Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 July 2020 | 12(10): 16251–16256
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
doi: https://doi.org/10.11609/jott.5700.12.10.16251-16256
#5700 | Received 14 January 2020 | Final
received 16 June 2020 | Finally accepted 19 June 2020
Ecology of the Critically
Endangered Singidia Tilapia (Teleostei:
Cichlidae: Oreochromis esculentus)
of lake Kayanja, Uganda and its conservation
implications
Richard Olwa
1, Herbert Nakiyende 2, Elias Muhumuza 3, Samuel Bassa
4, Anthony Taabu-Munyaho 5 &
Winnie Nkalubo 6
1,2,3,4,6 National Fisheries Resources
Research Institute (NaFIRRI), Plots 39-45, Nile
Crescent P.O. Box 343, Jinja, Uganda.
5 Lake Victoria Fisheries
Organization (LVFO), Plot 7B/E Busoga Square Bell Avenue P.O. Box 1625, Jinja,
Uganda.
1 richardolwa@gmail.com (corresponding
author), 2 nakiyende@yahoo.ie , 3 e_muhumuza@yahoo.com, 4
sambasa37@yahoo.co.uk, 5 ataabum@yahoo.com ,6 wnkalubo@yahoo.co.uk
Editor: Neelesh Dahanukar,
IISER, Pune, India. Date of publication: 26 July 2020
(online & print)
Citation: Olwa,
R., H. Nakiyende, E. Muhumuza,
S. Bassa, A. Taabu-Munyaho
& W. Nkalubo (2020). Ecology of the Critically
Endangered Singidia Tilapia (Teleostei:
Cichlidae: Oreochromis esculentus)
of lake Kayanja, Uganda and its conservation
implications. Journal of Threatened Taxa 12(10): 16251–16256. https://doi.org/10.11609/jott.5700.12.10.16251-16256
Copyright: © Olwa
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: This study was
carried out with financial
support from The Rufford
Small Grants Foundation, The Pro Natura Foundation Japan and
The Mohamed Bin Zayed Species Conservation
Fund.
Competing interests: The authors
declare no competing interests.
Author details: Richard Olwa is a
researcher with National Fisheries Research Institute currently managing a
project to conserve threatened fishes through creation of community
conservation area. Herbert Nakiyende is a research scientist with NaFIRRI, he heads the department of capture fisheries and
aquatic biodiversity conservation. Elias Muhumuza and Samuel
Bassa are researchers working with NaFIRRI to conserve and protect fisheries resources through
innovative research. Dr. Winnie Nkalubo is the Director of Research with National
Fisheries Research Institute and Dr.
Anthony Taabu-Munyaho is the Deputy Executive
Secretary for Lake Victoria Fisheries Research Organization, Uganda.
Author contribution: RO,
the principal investigator secured funds for this study, led the field team and
participated in data collection, analysis and writing of this article. HN, EM
and SB collected and analyzed data and wrote this article. WN provided technical advice, guidance and
support to the field team to facilitate successful implementation of the study
and writing of this manuscript. AT-M provided technical advice and reviewed
this article.
Acknowledgements: Our outmost credits go to The Pro
Natura Foundation Japan, Rufford Small Grant
Foundation, and The Mohamed Bin Zayed Species Conservation Fund for providing
financial support for this study.
Appreciations to associate professor Yasuaki Sato of Osaka Sangyo
University, Japan for his guidance, advise, and support which made this study
successful. We convey our gratitude to
government representatives particularly district fisheries officer and
assistant fisheries officer of Masaka for their
guidance, technical support and participation in data collection and
mobilization of local communities.
Appreciation goes to the National Fisheries Resources Research Institute
of Uganda for allowing time for Richard Olwa, Herbert
Nakiyende, Bassa Sammuel, and Elias Muhumuza to be
away from office duty to collect data, write, and review this article. We are grateful for the contribution of Dr. Winnie Nkalubo and Dr. Anthony Taabu-Munyaho of
National Fisheries Resources Research Institute for their technical guidance,
support, and valuable inputs. Thanks to
the lake Kayanja communities, especially the
fishermen and local leaders, for sacrificing their valuable time in
implementing the activities of the project.
Abstract: Singidia Tilapia Oreochromis esculentus is a Critically Endangered native tilapia
fish species endemic to lakes Victoria and Kyoga basins of East Africa,
however, it disappeared from these main lakes due to overfishing, environmental
degradation and predation by the introduced Nile Perch Lates
niloticus.
Remnant populations of this fish species is now restricted to satellite
lakes including Lake Kayanja of the Victoria
basin. This study provides updated
information about the population abundance, critical habitat, threats and diet
of Singidia Tilapia to inform conservation decisions
to revive its populations in the wild.
Fish data collection and mapping of nursery and breeding habitats of Singidia Tilapia on Lake Kayanja
was conducted between February 2016 and October 2017. In all the areas mapped and sampled, Singidia Tilapia (with a size range of 11–27 cm TL) was the
most abundant (43%) relative to exotic Nile Tilapia Oreochromis niloticus (21%) and Redbelly Tilapia Coptodon zillii
(36%). The emergence of introduced
(exotic) tilapias like Nile Tilapia recorded in this study could be attributed
to cage fish farming being carried out in this Lake. The diet of Oreochromis esculentus consisted mainly of detritus (60.8 %), plant
materials (27.7%) and blue-green algae (5.5%).
Destruction of critical habitats and presence of introduced fish species
were noted as the major threats to this fish and its habitats. The generated information could contribute to
guiding stakeholders to undertake appropriate actions to conserve this
threatened fish species and its habitats.
Keywords: Africa, conservation, Cichlid
fishes, recovery, threatened fishes.
INTRODUCTION
Singidia
Tilapia Oreochromis esculentus is a Critically
Endangered indigenous tilapiine cichlid (Twongo et al. 2006), endemic to lakes Victoria and Kyoga
basins of eastern Africa (Nagayi-Yawe et al.
2006). This fish species has suffered a
large reduction in extent of occurrence and is now restricted to a few refuge
impoundments and satellite lakes such as Kayanja of
the Victoria basins (Balirwa et al. 2000; Ogutu-Ohwayo & Balirwa
2006). Many researchers have documented
factors attributing to the decline in the populations of Singidia
Tilapia including the aggressive competition for food, spawning, and nursery
grounds with introduced Nile Tilapia Oreochromis niloticus,
predatory actions of Nile Perch (Mwanja et al. 2012),
and environmental degradation like pollution, habitat modification,
fragmentation & loss (Balirwa et al. 2003;Dudgeon
et al. 2006; Ogutu-Ohwayo & Balirwa
2006; Chapman et al. 2008; Njiru et al. 2008;
Lowe-McConnell 2009). Since this species
was assessed and published as Critically Endangered (Twongo
et al. 2006), no active research has been carried out to learn more about its
distribution patterns and population status, therefore, additional research was
needed to provide updated information and data about the feeding behavior,
population status, threats to its critical habitat and distribution to inform
conservation actions to halt the extinction of this species in the wild.
METHODS AND
MATERIALS
The study was implemented on Lake Kayanja, one
of the satellite lakes of Lake Victoria basin.
It is geographically located at 0.2830S & 31.8670E
(Figure 1). This Lake is
administratively found in the sub-county of Bukakata,
Masaka District in the central region of Uganda and
lying west of lake Victoria. The
habitats of lake Kayanja are dominated by wetlands
and riverine forests which provide structural heterogeneity for fish to escape
from predators, and thus having special significance for conservation of lake
Victoria’s fauna. A reconnaissance
survey was conducted to identify the sampling sites within the lake based on
indigenous knowledge of fishermen and key habitat characteristics including
lake depth, vegetation cover, and human activities in the vicinity. Three sites namely; Kawunguli,
Kasanje, and Bugiri were
selected for fish surveys to collect primary data on Singidia
Tilapia.
Collection of fish data
Fish surveys were conducted at pre-selected experimental sites for
collection of primary fish data.
Experimental gill-netting and electro-fishing techniques (Image 1 and 2)
were used to collect fish samples. At
each site, three fleets of graded multi-filament gill nets of mesh sizes
ranging from 25.4–139.7 mm at an interval of 12.7mm and sizes 152.4–203 mm at
25.4mm intervals. The fleets were set
parallel to the lake shoreline towards open water in the evening (17.00–18.00
h) and retrieved at dawn (05.00–06.00 h) the following morning. At each study site, geographical coordinates
were recorded using a Global Positioning System (GPS). At the shallow inshore areas of each site,
fish populations were sampled using a pulsed electro-fisher with an eight-watt
generator and two anodes (Amisah & Cowx 2000). Two
30-minute runs were made at each site at an interval of 15 minutes to allow
processing of the catch and recovery of conditions for fish re-occupancy. All the fish caught were measured for total
and standard lengths (TL and SL) in centimeters, and identified to species
level according to Greenwood (1966) guidelines.
A total of 45 fish stomachs of Singidia
Tilapia, Nile Tilapia, and Coptodon zillii indicating presence of any food were dissected
out, contents evaluated and preserved in 5% formalin solution in separate
numbered bottles for further analysis in the laboratory. The analysis of gut contents of preserved
stomachs followed procedures reviewed by Elliott & Bagenal
(1979). After rinsing the preserved
stomachs with tap water and blotting off the excess water, the contents of each
stomach to be analyzed were emptied into a petri-dish. Binocular (x10-80) and compound (x600)
microscopes were used to identify the contents.
At the lower magnification, large food items, such as, insects, fish or
their remains were identified and quantification was based on the point’s
method (Hynes 1950). All the collected
data were analyzed using excel spreadsheet to determine relative population
abundance, percent composition of the diet.
ArcGIS was used to generate distribution maps and critical habitats of Singidia Tilapia.
Mapping of critical habitats
A combination of scientific and indigenous knowledge was used to
identify and map critical sites such as spawning and nursery grounds vital for
the survival of Singidia Tilapia (Image 3) using the
GPS. The criteria used to map these
sites were based on known indicators such as presence of both mature (breeding)
and young (immature/juvenile) Singidia fish, and
characteristics of habitats such as shallow muddy bottom, presence of breeding
substrates like water lily, river inlets, and riverine forest preferred by of Singidia Tilapia
RESULTS AND
DISCUSSION
Distribution and abundance of Singidia Tilapia
Singidia
Tilapia was mostly found in areas identified and mapped as breeding and nursery
areas (Figure 1; Image 4). A total of
eight breeding sites of Singidia Tilapia were mapped
in lake Kayanja (Figure 1). These critical sites are characterized by
known indicators like shallow muddy bottoms, presence of waterweeds such as
water lily, river inlets, and riverine forest.
The surveys also revealed presence of introduced (exotic) tilapiines, i.e., Nile Tilapia Oreochromis niloticus and Redbelly Tilapia Coptodon zillii.
Population and abundance of Singidia tilapia
A total of 1,956 fish specimens representing 16 fish species were
collected from the study area, of which 43 individuals were Singidia
Tilapia, 21 were Nile Tilapia, and 36 were Redbelly Tilapia. Singidia Tilapia
was the most abundant (43%) relative to introduced (exotic) Nile Tilapia (21%)
and Redbelly Tilapia
(36%) in the study area. In terms of
numbers, Singidia Tilapia was most abundant in Bugiri followed by Kawunguli
sites, while Nile Tilapia was abundant in Kasanje
(Figure 2). The variability in the
distribution of Singidia Tilapia in lake Kayanja could be attributed mainly to habitat
characteristics, for example, Kawunguli and Bugiri sites are dominated by shallow muddy bottom, breeding
substrates like water lily, and river inlets which are preferred habitats for Singidia Tilapia.
The high number of Nile Tilapia in Kasanje
could be attributed to presence of the cage of Nile Tilapia in this area; we
believed some of these Nile Tilapia fish must have escaped to the surrounding
water from the cage.
Diet of Singidia Tilapia and the introduced
fish species
A total of 45 fish stomachs of Singidia
Tilapia, Nile Tilapia and Redbelly Tilapia were collected and analyzed to
determine their feeding behaviors. The
diet of Singidia Tilapia consisted of detritus
(60.8%) followed by plant materials (27.7 %), blue-green algae (5.5 %),
zooplanktons (4.5% and others (1.5%).
The Nile Tilapia was feeding mainly on plant materials (69.5%) followed
by fish remains (24.3%), and detritus (6.3%) (Figure 3). Coptodon zillii fed mainly on plant materials (68.7%) and
insects (29.3%). Plant materials were
the main diet for Nile Tilapia and Coptodon
zillii while Singidia
Tilapia fed mainly on detritus. Coptodon zillii fed
more on insect remains than any of the targeted fish species. This finding complements on what other
researchers have documented about the dietary requirement of native tilapias
and introduced tilapias (Nagayi-Yawe et al. 2006; Mwanja et al. 2012; Ogutu-Ohwayo
1990; Lowe-McConnell 2009).
The key threats to Singidia
Tilapia fish species
This study revealed the transformation of lakeshore into farmlands and
presence of introduced or exotic fish species were major threats that could
jeopardize the ecological integrity of lake Kayanja
and the conservation of endangered fishes in future. The following were some of the unwarranted
activities being undertaken on lake Kayanja and its
catchment areas
Cage fish farming of Nile tilapia in lake Kayanja
(Image 5), which competes with Singidia Tilapia for
food, spawning, and nursery ground.b)
Destruction of the buffer zones as result of cultivating crops up to the
lake shores (Image 6), and increasing the chances of unused agro-chemicals
such as fertilizers from farms to enter these lakes through surface runoffs,
thus polluting the aquatic environment, in addition to burning of vegetation by
fishermen.
Poor waste disposal and management due to the beach established for
recreational, leisure, and special events and activities at the shores of lake Kayanja. Generally
during and after such events, many contaminated polythene papers,
non-biodegradable plastic bottles, and human wastes find their way into the
lake, thus polluting the aquatic ecosystem.
Conclusions and
Recommendations
During the 19th and 20th centuries, Singidia Tilapia was one of the most abundant and important
artisanal and commercial fish species in Uganda. It disappeared from the main lakes such as
Victoria and Kyoga due to environmental degradation, predatory actions of the
Nile Perch, and aggressive competition for food & space from introduced
fishes particularly Nile Tilapia Oreochromis niloticus. Remnant populations of this fish species are
now surviving in satellite lakes like Kayanja. This lake is, therefore, acting as functional
refuge habitat for this Critically Endangered fish and other aquatic resources
that support the livelihoods of millions of people in Uganda. From this study, fish habitat modification,
fragmentation and loss, and presence of introduced or exotic fish species were
noted as the major threats that could jeopardize the ecological integrity of
lake Kayanja to support the conservation of
endangered fishes in future. The
following recommendations need to be undertaken by all the relevant
stakeholders to halt the risk of extinction of this fish species and other
vital aquatic resources in lake Kayanja
Recommendations
a) Engagement of all stakeholders
particularly government agencies and fishermen in best practices to abate,
minimize, and mitigate threats to fish and their habitats in Uganda.
b) Proper management guidelines
for satellite lakes to regulate and control development activities such as cage
fish farming, agriculture within and around these lakes.
c) Development and implementation
of strategic recovery plans to revive the population of Critically Endangered
fishes including Singidia Tilapia in the wild.
d) Gazettement, monitoring, and
protection of critical habitats for native tilapias not only in lake Kayanja, but also in other satellite lakes.
e) Promotion of fishing community
involvement in the conservation and management of satellite lakes fisheries
resources in Uganda.
f) Enhancement of public awareness about satellite lakes fisheries
resources among all stakeholders to make them know the values and contribution
of these resources to their wellbeing and livelihoods, as well as the actions
they need to undertake to conserve and sustainably use these resources.
For figures
& images - - click here
References
Amisah, S. & I.G. Cowx (2000). Response of the fish populations of the River Don in south Yorkshire to
water quality and habitat improvements. Environmental Pollution 108(2):
191–199. https://doi.org/10.1016/s0269-7491(99)00190-6
Balirwa, J.S., C.A. Chapman, L.J. Chapman, I.G. Cowx,
K. Geheb, L. Kaufman, R.H. Lowe-McConnell, O.
Seehausen, J.H. Wanink, R.L. Welcomme
& F. Witte (2003). Biodiversity and fishery
sustainability in the lake victoria basin: An
unexpected marriage? BioScience 53(8):
703–715. https://doi.org/10.1641/0006-3568(2003)053[0703:BAFSIT]2.0.CO;2
Balirwa, J.S., F. Witte, R.L. Welocomme, L. Chapman
& R.H. McConnell (2000). The Role of Conservation in
Biodiversity and Fisheries Sustainability. In: Lake Victoria 2000: a New
Beginning. International Conference, 16th–19th May, 2000, Jinja, Uganda. Book
of abstracts.
Chapman, L.J., C.A. Chapman,
L. Kaufman, F. Witte & J.S. Balirwa (2008). Biodiversity conservation in African inland waters: Lessons of the Lake
Victoria region. SIL Proceedings, 1922–2010. https://doi.org/10.1080/03680770.2008.11902077
Dudgeon, D., A.H. Arthington, M.O. Gessner, Z.I. Kawabata, D.J. Knowler, C. Lévêque, R.J. Naiman, A.H. Prieur-Richard, D.
Soto, M.L.J. Stiassny & C.A. Sullivan (2006). Freshwater biodiversity: Importance, threats, status and conservation
challenges. Biological Reviews of the Cambridge Philosophical Society
81(2): 163–182. https://doi.org/10.1017/S1464793105006950
Elliott, J.M. & T.B. Bagenal (1979).
Methods for Assessment of Fish Production in Fresh Waters. The Journal of
Animal Ecology 48(1): 329. https://doi.org/10.2307/4121
Greenwood, P.H. (1966). The Fishes of Uganda. The Uganda Society,
Kampala, 131pp.
Hynes, H.B.N. (1950). Food of the freshwater stickle-backs (Gasterosteus
aculeatus and Pygosteus pungitius)
with a review of methods used in the studies of the food of fishes. Animal
Ecology 19(1): 36–58.
Lowe-McConnell, R. (2009). Fisheries and Cichlid Evolution in the African Great Lakes: Progress
and Problems. Freshwater Reviews 2(2): 131–151. https://doi.org/10.1608/FRJ-2.2.2
Mwanja, W.W. P.A. Fuerst & L.
Kaufman (2012). Reduction of the “ngege”, Oreochromis esculentus (Teleostei: Cichlidae)
populations, and resultant population genetic status in the Lake Victoria
Region. Uganda Journal of Agricultural Sciences 13(2): 65–82.
Nagayi-Yawe, K.J., R. Ogutu-Ohwayo, Y.S. Kizito &
J.S. Balirwa (2006).
Population characteristics of Oreochromis esculentus
in the Victoria and Kyoga lake basins. Implications for conservation and
improvement of the stocks. African Journal of Ecology 44: 423–430. https://doi.org/10.1111/j.1365-2028.2006.00645.x
Njiru, M., J. Kazungu, C.C. Ngugi, J. Gichuki & L. Muhoozi (2008). An overview of the current status of Lake Victoria fishery:
Opportunities, challenges and management strategies. In: Lakes and Reservoirs:
Research and Management 13(1): 1–12. https://doi.org/10.1111/j.1440-1770.2007.00358.x
Ogutu-Ohwayo, R. (1990). The decline of the native
fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced
species, especially the Nile perch, Lates niloticus, and the Nile tilapia, Oreochromis niloticus. Environmental Biology of Fishes 27:
81–96. https://doi.org/10.1007/BF00001938
Ogutu-Ohwayo, R. & J.S. Balirwa (2006). Management challenges of freshwater fisheries in Africa. Lakes and
Reservoirs: Research and Management 11(4): 215–226. https://doi.org/10.1111/j.1440-1770.2006.00312.x
Twongo,
T.K., J.D.R. Bayona & M. Hanssens
(2006). Oreochromis esculentus. The
IUCN Red List of Threatened Species 2006: e.T15457A4587658. Downloaded on 16
June 2020. https://doi.org/10.2305/IUCN.UK.2006.RLTS.T15457A4587658.en