The diatoms of Longans lake-vegetation. Fossil diatom flora. [Translation from: Acta Phytogeographica Suecica 36 73-86, 1955. ]

Sediment samples were taken from Lake Langans in Sweden and fossilised diatoms analysed. Sample methods and environmental factors are discussed. Species with a characteristic occurrence are described. The article discusses diatom-thanatocoenoses as indicators of environment.

Studies on heterotrophic nitrification in a lake. [Translation from: Z.allg.Mikrobiol. 12 567-574, 1973. ]

In a lake the nitrogen compounds are liable to regular cycling in which nitrate is reduced and ammonium oxidised. As a nitrate maximum is regularly established in the upper part of the hypolimnion of a stratified summer lake, the authors have dealt in particular with the oxidising side of the nitrogen cycle. Described here are partial results of the nitrification in Plusssee. The Plusssee was chosen, since it is almost entirely without inflows, and, lying in a wooded basin, is well protected from the wind, and therefore stably stratified. In order to determine the number of autotrophic nitrificants the distribution of the Nitrosomonas and Nitrobacter spores in the lake were analysed. From the estimates on the determination of spore numbers of the heterotrophic nitrificants, 14 species in the pure culture were isolated and examined from morphological, biochemical and taxonomic viewpoints.

Waterfowl and their role in lake ecosystems. [Translation from: Wiadomosci Ekologiczne 19, 355-371, 1973.]

We know very little about the role of birds in different ecosystems, despite numerous interesting works of researchers and amateur ornithologist scattered throughout the world. Less attention is paid to freshwater ecosystems because of the difficulties encountered in the experimental methods as well as a lack of interest on behalf of hydrobiologists, for the activities of birds in these ecosystems. This article summarises types and morphoecological forms of waterfowl and their place in the lake ecosystem.

Selective plankton feeding by the coregonid ”bondella” (Coregonus sp.) of Lake Maggiore [Translation from: Translation from: Memorie dell'Istituto Italiano di Idrobiologia Dott.Marco de Marchi 31 181-203, 1974]

In recent times, some specialists have begun to study the subject of food selection of fish in an organized way, thus highlighting its importance. In the present work, the author intends to evaluate the impact of predation on the eupelagic zooplanktonic biocenosis of Lake Maggiore, producing, in this way, as far as possible, a basis for a better understanding of the population dynamics of the species of zooplankton directly involved. Another aspect which has been studied is that related to the mechanism of selective capture set in action by the predator. To this end the study tries to bear in mind that the subject should be interpreted as a function of numerous factors acting contemporaneously, that is as the interaction of characters peculiar to the predator and to the prey. The species studied, locally called ”bondella”, belongs to the family Salmonidae, subfamily Coregoninae and was introduced into Lake Maggiore in 1950.

The design of multimesh, multidepth gillnet fleets for use in the Lake Victoria Fisheries Research Project

Multimesh, multidepth gillnet fleets are useful in assessing fish stock abundance, size distribution and depth distribution. Using data collected on net mesh selectivity for Nile perch, Lates niloticus (L.), in the Kenyan waters of Lake Victoria, suitable mesh sizes for gillnet fleets for use in the Lake Victoria Fisheries Research Project were determined. The modal selection length for Nile perch in the mesh sized used in the earlier experiment were determined, as was the size range vulnerable to capture. Initial trials suggest 60% of the Nile perch swim within 5 m of the bottom. Setting and hauling of the nets is simple and quick, allowing the nets to be used at the same time as other sampling programmes.

Methodology of the Lake Victoria Fisheries Research Project's Co-management survey

In this book section, the theoretical background to the methodology is outlined, questionnaire development described, sample selection outlined and biases and shortcomings to the survey noted.

Synthesising co-management for Lake Victoria: discussions on models relating to concepts of sustainability and participative management

This book section aims to synthesise the results of the surveys related to the LVFRP by developing different strategies to implement a sustainable and participative co-management model.

Lake Victoria Fisheries Management Plan

The purpose of this Fisheries Management Plan (FMP) within the Lake Victoria Fisheries Research Project was to sustain the livelihoods of the communities who depend on the fishery resources of the lake and to reduce poverty, food insecurity and unemployment. To achieve this goals, a better management of the resources, which would mobilize and include stakeholders at local, regional, national and international level was believed to be the right strategy for success. (PDF contains 79 pages)

An alternative management strategy for Lake Victoria (Kenya)

In Kenya, fisheries resource management has been based on the top-down centralized approach since the colonial days. Stakeholders have never been consulted concerning management decisions. The 4-beaches Study was undertaken to investigate the potential for an alternative management system for Lake Victoria.

Co-managerial potentials for Tanzania's Lake Victoria fisheries perspectives from two landing sites

Two landing sites were chosen in Tanzania for the 4-beaches survey. The former, Ihale, is a large one with an avarage of 120 boats and direct connections to the fish processing factories. The latter, Mwasonge, is one of the smallest landing sites in the Mwanza region with totally different characteristics. This book section aims to analyse the results from these two sites in the context of the co-management potentialities in Tanzania and more generally on the Lake Victoria region.

Current status of the fish stocks of Lake Victoria (Uganda)

A total of 457 hauls were taken during experimental bottom trawl surveys in the Uganda sector of Lake Victoria between November 1997 and June 1999 to estimate composition, distribution and abundance of the major fish species in waters 4-60 m deep. Fifteen fish groups were caught with Nile perch, Lates niloticus (L.), constituting 94% by weight. Haplochromines and L. niloticus occurred in all areas sampled, while Nile tilapia, Oreochromis niloticus (L.) and other tilapiines were restricted to waters 30 m deep or less. The mean trawl catch rate in the zone where artisanal fishermen operate (i.e. in waters less deep than 30 m was 165 kg hr, of which 93.6% comprised L. niloticus. Species diversity and relative abundance decreased with increasing water depth.

Distribution and abundance of fish stocks in Lake Victoria, Tanzania

Trawl surveys to assess the stocks of Lake Victoria for estimates of biomass and yield, together with the establishment of exploitation patterns, are being undertaken under the Lake victoria Fisheries Research Project. Preliminary surveys to establish the sampling stations and strategy were carried out between October 1997 and February 1998. Three cruises to cover the whole of the Tanzanian waters were undertaken with a total of 133 sampling stations. Data on catch rates, species composition and distribution were collected.

Relative abundance and distribution of fish in Kenyan waters of Lake Victoria

Bottom trawl surveys were conducted in Kenyan waters of Lake Victoria during the period September 1997 and March 1999. The means of fish biomass for the two most important species: Lates niloticus (L.) and Oreochromis niloticus (L.) were estimated at 61.5 kg ha and 4.5 kg ha respectively. There were few L. niloticus greater than 80 cm TL and O. niloticus greater than 50 cm TL, though these species attain maximum sizes of 205 cm and 65 cm respectively. Oreochromis niloticus was mostly found shallower than 5 m though some specimens were encountered deeper than 10 m, suggesting that the species has extended its ecological range. Very low catches were obtained from areas under water hyacinth cover. Water in such areas was turbid with oxygen levels below the critical 3.0 mg L.

The relationship between boat size and fish catches in the gillnet fishery of Lake Victoria, Uganda

The number and size composition of gillnets, fishing grounds, and the quantity and composition of fish catches were related to the size of fishing boat. The overall number of gillnets per boat increased from 20.9 + or - 2.3 nets in 5-6 m long boats to 88.6 + or - 11.8 nets in 11-12 m long boats. The proportion of large mesh sizes, + or more than 127 mm, also increased from 40% in 5-6 m long boats to 100% in boats longer than 10 m. Fish catches are related to the size of boat and this should be considered when formulating management guidelines of the lake's fishery. Promotion of large fishing boats 8 m or longer and restriction on the number and/or mesh size of gillnets of smaller boats could increase ecological and socio-economic benefits.

The status of the artisanal fishery of Lake Victoria, Kenya, with notes on improvements to the catch data collection system

Catch and effort assessment surveys have been used to assess trends in fish landings in Kenyan waters of Lake Victoria since 1976. Landings reached a maximum of 200000 t annually in 1989-1991 as Nile perch, Lates niloticus (L.), catches increased due to an expansion in stock size and increased fishing effort. CPUE peaked at 180 kg boat day-1 in 1989 and decreased thereafter with increasing effort. By 1998 total Nile perch catches were half those at the beginning of the decade despite increased effort. Catches of Rastrineobola argentea (Pellegrin) have levelled off despite increased effort.