|Freshwater prawn from the Kunene river|
A. Ngulu, M.N Ekandjo, Le Diep Lan, O. Ndikwetepo and Le Thien Ly
Background information preceding the trip
Prawn breeding and rearing is one of the objectives of the South-South Cooperation (SSC). This task is to be carried out at Ongwediva office. As per recommendations given by the FAO consultant, Dr. Francois Rajts, Ongwediva office was tasked to collect prawn brooders during the course of September to October, from the Kunene River. Previous collections have been done at the Kunene River Mouth by the Swakopmund staff together with the North-west staffs. This area is known to support a larger population of these aquatic organisms as they are known to be breeding there.
The Kunene River Mouth is within a Nature Reserve and at the same time a mineral protected area. Therefore for one to access this area, you need two permits, one from the Ministry of Environment and Tourism and Mines and Energy respectively. As narrated by one staff member that once travelled to the Kunene River Mouth, the road towards the mouth is very bad, it runs along the coast, whereby it may be damp at some point, with other parts passing through the sand dunes. There is no filling stations therefore one need to carry extra fuel. This seems to have discouraged the consultant as he opted for a better accessed site. According to the consultant, in other African rivers the African Fresh Water Prawn are widely distributed and may be collected at any point along the River stretch and believed that should be the case with the Kunene River. The local staff who have experience on the Kunene River through Annual Fisheries Biological Surveys, had tried to advise the consultant on how difficult can it be to collect prawns along the Kunene River stretch, given its flow regime (fluctuation in both flow and water levels).
The Kunene River Flow Regime is influenced by the water needed to run the turbines at Ruacana Hydropower Scheme. Water is released during the working days and closed during weekends. This flow regulation affects the river and its aquatic organisms. Apart from the Ruacana Hydropower effect, the river flow is also influenced by the two falls, one at Ruacana and the other one downstream at Epupa.
The consultant was not convinced by the information given by the local staff, only when he managed to travel along the Kunene River, between Ruacana and near Kunene River Lodge that he was able to understand this river. Together with other staff, the consultant attempted to sample for prawns in this stretch without catching any. The team agreed that, collection should only be done downstream of the second falls (Epupa). Downstream of Epupa, a prawn was collected once in 2009, by attaching itself on a gill net, made to sample the fish species. It was again advised by local staff who conduct the Annual Fisheries Biological Survey that, although prawns have been recorded downstream of Epupa (Otjinugua/Marienfluss), it may not be found in a required amount. After hearing the revelation on how difficult is it to reach the Kunene River Mouth, the consultant recommended that collection should be done downstream of Epupa Falls in order to avoid complications in terms of logistic with regards to reaching the Kunene River Mouth.
Collection method and materials
After an approval was given by the permanent secretary, on Monday the 30 September 2013 a team of five staff, consisting of three (Ngulu A., Ekandjo M.N. and Le Diep Lan) from Ongediva and two (Ndikwetepo O. and Le Thien Ly) from Onavivi offices respectively, travelled to Otjinugua/Marienfluss, some 300 km downstream of Epupa Falls. On the second day (Tuesday the 01/10/2013), the team arrived at Otjinugua and immediately set about 83 traps of different types. These consisted of sixty (60) made out of Coca-Cola bottles, twenty (20) made out of pipes, two funnels made out of shade nets and one big trap using a paraffin lamp to attract the prey. Setting was done for three days. And the duration was twelve hours, i.e 18-17 hours in the afternoon and retrieved at 6-hours early morning. Traps were set along the reeds on either banks of the river.
Environmental parameters were recorded at 6.30 Am and at 5.30 Pm from during 2nd to 4th of October. On the first day, the water level was moderately low, just about 1.3 m. during the two consecutive days, water levels raised to above 2 m. This was due to the effect of the Ruacana Hydropower Scheme that started operation on Monday the 30th.
On the first day of retrieving, a total of eight prawns. These were all caught by the pipe made traps. On the second day of retrieving; only two prawns were caught, still by the pipe made traps. On the last day, nothing was caught. Therefore a total of ten prawns were caught of which one was very young. All the ten prawn caught died in the third day due to lack of dissolved oxygen in the water container where they were kept. There was no much effort made to aerate the container.
Temperature range from 25 ± 0.5 in the morning and 27 ± 05 in the afternoon. PH range from 7.2 ± 0.2 to 7.6 ± 0.2. Sample of phytoplankton where also collected, however it not yet send to Swakopmund for analysis.
Conclusions1. Although the objective of this trip (to collect about 1000 prawn brooders) was not achieved, on the science background, collecting about ten prawns at that specific site was an achievement. Apart from a single prawn recorded in 2009, to the author’s knowledge there are no documentations that indicate the presence of prawns in that stretch of the Kunene River.
2. The pipe-made traps were effective in collecting prawns, as they were the only type that managed to catch prawns at that site, as compared to other types of traps employed.
3. This was more like a fact finding mission (are the African fresh water prawns widely distributed throughout the Kunene River?) then a trip to collect brooders.
Recommendations1. Given the findings from this trip, it can be recommended that, the Kunene River Mouth should be the suitable site for easy collection of Prawn Brooders
2. The effective trap to be used should be that made out of a pipe.
3. The annual fisheries biological survey should also include traps to sample the Kunene River stretch of the presence of prawns at various river reach.
4. Proper planning with recognition of local knowledge should always be put into consideration in future to avoid the repetition of this
|Setting Prawn traps|
|Keeping collected prawn|