Population dynamics of an endemic and threatened Yellow
Catfish Horabagrus brachysoma(Günther) from Periyar River, southern Western Ghats, India
G. Prasad 1, Anvar Ali 2, M.
Harikrishnan 3 & Rajeev Raghavan 4,5
1,2 Laboratory of Conservation Biology, Department of Zoology,
University of Kerala, Kariavattom, Thiruvananthapuram, Kerala 695581, India
3 School of Industrial Fisheries,
Cochin University of Science and Technology, Kochi, Kerala 682016, India
4 Conservation
Research Group (CRG), St. Albert’s College, Kochi, Kerala 682018, India
5 Durrell
Institute of Conservation and Ecology (DICE), School of Anthropology and
Conservation, University of Kent, Canterbury, CT2 7NR, United Kingdom
Email: 1 probios2003@yahoo.co.in (corresponding author), 2 anvaraliif@gmail.com, 3 mahadevhari@hotmail.com,4 rajeevraq@hotmail.com
Date of publication (online): 26 February 2012
Date of publication (print): 26 February 2012
ISSN 0974-7907 (online) | 0974-7893 (print)
Editor: Anonimity requested
Manuscript details:
Ms # o2590
Received 29
September 2010
Final
received 03 January 2012
Finally
accepted 30 January 2012
Citation: Prasad, G., A. Ali, M. Harikrishnan
& R. Raghavan (2012). Population dynamics of an endemic and threatened
Yellow Catfish Horabagrus brachysoma (Günther)
from Periyar River, southern Western Ghats, India. Journal
of Threatened Taxa 4(2):
2333–2342.
Copyright: © G. Prasad, Anvar Ali, M.
Harikrishnan & Rajeev Raghavan 2012. Creative Commons Attaribution 3.0
Unported License. JoTT allows unrestricted use of this article in any medium
for non-profit purposes, reproduction and distribution by providing adequate
credit to the authors and the source of publication.
Author Details: G. Prasad works on diversity, distribution and
conservation of freshwater fishes and aquatic insects of the Western Ghats; Anvar Ali is interested in research on
taxonomy, biology and ecology of freshwater fishes; M. Harikrishnan works on sustainable fisheries and
aquaculture; Rajeev Raghavan is
interested in research that addresses the connectivity between freshwater
biodiversity, conservation and livelihoods in Western Ghats.
Author Contribution: GP, AA and RR designed the study; AA
collected the data; MH analysed the data; RR and GP wrote the manuscript.
Acknowledgements: The study was funded by the Kerala
State Science Technology and Environment Council (KSTEC), Government of Kerala,
India. The authors thank the many local fishers of Kalady, Angadikkadavu and
Manjaly for their help during the sampling. The authors are also grateful to
the Subject Editor for providing inputs and suggesting necessary changes that
greatly improved the manuscript.
Abstract: Based on the annual length frequency
data collected from three major fish landing centres along the River Periyar,
draining the southern Western Ghats, the von Bertalanffy growth function (VBGF)
estimates of Horobagrus brachysomawere worked out as asymptotic length (La) = 422mm total
length, growth co-efficient (K) = 0.55 yr-1 and growth performance
index (ø) = 4.99. The total mortality
rate (Z) was estimated at 5.64 yr-1, natural mortality rate (M) at
1.04 yr-1, fishing mortality (F) at 4.60 yr-1, and
exploitation rate (E) at 0.82 yr-1. Yield per recruit (expected lifetime yield per fish recruited in the
stock at a specific age) analysis showed an excessive fishing effort. Using the analysis of probability of capture
of each length class, the length at first capture (Lc) of H. brachysoma was estimated to be
110mm. An indication of both growth and
recruitment fishing is provided by the dominance of year 1 class in the
exploited population and the capture of immature individuals below first
maturity. Management of H. brachysoma fishing should include
setting of a minimum mesh size limit of 160–180 mm for gill nets as well as a
closed season starting from the month of May till August aimed at protecting
the spawning stock. This study on H. brachysoma, an endemic and threatened
catfish of peninsular India, provides hard evidence that species targeted by
artisanal fishermen, in small-scale tropical riverine fisheries, are vulnerable
to overexploitation.
Keywords: Artisanal fishery, Horabagrus brachysoma, overfishing,
small-scale fishery, threatened species
For
figures, images, tables -- click here
Introduction
Small scale freshwater fisheries contribute an important source of
food security and livelihood to billions of rural communities in the
tropics. However, lack of fundamental
data on such fisheries has led to failures in management aimed at preventing overexploitation, population
decline, and their impact on local livelihoods. Meanwhile, overfishing has currently become an important driver of
biodiversity loss in inland waters (Allan et al. 2005) and decline in
population of many species are occurring concomitantly with the increase in global
inland fish production. In Asia, the
world’s largest inland fish producing region, wild caught freshwater fisheries
have been showing signs of overexploitation with declines in catch per unit
effort, age at maturity and also the average size of fishes caught (Dudgeon
2000). In spite of being small-scale and
artisanal in nature, the fishery of several important freshwater fish including
mahseer (Bhatt et al. 2000, 2004; Raghavan et al. 2011) and catfish (Patra et
al. 2005) in India; major carps (de Graaf 2003) in Bangladesh; large cyprinids
in the Mekong basin (Baird 2006; Dudgeon 2000) and sturgeons in China (Wei et
al. 1997) have shown a characteristic decline in the last decade.
Exhaustive information is currently available on the demography,
population regulation and exploitation patterns of large numbers of marine fish
species. However, unlike marine
ecosystems, datasets on the dynamics of exploited populations of economically
important fish species in rivers, especially those in the developing countries
are largely unavailable. This is mainly
due to the lack of personnel and financial resources in such countries to
undertake research programs (Maccord et al. 2007). These deficiencies are also a cause and
consequence of the lack of attention that the sector receives from the
government (Anonymous 2002).
As with other small rivers in Asia, Periyar—a 244-km long river in
the southern Indian state of Kerala—supports a lucrative inland fishery, largely based on cyprinids
and catfish. This fishery, mainly
concentrated in the lower stretches of the river is predominantly
artisanal. The Yellow Catfish Horabagrus brachysoma is one such species which is targeted frequently by the
traditional fishermen of Periyar River using gill nets (odakku vala; Malayalam)
operated from canoes and also by using hooks and lines. Known locally as ‘manjakoori’, the Yellow
Catfish grows to a size of 450mm (Talwar & Jhingaran 1991) and is a
gourmet’s delight. Fingerlings of H. brachysoma, due to their vibrant yellow coloration are also becoming
increasingly popular in the international aquarium pet trade (Raghavan
2006). A multitude of stressors
including overexploitation, habitat alteration and pollution has, however,
resulted in the population decline of H. brachysoma in its native
ranges, with the fish getting listed as Vulnerable in the IUCN Red List of
Threatened Species (Raghavan & Ali 2011). The peculiar life history traits of the species, including a medium
resilience to overfishing and a minimum population doubling time of 1.4 to 4.4
years (Froese & Pauly 2009) also makes this species vulnerable to the
overfishing. In spite of its threatened status, declining numbers and specific
life history traits, exploitation of H. brachysoma for both the food and ornamental markets continues unabated (Ali
et al. 2007).
In Vembanad Lake, which is an extensive system of backwaters (and
a Ramsar wetland) into which Periyar and five other river systems drain, H. brachysoma is the focus of organized artisanal gill net fishery (Raghavan 2006). Landings of the Yellow Catfish in Vembanad
Lake have shown a wavy trend from 1995 until 2004, having increased and
decreased every few years (Kurup et al. 1995; Bindu 2006; Sreeraj et al. 2007). Despite early reports of the serious
population declines of H. brachysoma and co-occurring catfish species in the Vembanad Lake (Kurup et
al. 1993), no effort hitherto has been made to assess the dynamics of these
exploited stocks from either the lake, or from other water bodies of the
state. This paper is the first
comprehensive study on the population dynamics of this species.
Materials and
Methods
Study site
River Periyar has a total catchment area of 5243km2 and
a length of about 300km (Smakhtin et al. 2009). For a small-sized basin, Periyar nevertheless harbours a number of
endemic and threatened species (Molur & Walker 1998; Kurup et al. 2006)
which is approximately 70% of the fish species present in the Western Ghats
Hotspot (Smakhtin et al. 2009). The present
study was concentrated on the lower stretches of the Periyar River between 76010’–76023’N
& 10098’–10073’E (Fig. 1) where H. brachysoma is known to be fished intensively.
Data collection
The total length (mm) and weight (g) data of H. brachysoma subsamples were measured from well-mixed catches of six to 10
fishermen, operating from three major fish landing centres, namely, Kalady (76019’N
& 10010’E), Angadikadavu (76023’N & 10073’E)
and Manjaly (76010’N & 10098’E), located in the lower
stretches of Periyar River, from January to December 2005. Since males and females were easily
distinguishable, they were identified by their big, soft and distended belly
with swollen and reddish-pink vent (females) and reddish genital opening
(males). Measures of 2638 males and 3382
females were taken for the study. No
fish were collected or sacrificed for the purpose of the study. Sampling was carried out twice in each month
during the first quarter moon and full moon. Data was collected following the methodology of Gulland & Rosenberg
(1992) on the length based approaches to fish stock analyses published by the
Food and Agricultural Organization (FAO). During each sampling day, random sub samples of fish were obtained from
well mixed catches. The total length of
fish was measured to the nearest centimetre. A minimum of 200 fish were measured on each sampling day except on
occasions when the catches were low. Data obtained from the two sampling days in each month were later pooled
and recognized as a ‘monthly sample’ (mean 219.83 ± 18.60 males and 281.83 ±
26.95 females) by simple addition following Ama-Abasi et al. (2004). This was done to avoid any bias in the data,
as in some months there was a variation in the sample size obtained on the two
different days.
Data analysis
Parameters a and b in the length-weight relationship equation W =
aLb were estimated by least square regression after logarithmic
transformation. Age and growth were
estimated based on length-frequency data. It was assumed that the H. brachysoma growth conformed to the von Bertalanffy growth (VBG) model (von
Bertalanffy 1938): Lt = L∞ (1- exp [- K (t – t0)])
where L∞ is the asymptotic length (mm), K the growth constant
(month-1) and t0 time (months), when the theoretical
length is zero. Growth parameters were obtained using the ELEFAN program (Pauly
1987) from the fitted curve with maximum goodness-of-fit (Rn) index. The growth performance index (f) was computed
according to Moreau et al. (1986) as ø = Log K + 2 logLa. Mortality
coefficients, viz., total mortality (Z), instantaneous natural mortality (M),
fishing mortality (F) and exploitation rate (E) were estimated using FiSAT
program (Pauly 1980; Gayanilo & Pauly 1997). Natural mortality was calculated using the
empirical formula of Pauly (1980): In M = 0.0152 – 0.2791n La +
0.65431n K + 0.4631n T. The exploitation
rate was estimated using the formula E = F / Z (Gulland 1971). Although, we estimated the length-weight
relationship as well as age for both males and females separately, the growth
and mortality parameters were done only for the pooled populations. This was done so as to minimize any bias
because of the difference in number of males and females obtained which may
have influenced the results.
The probability of capture was estimated from the left ascending
arm of length-converted catch curve. The
right descending part of the catch curve was extrapolated backwards, such that
the fish that ought to have been caught, had it not been for the effect of
incomplete selection or recruitment, were added to those in the curve, with the
ratio of expected numbers to those that were actually caught being used to
estimate probabilities of capture. This
method provides reasonable estimates of mean size at first capture (Lc)
(Hoydal et al. 1982; Jensen 1982). By plotting the cumulative probability of
capture against mid-length, a resultant curve was obtained. From this curve the
length at first capture Lc was taken as corresponding to the
cumulative probability at 50%. The entire
length-frequency data was used to reconstruct the seasonal recruitment pattern
of the fish by projecting backward all the restructured length-frequency data
onto a 1-year time scale (Pauly 1987), along a trajectory defined by the
computed VBG function. Then, using the
maximum likelihood approach, the Gaussian distribution was fitted to the
back-projected data through NORMSEP (normal separation) procedure (Hasselbald
1966).
The relative yield-per-recruit model of Beverton & Holt (1957,
1966) as modified by Pauly & Soriano (1986) and incorporated in the FiSAT
program, was used to estimate the ‘relative yield-per-recruit’(Y/R) and
‘relative biomass-per-recruit’, assuming a selection ogive. The computed exploitation rate was compared
with the expected values of Emax (the value of exploitation rate
giving maximum relative yield-per-recruit), E 0.1 (the value of E at which
marginal increase in Y/R is 10% of its value at E = 0) and E 0.5 (the value of
E at 50% of the unexploited relative biomass-per-recruit) (Sparre & Venema
1992; Gayanilo & Pauly 1997). The
potential longevity of H. brachysoma was also calculated (Pauly & Munro 1984): Tmax =
3/K.
The yield isopleths diagram was used to assess the impact on yield
created by changes of exploitation rate E and the ratio of length at first
capture to asymptotic length (Lc/Lά) in relation to
changes in mesh size. The optimum exploitation length (Lopt) was
estimated from the empirical equation of Froese & Binholan (2000).
Results
Length-Weight Relationship
The length-weight relationship (LWR) of H. brachysoma males from the Periyar River was W = 0. 0093 L3.072 (n
= 51, r = 0.96, p < 0.01) and those for females was W = 0.0079 L3.172 (n
=61, r = 0.98, p < 0.01). LWR of combined sexes was found to be W = 0.0084 L3.105(n = 112, r = 0.972, p < 0.01). In all cases, the exponent of
length–weight relationship b was higher than 3 (males 3.072; females 3.127 and
pooled 3.105) and the 95% higher and lower confidence interval values were also
above 3 indicating that the growth of H. brachysoma in river
Periyar was isometric.
Exploited stock
The exploited population of H. brachysoma in Periyar
during 2005 was constituted by individuals ranging from 112 to 340 mm. The highest length class recorded among males
was 280–300 mm while the same in female populations was 320–340 mm. The fishery was dominated by individuals in
the size range of 170 to 250 mm in both males and females. The size classes 200–220 mm and 240–260 mm
(both 19% each) constituted the largest share in males whereas in females it
was the 240–260 mm size class (21%) followed by 220–240 mm (17%) size
class. Sex ratio was 1:1.3 which was not
significantly different from 1:1 (p > 0.05).
Growth
The growth parameters estimated in the male population of H. brachysoma from Periyar River are given in Table 1. The value of t0 as estimated by
the empirical equation given by Pauly (1979) was found to be -0.0108. The FiSAT output of restructured length
frequency data of male population of H. brachysoma in river Periyar with superimposed growth curve fitted with
highest levels of Rn is given in Fig. 2. The VBGF for male H. brachysoma based on the growth parameters in the present study was expressed
as: Lt = 388 [1 - exp-0.51(t+0.0108)]. The lengths
attained by male H. brachysoma following VBGF equation at the end of first, second, third and
fourth years were estimated to be 156mm, 249mm, 304mm and 338mm respectively.
For the female population (Table 1), the value of t0was found to be –0.0103. The FiSAT
output of restructured length frequency data of female population of H. brachysoma in Periyar River with superimposed growth curve fitted with
highest levels of Rn is given in Fig. 3. The value of t0 as estimated by empirical equation given by
Pauly (1979) plot was found to be -0.0103. The VBGF arrived at, based on the growth parameters in terms of female H. brachysoma, can be expressed as Lt = 400 [1 - exp-0.63(t
+0.0103)]. The lengths attained by
female H. brachysoma following VBGF equation at the end of first, second, third and
fourth years were estimated to be 188mm, 287mm, 340mm, 368mm and 383mm,
respectively.
For the pooled population (combined sexes), the value of t0 was found to be –0.0115. Fig. 4 provides the FiSAT output of restructured length frequency data
of pooled population of H. brachysoma in Periyar River with superimposed growth curve fitted with
highest levels of Rn. The VBGF in terms
of pooled H. brachysoma population was expressed as Lt = 422 [1 - exp-0.55(t
+0.0115)]. The lengths attained by
pooled H. brachysoma following VBGF equation at the end of one, two, three, four and
five years were estimated to be 180mm, 282mm, 341mm, 376mm and 395mm,
respectively.
Mortality
The FISAT output of mortality estimates of pooled population of H. brachysoma in Periyar River by catch curve method is depicted in Fig.
5. The total mortality (Z) was estimated
to be 5.64 yr-1 at a cut off length of 240mm. The estimates of natural mortality (M) were
determined as 1.04 yr-1. The
values of fishing mortality coefficient (F) and exploitation rate (E) were
worked out as 4.60 yr-1 and 0.82 yr-1, respectively. The optimum exploitation length (Lopt)
was worked out as 259mm. Using the
length converted catch curve method, the estimates of probabilities of capture
were L25 = 232mm, L50 = 260mm and L75 = 288 mm
(Fig. 6) and the Lc was found to be 110mm. These values were subsequently used
as inputs for relative Y/R of Beverton & Holt (1957, 1966) . The Lc/Lα
and M/K values used for Y/R analysis were 0.2606 and 1.8909 respectively. The
relative yield per recruit and biomass per recruit in H. brachysoma is presented in Fig. 7. The relative Y/R reached a maximum at an exploitation rate of 0.5744 yr-1and thereafter decreased with an increase in the exploitation rate. It may be
noted that the present exploitation rate E (0.82) has clearly exceeded the
optimum exploitation rate of Emax = 0.5744. The values of E0.1 and E0.5were estimated as 0.5538 and 0.3333, respectively. The results of length-based virtual
population analysis showed that F increases to a maximum of 2.7921 at a body
size of 240–260 mm (Fig. 8). The catch
increases substantially from 160–180 mm size groups and attains maximum at
240–260 mm.
Discussion
Length-Weight Relationship
Exponential value of the length-weight relationship ‘b’
in H. brachysoma from Periyar River followed the cubes law indicating an isometric
growth pattern, similar to the observations made by Kumar et al. (1999) from
Achenkovil and Ali et al. (2008) from Pampa rivers. Nevertheless, in Vembanad Lake, H. brachysoma showed an acute negative isometric growth pattern with ‘b’ values
in the ranges of 1.7616 (for males) and 1.9441 (for females) (Prasad et al.
2005). This negative growth pattern of
the Yellow Catfish in Vembanad Lake was attributed to the poor environmental
conditions prevalent in the lake ecosystem, especially the high level of
pollution coupled with poor availability of food items.
Growth
Horabagrus brachysoma is known to grow to a maximum size of 450mm (Talwar &
Jhingaran 1991). However, the maximum
size of this species that was obtained from the exploited stock in the Periyar
during this study was 340mm. The dominant
size class of H. brachysoma exploited from the river (170–250 mm) is more or less similar to
those from Vembanad Lake (160–300 mm) (Sreeraj et al. 2007). In general, H. brachysoma exploited
from various parts of Kerala belonged to more or less the same size class. Assuming that the fish grows throughout its
life, L∞ is the largest theoretical mean length that it could
attain in its natural habitat and K is the speed with which it grows towards
this final size (Etim et al. 1999). Growth comparison is a multivariate problem that must take into
consideration both the growth rate (K) and the asymptotic size (Lά).Thus, we used the overall growth performance index ø (Pauly & Munro
1984) as it meets these criteria, is easy to compute and exhibits the least
variance when compared with other alternative indices. The growth performance index value (ø) of
4.99 observed in the present study is significantly higher than that obtained
for many tropical freshwater catfish species including those belonging to the
families Schilbeidae (ø between 2.18 and 2.78) (Etim et al. 1999), Claroteidae
(ø = 2.32) (Abowei & Davies 2009) and Synodontidae (ø = 3.09) (Ofori-Danson
et al. 2001). As phi prime (ø’) is
largely considered to be a species-specific parameter with their values being
similar within related groups or taxa, the significantly high ø value
observed for H. brachysoma is an interesting observation. The maximum size that H. brachysoma attains during its life is 422mm and the life span estimated from
the equation tmax = 3/K (Pauly 1983) is 5.45 years. The comparatively low life span and high
growth performance index of H. brachysoma is uncharacteristic of freshwater catfishes, which are generally
considered to be slow growing.
Mortality
The total mortality (Z) and natural mortality (M) of H. brachysoma in the Periyar River were computed as 5.64 yr-1 and
1.04 yr-1 respectively. Natural mortality being positively
correlated with growth rates (Isaac & Ruffino 1996) was higher in H. brachysoma when compared to slow growing species of catfish such as Clarotes laticeps (0.87) (Abowei & Davies 2009), Schilbe intermedius(0.81) (Etim et al. 1999) and S. mystus (0.28) (Kolding et al. 1992). The exploitation rate (E) is an index used to assess if a stock is
overfished, on the assumption that optimal value of E is equal to 0.5. Computed
current exploitation rate E (0.82) is far higher than the optimum exploitation
rate Emax (0.5744) indicating that H. brachysomapopulations in Periyar River are being overexploited. Although the Yellow Catfish has a longevity
of 5.45 years, the exploited populations from river Periyar are constituted by
the year 1 class. H. brachysoma in Periyar is therefore caught before they grow large enough to
contribute substantially to the stock biomass, thus demonstrating growth
fishing.
Life history-exploitation relationship
The size at first maturity for H. brachysoma in Periyar
River was found to be 176.7 mm for females and 196mm for males (Chandran
2009). During the present study, it was
observed that the exploited population of H. brachysoma in the
Periyar during 2005 was constituted by individuals ranging in size from 112 to
340 mm, and that the fishery was dominated by individuals in the size range 170
to 250 mm in both sexes. The fact that
immature individuals of H. brachysoma are also fished out from the river indicates that recruitment
fishing is taking place, damaging the reproductive potential and reducing the
spawning stock of the species. Capture
of small fish before they mature and breed is also known to lead to a reduction
of fisher productivity and profit (Issac & Ruffino 1996).
Conservation and Management
Currently the fishery for H. brachysoma in Periyar
River appears to be unsustainable as is evident from the high rates of
exploitation and the occurrence of growth and recruitment fishing. Such unsustainable exploitation levels of
catfish in small-scale inland fisheries have been recorded from Volta Lake in
Ghana with Hemisyondontis membranaceus (Ofori-Danson et al. 2001) and Cross River, Nigeria with S. intermidius (Etim et al. 1999). Being
an open access fishery devoid of any management plan, the fishery for the
endangered Yellow Catfish in Periyar is vulnerable to collapse if management
interventions are not planned and put into practice in the immediate future.
Although regulating total harvest could be the single most
important management strategy for protecting H. brachysoma stocks,
implementation of a plan to reduce fishing effort in an artisanal subsistence
fishery is nearly impossible. This is
especially so in a region which has no history of any fisheries management in
inland waters. Management strategies forH. brachysoma in Periyar should hence be based on a combination of different
technical measures such as restrictions on gear, enforcement of size limits and
implementation of closed seasons. In order to allow Yellow Catfish juveniles to
reach sexual maturity before they are subjected to fishing mortality, a minimum
size limit needs to be set at a size greater than the mean size at first
reproduction. In the present scenario, a
minimum catch size limit of 200mm can be enforced so as to prevent recruitment
overfishing. Setting of size limits
should also be supplemented with restriction on the mesh size of the gill nets. Currently, the fishers in Periyar use set
gill nets with mesh sizes between 25 and 80 mm, resulting in the capture of
small-sized juveniles that are below the size at maturity. A minimum mesh size of 160–180 mm should
therefore, be mandatory for gill nets used by fishermen targeting H. brachysoma. If suitable gear restrictions are effectively implemented, there
is little chance that the fishery will come in contact with the animals to be
avoided (immature juveniles) (Charles 2001).
Another effective solution for the protection of H. brachysoma in Periyar can be through the use of closed seasons. Similar to the trawling ban (seasonal
closure) which has been effectively enforced in the marine waters of Kerala for
many years, a closed season starting from the month of May until August should
be put into practice in the riverine system. These months are known to be the spawning seasons of H. brachysoma in the major rivers of Kerala including Periyar (Chandran
2009). This closed season will
invariably safeguard the spawning process and bring to an end the capture of
ripe females.
Management of riverine fisheries in Kerala has received little or
no attention in the past with traditional fishing communities in Kerala often
maintaining a relationship of conflict or accommodation with state institutions
in fisheries management. Currently,
there exists a lack of mutual trust between formal institutions and the
traditional riverine fishing communities in Kerala. Formal institutional arrangements have lacked
the participation as well as representation of traditional riverine fishing
communities (Santha 2007). It is
therefore apparent that this top-down and centralized decision making process
has undermined the legitimacy and efficacy of fisheries management plans in the
region. Therefore, only an organized
effort involving the fisher communities can help in achieving success with the
fisheries management plans that have been suggested for H. brachysoma in Periyar.
As in the case of H. brachysoma, it is also possible that other commercially important and
threatened fish species such as Hypselobarbus
curmuca, Hypselobarbus kolus and Tor khudree which
are targeted by artisanal fishers in different reaches of the Periyar may also
be under significant fishing pressures. Hence, studies need to be directed at assessing the dynamics of exploited
populations of these threatened species for urgent management
interventions. Small-scale fisheries
have many features that make them vulnerable to collapse, including
overfishing, excess capacity, distortions in markets, climate change (Andrew et
al. 2007) and ineffective governance (Berkes et al. 2001). They have remained one of the most poorly
understood fishery systems in the world, especially in developing
countries. Management of resources in
small-scale artisanal fisheries has remained a challenge worldwide, largely due
to the scarcity of data on population, exploitation patterns and threats. The
results of the current study—the first such work on the dynamics of an
exploited fish population in a small-scale fishery in Kerala—could provide the
much needed input for policy makers and government institutions in the region
to develop and implement management strategies to improve equity and
sustainability of freshwater artisanal fisheries in Kerala.
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