A SURVEY OF FISHES OF THE TANA RIVER AT KORA AND A CHECKLIST OF FISHES OF THE TANA RIVER KEN CAMPBELL, CHRISTOPHER COE AND MICHAEL SAUNDERS Serengeti Ecological Monitoring programme Serengeti National Park, PO Box 3134, Arusha, Tanzania. INTRODUCTION The Tana River drains the southern and eastern slopes of Mount Kenya and the eastern slopes of the Aberdares, and is the largest river in Kenya. It passes through most of Kenya's agro-climatic zones (Sombroek et al •• 1980) from zone 1-9 (humid and cold) on Mount Kenya and the Aberdares, to VII-1 (very arid and very hot) over much of the lower Tana. The river has received little ecological attention especially in the Kora region and consequently knowledge of the fish fauna is poor. This scarcity of information is largely due to the lack of economic incentives for development and the inaccessibility of much of this region where road communications are difficult and at times impossible. The upper reaches of the Tana, above about 1500m, were examined by van Someren (1952) and notes on the fishes in the middle reaches have been made by copley (1958) • Whitehead (1959) made a collection of fishes on the lower Tana River below Garissa. Following this, a single collection has been made, by the Fisheries Department, Kenya, (Oduol, 1976) from six localities on the lower Tana River below Kora. TABLE 1 EXisting and potential Reservoirs along the Tana River, Kenya. Output (MW) Existing Reservoirs Masinga 1560 40 Kamburu 147 84 Gitaru 20 137 Kindaruma 16 44 Kiambere (under construction) 315 120 planned Reservoirs Usueni 330 Adamson's Falls 1730 Grand Falls 3600 Kora Hills 3800 Karura 74 175 The Tana River is now the focus of hydroelectric power development in Kenya with four dams in operation, one under construction and further dams at the planning stage (Table 1). Of the potential reservoirs one of the largest is planned for the Kora section of the Tana River (Tana and Athi Rivers Development Authority, 1982). Such impoundments will undoubtedly have a significant effect on the fish populations of the Tana, more so on the migratory species for which provisions are unlikely to be made in future hydroelectric and storage dams since very few Tana River fish species show economic potential. On the other hand a number of species are likely to benefit from the resulting changes in habitat. The present collection serves to establish baseline data on the fish population in the Kora section of the Tana River where the last rapids are situated and from where the Tana emerges onto its flood plain. In addition a checklist is presented of fishes recorded from the Tana River. METHODS Fish species were collected over a 90km stretch of the Tana River spanning the Kora Rapids above Garissa. This stretch of the Tana, which forms the northern boundary of the Kora reserve, can be divided into three main sections; the first from Adamson' s Falls to the start of the Kora rapids, the second constituting the rapids themselves, and the last section at the eastern edge of the reserve below the rapids. Seventeen localitites were sampled within this stretch, sample points being determined by accessability. Fish were captured with the aid of a 10mm mesh seine net, by hand net, by hand line and by lines strung from an otter board held in mid-stream. The seine net accounted for the major part of the collection and was the only technique employed at most sample points. Fish were preserved in the field after initial measurements of standard length and fresh weight. Tentative species identification was carried out in the field and the specimens were later exmined at the Nairobi National Museum. samples were also sent to the British Museum (Natural History) for further identification. RESULTS AND DISCUSSION A total of 1597 fish were captured from seventeen localities. Of these, 348 came from above the rapids, 286 from below the rapids, 52 specimens from a spring towards the western border of the Kora National Reserve, and the remaining 911 from several sites within the Kora Rapids section themselves. Twenty one species were identified (Table 2) and of these ten can be considered common along the Kora stretch of the Tana River. Of interest are two 'species pairs' one of Labeo and one of Barbus, with each 'pair' consisting of a small and a large species; L. greqori and~. mesops , .!!.. oxyrhynchus and B. zanzibaricus. All four species were found to be relatively common at Kora, but only L. greqori is previously recorded or the Tana River. Seven other species of Barbus are recorded from the Tana (see checklist, below), none of which were found at Kora. If these Barbus do in fact represent distinct species it is likely that the Tana River Barbus species have fairly restricted geographical ranges and that different pairs of Barbus may be found along the length of the Tana. This also indicates a degree of specilaistation similar to that found among the cichlid fish fauna of the African Great Lakes (Fryer and Isles, 1972; Greenwood, 1981). Similarly L. gregori is found in the lower Tana whereas L. cylindricus occurs in thelniddle reaches and was not found at Kora. 176 TABLE 2 Fish species recorded at 17 sample sites along the Tana River in Kora National Reserve. Species number percent Clarotes laticeps 180 11.3 Clarias mossambicus 9 0.6 Chiloglanis brevibarbis O. 1 Eutropius depressirostris 229 14.3 Synodontis sp. 45 2.8 Barbus oxyrhynchus 92 5.8 B. ?:anzibaricus 24 1.5 Labeo gregori 342 21.4 ~ mesops 89 5.6 Labeo sp. 11 0.7 Sarotherodon sp. 125 7.8 Anguilla nebulosa 4 0.3 Engraulicipris fluviatilis 44 2.8 Allestes affinis 82 5. 1 Glossogobius giuris 3 0.2 Petrocephalus catastoma 274 17 .2 Mormyrus kannume 13 0.8 Gnathonemus macrolepidotus O. 1 Discognathus sp. O. 1 Lebistes reticulatus 28 1.8 177 TABLE 3 Fish species Diversity, and Similarity in Species Ccrtposition at Simple Sites in Kora National Reserve on the Tana River. Percent Similarity beOileen Simple Sites 1 2 3 4 9 10 11 13 22 1 100 S 2 54 100 A S 3 1 9 100 MI 4 19 30 6 100 p T 9 35 32 0 40 100 L E 10 23 17 1 53 38 100 E 11 41 28 0 38 16 56 100 13 25 36 46 25 19 6 12 100 22 35 46 8 75 17 24 37 38 100 Species Diversity .760 .813 .497 .788 .567 .649 .790 .530 .833 No. 74 54 52 715 42 209 90 52 192 Nearest Neighbour Linkages 100% 75% 50% 25% 0 Site 11 -----------------------------+ I----~------+ Site 10 -----------------------------+ Site 2 ------------------------------+ 1----+ -------------+ Site 1 ------------------------------+ ---+ Site 22 ----------------+ 1------------------+ Site 4 ----------------+ -+ Site 13 -----------------------------------+ 1---+ Site. 3 -----------------------------------+ Site 9 -------------------------------------------------------+ 178 FIG. 1 ST~ND~RD LENGTHS OF CLAROTES LATICEPS AT FOUR ADJACENT SAMPLE SITES SITE 22 :: n, 50 ~ 40 z w 5 30 w [ 20 " 10 O'--...L..--'-----'_.L-~~_~~~~_~~_ o 50100 150200250300350400450500550600650 LENGTH (MM) SITE 1 40 30 - 20 10 o :----:'::~':_:_::':-:..J~_:_:l.-..JI__::.I.....-~--~~~~ o 50 100 150 200 250 300 350 400 450 500 550 600 650 LENGTH (MM) SITE 23 30 20 .---- .---- r-- 10 f-- o r o 50 100 150 200 250 300 350 400 450 500 550 600 650 LENGTH (MM) SITE 21 40 30 20 10 Ol..-~""':;'~.......l_.l....._..l--'--J..--l~l._..J-~~ o 50 100 150 200 250 300 350 400 450 500 550 600 850 LENGTH (MM) 179 'rABLE 4 Standard lengths of six fish species fran four adjacent sample sites at Kora. Standard T.ell<]th (Ilia) Site 1 site 21 site 22 Site 23 Species Min I'lean I"iax ~Iin ~Ean Max ~Iin ~Ean Max ~1i II I"i2an I-tlx Clarotes laticeps 64 153 318 266 341 532 26 54 173 85 239 3~5 No. 29 26 24 21 0 Barbus oxyrhynchus - - 51 64 88 - co No. 26 - B. zanzib3.ricus 138 136 206 - 94 144 192 212 No. 12 3 1 Labeo greqori 86 97 112 - 68 82 97 No. 3 62 L. meso12§. - - 124 159 202 No. 17 Allestes affinis 132 101 160 - 66 94 151 126 No. 17 19 1 Hiver"s edye r·lid-stream Sheltered by River"s edge dbove sandbank 100 III below sandbank sandbank species diversity was calculated for sample sites with greater than 40 individuals using the Simpson/Yule index of diversity, taking account of both the number of species and the number of individuals within species ISimpson, 1949). Similarity in species composition between sample sites was calculated using the sorenson coefficient of similarity as modified by Bray and Curtis (1957). A high species diversity was found at each sample point whereas the similarity in species composition between sample points was usually small, even between adjacent localities (Table 3). this situation is illustrated by a comparison between the species composition of localities 1, 4 and 22. sample locality number 1 was situated at the rivers' edge beside the expedition base camp. Locality number 4 was situated approximately 20 km downstream in a backwater within the Kora Rapids. Locality number 22 was situated within 50 metres of locality 1 on the downstream side of a sandbank separating the two sites. Sites 22 and 4 were both in slow flowing or still water and site 1 was near the main channel in relatively fast flowing water. All sites were sampled in a similar manner by seine net. The similarity in species composition between sites 1 and 22 was low but high between sites 4 and 22.