Evolution of the fish fauna of the Côte d’Ivoire watercourses treated with antisimuliid insecticides during the 1986-1987 campaign

oCP/VCU/HYBIo/ 88 .2 ORIGINAL. FRENCH EVOLUTION OF THE FISH FAUNA OF TTTE COTE DIIVOIRE I.IATERCOURSES TREATED WITH ANTISIMULIID INSECTICIDES DURING THE 1986-1987 CAMPAIGN (Report No. L2) SUMMARY Durlng the 1986-1987 campaign, three Ivorl,an rratercourses were the subject of an ichthyological monltoring: the Bandama at the Niakaramandougou station, the Comoe at the Ganse statlon and the Leraba at the Road-brldge station. These Ehree watercourses were treaEed alternately wlth Temephos, Chlorphoxim, Carbosulfan and Permethrin. For the monlE,oring of the evolution of the fish communlty, the investigatlons were centred on posslble qualltative as well as quantlEatlve changes. Four sampllngs were made for that purpose ln each of the four s tatlons 1. Analysls of t.he sEat.e of the flsh fauna of the Bandama aE Nlaka The Niaka statlon was treated for 27 weeks with B.t. and three weeks wlth Carbosulfan. The treatments were suspended for F-weeks, from January to October 1987. During the 1986-1987 canpaign, Ehe different inventorles of the fish fauna of the Bandaua made it possible to record 25 to 30 species at Niaka. The nost representaElve specles of this station are stl11 presenE ln these lnvent.ories and no species dlsappearance was mentioned. From the viewpoinE of number, t.he share of juvenile flshes ls very Srear-. In fact, the caEches made with the small-mesh nets represenEed 25.2% of the total catches in December 1986 ,57% ro May 1987 , 58% in Augusr 1987 and 42.37.ln Novenber 1987. This proves that the juvenlles represent a great proporEion of t.he available fish stock, whlch means that ghe regeneraElon potentiar remains at quite an appreciable level. The repopulatlon of the sEation is going on quite correctly despiEe the low catches. The great pressure exerEed by the local flshermen cergalnly has an lncidence on the different CPUE values. The mean coefflcient of condiElon values of the principal species at Niaka are pract.icallyldentical to those of the previous years. We can Eherefore say that the antisimuliid larvlcldlng has noE had anydrastic effect on Ehe fish fauna of the Bandama at the Niaka sEaEion. a a 2 ?.. Observatlon of the fish fauna of the Leraba The Leraba was treaEed at the road brldge for 18 weeks with B.t H-14 and for five weeks wlth Chlorphoxim, f rom January Eo October 19871-ftre treaEnents trere suspended for 20 weeks. As regards Ehe evolution of the ftsh fauna, Ehere has been no signiflcant qualltative change ln the composltlon of Ehe community. No signlficant decrease ln catches attrlbutable to the lnsectlcide spraying was deEecEed. As a matter of facE, 3O specles were sarnpled ln the Leraba uslng g111 nets. Schllbe nystus has re-esEabllshed itself very satisfactorlly insofar as it ls vying with AlesEes baremoze for supremacy. The catches made wlth small-mesh nets represented 63.2i( of the toEal CPUEs ln Novenber 1986, 70.47. in May L987 , 49 .3"1 In August 1987 and 45.52 in November L987. Thlsfact shows that juvenlle flshes are dominant in the catches. It can therefore be sald that the fish resources regeneratlon potential of the Leraba remalns at an appreclable leve1. There has been no significant change in the coefflcienEs of conditlon of the principal species representative of the Leraba. In concluslon, the antlslmullid insect.icide spraylngs have noE had any harmful and irreverslble lmpact on the flsh fauna of the Leraba. 3. EvoluElon of the fish fauna of the Comoe At Ganse, the Comoe was subjected Eo only 14 weeks of larviciding (12 weeks wlth B. t. and two weeks wlEh Chlorphoxiu), from February to OcEober L987. The G-tmenEs were suspended for 28 weeks. Durlng the 1986-1987 campaign, 28 to 3O specles were sampled with gill nets in this station. None of the maln specles representative of the statlon has disappeared. The 1ow total CPUE values were somewhat preoccupylng but we think Ehls situat.lon ls only clrcumstanEial and not attributable to the effecEs of the insectlcldes, especlally since Ehe samplings were made during Ehe periods of t,reat.ment suspension. The greac and brutal pressure exercised by the "Bozo" fishernen ls probably the real cause. Furthermore, the caEches made wit.h small-mesh nets present.ed 58.L7" of the toEal CPUEs in December 1986, 61.47" in May 1987, 53.L7" it August 1987 and 68 .9% in November 1987. This proves that the juvenile flshes constituEe Ehe greater part of the caEches. We can deduce from Ehat Ehat the repopulation poEentlal of the station is very appreclable. The situaElon is therefore noE alarmlng. EuEropius mandibularis, Chrysichthys nlgrodigiEatus, Alestes baremoze and PeEr ocephalus bovei and Brycinus nurse are the most abundant species. In conclusion, any greaE change in Gans e. Ehe antisimuliid insecEicides seem noE Ehe sEructure of the fish communlty of t.o have caused the Comoe aE