Spatial and temporal distributions and some biological aspects of commercially important fish species of Lake Tana, Ethiopia

摘要

The distribution of fish species in Lake Tana was studied from November 2009 to July 2011based on samples collected every other month using gill-nets of 60, 80, 100, 120 and 140 mm stretched mesh size. Labeobarbus species., Claris gariepinus, Oreochromis niloticus, and Varicorhinus beso are commercially important fish species and form 68 %, 18 %, 14 % and 0.5 % of the pooled experimental fish catch. There was significant variability among years and sampling sites of both temporal and spatial aspects, Mann–Whitney U tests were used for pair wise comparisons of sites and years. Population densities of Labeobarbus spp. and V. beso were significantly declining, in contrast, the composition of O. niloticus did not change, but C. gariepinus increased by 100 % in catch composition. The most likely explanations for the total decline in abundance of fish species are the increase of the illegal commercial gill-net fishery targeting their spawning aggregations in the wetlands and river mouths, and the increasing trend of the degradation of spawning and nursery habitats both in the lake and major tributary rivers of the catchment area. Therefore, there should be a need for urgent development of a management plan focusing on ensuring sustainable utilization of a resource by fishing effort, gear mesh size and gear type restrictions, and control the spawning grounds from different type of human encroachment and design closing seasons and spawning grounds during the breeding seasons of different fish species of Lake Tana..