¹Wageningen, the Netherlands
²Bennekom, the Netherlands
³Fisheries and Oceans Canada, Burlington, ON, Canada

Introduction

   Back in 1992, the Workshop on People, Fisheries, Biodiversity and the Future of Lake Victoria concluded that the environment of the lake was changing rapidly and that the fishery was unsustainable at the level of production at that time. Also the conference, Lake Victoria 2000, Opportunities for the Future, held in 2000 similarly produced a long list of recommendations. GLOW III (2002), and to a lesser extent GLOW IV (held in Bagamoyo, Tanzania, in February, 2006), concluded that the Nile perch was overexploited and that the participants in these conferences were concerned about the ever increasing fishing effort and other pressures on the lake’s resources. Despite the formation of Beach Management Units (BMUs), who have the power to enforce certain fisheries rules and regulations, it remains difficult to control the number of newcomers into the fishery. Although not yet perfect, the involvement of fishing communities will be of paramount importance in managing the lake’s resources. Every second year, frame surveys are conducted on the lake to take stock of the fishery and to enumerate the number of landing sites, fishermen, fishing units, gears, etc. These numbers are still on the increase as a result of the open-access character of the fishery. Without a ceiling for the number of fishing units the fishing effort will be difficult to control.
The critical reader would argue that the warning of “unsustainability” which was previously heard did not discourage the three countries, and their stakeholders around the lake, from participating in and promoting the Nile perch fishery development with their investments.
The long unsustainable exploitation of the Nile perch stocks has meanwhile (July 7, 2007, The Nation, Nairobi) led to the situation that their catches have decreased to low levels. As predicted by scientists, the removal of the perch has led to an increase in the stocks of other fish species (biodiversity), and in particular of dagaa, which is now emerging as a principal target species. The fishery thus lost a great deal of its monetary value, but the availability of fish to local populations has greatly increased.

Synthesis and conclusions

   Eutrophication, the introduction of the predatory Nile perch and intensive fishing have led to a succession of change in Lake Victoria, which has triggered much debate about man-induced environmental changes and the immediate beneficial effects of the Nile perch to local and national economies.
The eleven papers presented here illustrate the current situation of the principal fisheries resources and their sustainability, and present recommendations for better focused and more effective fisheries management. The elements discussed here are respectively the freshwater shrimp Caridina, the group of endemic Haplochromine cichlids, the small pelagic dagaa, and other small or medium sized fish species, Nile perch and Nile tilapia.
The freshwater shrimp Caridina nilotica is an important food source for many fish species and the sustainability of the fisheries partly depends on its abundance. Nile perch stomachs reveal that Haplochromines constitute their main food, followed by Caridina and dagaa. The relative importance of Caridina decreases in the diet as the perch increase in size. It also forms an important component of the diet of the Nile tilapia, which has become an opportunistic feeder. The small pelagic dagaa (Rastrineobola argentea) feeds on zooplankton, Caridina nilotica and insects. At present, some 17,000 t of Caridina are caught as a by-product in the dagaa fishery in the Tanzanian part of Lake Victoria.
Feeding flexibility enabled the survival of Brycinus sadleri in the changing environment. Daytime diet shifted from strictly plant material to a broader diet of zooplankton, insect larvae, shrimp, and fish. With increased growth they switch to larger shrimps, insect nymphs and fish. Reduced competition has led to a situation where adult fish now take surface insects at night. These shifts reflect optimal foraging behaviour and diel vertical migration.
Lake Victoria’s original fish fauna was dominated by haplochromines representing over 80% of the fish biomass. They formed specialised trophic groups: piscivores, insectivores, molluscivores, detritivores and zooplanktivores. In the 1980s a combination of exploitation, predation by the introduced Nile perch, and eutrophication, led to their virtual disappearance from the sublittoral and offshore areas. As Nile perch was heavily fished in the 1990s, some species recovered. Decline and recovery rates suggest that Nile perch predation and eutrophication were the main factors determining their fate.
Small pelagic fish were the most successful in adapting to change. Rastrineobola argentea’s relative fecundity is enormous. Its food consists mainly of zooplankton, which is overly abundant. In response to increased predation and fishing, the species has reduced its size at maturity and maximum size. (typical r-selected life strategy). In addition, larval densities of R. argentea relate significantly to a combination of the abiotic factors water conductivity, temperature, transparency and dissolved oxygen. The measured biomass of this species was some 480,000 t and its estimated potential yield, 580,000 t. The majority was found below 40 m depth. Biomass is thought to have increased as a result of lower predation pressure by Nile perch.
The increased use of endemic species as bait impedes their recovery; juvenile Clarias, haplochromines, dagaa, Synodontis, Mormyrus and Labeo. Annual weight of mostly undersized and illegally caught baitfish was estimated at 7,500 t. The size of the perch caught is bait-dependent; with Clarias bait 20% of the perch is above the recommended upper size limit. Using haplochromines and dagaa, 62% is below the lower size limit.
Oreochromis niloticus is now caught at a smaller mean size than before, whereas its instantaneous growth coefficient and mortality rates have increased. It matures at a smaller size; originally fed almost entirely on algae, but now diversified its diet to insects, fish, algae and plant material. Studies of its reproductive effort indicate that this species is under stress (size-selective exploitation). O. niloticus allocates more energy for reproduction than for somatic growth (i.e. increased turnover rate).
Studies of growth, mortality and reproduction were deployed to assess the status of the Nile perch stocks. Over 80% and 99% of the commercial catch is below the size at first maturity for males and females, respectively. Bottom trawl studies suggest good recruitment, but yield per recruit indicates unsustainable exploitation. The current annual yield exceeds the sustainable harvest level by some 27%. It is recommended to reduce the exploitation rate by half and increase the size at first capture.
Difficulties impeding effective fisheries management include difficulties in transferring regulatory power to fishing communities, and establishing adequate ‘co-managerial’ framework and implementation of managerial action. A management structure is proposed, based on three levels of administration which have at their core ‘beach committees’, and which serve as forums for negotiated managerial outcomes.

Management

   In a rapidly changing environment like Lake Victoria new changes are no doubt already underway; which in due course may again invalidate our current recommendations and pose new questions. How can fisheries managers and policy makers benefit in a timely fashion from the research results and the peer-reviewed papers? Are these managers and policy makers subscribing members of the AEHMS? Will they receive hard copies of the papers? In other words how can the Society contribute to the information flow and publicizing its results? It is not in the Society’s mandate to distribute complimentary copies of the current issue, just like that.
Interestingly, the press may play an important role, provided responsible reporting takes place. Journalists have the task of informing a large audience responsibly. There is always the risk that too negative a picture is drawn of situations particularly when fishermen are cited. Since the GLOW III conference numerous newspaper articles appeared in the national and regional newspapers in the three East African nations, not only about overexploitation of the resources, but also about the national revenues, employment, and upcoming interventions.

Managing natural resources requires a certain infrastructure and Lake Victoria is blessed with the LVFO, the Lake Victoria Fishery Organization (as a specialized institution of the East African Community), and since early 2007 with the Lake Victoria Basin Commission (LVBC). Not only these high-level authorities are involved in the lake’s management, but also non-governmental associations like the Lake Victoria NGOs Advocacy Network - East Africa, which is a regional initiative of, among others, the Uganda Fisheries and Fish Conservation Association, Indigenous Fisherpeople’s Network (Kenya), Tanzania Fishers Union, Kagera Development Trust Fund (Tanzania) and the KIVULINI Women Right’s Organisation (Tanzania). The latter groups could become important stakeholders in co-managing the fishery resources, particularly by disseminating research results to the groups for whom they serve as intermediaries.

It is our sincere hope that the building blocks presented in this issue may be used for strengthening the management of the fisheries. The time has come that the warnings and recommendations be taken seriously, for the sake of the lake and its riparian population.