Threats to Fish Diversity
- River Ganga is experiencing tremendous challenges towards fish biodiversity due to several anthropogenic disturbances like construction of dams and barrages, pollution, over fishing, exotic invasion, climate change etc. The upper zone of river Ganga from Rishikesh to Narora is regulated by series of dams and barrages diverting 90% of the flow during lean seasons, thereby, adversely affecting the ecosystem.
- Decreased water flow in river Ganga has created negative impact on the migratory fish species. The impact of damming is vivid in case of the migratory species like Indian Shad (Tenualosa ilisha) and Golden Mahseer (Tor putitora) in upstream.
- Blockade in water flow causes dwindling effect in turbidity to which species are adapted to the rivers. It also hinders the normal flooding of floodplain wetlands, thus, hampering fish diversity. Severe loading of silt in the river due to heavy deforestation and catchment activities also results in choking of wetlands impairing fish breeding and recruitment process .
- The rapid urbanization along the river bank has led to the discharge of 75% of untreated sewage in the river. In addition to this, bioaccumulation of heavy metals in river water, sediment and fishes was found in the middle stretch of the river at Kanpur, Allahabad and Varanasi.
- Increased catches of invasive species like common carp and tilapia has also altered the fishery dynamics of river Ganga replacing endemic fish species.
- Inadequate rainfall in entire Ganga basin in recent years coupled with reduced water flow due to water abstraction has certainly resulted breeding failure of fish species and subsequent juvenile recruitment.
- Additionally, huge destruction of fish juveniles using mosquito nets and bag nets are one of the prime reason behind serial depletions of fish stocks in the river. This leads into considerable depletion in population of potential young ones from the fish population before attaining their complete biological maturity.