The Bagnet (Dai) Fishery in the Tonle Sap River by Deap Loeung Senior Researcher of the Project for Management of the Freshwater Capture Fisheries of Cambodia 1. Introduction Bagnet fisheries or Dai fisheries were introduced to Cambodia in the years 1873-89 by Vietnamese fishermen working for Chinese merchants. In the Vietnamese language a bag is called a "Dai". The use of these gears was encouraged by the French colonial authorities because the large catch of small fish, especially Trey Riel/Linh, was used to produce fish oil to replace engine oil during World War I. Fish oil production was considered a high priority. The French authorities only allowed people to use surplus production for food after they had fulfilled their military needs (Tana, 1998). Nowadays, fish oil production is very small and most of the fish is used for human food. Bagnet fisheries contribute a significant portion to the total catch of the freshwater fisheries in Cambodia. They are located in the lower part of the Tonle Sap River, 4-30 km north of Phnom Penh and are considered to be large-scale inland water fisheries (Map). The fisheries exploit largely the current years' crop of small fish species migrating out of flooded areas around the Great Lake and Tonle Sap River to the Mekong River. The migration is strongly influenced by the lunar phase (Lieng et al., 1995). According to the official 1995 fisheries statistics of the Department of Fisheries (DoF), the bagnet fisheries has in recent years contributed 10-20 % to the total annual inland fish production of 65,000-75,000 tons. However, such fisheries data in general are limited and unreliable, and a new approach was required on a country-wide scale. To facilitate the design of a new data collection scheme, preliminary low frequency data collection has been carried out. The bagnet fisheries were sampled from December 1994 up to the present using the new sampling design. Dai fisheries developed, but their number was regulated by the government through a system of auctioning a limited number of fishing locations. In 1938-39 the number of dais was 106 units. But from then on it gradually decreased to 86 in 1983, 73 in 1994-95 and to 63 in 1995-96 (Lieng et al., 1995). 2. Bagnet or Dai Gear and Operation Bagnet fisheries are allowed to set up operations in the middle of September and start in early October. They continue fishing until March when the current of the Tonle Sap River has become very slow. Dai units are operated singly, but are joined with three to eight others in rows across the river, which sometimes form large barrages that leave just enough space for navigation. Two bamboo rafts about 25 m apart are linked together by bamboo poles and held stationary by anchors in the river. A sampan is placed between them, ensuring stability to the whole structure. A cone-shaped net is placed in the water between the two rafts by ropes. Its mouth diameter is 25 m and the net is 120 m long. Mesh size is 15 cm at the entrance and 1 cm at the bag. When catches are low, an open-weave basket made of bamboo and rattan is attached to the last part of the bag, which can be winched onto the wooden platform where the catch is deposited for sorting (Fig. 41). The Dai is kept open by the force of the water current with the help of anchors and two vertical bamboo poles fixed to the rafts. Fish moving down-stream with the receding floodwater enter the net. When fish migration is at its peak, the bag is emptied every 20-25 minutes day and night, and may hold up to 500 kg of fish per lift. But on days when few fish are migrating, the frequency of lifting is much less. Migration usually peaks in December and January, especially in a time-window from 6-1 days before the full moon, when the river seems to be packed solid with fish. 135 3. Auction System and Fish Handling Practices Under the Cambodian fisheries law (#33 Kror Chor, dated 9th March, 1987), a bagnet or dai unit is classified as a fishing lot. Fishing lots are concessions auctioned by the government to the highest bidder for exclusive exploitation over a two year period. It is one of the government's instruments for extracting a resource rent from fisheries. The auction is overseen by a committee consisting of the director of the central fishery department, the governor of the province and the provincial finance director. Dai ownership is divided among ethnic lines as follows: 46% Khmer, 50% Cham (Muslim) and 4% Vietnamese (Lieng et al.,1995). Usually, fresh fish are sold on the dai unit to middle persons who take them mainly to the riverbank for resale to fish processors, but also to the Phnom Penh city markets. More valuable fish such as Trey Krom, Po, Chhkok, Chhpin and Pra are often kept alive in the cages below the working platform of the dai. Fresh fish consumption is important among people living close to fish production areas and the markets, but in rural areas far from natural water bodies or markets, processed fish is more important. At peak periods, when catches are very large, most fish is processed into fish paste (Prahoc), fermented fish (Phaok), sweet fish (Mum), smoked fish and fish sauce. Surplus fish is dried for pig feed or fertilizer. Species used for processing are the small fish species like Trey Riel, Linh, Sloek Russey, Kros, Kaek, Khnang Veng and Kanh Chruk (Fig. 45 and 46). 4. Sampling Method 4.1 Stratification by yield level The dais units in Phnom Penh and Kandal (68 dais in 15 rows) are divided into two groups: the high yielding ones and the low yielding ones. This stratification is based on the census that was done by the fisheries department in the 1996-97 season. 4.2 Stratification in time Catches vary strongly with lunar periodicity. There is a peak period of 4-6 days before full moon and a low period during the rest of the month. In the peak period sampling intensity needs to be high. Dais to be sampled are chosen at random. Figure 39: Dai stratification scheme for sampling purposes Total Dais (68) 8 high yielding dais 60 low yielding dais Peak Period Peak Period 8 dais are sampled 14 dais are sampled 10 Hauls/dai = 80 10 Hauls/dai = 140 Low Period Low Period 8 dais are sampled 7 dais are sampled 10 Hauls/dai = 80 10 Hauls/dai = 70 136 4.3 Catch and effort estimation To estimate the effort of a dai unit we measure the time it takes to carry out at least 10 lifts and record the total catch per haul. In the peak period the number of lifts per 24 h is counted. Differences in day and night catches per lift are important. Night catches are higher. However, the number of lifts at night is less than during the day, and thus should be accurately assessed on sampling days, as variation in effort has a greater impact in the catch estimation process than the variation in the catch itself. Table 34: Effort Information form Type of Dai: Time of observation from .............................. to ................................... Observed number of lifts per dai unit .................................... Catch per lift Catch per lift No Time No Time (Kg) (Kg) 1 6 2 7 3 8 4 9 5 10 Through the above table we can calculate the number of lifts per day and the average quantity of fish caught per lift. 4.4 Species composition Samples to determine the species composition of catch are taken from 3-4 hauls at the time we record the catch and effort of catch. A sub-sample of fish is sorted by species, weighed and counted before it is recorded on the forms. 5. Results and Conclusions ARTFISH, computer software designed by FAO ( Stamatopoulos 1995), is used to estimate the effort and the catch by species of the dais both in Kandal and Phnom Penh. The overall catch estimated since the 95/96 fishing seasons is shown in the table below: Table 35: Dai catch in tons Season No of Month Total Year dais Oct. Nov. Dec. Jan. Feb. Mar. 1995-96 63 128 386 5,379 6,979 1,569 14,429 1996-97 68 8 71 363 10,104 1,581 3,361 15,488 1997-98 68 92 989 11,043 1,602 945 14,671 1998-99 68 12 19 4942 3,803 119 8,894 137 Figure 40: Average October water levels (m) in Kompong Chhnang town in 1994-98 and the estimated catch of the Dai fisheries in the Tonle Sap river in the period from October-March, 1995-99 16 16 15 15 14 14 tons in thousand catch Dai Dai catch 13 13 12 12 11 11 10 10 Water level 9 9 Average October water level in meters 8 8 7 7 1994-95 1995-96 1996-97 1997-98 1998-99 Year The figure shows that the catch has declined strongly when the water level declined strongly, as measured against annual flood levels in Kompong Chhnang province. So it means that when less land is inundated there is less food for fish and less fish production. The Dai fisheries aim at capturing migratory fish species. Long-term monitoring of water level, flood forest habitat, species composition, fish sizes and the overall catch will reveal trends and reflect what is happening with the populations.