Past and recent trends in the exploitation of the great lakes fisheries of Uganda

Uganda's fish production has shown a substantial increase from a level of 61,500 tonnes in 1961 to a total of 214,302 tonnes in 1988. During this period significant changes also occurred in species composition, fishing factors, and patterns of utilisation. This paper briefly summarises the fisheries of Uganda's great lakes and reviews past and present trends in their exploitation, as reflected in available catch and effort data collected through the Fisheries Department statistical reporting system.

Fisheries resources evaluation survey of Lake Wamala during May 1993

During the period 25th - 29th May 1993 a team of research scientists and from UFFRO conducted a fisheries resources evaluation survey of Lake Wamala. This was a follow up of the previous surveys on the lake aimed at accessing the status of the fisheries of the lake with particular respect to the species composition, size structure of the harvestable fish stocks and the relative abundance of the stocks.

Induction of apoptosis by UV in the flat oyster, Ostrea edulis

Apoptosis is a fundamental feature in the development of many organisms and tissue systems. It is also a mechanism of host defense against environmental stress factors or pathogens by contributing to the elimination of infected cells. Hemocytes play a key role in defense mechanisms in invertebrates and previous studies have shown that physical or chemical stress can increase apoptosis in hemocytes in mollusks. However this phenomenon has rarely been investigated in bivalves especially in the flat oyster Ostrea edulis. The apoptotic response of hemocytes from flat oysters, O. edulis, was investigated after exposure to UV and dexamethasone, two agents known to induce apoptosis in vertebrates. Flow cytometry and microscopy were combined to demonstrate that apoptosis occurs in flat oyster hemocytes. Investigated parameters like intracytoplasmic calcium activity, mitochondrial membrane potential and phosphatidyl-serine externalization were significantly modulated in cells exposed to UV whereas dexamethasone only induced an increase of DNA fragmentation. Morphological changes were also observed on UV-treated cells using fluorescence microscopy and transmission electron microscopy. Our results confirm the apoptotic effect of UV on hemocytes of O. edulis and suggest that apoptosis is an important mechanism developed by the flat oyster against stress factors.

Invertebrate communities of Nabugabo Lakes: a vital support resource for the fisheries and ecosystem diversity

A field study of the invertebrate communities of the Nabugabo lakes(Nabugabo,Kayanja and Kayugi)showed the occurrence of copepoda, cladocera and rotifera(micro-invertebrates or zooplankton); Ephemeroptera and Diptera(macro-invertebrates or zoo-benthos). The most commonly encountered taxa were thermocyclops neglectus, moinamicrura,several rotiferan species(micro-invertebrates);P.adusta,chironomus, tanipodinae and trichoptera(macro- invertebrates). These organisms are assumed to be readily available as food sources for fishes in the Nabugabo lakes. Higher abundance and diversity of invertebrates occurred in Lake Nabugabo compared to Kayanja and Kayugi. There were no major differences in diversity and abundance of organisms between inshore and offshore areas of the different lakes. The highest diversity of macro-invertebrates(up to 15 taxa)was recovered from roots of macrophyte(higher water-based plants)such as Miscanthidium and Papyrus. The zooplankton of Nabugabo lakes typify a tropical assemblage with few species among genera and dominance of the communities by small-bodied organisms. Some taxa,common to many other water bodies such as Mesocyclops spp.,Calanoids(Copepoda), Caridina nilotica (Decapoda)were noticeably missing in the Nabugabo lakes community, probably due to environmental limitations including low conductivity and pH. Where they occur,these missing taxa have been shown to be key forage items for fishes and therefore their absence in Nabugabo lakes may have implications with respect to potential for fishery production. However other valuable invertebrate types such as cyclopoid copepods,ephemeroptera, chironomid and chaoborid larvae do occur in sufficiently high diversity and abundance to support viable fisheries resources. The high diversity and abundance of invertebrates associated with aquatic macrophytes such as Papyrus and Miscanthidium need to be protected through control of access and utilisation of shoreline vegetation.

Socio-economic aspects of Nabugabo satellite lakes, fisheries and their implications for management

A number of fish species once native only to Lakes Victoria and Kyoga have considerably declined over the years, and in some cases disappeared, due to over exploitation, introduction of exotic species especially the Nile Perch, and environmental degradation resulting from human activities. Some of the species have been observed to survive in satellite lakes in the Victoria and Kyoga Lake basins. The Nabugabo satellite lakes contain the endemic Cichlid fish species, Oreochromis esculentus and two haplochromine species previously found only in Lake Nabugabo. There is, therefore, need to conserve these species by ensuring sustainable use and management of the resources. The study revealed that the Nabugabo lakes provide a range of socio-economic benefits accruing from fishing, farming, logging, resort beach development and watering of animals. However, although these activities impact on the lakes ecosystems, the participation of resource users in management is limited because of the weak local management institutions operating on the lakes, hence the need to strengthen them through capacity building. It is recommended that Government should work jointly with the beach committees and fishing community in a participatory way to eliminate the use of destructive fishing practices and control the other environment degrading activities.

Disruption of amylase genes by RNA interference affects reproduction in the Pacific oyster Crassostrea gigas

Feeding strategies and digestive capacities can have important implications for variation in energetic pathways associated with ecological and economically important traits, such as growth or reproduction in bivalve species. Here, we investigated the role of amylase in the digestive processes of Crassostrea gigas, using in vivo RNA interference. This approach also allowed us to investigate the relationship between energy intake by feeding and gametogenesis in oysters. Double-stranded (ds)RNA designed to target the two α-amylase genes A and B was injected in vivo into the visceral mass of oysters at two doses. These treatments caused significant reductions in mean mRNA levels of the amylase genes: −50.7% and −59% mRNA A, and −71.9% and −70.6% mRNA B in 15 and 75 µg dsRNA-injected oysters, respectively, relative to controls. Interestingly, reproductive knock-down phenotypes were observed for both sexes at 48 days post-injection, with a significant reduction of the gonad area (−22.5% relative to controls) and germ cell under-proliferation revealed by histology. In response to the higher dose of dsRNA, we also observed reductions in amylase activity (−53%) and absorption efficiency (−5%). Based on these data, dynamic energy budget modeling showed that the limitation of energy intake by feeding that was induced by injection of amylase dsRNA was insufficient to affect gonadic development at the level observed in the present study. This finding suggests that other driving mechanisms, such as endogenous hormonal modulation, might significantly change energy allocation to reproduction, and increase the maintenance rate in oysters in response to dsRNA injection.

Fisheries ecology in the interface zone of Lake Nabugabo

This study was carried out in the interface zone of Lake Nabugabo, which is situated to the west of Lake Victoria. Four study sites were chosen from the south-western to the eastern ends of the euhydrophyte-dominated interface zone, which was about 10 km long, 10 to 50 m wide, 2 m deep and characterized by a thick layer of peat at the bottom. Nymphaea caerulea was the most dominant and widespread euhydrophyte species except in the eastern tip of the lake where it was replaced by Nymphaea lotus. Interspersed among these lilies was Ceratophyllum demersum in certain bays which were thought to be either water inlets or out-flows; Utricularia and Nymphoides indica were associated with monospecific stand of N. caerulea in the south- western end of the zone. The microinvertebrates were dominated by Copepoda (represented mainly by Cyclopoida), and Rotifera, with Cladocera occurring sporadically, while the macroinvertebrates were represented by Mollusca, Acarina, and seven insect orders of which Diptera (represented by Chironomidae) was the most dominant and widespread. Snails were found to have increased in abundance and distribution since the early 1960's. Nymphaea-Ceratophyllum mixed habitats had far more larval fishes and macroinvertebrates than monospecific stands of N. caerulea. Generally, the eastern end of the interface zone had more macroinvertebrates and larval fishes than the south-western end. Food habits of larval fishes were dominated by chironomid larvae; others consumed included detritus, aufwuchs and, periodically, cladocerans.

Productivity factors and fish production and their fisheries management concerns

The fundamental purpose of fisheries management is to ensure sustainable production over time from fish stocks, preferably through regulatory and enhancement actions that promote economic and social well being of the fishers and industries that depend on the resource. To achieve this purpose, management authorities must design, justify and administer (enforce) a collection of restraints on fishing and fishery-related activities. Productivity and management of the fisheries should be based on the understanding that they are complex and dynamic systems. Physical, chemical and biological components support a community of organisms that is unique to the these systems. All these components are in constant change but mainly dictated by human interference in the water body ecosystem.

Lake Victoria fisheries catch assessment survey (CAS) information June 2006

The National Fisheries Resources Research Institute (NAFIRRI), the Department of Fisheries Resources (DFR) and the districts in and around Lake Victoria jointly conduct Catch Assessment Surveys (CAS) with a major objective of providing information on the magnitude of fish catches in the lake. Fisheries contribute as high as 12% to Uganda's GDP. Catch assessment surveys are some of the avenues used to collect information for monitoring fish population dynamics as well as the magnitude, distribution and trends of fishing effort and fish catches. They are necessary for making sound decisions for the management of Lake Victoria fisheries. This information provides the Catch Per Unit of Effort (CPUE). The CPUE is used together with frame survey data to estimate total fish catches.

The fisheries of the Kyoga lakes and the likely impact on them by human activities in the catchment

A review of the historical development of the fishery resources of the Kyoga basin shows that the fishery based on the alien fishes which surplanted the indigenous species in the 1960's and early 1970's has been evolving. The record catches of the 19705 and early 1980's were mainly influenced by increased nutrient supply and enlarged lake volume. The sudden collapse in the fishery particularly of the Nile perch in the mid 1980's was most probably imposed by bad fishing regimes. However, future trends in the fisheries of the Kyoga basin will most likely be controlled by nutrient availability and dynamics as well as by the impact of mans activities in the Kyoga catchment.

Commercialization of the fisheries of Lake Victoria and its implications for local livelihoods

The purpose of this paper is to examine the impact of commercialization on the livelihood of local people. The paper attempts to provide an understating of the key elements of the local livelihoods and how they are affected by the process of commercialization within fisheries.

Lake Victoria Fisheries Service Annual Report 1959/60

The Annual report provides information on work carried out on Lake Victoria by the Lake Victoria Fisheries Service during the period 1959/60. It provides annual catch statistics, fisheries control and legislation.

Multijurisdictional fisheries performance reporting: How Australia’s nationally standardised approach to assessing stock status compares

Australian marine wild-capture fisheries are managed by eight separate jurisdictions. Traditionally, fishery status reports have been produced separately by most of these jurisdictions, assessing the fish stocks they manage, and reporting on the effectiveness of their fisheries management. However, the format, the type of stock status assessments, the thresholds and terminology used to describe stock status and the classification frameworks have varied over time and among jurisdictions. These differences complicate efforts to understand stock status on a national scale. They also create potential misunderstanding among the wider community about how to interpret information on the status of fish stocks, and the fisheries management and science processes more generally. This is especially true when considering stocks that are shared across two or more jurisdictional boundaries. A standardised approach was developed in 2011 leading to production of the first national Status of key Australian fish stocks reports in 2012, followed by a second edition in 2014 (www.fish.gov.au). Production of these reports was the first step towards a broader national approach to reporting on the performance of Australian fisheries for target species and for wider ecosystem and socioeconomic consequences. This paper outlines the challenges associated with moving towards national performance reporting for target fish stocks and Australia’s successes so far. It also outlines the challenges ahead, in particular those relating to reporting more broadly on the status of entire fisheries. Comparisons are drawn between Australia and New Zealand and more broadly between Australia and other countries.

Mass mortality in bivalves and the intricate case of the Pacific oyster, Crassostrea gigas

Massive mortality outbreaks in cultured bivalves have been reported worldwide and they have been associated with infection by a range of viral and bacterial pathogens. Due to their economic and social impact, these episodes constitute a particularly sensitive issue in Pacific oyster (Crassostrea gigas) production. Since 2008, mortality outbreaks affecting C. gigas have increased in terms of intensity and geographic distribution. Epidemiologic surveys have lead to the incrimination of pathogens, specifically OsHV-1 and bacteria of the Vibrio genus, in particular Vibrio aestuarianus. Pathogen diversity may partially account for the variability in the outcome of infections. Host factors (age, reproductive status…) including their genetic background that has an impact on host susceptibility towards infection, also play a role herein. Finally, environmental factors have significant effects on the pathogens themselves, on the host and on the host-pathogen interaction. Further knowledge on pathogen diversity, classification, and spread, may contribute towards a better understanding of this issue and potential ways to mitigate the impact of these outbreaks.