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

Objective:To know spatial,temporal distributions and some biological aspects of commercially important fish species of Lake Tana.Methods:Distribution of fish species in Lake Tana was studied from November 2009 to October 2012 based on samples collected every other month using gillnets of 60,80,100,120 and 140 mm stretched mesh sizes.Labeobarbus species,Clarias 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.Results:The composition of Labeobarbus spp.and Varicorhinus beso shows significant decline.On the other hand,the composition of Oreochromis niloticus did not change,but Clarias gariepinus increased by 100%by catch composition.The most likely explanations for the total decline in abundance of fish species are the increase of the illegal commercial gillnet 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.Conclusions: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 controlling the spawning grounds from different types of human encroachment and designing closing seasons and spawning grounds during the breeding seasons of different fish species of Lake Tana.