Abstract of Ph.D thesis
A study of the diversity and ecology of the freshwater fishes of four river
systems of Uttara Kannada District, Karnataka, India.
Introduction
The Uttara Kannada district (74°9’
to 75°10’ E longitude and 13° 55’ to 15° 31’ N latitude) which
lies along the central part of the hill ranges called the Western Ghats, has
a number of perennial as well as temporary water bodies, like tanks, pools,
lakes and also streams and rivers (see Map below). There are both smaller
east flowing (Dharma, Varada) as well as larger west flowing rivers (Kali,
Aghanashini, Bedti, Sharavati, Venkatapura, etc.). There has been very little
work on the fish communities of this region, except for taxonomic accounts
of fishes in some areas. Four of the west flowing rivers were chosen to study
the diversity, distribution and ecology of the freshwater fish communities
of these rivers. There are varying levels of human disturbances on these river
systems. Amongst the four rivers that were studied, Kali has four major dams
constructed along the river stretch: at Supa, Bommanahalli, Kodsalli and
Kadra. Sharavati also has 2 major dams: at Linganamakki and at Gersoppa. At
Dandeli, effluent discharge from industries built near the banks of Kali has
affected the water quality of this region. Bedti is polluted to some extent
by sewage discharge from the town of Hubli and surrounding areas, while Aghanashini
has very minimal levels of effluents from agricultural wastes and pesticides
from plantations and settlements along its banks. Local fish kills by poisoning
and dynamite fishing for harvesting big numbers of fish without much effort
are also causing a loss in species numbers and abundances. Thus, a study
of the species diversity of fish community, their composition, and distribution
patterns and effects of these disturbances is much needed to put forth the
statement on a need to protect and conserve these natural habitats and the
existing fish diversity in these river systems.
Objectives of the study
The main objectives of the thesis were:
•To study the diversity and compositions of the fish
species found in these four rivers.
•The distribution patterns of these species (at various
scales of the study i.e. diurnal, site-wise, habitat-wise, regional, and across
rivers) and the status of these species in terms of their rarity, endemicity,
or being endangered.
•Variation of species compositions with habitat types
as well as variation along the stream gradient (from the headwaters to the
downstream regions).
•Correlation of fish community structure with environmental
gradients (changes in physical parameters of the stream along the stream).
•To understand the correlation between morphological
features with the habitat and feeding ecology of some of these species.
•To study the kinds of human disturbances that might
be affecting fish communities and the changes in species compositions caused
due to these disturbances.
Methodology
Data on the fishes found in these regions, physical
characteristics of the study sites (stream parameters), chemical characteristics
of the waters, riparian vegetation, etc. were collected. Sampling for fish
was done over a period of two years (December 1996 – April 1999) where 24
sites pre-selected for sampling on a regular basis were chosen and were sampled
at different times of the year, and during both day as well as night. The
sites were selected such that they were a representation of the natural conditions
in these rivers, while some sites were selected at the site of human disturbances
like pollution discharge so as to study the effects of these on the species
compositions. A total of 6 sites were selected on each river, with 3 sites
on the upghat (on the Western Ghats, with an elevation of more than 300m)
and 3 on the mid-elevation and the downghat regions. Thus there are a total
of 8 “environmental regimes”, comprising of the 'upghat' and 'downghat' regions
in each of the four rivers. Only perennial streams were chosen for sampling.
A study of the relative abundance of the different kinds of habitat types
was also conducted. Fishes were sampled using conventional methods like gill
nets, cast nets and drag nets. At some sites hooks were used to catch some
rare or elusive species. Sampling was done at different habitat types present
at each site. To study the ecomorphology of fish species, measurements of
the morphological features of 18 of the most abundant and widely distributed
species was conducted. This data along with data on habitat preferences and
secondary data on the feeding preferences of these species were used to study
the correlation of morphological characters with habitat and feeding behaviours.
Results
The main results of the study are as follows:
•A total of 10,771 individuals
belonging to 92 species were identified. 25 species from this collection (27.2
%) are endemic to the Western Ghats. Out of a total of 25 families,
the Cyprinidae is the most dominant group, represented by 45 species. A new species of catfish, Batasio sharavatiensis,
was also recorded (Bhat 2003; Bhat, 2004).
•Species richness comparisons across the four rivers
(upon rarefaction of the data) show that per 1000 individuals sampled in each
river, Sharavati has the highest species richness while that for Aghanashini
was the lowest. Bedti has the highest abundance in terms of the number of
individuals collected per sample.
•Frequency distribution patterns show that 32 species
are restricted to only one site out of the 24 sites studied. At the regional
scale, 58 species were found to occur in 1, 2, or 3 environmental regimes,
and 34 species in 4 or more regimes. 28 species were found to occur in all
four rivers. These species seem to be widely distributed among the environmental
regimes, since 18 of these 28 species are found to be present in 6 or more
of the environmental regimes.
•Bedti and Aghanashini are the most similar in terms
of their species composition, while Sharavati is the least similar to the
other three rivers.
• Comparisons of species composition
at the regional scale show that similar regions on different rivers are closer
to each other in their fish species composition as compared to different regions
on the same river (i.e. 'upghat' regions across rivers are more similar than
'upghat' and 'downghat' regions within the same river) (Bhat, 2003).
•Species richness across habitats varies, with pools
being highest in species richness. Riffles have the lowest species richness
value and most of the species found here are common to pools and runs.
•Changes in species richness as well as composition
are found, along the upstream to downstream gradient in rivers, with downstream
regions showing higher species richness than the upstream regions. These are
associated with changes in stream habitat and stream physical characteristics.
(Bhat,2004)
•A study of the ecomorphology of fish species shows
that characteristics like the body size and shape, head dimensions and characters
associated with feeding, like mouth position, presence of barbels, position
of the eye, etc. vary in species as an adaptation to their habitat and feeding
preferences. These morphological variation, however,
were weakly correlated to habitat parameters. This indicates other factors
like interspecific interactions (competition, predation), physiology, and
behavioural aspects to be more important in structuring communities.
(Bhat, accepted)
•The Index of Biotic Integrity,
a method used for ranking sites according to the extent of human disturbances
and their effect on fish community richness and composition, was used to score
and rank 16 sites located on these rivers. The results of this study
show that sites on Kali, like at Dandeli and Bommanahalli are the most affected
by disturbances, while study sites on Aghanashini as well as Bedti seem to
be fairly undisturbed in terms of their fish community composition. Thus,
this method can be used as a preliminary study for preparing conservation
plans for a region, using fish communities as indicators of disturbance.
(Bhat, in preparation)
Map of the Indian subcontinent showing the location of the Western Ghats
and my study region in Uttara Kannada District (enlarged part)
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