Ghana invertebrate monitoring report for 1996/97

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ECOLOGICAL GROUP Nineteenth session Odienn6. 4 - 6 February. 1998 OCP/VCU/HYBIO/98.7 ORIGINAL: English GHANA INVERTEBRATE MONITORING REPORT FOR 1996197 J. Samman In Ghana, the Invertebrate Monitoring Activities of the Onchocerciasis Control Programme started inlate 1974. During the reporting period (November 1996 - October 1997),the rivers Pru and Oti were sampled during the dry season as requested by the Ecological Group. Daytime and night-time drift samples were collected from the two rivers while Surber samples were collected only from the Pru. zuVER OTI: Regular sampling on River Oti at Sabari started in 1975 while weekly treatment on the river began in 1977 and stopped in 1992. Previous pre-treatment and post-treatment records showed that until treatment stopped, reductions in the number of invertebrates per taxon and in the number of taxa were being recorded in the drift each year. Affected populations started to recover but at a slow rate after treatment had stopped. During the period under view, recovery among some populations continued. High drift indices were recorded among most of the ephemeropterans. The Leptophlebiidae appeared to have fully recovered. The Baetidae and the Caenidae, the commonest taxa in the river were however, yet to recover fully. The Heptageniidae and Oligoneuriidae, on the other hand, continued to be rare this year. RIVER PRU: Treatment on the Pru started in 1985 ie. five years after monitoring had begun on the river. During the period under review, Pru was treated with etofenprox, phoxim and B.t.-14. Earlier reports noted that for several years there had been some marked reductions in the Pru invertebrate drift indices. Since 1992, there has, however, been a continuous increase in the drift of most taxa. This year, there appeared to be full recoveries among populations of the Baetidae, Caenidae and Leptophlebiidae which are the most predominant ephemenopterans in the river. Tricorythidae which had been absent in River Pru for 3 years was seen in 1996 and 1997 . Neoperlasp. which had also not been seen since 1993 continued to be rare in the river this year. In February 1997, a poisonous agro-chemical was used in illegal fishing on the Pru. It was a catastrophe which seriously affected all forms of animal life in the river. The effect on invertebrates was, however, short lived.