Summary of Ghana fish monitoring annual report for 1996

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ECOLOGICAL GROUP Eighteenth session Accra. 29-31 Januar.y 1997 OCP/VCU/HYBIOIg7.6 ORIGINAL: English SI.JMMARY OF GHANA F'ISH MONITORING ANNUAL REPORT FOR 1996 E.K. Abban The Onchocerciasis Control Programme (OCP) has been a campaign in West Africa to reduce the incidence of river blindness to a level which will no longer constitute an obstacle to human and socio-economic development. Among the major operational activities of the OCP since its inception in 1974, has been the larviciding of identified segments of rivers. The larviciding has been aimed mainly at controlling infected populations of the disease vector, Simulium. The monitoring of aquatic organisms in larvicided rivers, aims at assessing potential long term impacts of larviciding on non-target fauna, including fish. During the current reporting year rivers on which fish populations were regularly monitored in Ghana, were the Oti and Pru at Sabari and Asubende respectively. For a summary assessment of the status of fish communities and populations in rivers subjected to larviciding, two broad characteristics of their fishes have been monitored. These have been estimation of catch per unit effort (CPUE) of fishing and the coefficient of condition (K) of fishes. During the current reporting period (ie, October 1995 to September 1996) estimates of CPUE (total and for regularly occurring species) indicated the following. On river Oti, total CPUE involving catch by all mesh-sized nets over the year showed an 84% (by weight) increase compared to catches of the previous year. The increase was however, not due to increase in catches by all categories of nets neither was it due to increased catches during all hydrological seasons. The over all increase in CPUE was attributed to "Spot increases" in CPUE of different mesh sizes of nets at various time of the year. Only 17.5 mm mesh nets recorded increases in CPUE, ranging from 13% to 133% from January till September. For all other meshes CPUEs recorded during, at least, two of the four hydrological periods of the year were below observations made during the previous year. On the river Pru, the overall CPUE recorded during the current reporting period was 26.44% in excess of records of the previous year. The total increase was accounted for by increase of 99%, 44% and 14.35% during the October-November-December, January- February-March; and April-May-June; hydrological periods respectively. During the high- water hydrological period (July-September-October) CPUE recorded was lower compared to comparable records of the previous year. The situation was attributed to high levels during July till September of the current year compared to the previous year. 2The generally recorded higher CPUE on the Pru during the current year was apparently a continuation of increase catches on the Pru started during 199411995 compared to decreasing trends observed between L992 till 1994. Fish Condition (K) Over the years, the seasonal mean "condition" of nine regularly occurring species* (see list below) in catches on the Oti river have been monitored. During the current reporting year, the seasonal slight fluctuations in the condition of the fishes were comparable to those observed in previous years. Seasonal mean K values for individual species were also generally comparable. However, for six of the nine fish species seasonal K values estimated during the current year were more comparable to the highest value obtained for a species per season during the past three to four years. The observation was considered as a possible indication of improving environmental status of the river for fish in general. xSpecies monitored penitered: Petrocephalus bovei, Brycinus mncrolepidotus, B. nurse, B. leuciscus, Schilbe intermedius, S. mystus, Labeo senegalensis, Synodontis ocellifer and S. schall/ gambiensis; On the river Pru, the species monitored for detectable long term changes in "condition" have been; Polypterus senegalus, P. bovei, S. intermedius, S. tnystus, Hippopotarnyrus pictus, B. nurse and B. leuciscus. Observations on seasonal mean K values and trends in all the species were highly comparable to estimates of previous years.