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

Vembanad Lake
exploited from Vembanad Lake which forms nearly
21% of the exploited stock of M.rosenbergii of
Vembanad Lake. As most of downstream regions
are congenial for the completion of larval
metamorphosis, it could be area, wbich is also
contributing to the replenishment of the stock.
Based on the present exploitation it appears only
one third of the berried females are able to reach
the breeding ground where the hatching and
larval metamorphosis are completed. The rest are
destined to be caught at different regions of the
lake during downward migrations.
The catches had gone down to 39 t in 1988-89and
it recorded an increase upto 129 t. in 1995-96, it
could not reach the level of 400 t of 1967.However,
the increase in the catches in 1994-95& 1995-96as
compared to 1980s is due to the closure of the
barrier for a shorter period i.e. from 160 days to
106 days. The stock may have revived as the
opening of the barrier in April (Table 2) might
have facilitated the post larvae and juveniles
trapped in the downstream part of the lake to
continue their return migration to upstream
waters (Kurup, 2000).
The other reason for the revival of stocks may be
the increased availability of nursery/grow out
areas. It has been reported that more than 60% of
the paddy fields in lower Kuttanad and Kayal are
now follow aquaculture during the monsoon
months (KWBSP,1990) for various reasons. Most of
the polders in lower Kuttanad and Kayal provide
ideal nursery ground for the subadults and
juveniles. The reduced use of pesticides in
Kuttanad may be one of the contributing factor for
the revival of the fishery.
iii. Fishery Resources
Vembanad Lake water body has an area of 21,050
ha of which the estuarine northern portion has
12,440ha and the freshwater southern portion has
8,610 ha. The study on the fish fauna was made by
Kurup et at. (1993) employing two vessels - "Flying
Fish" and "Dutchman" made available by the Indo-
Dutch Co-operation Programme on the Kuttanad
Water Balance Study Project. The area was
divided into .10 zones (Fig.2). The total number of
units of similar gears operated in each sub zone
was enumerated and at least 30% units were
examined by them for the total weight, length
frequency, sex, maturity stages etc.
a. Species composition:
From the lake, 115 species belonging to 84 genera,
94
six species of penaeid prawns, four species of
palaemonid prawns and three crabs were
identified. The annual production from the entire
lake during July 1988 to June 1989 period was
estimated as 7202.1 t of which penaeid prawns
with a catch of 4383 t contributed 60.86%, fishes
34.8%(2506.1 t), crabs 181 t (2.51%) and
palaemonids 131.6 t (1.83%). The average annual
production per hectare was 342.14 kg. (Kurup et
aI., 1993). The northern portion of the barrier
yielded 93% of the catch while the southern
portion yielded only 7%. The average annual yield
of the northern sector was 538 kg/ha as against 59
kg/ha by the southern sector.
b. Groupwise landings :
During July-December except in September, fishes
dominated the catch. The percentage wise species
composition of the important fin fishes as worked
by Kurup et al. (1993) is as follows: sciaenids (8.32
%, glassy perchlets - 4.69 %, catfishes - 4.34%,
pearl spot 4.5%, mullets 2.77%, estuarine spat
2.28%, gerrids 1.56%, half beaks 1.16%. The
followingspecies contributed more than 100 tonnes
to the fishery of the lake: Daysciaena albida,
Ambassis gymnocephalus, Etroplus suratensis,
Tachysurus maculates, Tachysurus
subrostratus, Ehirava fluviatilis, Gerres
filamentosa and Liza parsia.
c. Seasonwise / Gearwise landings
The month of February, with a landing of 1021.23
t recorded the highest landing followed by 224.38
t in July. Premonsoon and post monsoon months
recorded 44.1 and 34.13% of the catches. Fishes
were dominant during monsoon followed by postmonsoon.
This was true for palaemonids also.
Penaeid prawns and crabs were dominant during
premonsoon period.
Two of the stationary nets - stake net and dip net
accounted for 72.48% of the total catch from the
lake. The stake net contributed nearly 52% and
the dip net about 21%. Among the wandering
gears, gill net 10.15%,seines 9.68%, cast net 3.49%
and line fishing 2.54% was the major contributors.
Maximum catch from the stake net was recorded
during January.
Kurup (1982) has reported 106 species of fishes.
Menon and Raman (1961) reported seven species
of penaeid prawns frqm the lake. Kurup et al.
(1993) recorded six of them. Kathirvel et al. (1973)
reported Portunus pelagicus and P. sanguinolentus
as a migrant species.