International Journal of Marine Science 2015, Vol.5, No.23 1-13
2
2005). Our attempt was to gather all information on
the distribution of fish species to provide a spatial
context for understanding the relationship of
environmental factors on fish assemblage in
Vembanad estuarine system.
The backwaters in Kerala form a habitat for over 200
resident and migratory fish and shellfish species and
fishing activities in these water bodies provide the
livelihood to about 2,00,000 fishers and provide full
time employment to over 50,000 fishermen (Bijoy
Nandan, 2008). There is limited information on the
fishery catch and its production trends from the
coastal backwaters of the west coast of India. But,
scattered information is available on the fishery
composition, abundance and catch from the Vembanad
backwater (Shetty, 1965; Kurup., 1982; Kurup et al.,
1993; Bijoy Nandan, 2008; Harikrishnan et al., 2011;
Bijoy Nandan et al., 2012; Asha et al., 2014).
Jayachandran et al., (2013) observed the influence of
environmental factors on fish assemblage in
Kodungaloor – Azhikode estuary, south west coast of
India. The study on physical habitat characteristics
structuring the fish assemblage in the Vembanad
estuary is also limited. In view of this, the study is
significantly aimed to observe the environmental
factors structuring the fish assemblage of an estuarine
system on the west coast of India.
1 Materials and Methods
1.1 Study area
Vembanad estuarine system is one of the largest
estuaries on the south west coast of India and an
important Ramsar site. It is bordered by Alappuzha,
Kottayam and Ernakulam districts of Kerala covering
an area of about 200 sq. km and extending 80 km in a
NW-SE direction from Munambam in the north to
Alleppuzha in the south (09˚00’ -10˚40’N and
76˚00’-77˚30’E). The width of the estuary varies from
500m to 4km and the depth from <1m to 9m. The
backwater has two permanent openings into the
Arabian sea – one at Cochin and the other at Azhikode.
Manimala, Meenachil, Pamba and Achenkovil rivers
flows into the estuary south of Thanneermukkom and
Muvattupuzha river flows into north of
Thanneermukkom barrage. The Vembanad estuarine
system has a freshwater dominant southern zone and a
salt water dominant northern zone, both separated by
the Thanneermukkom barrage (1,400 metres) where
the estuary has its minimum width. The barrage, a
bridge cum - regulator was constructed in 1976, to
prevent salt water intrusion and to promote double
cropping of paddy in about 55,000 ha. of low lying
fields in the area (Padasekharams). The barrage
remains closed during summer months (January – May)
and with no proper flushing in the upper reaches of the
estuary. The faulty condition of the barrage and the
reclaimed areas that is filled with red earth forming
road along the Thaneermukkom barrage permanently
prevented the connectivity of the south and northern
parts of the estuary. The unscientific operation of the
sluice gates of the barrage, their rusted condition failed
to safeguard the fishery as well as agricultural activity
that have also blocked the connectivity of the wetland
to the Lakshadweep Sea (Arabian Sea) for a major part
of the year. This has severely affected the ecological
characteristics of the estuarine ecosystem and
restrained the seasonal intermixing of fresh and saline
water and thereby interfering with the natural cleansing
mechanism of the estuary, threatening accelerated loss
of habitats and biodiversity (Anon, 2007). Construction
of the new shutters have been initiated in the 470m
long reclaimed portion in the middle part of the barrage
(Anon, 2014).
1.2 Data collection
Ten sampling stations were selected in the estuary, (9
0
30’ 069’’N & 76
0
21’ 268’’ E - 9
0
53’ 519’’N & 76
0
18’
139’’E) for sampling and analysis of various
parameters (Figure 1). Catch composition, diversity of
fish species and environmental parameters were
collected on a monthly basis from February 2012 to
January 2013 period. Observations were made
seasonally viz., pre monsoon (March – May),
monsoon (June – September) and post monsoon
(October –January) periods. Landing centre based
direct data collection method was adopted for the fish
landing estimation and the major landing centres;
Alappuzha, Kumarakam, Muhamma, Thaneermukkom,
Vaikkom, Chembu, South Paravoor, Aroor, Arookutty
and Thevara were spread around the backwater system
(FAO, 2002; FAO. 2003; Sparre and Venema, 1992).
Gill net was widely used in Vembanad estuary along
with stake net, seines, Chinese dip net, cast net and
hook and line. Gill net size varied from 30 - 150m and
mesh size in the range 22 – 150mm in different
designs. Finfishes from the gill net were used for the
fish catch composition, fish diversity and assemblage
