Fish populations, gill net catches and gill net selectivity in the Kunene River, Namibia

Type Report
Title Fish populations, gill net catches and gill net selectivity in the Kunene River, Namibia
Publication (Day/Month/Year) 2008
The Kunene River
The Kunene River originates near Huambo in Angola, from where it flows in a southerly
direction towards Namibia. The catchment area is 107000 km2
. In Angola, the upper
reaches are relatively steep, while the middle sections form floodplain habitats. Once the
river reaches Ruacana in Namibia, it turns west towards the sea, forming the border
between Angola and Namibia for a distance of approximately 340 km. Floodplains are
absent along the Namibian section.
The objective of this report is to provide baseline information about the fish resources in
the Kunene River to form the biological foundation for recommendations for a sustainable
management. Based on fish survey data from the period 1994-2004, the fish resources are
described through studies of species diversity, relative importance of the different species,
life history parameters, catch per unit effort and gill net selectivity.
Fish were collected at 18 locations with gill nets and seven other sampling methods
(collectively called “other gears”), such as seine nets, cast nets, electrofishing apparatus
and rotenone. The gill nets (22-150 mm mesh size) were used to survey open, deep-water
habitats in the main stream near the shore and in deep backwater areas. Other gears
targeted mainly small species and juveniles in shallow, vegetated and rocky habitats. Ten
surveys were carried out in the period 1994-2004. A total of 16959 fish were caught, of
which 6862 with multi-filament gill nets and 10097 with other gears. The most important
species were identified by using an index of relative importance (IRI), which is a measure
of the relative abundance or commonness of the species based on number and mass of
individuals in the catches, as well as their frequency of occurrence.
A total of 50 fish species were identified, of which four were marine species. In addition,
Synodontis spp., an unknown freshwater species, an unknown marine species and Gobiidae
spp. were recorded. The families represented with the highest number of species were
the Cyprinidae and Cichlidae, with 14 and 12 species, respectively.
Thirtyfive species were identified in the multi-filament gill nets catches, of which two were
marine species. The four most important species, Schilbe intermedius, Brycinus lateralis,
Barbus mattozi and Labeo ansorgii constituted together an IRI of 69%. The Schilbeidae
(one species) and the Characidae (two species) were the most important families in the gill
net catches (IRI of 46%). Marcusenius macrolepidotus was the most important species in
the gill net catches in the river mouth, whereas Schilbe intermedius was the most important
species in the rest of the river.

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