Inland aquatic fisheries form an important source of livelihood for a significant proportion of population in India. Climate change is projected to have a huge impact on inland aquatic ecosystems and the fisheries sector in India. While there are a number of studies on the impacts of climate change on freshwater ecosystems and fish, most of these are from the temperate countries. Very few studies exist from the tropical regions.

Climate change projections indicate that India could experience hotter and wetter scenarios and these variations in climate can greatly affect the productivity and sustainability of freshwater ecosystems.

How will changing climate trends affect the major river basins of the Peninsular region of south India, fish catch, fish diversity? What do fisherfolk think about climate change and its effect on freshwater fisheries? A paper published in the Journal of Water and Climate Change attempts to answer these questions.

Impact of climate change on rivers in India

Recent studies on climatic extremes indicate varying scenarios for major river basins of India. For example, temperatures have increased by 0.20–0.47 °C and the precipitation has decreased by 257– 580 mm over the Ganga river basin over the last few decades.

The Godavari, the longest river in Peninsular India is also experiencing a significant increasing trend in Tmax (maximum temperature) during post-monsoon and Tmin (minimum temperature) during monsoon indicating the presence of changing seasonal cycles over the river basin. These changes have had a significant impact on the fish yield and their reproductive patterns.

The Krishna, the second largest east–flowing Peninsular river is also showing an increasing trend in the mean monthly maximum and minimum temperatures under projected scenarios. An increase of 1.67–2.57 °C has been projected by the end of the 21st century. Predictions indicated an increase in mean monthly minimum temperature by 2–4 °C in 2050 and a decline in the number of rainy days.

The Cauvery River is one of the major rivers of the Peninsula. The Cauvery has a total drainage area of 81,155 km2 (2.5% of the total geographical area of the country) and is more intensively dammed than any other river in India. The annual rainfall over the basin during 1950–2010 has increased, with higher maximum rainfall observed during 1950–70. However, the seasonal trend shows a decrease in the number of rainy days during the south west monsoon and an increasing trend during the northeast monsoon. The minimum temperature appears to be marginally declining while the maximum temperature shows an increase of 0.022 °C.

How will these changes affect fish?

It is predicted that decline in the number of rainy days will lead to decline in the gross per capita availability of freshwater fishes in India from 1,820 m3 /year in 2010 to 1,140 m3 /year in 2050.

In river basins where surface run-off rates increases the seasonal inundation of the floodplains, the fish production may increase due to entry of migrant species into the spawning and feeding grounds. However, this increased fish yield due to the flooding may be offset by the decline during the dry season. In addition, structures such as dam, embankments can lead to reduced water flows and increased droughts with dry season leading to reduced productivity of inland fisheries.

The change in course of rivers may lead to introduction and increase in invasive species, introduction of diseases among fish.  Increased run-off, discharge rates, flooding and dry season water level in river basins may lead to increase in populations of plankton as well as fish. Changes in the timing of floods may trigger production of fish at the wrong time and change the time of biological production in the river ecosystem.

Climate change may also lead to introduction of entirely new species of fish and help in increased fish production due to increase in rainy days at some locations. While some inland fish may become stressed due to climate change, resulting in weaker immune systems and lower reproductive success, others may flourish and become more competitive.

An increase in water temperature can cause changes in sex ratios, alterations in the time of spawning, migration and peak abundance among fish. The study on the reproductive biology of fishes in River Cauvery revealed that carps and eels showed advanced and extended spawning periods.

Socioeconomic impacts of climate change

Inland fishing operations and livelihoods may also suffer because, when rainfall decreases, opportunities for farming, fishing and aquaculture will be reduced. Less predictable rain/dry seasons will lead to decreased ability to plan livelihood activities like farming and fishing.

The fisherfolk too are slowly experiencing the impact of climate change with majority of them acknowledging the changes in temparature and sea level, extreme rainfall events and increase in salinity.

The way forward

The impact of climate change on fisheries cannot be generalised, but can have major economic consequences for the fishing communities, stakeholders and national economies argues the paper.

Successful adaptation strategies require responses at spatial and temporal scales with interdisciplinary approaches to address climate change impacts that include:

• Improving resilience and reducing stressors like pollution and habitat degradation.
• Ecosystem-based fisheries management approach towards the riverine fisheries
• Capacity building among stakeholders and fisher communities
• The identification of climate resilient species and ecological resilience studies to help in the prioritisation of the conservation needs of species.
• The development of model climate smart villages and waterbodies
• Involvement of fisherfolk, researchers, managers, stakeholders, governmental and non-governmental organisations in tackling the adverse impacts of climate change