Aquatic fauna Survey of the Kovi Water
Catchment, Guadalcanal Island,
Solomon Islands
by David Boseto
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Contents
Title............................................................................................................................................1
Contents.................................................................................................................................... 2
Acknowledgment...................................................................................................................... 3
Summary................................................................................................................................... 3
1.0 Introduction.........................................................................................................................4
1.1 Aim of the survey and report...............................................................................................5
2.0 Study Sites….......................................................................................................................5
2.1 Types and Description….....................................................................................................5
2.2 Survey Method....................................................................................................................7
2.3 Taxa Identification……...…………...................................................................................7
3.0 Results…………………………….....................................................................................8
3.1 Fish…..................................................................................................................................8
3.2 Prawns…….........................................................................................................................9
3.3 Snails..................................................................................................................................10
3.4 Introduced species .............................................................................................................11
3.5 Other observation.............................................................................................................. 12
4.0 General Discussions.......................................................................................................... 12
5.0 Conclusion and Recommendations................................................................................... 13
6.0 Literature Cited..................................................................................................................14
7.0 Maps and Photo Plates
Figure 1. Map of the Kovi Catchment Area and Kovi River surveyed sites and the Water Sink
Holes.…………………………………………………………………………………………………………………………………….………5
Figure 2: Anguilla mamorata…………………………………………………………………………………………………………..8
Figure 3: Macrobrachyium lar………………………………………………………………………………………………..……….9
Figure 4: Macrobranchium sp………………………………………………………………………………………..………………10
Figure 5: Neritina petittii…………………………………………………………………………………………….………………… 10
Figure 6: Melanoides tuberculata…………………………………………………………………………………………………..11
Figure 7: Bufo marinus……………………………………………………………………………………………………………………11
Figure 8: The headwater Kovi River flowing out of Limestone Rock………………………………………………..15
Figure 9: The headwater of Kovi River…………………………………………………………………………………….………15
Figure 10: Small fall at Kovi River…………………………………………………………………………………………………….16
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Figure 11: Deep pool at Kovi River………………………………………………………………………………………………16
Figure 12: Water Sinkhole near site two……………………………………………………………………………………..17
Figure 13: The second sinkhole near site 3………………………………………………………………………………….17
Figure 14: The Substrate type commonly observed at Kovi River………………………………………………..18
Figure 15: The Substrate type commonly observed at Kovi River………………………………………………..18
Tables
Table 1. Location of the surveyed sites, Water Sinkholes, altitudes above Sea level and
habitat types..…………………………………………..……………………………….…..6
Acknowledgment
I would like to thank the Ministry of Mines and Energy (MME), Pacific Horizons
Consultancy Group (PHCG), and the landowners of the Kovi watershed for organizing the
field survey. I am thankful for the Keidanren Nature Conservation Fund who provided
funding through IUCN Oceania Regional Office to fund the field trip. I would also like to
thank Mr. Robson Hevala (PHCG) for assisting me in the field survey and for providing the
photograph of the Anguilla marmorata and the aquatic insect that were taken during the
survey. I would also like to thank Mr. Nigel Tutuo for his assistance with the map and
Myknee Sirikolo and Patrick Pikacha their support and guidance.
Summary
The Kovi Water Catchment has a very intact forests and the surrounding watershed system. It
is located in an undisturbed area within a unique terrain and landscape. The Kovi River
contributes to the water source for the city of Honiara.
Kovi forms one of a number of water catchment limestone landscapes that exist in North
Guadalcanal, notably the Mt Austen area, the Kongulai catchment, and the upper Mataniko
catchment.
The Kovi River flows through a lowland rainforest and fused limestone, sand and gravel
substrate before submerging into underground sinkholes and emerges at Kongulai Water
Catchment.
This survey recorded two giant mottled eel (Anguilla marmorata), two species of freshwater
prawns (Macrobrachium lar and Macrobrachium sp.) and two species of freshwater snails
from the genus (Neritina petittii and Melanoides tuberculata). The aquatic vertebrates and
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invertebrates were very low because of unsustainable harvesting of the resources for food by
local populace.
Myknee Sirikolo and Patrick Pikacha surveyed the terrestrial flora and fauna of the Kovi
Basin separately. Their report and this report will be collated together into one report that will
provide a brief overview of the biological and ecosystem values for the Kovi Basin
Catchment.
1.0 Introduction
The freshwater fauna of Solomon Island is rich but was poorly surveyed until 2005. The first
study of Solomon Islands freshwater fishes occurred on the island of Guadalcanal by Gray in
1974 (Gray, 1974). Gray surveyed a total of 36 sites around the island of Guadalcanal and
recorded a total of 36 species from 30 genus and 21 families. In 2005 and 2006, a number of
surveys were carried out on 10 sites on Guadalcanal and recorded a total of 11 species from
nine genus and four families. Therefore the total number of known freshwater fishes on
Guadalcanal is 47 species from 39 genus and 23 families (Polhemus et al. 2008, Gray, 1974).
This represents 70 % of the freshwater fishes of Solomon Islands. During this survey only
one percentage of the freshwater fishes was recorded along with two prawn species and two
snail species were recorded.
This report forms part of the Biodiversity Survey on the Fauna and Flora of the Kovi Water
Catchment areas. The first team comprised of Myknee Sirikolo, Patrick Pikacha, a
representative from PHCG and traditional landowners. The second team composed of myself,
a representative from PHCG and traditional landowners.
This field surveys was conducted between 10th and 11th August, 2011, with the findings
summarized in this report.
1.1 Aim of the survey and report
The objectives of this survey are;
1. To identify and compile an inventory of the aquatic fauna of the Kovi/Kongulai Water
2. To produce a freshwater habitat map and the species that the recorded within each habitat
3. Identify important aquatic ecofauna areas.
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2.0 Study Sites
2.1 Types and Descriptions
The Kovi/Kongulae watershed (Fig 1) has a total of 14 km2 located within an intact basin like
lowland rainforest that is enclosed by ridges with uphill forest types. The Kovi River is
surrounded with riparian trees and palms and riparian vegetation like the mosses, herbs and
ferns that form patches of shrubs along the river edge.
The Kovi catchment is an extent of limestone landscapes that exist at Mt Austen area, the
Kongulai catchment, and the upper Mataniko catchment. The Kovi River (Fig 1) is 2.1 km2
in a straight line. It is sourced from ground water that flows out of a limestone rock over a
limestone substrate and patches of like sand and pebbles before sinking into two underground
caverns.
Figure 1. Map of the Kovi Catchment Area and Kovi River surveyed sites and the two Water
Sink Holes.
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Table 1. Location of the surveyed sites, Water Sinkholes, altitudes above Sea level and
habitat types. Note that N denotes Northing and E denotes Easting.
Date
Sites Area within the GPS Reading Altitude (m)
(UTM
River
Reading)
Substrate type
10/8/11 1
Areas around the 8954080 N
first water sink hole
595290.8 E
343
Fused lime stone
bed and patches
of sand
and
gravels
11/8/11 2
Areas around the 8953711 N
second water sink
594532.4 E
hole
354
Fused lime stone
bed and patches
of sand
and
gravels
11/8/11 3
Upper reach to 8951877 N
head of the river
593840.8 E
450
Fused lime stone
bed and patches
of sand
and
gravels
10/8/11 1
This site is between 8953803 N
Site 1 and Site 2
5944987.1 E
350
Fused lime stone
bed and patches
of sand
and
gravels
This site is between 8953803 N
Site 2 and Site 3
594595.3 E
361
Fused lime stone
bed and patches
of sand
and
gravels
Water Hole Sink 1
340
Fused lime stone
bed and patches
of sand
and
gravels
352
Fused lime stone
bed and patches
of sand
and
gravels
Night
Survey
10/8/11 2
Night
Survey
8954130 N
595334.7 E
Water Hole Sink 2
8953747 N
594595.3 E
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2.2 Survey Methods
A total of three 200 m transect line was laid along the river. Continuous snorkel along the
river to count aquatic fauna within and two meters on either sides of the transect line.
Aquarium nets were used to catch the freshwater prawns. Nocturnal species such as eels were
detected by investigating rocky interstitial space with the aid of underwater torches. We
surveyed a wide range of habitat type and water column (shallow fast flowing ripples, slow
flowing areas and large pools), the underside of large rocks, in small crevices, and under
streamside vegetation. Two opportunistic surveys were carried over two nights at two
separate sites between sites one and two and sites two and three to look for additional or night
aquatic fauna.
At each of the sampling sites the substrate type and the flow rate were recorded. The habitat
type and water flow will determine the fishing methods used at each site. These physical
characteristics were recorded before the fish surveys began.
Approximately 2 hours were spent sampling at each site. The only equipment used for this
survey is the aquarium nets and underwater cameras. The aquarium nets are very effective in
collecting aquatic fauna and the underwater camera was used to take pictures of the aquatic
fauna observed while swimming through the transect line. An Olympus Stylus Tough 6020
and Lumix DMC SP10 digital camera was used during this survey.
2.3 Taxa Identification
The aquatic taxa observed and collected were identified by using taxonomic keys for fish
(Allen 1991), prawns (Marquet et al. 2003) and snails (Haynes 2001).
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3.0 Results
3.1 Fish
Anguillidae (Eels)
Figure 2: Anguilla mamorata Quoy & Gaimard, 1824
Recorded from Sites 2 & 3
Photo: Picture taken by Robson Hevala
Anguilla marmorata (Fig 2) are known as the catadromous fish. The adult eels live in rivers.
They migrate to the ocean to breed and their juveniles return to river. During this survey, a
single species was recorded from Sites 2 & 3. The abundance of eel fish is very low.
According to the local guides the eels are highly harvested for consumption. Hence, this can
contribute to the lower number of the eels observed. Furthermore, there is no continuous
connective of the Kovi River into the ocean therefore, this can contribute to their low
abundance. Anguilla marmorata is a widely distributed species from west to the east pacific.
According to the IUCN Red List Status for the Anguilla marmorata is not evaluated.
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3.2 Freshwater Prawns
Family: Palaemonidae
Figure 3: Macrobrachyium lar (J.C. Fabricius, 1798)
Recorded from Sites 1, 2, and 3
Macrobrachium lar (Fig 3) is known as the Tahitian or monkey river prawn and was
observed in all the sites with very low abundance. The sites and the number countered within
the 200 meters were given in the brackets followed by the site number; Site one (5), site two
(3) and site three (15). There were no M. lar observed during the night survey. According to
the local guides, the nearby villages usually harvest the prawns for consumption. The local
guides also mentioned that people as far as from Honiara they come into the Kovi River
without their knowledge to harvest the prawns. This is a widely distributed species in large
Rivers throughout the Pacific.
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Family: Palaemonidae
Figure 4: Macrobranchium sp
Reported from site 3 only
Three Macrobranchium sp (Fig 4) were recorded from site three only. They were also very
low in abundance. According to the local guides their people and poachers usually harvested
the prawns for food.
3.3 Snails
Neritidae
Figure 5: Neritina petittii Reeluz, 1841
Recorded from Sites 1, 2 & 3
The Neritina petittii (Fig 5) are the common snails recorded from the Kovi River. They are
abundant on all the sites surveyed. They are part of the biomass of island streams (Haynes,
2001). The genus Neritina is one of the many species that were eaten by local Solomon
Islands. During this trip some of our local guides collected them and eat them. This species
distributed from South East Asia, Solomon Islands, Vanuatu, Fiji, Samoa, Guam and Ponape
(Haynes 2001).
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Thiaridae
Figure 6: Melanoides tuberculata (Muller, 1774)
Recorded from Sites 1, 2 & 3
The freshwater snail (Melanoides tuberculata) (Fig 6) was recorded from all the sites but
with very low abundance. They can repopulate themselves in the Kovi River because their
eggs can mature without fertilization. They develop their eggs in the mantle cavity and later
developed into adults (Haynes, 2001). This species is widely distributed in the Pacific from
Papua New Guinea in the West Pacific to French Polynesia to the East.
3.4 Introduced Species
Bufonidae
Figure 7: Bufo marinus (Linneaus, 1758)
Recorded from Sites 1, 2 & 3
This pristine lowland rainforest river was infested with the cane toad. The cane toad tapoles
were very abundant in all the three sites. During one of our night survey we recorded an adult
cane toad of 25 centimeters in length. The present of cane toad within the Kovi River can be
attributed to the road that was cleared from the disturbed area into the pristine lowland rain
forest. The other means could be by humans transporting them into the Kovi watershed. This
species is widely distributed throughout the Pacific countries (Eldredge, 2000).
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3.5 Other Observation
During the course of this survey a number of different aquatic insects were observed along
the transect lines and on the riversides. The aquatic insects require an entomologist to collect
and record these taxa for the Kovi River Catchment.
4.0 General Discussion
The Kovi River is one of the main sources of fresh water that supplies the city of Honiara.
The Kovi/Kongulai was located within a pristine lowland rain forest river with a unique lime
stone karst substrate habitat. The 2.1 km2 long river seeps into two separate water holes that
are believed to be drained into the Kongulai River.
The oceanic islands needed greater connectivity between the rivers and ocean. The
connectivity will allow the movement of the freshwater species between marine and the
freshwater systems (Allen, 1991; McDowall, 1993; McDowall, 2004; Jenkins et al. 2010).
For example the fish in the sub family Sicydiinae, some snails and crustaceans are known as
ampidromous species which means that their adults live and breed in freshwater. Their larvae
are transported into the ocean where they are developed into juveniles before returning to the
rivers to complete their life cycle (Keith, 2003; McDowall, 2004).
The only fish recorded from this survey is the giant long finned eel. The eel fish is known as
catadromous fish that live in freshwater as adult, migrate to the ocean to breed and their
juveniles return to freshwater. The eel fish can cross-lands and look for new streams and
rivers to inhabit. There were no records or sightings of the other finfish during this survey.
This can be attributed to the lack of water connectivity that will allow the fish to move
between the freshwater and ocean in order to complete their life cycles.
The low abundance of the eel fish and prawns could be due to lack of connectivity of the
Kovi River and the ocean, which means that there is no continuous flow of surface water that
runs into the ocean. The river-ocean connectivity is important for finfish, eel fish, prawns and
snails life cycles as they move between fresh water and ocean water to complete their life
cycle. This is a very important process as it repopulates the aquatic fauna populations.
In addition low abundance of the eel fish and prawns within the Kovi River can be attributed
to the unsustainable harvesting by the local people and poachers for food. This is an isolated
area but it is easily accessed by nearby villages and people from the Honiara city. The
unsustainable harvesting of the eel fish and prawns has a negative impact on the aquatic
fauna population.
The freshwater invertebrate and vertebrate fauna was very low in diversity and abundance in
the Kovi water catchment. However, Kovi River catchment has other aquatic fauna for
example the aquatic insects, odonata and many other fauna observed during this survey that
are yet to be studied. Once studies on the aquatic insects and the other aquatic fauna are
carried out then that could increase the diversity of the aquatic fauna for Kovi Water
Catchment.
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The other threat to the aquatic fauna of the Kovi Water Catchment is the cane toad that is
very abundant in the Kovi River. Cane toad were brought into the Solomon Islands during
the second world war by US military to control mosquito larvae however they became
established and very dominant over other species by reproducing very fast (Eldredge, 2000).
5.0 Conclusions and Recommendations
This survey concludes that Kovi River is a pristine water catchment that was highly exploited
by humans in terms of harvesting of the eel fish, prawns and snails. This result was reflected
in this survey due to the low number of the fauna recorded in this study. Therefore, the
following mitigations are suggested in order to repopulate the eel fish, prawns and snails of
Kovi River;
1. To prohibit the harvesting of the eel fish, prawns and snails. These resources should
be monitored until they reach a level that can be allowed to harvest.
2. There is a need to engage other aquatic taxa specialists and expertise in order to fully
evaluate the biodiversity of the Kovi Water Catchment.
3. Resource owners should be informed about the current state of the level of the
resources that are recorded from this survey and they should formulate a management
plan for the Kovi Water Catchment.
4. Monitor and eradicate the introduced species such as the cane toad that are using the
Kovi River as their breeding site.
In addition to the mitigation I would like to recommend that the Kovi River be protected
because of its ecological importance in terms of the aquatic fauna that are recorded from this
survey and the potential that it holds for other aquatic insects that are yet to be discovered.
Furthermore, Kovi River provides an important ecosystem services in terms of drinking,
cooking and bathing water to the population of the Honiara city.
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6.0 Literature Cited
Allen GR. 1991. Field Guide to the Freshwater Fishes of New Guinea. Publication No.9 of
the Christensen Research Institute, Madang, New Guinea.
Eldredge, L.G. 2000. Non indigenous freshwater fishes, amphibians and crustaceans of the
Pacific and Hawaiian islands. pp 173 – 190. In G. Sherley (ed), Invasive species in the
Pacific. A technical review and draft, Regional Strategy. South Pacific Regional
Gray WN. 1974. The fishes of the Solomons. Part 1: The freshwater and brackish water
fishes on Guadalcanal. Solomon Islands Museum Association, Honiara.
Haynes A. 2001. Freshwater snails of the Tropical Pacific Islands. Institute of Applied
Sciences, University of the South Pacific, Suva, Fiji.
Jenkins AP, Jupiter SD. Qauqua I, Atherton A. 2010 . The importance of ecosystem-based
management for conserving aquatic migratory pathways on tropical high islands: a case study
from Fiji. Aquatic Conservation: Marine and. Freshwater Ecosystem. 20: 224-238
Keith P. 2003. Biology and ecology of amphidromous Gobiidae of the Indo – Pacific and the
Caribbean regions. Journal of Fish Biology 63: 831–847.
Marquet G, Keith P, Vigneux E. 2003. Atlas des poissons et des crustacés d’eau douce de
Nouvelle – Calédonie. Patrimoines Naturals, Paris.
McDowall RM. 1993. A recent marine ancestry for diadromous fishes? Sometimes yes, but
mostly no! Environment Biology of Fishes 37: 329–335.
McDowall RM. 2004. Ancestry and amphidromy in island freshwater fish faunas. Fish and
Fisheries 5: 75 – 85.
McDowall RM. 2008. Early hatch: a strategy for safe downstream larval transport in
amphidromous gobies. Review Fish Biology Fisheries 19: 1–8
Polhemus DA., Englund RA., Allen GR., Boseto D., and Polhemus JT. 2008. Freshwater
Biotas of the Solomon Islands, Analysis of Richness, Endemism and Threats. Bishop
Museum Technical Report 45, Honululu, Hawai’i.
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7.0 Photo Plates
Kovi River
Figure 8: The head water Kovi River flowing out of Limestone Rock.
Figure 9: The head water of Kovi River
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Figure 10: Small fall at Kovi River
Figure 11: Deep pool at Kovi River
16
Figure 12: Water Sinkhole near site two.
Figure 13: The second sinkhole near site 3.
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Habitats
Figure 14: The Substrate type commonly observed at Kovi River.
Figure 15: The Substrate type commonly observed at Kovi River.
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