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International Journal of Marine Science 2013, Vol.3, No.2, 4
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13
during south west monsoon season; salinity variation in
the water column could have resulted in the reduction
of total fish landing pattern. Conversely, some fishes
attracted to estuary during monsoon period due to
physiological/behavioural attraction to river discharge
and precipitation; lower salinity preference for part or
whole of life cycle (Day, 1989). Correlation coefficient
of fish abundance and its environment variables in the
estuary showed positive correlation Salinity (r=0.959,
p<0.01), pH (r=0.988, p<0.01) and transparency
(r=0.962, p<0.01). Turbidity showed a negative
correlation with fish assemblage in the KAE (r=-0.992,
p<0.01) during the study period. Linear regression
analysis shows that the multiple correlation coefficient
(R), using all the predictors simultaneously, is 0.79
(R
2
=0.63) and the adjusted R
2
is 0.50, indicating that
50% of the variance in fish landing can be predicted
from the Chl-
a
, water temperature, salinity variations
combined. The model of Chl-
a
, water temperature and
salinity significantly predicts the fish landing, F (3, 8) =
4.69, P<0.05. Mass fish surfacing and few mortality
was also observed in the EMZ of KAE during fall of
south west monsoon by the influence of depleted
oxygen content due to degradation of organic matter
accumulated in the basins of estuary and changes in
salinity.
The major fishing gears employed in the estuary were
gillnets, cast nets, stake nets, scoop nets, ring nets,
traps and Chinese dip nets. Gill net was most widely
used fishing gear in the estuary and it has contributed
53% to the total fishery; it also exhibited highest CPUE
value among the several type of fishing gears employed
in the estuary. Present study noticed a significant
reduction in the fish production from the earlier studies
by (Anon, 2001) and (Harikrishnan et al., 2011) in the
same estuary, a significant intra annual variation in fish
productivity were also observed during the study. This
seasonality in fish catch at the estuary indicate that
monsoon induced sudden changes in the water quality
support less biological populations and communities
while less disturbed seasons characterized maximum
fish stock and variety of species. The drastic reduction
in annual fish landing in the estuary could be due to
habitat degradation caused by intense sand mining,
aquaculture, pollution, artificial breaching, urban
encroachment and harbour development. Unfriendly
fishing practices, size and recruitment over fishing and
associated factors were the major reason for fish
diversity loss in the KAE.
Anthropogenic activities, over fishing and various
types of pollutants from different point and non-point
sources have a crucial role in the habitat degradation.
The proper assessment of variation in estuarine fish
production as well as fish diversity is important for
management of fisheries resources of an ecosystem.
Juvenile estuarine fish populations are strongly
affected by climatic variability, which may affect fish
production potential through changes in either growth
or abundance (Martin and Michael, 2002). KAE was
important ecological buffers for many of the marine
fish species as a location for breeding and larval
development. However, KAE was potentially critical
for dampening climate variability induced stock
fluctuations and this recall the important for
sustainable management of fisheries; particularly
during recruitment of fish stock and this highlights the
importance of estuaries. The declined fish stocks in the
estuary can be attributed to inadequate fishery
surveillance by the authorities and it lead to overfishing,
mortality juveniles and removal of brood stock during
reproductive seasons. The large scale seasonal
variability on environmental variables implies that
seasonal variation can have an important role on fish
abundance in the estuary. However, climatic variations
can affect the natural fish stocks and these variations
would be affect the fishery environment and ecosystem
as a whole.
4 Materials and methods
4.1 Study site
The study site encompassed the transition from an
oligohaline estuarine system to the adjacent marine
environment with sampling stations spaced at each of
two regions, including the estuarine upper zone (EUZ)
and estuarine marine zone (EMZ) in the
Kodungallur-Azhikode estuary (KAE), is a northern
extremity of Vembanad wetland ecosystem (Figure 3).
KAE (10°11'~10°12' N and 76°10'~76°13' E) having an
area of 700 ha. Tides in the estuary are semidiurnal,
with microtidal tidal range; tidal effects extend to
approximately 25 km landward of Azhikode
(Revichandran and Abraham, 1998; Martin et al., 2011).
The KAE is fed by the tributaries of Periyar River and
it has remained open to tidal flushing from the sea at
Munambam.