A mesocosm analytical study on the impact of freshwater mussel (Lamellidens marginalis Lamarck) mediated bioturbation and biodeposition on some ecological factors of a freshwater lake

The biotic potential of the benthic filter feeding freshwater bivalve mollusc Lamellidens marginalis (Lamarck) influencing the nutrient dynamics of the bottom sediments of the lake by means of biodeposition and bioturbation activities were analysed using a lake mesocosm experiment. Five control as well as experimental mesocosms was maintained up to 60 days (d). The factors studied included the percentage of water content of the sediment, percentage of total nitrogen, percentage of organic matter along with the total phosphorus and humic acid content. While total phosphorus and humic acid content of the experimental mesocosoms showed gradual and significant increases from 30d of the experiment to reach the maximum levels after 60d, the percentage of organic matter registered significant increases right from 15d onwards and reached the maximum values after 60d. On the other hand, while the percentage of water content of the sediments of the experimental mesocosoms increased only up to 30d experiment, percentage of nitrogen was increased during the first half and at the fag end of the experiment. All the investigated ecological factors were found to be significantly influenced by the presence of L. marginalis in the experimental mesocosms. The study indicated that the mussel influence the nutrient dynamics of the inhabitant ecosystem through the processes of excretion, biodeposition of pseudofaeces and faeces, along with the bioturbation of the sediments brought about by their ploughing movements. KEYWORDS: freshwater mussel, Lamellidens marginalis, bioturbation, biodeposition, mesocosms.

Recent observations on the exploitation of the fish stocks of Lake Victoria, Uganda

The data from the able sources has been used in this paper to make observations on the exploitation of the fish stocks in Lake Victoria since 1981. The paper focuses on species composition of the catch, catch rates, average size of the individual fish landed and fish production. On the basis of these parameters and developments in the fishery, the paper also presents some observations and comments on the future prospects of the fish stocks in the lake.

The effect of ecological changes in Lake Victoria on the present trophic characteristics of Oreochromis niloticus in relation to the species' role as a stabilizing factor of biomanipulation

The Lake Victoria ecosystem has experienced such a profound ecological change that Oreochromis niloticus - an introduced species, is the only important cichlid (out of the original 250 + spp) left in the lake. It is the basis of an important commercial fishery which is intensely exploited by sophisticated methods. An investigation of its feeding habits at present indicates that the species could also playa major role in the energy flux of the lake. Fisheries management in Lake Victoria will thus require multi-disciplinary studies which reflect a total ecosystem approach.

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.

The effect of Lampara net on the catch rates and size of the fishing harvest of Rastrineobola argentae (mukene) in selected parts of Lake Victoria, Uganda

This study was undertaken in Napoleon gulf, and part of the off shore area of Lake Victoria Uganda in the landing site of Lufu in Buvuma district in the month of October 2015 for three days of sampling. It was conducted in four landing sites; Busana, Kikondo from Buikwe district and Lufu landing site from Buvuma district. The main aim was to determine the effect of Lampara net on the catch rate and size of the Rastrineobola argentae (mukene) harvested on Lake Victoria using various mesh sizes. The study focused on the 5mm and 10 mm mesh sizes of the Lampara net. A total of 109 boats were sampled; from the 5 mm mesh sizes indicated catch rates of 78-200 kg/boat/day and yet for 10 mm mesh size was at 248 kg/boat day. Statistical tests were carried out on the these two mesh sizes using One way Anova and indicated in catches was (Anova F=7.476; P<0.05) and for the price values was (Anova F=5.488 ; P<0.05). This is an indication that despite the fact that the mukene fishery is on the increase, a time will come when it also be depleted so a need to use the rightful fishing gear of 10mm mesh size is advisable for the biodiversity conservation.

The impact of exploitation, competition, and predation on the changing stocks of Lake Victoria

The dramatic decline in fish species diversity in Lake Victoria has been attributed to predation by Nile perch, Lates niloticus Linne, without sufficient justification. Exploitation, interspecific competition and hybridization had profound impact on the decline of the indigenous commercial fish species. The roles of exploitation, competition and hybridization, and of predation by the Nile perch on changes in species diversity have been discussed. Lates was largely responsible only for the decline of the haplochromine stocks.

Final report of the fisheries catch assessment survey conducted in December 2015 on the Ugandan waters of Lake Victoria

This CAS report provides estimates of the quantities of fish landed in the riparian districts sharing the Ugandan waters of Lake Victoria; the monetary value of the fish catches; the contribution of different fish species to the catches; and the trends in fish catch rates, and the monthly catches for the sampled month since the beginning of harmonized CAS activities in July 2005 to December 2015. The report also compares the annual catch and gross beach value of catch landings in 2005, 2006, 2007, 2010, 2014 and 2015. A total of 15 CASs have been undertaken in the Uganda sector of the lake with data gaps in 2009, 2012 and 2013 due to financial constraints. The annual catch estimates for the years 2010, 2011, 2014 and 2015 were based on one sampling covering the rainy season and may not capture changes that could occur in dry season. There is need to include dry season sampling in future surveys.

Some causes of unreliability of fishery statistics on the African great lakes and possible ways of bettering the statistics

This paper is based on a two year's intensive statistical data collection survey on Lake Kyoga, observations made on Lake Victoria over the last decade occasional visits on Lake Albert (Mobutu) and Lake Malawi. World over, scientists have kept doubting the fisheries statistical figures presented by various African countries. Some countries fail to present any figures. This paper, therefore, narrates most of the causes and possible solutions to those problems.

A report on the survey of Lakes Opeta and Bisina to further collect data on presence of Hydrilla verticilata and potential biological control agents

Reports of hydrilla (Hydrilla verticilata) infestation lakes Bisina and Opeta were verbally communicated by some members of FIRRI who undertook surveys during the LVEMP 1 phase (1997 to 2004) to assess the diversity and stocks of fishes in the Kyoga basin satellite lakes. This issue was taken up by FIRRI and NAARI staff who work on aquatic weeds management to ascertain and quantify the presence of H. verticilata and other aquatic weeds, with the sole aim of finding ways and means of controlling one of the world's worst aquatic weeds, H. verticilata.The survey on Lake Opeta indicated that this weed was rare since only a few small broken pieces were sited at the lake's outflow through an extensive wetland to Lake Bisina. It was therefore concluded that it was not economically viable to allocate resources for further survey of H. verticilata on Lake Opeta. This finding therefore discredited the previous (informal) reports that H. verticilata was well established on Lake Opeta. It should be noted that the reports came from scientists who were not well versed with systematics of aquatic plants.