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

Vembanad Lake
currents in these areas have reduced. This has
adversely affected the stake net fishery.
Chinese dip nets are abundant in the lower
reaches of the estuary, which is operated round
the year except during monsoon.
or
There are 23 types of gill nets identified by Kurup
et al. (1989). "Ozhukku vala", "Neetu vala" and
"Chemmeen vala" are extensiveiy operated in the
Cochin backwaters for pep.aeid prawns. More than
90% of the Etroplus suratensis are caught from
the upstream region -using "Karimeen vala".
I
About five types of cast nets are operated in the
lake, which are specifically designed for P.
indicus, palaemonids, pearl spot and other fishes.
The cast net operations start from June and
extend up to November.
Landings by two stationary gears namely stake
and gill net accounts for 72048% of the total catch
of the lake. Out of these, stake net alone
contributed more than 50% of this the rest of the
catch was contributed by gill net, seine net, cast
net and long liners in that order.
Fishers of Vembanad Lake employ an incredibly
complex array of fishing gears. The differences in
the gears employed have a direct bearing on the
dissimilarity of the resources (Kurup and
Sammual, 1985). Among the various gears
employed about three fourth of the landings are
from stationary gears. Out of this nearly 50% of the
catch comes from stake net which is comparable
to the fixed bag net fishery of the Hooghly - Matlah
estuarine system (Datta et al.,1971). The
stationary gears are almost e.ntirely confined to
the down stream regions of the lake. It is felt that
blocking of the regions proximal to the sea with
stationary gears, is inimical to the lake fishery,
because they either indiscriminately filter out the
incoming prawns and fishes irrespective of their
size or destroy out wardly migrating fishes such as
Mugil cephalus, Liza parsia, Chanoschanos etc.
In the downstream regions of the lake, the fishing
methods and gears used are much diversified and
they show both seasonal and regional variations.
During the pre-monsoon seasons, the fishermen
belonging to the upstream region of the lake and
Quilon and Kanyakumari migrate to lower zones
for fishing penaeid prawns resources. This type of
migration is comparable to the migratory fishers
(Jbingran, 1985) of the Hooghly- Matlah estuarine
system.
Based on the ecology, the distribution of fish has
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been studied by Kurup and Samual (1987). The
three factors they studied were temperature,
salinity and dissolved oxygen, which has a direct
bearing on the occurrence and abundance of the
organisms inhabiting the estuarine system.
The classification of McLusky (1974) for estuarine
organisms based on their salinity tolerance was
found to be suitable for classifying the fishes of
Vembanad lake.
Oligohaline fishes : These are mainly freshwater
species, some of which can tolerate salinity
upto 5%0.
True Estuarine Fishes: These fishes are true
estuarine organisms adapted to tolerate wide
range of salinity fluctuations. This group of fish
really constitutes major stocks and is present
in the lake throughout the year.
Marine Fishes: Based on the salinity tolerance
the marine fishes inhabiting the lake has been
classified into two categories: -
a. Euryhaline marine fishes
b. Stenohaline marine fishes
Almost all the freshwater species listed in
Vembanad Lake were reported from various river
systems of Central Travancore (John 1936, Silas,
1949). So it may be presumed that these fishes
undertake regular migrations from the
southernmost region of the Vembanad lake to the
adjoining rivers viz. Pamba and Achancoil. Of the
22 species list under oligohaline fishes, six are
commercially important.
Most of the true estuarine species which inhabit
all the sectors of the lake are commercially
important since their dominance is observed in the
catches throughout the year. The relative
abundance of these true estuarine species have a
direct reiationship with the prevailing salinity.
T.maculates, Gerres filamentosus, G.setifer,
D.albida are the most thriving species. Etroplus
suratensis and L.parsia are also commercially
important. Out of the 41 euryhaline marine species
eleven are commercially important. A.chacunda,
S.commersonii, T.mystax, T.purava, E.tauvina,
L.johni. L.calcarifer are important.
Out of the 48 species of stenohaline fishes reported
from the lake, the regular occurrence of the
species were recorded from the mouth and lower
reaches during the premonsoon season -
A.djeddaba, T.blochi, J.belangerii, V.sehelihave
importance commercially.