Wetland & Fish Ecology - Enviro Dynamics Namibia

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Discussion fish survey data:
The fish community of iishana consists of five pioneer species also found further south
in the Omadhiya wetlands and even Etosha Pan. These species are Barbus
paludinosus, Barbus poechii, Clarias gariepinus, Clarias ngamensis and Oreochromis
andersonii, all known to be pioneer, colonising fish species especially successful in
unstable aquatic environments. There are few other species collected in 2012, some
which were previously regarded as rare, but seem to have colonised some of the
more permanent waters around Oshakati in 2012. These other species were only
collected in sites associated with the Okatana River and channel including
Marcusenius macrolepidotus, Petrocephalus catostoma and Tilapia sparrmanii.
These fish were first collected in iishana during the 2008 and 2009 floods and now
seem to have established themselves in more permanent water bodies. Other fish
species not collected during the previous floods may have derived from the Kunene
River via the canals of the interbasin water transfer scheme and through connections
with the wetlands associated with the canal and Okatana River, establishing
populations. This group includes Barbus radiatus as well as some other species such
as Tilapia rendalli. The picture is not clear however, as many species occur in both
the upper reaches of the Cuvelai and also in the Kunene River.
The conclusion is drawn that the iishana have a low diversity of pioneer fish species
during low floods. In good flood years, or efundja as happened in 1976 and again in
2008 to 2010, the number of fish species entering the iishana from the northern
reaches higher up the river increases. Eventually, most fish die as waters dry out
during dry cycles.
Another trend in 2012 is that the actual number of fish collected in the shallow, drying
out iishana was low. Sites associated with the canal and Okatana River fed by
overflow from the Calueque-Oshakati Canal, has a greater diversity and higher
numbers of fish, partly derived from the canal that is connected directly to the
Kunene. From a fish conservation point of view such connection and invasion by
foreign fish is not favourable for the integrity of the Cuvelai River and especially not
for the Etosha National Park and Etosha Ramsar site. Maintenance of this asset by
allowing the original fish species living in the upper Cuvelai and iishana to migrate
down the river and iishana where they can be harvested by local communities,
adding valuable natural resources, would be the preferred natural pattern.
Draft Environmental Impact Assessment: Oshakati Flood Mitigation Project
Specialist Study: Wetland Ecology and Fish Ecology Imputs
July 2012