Summary of the annual ichtyofauna report of Cote d'Ivoire (1997-1998): summary

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AF".RIQUE DE L'OUEST ECOLOGICAL GROUP Twentieth session Lom6.3-5 March 199q OCP/VCU/HYBIO/99.3 ORIGINAL: French STJMMARY OF TIM AT,.{NUAL ICHTYOFATJNA REPORT OF COIE D'IVOIRE (1997-r998) Kouassi N'Gouan Cyrille Summary This reporting period spars the period of December 1997 through 1998. The stations concerned were Pont frontiere on river Lrraba, Ganse on the Comoe and Niaka on the Bandama river. The paruneters anatyzed were as follows: specific richness, total CpUEs per mesh category and per main species, as well as the condition coefficient of these principal species. These parameters were analyzed on the basis of the season under review and of the entire monitoring period. 1. The number of fish species found during the season is in the same range as that of the previous season; 37 at Pont frontiere, 34 at Ganse, and 36 at Niaka. The number of species found by sampling at the three stations confirmed the increased observed since 1993. The Barbus sublineatus and Barbus trispilos, which were noticed during the previous season confirm the presence tliese species at the pont frontiere site. 2. The total average catches per unit effort by sampling, by number and by weight have increased at the Ganse and Pont frontiere stations, as compared to the last two seasons. At Niaka, however the average values of this season are in the same range as those of the last two seasons, with a slight decrease in figures. 3. With respect to the entire monitoring period, the numbers, so far as capnrres are concerned' are in the same range as those of 1974175 atthe Pont frontiere and Ganse stations. However, with regard to weight, though there was an increase, the capture numbers were still Iow as compared to the start-up period. 4- During the season under review, smalt-sized mesh was the most efficient at pont frontiere and Ganse. At Niaka, small and medium-sized nets recorded the same amount of catch. Big- sized nets recorded the least amountof catch at the three stations. Over the whole monitoring period, a remarkable and somewhat regular increase in catches, both in number and weight, of small-sized and medium-sized nets has been noticed since 1993 at all three stations. OGP/TCU I(IBIEIIIIE COURRIER ARNIVEE 5- Analysing the stahrs of mean CPLrEs. by number and per sampling over the survey period(1974-1984) one could uotice three main phases at the stations. The first spans the 197.4- 84 period at Pont frontiere and Niaka, anl from 1975-82at Ganse. This period is characterised by a fall in CPITEs and by spraying with Abate only. The second.phase was betrreen 1984 and 1992 at Pont frontiere, from 1982 to 1993 at Ganse and 1984 through 1993 at Niaka. This phase was characterised by a sabilized CPLIEs within a certain range of values and by alternate spraying with several insecticides, with more or less long suspension periods. And.finally, the last period covers the l9V2-L998 years at Pont frontiere, 193-98 at Ganse and Niaka. This period is characterised by the increase in CPUEs and by the cessation of larviciding. At all three stations, the trends observed during the first rwo periods are fractgred by higrrs which are noticed in years characterised by hydrological peculiarities. These findings are highlighted in the repffi. 6. Overall, most of the species recorded significant increases in their CPUEs, in number and weight during the season at the Pont frontiere and Ganse stations. The principal species at the Pont frontiere site are the Schilbe mandibularis, Schilbe intermedius, Aleslqs_bargmozc and Petrocephalus bovei. At Ganse, the principal species are: the Alestes baremoze, Schilbe mandibularis and Chrysichthys rnaurus. At Niaka, though there was an increase in CPUE, in number and weight, of species this increase are in modest proportions as compared to the o&er two stations. The principal species here are:the Brycinus nurse and Alestes baremoze. 7 . The mean,condition coefficients of the principal species didn't change much during the season under review. But analyses of the mean value trends by year, for these 5pecies over the entire monitoring period, show slight increases for some of them. This goes, for instance, for the Alestes baremoze at all the surveiliance stations. The same goes for the Petrocephalus bovei and Chrysichthys maurus at Pont frontiere and Ganse,the Synodontis schall and Synodontis comoensis at Pont frontiere. At Niaka, the trend is that of an increase for the Characidae Brycinus nurse, Brycinus macrolepidotus and the Schilbe mandibularis. a