doi:10.1038/nindia.2017.44 Published online 27 March 2017
Here’s some good news for urban mangroves, often considered unsightly by city planners for their scraggly, above-water roots and seen as a waste of precious real estate by land developers.
Environmental economists have now found a strong economic reason to conserve and increase mangrove area. A new study says every hectare of these evergreen trees contributes to 1.86 tonnes of annual marine fish catch in India1. This is about 23% of India’s total catch, roughly translating to Rs 68 billion.
Giving this economic spin to an issue largely considered environmental, Lavanya Ravikanth Anneboina and K. S. Kavi Kumar of the Madras School of Economics say that in addition to fish catch, mangroves also add value with other ecosystem services. These include wood, coastal protection, erosion control, carbon sequestration, water purification, tourism, recreation, education and research. Coastal protection and carbon sequestration alone added up to Rs 754 billion and Rs 1.65 billion in 2012-13 prices.
Mangroves make for 4,740 square kilometres or 0.14% of India’s geographical area. Assigning an economic value to mangroves could give policy makers and administrators reasons beyond ecological or biological to push for conservation of these precious resources.
Marine fish breed and nurse young ones in the mangroves. Young fish grow in the secure maze of breathing roots before venturing into the sea. The researcher duo used an econometric analysis model to predict the technical efficiency of fish production in these mangroves. They used a stochastic ‘frontier production function’ to estimate the maximum potential output from territorial waters of each state housing mangroves. They found that states on the western coast of India – Gujarat, Kerala, Maharashtra – have higher technical efficiency than those on the eastern coast such as Odisha and Puducherry. However, real catch could also be limited by other variables like production inefficiencies and impact of state policies and support, they say.
“The mean value of technical efficiency is estimated to be about 45%, which implies that these states on an average could increase marine fish output by 55% without additional resources but through more efficient use of existing inputs and technology,” Anneboina and Kumar note.
The authors used annual fish production statistics from the Central Marine Fisheries Research Institute (CMFRI). They also considered variables such as the state government’s plan outlay, financial and policy support for the fisheries sector, and the total number of marine fishing vessels while computing efficiency.
Every square kilometer of mangroves was estimated to increase fish production by 185.84 tonne. Considering that India has 4,740 sq km of mangroves, this works out to 880,881.6 tonnes per year – a whopping 23% of the country’s marine production.
“Along with other inputs necessary for increasing marine fish production, mangroves play a significant role in strengthening the harvest from Indian coasts,” Kavi Kumar says.
The study might be especially significant for urban locations such as Mumbai and Navi Mumbai (with about 75 sq km of mangroves) that face many pressures. Chief conservator of forests of the Mangrove Cell in Maharashtra, N. Vasudevan, says there’s continuing pressure to convert mangrove fringes into slums to accommodate a large number of migrant workers pouring into these cities. Mangroves are also vulnerable to construction debris and urban garbage dumped on them.
Mangrove ecologist V. Selvam, executive director of Chennai-based M. S. Swaminathan Research Foundation, says the height of the soil surface in the mangroves keeps increasing steadily as the roots trap silt from the water. The trapped soil catch falling leaves to create a living platform and offer protection against increasing sea levels, storm surges and high waves. Villages protected by mangroves and other coastal vegetation in Tamil Nadu survived the impact of the 2004 tsunami better than those that did not have the same protection2.
The new econometric analysis strengthens the advocacy to protect mangroves, traditionally seen as bulwarks for coastlines battered by climate change-induced sea level rise.
1. Anneboina, L. R. & Kavi Kumar, K. S. Economic analysis of mangrove and marine fishery linkages in India. ISS Environ. Sci. Tech. 24, 114–123 (2017)
2. Danielsen, F. The Asian tsunami: A protective role for coastal vegetation. Science 310, 643 (2005)