quantity (MRC and UNEP 1997). Annual bag net (Dai) ﬁsh catch and maximum water level in the TS Lake have been shown to be positively correlated with one another (Lieng et al. 1995; Van Zalinge et al. 2003). Other studies have explored the relationship between bag net ﬁsh catch, hydroecology, and water quality (Nguyen et al. 2007, 2008). Exploitation however, may be a more important threat to freshwater ﬁsh, including those inhabiting ﬂood plains such as TS Lake (Welcomme 1979). On average, freshwater species worldwide are more imperiled than marine species because of adverse anthropogenic impacts on river and lake water- sheds, in addition to ﬁshing pressures (Arthington et al. 2003). Fisheries in the TS ecosystem are complex and consist of limited access ﬁsheries consisting of large-scale ﬁshing, and open access Journal of Great Lakes Research 35 (2009) 169–174 ⁎ Corresponding author. Tel.: +81 55 220 8522. E-mail addresses: trhyen2001@yahoo.com (N.T.H. Yen), sunada@yamanashi.ac.jp (K. Sunada), tetsu@yamanashi.ac.jp (S. Oishi), kou.ikejima@gmail.com (K. Ikejima), tiwata@yamanashi.ac.jp (T. Iwata). 1 Tel.: +66 2 661 6453. 0380-1330/$ – see front matter © 2009 Published by Elsevier Inc. doi:10.1016/j.jglr.2008.11.014 Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr