Summary annual report of Côte d’Ivoire (ichtyofauna) 1996-1997 season

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ECOLOGICAL GROUP Nineteeth session Odienne. 4 au 6 February 1998 OCPA/CU/HYBIO/98.5 OzuGINAL :French SUMMARY ANNUAL REPORT OF COTE D'IVOIRE (ICHTHYOFAUNA) 1996 -1997 SEASON Kouas si N' Gouan Cyrille This season , the campaign of sampling of the ichthyofauna was carried out from December 1996 to October 1997 n the stations of Niaka (Bandama), Gans6 (Como6) and Pont FrontiEre (lfraba). The observations made concerned the usual parameters (species richness, CPUES, Reproduction) and the use of ichthyotoxins in our rivers. The results observed were the following : 1) The number of species observed during the season was 36 at Pont FrontiEre, 35 at Gans6 and Niaka. For each catch operation, the number of species caught was on the increase at all stations. Some new species were encountered this season. They are Barbus trbpilos and Barbus sublineatus at Pont Frontidre. Pellonula leonensis reappeared in the catches at this station since it disappeared in 1985. 2) The total CPUEs in terms of both weight and number were highest during the dry season. Catches were higher at Pont Frontidre in terms of number but lower in terms of weight compared to the previous campaign. There were therefore more juveniles and small size fishes caught du;ing this campaign. At Niaka, catches remained stationary in number and weight compared to the previous campaign. At Gans6, the catches remained in the same proportion in terms of number as those of the previous campaign. However, in terms of weight, the catches were clearly lower than those of the previous campaign. Similarly to the situation at Pont Frontidre, there were more juveniles and small size fishes caught during this campaign. Compared to the other years of monitoring, the overall mean CPUEs were on the increase. 3) With respect to catches per category of mesh size, the small sized mesh proved more efficient at Pont Frontidre and Gans6. At Niaka on the other hand, the medium sized were stightly more efficient. The large sized mesh recorded the lowest CpUEs as usual. 4) The increase in CPUEs recorded shce 1993 in all the stations is due to an improvement in the catches by the small sized mesh at the stations of Pont FrontiEre and Gans6. At Niaka the increase is due to the medium and small sized mesh. 5) As regards species richness, the principal species characteristic of each of the stations have remained unchanged. They are Schilbe mnndibul,ais, Alestes baremoze and Schilbe intermedius at Pont aFrontidre ; Alestes baremoze, schilbe mandibulais and chrysichtys maurus at Gans6 ; Brycinus nurse and Alestes baremoze at Niaka. However, some new species were striking due to the importance oftheir cPUEs' They tre Petrocephalus bovei at all thregstations, synodontisschall at pont Frontidre,Brycinus macrolepidotus and Hydrocinus forskalii at Niaka. Significant increases in cpUEs were recorded among the species of Pont Frontidre. At the other stations, however, the CpUEs of theseprincipal species have remained stationary or have slightly decreased. 6) The seasonal mean condition coefficients of the principal species in the different stations didnot show any significant changes during this season. Ttreir values, therefore, have remained stablethroughout the season. Compared to the previous years, these condition coefficients are within the range of values characteristic of each species. 7) Brycinus nurse, Brycinus Macrolepidorzs and Alestes baremoze reproduce during the rainy season' This observation is consonant with the results of previous studies. From one season to theother, there are some slight fluctuations in the delimitaiion of these reproduction periods. ForChrysichtys ffttutrw, however, is reproductionperiod could not be identified due to the small number of individuals observed and to the mode of repioduction of this species. 8) with regard to the use of ichthyotoxins, the practice is encountered on the rivers and watercourses of C6te d'Ivoire. However, it is clandestine. in the southern part of the country (in lagoon areas), people use phyto-sanitary products. In the northern half of the country, however, the tendencyis to use plant extracts. 9) In conlusion, an overall improvement of species richness was noted in all the stations. There was also an increase of overall CPUEs in respect to the categories of mesh size and the principal species, especially at Pont FrontiEre, a station where the suspinsion of antiblackfly spraying is the oldest' Given that these increases were due to the catches from the small sized mesh, we can say thatthe recruitment and/or small size fishes were on the increase in the rivers during this campaign.Consequently, there are some changes leading to an improvement which is noticeable at these stations.Does this situation have any relation to the cessation of antiblackfly larviciding though ? we think thequestion deserves further investigation during the next campaign.