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- Title
Fish distribution and zonation along a tropical African river, the Rokel/Seli River, Sierra Leone, West Africa.
- Authors
Payne, A. I.; Wakeford, R. C.; Ndomahina, T. E.
- Abstract
The Rokel/Seli River descends from the Guinea highlands and drains westward through Sierra Leone into the Atlantic Ocean. It lies within the Upper Guinean faunal region. The river has low mineralisation and buffering with conductivity varying from 14-55 μS and pH from 6.8-7.8 whilst temperature ranges from 21-32°C. Sampling along its length over a 12 month period showed that the number of species diminishes significantly upstream from 50 at the richest downstream point to 6 in the highest streams sampled. The major change occurs at the Bumbuna Falls which, at 136 m above mean sea level, also lies at the point of maximum change in gradient between the upland rhithron zone and the lowland potamon zone. The region above the Falls has 29 species, while 62 were recorded from the lowland reaches of the river. The Falls appear to be a barrier to fish movement as well as a barrier to the distribution of some species such as Lates niloticus. Yields from fishing also increase downstream from 0.87 t.km-1 in the upper area to 2.58 t.km-1 in the lowland reaches. Three fish freshwater zones were identified: an uppermost 'small cyprinid zone', typified here by Barbus liberiensis, starting around 290 m.amsl; a 'large cyprinid zone' characterised by Barbus sacratus, and Labeo parvus from above the Falls at 165-290 m.amsl, and a lowland zone, below 136 m.amsl, dominated by cichlids and catfishes. The large cyprinids move into the upper small cyprinid zone during the spawning migrations of the early rains. A total of 68 freshwater species was found throughout the system, rather higher than would be predicted from other African rivers. The fish assemblage is also very characteristic, having more than 35% of the species as regional endemics confined to they Upper Guinean region with the small cichlids and tilapias showing particularly high levels of endemism.
- Subjects
WEST Africa; NILE perch; FISH anatomy; SPECIES distribution; CYPRINIDAE; BARBUS
- Publication
Smithiana Bulletin, 2010, Vol 12, p25
- ISSN
1684-4130
- Publication type
Article