Wetland & Fish Ecology - Enviro Dynamics Namibia

65
During low floods, especially after a long dry period, there is very little fish life in the
few open water ponds remaining in the oshana system – all fish have died or been
caught out by local people.
Permanent waters acting as refugia play a very important role to maintain fish
species presence during the recurring dry periods.
Against this background the impact of the dike and associated channels have very
little direct impact on fish diversity or the fishery except for those aspects discussed
elsewhere.
If the dike and channels are to have a positive impact on the livelihood of the local
communities, it has to do with fishery management and specifically with protection
of fish life in more permanent water bodies to act as inocula for new populations
breeding and distributing in the iishana once inundated. This project may convince
policy makers that it is worthwhile to invest in education and law enforcement to
identify refugia in the oshana region where fish can be protected during dry seasons
to repopulate the oshana system in the next rainy year.
The ‘no fishing’ signs erected at several of the deeper borrow pits such as the one at
the bridge on the Okatana road show that authorities are aware of this and are
restricting fishing in these refugia.
Proof of successful breeding of fishes in Namibian oshana reaches of the Cuvelai
System has been obtained earlier (van der Waal 1991, 2000) and further evidence
collected now as juvenile fish.
A) IMPACT RELATED TO DIKE AND IT’S CHANNEL:
The dike and the channel alongside it will not have a large effect on wetland and
fish diversity but the fishery locally and further downstream may be affected through
any negative effect resulting from altered water quality or flood modification.
The construction phase of the dike may have a serious impact on aquatic life if work
is not completed and levelled and compacted and covered in time with suitable
sand or other less fine material before the next flood. If not, large scale deterioration
of flood water with erosion can be expected, smothering vegetation downstream as
well as preventing feeding and breeding of fish.
This will then have a similar negative effect on the fishery around Oshakati as well as
the area south as far as the Omadhiya Pans.
How the excavation is done can be critical. The bulldozing procedure should be
sensitive to the iishana and as far as possible follow the natural contours of the
existing iishana. Any bulldozing of the oshana floor should not be perpendicular to
the flow direction.
Draft Environmental Impact Assessment: Oshakati Flood Mitigation Project
Specialist Study: Wetland Ecology and Fish Ecology Imputs
July 2012