Ecology, fish biology and fisheries in the lower Songkhram river basin

Results show that the duration of the flood period of the lower Songkhram River Basin was 3-4 months, from June to September. One hundred and forty-nine fish species representing 33 families were found, with an average standing crop of 90.8 +- 60.1 kg/ha. Catch per unit of effort of stationary trawl nets was 34.7 +- 34.2 kg/net/day. The average Shannon-Weiner diversity index was 4.696 at the time of the flood recession and 3.665 at other times of the year. Piscivorous and insectivorous fishes, Micronema spp. (12.64 percent), Paralaubuca spp. (7.27 percent), Cyclochelichthys repasson (5.94 percent), Hampala macrolepidota (5.34 percent), Hemibagrus nemurus (4.23 percent), Toxotes microlepis (3.46 percent), Kryptopterus spp. (3.40 percent), Pteropangasius pleurotaenia (3.36 percent), Morulius chrysophekadion (3.24 percent) and Ompok bimaculatus (3.13 percent) dominated in terms of biomass in the mainstream area. Fish community structure of main stream differed significantly between samples taken during day and night which were higher than the difference between sampling stations. Also fish community structure of tributaries differed significantly between different sampling stations which higher than that different between day and night samplings. The total catch of the main fishing gears was estimated to be 1,400 tons/year. This comprises of 149.1 tons caught in stationary trawl nets, 245.3 tons caught by beach seine net, 181.4 tons caught in bamboo traps, 278.8 tons caught by raft mounted lift net, 24.0 tons caught by V-shaped scoop net, and 522.5 tons caught in the barrage fisheries. The one hundred thirty-six stationary trawl net fisheries were operated primarily between September 19 and October 23, 2001 during the receding flood, corresponding to the period of maximum river velocity along the mainstream. The sixty-four barrage fisheries were active from October 2001 to January 2002, and fifty-six beach seine nets were used over a period of 5-7 months from November 2001 until June 2002.