Title: Trends in fish production and catch composition in Kaptai Lake, Bangladesh
Author: Sarker Mohammed Rafiqul Alam
Supervising Institution: IHE Delft - Institute for Water Education
Kaptai Lake is a manmade lake harbours many indigenous fish to breed. Since the inception of Karnafuli Hydroelectric Power Plant, catch of Indian Major Carp (IMC) was falling down. The concern of the authority is that the prescription of fingerling stocking programme is not working. Some believe that mass mortality of released young fish yielded no impact on the recruitment of IMC. There is a voice against the gear-use who believe that indiscriminate use of fishing gear causing the depletion of IMC population. So, it is a high time to find out the loopholes in the management procedures. In my study, I tried to explore the effect of gear on IMC stock. To do this I calculated catch per unit effort of different gear as well as catch composition of different fish-groups including IMC were identified. Field level study was done in the four fishing sites of Kaptai Lake in December 2018, catch per haul was measured, fishers were asked about the number of hauls and species-wise sorting and measurement were done on board, except for the catch of small-meshed seine net. Sample was taken from the small-meshed seine net and measured at home. The whole-catches of all other gears were measured except for the catch of small-meshed seine net. Then catch composition and CPUE of gears regarding gear selectivity, were calculated and compared with previous study. Catch composition of a gear was expressed as the percentage of shares contributed by each group of fishes to the total catch of that gear. A value of P < 0.05 was accepted as at the level of significance. CPUEs of different gears were found, from 1.65 ± 1.88 kg unit-1day-1 to 41.95 ± 20.69 kg unit-1day-1. In 1997 CPUE of small-meshed seine net was observed 20.6 kg unit-1day-1 but in 2018 it was found 41.95 kg unit-1day-1. In small-meshed gillnet CPUE was calculated as 5.83 kg unit-1day-1 which was not calculated in 1997. CPUE of large-meshed gillnet found higher than that of gillnet in 1997. Overall CPUE was found higher than that of in 1997. The catch of the most of the gears were dominated by catfish and clupeids. IMC dominated catch was found in case of large-meshed seine net and cluster hooks, the rare used gear in December. Some gears were altered to catch catfish and clupeids, and no gear was modified to catch IMC. It might be due to the scarcity of IMC. Analysis on the fishing license reflects the dominance of gillnet in the Lake. Two of the most commercial gears, gillnet and small-meshed seine net were almost devoid of IMC. We did find only two individuals of IMC L. rohita and C. cirrhosus during our survey period. Catch composition showed the strong presence of a catfish, S. aor and an IMC, L. calbasu, other than the clupeids in the catch of all types of fishes. It might be due to the inherent quality of these two species to breed in the Lake’s environment. It has been decided that the gear selectivity is not responsible for carp production loss. Rather huge mortality of the fingerling and losing of breeding ground might be the potential cause of carp population depletion. However, more intensive study needs to be done before accepting a decision. Post stock intensive monitoring is essential. Potential breeding ground of IMC should be identified and protected for the brood of IMC, which will boost up the IMC stock.