Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 December 2025 | 17(12): 28066–28075
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.10066.17.12.28066-28075
#10066 | Received 27 July 2025 | Final received 09 September 2025 |
Finally accepted 16 December 2025
Distribution of Smooth-coated
Otters (Mammalia: Carnivora: Mustelidae: Lutrogale perspicillata)
in the coastal mangroves of Maharashtra: a case study of Savitri River and Kalinje Mangrove Ecosystem
Swanand R. Patil
1 & Manas Manjrekar 2
1 Arcane Conservancy, A 207 Saikrupa, BS Road, Dadar West, Mumbai, Maharashtra 400028,
India.
2 Research and Capacity Buildling, Mangrove and Marine Biodiversity Conservation
Foundation of Maharashtra, India.
1 swanandpatil6@gmail.com
(corresponding author), 2 dd.research.mfn@gmail.com,
Editor: Anonymity requested. Date of publication: 26 December 2025 (online & print)
Citation: Patil, S.R. & M. Manjrekar (2025). Distribution
of Smooth-coated Otters (Mammalia: Carnivora: Mustelidae:
Lutrogale perspicillata)
in the coastal mangroves of Maharashtra: a case study of Savitri River and Kalinje Mangrove Ecosystem. Journal of Threatened Taxa 17(12): 28066–28075. https://doi.org/10.11609/jott.10066.17.12.28066-28075
Copyright: © Patil & Manjrekar 2025. 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: Mangrove and Marine Biodiversity Conservation Foundation of Maharashtra (Mangrove Foundation) dated MFN/DDR&CB/553/2022-2023.
Competing interests: The authors declare no competing interests.
Author details: Swanand R. Patil, founder and director - Arcane Conservancy Trust. Member IUCN SSC Otter Specialist Group. He is
a wildlife biologist working on the ecology and conservation of otters and small carnivores in riverine and mangrove ecosystems of India, with experience in field surveys, camera trapping, and community-based conservation. Dr. Manas Manjrekar, deputy director - Research and Capacity Buidling - Mangrove Foundation. He co-ordinates the research projects and capacity building, training and awareness programmes related to coastal and marine biodiversity conservation of the Mangrove Foundation in Maharashtra.
Author contributions: SRP has conceptualized and designed they study; conducted field surveys, sign surveys, and data collection; performed data analysis and interpretation; and led manuscript writing and revisions. MM provided project faciliation, administration support, and coordination with revelant authorites, and contributed inputs towards study planning and implementation. Both authors reviewed and approved the final manuscript.
Acknowledgements: We sincerely thank the Mangrove Foundation, Goverment of Maharashtra, for financial support that made this study possible. We would also like to thank the executive director and the joint director of the Mangrove Foundation and the field staff of the Mangrove Cell for their support during the study. We would also like extend the gratitude to the reviewers whose comments improved the quality of this manuscript.
Abstract: This study aimed to document the
distribution of Smooth-coated Otters Lutrogale
perspicillata within two ecologically distinct
but poorly studied habitats in Maharashtra.: the Savitri River covering a 65 km
stretch from Mahad to Bankot in Ratnagiri District,
and the Kalinje Mangrove encompassing 8.4 km2
in Raigad District. Using indirect sign surveys, we estimated that otters
occupied 36% of the surveyed length of the Savitri River and 13% of the Kalinje Mangrove area. Encounter rates were recorded at
0.65 signs/km in the Savitri River, and 0.41 signs/km in the Kalinje Mangrove. These observations contribute to baseline
understanding of otter habitats in these landscapes and offer useful insights
for conservation. Promoting long-term protection of otters will require
collaboration with diverse stakeholders including fisherfolk, students and
local forest departments to foster awareness, encourage co-existence, and
integrate otter conservation into community-based stewardship.
Keywords: Encounter rate, GIS, habitat,
otter conervation, percentage of occurrence,
research, survey.
INTRODUCTION
India is home to three otter species: the Smooth-coated
Otter Lutrogale perspicillata,
the Asian Small-clawed Otter Aonyx cinerea, and the Eurasian Otter Lutra
lutra. Since most freshwater sites lie outside
protected areas or Ramsar-listed wetland sites, otter
populations face threats from land use changes. According to the Amendments in
the Wild Life (Protection) Act, 2022, these otters are listed as Schedule
species, prohibiting hunting, trapping, trade, or killing. Populations continue
to decline due to unsustainable development, large-scale wetland conversion,
deteriorating water quality, and poaching (Duplaix
& Savage 2018).
In the tropics, protected areas
occupy less than 10% of the total area, and a substantial amount of
biodiversity exists outside protected areas (Schmitt et al. 2009). In
landscapes lacking protected areas, human-modified landscapes often provide
critical habitats and refuges for biodiversity (Chazdon
et al. 2009). As protected areas continue to shrink
and human-modified landscapes continue to expand, conservation and research
attention must be focused on these heterogeneous landscapes, especially river
basins. Conservation of charismatic species like otters in such a heterogeneous
landscape is critical, as they occupy some of the best habitats available for
them. The habitats are essential for otters, providing space for spraint
deposition, grooming, and creation of holts (dens), which play a vital role in
their social interactions and in marking territories.
Our main objective is to improve
the understanding of Smooth-coated Otters in the Kalinje
Mangrove of Raigad District, and along the Savitri River between Raigad and
Ratnagiri districts of Maharashtra.
METHODS
Study Area
Kalinje (18.039o N, 73.029o
E) is a small village situated between Harihareshwar
and Shrivardhan, known for its stunning mangroves and
diverse wildlife. Most people residing here are either fishermen, drivers, or
employees. In recent years, mangrove tourism has become popular as more and
more people are recognizing the values of this unique ecosystem. The Mangrove
Foundation of the Maharashtra Forest Department has undertaken a
community-based conservation initiative, called Kalinje
Ecotourism, for the upliftment of local communities.
Savitri River (18.048o
N, 73.165o E) is one of five rivers originating from Mahabaleshwar
in Maharashtra. It flows through Bankot Village en route to the Arabian Sea, and
forms a natural boundary between Ratnagiri and Raigad districts. Most villagers
residing on the banks of the Savitri are involved in fishing and agriculture.
Baseline data on the distribution
of otters in Raigad, Maharashtra.
Sign surveys: For the study of the
distribution of otters and their habitat preference, the sign survey method was
used. Sign surveys are generally done by looking for indirect evidence of the
species such as scat/spraints (Image 11), latrines, pugmarks (Image 8),
leftover food, and dens/burrows/holts (Images 9 & 10). Our study area was
divided into multiple transects of 1,000 x 50 m (Prakash et al. 2012; Atul et
al. 2014; Patil & Yardi
2022). To ensure spatial independence, transects werelaid
at intervals of 500 m. The study area was thoroughly surveyed for “otter sites”
(signs/evidence of otter presence) and “non-otter sites” (signs/evidence of
otter absence), recording:
Date and time of the survey.
GPS location.
The presence & absence of
otter signs.
Anthropogenic activities or any
other disturbances.
Den locations: The active dens
were noted as “active plots” and inactive dens were marked as “inactive plots”
(Images 9 & 10).
Spatial habitat data: GIS software was used to map
down vegetation cover, otter distribution, and denning sites along the river
stretch. As vegetation cover plays a major role in the selection of denning
sites, it served as an aid in the evaluation of potential wildlife habitats.
Observed anthropogenic activities along the river stretch were also mapped to
understand the impact on the distribution pattern of otters.
Analysis: To estimate the percentage of
area occupied by otters, we used Principal Component Analysis (PCA) coupled
with logistic regression. These scores were considered as percentages of the
Occurrence of Otters.
Encounter rate method: Based on the survey/transect
length, which was Savitri River as well as Kalinje
Mangrove. The transect length was kept the same throughout the site and
duration (Manjrekar & Prabu 2014).
No. of sightings
Encounter Rate = ––––––––––––––––
Total km covered
The analysis was carried out
separately for both Savitri and Kalinje. We also analysed seasonal encounter rates by considering
pre-monsoon and post-monsoon surveys.
RESULTS
Savitri River
To achieve the study’s
objectives, a 1 x 1 km grid was deployed along the entire Savitri River,
starting from Mahad to Velas, using Google Earth and
ArcGIS software. A total of 124 grids were created along the Savitri River
(Image 2).
Of these, 103 transect surveys
were conducted, covering the river from Bankot to
Mahad on the right bank and from Mahad to Bagmandala
on the left bank. Certain sites, such as Umroli and Nigdi, remained inaccessible owing to presence of
crocodiles (Image 3). Out of the 124 grids, 92 were surveyed, with 34 grids
showing positive otter presence.
From the 103 surveys conducted
along the Savitri River, 37 surveys yielded positive otter signs (Image 7),
indicating that 36% of the area was occupied by otters. The sign surveys were
influenced by tidal variations (high and low tides), which affected the
detection probability of signs. In total, 67 otter signs were observed during
the surveys, including denning areas (holts) and defecation areas, primarily on
mangrove island patches.
Kalinje Mangrove
A total of 19 grids were created
in the Kalinje Mangrove (Image 4). Each grid had a
survey transect with fixed replicates. These surveys assessed the presence or
absence of otters, recorded habitat parameters, and noted any threats to the
habitat. Additionally, camera trapping was conducted at selected sites based on
the presence of direct and indirect otter signs. A total of 296 hours were spent on camera trapping across the Kalinje
and Savitri areas (Images 5 & 6).
In the Kalinje
Mangrove, 19 grids were surveyed, and 39 transects were conducted. Priority was
given to active otter sites to maximize sightings. Surveys were also carried
out at and near fish and prawn farms, where informal interviews with workers
confirmed regular otter visits. A total of 12 boat surveys were also conducted.
Two FnX IR Camera traps were deployed in areas with a
high concentration of otter signs, such as defecation or denning areas.
Of the 19 grids surveyed, 8
showed otter signs in the Kalinje Mangrove (Image 7).
From the 39 surveys conducted, five yielded positive otter signs, contributing
to an estimated 12.82% of the area occupied by otters. A total of 16 otter
signs were recorded, with six signs observed in mangrove patches and 10 signs
on muddy embankments near prawn farms, particularly on the ‘bandhs’ (Hindi: Mud
embankments) of abandoned prawn farms.
Comparative Seasonal Analysis
Between May 2022 and February
2023, 103 surveys were conducted along the Savitri River and 39 transects in
the Kalinje Mangrove. The total distance covered was
103 km for the Savitri River and 39 km for the Kalinje
Mangrove. The encounter rate for otter signs (pugmarks and spraint) was 0.65
signs/km along the Savitri River and 0.41 signs/km in the Kalinje
Mangrove.
Seasonal patterns were analyzed
to understand otter detection probability during pre- and post-monsoon seasons
(May–June and November–January). Due to the shorter study duration in the
pre-monsoon period, achieving the same number of surveys for each season was
challenging.
For the pre-monsoon season, three
surveys were conducted in the Kalinje Mangrove and 15
in the Savitri River, resulting in detection probabilities of 0.53 signs/km and
0.66 signs/km, respectively. In the post-monsoon season, 88 transects were
conducted along the Savitri River and 36 in the Kalinje
Mangrove, yielding encounter rates of 0.67 signs/km and 0.38 signs/km, respectively.
Conclusions
The estimated proportion of the
length of Savitri River occupied by Smooth-coated Otters was 36% based on our
sign survey. This suggests that otters are relatively widespread across
approximately one-third of the surveyed areas, utilizing different sections of
the river for foraging, resting, denning, and other activities. In contrast,
the Kalinje Mangrove showed a lower occupancy rate of
12.8%, indicating a more limited distribution of otters in this habitat.
Our encounter rates of 0.65
signs/km in the Savitri River and 0.41 signs/km in the Kalinje
Mangrove reflect the challenges of detecting otter signs in dynamic
environments where tides regularly submerge and expose the riverbanks. This
fluctuation likely reduces the visibility of otter signs, impacting the
detection probability and suggesting that our estimates may be conservative.
The principal component analysis
(PCA) further supports these observations. In Savitri River, PC1 accounted for
35.9% of the variance and revealed that otter presence is positively associated
with key riverine features such as main river channels, creeks, bandhs, and
sandy banks. These variables were consistently linked to habitat use,
underscoring their ecological importance. In contrast, PC2 in the Kalinje Mangrove accounted for 12.8% of the variance, with
otters showing a preference for creeks and bandhs, although the overall
influence of habitat variables was lower, reflecting limited habitat
suitability in this mangrove-dominated system. Additionally, farmland and rocky
banks were negatively associated with otter presence across both landscapes,
likely due to disturbance and poor suitability for resting and denning. These
results suggest that otters prefer relatively undisturbed, structurally diverse
aquatic environments, and actively avoid modified banks.
The survey suggests that without
such baseline data, there will be a lack of informed decision-making, which
might lead to a further decline in the population of the species or its
suitable habitat. The presence/absence data will be vital in creating
conservation hotspots.
A significant amount of otter
distribution lies outside protected areas, emphasizing the need for research
projects that can generate information on such species. This information could
be useful in future with respect to undertaking sustainable developmental
activities and implementing effective conservation measures (Defries et al. 2010).
Advances in technology such as
camera traps have proven invaluable in this research. These tools allow for the
non-intrusive monitoring of otters, providing insights into their behaviour and activity patterns.
In conclusion, this study
highlights the need for ongoing research and the integration of modern
technologies in wildlife conservation. Our data suggest that otters have a
relatively widespread distribution over approximately one-third of the surveyed
area, utilizing different sections of the river for foraging, resting, denning,
and other activities.
Table 1. Results
of principal component analysis with eigenvalues,
percentage of variance, and the
contribution of habitat variable of Smooth-coated
Otters in Savitri River
(PC1) and Kalinje Mangrove
(PC2).
|
Variable |
PC1 – Savitri River |
PC2 – Kalinje
Mangrove |
|
Main River |
0.740 |
0.180 |
|
Creek |
0.690 |
0.540 |
|
Bandh |
0.710 |
0.480 |
|
Sandy Bank |
0.650 |
0.320 |
|
Farmland |
-0.600 |
-0.620 |
|
Rocky Bank |
-0.670 |
-0.220 |
|
Elgen Values |
4.31 |
1.54 |
|
% Variance |
35.92% |
12.82% |
|
%Cumulative Variance |
35.92% |
48.74% |
Table 2. Table
summarizing the key results for both study locations.
|
Parameters |
Savitri River |
Kalinje Mangrove |
|
Total length |
65.26 km |
8.40 km2 |
|
Total number of grids |
124 |
19 |
|
Total number of grids surveyed |
92 |
18 |
|
Total number of transects
carried |
103 |
39 |
|
Encounter rate |
0.65 signs/km |
0.41 signs/km |
|
Detection probability
pre-monsoon |
0.53 signs/km |
0.66 signs/km |
|
Detection probability
post-monsoon |
0.67 signs/km |
0.38 signs/km |
Table 3. GPS locations
of otter signs.
|
|
Latitude |
Longitude |
Type of sign |
Species ID |
|
1 |
17.985 |
73.081 |
Defecation area |
Smooth-coated Otter |
|
2 |
17.98586 |
73.084 |
Scat/Spraint |
Smooth-coated Otter |
|
3 |
17.985 |
73.085 |
Scat/Spraint |
Smooth-coated Otter |
|
4 |
17.985 |
73.086 |
Scat/Spraint |
Smooth-coated Otter |
|
5 |
17.984 |
73.087 |
Scat/Spraint |
Smooth-coated Otter |
|
6 |
17.984 |
73.087 |
Scat/Spraint |
Smooth-coated Otter |
|
7 |
17.981 |
73.092 |
Scat/Spraint |
Smooth-coated Otter |
|
8 |
17.981 |
73.092 |
Scat/Spraint |
Smooth-coated Otter |
|
9 |
17.981 |
73.092 |
Scat/Spraint |
Smooth-coated Otter |
|
10 |
17.981 |
73.094 |
Scat/Spraint |
Smooth-coated Otter |
|
11 |
17.98094 |
73.095 |
Defecation area |
Smooth-coated Otter |
|
12 |
17.979 |
73.098 |
Defecation area |
Smooth-coated Otter |
|
13 |
17.980 |
73.098 |
Defecation area |
Smooth-coated Otter |
|
14 |
18.04178 |
73.038 |
Defecation area |
Smooth-coated Otter |
|
15 |
18.048 |
73.046 |
Defecation area |
Smooth-coated Otter |
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FULL PDF
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