Spatial and temporal variation in the distribution and density of pelagic fish species in Lake Victoria, East Africa

The distribution and densities of three pelagic fish taxa (Nile Perch, Lates niloticus, Rastrineobola argentea [Dagaa], and the haplochromine cichlids) in Lake Victoria were estimated through 17 lake-wide acoustic surveys conducted in two series (August 1999–August 2002 and August 2005–September 2011). Nile Perch densities were estimated through echo-counting, while Dagaa and haplochromines by echo-integration. Mixed generalized linear model estimates indicated up to 30% decline in Nile Perch densities in the deep and coastal areas and up to 65% reduction in the shallow inshore areas over the study period. There was a twofold increase in Dagaa densities and a 10% increase in haplochromines. The distribution and densities of these species were influenced by season, stratum and year of survey. In addition to fish exhibiting seasonal clustering in the upper layers of the water column, they also appeared to spread to shallow inshore waters. The Nyanza, Speke, and Emin Pasha Gulfs demonstrated diverse spatial stock oscillations in abundance, and distribution which call for a need to include area disaggregated considerations in stochastic models when predicting dynamics of fish stocks.

[1]  G. Kling,et al.  Multiple stressors cause rapid ecosystem change in Lake Victoria , 2010 .

[2]  I. Everson,et al.  Acoustic estimates of commercial fish species in Lake Victoria: Moving towards ecosystem-based fisheries management , 2013 .

[3]  D. MacLennan,et al.  Spatial and temporal changes in the distribution of Rastrineobola argentea in Lake Victoria , 2007 .

[4]  W. Ligtvoet,et al.  Species Extinction and Concomitant Ecological Changes in Lake Victoria , 1991 .

[5]  F. Witte,et al.  Dwelling at the oxycline: does increased stratification provide a predation refugium for the Lake Victoria sardine Rastrineobola argentea? , 2001 .

[6]  D. MacLennan,et al.  Spatial distribution and temporal changes in the fish populations of Lake Victoria , 2003 .

[7]  R Core Team,et al.  R: A language and environment for statistical computing. , 2014 .

[8]  Comparing echosounder efficiency using field observations , 2013 .

[9]  C. Nyamweya,et al.  Increase in Anoxia in Lake Victoria and Its Effects on the Fishery , 2012 .

[10]  F. Witte,et al.  Species Distinction and the Biodiversity Crisis in Lake Victoria , 2007 .

[11]  Murdoch K. McAllister,et al.  Stock assessment for fishery management - A framework guide to the stock assessment tools of the Fisheries Management Science Programme (FMSP) , 2006 .

[12]  Eter,et al.  Status of the Major Commercial Fish Stocks and Proposed Species-specific Management Plans for Lake Victoria , 2009 .

[13]  Gunnar Stefánsson,et al.  Analysis of groundfish survey abundance data: combining the GLM and delta approaches , 1996 .

[14]  Species Extinction , 2006 .

[15]  A. J. Cordone,et al.  Batho-spatial distribution pattern and biomass estimate of the major demersal fishes in Lake Victoria , 1974 .

[16]  P.A.M. van Zwieten,et al.  Are the Lake Victoria fisheries threatened by exploitation or eutrophication? Towards an ecosystem-based approach to management , 2008 .

[17]  I. Everson,et al.  Distribution and exploitation of Nile perch Lates niloticus in relation to stratification in Lake Victoria, East Africa , 2013 .

[18]  M. Graham.  The Victoria Nyanza and its fisheries : A report on the fishing survey of lake Victoria, 1927-1928, and appendices , 1929 .

[19]  O. Seehausen,et al.  Differential decline and recovery of haplochromine trophic groups in the Mwanza Gulf of Lake Victoria , 2007 .

[20]  Y. Mgaya,et al.  Target strength measurements of Nile perch (Lates niloticus: Linnaeus, 1758) in Lake Victoria, East Africa , 2012 .

[21]  I. Cowx,et al.  Are the exploitation pressures on the Nile perch fisheries resources of Lake Victoria a cause for concern , 2006 .