Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 July 2020 | 12(10): 16257–16261
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.6201.12.10.16257-16261
#6201 | Received 21 May 2020 | Final received
23 June 2020 | Finally accepted 20 July 2020
Length-weight relationships of
two conservation-concern mahseers (Teleostei: Cyprinidae: Tor) of the river Cauvery, Karnataka,
India
Adrian C. Pinder
1, Rajeev Raghavan 2, Shannon D. Bower 3 & J. Robert Britton 4
1,4 Faculty of Science and
Technology, Bournemouth University, Poole, BH12 5BB, UK.
1,2 Mahseer Trust, c/o Freshwater
Biological Association, East Stoke, Wareham, Dorset, BH20 6BB, UK.
2 Department of Fisheries Resource
Management, Kerala University of Fisheries and Ocean Studies (KUFOS), Kochi,
Kerala 682506, India.
3 Infinity SES, 507 McLeod St.,
Ottawa, Ontario, Canada.
1 apinder@bournemouth.ac.uk
(corresponding author), 2 rajeevraq@hotmail.com, 3 shannonbower@infinityses.com,
4 r.britton@bournemouth.ac.uk
Editor: Mandar Paingankar,
Government Science College Gadchiroli, Maharashtra,
India. Date of publication: 26 July 2020
(online & print)
Citation: Pinder,
A.C., R. Raghavan, S.D. Bower & J.R. Britton (2020). Length-weight relationships of
two conservation-concern mahseers (Teleostei: Cyprinidae: Tor) of the river Cauvery, Karnataka,
India. Journal of
Threatened Taxa 12(10): 16257–16261. https://doi.org/10.11609/jott.6201.12.10.16257-16261
Copyright: © Pinder
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: Pinder, Bower, and Raghavan’s participation was supported by the Fisheries
Society of the British Isles
and the Mahseer Trust. Bower was also funded by the
Ontario Graduate Scholarship,
Too Big to Ignore, and Mitacs Research Grant.
Competing interests: The authors
declare no competing interests.
Author details: Adrian Pinder is based at Bournemouth University (UK) and is the Director of Research
at the Mahseer Trust. He is a fish ecologist with a special interest in the
conservation of threatened species. Rajeev Raghavan is interested in
conservation of aquatic biodiversity of Western Ghats with special reference to
freshwater fishes. Shannon Bower’s
primary area of research is fish and fisheries, with an emphasis on
recreational fisheries, social-ecological systems analysis, sustainable
development, and partnerships. This work has taken her around the world,
offering insights into the role cultural systems and beliefs play in our
relationships with the world aquatic and the solutions we create to solve our
problems. Rob Britton is a Professor at Bournemouth University. His
research interests cover the impacts on aquatic fauna of anthropogenic
stressors, including invasive alien species, habitat loss and climate change.
Author contribution: All authors contributed equally
to the study design and data collection. ACP and JRB did the data analysis. ACP
wrote the first draft. All authors contributed equally finalizing the
manuscript
Acknowledgements: The authors wish to thank Naren Sreenivisan and the
Wildlife Association of South India (WASI) for the provision of angler catch
data from the Cauvery Wildlife Sanctuary. We thank Coorg Wildlife Society for
access to their waters for sampling purposes and all the anglers’ who
contributed to the collection of data. We are also grateful to A. Harrison for
assistance in the production of Figure 1.
Abstract: Length-weight (LW) relationships
are presented for two conservation-concern species of mahseer (Tor spp.)
from southern India’s river Cauvery.
Constructed from angler catch data, these are the first available LW
relationships for the Critically Endangered Tor remadevii
and the non-native and locally invasive Tor khudree. For T. remadevii,
the value of b, the allometric parameter, was 2.94 (95% CI: 2.75–3.14)
and was not significantly different from 3.0, indicating isometric growth (t =
0.61, P = 0.54). For T. khudree, b was greater at 3.18 (95% CI: 3.01–3.38),
but with this also not significantly different from 3.0 (t = 1.91, P =
0.06). Outputs are discussed with
reference to species conservation and recreational catch-and-release fisheries.
Keywords: Angling, Critically
Endangered, invasive fish, Tor khudree, Tor
remadevii.
Introduction
Despite its global iconic status
as a premier sport fish and the largest growing of all mahseers (Tor
spp.) (Pinder et al. 2019), the formal taxonomic
identity of the mega-faunal Hump-backed Mahseer has until recently eluded
ichthyologists since first being brought to their attention in the 19th
century (Jerdon 1849). Now known to be endemic to the Cauvery River
catchment (Pinder et al. 2015a), recent research has
confirmed this fish to be conspecific with Tor remadevii
(Pinder et al. 2018a), a species for which the formal
description was based on 19 juvenile specimens collected from the river Pambar, the southernmost tributary of the river Cauvery in
Kerala, India (Kurup & Radhakrishnan 2007,
2010). Due to estimated population
reductions in excess of 90% and an extremely limited distribution range, T. remadevii was recently assessed as Critically
Endangered on the IUCN Red List of Threated Species (Pinder
et al. 2018b), making it the most imperilled of all Tor species.
Introductions of T. khudree into the river Cauvery from the 1970s has been
implicated in the collapse of the endemic T. remadevii
population (Pinder et al. 2015a; Pinder et al. in press).
In recognition of the non-native and invasive status of T. khudree outside its native distribution range, India’s
current National Wildlife Action Plan 2017–2031, includes the action of
actively removing T. khudree from Cauvery,
through angling or other suitable means, to reduce the population of this
undesirable species. This goes
hand-in-hand with a further recommendation, that captive bred ‘orange-finned’
mahseer T. remadevii should be stocked to
assist the recovery of this endemic species (Ministry of Environment, Forests
and Climate Change, 2017). Furthermore,
due to the establishment of T. khudree beyond
its native range throughout much of southern India (see Pinder
et al. in press), this species has recently been reassessed on the IUCN Red List
from Endangered to Least Concern (de Alwis Goonatilake et al. 2020).
Here, the derivation of
length-weight relationships from data collated from angling catches on the
river Cauvery provides important biological parameters for both species for the
first time. The results are discussed in
relation to their indication of body allometry, their contributions to existing
knowledge and persisting knowledge gaps which require urgent attention to
better understand the biological and ecological mechanisms which may drive
competitive interactions between these two species. Outputs are also discussed in the context of
recreational catch-and-release fisheries and how stakeholders can utilise the
data presented here to assist the urgent conservation of T. remadevii.
Materials
and methods
Historic length-weight statistics
for T. remadevii were recovered from the
former angling camps and protected reaches of the middle River Cauvery that
extend across 24km between Doddamakali Nature Camp
(12.3070N & 77.2150E) and Mekedatu
Gorge (12.2590N & 77.4470E), Karnataka, India (Fig.
1). Data used in the analysis date from
1976 to 1990 and were seasonally restricted between the months of December and
May when river flows are suitably reduced to allow the recreational fishery to
operate. These fish were captured by
rod-and-line angling, with their fork lengths and weights recorded before
release. Lengths were measured using
non-rigid tape measures and weights from ‘spring-balances’. For the latter, due to the combination of the
size of some of the fishes (> 40kg) and their recording in field conditions,
the weights were typically recorded to the nearest 250g.
For T. khudree,
length-weight data of individual fish were collected from the upper river
Cauvery (Ammangala Village, Valnur;
12.4570N & 75.9600E, in Kodagu District (Coorg),
Karnataka, India (Fig. 1) during March 2014 and between February and April
2015. Captured using rod and line
tactics, the data for each fish were recorded by trained fishery professionals. Fish lengths (FL) were recorded using a
standard rigid measuring board (to 0.1cm) and weights recorded using a
protective weigh sling and a spring balance appropriate to individual fish size
(models: Salter Super Samson 20kg/100g and 5kg/25g). All fish were released following their
processing.
To assess the length-weight
relationships of each species, and to, thus, investigate allometry, their data
were fitted to the linear form of the length-weight power function W = aFLb, where a is the
intercept parameter (shape coefficient) and b is the regression
coefficient (allometric parameter), and where the linearised
form of the equation is ln(W) = ln(a)+bln(FL). In fishes, when the value of b is not
significantly different from 3.0 (tested here via a 2-tailed t-test), it
implies isometric growth, where there is a cubic increase in fish weight as
length increases (Ali et al. 2013). If b
is significantly lower than 3.0, it implies negative allometric growth and
significantly higher than 3.0 implies positive allometric growth (Riedel et al.
2007). Should non-isometric growth be
apparent then the factors driving this deviation can be explored (Ali et al.
2013).
Results
The length-weight relationships
were derived from a sample of 90 T. remadevii and
59 T. khudree.
The subsequent values of a and b, and their associated
statistical information, are provided in Table 1. For T. remadevii,
the value of b, the allometric parameter, was 2.94 (95% CI: 2.75–3.14)
and was not significantly different from 3.0, indicating isometric growth (t =
0.61, P = 0.54). For T. khudree, b was greater at 3.18 (95% CI:
3.01–3.38), but with this also not significantly different from 3.0 (t = 1.91,
P = 0.06). Linearised
relationship of fork length (cm) versus weight (g) for both species is provided
in Figure 2.
Discussion
The results suggest that the
growth of both the Tor species analysed were isometric, i.e., there was
a cubic increase in fish weight as length increased. These data are important in the context of
biological information on these fishes that, to date, has been extremely
limited.
Indeed, the substantial
population decline of endemic T. remadevii
that has occurred in the last 15 years now prevents the contemporary sampling
of their populations to obtain new biometric data (Pinder
et al. 2015a, 2018b). The high
historical recreational and trophy value of this fish has, however, resulted in
collection of data by anglers in previous years, enabling these data to be used
here and highlighting the inherent value of angler log books to provide
important biological data from catch data (Cooke et al. 2000; Pinder & Raghavan 2013; Pinder
et al. 2015b). This did, however, result
in the use of data collected by anglers in extreme field conditions (e.g., high
air temperatures) using relatively crude equipment (spring-balances recording
to an accuracy of 0.25kg). Nevertheless,
some of the fish in the dataset were large, over 40kg, and thus would be
inherently difficult to weigh to a greater level of accuracy unless killed and
also were unable to be captured by alternative methods to angling. Consequently, despite the method of data
collection, it is argued these data have high value in the context of this
conservation-dependent species that is currently close to extinction (Pinder et al. 2015a) and for which no adult length-weight
data currently exist.
Due to the previous taxonomic
confusion regarding the taxonomy of southern Indian Tor species (Pinder & Raghavan 2013; Pinder
et al. 2018a, 2019) many previous studies have erroneously synonymised the ‘nom
de plume’ Tor (or Barbus) mussullah (under the guise of the Hump-backed
Mahseer (now known to be T. remadevii)) with T.
khudree.
As a consequence, much of the biometric data presented in the scientific
literature, and open access resources (e.g., FishBase)
for T. khudree need to be treated with
appropriate caution. With reference to
previous scientific studies where a high level of confidence can be applied to
correct taxonomic use, the data reported here dramatically revise the maximum
lengths and weights for both species (Table 2). Moreover, despite an absence of
length records, other published data sources report weights of the Hump-backed
Mahseer (T. remadevii) to 54.4kg (Wild Life
1977) and T. khudree to 27.9kg (Pinder et al. 2015a).
The results presented here
provide the first biological data that can act as a base on which to build
knowledge that is urgently required in a conservation context to both better
understand the invasion consequences of T. khudree
and to inform planning for the population restoration of T. remadevii, including understanding novel species
interactions, and the range of biological parameters and ecological plasticity
that may drive competitive advantages between these species (Pinder et al. in press).
Given the isometric growth of
both species, these data can now be applied in a conservation context by
enabling sport anglers using catch-and-release angling techniques to keep the
fish in the water for unhooking, with weights then estimated from measured
lengths. This would eliminate a high
proportion of the manual handling and air exposure of the fish, minimising the
stress that this is known to cause, along with the associated elevated risk of
post-release mortality (Cooke & Suski 2005; Cook
et al. 2015; Bower et al. 2016).
Table 1. Length (fork, cm) weight
(g) relationship for Tor remadevii and Tor khudree from the river Cauvery, southern India, where
W=aLb, n = sample size; r2
= coefficient of determination. All
length-weight relationships were significant at P < 0.001. All data represent the first reporting of the
length-weight relationship for the species.
Species |
n |
Length range (cm) |
Mean length (cm) |
Weight range (kg) |
Mean weight (kg) |
a |
95% CI a |
b |
95% CI b |
r2 |
T. remadevii |
90 |
40–175 |
111.83 |
1.5–45.3 |
19.7 |
0.016 |
0.006–0.040 |
2.94 |
2.75–3.14 |
0.91 |
T. khudree |
59 |
15.5–83 |
34.92 |
0.06–8.8 |
0.87 |
0.007 |
0.003–0.012 |
3.18 |
3.01–3.38 |
0.95 |
Table 2. Summary of maximum
length and weights reported from this study and previous studies (*Kurup & Radhakrishnan 2007; **http://www.fishbase.org/,
version 12/2019)
Species |
Previous maximum reported size |
Data presented
here |
||
|
Max length (cm) |
Max weight (kg) |
Max length (cm) |
Max weight (kg) |
Tor remadevii |
33.2 (TL)* |
N/A |
175 (FL) |
45.3 |
Tor khudree |
50 (TL)** |
2.7** |
83 (FL) |
8.8 |
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