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  • Writer's pictureS Liefferink & R Tate

Freshwater Biodiversity of Inland Valley Swamps - Sierra Leone

Updated: Apr 10, 2023

An open canopy Inland Valley Swamp in the Little Scarcies River system, Sierra Leone

The lowland rivers of Sierra Leone are located on a coastal plain with a network of coastal tributary systems draining into major river systems such as the Great Scarcies, Little Scarcies, Rokel, Jong, Sewa, Waanje, Moa and Mano Rivers.

The freshwater habitats in this area are subjected to significant unimodal flood regimes which peak in between July and September annually. This large difference in rainfall forms extensive floodplains in the areas adjacent to the rivers which are connected to adjacent major river systems, this is clearly evidenced in rivers such as the lower Sewa and Jong River systems. These floodplains form critically important habitats for a diverse and abundant fishery.

In the source zone of minor tributaries to the larger rivers, wetlands known as Inland Valley Swamps (IVS) occur. The swamp areas referred to are classified as being either channeled or unchanneled valley bottom wetland's but are called IVS in Sierra Leone. This IVS habitat is the focus of this post.

The habitat types present in the area surveyed include in sequence of Strahler order, open canopy Inland Valley Swamps (IVS), closed canopy IVS, foothill and lowland rivers.

The areas surveyed thus far were confined to the coastal plain of Sierra Leone. The information presented here is restricted to these areas. Fish of the area's surveyed are consistent with the Upper Guinean Ichthyological Province.

Map of the areas visited and presented in this post
Rainfall in the coastal region of Sierra Leone

Much of the forested habitats of Sierra Leone have been transformed to farm bush and shifting agriculture, this includes wetlands and swamp areas. Where these areas once consisted largely of closed canopy systems, these have subsequently been transformed in open canopy habitats.

In addition to the extensive deforestation which has occurred in Sierra Leone, wetlands are under increasing pressure from the development of swamp rice which directly impacts and often contaminates on these sensitive habitats. If you would like to learn more about the hydrology of these systems, the work by International Institute of Tropical Agriculture by the authors Windmeijer and Andriesse (1993) provides great information (see the references for a copy).

Despite the level of land cover modification the open and closed IVS habitats contain extremely pure and clear water with high densities of aquatic vegetation as pictured below in a tributary of the Jong/Tia River. It is expected that the constant perennial inundation of the main channels is the responsible for the formation of the dense stands of aquatic vegetation.

A typical example of an open canopy Inland Valley Swamp in Sierra Leone

The open canopy systems are host to an abundant fish fauna, where many species commonly found in the aquarium trade can be located. The open water of the open IVS typically contains schools of Bryconalestes longipinnis and Hemichromis fasciatus which are found in high abundances and Frequencies of Occurrence across coastal Sierra Leone.

The dense aquatic vegetation and margins of the streams are suitable habitats to more specialized fish fauna such as Epiplatys annulatus, Poropanchax normanii and Epiplatys fasciolatus which are abundant in these habitat types. The water quality parameters for these habitats is pure water with low levels of dissolved solids (<15 µS/cm ), slightly acidic pH and above 6 mg/l dissolved oxygen.

Top left: Poropanchax normanii Top right: Epiplatys annulatus Bottom: Epiplatys fasciolatus

The closed canopy IVS habitat types have sandy substrates and areas with accumulated woody and leafy debris which are important habitat types for the endemic fish fauna. Where the canopy opens aquatic plants can be found where stands of submerged Nypmhea and Comelina have been observed.

These habitats are also suitable for common and popular aquarium species such as Pelvicachromis rollofii, Anomalochromis thomasi and Rubricatochromis which rely on the woody debris and detritus supplied by the closed canopy.

Top Rubricatochromis sp, Bottom Left: Anomalochrmois thomasi, Bottom Right: Pelvicachromis rollofii

The margins of closed canopy IVS habitats often consist of floodplains. Woody vegetation in the form of swamp forest creates canopy cover, while stands of permanently flooded Raphia palm also occur.

After periods of rainfall and bank-full floods, the floodplains adjacent to the IVS habitats become inundated, and floodplain pools form as the flood peak recedes. It appears that these pools are sustained through bed/interflow with the main channels adjacent to the pools. The maintenance of the inundation period for these isolated pools has enabled the evolution of specialized species, including Scriptaphysemion chaytori and Callopanchax occidentalis.

These pools are also often inhabited by Epiplatys annulatus and Clarias sp..

Top: Scriptaphyosemion chaytori , Middle: Scriptaphyosemion chaytori Bottom: Callopanchax occidentalis

Photographs of the remaining species which were found in the IVS habitats are presented below.

It is worth noting that the Lepidarchus adonis was very rare in the areas surveyed, only being found in one location in an affluent of the Tia/Jong River.

Top: Epiplatys barmoiensis Middle: Lepidarchus adonis Bottom: Neolebias unifasciatus

Top: Petrocephalus levequei Middle: Brienomyrus brachyistius Bottom: Malapterurus cf. barbatus

Top: Bryconalestes longipinnus Middle: Hemichromis fasciatus Bottom: Ctenopoma cf. kingleyea

The IVS habitats host a vibrant community of Odonata with a colorful appearance. These slow flowing, densely vegetated habitats are suitable to a remarkable diversity of dragonly and damselfly species, and the open IVS habitat, in particular, boasts high abundances of these striking insects.

Top: Ellattoneura girardi Middle: Ceriagrion rubellocerinum Bottom: Agriocnemis sp.

Top left: Trithetrum navasi Bottom Left: Neodythemis klingi Right: Oxythemis phoenicoscele


Windmeijer and Andriesse (1993)
Download PDF • 9.00MB

The next post will focus on foothill river systems like those shown below!


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