Summary of the annual report of OCP’s hydrobiology section

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ECOLOGICAL GROUP Nineteenth session Odieme, 4-6 February lQa8 OCP/VCU/HYBIO/98.4 ORIGINAL: French Revision I SUMMARY OF THE ANNUAL REPORT OF OCP'S HYDROBIOLOGY SECTION This year again, the hydrobiology section pursued its activities of i) monitoring of the Marahoue, ii) snrdy of the long term impact of Vectron on the non-target entomic fauna and iii) management of aqutic surveillance daa. In addition, in compliance with the recommendations of the Ecological group, rhe section organized working sessions in Ouagadougou to prepare the consolidated report on the 20 yerJr hydrobiological surveillance activities. From January 1996 to April 1997, only four of the seven operational insecticides were used on the Marahoue at Danangoro and Entomokro. These insecticides were B-r. H-14 used during the low- water period at less rhan l5m%, phoxim and pyraclofos during the spate periods between l5mr/s and 75m3ls and hnally, permethrin used during the spate period in tbur cycles at discharge rates above 150m3/s. The alternate use of these insecticides according to the diff-erent discharge rates, as well as the reprort of sspersion prriods, have made it possible to limit their harmful effecs on the non-target aquatic tauna. I. Srudy of Saxicolous Fauna at Danangoro At Danangoro the densities of the overall fauna showed a continued increase between November 1996 and March 1997, rising from 180.4 individuals/surber sample to 4550.8 individuals/surber sample. Organisms such as rhe Ephemeroptera (the most susceptible to insecticides) also showed some proliferation during the monitoring period. The Trichoptera and Chironomidae which are the least susceptible organisms to insecticides showed nanral variations in *reir dersities partly linked to the variations in the thickness of tlre plant cover on the rock slabs. The taxonomic richness of the saxicolous fauna at Danangoro was 22 taxa for the 199611997 period compared to 28 taxa in the pre-larviciding period. As in previous year, it was especially characlerized hy the ahsence of the Tricorythidae. The taxonomic richness of the fauna collected from night time driti samples was diversified, varying heween 26and 30 taxa and showed the absence ol'Ephemeridae, Oligoneuridae and Neoperla s.p. The srucly tlf rhe relative corn;'xrsition of the saxicolous populatirtns showed a predominance of the 1'richoptera tirllowed by rhe Chironomidae and Ephcrneroptera in 199611991. 2A comparison of the relative fiequencies of rhe principal taxonomic groups of rhe 1996t1997 period wittr those observed during the pre-larviciding peri<d, as well as with rhe fiequencies recorded at dift'erent periods of use of the insecticides made it possible to classity the latter on a scale of increasing toxicity in respect ro Ephemeroptera. The frequencies of the Ephemeroptera in l996tlD7 were tower than lhose observed during the pre-larviciding period as well as the periods of use of temephos <tr B.t. H-14. Conversely, they were higher than Ore fiequencies recorded during the periods of larviciding with clorphoxim as well as rhose during the alternate use of the following insecticides: permethrin-pyraclofos-phoxim and B.t. H-14 in 1994195 or carbosultan-pyraclofos-phoxim and B.t. H-14 in 1995t96. II. Srudy of saxicolous tauna at Entomokro At Entomokro, the densities of tlre overall fauna also showed a continued increase between November 1996 and March 1997. They rose from 170 individuals/surber sample to 6297.8 individuals/surber sample in March I997. The densities of the Ephemeroptera were slightly lower than those observed during rhe pre- larviciding period but on lhe whole, they were higher rhan rhe densities recorded in 1995/96. The densities of Trichoptera and Chirornmidae were higher than ttrose recorded in 1995t96 as well as *rose of the pre-larviciding period. The taxonomic richness of the saxicolous fauna at Entomokro was more diversit'ied than that at Danangoro. ln 1996197 the same number of taxa (26) as during the pre-larviciding preriod was recorded. The taxonomic diversiry of the fauna collected from rhe night time drift samples showed the absence of Ephemeridae, Oligoreunidae and Neoperla s.p. The richness and diversiry of the fauna in rhe night time drift in 1996/97 ret'lected the very limited impact of rhe insecticides used ar Entomokro. A look at the relative composition of the saxicolous populations at Entomokro shows a predominance of the Trichoptera followed by ttre Ephemeroptera and the Chrironomidae. The variations in the relative tiequency of trichoptera and Chironomidae at Enlomokro do not seem to be related ro the use of the antiblackfly larvicicles. A comparison of he proportion of the Ephemeroprera in 199611997 with those observed during the dift-erent periods of larviciding shows that their relalive tiequencies are lower than those recorded during the pre-larviciding period, as well as during Ore prerio<J when B-1. H-14 was used. On the other hand, tlrey are higher than the tiequencies observed cluring temephos and chtorphoxim, as well as those dtrring the alternare use of the insecticides in 1994/95 and r9g5196