Fishes of the N ’ sele River ( Pool Malebo , Congo basin , Central Africa ) : a list of species collected in the main channel and affluent tributaries , Kinshasa Province , Democratic Republic of Congo

A list of fishes collected in the N’sele River, a large affluent tributary of Pool Malebo, in the Democratic Republic of Congo is provided. Sites along the main channel and its affluent tributaries were sampled and 148 species distributed in 27 families are reported. Despite close proximity to the megacity of Kinshasa, the ichthyofauna of the N’sele River has not previously been documented, and in the course of the current study, 19 of the 148 species are recognized as new records for the region. Due to difficulties of access much of the middle reach of the N’sele River remains to be inventoried and, while the present report documents high diversity in this system, the list is likely to be incomplete. Although preliminary, the current report provides a solid foundation for further work in a region that is undergoing rapid environmental degradation.


Introduction
The N'sele River is the largest affluent tributary entering the Congo River at Pool Malebo (formerly Stanley Pool), a 25 km-wide and 35 km-long expansion of the river that forms the boundary between the lower and middle Congo ichthyofaunal regions (Stiassny et al. 2011).The confluence of the N'sele river is located at the southeast of Pool Malebo, about 30 km from the center of the megacity of Kinshasa.The N'sele headwaters arise near the Angolan border, in the foothills of the Kasai Shield, at an elevation of about 900 meters above sea level (m.a.s.l.) and descend gradually through the rich alluvial N'sele Valley more or less due south to the Pool at an elevation of 280 m.a.s.l.(Figure 1).The river is relatively short and flows over a straight-line distance of only some 170 km, however for much of its reach the N'sele main channel is highly sinuous.Georeferenced sonar depth data collected from the confluence with Pool Malebo upstream along a stretch of approximately 50 km indicate that dry season (June -August) depths in the main channel average between 2-4 m, but depths of less than 1 m were recorded in many places along the channel (Figure 2), rendering navigation problematical (Poll 1959).Flow in the main channel is generally strong throughout the year and, due to extensive erosion in the basin, N'sele waters carry a heavy sediment load into Pool Malebo.While for much of its length the N'sele is shallow and highly sinuous, flowing over a predominately sandy substrate, in its upper reaches rapids interrupt the river as the main channel gradually widens and descends in elevation.A dense secondary network of tributaries of varying sizes, draining often markedly different biotopes, supply both banks of the N'sele main channel, and the entire watershed covers an area of approximately 6,000 km 2 (Mota et al. 1998).
Abstract: A list of fishes collected in the N'sele River, a large affluent tributary of Pool Malebo, in the Democratic Republic of Congo is provided.Sites along the main channel and its affluent tributaries were sampled and 148 species distributed in 27 families are reported.Despite close proximity to the megacity of Kinshasa, the ichthyofauna of the N'sele River has not previously been documented, and in the course of the current study, 19 of the 148 species are recognized as new records for the region.Due to difficulties of access much of the middle reach of the N'sele River remains to be inventoried and, while the present report documents high diversity in this system, the list is likely to be incomplete.Although preliminary, the current report provides a solid foundation for further work in a region that is undergoing rapid environmental degradation.

Materials and Methods
The list of species provided here is based on collections made during three field expeditions to the N'sele region, two during the dry season (July-August 2009, 2011), and one during the protracted rainy season (March 2010).Collections made at fifteen sites along two stretches of the N'sele River are reported on (Table 1, Figure 1).Sites 1-13 are located from the river mouth to approximately 50 km upstream, a reach that was accessible by shallow draft local pirogue.Sites 14 and 15 are located in tributaries of the upper N'sele, at least 85 km upstream from sites 1-13, and accessible from the south by road from the town of Mbanza-Ngungu in Bas Congo Province.Sites were selected to sample accessible regions of the river and affluent streams, representing a diversity of riparian habitats and subjected to varying degrees of anthropogenic impact (Figures 4, 5 and 6).Fishes were collected and euthanized prior to preservation in accordance with recommended guidelines for the use of fishes in research (AFS/AIFRB/ ASIH, 2003).All materials reported on in this study are housed in the Ichthyology Department of the American Museum of Natural History (AMNH), New York, and associated data are accessible at http://sci-web-001.amnh.org/db/emuwebamnh/index.php.
A georeferenced sonar depth data trace was compiled for the surveyed 50 km reach of the N'sele River main channel (Figure 2).Universal Transverse Mercator (UTM) coordinates were obtained using a Trimble Ag132 GPS receiver with Omnistar satellite-based differential correction (DGPS), and sonar depth data was measured using a Cruz Pro ATU-120B sonar transducer with 300 m depth capability.The GPS and sonar equipment was affixed to a wooden pirogue with the sonar transducer fastened to a hinged pole mounted at the gunwale and enclosed within a plastic water bottle to eliminate dragcaused cavitation across the face of the sensor.

Notes on Collection Sites
Site 1 (downstream of N'sele bridge, Figures 4A, 5A) collection made in main channel in shallow water along the bank in reeds and emergent grasses.Water flowing rapidly over a sandy substrate with muddy accumulations near shore, width of channel about 90 m.Site 2 (Malebo, Figure 4A, 5B) a shallow water embayment of the main channel, collection made behind sand spit.Banks mostly denuded, but with some grasses and reeds along the sandy shoreline.Site 3 (Nganda Yala, Figures 4A, 5C   with numerous emergent root wads and macrophytes.Site 9 (N'sele below Kisangani Village, Figure 4D, 6A) collections along shoreline, in shallow, still water over a sandy substrate with muddy accumulations near shore, width of channel about 70 m.Surrounding region heavily denuded of vegetation.Site 10 (Mayi Mpembe River, near confluence, Figure 4D, 6B) a large, left bank tributary flowing through savanna grasslands, with heavily degraded riparian cover.In the region collected, water flow is fast and deep (4-5 m), with a substrate of pebble and sand mix.Site 11 (Ngadiadia River, near confluence, Figure 4E, 6C) a medium sized, right bank tributary flowing through heavily degraded gallery forest and large grassy banks with numerous reed beds.Flow is strong and fast, but water depth relatively shallow, about 2.5 m at maximum depth.Substrate is sandy with large muddy accumulations in backwaters.Site 12 (Masaba River, near confluence, Figure 4E, 6D) smaller than preceding site, but similar with strong flow over relatively shallow (2.5 m) depths.Riparian cover of dense grasses with numerous reed beds in the region collected.Upstream the basin is heavily degraded with forest clearance for agricultural development and livestock grazing (Figure 6H).Site 13 (Mushie River, near confluence, Figure 4F, 6E) a small, relatively shallow (2 m at deepest points) stream with relatively rapid flow in the main channel but with many still backwaters.Substrate is mainly mud but with patches of sand and fine gravel interspersed.The stream flows through dense, relatively intact gallery forest and is heavily shaded with numerous emergent and floating macrophytes, and fallen logs.Site 14 (Tubi River, 1.5 km from confluence with Upper N'sele, Figure 4G, 6F) a small, black water stream flowing through a patchwork of cleared or heavily degraded forest with intensive market garden development throughout the region.Riparian cover denuded for charcoal production and firewood.The stream is shallow (1-1.5 m) with moderate flow over a fine sand substrate with dense accumulations of leaf litter and woody debris.Site 15 (Zodi River, 3 km from confluence with Upper N'sele, Figure 4G, 6G) a shallow (1-1.5 m), clear water stream with rapid flow over bedrock.Riparian zone of degraded secondary growth forest.

Fish sampling
Standard fishing techniques were employed (Lang and Baldwin, 1996) and, depending on habitat and conditions, included dip, cast, fyke, and seine nets, as well as hook and line.To ensure comprehensive sampling in isolated stretches of affluent tributaries, and with permissions, the controlled use of the ichthyocide rotenone was employed.Where adequate locality data was available, additional fishes were purchased from local fishermen who fish mainly in the main channel of the river with cast nets deployed from local pirogues.

Results and Discussion
A total of 2210 individuals belonging to 148 species, distributed in 27 families and 15 orders are represented in Table 2, with their distribution among sites indicated in columns 1-15.In column 16 distribution data culled from the IUCN assessment of the status and distribution of central African fishes (Brooks et al. 2011), is used as the best available source to indicate which species have previously been recorded as present in the N'sele region.
Based on these data we recognize 19 species (Table 2, column 16) that have not previously been recorded from Pool Malebo or surrounding regions, and a selection of these is illustrated in Figures 7-9.
Despite proximity to the megacity of Kinshasa, access to the N'sele River remains difficult and in the course of the present study we have been able to survey the main channel and associated tributaries along a relatively short course of the river.Much of the middle reach of the river remains to be surveyed and it is probable that the full tally of species from the system will be higher than that reported here.Despite these limitations, a total of 148 species is noteworthy for an African river of this size, particularly given the homogeneous nature of the main channel and highly degraded state of much of the basin.By comparison, a recent survey of the nearby, and considerably larger, Inkisi River (Figure 1), recorded the presence in that system of only 61 species (Wamuini Lunkayilakio 2010).Similarly, a comprehensive study of the Lefini River, a large right bank affluent tributary of the middle Congo in the Republic of Congo with a drainage area more than twice that of the N'sele, reported the presence of 140 species in that system (Ibala Zamba 2010).
The location of the N'sele basin may partly account for the unexpected richness of its fish fauna.The headwaters of the larger left bank tributaries of the N'sele are located in close proximity to those of the Inkisi River, a major left bank tributary of the lower Congo River (Figure 1), and the presence in the N'sele (but absence in Pool Malebo) of species such as Paramormyrops cf.kingsleyae, Barbus vanderysti, Garra ornata and Clariallabes manyangae, may reflect faunal exchange during periods of flooding or past stream capture with the Inkisi.Similarly headwaters of some larger right bank tributaries of the N'sele are located in close proximity with those of the Mayi-Ndombe (Black) River, a large left bank tributary of the middle Congo River (Figure 1).The presence in the N'sele of taxa such as Marcuseius kutuensis, Barbus humeralis, Amphilius maesii, Phractura scaphyrhynchura and Heterochromis multidens, species more typical of the middle Congo (but absent from Pool Malebo), may reflect that association.And of course the outflow of the N'sele into Pool Malebo provides ample opportunity for colonization to and from the Pool, and the presence in the N'sele of species such as Leptoglanis xenognathus, Belonoglanis brieni, Clariallabes teugelsi and Poropanchax myersi suggests such an interchange.It is of interest to note that of the 148 species recorded from the N'sele, 45 were collected exclusively in tributaries (species in bold type in Table 2), and have yet to be found in the main channel of the river.While this may reflect an artifact of collecting effort throughout the channel, it is nonetheless suggestive that the N'sele tributaries, draining often markedly different biotopes, harbor a significant proportion of species richness in the system.
Papyrocranus congoensis (Nichols and La Monte, 1932) ) commercial port and boat landing, heavily disturbed area.Collections made along sandy shore and in fringing grasses.Site 4 (N'sele between Benzale and Manzambi, Figures4B, 5D) collection made in main channel along bank in reeds and emergent grasses, at depth of 1.5 m.Rapid water flow over a mixed substrate of sand, mud and woody debris.Width of channel about 40 m.Site 5 (Mopimbi River, near confluence, Figures4B, 5E ) collections made from confluence to 200 m upstream.Clear water flowing rapidly over a sand-mud substrate at depths ranging from 2-3 m near the confluence to 5 m further upstream.Surrounding gallery forest highly degraded for firewood and charcoal production.Site 6 (Koke ya Mbila River, near confluence, Figure4C, 5F) a large forested tributary that arises in the eastern portion of the Bombo Lumene hunting reserve.In the section surveyed gallery forest is more or less intact, and clear water flows over a sandy substrate, intermixed with patches of fine gravel and silt.Banks shaded, undercut with overhanging vegetation.Site 7 (Mopili River, near confluence, Figure4C, 5G) deep (5 m), heavily silt-laden waters flow over a sand and mud substrate through severely degraded gallery forest in a region of intensive agricultural activity.Site 8 (Bokungu River, near confluence, Figure4D, 5H) a small, shallow, clear water stream flowing slowly over a fine sandy substrate.Gallery forest intact and stream banks shaded,

Figure 1 .
Figure 1.Location of N'sele River and associated drainages into Pool Malebo, with collection sites numbered (rhs).

Figure 2 .
Figure 2. Depth variation measured along a 50 km stretch of the N'sele River (August 2009).Georeferenced sonar depth trace is superimposed on a Google Earth projection (rhs).

Figure 3 .
Figure 3. Habitat degradation: A) Charcoal kiln (lhs) and sacked charcoal awaiting collection for transport down river; B) Charcoal sacks being rafted down river for sale in Kinshasa; C) Cleared bank resulting in erosion of sand into the channel; D) Forest clearance and resultant erosion.

Figure 4 .
Figure 4. Google Earth projections: A) -G) Collection site locations and surrounding land cover.Red stars indicate main channel collections and white stars indicate collections within affluent tributaries.H) First cross channel rapid on the N'sele main channel, located about 40 km upstream of the river mouth.

Table 1 .
but with a Collecting sites: geographic and physicochemical data.

Table 2 .
Brooks et al. (2011)ected at sites 1-15.In column 16 distribution data culled fromBrooks et al. (2011)is used to indicate which N'sele species are known to occur in Pool Malebo and/or adjacent regions.Species in bold were collected in affluent tributaries but not in the N'sele main channel.