Former Fellow Anthony Taabu-Munyaho to defend his PhD tomorrow
On Friday, April 11, former UNU-FTP fellow Anthony Taabu-Munyaho from Uganda will defend his PhD. The defense will be held in Askja, room 132 at the University of Iceland at 14:00. The title of the thesis is: Anthropogenic and environmental impacts on the abundance and distribution of commercial fish stocks of Lake Victoria, East Africa.
Opponents are
Professor. Ian G. Cowx, BSc, PhD, CEnv, FIFM, Director, Hull International Fisheries Institute,School of Biological, Biomedical and Environmental Sciences,University of Hull.
Lauren J. Chapman,Professor of Biology,McGill University, Canada.
The doctoral committee include:
Gudrun Marteinsdottir,Professor of Fisheries Science
Institute of Life and Environmental Sciences,
University of Iceland.
Gunnar Stefansson,Professor,
University of Iceland.
Dr. Timothy B. Grabowski,
Assistant Unit Leader – Fisheries,
U.S. Geological Survey,
Texas Cooperative Fish & Wildlife Research Unit,
Texas Tech University.
Gisli Mar Gislasson,Professor of Limnology
Institute of Life and Environmental Sciences,
University of Iceland.
The ceremony will be conducted by Professor Jörundur Svavarsson, Chair of the Biology Department.
Abstract:
Stocks of commercially targeted fish species are generally exposed to changes associated with human exploitation and natural ecosystem alterations. Invasion or introduction of new species often results in dramatic changes in composition and dynamics of the erstwhile systems. Understanding the dynamics of fish stocks, particularly how the natural environment and fishing effort interact to influence productivity and ecosystem balance, is a prerequisite to sustainable management. This study analysed changes in abundance, proportions and distributions of exploited fish stocks in Lake Victoria and correlated them with plausible causative factors. Observed trends in the status of commercial fish stocks of Lake Victoria illustrate a classical example of man’s influence on ecosystem modification. The stocking of Lake Victoria with a voracious predator, the Nile perch (Lates niloticus), and four tilapia species in the 1950s and early 1960s transformed the ecology of the lake, leading to an increase in productivity and acceleration of eutrophication. The overall fish biomass in the lake after the Nile perch establishment rose from approximately 1.5 million tonnes in the 1970s to- and continues to oscillate around 2.5 million tonnes. However, the species proportions have changed from the dominance of haplochromine cichlids (>80% in the 1970s) to Nile perch (>70% in the 1980 – 1990s) and more recently, the native cyprinid dagaa (Rastrineobola argentea) and resurging haplochromines (> 65%). Factors contributing to these observed changes have been variously attributed to anthropogenic perturbations and eutrophication. The findings reported herein suggest the introduction of the Nile perch as a pivotal event in all the subsequent ecosystem changes. Its establishment orchestrated ecological change through extirpation of haplochromines and increased fisheries production. Consequently, the historical decline and recent recovery of haplochromines, as well as the increased dagaa biomass, suggest that the previously dominant Nile perch peaked by the early 2000s and has subsequently declined. Management should therefore target manipulation of factors controlling the Nile perch stock dynamics which include: prey biomass, spatial and temporal distribution patterns, and fishing effort.