Lake Victoria Fish Stocks and the Effects of Water Hyacinth

Abstract

This article analyzes the effects of the invasion of water hyacinth on fishing in Lake Victoria. The authors built two fairly standard Schaefer-type models that have one innovation: They allow the water hyacinth abundance to affect catchability. The authors estimated static and dynamic catch per unit of effort functions for Lake Victoria fisheries, investigating the trend in the lake's stocks during the period 1983 to 2000 and focusing particularly on the effect of the water hyacinth on fish stocks and on catchability coefficients. The results show that although fish stocks have fallen since 1990, this decline appears to have been at least temporarily halted by the declining catchability of fish because of the growing abundance of water hyacinth. The impact of the hyacinth on the catchability of fish was greatest in the Kenyan section of Lake Victoria. Although hyacinth has many negative effects, it effectively hinders fishing and thereby paradoxically stops or at least postpones serious overfishing.