Influence of drought and flooding on the colonisation of floodplain pans by riverine fish in the Zimbabwean lowveld

Abstract

Received 11 May 2009, accepted 31 July 2009Temporary floodplain pans in southern Africa are defined as ‘seasonal freshwater palustrine wetlands, up to 2 m deep and with a maximum surface area of 8 ha, adjacent to a well-defined river channel’. They are seasonally or periodi-cally inundated when the river overflows its banks in a flood event, and their substrate is dominated by alluvial or hydric soils (Cowan 1995). Floodplain pans play an important role as refugia and breeding habitats for freshwater fish (Coke and Pott 1971). In southern Africa, extensive floodplains are found on large rivers such as the Zambezi, Kafue, Limpopo and Pongolo (Davies and Day 1998), and, in Zimbabwe, floodplain pans occur in the middle Zambezi (Mana Pools) (Goudie and Thomas 1985) and in the Save–Runde system (Dallas 1998).The hydrological regimes of floodplain pans follow a seasonal pattern of filling up in the wet season and then drying out after the rains end. During the dry season and in periods of extreme drought these pans are totally dry but, as soon as they receive some water, explosive biological activity begins. Early colonisers include insects and birds, which are highly mobile, followed by groups such as gastro-pods, crustaceans, and some amphibians and fish, which all have resting stages that allow them to survive without water (Davies and Day 1998). Most fish species can only colonise the pans once the river has risen sufficiently to connect with them. This study investigated changes in the fish communi-ties in relation to drought and flooding in four floodplain pans in the Save Valley Conservancy, south-eastern Zimbabwe. The pans are situated in the alluvial floodplain of the Save River, which covers approximately 40 km