Threatened Fish Biodiversity of Kaptai Lake in Bangladesh

January 24, 2020

M. Gulam Hussain
Photos by M. Gulam Hussain

The Kaptai Lake, the largest man-made freshwater reservoir in Bangladesh, as well as in the Southeast Asia region, has a total surface area of 68,800 hectares. In 1961, the lake was created by damming the river Karnafuli at the neck of Kaptai town at the district of Rangamati in the Chittagong Hill tracts primarily for hydroelectric power generation (see Figure 1). The commercial exploitation of fisheries resources from the reservoir was initiated in 1965. At the start of the exploitation, fish production of the lake was dominated by indigenous major carp species. The available statistical data conspicuously showed that the production supported by the major carp species was greatly declined due to a high abundance of another two small indigenous species as briefly explained below.                                    

Figure 1. Map of Kaptai Lake, Rangamati, Bangladesh (Source: Blangapedia, 2014)
Figure 1. Map of Kaptai Lake, Rangamati, Bangladesh (Source: Blangapedia, 2014)

From the beginning, Kaptai Lake was a unique freshwater ecosystem and rich in fish biodiversity. Ahmed (1999) reported a total of 73 fish species belonging to 47 genera and 25 families in the lake. Indigenous carp species, including rohu (Labeo rohita), catla (Catla catla), mrigal (Cirrhinus mrigala), and Klabasu (Labeo calbasu), along with some other large fish were the predominant species and contributed to over 81% of total landings during 1965-1966 (Bangladesh Fisheries Development Corporation (BFDC)’s landing records) in Kaptai Lake. Subsequently, the carps and other commercial species production have been sharply decreased over time due to the dramatic increase of two clupeid species (i.e., Chapila (Gudusia chapra) and Keski (Corica soborna)), which is a setback for overall Kaptai Lake fish biodiversity and production. Some studies revealed that in recent years the production of Chapila (see Figure 2) and Keski (see Figure 3) respectively are >30% and >31% of total fish production (>10,000 metric tons) in Kaptai Lake. Since impoundment, the reservoir has undergone major changes in its catch composition. BFDC’s production records also show a declining trend in the productivity of high-value fish (Ahmed et al., 2006).       

Figure 2. A handful Chapila (G. chapra) at Kaptai Lake
    Figure 2. A handful Chapila (G. chapra) at Kaptai Lake

         

Figure 3. A handful Keski (C. soborna) at Kaptai Lake
    Figure 3. A handful Keski (C. soborna) at Kaptai Lake

A November 2019 survey based on Kaptai Lake fisheries resources and a fish biodiversity study supported by the Bangladesh government disclosed that a total of 49 fish species, including three endemic (i.e., rohu, catla, and Mrigal) and two exotic (common Crap and Nile tilapia), are presently available as per discussion and interviews with a number of stakeholders and visiting BFDC’s Fish Lending Centers in Kaptai and Rangamati.

Among those listed, 10 species are commonly available, 14 species are moderately available, 21 species are less available, and nine species rarely available. Both less available and rarely available species can be categorized as vulnerable species and on the way to being endangered within a few years of time. On the other hand, a total of four fish species are not available at all during this season in the harvest. Among this list, at least one or two species (i.e., Golen Mahseer, Tor tor, Figure 4 and Nandina, Labeo nandina) are already extinct, and other species are either endangered or critically endangered.     

Figure 4. Golden Mahseer, Tor tor, population has already been extinct or critically endangered in Kaptai lake and adjacent Karnafuli river basin
Figure 4. Golden Mahseer, Tor tor, population has already been extinct or critically endangered in Kaptai lake and adjacent Karnafuli river basin

Currently, researchers have critically identified the potential major causes of rapidly declining fish biodiversity in Kaptai Lake: i) natural habitat and fish breeding ground degradation because of gradual deterioration of aquatic ecosystem, ii) reduction of optimum depth of the wetland, iii) increased turbidity of water, iv) heavy siltation and erosion on reservoir basin; v) heavy fishing pressure by using illegal and banned fishing crafts and gears, vi) disrespecting the fishing ban period by local fishers, vii) excessive growth of undesirable clupeid and other species. One of the suggested remedies is to conserve these threatened fish biodiversity through adopting a comprehensive reservoir-management plan (Dr. Khan Kamal Uddin Ahmed, personal communication).    

The fish biodiversity of the largest man-made reservoir in Bangladesh, Kaptai Lake, has been threatened due to dramatic increase of undesirable clupeid and other small fish species. As a result, indigenous major carp and other commercial fish species have been greatly declined. In addition, a recent survey on Kaptai Lake fisheries resources and fish biodiversity revealed and critically identified the potential causes of alarmingly declining fish biodiversity of the lake ecosystem. Adoption of comprehensive reservoir management plan will be the suggested remedy for the situation. 

References

Ahmed, K. K. U., Rahman, S., & Ahammed, S. U. (2006). Managing fisheries resources in Kaptai reservoir, Bangladesh; Outlook on Agriculture, 35(4), 281–289.

Ahmed, K. K. (1999). Options for the management of major carp fishery in the Kaptai Reservoir, Bangladesh (Unplublished doctoral dissertation). School of Environment, Resources and Development, Asian Institute of Technology, Bangkok.

Banglapedia (2014). Kaptai Lake. National Encyclopedia of Bangladesh. 4 p.

M. Gulam Hussain is the Bangladesh Country Coordinator at the Feed the Innovation Lab for Fish and the former Director General at BFRI.