The following concluding comments are made in the context of aquatic weeds, their control and the effect on fishculture and the fisheries.
The presence of weeds - emergent, floating and submersed - on the lake produces three important impacts.
the loss of lake surface, and therefore productive capacity for fishery purposes
it makes access by the fishermen into such areas difficult or impossible, and therefore reduces the fish catch
the overgrown areas represent fish refugia, important from the conservation viewpoint.
The dense weed growth is the natural response of this shallow lake to a high nutrient input and reduced flows. The inevitability of this process of lake senescence implies that to slow down the ageing of the lake will demand continuous maintenance work. As it is necessary to carry out this work in standing water using floating equipment, capital expenditure, maintenance and running costs are high.
Although there is some doubt as to the actual levels of fish yield on Lake Edku - an overall yield equivalent to 0.5 t/ha/year (of productive water area), on a sustained basis, is probably the maximum that can be anticipated. If the total productive area of the lake is assumed to be 100 km2 the maximum sustained harvest will be about 5 000 t/year with a 1985 lakeside gross value of ca. LE 7–8 million. Any capital and recurrent expenditure for weed eradication and control must be evaluated with respect to this probably maximum return.
Apart from an increase in yields from the catch taking the stocked grass carp, it is considered likely that weed clearances will have a significant effect on the present high yield of the fishery. The grass carp may add 1 000 or 2 000 t/year to the lake harvest.
Immediate inputs are required in the improvement of fisheries statistics. The first step should be to train fisheries staff locally, and to take necessary measures that more precise information is obtained on fish stocks, fish population dynamics, fishing gears and boats, catch per unit of effort, seasonality of fishing and on marketing. Such data are basic for strengthening fisheries management and for formulating fishery development strategies for Lake Edku, including further needs for aquatic weed management and control.
Permanent fishing boat access points to the lake should be established, kept cleared and maintained open as necessary. Fisheries demand easy access to openwater, fishable areas. This requirement demands close liaison with the Fisheries Department.
In the areas of the fish landings, programmes for the control of submersed plants and floating water hyacinth should be initiated and continued as long as necessary - see also the recommendations of the Consultant Weed Control Specialist (Field Document 2).
Grass carp fingerlings should be stocked at a survival rate of 200/ha of open water surface. This stocking should be repeated annually with no fishing restrictions.
Consideration should be given to the physical improvement of the major fish landings, by the provision of hard-standing jetties, adequate clean water supplies and sanitary facilities, etc.
A management programme for fingerling production should be developed in cooperation with the fish hatcheries and the irrigation authorities in the Beheira Governorate. This programme should provide adequate numbers of grass carp fingerlings for the control of weeds in irrigation canals, as well as stocking the Barsik Fish Farm ponds and Lake Edku.
Although a detailed evaluation has not been made, in general the Department of Fisheries and the Barsik Fish Farm are adequately equipped. With relevance to weed control and improved management techniques, it is suggested that portable/transportable pump units, petrol or diesel powered, are obtained.
It is essential to improve the system of data collection for the management of the Lake Edku fishery. The present imprecision of much of the data does not allow for a rational management programme to be developed.
The problem as perceived on Barsik Fish Farm ponds is essentially that of emergent reed growth resulting from a lack of preparation of the ponds before they are put into production. This problem is further compounded by poor fishculture management practices.
In the first three seasons of production it is evident that management difficulties have arisen from:
the excessive size of the ponds which make all management and maintenance activities difficult
the small inflow to the ponds, relative to their size, demands excessively long filling periods
shortage of fingerlings for stocking, especially grass carp
a shortfall in the quantities of feed stuffs available for the production ponds.
There are considerable problems of pond bund erosion now appearing (a problem compounded by the large area of the ponds and the resulting wave action). Much of this erosion can be reduced if growths of reeds are left in place until a bund plant-cover can be established.
The growth of emergents and sub-aquatic weeds in the farm canals will require constant routine attention by mechanical, manual and chemical means. Water hyacinth presents little difficulty within the farm, but its presence in the supply canals can be considerably controlled by removal of the source nursery areas for this plant, particularly in disused drainage canals nearby.
The main thrust of these recommendations is that after an initial thorough preparation of the ponds, an effecient production programme with optimum fish density and species mix, will maintain the ponds weed free.
The production programme should be modified to use only those ponds that have been adequately prepared and to use these to maximum production efficiency. Ponds with problems of drainage, insufficient depth or weed growth should remain fallow until they can be rehabilitated.
For ponds with a very heavy weed growth, a pond by pond programme should be established with each pond being drained, dried out before the weeds are cut and cleared.
Ponds with a relatively light weed growth, or where weeds have regrown after an initial clearance, should be cleared by using floating cutters.
Cut reeds may be burned in situ. Consideration should be given to using cut reeds as mats for bund protection against erosion.
A fringe of reeds should be left on the pond margins, especially at the ends of the long axes of the ponds where the bunds are subject to the effect of the prevailing winds. See Consultant Aquatic Weed Specialist's report (Field Document 2) for recommendations of other plantings for bund stabilization and erosion protection.
Pond filling times should be reduced as far as possible. Portable auxiliary pumps should be used to speed up the filling process.
Consideration should be given to reducing pond size by the construction of cross-bunds. The creation of more ponds should not significantly decrease the total water area and area loss will be compensated by increased and more efficient levels of production.
For especially aquatic weed control purposes, grass carp should be stocked in all production ponds at a survival rate equivalent to 200 to 300 fish/ha.
Stocking rates of other species should be adjusted for survival rates adequate to achieve the target carrying capacity of the ponds. This will vary with the species mix and will be in the region of 10,000 fish/ha. Such mix would substantially increase production levels under optimal feeding conditions.
Adequate levels of feeding should be maintained. Should the supplies of feedstuff become inadequate, ponds should be left fallow and not subject to low production and the resultant weed regrowth, etc.
Alternative feed supplies should be sought. Feeding of waste from grain milling and other food preparation activities may be done without pelleting.
As recommended by the Consultant Aquatic Weed Specialist, the farm canals should be routinely cleared by mechanical and chemical means.
As recommended by the Consultant Aquatic Weed Specialist, the water hyacinth and other weed nuisance in the input drain should be cleared and the source of the water hyacinth eliminated.
