Lake Victoria Fish Stocks and the Effects of Water Hyacinths on the Catchability of Fish

EfD Discussion Paper
1 January 2008

This study of the deleterious effect on fishing by the water hyacinth invasion of Lake Victoria found an unusual positive: the decline of fish catchability caused by the the abundance of water hyacinths has paradoxically stopped or at least postponed serious overfishing.


This paper analyses the effects of the invasion of water hyacinths on fishing in Lake Victoria.
We built two fairly standard Schaefer-type models that have one innovation: they allow the water
hyacinth abundance to affect catchability. We estimated static and dynamic CPUE (catch per unit of
effort) functions for Lake Victoria fisheries. We investigated the trend in the lake’s stocks during the
period 1983–2000 and focused particularly on the effect of the water hyacinth on fish stocks and on
catchability coefficients. The results shows that while fish stocks have fallen since 1990, this decline
appears to have been at least temporarily halted by the declining catchability of fish due to the growing
abundance of water hyacinths. The impact of the hyacinth on the catchability of fish was greatest in the
Kenyan section of Lake Victoria. Although the hyacinths had many negative effects, one important
effect has been to effectively hinder fishing and, thereby—paradoxically—stop or at least postpone
serious overfishing.

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Publication | 8 April 2008