Biodiversity and Fishery Sustainability in the Lake Victoria Basin: An Unexpected Marriage?

Abstract

Articles Overfishing, environmental degradation, and redistribution of surface water have placed great stress on inland fisheries throughout the world. Human activities usually shift the balance among fish species, causing the extirpation of many indigenous species and the dominance of a reduced set of often introduced fish species. The result has been a massive reshaping of fish communities in the world's fresh waters over the past few centuries, with the pace of change quickening of late in the tropics.It has been known for some time that fishes react to environmental degradation and fishing pressures with a characteristic series of changes. If too much of the brood stock is caught, fewer and fewer recruits appear in the population in succeeding years. This is called recruitment overfishing. The impact is somewhat different if the large fish in a population are taken first, then smaller ones, and so on. The mean size of individuals drops, and there is selection for individuals that mature at a smaller and less fecund size. This is growth overfishing. Each of these phenomena has a counterpart corresponding to effects that become apparent when more than one species or stock is taken into consideration.Three decades ago, Regier and Loftus (1972) observed a multispecies analog to growth overfishing while they were researching the anthropogenic transformation of fish communities in the Great Lakes of North America. What they described-the successive removal of the largest-bodied species-was later generalized Henderson 1973, Welcomme 1995) and has been called the "fishing-down Uganda, Box 343, Jinja, process." Greater fishing pressure can initially bring about a higher catch, followed by a plateau over a range of increasing exploitation as component fish stocks are serially depleted. First large, and then successively smaller, species are removed and their places taken by even smaller and faster-growing ones, producing an illusion of sustained productivity that conceals deep changes in community and food web structure. Eventually there are no more economically exploitable stocks, and both the fishery and the fish community collapse or are changed beyond recognition (Welcomme 1995(Welcomme , 2003. John S. Balirwa is acting director of the Fisheries Resources Research Institute ofIn Africa, overfishing is a recurrent problem closely tied to environmental conditions. Africa has suffered food crises for decades, exacerbated in the Sahelian zones by prolonged drought through the late 1970s and the 1980s. When severe drought compromises production of livestock, rural communities turn to hunting and fishing to satisfy their protein needs. What worked for a long time when people were relatively few can have quite different impacts on wildlife at the currently very high human population densities. Thus, food crises, together with a political orientation of open access to wild resources such as fish, have led to a rapid increase in fishing pressure. This effect is further compounded by the rapid improvement and disseminat...

Developmental stages until hatching of the Lake Victoria cichlid Haplochromis piceatus (Teleostei: Cichlidae)

“…The haplochromine cichlids of Lake Victoria (East Africa) have been intensively studied in the last few decades, generating much information about their speciation (Greenwood, 1974;Meyer et al, 1990;Seehausen et al, 1997a;Galis and Metz, 1998;Nagl et al, 2000;Verheyen et al, 2003;Maan et al, 2004;Watanabe et al, 2004;Seehausen, 2006;Verzijden and ten Cate, 2007), as well as how they were affected by the introduction of the Nile perch and the environmental degradation in and around the lake (Barel et al, 1985;Ogutu-Ohwayo, 1990;Witte et al, 1992Witte et al, , 2008Seehausen et al, 1997b;Balirwa et al, 2003).…”

Ecological, environmental and socioeconomic aspects of the Lake Victoria's introduced Nile perch fishery in relation to the native fisheries and the species culture potential: lessons to learn

“…The research record suggests otherwise. For the Lake Victoria fisheries the best available information includes at least 2000 references ranging from probably unused historical records found in Graham (1929), EAFFRO (1953EAFFRO ( -1967, associated records of the Lake Victoria Fisheries Service (LVFS), Annual Reports of Fisheries Departments to information summarized by Balirwa et al (2003Balirwa et al ( , 2004, LVFO (2005) and most recently, Pringle (2005) and Matsuishi et al (2006). As a follow-up to lack of information since the last century, Pringle (2005) recalls evidence of reported overfishing with imported nets.…”

“…In Lake Albert, the large-sized 'moon fishes' (Distichodus and Citharinus) drastically declined in commercial catch by the 1950s while the Lake George-based 'The Uganda Fish Marketing Cooperation' (TUFMAC) collapsed after overfishing the tilapia stocks by the 1960s. In all these lakes, the intensification of fishing led to a shift (fishing down process: Balirwa et al, 2003) to small-sized species (e.g. R. argentea in Lakes Victoria, Kyoga, and Nabugabo, and, Neobola bredoi in Lake Albert).…”

Trade and resources: Welfare effects of the Lake Victoria fisheries boom

“…Lake Victoria was known for more than 600 7 endemic species of haplochromis cichlids. About 40% of these species disappeared and the Nile perch seems to have been a key contributor to this mass extinction with contributions from environmental changes (Balirwa et al, 2003 First, an autarchy country starting to trade an open-access natural resource may experience negative welfare effects from trade. Second, any resource-abundant country with a too large labor force to accommodate specialization in natural resource production, will by necessity obtain lower welfare in the new equilibrium.…”

“…On the other hand, high interest rates in the informal credit markets combined with the license cost slow down the entry. Concerning the biological development of the stock, the reduction in cpue indicates a severe reduction of the Nile perch stock, and a number of biological studies have predicted a collapse if the increase in exploitation pressure is not halted (Pitcher and Bundy, 1995;Mkumbo et al, 2002;Balirwa et al, 2003;;Njiru et al, 2007). iv…”