Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 July 2020 | 12(10): 16380–16384
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.6222.12.10.16380-16384
#6222 | Received 25 May 2020 | Final received
21 June 2020 | Finally accepted 26 June 2020
Population dynamics and
management strategies for the invasive African Catfish Clarias
gariepinus (Burchell, 1822) in the Western Ghats
hotspot
Kuttanelloor Roshni 1 , Chelapurath Radhakrishnan Renjithkumar
2, Rajeev Raghavan 3, Neelesh Dahanukar 4 &
Kutty Ranjeet 5
1,2,5 Department of Aquatic Environment
Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi,
Kerala 682506, India.
3 Department of Fisheries Resource
Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi,
Kerala 682506, India.
4 Indian Institute of Science
Education and Research (IISER), Pune, Maharashtra 411008, India.
1 roshni.phd@gmail.com
(corresponding author), 2 renjith.kumar347@gmail.com, 3 rajeevraq@hotmail.com,
4 neeleshdahanukar@gmail.com, 5
ranjeet.kufos@gmail.com
Editor: Anonymity
requested. Date of publication:
26 July 2020 (online & print)
Citation: Roshni, K., C.R. Renjithkumar, R. Raghavan, N. Dahanukar
& K. Ranjeet (2020). Population dynamics and
management strategies for the invasive African Catfish Clarias
gariepinus (Burchell, 1822) in the Western Ghats
hotspot. Journal of
Threatened Taxa 12(10): 16380–16384. https://doi.org/10.11609/jott.6222.12.10.16380-16384
Copyright: © Roshni et al. 2020. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Kerala State Council for
Science, Technology & Environment (KSCSTE), Government of Kerala, India.
Competing interests: The authors
declare no competing interests.
Acknowledgements: The first author acknowledges
funding from the Back-to-Lab-Programme of the Kerala State Council for Science,
Technology & Environment (KSCSTE), Government of Kerala, India. The authors are also thankful to local
fishers at the Periyar National Park for assisting in
collection of samples.
Freshwater biodiversity is in
peril, threatened by a range of (often interacting) stressors including
flow-regulation, pollution, invasive alien species, climate change, and
overexploitation (Dudgeon et al. 2006; Strayer & Dudgeon 2010). Of these, biological invasion is one of the
most widespread and damaging stressors on freshwater ecosystems (Strayer &
Dudgeon 2010), responsible for the extinction of over 17 fish species, and the
imperilment of over 450 threatened fish species worldwide (IUCN 2019).
The freshwater ecosystems of
India’s Western Ghats (WG) Hotspot harbour more than 300 fish species, of which
65% are endemic (Dahanukar et al. 2011). Though much of this endemism is concentrated
in the southern region of the WG Hotspot, inside terrestrial protected areas,
no management or monitoring plans are in place for freshwater taxa (Raghavan et
al. 2016). For example, a threatened
species of mountain catfish Glyptothorax madraspatanus was extirpated from Eravikulam
National Park, a protected area in the WG due to the invasion by the Rainbow
Trout Oncorhynchus mykiss (Thomas et al. 1999). In a similar situation, four alien species
compete for resources with eight point-endemics in the watershed of the Periyar National Park, one of WG’s intensively-managed
protected areas (Molur & Raghavan 2014).
The African Sharp-tooth Catfish, Clarias gariepinus
(Burchell 1822) is one of the world’s most successful aquatic invader (Booth et
al. 2010), in view of its spread and impacts to native fauna in close to 30
countries (GISD 2020). Diverse life
history traits including eurytopic nature, pseudo-lungs, trophic flexibility,
predatory & piscivorous feeding habits, fast growth, and high mobility (Kadye & Booth 2012; Weyl et al. 2016) has facilitated
their invasion across tropics; unmanaged aquaculture, and stock enhancement
being the major reasons (Weyl et al. 2016).
Although extensive information is available on the occurrence and
distribution of invasive C. gariepinus, there
has been very little focus on understanding the population dynamics of invasive
populations (Booth et al. 2010). In the
present paper, the demographics of invasive C. gariepinus
in the watershed of the Periyar National Park, an Alliance
for Zero Extinction (AZE) site, and one of the most critical habitats for
freshwater fish conservation in southern Asia (Molur
& Raghavan 2014) is determined, to inform management and conservation
action.
The Periyar
Lake-Stream system inside the Periyar National Park
(9.1600N & 76.5530E) (an IUCN Category II protected
area) is an AZE site known to harbour the only global population of three
endangered cyprinids (Hypselobarbus periyarensis, Tariqilabeo
periyarensis & Lepidopygopsis
typus) (Molur & Raghavan
2014). This critical habitat is,
however, threatened by four alien species, Oreochromis mossambicus
(Peters, 1852), Cyprinus carpio (Linnaeus, 1758), Poecilia
reticulata (Peters, 1859), and Clarias gariepinus. An
organized small-scale fishery primarily focused on gillnets (32–110 mm) is
carried out in the lake by local tribal fishers, and the resultant catch is
sold at a nearby landing centre organized by the Kerala State Forest and
Wildlife Department.
Clarias gariepinus samples (n=344) exploited using
gill nets (40–110 mm mesh size) and sold at the local landing centre, were
collected at monthly intervals from December 2018 to November 2019, measured
for standard lengths (LTS, to the nearest mm) and body weight
(MB, to the nearest g).
A large share of the sample comprised of dead fish, and only a small
number of individuals were alive at the time of collection. These were euthanized immediately by
immersing in ice-slurry. The length data
were grouped into 5cm class intervals with the smallest mid-length of
2.5cm. The length-mass relationship (MB
= aLTb) was determined
following Pauly (1984) and the parameters (a, b) were
estimated by least squares regression of log-log plot (Zar
1999). The null hypothesis that n=3
(i.e., individuals show isometric growth pattern; Froese 2006) was tested using
two-tailed t-tests. The statistical
analysis was performed in PAST 3.20 (Hammer et al. 2001).
The von Bertalanffy
growth parameters, asymptotic length (L∞) and growth coefficient (K) were
estimated from length-frequency data using the electronic length frequency
analysis I (ELEFAN I) incorporated in FAO-ICLARM Stock Assessment Tools II (FiSAT II) software (Gayanilo et
al. 2005). Based on L∞
and K values, growth performance index (Ø) and potential
longevity (3/K) were estimated (Pauly &
Munro 1984). Instantaneous total
mortality (Z) was estimated using
length-converted catch curve (Pauly 1984); natural
mortality (M) was determined by Pauly’s
empirical formula (Pauly 1980). In (M) = -0.0152-0.279, In (L∞)
+ 0.6543 In (K)+0.4634 In (T), where T is the annual mean
temperature of the water in which the fish occurs (26°C for the study area); instantaneous
rate of fishing mortality (F) was computed as F=Z–M
and exploitation rate (E) was as E=F/Z (Gulland
1970). The Emax
(maximum yield per recruit) and E50 (exploitation
that retains 50% of the biomass) were predicted using relative yield per recruit (Y/R) and relative biomass per
recruit (B/R) analysis using knife-edge selection method (Pauly 1984). From
length-converted catch curve, the length at first capture (Lc)
was analysed. Growth parameters were used to determine the reproductive
pulses per year, and the relative strength of each pulse using recruitment
analysis (Moreau & Cuende 1991). Growth and mortality parameters were used to
perform virtual population analysis (VPA) (Hilborn
& Walters 1992). Fishing mortality
was considered as the terminal fishing mortality Ft. To understand how the population in different
size classes might be affected by an increase in the fishing mortality, VPA was
performed with different values of Ft.
To develop an effective eradication plan for the local C. gariepinus population, the threshold value of Emax above which the population would be
overexploited in Y/R analysis was plotted against Lc.
To understand whether a change in the fishing regime, especially with
respect to the length of first capture, can facilitate eradication of C. gariepinus, we performed YR analysis and plotted
threshold value of Emax, above
which the population will collapse, against varying length at first capture (Lc).
Length and weight measurements of
C. gariepinus collected from the Periyar Lake ranged 17.9–86.7 cm LTs and
80–6,300 g. The LWRs was defined by the
equation W=0.0132 L2.8719, and the b value
2.8719 was significantly lower than the cubic value (t=5.0092, P<0.0001)
expected under isometry, indicating that C. gariepinus
shows a negative allometric growth pattern (A-) in the Periyar Lake. The b
value obtained in our study is similar to native C. gariepinus
populations in Kenya (2.81; Macharia et al. 2017) and introduced populations in
a reservoir in the WG (2.9; Pillai et al. 2016).
The occurrence of juveniles
(17.9cm) as well as mature females (31.5cm) suggests that the species has
successfully established and colonized the lake. The von Bertalanffy
growth curve shows an asymptotic length of 91.88cm and a growth coefficient of
0.54 year–1 (Figure 1a; Table 1) which was greater than those
observed for various native populations of C. gariepinus,
i.e., L∞: 80–124 cm, K=0.06–0.49 year–1 and
Ø=2.96–3.36 (Clay 1984; Wudneh 1998; Okogwu 2011; Tesfaye & Wolff 2015; Macharia et al.
2017). The estimated growth performance
index of 3.66 (Table 1) is also higher than that reported for C. gariepinus in its native range (Clay 1984; Wudneh 1998; Abdulkarim et al.
2009; Tesfaye & Wolf 2015). No
estimates of growth parameters are available from any invasive populations of C.
gariepinus.
The total mortality (Z) of
C. gariepinus in Periyar
Lake was estimated as 1.34 year–1 (Table 1). The natural mortality
rate of 0.84 year-1 (Table 1) is comparable to an invasive
population in South Africa (Booth et al. 2010), but lower than native
populations in Nigeria (Abdulkarim et al. 2009),
suggesting that C. gariepinus has no natural
fish predators in its invasive habitat in the WG. The low fishing mortality and exploitation
rate (Table 1), which is much below the optimum exploitation rate (Emax=0.68) indicate minimal fishing
pressure favouring population expansion.
In addition, recruitment analysis suggested continuous recruitment
throughout the year with two peaks (Figure 1b) similar to populations in Western
Africa (Kwarfo-Apegyah & Ofori-Danson 2010).
The VPA (Figure 1c) suggests a
high survival rate due to low natural mortality and fishing pressure. A simulation of VPA for increasing fishing
mortality (Figure 1d) revealed that greater fishing pressure could
exponentially reduce the juvenile population but will not result in population
eradication. Further, adult individuals
may not be significantly affected, probably because of high survival rate due
to low fishing mortality and predation.
Our analysis further suggests that using this experimental fishing
regime will not result in eradication of the local C. gariepinus
population. Analysis to understand the
changes in the fishing regime suggests that the threshold value of Emax required to overexploit the species
decreases exponentially with decrease in Lc
(Figure 1e). The length at first capture
in our experimental fishing was 29.90cm (Figure 1c), i.e. 32.54% of the
asymptotic length. Reducing this value
to below 10cm, comprising mainly of immature individuals (see Hossain et al.
2016 for size at first maturity values), will no doubt be the best management
strategy for eradication. This may be
achieved through mesh size selectivity, and specifically targeting spawning
grounds to capture young, immature individuals.
Understanding the population
biology of an invasive species is important for its long-term management (Booth
et al. 2010). Rapid growth, high growth
performance index, low fishing mortality and year-round recruitment
significantly contribute to the successful invasion of C. gariepinus in Periyar Lake,
and possibly throughout its invasive range.
Though it might be difficult to eradicate C. gariepinus
from the lake, where they have already established a strong population,
effective management and control can be achieved by targeting fish smaller than
10cm. Further studies to understand the
reproductive biology and ecology, and its links to the demographics of C. gariepinus will help inform improved management
measures for this invasive species in a critical freshwater AZE Site.
Table 1. Growth, mortality and
exploitation parameters of Clarias gariepinus from Periyar Lake.
Demographics and
exploitation parameters |
Value |
Asymptotic length (L∞;
cm) |
91.88 |
Growth coefficient
(K: year-1) |
0.54 |
Growth performance
index (Ø) |
3.66 |
Longevity (3/K;
years) |
5.56 |
Total mortality (Z:
year-1) |
1.34 |
Natural mortality (M;
year-1) at 26◦C) |
0.84 |
Fishing mortality (F;
year-1) |
0.50 |
Current
exploitation rate (E) |
0.37 |
Length at first
capture (Lc; cm) |
29.90 |
E0.1 |
0.46 |
E0.5 (Optimum) |
0.31 |
Exploitation rate
producing maximum yield (Emax) |
0.54 |
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