The composition of fish communities of nine Ethiopian lakes along a north-south gradient: threats and possible solutions

in Animal Biology
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Fish populations of nine Ethiopian freshwater lakes were quantitatively sampled with a standardized protocol, using multi-mesh gill nets. In total, 27 species were identified, but only 14 species were common. Based on the common species, the fish communities showed large differences in their species composition, except for Lake Abaya and Lake Chamo which were similar. Most fish species were observed in only one or two lakes. Compared with the information reported in literature the present study generally underestimated the species richness. The empirical model of Amarasinghe and Welcomme (2002) for African lakes was used to estimate fish species richness, which was compared with species presence reported in literature. Biodiversity in the two northern highland lakes is low, but not lower than the model estimate. Lake Tana has a high biodiversity which is close to what is estimated by the model, but three Rift Valley lakes have low biodiversity, lower than estimated by the model. There are also strong indications for the Rift Valley lakes that species richness was higher in the past because the species richness reported in the older literature was generally much higher than those observed by us in the present study and those reported in the more recent literature. Threats like overfishing, high sediment load and degradation of habitats were identified. It is recommended that Ethiopia should develop guidelines for fishery legislation and implement it through an enforcement agency. Moreover, catchments management should be practiced to save the water bodies and their fish communities.

The composition of fish communities of nine Ethiopian lakes along a north-south gradient: threats and possible solutions

in Animal Biology

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Figures

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    Map of Ethiopia showing the locations of all nine study lakes in Ethiopia and the position of Ethiopia in Africa.

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    Environmental parameters showing (a) water temperatures (°C), (b) sediment load (mg l−1), and (c) Secchi-disk depth (m) in the nine study lakes. For abbreviations of lakes see table 1. Error bars indicate +1 SD (n = 3).

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    The relationship between mean water temperature (°C) and altitude (m) observed in the nine study lakes. The linear regression between temperature and altitude is significant (R2=0.64, P<0.01).

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    Multiple pair-wise comparisons (Tukey post-hoc test) of (a) chlorophyll content (μg l−1), and (b) Catch Per Unit Effort (CPUE, kg) among lakes. For abbreviations of lakes see table 1. Identical letters indicate a non-significant difference (P0.05).

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    Community structure in terms of species composition (%) based on (a) numbers, and (b) on biomass. Numbers below columns represent CPUE in numbers (a) and biomass in kg wet weight (b). For abbreviations of lakes see table 1, for abbreviations of fish species see table 2. For clearness, the endemic Labeobarbus spp. (LB) in L. Tana were pooled together. Species representing a relative density or biomass < 3% were pooled in the Rest group.

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    Number of fish species observed in the nine study lakes according to recently published studies, according to estimates based on the empirical model for African lakes (Amarasinghe and Welcomme, 2002) and according to the present study. Literature used: L. Tana (Nagelkerke and Sibbing, 2000; De Graaf et al., 2006), Koka Res. (Vanden Bossche and Bernacsek, 1991), L. Ziway (Vanden Bossche and Bernacsek, 1991), L. Langano (Seyoum, 1990; Golubtsov et al., 2002), L. Awassa (Golubtsov et al., 2002; Bjørkli, 2004); L. Abaya (Vanden Bossche and Bernacsek, 1991) and L. Chamo (Golubtsov et al., 2002).

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