06-bioresourcesstatu.. - M. S. Swaminathan Research Foundation

The Vembanad Lake stretching 96.5 Km and
covering an area of 87,000 hactares is the largest
and most important lake of southern India. From
the fishery point of view the lake is very important
as it happens to be the nursery ground of many of
the marine fishes and prawns and more
importantly that of giant freshwater prawn.
For the development of agriculture two
development projects. They were (a) Thottapally
spill-way and (b) Thanneermukkam salt barrier
Of these, the former was completed in early forties
and the latter in 1975. The expectation was that
it would increase the area of paddy cultivation.
Unfortunately the desired results were not
obtained. The flood discharge through the
Thottapally split-way is only 1/3 of what was
designed for. Thus flooding of paddy fields
continued. The Thanneermukkam barrier
constructed on Vembanad Lake resulted in
flooding on the north of barrier. Foraging area of
the marine prawns was also reduced. Moreover,
the giant freshwater prawn, which requires slight
saline waters, was unable to cross the barrier and
was caught in.
The present report describes the meteorology and
flora and fauna of the Vembanad and adjacent
regions. The exploitation of clam fisheries before
and after the construction of the barrier has been
analysed. From the fishery point of view the
published literature shows there are 115 species of
fish belonging to 84 genera and six species of
penaeid prawns, four species of palaemonid
prawns and three species of crabs have also been
VEMBANAD LAKE
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reported. The details of species with annual
production has been detailed out in: the report. It
has been observed that the fishing pressure has
increased over a period of time and at present
decline in the catch has been noticed. One of the
reasons for this is the catch of juveniles in large
quantities. Penaeid prawns have also shown a
decline in recent years. The chief among thelli are
the M. dobsoni, M. monoceros and P. indicus.
Among the two palaemonid prawns available here
M. rosenbergii and M. idella, the former has
received maximum attention. After the
construction of the barrier these species are
unable to perform their breeding migration
upstream to the northern side of the barrier where
they get the required salinity for spawning. Tl!e
berried females are also subjected to heavy fishing
during this period resulting in recruitment over
fishing.
The present study has brought out the necessity of
opening of the Thanneermukkam barrier for more
time in order to give more nursery ground of fishes
and prawns, as well as the reduction in the
number of stake net to ease the pressure on the
penaeid prawns. Most important of them is the
total ban on catching the berried females of M.
rosenbergii in order to revive the fishery of this
resource.
Attempts should be made to increase the area of
mangrove vegetation to develop further an
existing bird sanctuary. The mangrove vegetation
would improve the nursery/recruitment grounds of
penaeid, non-penaeid prawns and fishes.