APPENDIX 4: CATCH MONITORING SURVEY

A catch monitoring survey was carried out at Makungwa and Rukuzye dam between March 199] and March 1992 to estimate the total yield from these reservoirs.

All fish catches at these reservoirs were to be measured during 5 days per month. Since it was anticipated that there was a difference in fishing effort between week days and weekend days, 2 weekend days and 3 weekdays per month were randomly chosen. The recording took place 12 hours per recording date, starting at 12.00 hours or at 0.00 hours.

In total 28 different men and Rukuzye and 99 at Makungwa were interviewed. No women were met during the survey. Catches were recorded for the rod and line and net fishery, and on one occasion for a trap fisherman. The nets were in all cases used as seine nets.

The number of records was limited, and changes to the original monitoring schedule were made for unclear reasons. During some months no weekend days were monitored, and the stratification of the monitoring schedule was therefore lost. This, plus the limited number of records, made it necessary to group the data per 3 month periods for the analysis. The number of days recorded and the number of records per period, per dam and gear are given in table 1.

The reliability of the data can be questioned. The enumerator should only have recorded catches from fishermen who stopped fishing during the recording period. In some cases it was clear that also people who continued fishing were recorded, but in other cases this was not obvious. It is of course difficult to meet people just when they stop fishing, especially around a large dam. This may have resulted in the underrecording of the hook and line catches. Zero catches were apparently not always recorded, which resulted in an underestimation of the number of fishermen and an overestimation of the catches per hour.

There was a significant difference in fishing effort between week days and weekend days. Therefore the effort was kept separate for the different days. There was no difference in length of fishing session or catch per hour between week and weekend days. These data were grouped. The fishing effort, length of fishing sessions, catch per hour and estimated total catch per period and per dam and gear are given in table 2.

The total yield from the rod and line and net fishery is estimated at 6000 kg/yr, for Makungwa dam (94% for net fishery and 6% for rod and line) and at 2200 kg/yr. for Rukuzye dam (79 and 21% for nets and rod and line, respectively). Yields per hectare per year are respectively 600 and 100 kg. The monitoring of catches was done during a year of extreme drought and especially the water level in Makungwa dam went very low. It was easy for the net fishermen to reach all areas with their seine nets, and as a consequence they fished out most of the fish. The high catches at Makungwa were probably unique for that year only and can not be considered sustainable. The yield is therefore more related to the biomass of the reservoir than to its production.

Catches are always effected by annual fluctuations and the monitoring of catches during one year does not recognise these fluctuations. However, one year of records could give an indication of the average annual yield in those cases where fluctuations are not too great. Small Water Bodies are often affected by strong water level fluctuations that influence both the production and the catches. The catch monitoring survey was carried out during the driest year recorded in southern Africa, and water levels were exceptionally low. Especially for Makungwa dam the yield during the year of monitoring probably does not even give an indication of the average annual yield.

Table 30 gives the species composition of the catches in the two reservoirs by gear. It is obvious that the net fishery concentrated on the tilapia species, while the rod and line fishery targets a wider variety of species. The average sizes of the tilapia species in the seine nets are 43 and 20 gr. The minimum mesh size for nets in Zambia is 3.5 inch (89 mm.) stretched mesh, which would catch tilapias above 150 grammes. The catches indicate that the fishermen used much Smaller mesh sizes.

Table 28: Number of records collected during creel survey per day. dam and gear

Table 29: Fishing effort, catch per hour and estimated total catch per dam and gear

Table 30: Species composition in percentage in number and weight per dam and per gear