The distribution and abundance of Copepoda and Cladocera in the Lake Victoria, Kenya

Fourteen stations were sampled in the Kenyan waters of Lake Victoria in order to assess distribution and abundance of zooplankton. Seven stations were selected in the Nyanza gulf while the rest were in the open waters of the lake. Zooplanktons samples were collected monthly from November 1998 to January 1999, using a 1.5 m long Nansen type plankton net of 243 mu m mesh size and 50 cm diameter. Representative specimens were dissected and identified to species level

An assessment of co-management potentials in the Lake Victoria fisheries of Kenya

Co-management is a system or a process in which responsibility and authority for the management of common resources is shared between the state, local users of the resources as well as other stakeholders, and where they have the legal authority to administer the resource jointly. Co-management has received increasing attention in recent years as a potential strategy for managing fisheries. This paper presents and discusses results of a survey undertaken in the Kenyan part of Lake Victoria to assess the conditions - behaviour, attitude and characteristics of resource users, as well as community institutions - that can support co-management. It analyses the results of this survey with respect to a series of parameters, identified by Pinkerton (1989), as necessary preconditions for the successful inclusion of communities involvement in resource management. The survey was implemented through a two-stage stratified random sampling technique based on district and beach size strata. A total of 405 fishers, drawn from 25 fish landing beaches, were interviewed using a structured questionnaire. The paper concludes that while Kenya's lake Victoria fishery would appear to qualify for a number of these preconditions, it would appear that it fails to qualify in others. Preconditions in this latter category include the definition of boundaries in fishing grounds, community members' rights to the resource, delegation and legislation of local responsibility and authority. Additional work is required to further elaborate and understand these shortcomings

Report on the physical, bacteriological and biochemical analyses of seawater samples collected off existing sewage outfalls in the Sierra Leone River Estuary

The studies reported were undertaken as part of a wide environmental feasibility study for the establishment of a modern sewage system in Freetown. The aim of this part of the study was to determine whether the hydrological regime of the Sierra Leone River Estuary would permit the large-scale introduction of sewage into the estuary without damaging the environment. The important factors were whether: 1) there would be sufficient dilution of the sewage; 2) fleatable particles or other substances would create significant adverse effects in the estuarine ecosystem. The outfall sites are described together with the sampling stations, methods and analyses. Results include: 1) T/S profiles; 2) chemical analysis of the water. A review of literature on the Sierra Leone River Estuary is included which provides information on the plankton, benthos and fisheries. Results suggest that at certain points where local circulations occur it would be inadvisable to locate untreated sewage outfalls. Such points are frequently observed in small embayments. These studies have been of short duration but the data can serve as baseline for more extended investigations which would give a more complete picture of the seasonal patterns in the estuary.

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.

The role of Caridina nilotica (Roux) in the Lake Victoria fisheries with reference to Lates niloticus (L.)

Caridina nilotica (Roux) (Decapoda: Atyidae) was investigated over a period of four months in three zones of Lake Victoria. Abundances were estimated by vertical net sampling. The importance of C. nilotica in the diet of the three commercial fish species was investigated. Caridina nilotica is a primary food for Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin). A quantitative study of C. nilotica in the fishing area indicated high biomass which can support the Lake Victoria fisheries.

The diversity and abundance of zooplankton in the Lake Victoria and Kyoga basins and their relationship to fish production

Biological diversity of an ecosystem is considered a reliable measure of the state of health of the ecosystem. In Uganda's large lakes, the Victoria and Kyoga, the past three decades have been characterized by profound changes in fish species composition following the introduction of the piscivorous Nile perch (Oguto-Ohwayo 1990). Over 300 haplochromine cichlid species comprising a wide range of trophic groups were lost along with a host of non-cichlid fishes which occupied virtually all available ecological niches and in the lakes (Witte 1992). A second major ecological event has been the gradual nutrient enrichment of the water bodies (eutrophication) from diffuse and point sources, while at the same time pollutants have also gained entrance into the water systems in pace with indusfrial development and human population increases in the lake basins. Eutrophication and pollution have drastically altered the physical and-chemical character of the water medium in which different fauna and flora thrive. In Lake Victoria these alterations have resulted in changes of algal species composition from pristine community dominated by chlorophytes and diatoms (Melosira etc) to one composed largely of blue-green algae or Cyanobacteria (Microcystis, Anabaena, Planktolyngbya etc) (Mugidde 1993, Hecky 1993).

Some characteristics of the fish fauna of a dam in the Lake Victoria region of Tanzania including the effects of multispecific stocking with tilapia species

Malya dam had been stocked with several species of Tilapia. However all but the species endemic to the region, T esculentus, made only marginal contributions to the fishery. T. zilli particularly had failed to establish itself, probably because its niche had been previously filled by T. rendalii. Planktivorou Tilapia species predominate in Malya dam but in smaller dams in the region herbivoorous tilapia are relatively more abundant. Six non-cichlid species and one of Haplochromis were found in the dam. Tilapia esculenta the most economically important species, was estimated to grow within 9-10 cm first year and 16-18 cm second year. The largest, specimen caught was 30.5 cm and the smallest mature individual 19 cm. The fish of the dam grew more slowly and matured at a smaller size than those of the same species in Lake Victoria The biological pattern of T. esculenta in Malya dam was similar to that of this species in Lake Victoria.

Reduction of the “ngege”, Oreochromis esculentus (Teleostei: Cichlidae) populations, and resultant population genetic status in the Lake Victoria region

Ngege, Oreochromis esculentus, originally formed the mainstay of the Lake Victoria Region (LVR) fisheries. Together with its indigenous congener O. variabilis, it was displaced from Lakes Victoria and Kyoga of LVR and was found to survive as isolated small populations within the peripheral minor lakes and reservoirs around the two lakes. Displacement of the two LVR indigenous tilapiines was thought to be principally driven by changed lake environment and predation by the introduced Nile perch, but also competition and genetic swamping by the closely related introduced and comparatively more ecologically versatile tilapine species. In a study carried out in the LVR between 1993 and 2003, micro satellites and RAPD markers were used to analyse the remnant populations so as to establish the population structure and extant genetic diversity of O. esculentus. Analyses indicated that the surviving O. esculentus retained a high proportion of genetic diversity with high differentiation between units an indication of genetic exchange between indigenous and introduced Nile tilapia where the two forms co-existed. While this heightened concern for genetic swamping of the remnant population units by the introduced tilapiines it was noteworthy that in a few of the satellite lakes where the O. esculentus was dominant evidence for introgression was weak.

Aquatic weeds hotspots in the Lake Victoria basin Uganda and on Lake Kyoga: implications for their management

Proliferation of invasive aquatic weeds has developed into a major ecological and socio economic issue for many regions of the world. As a consequence, inference on where to target control and other management efforts is critical in the management of aquatic weeds (Ibáñez et al., 2009). Notwithstanding, aquatic systems in Uganda in general and in the basins of Lakes Victoria and Kyoga in particular, have fallen victims to aquatic weeds invasion and subsequent infestation. If these aquatic weeds infestations are to be minimized and their impacts mitigated, management decisions ought to be based on up-to-date data and information in relation to location of infestation hotspots. Aquatic systems in the basins of the two production systems are important sources of livelihoods especially from fish production and trade yet they are prone to infestation by aquatic weeds. Thus, the invasion and subsequent infestation of aquatic ecosystems by aquatic weeds pose a major conservation threat to various aquatic resources (Catford et al., 2011; Kayanja, 2002). This paper examines the extent to which aquatic weeds have infested aquatic ecosystems in the basins of Lakes Victoria and Kyoga. The information is expected to guide management of major aquatic weeds through rational allocation of the scarce resources by targeting hotspots.

Atmospheric chlorofluoromethanes as tracers of ocean circulation and mixing: measurement and calibration techniques and studies in the Greenland and Norwegian seas

EXTRACT (SEE PDF FOR FULL ABSTRACT): An analytical system was designed and constructed for the rapid and accurate shipboard measurement of anthropogenic chlorofluoromethanes in seawater and in air, using electron capture gas chrometography. The distribution of these compounds in the marine atmosphere and the water column in the Greenland and Norwegian seas were studied during February and March, 1982. The compounds, dissolved in the ocean from the atmosphere, can be used as tracers of subsurface ocean circulation and mixing processes.

Use of ocean and estuarine habitats by young-of-year bluefish (Pomatomus saltatrix) in the New York Bight

Young-of-year (YOY) blue-fish (Pomatomus saltatrix) along the U.S. east coast are often assumed to use estuaries almost exclusively during the summer. Here we present data from 1995 to 1998 indicating that YOY (30–260 mm FL) also use ocean habitats along the coast of New Jersey. An analysis of historical and recent data on northern and southern ocean beaches (0.1–2 m) and the inner continental shelf (5–27 m) during extensive sampling in New Jersey waters from 1995 to 1998 indicated that multiple cohorts occurred (June–August) in every year. When comparable collections of YOY were made in the ocean and in an adjacent estuary, the abundance was 1–2 orders of magnitude greater on ocean beaches during the summer. The YOY were even more abundant in ocean habitats in the fall (September–October), presumably as a result of YOY leaving estuaries to join the coastal migration south. During 1999 and 2000, YOY bluefish were tagged with internal sequential coded wire microtags in order to refine our under-standing of habitat use and movement. Few (0.04%) of the fish tagged on ocean beaches were recaptured; however, 2.2% of the fish tagged in the estuary were recaptured from 2 to 27 days after tagging. Recaptured fish grew quickly (average 1.37 mm FL/d). On ocean beaches YOY fed on a variety of invertebrates and fishes but their diet changed with size. By approximately 80–100 mm FL, they were piscivorous and fed primarily on engraulids, a pattern similar to that reported in estuaries. Based on distribution, abundance, and feeding, both spring- and summer-spawned cohorts of YOY bluefish commonly use ocean habitats. Therefore, attempts to determine factors affecting recruitment success based solely on estuarine sampling may be inadequate and further examination, especially of the contribution of the summer-spawned cohort in ocean habitats, appears warranted.

Occurrence of whale sharks in coastal waters in the Indian Ocean: an interesting coincidence

Salinity, temperature and pressure are parameters which govern the oceanographic state of a marine water body and together they make up density of seawater. In this contribution we will focus our interest on one of these parameters, the salinity: accuracy in relation to different purposes as well as observation technique and instrumentation. We will also discuss the definition of salinity. For example most of the Indian Ocean waters are within the salinity range from 34.60-34.80, which emphasize the importance of careful observations and clear definitions of salinity, in such a way that it is possible to define water masses and predict their movements. In coastal waters the salinity usually features much larger variation in time and space and thus less accuracy is sometimes needed. Salinity has been measured and defined in several ways over the past century. While early measurements were based on the amount of salt in a sea water sample, today the salinity of seawater is most often determined from its conductivity. As conductivity is a function of salinity and temperature, determination involves also measurement of the density of seawater is now more precisely estimated and thus the temperature. As a result of this method the Practical Salinity Scale (PSS) was developed. The best determination of salinity from conductivity and the temperature measurements gives salinity with resolution of 0.001 psu, while the accuracy of titration method was about ± 0.02‰. Because of that, even calculation of movements in the ocean is also improved.

The effect of hook size on the catch rate and size of the Nile perch Lates niloticus (Linne) fishery in the Napoleon Gulf, Lake Victoria, Uganda

This study was undertaken in Napoleon gulf, Lake Victoria Uganda from July – December 2009. It was conducted in four landing sites; Bukaya (0.41103N, 33.19133E), Bugungu (0.40216N, 33.2028E), Busana (0.39062N, 33.25228E) and Kikondo (0.3995N, 33.21848E) all from Buikwe district (Formerly part of Mukono district). The main aim was to determine the effect of both hook size and bait type on the catch rate (mean weight) and size composition of Nile perch (Lates niloticus) (LINNE) fishery in the Napoleon Gulf, Lake Victoria. The main hook sizes investigated during the experiment were 7, 8, 9, 10, 11 and 12 that were dominantly used in harvesting Nile perch in Napoleon Gulf, Lake Victoria. In this study length, weight and bait type data were collected on site from each boat at that particular fishing spot; since most fishermen in the Napoleon Gulf could sell their fish immediately the catch is caught there and then. The results indicated a total of 873 Nile perch fish samples collected during the study. Statistical tests, descriptive statistics, regression and correlation were all carried out using the Statistical Package for the Social Sciences (SPSS) in addition to Microsoft excel. The bait types in the Gulf ranged from 5-10 cm Total length (TL) haplochromine, 24.5-27 cm TL Mormyrus kannume and 9-24 cm TL Clarias species. The bait types had a significant effect on the catch rate and also on the size composition the fish harvested measured as Total length (ANCOVA F=8.231; P<0.05) despite the fact that bait type had no influence on mean weight of fish captured (ANCOVA F=2.898; P>0.05). Hook sizes used by the fishers had a significant effect on the both the size (TL) composition (ANCOVA F=3.847; P<0.05) and the mean weight (ANCOVA F=4.599; P<0.005) of the Nile perch captured. Investigations indicated hook sizes seven (7) and eight (8) were the ones that harvested the Nile perch above the slot size of 50 cm total length. In general hook sizes indicated to be the main drive in the harvesting of the Nile perch though bait type also contributed toward that. Generally there is need for management to put a law in place on the minimum hook size to be used on the harvesting of the Nile perch and also monitored by the Fisheries Management as a regulatory measure. In addition to that aquaculture should be encouraged to farm the fish for bait at a higher scale in the region in order to avoid depleting the wild stocks already in danger of extinction. Through this kind of venture, both biodiversity conservation and environmental sustainability will be observed in the Lake Victoria basin.

Noise levels and sources in the Stellwagen Bank National Marine Sanctuary and the St. Lawrence River Estuary

Although ambient (background) noise in the ocean is a topic that has been widely studied since pre-World War II, the effects of noise on marine organisms has only been a focus of concern for the last 25 years. The main point of concern has been the potential of noise to affect the health and behavior of marine mammals. The Stellwagen Bank National Marine Sanctuary (SBNMS) is a site where the degradation of habitat due to increasing noise levels is a concern because it is a feeding ground and summer haven for numerous species of marine mammals. Ambient noise in the ocean is defined as “the part of the total noise background observed with an omnidirectional hydrophone.” It is an inherent characteristic of the medium having no specific point source. Ambient noise is comprised of a number of components that contribute to the “noise level” in varying degrees depending on where the noise is being measured. This report describes the current understanding of ambient noise and existing levels in the Stellwagen Bank National Marine Sanctuary. (PDF contains 32 pages.)