|Extract of Report|
Full report available: Contact Mr. Evans Simasiku at: email@example.com
Compiled by KIFI RESEARCH UNIT
Edited by: Evans Simasiku
|Research team at KIFI and Katima Mulilo Regional Office, 2012|
Table of contents
4. Results and Discussions
The Caprivi Region in Namibia is a narrow strip of land extending eastwards from the northeast corner of the country, and is bordered by Angola and Zambia to the north, Botswana to the east (Figure 1.). The region is flat and characterised by numerous swamps and slow-flowing rivers. A major swamp system is centered on Lake Liambezi (Figure.1). The lake is shallow (<6m deep), semi-endorheic, and characterised by cyclic episodes of filling and drying. In the “good” years the lake is highly productive. In the “bad” years, the lake is completely dry and used for extensive cattle grazing and growing small patches of maize and sorghum. Periods of drying and filling are characterised by extremely unstable conditions and large fluctuations in water quality and composition and abundance of biota. Lake Liambezi supported an important subsistence fishery in the 1970s and 1980s until it dried up in 1985 (van der Waal, 1976). Some inflows were recorded during the 2000 and 2003 floods, and since 2007 the lake has received more floodwaters, culminating in April 2009 in a major flood, causing the lake to fill up completely. Once again, the fishery in the Lake is very important. More-than 100 fishermen thrive on fish with an estimated weekly harvest of about 5 tons tapped out from the lake, of which 2 tons is exported through local markets to Zambia and Congo. While the work of van der Wall in the 1970’s is important, no recent work has been conducted within the context of monitoring, management and regulation since the Lake replenished in 2009. Of particular relevance is the information on its species composition, catch per unit effort, annual landings, gear type and efficiency.
The aim of this report is to contribute towards a holistic monitoring protocol for the Lake Liambezi fishery in the Caprivi Region and provide management recommendations for the sustainable utilisation of the commercially important cichlids species such as Oreochromis andersonii, Oreochromis macrochir and Tilapia rendalli. Leg 2 aimed to:
a) Determine the overall species composition caught by monofilament and multifilament gillnets of different mesh sizes.
b) Determine the CPUE of all species per gillnet type and mesh size.
c) Depict the biomass proportion of each species in monofilament and multifilament gillnets
d) Determine the size at which O. andersonii is selected for in different sized nets.
3. Sampling methods
Capture experiments were carried out simultaneously in March 2012 in the same area of the Lake to give approximately identical fishing conditions. Data were collected using gillnets similar in length and mesh sizes to those commonly used by commercial fishers throughout Lake Liambezi. Three stratified offshore habitats were selected for this study (Figure .1): Sampling was archived with a series of 10 gillnet panels comprising two net types, (5 x monofilament and 5 x multifilament nets). Individual nets had a length of 100 m long, with the stretched mesh sizes of 3” inches 3.5”, 4”, 4.5”, and 5” (Table 4.1). The depth and hanging ratio of each net were 38 meshes and 0.50. Gillnets were randomly set in the offshore waters at approximately 17h00 and lift at 06:00. Soak time difference between nets was minimized by hauling in order of setting (Losanes et al. 1992). On landing, the fish caught in each net were removed and sorted into species according to net and mesh sizes using the taxonomic keys by Skelton (2001). All fish were measured to the nearest millimeter total length (TL) or fork length (FL) depending on the species, and weighed to the nearest gram (g) to determine and compare the CPUEs of the two net types. Fish caught were grouped into 10 mm TL length class to determine the selectivity parameters for the gear.
Figure 1. Map of Lake Liambezi, showing all the sampling zones (A – B).
Figure 4.1. Hepsetus odoe (African pike), the overall abundant species caught by the commercial experimental gillnets in Lake Liambezi, in March 2013.
Figure 4.2 . Combined catch per unit of effort of all caught species by weight, in Lake Liambezi
- Continuous monitoring on the lake, to avoid stock depletions and ensure sustainable exploitation.
- The minimum mesh size as stipulate by the Inland act should be increased from 3” to 3.5”
- The collapse of the Lake Malombe cichlid fishery in Malawi should be set as learning curve for all African lakes
Figure 4.6. Immature fish selected by the 3” monofilament gillnet.