Reservoir Fisheries of Asia

The gross efficiency of the fisheries production (i.e. actual catch/ primary
production) in Ubolratana reservoir was about 0.003 (Chookajorn et al., 1994)
and was about 0.005 in Sirindhorn (Jutagate et al., 2002). These figures imply
the underutilised food resources in the system at Ubolratana Reservoir and
fully utilised food resources resulting high biological productivity in Sirindhorn
Reservoir. The fish biomass in Ubolratana reservoir was less than 10 t km -2
but was over 25 t km -2 as in Sirindhorn Reservoir (Thappanand et al., 2008).
Sidthimunka et al. (1978) reported that the biomass of benthic animals including
annelids, crustaceans, mollusks and insects in Thai reservoirs, can fluctuate
between 6 and 16 t km -2 .
Fisheries
The majority of fishers in the Thai reservoirs are subsistence fishers. They use
different gears based on season, water level and fishing ground. The fish landings
are mostly of indigenous species, which form over 80 percent of the production
(Figure 3 and Box 1). In general, most fishers use gillnets, longlines, cast nets,
scoop nets and big lift nets. Gill net mesh sizes range from 2.5 to 18 cm, and
4.5 to 7.0 cm are the most popular. The larger mesh gillnets are used during
the rainy season. For the longlines, the hook sizes range from 2.7 (hook No. 23)
to 22.7 mm (Hook No. 4) (Jutagate and Mattson, 2003). There are two types
of lift nets; fixed lift-nets and movable lift-nets. These are used for catching
small clupeids. The net dimension of lift net is of 8x8 m 2 and mesh size is 2.5 cm
(Sihapitukgiat et al., 2002).
Except for the lift net fisheries for the small clupeid C. aesarnensis in
Northeastern region reservoirs (Sirimongkolthaworn 1992; Jutagate et al.,
2003a), the fishing is often not targeted. The reservoir fishers take all species
regardless of size variation (Bhukaswan and Chookajorn, 1988). The average
fish yield in Thai reservoirs is about 48 kg ha -1 yr -1 (Bhukaswan and Chookajorn,
1988; Moreau and De Silva, 1991). The empirical model between catch per unit
effort and fishing effort in Thai reservoirs showed that the estimated maximum
sustained yield and optimum fishing effort were 93 kg ha -1 yr -1 and 10 fishers
km -2 , respectively (De Silva et al., 1991).
Stock enhancement programmes
Stock enhancement in Thai reservoirs has been carried out since the early 1950s
(Pawaputanon, 1992). During 1960s to 1980s, introduction of Chinese and Indian
carps was widely practiced in the inland water bodies countrywide. In Thailand,
stocking programs are not only carried out in reservoirs but also in rice-fields,
rivers and swamps. Stocking is generally considered as a means of providing
benefits to poor communities (Coates, 2002). The popular species stocked are
grass carp Ctenopharyngodon idella, mud carp Cirrhinus molitorella, silver
carp Hypophthalmichthys molitrix, common carp Cyprinus carpio, bighead
carp Aristichthys nobilis (Pholprasit and Waiwuttho, 1970; Benchakarn, 1972;
Duangswasdi and Janesirisak, 1973), mrigal Cirrhinus mrigala and rohu Labeo
104 | Reservoir Fisheries in Thailand