Cage farming in the environmental mix of Lake Victoria: An analysis of its status, potential environmental and ecological effects, and a call for sustainability

Abstract

Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hotspot hosting over 500 endemic haplochromine cichlids that were later decimated by exotic introductions and anthropogenically driven environmental and ecological changes. The environmental and ecological changes in the lake over the years have been attributed to overfishing, eutrophication, introduction of exotic species, pollution and possibly climate change. The lake's capture fishery, which is the main economic activity directly and indirectly supporting over 40 million people, has continued to decline after experiencing a boom between the 1970s and 1990s following the introduction of Nile Perch (Lates niloticus) and Nile Tilapia (Oreochromis niloticus). In order to augment capture fisheries from the lake, cage culture was introduced in 2005, but its sustainability and influence on the ecology of the lake are not well understood. In this review, we examine the genesis of degradation of Lake Victoria and assess the role of cage culture as both a solution to the current situation and a cause for concern for the ecology of the lake. To compile this review, we utilized data in the grey and published literature. Studies show that the degradation of the lake can be traced back to the 1930s when the trophic status and ecology of the lake started showing signs of anthropogenic influence. The Nile Perch was introduced in early 1960s to replenish the fishery but its ecological impacts were felt in 1970s and 1980s when the native haplochromine species started to disappear from catches. Progressively, the ecological changes and management concerns in the lake have become a complex mix of exotic species introductions, eutrophication, and overfishing. In this mix of persistent ecological changes, the once thriving capture fisheries revolving around the two exotic species (L. niloticus and O. niloticus) have significantly declined threatening the livelihoods of millions of people directly and indirectly involved in the fisheries. These declines necessitated the introduction of cage culture in 2005 to fill the increasing demand for fish from the lake. Ever since, cage numbers have increased tremendously (>6 000 by 2020) and is now operated by over 60 different firms which are owned either individually or by groups. Over 70% of the cages have been installed in shallow areas within the Winam Gulf which goes against the guidelines on cage installation and operation; regulations on cage farming were introduced after the activity had gained momentum in the lake. Limnological data in areas of the lake that have been stocked with cages has shown evidence of negative effects on water quality. This decline in water quality can be attributed to remnant feeds used in cages, of which 50% are the sinking types, and wastes from fish excretion and egestion. Although data are limited, the potential influence of cage farming on the already altered ecology and environment of Lake Victoria needs to be recognized and investigated. This study recommends studies targeting operations of cages in the lake, including a comprehensive environmental audit to inform their sustainability and relevant policy.

Trends in Water Quality in a Tropical Kenyan River-estuary System: Responses to Anthropogenic Activities

“…Nonetheless, changes in nutrient concentrations are shaped by both point and non-point sources of pollution [1,3,[6][7][8][9]. During spates, there is a lot of surface water run-off that carries much of the dissolved nutrients that are linked with sediments and also it is in such a season that leaching do occur from farmlands.…”

“…Globally, pollution of surface water is on the trajectory owing to rapid human population that is exerting enormous pressure on the environment. Anthropogenic activities have led to elevated physico-chemical water quality attributes of environmental concern because they have resulted into eutrophication and decreased biodiversity in aquatic ecosystems [1][2][3][4][5][6][7][8][9][10]. It has been confirmed that freshwater bodies although smallest in terms of surface area are the most important in sustaining human life and yet they are the most compromised in terms of integrity and their depletion is alarming [6][7][8][11][12][13][14][15].…”

“…Surface run-off from urban leachate fills have got possible likelihood of causing eutrophication in the receiving estuaries [40]. It has been reported that domestic and industrial effluents coupled with soil erosion increase nutrient levels in aquatic ecosystems [3,13,41,42] Therefore, the estuarine ecosystems along the south coast of Kenya, which are dotted with enormous levels of soil erosion fueled by loosely packed soils within their catchment areas are likely to suffer from nutrient enrichment and eventual eutrophication.…”

Water Quality and Growth Performance of Nile Tilapia (Oreochromis niloticus), Chia (Salvia hispanica) and Lemon Grass (Cymbopogon citratus) in a Media-based Aquaponics System

“…However, food production is an anthropogenic activity that has increased the use of fertilizers and available freshwater resources [2,3]. Freshwater scarcity is one of the most pressing global issues, affecting more than 40% of the world's population [4,5]. Furthermore, conventional food production systems are unable to meet the growing demand for the world's population due to arable land loss, water quality and quantity limitations, soil degradation, and nutrient depletion [6].…”

Environmental impacts of tilapia fish cage aquaculture on water physico-chemical parameters of Lake Kivu, Democratic Republic of the Congo

“…In addition, the low investment cost, convenience of installation and maintenance are also contributing to the expansion of cage activities (Gentry et al, 2017;Musinguzi et al, 2019). This is evident in Lake Victoria, where a rise in cage numbers from 1,663 to 4,537 between 2016 and 2019 and to 6,000 in 2021 is a glaring sign of sustained acceptance of cage aquaculture (Hamilton et al, 2020;Nyakeya et al, 2022). World inland aquaculture production as of 2021 was at 50% of the total fisheries production whereas in Africa, aquaculture contribution was at 18% with inland aquaculture constituting 92% of the total aquaculture production (FAO, 2022).…”