Comparative evaluation of the impact of carbosulfan and permethrin sprayings on the fish fauna of the Bandama and the Marahoué: report no.13

)ocP/vcu/HYBro/88.3 ORIGINAL: FRENCH COI'{PAR,ATIVE EVALUATION OF THE IMPACT OF CARBOSULFAN AND PERUETIIRIN SPRAYINGS ON THE FISH FAUNA OF THE BANDA}.IA AND THE MARAHOUE (Report No. 13) Summary The Onchocerciasls Control Programme carried out an experlmental Carbosulfan larviclding campaign for 22 weeks in the Bandama (fron the 14th week to the 33rd week of 1986) and for eight weeks in the Whlte Bandama(fron the 33rd week Eo the 4oth week of 1986) ln order to test, the level of toxiclty of the different Carbosulfan formulatlons on Ehe fish fauna of the treated rivers. At Ehe same time, a simllar operatlon was conducted wlth Permethrin on the Marahoue, downstream from the Mankono station. We had Ehe responslblllty of followlng the evolution of the fish comrnunltles subjected to these sprayings. Three stations were selected to monltor the Carbosulfan operat.lon: Tiassale, l'larabadiassa and Nlakaramandougou, whlle for the Permethrln operaElon, observatlons were made on the Danangoro statlon. Thls study rdas almed at maklng pre- and posE-treatment catches ln the treated zone and observing the posslble effect of the flrst Carbosulfan sprayings on the fish fauna of t.he Bandama. For the purpose of a comparatlve evaluation of the posslble effects of the product on the non- target fauna, the "untreaEed" Badikaha staEion was selected as a conErol station, on the one hand, and samples rdere taken ln July 1986, i.e., before the beginning of the experluental spraying campaign, on Ehe oEher hand. The data collected in July 1986 at Badlakaha, as well as in the treated stations served as reference for the comparisons. EFFECTS OF CARBOSULFAN The followlng observatlons were made: Ehe lnsectlclde Lraves did noE cause any masslve flsh mortallty at the different spraying polnEs because no dead fish floaEing on Ehe water surface was noted during the sprayings; - the successive insecElcide waves in the lower Bandama did not cause any massive f lsh mort.alit,y ln Ehe Tiassale staEion; - Ehe number of flsh species caught remained practically the same durlng and afEer the Carbosulfan campalgn; 1 I .1 Evolutlon of the conposition of Ehe comnunlty I2 the number of specles caught ln the treated stat,lons was practlcally the same as that obtalned during the pre-treat.menE sampllng and not slgniflcantly different fron that of the control statlon; the samplings nade with drifE and cast nets revealed the qulte considerable presence of juvenlle flshes; no specles disappearance was observed as regards the princlpal specles whlch make up the ftsh fauna of the treated statlons; - specles which, in one way or the other, rrere absent frou our catches were found elther in the drlft and cast net catches or in the catches of commercial fishermen. L.2 Quantltative evolutlon of catches The following dlfferenE observations were made: the CPUEs are generally greater at Badlakaha than ln the treated statlons. Thls can be explained by the fact thaE the pressure exerclsed by the flshermen ls great.er in the Ereated stations than aE Badiakaha; the total CPIIEs obtalned ln the treated stations durlng and after the lnsectlcide treatnents are not. signlflcantly different from t.hose obtained before the start of the Ereatment canpaign; the successlve lraves of Carbosulfan in the lower Bandama dld not have any lncidence on the flsh catches; the 1ow level of catches at Tlassale ls of the current whlch made fishing dlfficult; probably due to the force the great cat.ches nade by the small-mesh nets proved that juvenile flshes occupy a good position ln the stocks, are available and that the sEock regeneraElon capacity has noE been seriously disrupted in the treated stations; the evolutlon of the total CPUEs of the main species does not reveal any greaE change. 1.3 EvoIuEion of the coef f lcient.s of condi t.lon The comparat.ive study of the values of the coefficients of condition of the maln species caughE ln the treaEed stations and of those of the control staElon did noc reveal any parElcularity. The same is true of the comparlsons made ln relatlon to the resulEs obtalned before the beginnlng of Carbosulfan spraylng campaign. In concluslon, Carbosulfan has not had harmful effect.s on the flshfauna of che Bandama- tle regret Ehat we were not able Eo use drifE net.safter the cessatlon of the carbosulfan spraylng (ic was beyond our cont rol) . a a I3 2. Effects of Pernethrln The t'larahoue ldas selected for the evaluatlon of the medlum-term effecEs of Talcord Permethrln on the flsh fauna. Since the eratercourse ls already subjected to an alternatlon of different lnsecticides and conslderlng the risks of selectlon of reslstance to pyrethrolds ln the cotton-growing areas, the upstream part of t.he river includlng the Mankono statlon was not lncluded ln Ehe treatnents. However, Iile consldered lt as a control statlon. 2.1. EvoluEion oJ the composltlon of the comnrunlty For reasons beyond our control, we were not able to carry out all the planned sampllngs, malnly because the statlon was dry ln March and May 1987. The results were also lnfluenced greatly either by insufflclent rrater at the station or by dlsruptlons caused by unknown people who ln August 1987 undertook fishing wlth herblcides. This resulted in a conslderable decrease ln the number of specles caught. However, the drift net catches gave reassuring results ln that Ehe presence of juvenlles was conslderable. 2.2. Quantitative evolution of catches The CPUE values rrere very low at Ehe Danangoro statlon compared with those for I'lankono. The very low resulEs for August 1987 can be explained by the facE thaE our samplings were made the day after the use of herblcldes by the vlllagers. It would therefore be rash to draw conclusions because Ehey would not reflecE Ehe field realltles. At the very Eost, we can affirm that Ehere have not been great changes ln the coefficlent, of condition values of the maln specles.