Wetland & Fish Ecology - Enviro Dynamics Namibia

79
4.8 IMPACTS OF FLOODGATE OPERATION (DURATION AND TIMING OF
FLOWS) ON IISHANA AND FISH:
These impacts have to do with the free migration of fish and aquatic invertebrates in
this network of inter-connected iishana through the system, including the Okatana
River to reach other iishana and the pans downstream. The broader issue is the
migration of fish and other aquatic fauna through infrastructure that could block
their route throughout the region. Clarke (1998a) who studied iishana found little
evidence of such impacts and assumed that enough fish were able to move
downstream; however his study was nearly 15 years ago and there has been an
increase both in the number of people living and fishing in the area as well as in the
availability of fine meshed and mosquito nets often found completely barring
bridges and culverts and even siphon entrances. This is an issue that needs to be
addressed by MFMR regulations and their enforcement.
4.8.1 IMPACT RELATED TO DIKE AND ITS CHANNEL:
Fish migrations down the Cuvelai and its associated iishana ending in the channel in
front of the dike will all be deflected along the featureless banks of the channel next
to the dike. An increase in predation of smaller fish by catfish and piscivorous birds
can be expected. When floodgates are opened, some of the dammed water runs
down the channelized Okatana River, fish will move through increasing their
vulnerable to injury and predation by birds and predatory fish.
Of greater concern is the increased opportunity for fishing by local people using
modern day effective fishing gear. The use of long fish funnels and fykes and nets at
culverts and bridges is prohibited in the fisheries legislation but little specific law
enforcement is taking place to enforce these fishery regulations in the oshana
region, the argument being that as result of the temporary or ephemeral nature of
the fish habitat, all fish will anyway succumb and so are free to be harvested.
For long-term benefit of the fisheries as natural resource, such a laissez faire
approach is not conducive. Neither is it according to the traditional natural resource
management of fish resources in the area where limits were set by traditional chiefs
on appropriate fishing times and gear types (van der Waal, 2000). If the optimal
benefit of these artisanal fish resources for local communities is a goal of the MFMR,
all bridges and culverts and sluices should be no-fishing zones allowing free passage
for migrating fish.
4.8.2 IMPACT OF DEEPENING AND LINING OKATANA RIVER IN OSHAKATI:
The deepening and straightening of the Okatana River in Oshakati will have a slight
positive effect if more water is kept for a longer period of time and if natural
vegetation is allowed to grow back in areas where it was disturbed by deepening,
compaction and channelization.
There are also negative impacts expected:
Draft Environmental Impact Assessment: Oshakati Flood Mitigation Project
Specialist Study: Wetland Ecology and Fish Ecology Imputs
July 2012