Institute of aquatic biology (Ghana): summary of 1988/1989, hydrobiological monitoring report

ONCHOCERCIASIS CONTROL PROGRAMME II.I IJIIST AFRICA PROGRAMME DE LUTTE CON?RE L-ONCHOCERCOSE EN ATRIQUE DE L-OUEST ECOLOGICAL GROUP Eleventh session Kara, 27 February-2 l,larch 1990 0cP/vcu/HYBro/90.9 TNSTTTUTE OF AQUATTC BTOLOGY (GHANA) SUMMARY OF 1988/1989 HYDROBIOLOGICAL MONITORING REPORT -2 INSTITUTE OT AQUATIC BIOLOGY, GHANA suMr"rARy 0E FISIT ITONIToRTNG 19B8A8g E.K. Abban, J.K. Ofori, H.R. Dankwa and p.K. Oforl-Danson Monitoring of fish to assess possible influence of larvlcides used to control Simuliun- populations cont.ained in Ghana during the 1988/89 year (i.e. octoberrEEE:Gptember, 1989). Rivers monit,ored were Ehe oti, ?ru and the B1ackVo1ta. The sites monitored on each river, sanpling procedure and frequency were all as sEipulaEed by OCP protocol. Estiuates made of fish catches (CPUE) in rhe ri.vers during Ehe current year were generally lower compared t,o caEches of theprevious year. In the Oti, total CPUE recorded between January and July per sampling round were all lower compared Eo data for comparable hydrological periodduring 1988. However, Brycinus nurse and B. leuciscus, among species considered asfrequently occurrlng in the Oti, recorded higher catches during 1989 compared to CPUEs for the species in 1988. Estimates of changes in rhe'condition- (K) of fishes in rhe rivers stronlea Ehat the influence of hydrology and thus ecology on K of fishes rdas stil1 operative. The -condition' of fishes during 1988 were generally maintained in all rivers during the currenE year. Petrocephalus bovei however, recorded a slightly improved K in river Oti during 1989 conpared to 1988. B. leuciscus had a poor mean condition in 1989 compared to 1988 in_ the Black voltil Length frequency distribuEion of species consldered predoninanE in the Oti and Pru during the year showed paEterns similar to those.of 1988. It was evident from the patterns that hydrology influenced Ehe size range of a species caught. The range of sizes of mosE species caught lasE year was the same during Ehe current reporting year. The results obtained during 1989 could therefore be said to be comparable to those obtained in the prevlous yearo The observed reduction in CPIIE could not be directly relaEed to hydrology because caEches during the flood period of 1987/88 were slightly higher than those of. 1986/87 . It could have therefore been expected that CPUEs during f988/89 would be higher than those of the prevlousyear. The nainEenance of the 'condltion- where Ehere was no lmprovement was considered an indicaEion that most fish found their food naEerial ln the river systems and used them. -3 INSTITUTE OF AQUATIC BIOLOGY GHANA J. Saman and J.S. Amakye SUMMARY During the period under review, Lhe Institute of Aquatic Biology decided to continue (ar its own cost) witir the regular invertbrate monitorLng on the 3 rivers: the Black Volta aL Bamboi, the Ori at Sabari, and the Pru aE Asubende, even Ehough the OCP had decided to discontinue with t.he exercise with effecE from May 1987. Additional monitoring siEes were selected and some special st.udies were also undertaken on Ehe Black Volta at Agbadzikrom and Chache during the pe riod . Available records frora the OCP indicat.ed that the Black Volta and its tributaries were Ereated with B.E. H-14, chlorphoxim, carbosulfan and permeEhrin during the period under reviewl-The Pru river was treated with B.c I{-14 and chlorphoxim. There was very litrIe information on t.reaEment on the Oti. In Oti, comparison of the reporting period-s data wiEh those of the prevlous two years showed thaf the drift indices of Ehe najority of che invertebrates continued to be low. There appeared to be even furE.her decreases in the Leptophlebiidae and the Heptageniidae populations. There was on the ot,her hand an insignificanE increase in the drift of the Caenidae. In the Pru river, there were indications t,hat the drift indices of the majority of the invertebrates slightly increased when chlorphoxlm treaEment on Ehe river was suspended for some 5 months. There was no improvement in the drift of the invertebrate fauna in the Black Volta at Bamboi. In addltion Eo the lleptageniidae and Ehe Tricorythidae, the Hydracarina (which is hlghly susceptible to permethrin) also became very rare ln -the river. The drlft ratios of all Ehe predominant, groups were also -bmparatlvely low during the period under review. Some preliminary studies conducLed on the Black Volta at Bamboi, Agbadzikron and Chache indicated that Ehe river was generally poor in inverE,ebrate fauna and that the insecticide treatment on the river might have affected the invert,ebrat,es in the whole river course. r Among the sEaEions visiced on ttre Black Volta, the Chache statlon was select.ed for regular lnverEebrate monitoring. In conclusion lE is noted t.hat iE. ls not surprising that the regular use of insecticides in a river over a decade or so could have some effects on Ehe rlver biota. However, in order Eo ascerEain the reducing densities in the fauna and Eo det.ermine the seriousness of the treatment effect.s in the rivers, it, ls recommended that, next year (October 1989 to September 1990) the stations be sampled at regular (monthly) intervals. There is some perlod{clEy ln the abundance of Ehe majoriry of the Eaxa. This is known for sone taxa, iE is yet to be determined for others. The data to be collected ln t.he next year would be conpared with the data on t.he rivers during the pre-treat.ment period or durlng Ehe early years of Ereatment. when monthly samples were collected.