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

Abstract

Inland fishery ecosystems in Africa are characterized by patterns of overexploitation, environmental degradation and exotic species introductions. Ecological complexity and diversity of aquatic habitats dictate that fishes in general are not evenly distributed in a water body. However, fisheries management regimes tend to ignore this basic principle, assume generalized conditions in a water body, and focus more on ‘desired’ objectives such as maximizing catch. The result is to disregard fish habitat boundaries and anthropogenic influences from the catchment that influence fish production. Overexploitation and environmental degradation disrupt sustainable socioeconomic benefits from the fisheries, create uncertainty among investors, but leave some managers calling for more information with the expectation that the fisheries will recover with time. Open access to the fisheries and full control of fishing effort remain challenges for managers. Exotic species introductions and fish farming can increase production, but such interventions require firm commitment to sound ecological principles and strict enforcement of recommended conservation and co‐management measures in capture fisheries. The general tendency to downplay fishing effort issues, other ecosystem values and functions or rely on temperate fisheries models until a new cycle of overexploitation emerges, characterizes many management patterns in inland fisheries. Aquaculture is not an option to challenges in capture fisheries management. Aquaculture should be developed to increase fish production but even this practice may have negative environmental impacts depending on practice and scale. Decades of information on Lake Victoria fisheries trends and aquaculture development did not stop the collapse of native fisheries. The successfully introduced Nile perch (Lates niloticus) has shown signs of overexploitation and aquaculture has again been considered as the option. By reviewing significant trends associated with Nile perch and its feasibility in aquaculture this paper uses Lake Victoria to illustrate ‘special interest management’ targeting selected species of fish rather than the fisheries.

Metrics of ecosystem status for large aquatic systems – A global comparison

“…Size-at-maturity has been declining for R. argentea since 1970s and for O. niloticus since early 1990s (Njiru et al, 2006;Wanink, 1998). Size-at-harvest has also declined for haplochromines and R. argentea but initially increased for Nile perch then declined during the latter part of the 30-year period (Balirwa, 2007;Ogutu-Ohwayo 2004;Wanink, 1998;Witte et al, 1995). O. esculentus size-at-harvest declined between 1920 and 1970, likely derived from the shift to smaller mesh sizes (Ogutu-Ohwayo, 1990) precipitated by declining harvest of large fish.…”

Species richness of exotic and endangered fishes in Japan’s reservoirs

“…Notable examples include the increase of fast growing algae after the introduction of Nile tilapia Oreochromis niloticus in Brazilian reservoirs (Figueredo and Giani 2005), the reduction in the numbers of small fish and crustaceans following the introduction of largemouth bass Micropterus salmoides and bluegill Lepomis macrochirus in Japanese irrigation ponds (Maezono and Miyashita 2003), and the extinction of over 200 endemic haplochromine cichlid species after the introduction of Nile perch Lates niloticus in Lake Victoria, Africa (Witte et al 1991;Balirwa 2007).…”

Transactional Fish-for-Sex Relationships Amid Declining Fish Access in Kenya

“…By the 1980s, the fishery entered a period of rapid growth with the catch of Nile perch a key factor in driving migration to the lakeshores, infrastructure development, and a burgeoning international export market (Balirwa, 2007;Johnson, 2010). Ecologically, Nile perch overwhelmed the area's tremendous biodiversity and caused the demise of over 300 cichlid species (Witte et al, 1992).…”