Pangani - Fish and invertebrate life histories and important fisheries of the Pangani River Basin

This report describe the relationships between the timing and magnitude of freshwater flows in the Pangani system and the biology and life history characteristics of its key fish and invertebrate species. Such information could be used to infer what the historic abundance levels and distribution patterns were for these species in the Pangani catchment (where such information is lacking); predict how abundance and distribution patterns may change in the future under altered flow patterns; and derive the relationships between water level and fishery production that will be used to predict changes in catches in Nyumba ya Mungu, Lake Jipe, Kalimawe Dam and the Pangani estuary under different flow and water-level scenarios.

This report is the product of two, short, desk-based Specialist Studies of the Pangani River Basin Flow Assessment (PRBFA) Initiative. Based on published literature, information from the Internet
and from a five-day field visit in June 2007, the report describes the main aquatic biotopes of the Pangani River Basin, an area of over 43,000 kmē.

The relatively high conductivity within the largely volcanic basin is confirmed and a description is given of the fish and invertebrates that reside in the different water bodies - mountain streams,
crater lakes, rivers, man-made reservoirs, floodplains and the mangrove fringed estuary. Finfish and invertebrates (in this case, crustaceans) of commercial importance are further
described, particularly in relation to their life histories and response to changes in river flow variables. Included is an updated list of freshwater fish in the Pangani system.

The fishery of Nyumba ya Mungu and of estuaries comparable to the Pangani are described with data from various sources. Hydrological data are used to discern linkages in fisheries output and water levels (river flow or surface area) and conceptual relationships are developed, highlighting probable links between the timing and magnitude of freshwater flows in the Pangani system and
the flow-related requirements and life-history characteristics of each species.

The years 2006 and 2007 were exceptional with regard to rainfall, water levels and flows and thus the findings of several field studies conducted during that period probably do not reflect the average situation in the Pangani Basin. For example, the conductivity situation as recorded in this study, which was comparable to the early post-impoundment studies in Nyumba ya Mungu as reported in Bailey (1996) needs close monitoring over extended time periods across the entire Basin before conclusions can be drawn on the potential impacts of (increasing) conductivity on the fish, invertebrates and fisheries.

The Pangani Basin as whole has a comparatively high fish biodiversity, probably a reflection of the wide range of available habitats. Some of the characteristic species of African rivers and floodplains that have been linked to the Congo Basin such as the Rufiji and the Ruvu are absent from the Pangani (e.g. Citharinus, Distichodus, Alestes, Hydrocynus), probably a result of the geological history of the region. Various Cichlidae and the catfish Clarias gariepinus dominate the catches but virtually all species present are harvested in any life stage accessible to fishing gears.

Invertebrate biodiversity is high in the Basin but its knowledge is still incomplete. Harvesting is almost entirely restricted to estuarine crustaceans (prawns and crabs).

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