Fish population goes down in Saptakoshi

By Baburam Karki,Baraha Kshetra, Mar. 27: Fish population in the Saptakoshi River and its tributaries have declined over the past few years, researchers said.

Ichthyologists have identified habitat degradation, embankments and river pollution as key factors contributing to the decrease in fish species in the Saptakoshi River, which hosts 50 per cent of the country's total fish population.

The initial findings of the study showed that the fish population have declined this year as compared to the previous years. Factors such as crusher industries near rivers, increased fishing activities and harmful practices like electric shocks and poison use have contributed to the shrinking fish population.

Alok Paudel, an ichthyologist, attributed the decline in the fish population to habitat degradation, which has naturally impacted fish populations in the Koshi and other rivers.

Concerned by the declining bird population in recent years, Bird Conservation Nepal has initiated a fish count in the Saptakoshi River to assess the condition of fish -- a primary food source for many bird species.

According to Khadananda Paudel, president of Bird Conservation Nepal, the number of water birds has been decreasing annually, prompting the fish count to better understand their food supply. Although the study is ongoing, early observations suggested a sharp reduction in fish compared to previous years.

Paudel said that fish numbers are also declining in the tributaries of the Koshi River, including the Dudhkoshi, Sunkoshi, Melamchi, Indrawati and Bhotekoshi rivers. Hydropower projects constructed in river areas have also disrupted fish habitats, further contributing to their decline.

The construction of dams has disturbed their movement along the river side, which affects their life cycle. “The fish species like Sahar fish face extinction when their pathways are blocked due to dam construction by the hydropower projects. 

Similarly, Rajbam fish (Indian mottled eel), known to travel from the Koshi River to the Bay of Bengal for reproduction, are severely affected by these obstructions.

The construction of dams along Nepal-India river routes has worsened the situation. Fish crossing these dams during migration often cannot return and the absence of fish-friendly structures further hinders their movement. 

As a result, Rajbam numbers have been steadily declining in Nepal’s rivers. Experts warned that this decline will impact aquatic ecosystems, birds and other wildlife dependent on fish, as well as local communities reliant on fishing.

Gulafi Mukhiya, a resident of Koshi Rural Municipality-3 who has depended on fishing for generations, said, “In the past, we used to catch a full basket of fish with just one net cast. Now, even after fishing all day, we barely catch two kilograms.”

Despite seasonal fishing restrictions in June, July, and August, illegal practices such as using electric current, poison and fine-mesh nets increase the risk of decline in fish species.

Communities such as Darai, Kumal, Malaha, Tharu, Bote and Baramu, who rely on traditional fishing methods for their livelihood, have to pay an annual fee of Rs. 100 for fishing permits, according to the Koshi Tappu Wildlife Reserve. This decision has made it difficult to protect fish populations, officials said.

The Jalkapur fish (butter catfish), once common in the Saptakoshi River, has now disappeared, leaving the Malaha community, which used to be heavily dependent on this species, are not struggling.

Ramdev Chaudhary, Chief Conservation Officer at the Koshi Tappu Wildlife Reserve, said that the Koshi River is home to 141 fish species. However, despite monsoon being the peak breeding season, unregulated fishing activities outside protected areas have disrupted reproduction cycles.

He also said that a single pair of fish can produce up to 80,000 fry in a season, highlighting the impact of uncontrolled fishing on population growth.