The
Adyar River originates from Chembarambakkam Lake in Kancheepuram district and
flows 42 kilometers East-ward to confluence in the Bay of Bengal. Before
merging into the sea, the river forms a unique ecosystem with a mixture of
fresh and salt water, termed as Estuary
or Mugathuvaram (river-mouth) in
Tamil. Estuary originates from Greek word aestus which means tide or boiling of the sea. As the name suggest, this ecosystem is dynamic
as sea water is flushed back and forth, throughout the day, due to action of
high and low tides.
Fish,
crab and prawn enter the estuary to lay eggs. Once hatched, the juvenile fish
use the estuary as nursing grounds. Fish feel safe from predators hiding behind
the roots of mangroves and on land, the lush branches of mangroves provide home
for birds, even some migrants. Mangroves are plants which require both fresh
and saline water for their survival and they are an integral part of an
estuarine ecosystem. Mangroves draw nutrients from water since the river
deposits rich silt and essential nutrients along with the flow. In turn,
mangroves support the estuary by supplying organic matter, through litter such
as leaves, fruit, bark and flowers. The organic matter is further broken down
by microorganisms which ultimately become food for fish. The coastal areas are
enriched by presence of the estuary as it supplies food for life forms in the
near shore areas, ensuring a complete ecological cycle. Although, the estuary
is located close to sea, the species which inhabit the estuary and the sea are
completely different.
Unfortunately,
this would have been an ideal sight of Adyar estuary few years ago. Rapid urban
development and improper management of our city’s waste has altered the
estuary, conversely, declining its ecological wealth.
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| Sewage and encroachment in the Adyar estuary |
Adyar
estuary was once home to wide variety of fish, crabs, prawn and shells. Many
fishermen were directly dependant on the estuary for sustenance as it harbored
few fish species of economic importance. However, the decline in the diversity
of fish species can be attributed to the introduction of an invasive
species. According to literature, in the
early 1950’s, 15,000 individuals of Tilapia fish (Oreochromus mossambica) were released from below Saidapet Road
Bridge. Unfortunately, initiatives to boost fisheries lead to the displacement
of commercially important species of fish, in the estuary. A simple definition
of an invasive species is any organism which has the capacity to take over
native species and create a proper home for itself. Tilapia are contenders of “100 of the world's
worst invasive alien species" enlisted by the International Union for
Conservation of Nature (IUCN). Tilapia, a native species of Africa, mostly
inhabits freshwater bodies such as lakes, ponds and rivers also extensively
bred for the aquarium industry. Within few years after introduction, it was in
1958, Tilapia was starting to be reported in fishermen's catches from the
estuary. Mullets (Mugil Cephalus),
known as Madavai in Tamil, were the first victims. Pearl Spot (Etroplus suratensis), “One of the most
economically important species of fish” during the 1950’s were displaced by
Tiliapia without any trace, three decades later. Similar parallels can be drawn
from Lake Victoria in Africa, the second largest lake in the world. An invasive
species, Nile Perch was introduced into the lake to boost fisheries and it
displaced nearly 300 species of fish. Fishermen on one side, gained export
exchange out of it. However, Hubert Sauper, in his documentary Darwin’s Nightmare, shows the other side
of this fishy tale
The
Adyar estuary is well connected to the sea through a small opening, called as
the river mouth. However, the estuary is cut off from the open sea for a period
of 6 to 9 months. The closure of the river mouth is due action of water
currents. Have you noticed? When you leave your bag on the beach and go for a
swim, you always notice yourself ending up far away from your bag or friend,
placed on the shore. You won’t even realize that you have moved far off. This
is due to the action of long shore currents or long shore drifts that flow
constantly along Chennai coast. Usually, the flow is towards South to North for
9 months and North to South for 3 months.
The
problems of waste management grew along with the rapid urbanization of Chennai.
Most of us don’t even know what happens to the garbage once it leaves our
dustbins. However, we see them being piled up somewhere and burnt or dumped
near water bodies which will ultimately end up in the sea. Unlike us, fish
breathe through their gills requiring certain amount of oxygen dissolved in the
water. Due to increased outlet of domestic sewage, most of the dissolved oxygen
is used up by microorganisms. Once the levels of dissolved oxygen level
decrease, it leads to the mortality of fish in that particular water body. Contamination
of the estuary is another important factor which promotes the succession of
invasive species such as Tilapia, since they are adapted to survive in harsh
conditions.
It
has been argued that slum communities along the Adyar River, are one of
contributing factors to the pollution by encroaching the banks and reducing its
breath of the river. However, the encroachment by high rise building and sewage
which is silently dumped through underground sewers into the estuary is never
spoken about.
The
Adyar estuary is under peril. Cleaning up the river only in an aesthetic sense
will never be of any help. The estuary will remain as an iconic example for the
generations to come to learn how not to treat a river.
In
two months time, the Fisheries Department has plans to introduce Tilapia into
Poondi reservoir, which supplies fresh water to Chennai city. Once again, Tilapia
will be cultivated in cages to boost aquaculture. Even if few fishes manage to
escape the cages, then history might repeat itself, spelling catastrophe. It is
time to think. Have we not learnt our lessons, already?
Rahul Muralidharan
Rahul Muralidharan
