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International Journal of Marine Science 2013, Vol.3, No.2, 4
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11
Fish landing pattern in the estuary was tremendously
distorted during monsoon season due to various stress
factors induced by heavy river discharge. Many of the
marine fish species in the estuary declined during
monsoon due to sudden changes in salinity,
temperature and other physico-chemical and biological
conditions in the estuary (Table 4, 5). Whereas, shrimp
catch slightly increased during monsoon.
Fin fishes
contributed 69.62% to total fishery of KAE; catfish
(8.46%),
Etroplus maculates
(5.69%),
Etroplus
suratensis
(6.43%), mullets (5.65%), and
Sillogo
sihima
(4.95%) were the major fin fish group. Among
cat fishes
Plicofollis dussumieri
,
A. subrostus
were the
major species observed in the present study.
Crustaceans contributed an average of 23.47% to total
landing;
Methapenaeus
dobsoni
(8.01%),
Fenneropenaeus indicus
(6.22%),
Metapenaeus
monoceros
(4.52%),
Penaeus monoden
(1.45%),
Macrobrachium rosenbergii
(1.43%) and crabs
(1.83%). Bivalves (6.84%) and oysters (0.07%) also
contributed to total fishery of KAE and the major
bivalve species were
Villorita cyprinoides
,
Paphia
malabarica
and
Meretrix casta
, whereas
Crassostrea
madrasensis
and
Saccostrea cucullata
were the oysters
noticed in the KAE. Overall similarity 71.26 % was
observed in the month wise total fish landings of the
KAE with highest similarity observed between
December and February months; an apparent cluster
formed between the months of monsoon and post
monsoon season. Seasonal mean fish landing in the
KAE was highest during pre-monsoon (397.9 t)
followed by post monsoon (311.5 t) and south west
monsoon period (199.2 t). Monsoon season dominated
by cat fishes (19.9 t),
Etroplus suratensis
(13.2 t),
mullets (11.7 t) and
Chanos chanos
(2.9 t).
Fenneropenaeus indicus
(21.4 t) and
Metapeaneus
dobsoni
(12.5 t) were the major species of shrimps
supported monsoon fishery of KAE. Fishery in the post
monsoon season formed by cat fishes (24.6 t), Gerres
sp. (18.5 t),
Etroplus maculatus
(17.9 t),
Etroplus
suratensis
(17.5 t), mullets (15.9 t),
Sillago sp.
(16.1 t),
Ambassis sp.
(15.3 t) and
Chanos chanos
(14.2 t).
Metapeaneus dobsoni
(27.5 t) and
Fenneropenaeus
indicus
(16.4 t) was dominant in post monsoon fishery.
Clupeids and Carangoides were also appeared in the
fish catch during pre-monsoon period; 16.2 t and 3 t
respectively. Among complex array of fishing gears in
the KAE, gill nets contributed 45% of the total fish
catch followed by Chinese dip nets (18.31%), Stake
nets (19.96), cast net (7.15%), ring nets (4.19%), scoop
nets (3.39%), hook and lines (2%).
3 Discussions
3.1 Environmental gradients and species richness
This study investigated the variation in fish abundance
and its species composition in the Kodugallur-
Azhikode estuary (KAE) in relation to prevailing
environmental conditions. A total of 63 fin fish species
were collected from the estuary during the study. Six
species of penaeid shrimps, one species of palemonid
prawns, two species of crabs, four species of clams and
two species of edible oysters were also observed in the
assemblages. In this estuarine system, environmental
gradients are often steep due to the large watershed to
surface area ratio and associated freshwater influence.
This can cause dramatic shifts in salinity and
temperature that estuarine organisms must either adapt
to, or avoid (Vernberg, 1982). The estuarine fishes can
be divided into two broad categories according to
whether they spawn in estuarine systems or the sea; the
former group is referred to here as estuarine and the
latter group marine. The main feature of the life cycle
of most marine species utilizing estuaries are divided
into a juvenile period that is predominantly estuarine
and an adult stage that is primarily marine (Wallace,
1975a). Although some species may attain sexual
maturity within the estuarine environment, spawning
always occurs in the sea (Wallace, 1975b) where the
relatively stable marine environment is more suitable
for the survival of the egg, embryonic and larval stages.
Similarly, Fish diversity in the estuary was quite high in
saline water dominated areas compared to fresh water
dominated sites. Estuarine mouth zone (EMZ)
dominated by marine and true estuarine fish species
whereas estuarine upper zone (EUZ) supported mainly
fresh water species.
3.2 Assemblage structure and assemblage-
environment relationships
Estuarine environment contribute substantial amount
to the total inland fish production and it also support
diverse aquatic fauna as a location of breeding,
spawning, larval development and feeding. Climatic