Physical and chemical characteristics of water in selected locations in Lake Victoria, Tanzania

A study conducted during the period of March/April 2002 aimed at measuring physical and chemical parameters in Tanzanian portion of Lake Victoria. Temperature and conductivity values were homogeneous among and within the study stations. Levels of dissolved oxygen (DO) ranged from 4 - 9 mgl-1 and there was significant difference between stations (P < 0.05). Water transparency was poor (< 2 m secchi depth) and differed from one sampling station to another. Ammonium nitrogen (NH4+-N), with few exceptions, showed the highest concentrations both at the bottom and near-surface followed by total phosphates (TP), nitrate nitrogen (NO2+NO3--N), nitrite nitrogen (NO2--N) and Soluble Reactive Silicon (SRSi). Concentrations of NH4+-N, TP and SRSi were high at bottom waters and the reverse was true for NO2+NO3--N and NO2--N. Differences in nutrients and physical water parameters among sampling stations were statistically significant (P < 0.05). However, temperature and nutrient levels at studied areas were higher than that of 50 years ago and the trend reversed for DO and transparency. This indicates that Lake Victoria is receiving organic materials from the catchment area leading to the decline of water quality. Long-term efforts for rehabilitation, conservation and sustainable management of the lake are suggested. Tanzania Journal of Science Vol. 30 (2) 2004: pp. 65-7

Changes in population structures of the major species in selected satellite lakes around Lake Victoria following changes in fishing effort

This paper evaluates the impacts of reduction in effort, increase in mesh sizes, and prohibition of illegal fishing gears in selected satellite lakes around Lake Victoria. The study was carried out in six satellite lakes by making investigations on fish collected from experimental and artisanal fisheries. The fishes were analysed for length frequencies, weight and numbers caught to determine the population structure of the fishes. Indiscriminate fishing by deploying illegal gears and increased fishing effort due to open access policy, the catch and diversity of the species in these lakes has declined. Establishment of Conservation Management Units (CMUs) as an enforcement measure in some satellite lakes seems to succeed in controlling the illegal practices and a positive sign of recovery of some species and size increase of the exploitable fish species was noted in lakes Ikimba and Kirumi where enforcement has been effected. From March 2002 to January 2003 the maximum size of Oreochromis niloticus and O. esculentus had increased from 28 cm to 33 cm and 25 cm to 27 cm in Lake Kirumi and Lake Ikimba, respectively. Nevertheless, fish species diversity in these lakes is still low. Recommendations on the way forward are given Tanzania Journal of Science Vol. 30 (2) 2004: pp. 53-6

A meeting framework for inclusive and sustainable science

The ABCD conference format (All continents, Balanced gender, low Carbon transport, Diverse backgrounds) mixes live-streamed and pre-recorded talks with in-person ones to reflect a diverse range of viewpoints and reduce the environmental footprint of meetings while also lowering barriers to inclusiveness

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

From the 1950s onwards, programmes to promote aquaculture and improve capture fisheries in East Africa have relied heavily on the promise held by introduced species. In Tanzania these introductions have been poorly documented. Here we report the findings of surveys of inland water bodies across Tanzania between 2011 and 2017 that clarify distributions of tilapiine cichlids of the genus Oreochromis. We identified Oreochromis from 123 sampling locations, including 14 taxa restricted to their native range and three species that have established populations beyond their native range. Of these three species, the only exotic species found was blue-spotted tilapia (Oreochromis leucostictus), while Nile tilapia (Oreochromis niloticus) and Singida tilapia (Oreochromis esculentus), which are both naturally found within the country of Tanzania, have been translocated beyond their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, 2070) East African climate. These models indicated that presence of suitable habitat for these introduced species will persist and potentially expand across the region. The clarification of distributions provided here can help inform the monitoring and management of biodiversity, and inform policy related to the future role of introduced species in fisheries and aquaculture

The status and distribution of freshwater fishes in the Lake Victoria basin

In terms of hydrology, the Lake Victoria Basin is part of the Nile system, most of which is within the Nilo-Sudan ichthyofaunal province. However, the ichthyofauna of the Lake Victoria Basin differs substantially from most of the downstream Nile basin. It has traditionally been assigned to the East Coast ichthyofaunal province together with the faunas of the systems of Lakes Kyoga, Edward and Kivu, and the coastal rivers of Eastern Africa (Greenwood, 1983; Roberts, 1975; Snoeks et al., 1997). This viewpoint has been challenged and inclusion of the Lake Victoria ichthyofauna into the Nilo-Sudan province has been suggested (Lévêque, 1997; Witte et al., 2009). More recent biogeographic and genetic studies have revealed that Lake Victoria and the smaller lakes in the region harbour a mosaic ichthyofauna composed predominantly of Nilotic and Congolese elements with quite balanced contributions from the two (Meier et al., 2017; Seehausen, 2002). Most of the non-endemic species of Lake Victoria are shared either with the Nile or with the Malagarasi (Congo) system, and very few are shared with coastal rivers. Most of the endemic species have their closest relatives either in the Nile or Congo systems. The large endemic cichlid species radiation evolved from a population of hybrid origins between cichlids from the Nile and the Congo (Meier et al., 2017). The endemic Nothobranchius killifish too derive from two lineages that have their nearest relatives in the Sahel and the Congo respectively (Dorn et al., 2014). Cichlids form the major component of the fish fauna of the Lake Victoria Basin. Other impor tant families are the Cyprinidae, Mormyridae, Clariidae and Poeciliidae. Prior to major anthropogenic disturbances, including the introduction of the Nile Perch (Lates niloticus) and severe habitat deterioration, the system harboured between 600 and 1,000 species of cichl ids, al l but four of them endemic haplochromines (Kaufman et al., 1997; Seehausen, 2002, 2015; Witte et al., 2007). Since the 1980s, an estimated 200 haplochromine species have, however, likely gone extinct and other species have become severely threatened (Seehausen et al., 1997b; Witte et al., 1992, 2007). Unfortunately, several hundred of the haplochromine species remain undescribed, and this includes both extant species and those likely to now be extinct. The numbers of non-cichlids reported in the past appear to have been underestimations, with 69 non-cichlid species listed from the area (excluding the Lake Kyoga region) by this project compared to Snoeks (2000) reporting 45 for Lake Victoria, and Witte et al. (2009) reporting 46 for Lakes Victoria and Kyoga together