Stock assessment of Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin) using fishery dependent data from the Tanzanian waters of Lake Victoria

Catch data were collected from three beaches in the Mwanza area of lake Victoria, Tanzania for Oreochromis niloticus (L.), Rastrineobola argentea (Pellegrin) and Lates niloticus (L.). Sampling took place in October 1997 and February, June and September 1998. The CPUE for O. niloticus was 3.9 to 6kg boat super(-1) and for R. argentea from 98 to 282 kg boat super(-1). There was no obvious trend in catch rates for L. niloticus. The modal length for O. niloticus recorded at Chole beach was 34cm TL. In February, fish were larger (41-45 cm) than in the other surveys. Rastrineobola argentea caught in October 1997 had modal length at 65 mm TL with some smaller fish. In February and June prominent length modes occurred at 45 and 58 mm respectively, which may represent the same cohort as the small fish caught in October 1997. In September 1998, there were two length modes at 46 and 60 mm. The 60 mm fish may represent the same cohort seen in previous surveys, suggesting growth from approximately 30 mm to 60 mm in an eleven-month period. Lates niloticus landed at Kayenze beach over the four surveys had a modal length of 46 cm TL. Fish species encountered on the three beaches during the surveys were O. niloticus, R. argentea, Bagrus docmak Forsskall, Clarias gariepinus (Burchell), Protopterus aethiopicus Heckel, Labeo victorians Boulenger, Synodontis afrofischeri Hilgendorf, Synodontis victoriae Boulanger, Schilbe intermedius (L.), Brycinus jacksonii (Boulanger), Mormyrus kannume Forsskall and Haplochromine cichlids

Results of the first hydroacoustic survey of the Ugandan waters of Lake Victoria

A lakewide hydroacoustic research programme was designed in the Ugandan waters of Lake Victoria in order to ascertain the status of fish stocks. Data obtained from the hydroacoustic surveys were complemented with by catch data from multi mesh gillnets and frame trawls to validate acoustic estimates. Fish were distributed over the whole survey area, though the densities and species composition varied from place to place. Echo traces showed the fish formed schools during daytime and became more dispersed towards evening. Approximately equivalent indices of abundance were estimated for Rastrineobola argentea and Haplocromines. The distribution of the freshwater prawn, Caridina nilotica and the lakefly Chaoborus sp. was patchy. Dense swarms of Chaoborus larvae were observed to disperse from the lake bottom as the night approached thus assuring echo-traces formed by fish on the echogram and making their interpretation difficult. Caridina nilotica were observed to form dense echo-traces at the thermocline

Forage strategy of juvenile Lates niloticus (L.) in Lake Victoria, Kenya

Six KMFRI stations located in Nyanza Gulf of Lake Victoria (Kenya) were sampled in order to investigate the forage strategy of juvenile Lates niloticus. Thirty speciemens were collected using a bottom trawl at each station and sorted into three size classes 1-2 cm and 3-20 cm total length. Stomach contents were analysed and taxonomic keys used to identify zoplankton and other insects. Caridina nilotica was the dominant food item in both frequency of occurrence and numerical abundance. In fish examined from 1-2 cm T.L., cladocerans were prominent food items, while at 2-3 and 3-20 cm, C. nilotica was dominant

Zooplankton-fish interactions in the littoral zone of Nyanza Gulf, Lake Victoria

Samples of zooplankton and fish were collected from six sampling points in Nyanza Gulf, Lake Victoria in Kenya from June to December 1998, using 76 mu m memo-filament mesh size strainer and an 80 mu m mesh size plankton net. Identification and enumeration were done in the laboratory. Occurrence, numerical and points methods were used in stomach anlaysis of fish. Copepoda, Rotifera and Cladocera were the major zooplankton groups identified, zooplankton such as Moina, Daphnia and Caridina nilotica were important prey items for Lates niloticus, Oreochromis niloticus and Rastrineobola argentea

Reproductive biology of Orechromis niloticus (L.) (Pisces: Cichlidae) in the Nyanza Gulf of Lake Victoria

Fish samples were collected using seine and trawl nets in Nyanza Gulf, Lake Victoria (Kenya) in order to study the reproductive and gonadal patterns of Oreochromis niloticus; samples were collected from June 1998 to February 1999. The variation in relative condition factor and monthly variation in gonad weight showed spawning took place between June and July. Most ripe fish were recovered between November and February, while a slight drop in GSI for males was noted between November and January. External factors triggering reproductive strategy are now being addressed

Feeding ecology and population characteristics of Oreochromis niloticus (L.) and trophic interactions in the fish community of Nyanza Gulf, Lake Victoria, Kenya

Oreochromis niloticus (L.) were caught by beach seining, hook and line and trawling from Nyanza Gulf, lake Victoria (Kenya) in order to study their feeding ecology and population characteristics. Collected fish were weighed and TL measured immediately after capture. Fish were dissected and sexed. Stomach contents were removed and preserved in 4% buffered formalin for laboratory analysis. In the laboratory items were sorted into categories such as three quarters, half and quarter and awarded 20, 15 and 5 points respectively. Main food items for O. niloticus from November 1998 to March 1999 were insects, algae, fish and plant material. Increase in insects in the diet of O. niloticus might be attributed to the lake infestation by water hyacinth which harbours different species of insects

Recent trends in the distribution patterns and catch rates from trawl surveys in Lake Victoria, Tanzania

Trawl surveys to assess the stocks of Lake Victoria (Tanzania) 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 Tanzanian waters were undertaken with 133 sampling stations. Data on each rates, species composition, and distribution were collected. Three sampling areas were designated: area A, B and C. In each area, almost the same distribution pattern over depth was found. Lates niloticus (L) formed over 90% of the total catch. Most L. niloticus were from 5-40 cm TL. Abundance decreased with depth, few fish were found deeper than 40m and most fish were caught at <20 m deep. Catch rates varied considerably between stations and areas. Area A had the highest catch rates with little variation over the stations. There is an indication of recovery of species diversity compared with the surveys of RV Kiboko(1985 and 1989)

The fish stocks of Lake Victoria, Uganda

An experimental bottom trawl survey was carried out in the Uganda sector of Lake Victoria from November 1997 to December 1998 to estimate the composition, distribution, and abundance of the major fish species. In 12 cruises, 295, thirty-minute hauls were taken in waters from 4-60 m deep. Nile perch, Lates niloticus (L) made up 95% of the catch by weight. Haplochromine cichlids and L. niloticus occurred in all areas sampled while Nile tilapia, Oreochromis niloticus (L.) and other tilapiines were restricted to waters less than 30 m deep. In waters deeper than 40 m, catches were generally near zero. Species diversity and abundance decreased with increasing water depth. In waters less than 30 m deep, the area where the artisanal fishermen operate, the mean catch was 126kg hr super(1)

Media of communication among fishermen around Kainji Lake basin

The findings are presented of a study conducted in the framework of the Nigerian-German Kainji Lake Fisheries Promotion Project to examine the role and structure of communication in fishing villages around Kainji Lake in Nigeria. The major aim was to be able to utilize the knowledge at a later stage in the project cycle to pass on fisheries extension messages to fishing communities. The study had the following terms of reference: 1) describe the structure and processes of communication of fishermen around Kainji Lake; 2) identify the formal and informal media of communication used by the fishermen to communicate information concerning their job; 3) describe the problems inhibiting usage of the different media identified; 4) ascertain the extent of use of mass media by fishermen around the lake; and, 5) identify acceptable ways by which fisheries information can be repackaged for the use of extension workers. (PDF contains 58 pages)

Nutritional habits and food consumption pattern of fishing communities around Lake Kainji, Nigeria

The findings are presented of a nutrition survey carried out in the framework of the Nigerian-German Kainji Lake Fisheries Promotion Project in March/April 1995. The major aim of the study was to obtain closer information on the food habits and food consumption patterns of the fishing population, especially the quantification of fish and small fish in particular, consumed at the household level. A standardized questionnaire was used to collect relevant information on demographic, education and occupational profiles; the information was collected in 39 villages in the southern sector of Kainji Lake. (PDF contains 75 pages)

The nutritional status of pre-school children, Kainji Lake communities, Nigeria: a baseline survey

This survey was carried out to provide the Kainji Lake Fisheries Promotion Project (KLFPP), whose overall goal is the improvement of the standard of living of fishing communities around Kainji Lake, Nigeria, and an increase in the availability of fish to consumers, with nutritional status baseline data for long-term monitoring and evaluation of the overall project goal. In a cross-sectional survey, baseline anthropometric data was collected from 768 children, aged 3-60 months in 389 fisherfolk households around the southern sector of Kainji Lake, Nigeria. In addition, data was collected on the nutritional status and fertility of the mothers, vaccination coverage of children and child survival indicators. For control purposes, 576 children and 292 mothers from non-fishing households around Kainji Lake were likewise covered by the survey. A standardised questionnaire was used to collect relevant information, while anthropometric measurements were made using appropriate equipment. Data compilation and analysis was carried out with DATAEASE registered and EPI-INFO registered software, using NCHS reference data for the analysis of anthropometric measurements. The prevalence of stunted children in fishing households was high at 40%, while the prevalence of wasted and underweight children was likewise high at 10% and 29% respectively. Children from non-fishing households had a marginally lower prevalence of stunting, wasting and underweight with 37%, 7% and 25 % respectively, although these differences were not statistically significant. Considering the fact that the survey was carried out during a period of relative food abundance, the prevalence of wasting and underweight children is likely to be much higher during periods of food shortage. The prevalence of stunting, wasting and underweight was relatively high for children aged 3 to 23 months, suggesting an increased risk of malnutrition during this period, most likely associated with inadequate weaning practices. The prevalence of malnourishment amongst women of child-bearing age was relatively high, irrespective of occupation of the household, with an average of 11% undernourished and 6% wasted. Vaccination coverage was very low while infant and child mortality were extremely high with about 1 in 5 children dying before their fifth birthday. Based on the ethical obligation to maximise the potential benefits of the survey, recommendations for activities to improve community nutrition and health were made for communication to relevant authorities. (PDF contains 52 pages)

Identification of non fishing income opportunities around Kainji Lake

The findings are presented of a study carried out in the Kainji Lake region of Nigeria in order to identify alternative income opportunities for the fisherfolk, so as to increase their acceptance of fishery management measures and also to reduce the harmful short-term economic effects that such management options can have. A description is given of the main non-fishing income earning activities in the Kainji Lake area and an assessment is made of the economic viability and expected acceptance of the identified income earning opportunities. (PDF contains 84 pages)

Post harvest losses in the fisheries of Kainji Lake

An assessment is given of the post-harvest losses in the Lake Kainji fisheries of Nigeria. The study focussed on quantifiable information on post-harvest technology and post-harvest losses from fisherfolk, fish processors and fish traders operating within the Kainji Lake basin. The information was obtained from questionnaires sent to a total of 665 respondents, comprising 317 fishermen, 115 fish processors, 125 fish buyers, and 111 fish sellers in 45 fishing villages and collection centres within the lake basin. Considering the total catch from gillnets, longlines, traps and cast nets estimated at 14,000 in 1995 about 1,000 t of fish was either discarded or lost value due to spoilage during handling by fisherfolk. Assuming an average prices of 80 Naira/kg of fish, the loss to the economy amounted to 80 million Naira annually. Appropriate recommendations are made to significantly reduce post-harvest losses in the Kainji Lake fishery. (PDF contains 91 pages)

Fishing gear survey of Kainji Lake, northern Nigeria, 1996

A survey was carried out in September 1996 alongside the annual frame survey of Kainji Lake, Nigeria. As in the previous surveys, there were 6 main fishing gear types in use on the lake, which included gill nets, drift nets, beach seines, cast nets, longlines (baited and foul hooking) acid fishing traps. A total of 813 canoes were sampled. The canoe lengths were similar to the previous gear surveys. Altogether 466 gill nets were measured. They had an average length of 149 m, and were mostly bottom set. Of the gill nets measured 68% had a mesh size below 3 inches the minimum mesh size allowable according to the Niger and Kebbi State Fisheries Edict, 1996. Of concern was the large increase in the number of 1 inch meshed nets recorded on the lake. Drift nets had a mean length of 74 m. A total of 88% of all drift nets measured had a mesh size below 2.5 inches, the minimum mesh size stipulated in the State Edict. A total number of 102 beach seines were sampled with a mean length of 110 m, the mesh size in use on the lake remained as 0.1 inches under the Edict beach seines are banned from fishing in Kainji Lake. The decline in the lengths of the beach seines (and therefore catch rates) recorded since l995 was encouraging in the light of the destructive nature of these nets. A total of 30 cast nets were sampled, they had a mean diameter of 9.8 and a mean mesh size of 1.9 inches. All the nets had a hanging ratio of 0.5. Of the cast nets measured 40% had a mesh size below the minimum size of 2 inches recommended by the State Fisheries Edicts. Of concern was the continued rise in the number of gill nets with mesh sizes less than 2 inches. There were 2 types of longlines in operation on the lake. The baited and the foul hooking longlines. They were mostly bottom set and the hook size nos. 12-14 (Kirby sea hook) were predominant. Two types of fishing traps were identified, one was covered with a mesh of thin cane, one with netting material. The fishing traps had a mean height of 0.8 m and a mean width at the vase of 0.53 m. The mean mesh size used was 0.86 inches. Citharinus was reported as the most targeted of all fish species on the lake. Synodontis membranaceous was also targeted by most gears especially the smaller meshed nets. Labeo and Tilapia were low on the list of targeted species but their incidence remains high in the catches. (PDF contains 27 pages)

Frame survey of Kainji Lake, northern Nigeria, 1996

Since 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gearSince 1993, annual frame surveys have been conducted by the Nigerian-German Kainji Lake Fisheries Promotion Project to determine the distribution and number of fishing localities, fishing canoes and fishing gears around Kainji Lake, Nigeria. The total number of fishing localities has increased from 221 in 1993 to 286 in 1996. The fishing localities included 245 permanent fishing villages, 29 permanent fishing camps, 8 temporary fishing camps (with fishermen from Kainji Lake) and 4 temporary fishing camps (with fishermen from outside Kainji Lake area). There was an increase in the total number of fishing entrepreneurs, fishing assistants and fishing canoes over the years. A total number of 5,499 fishing entrepreneurs, 12,449 fishing assistants and 9,278 fishing canoes were recorded during the 1996 frame survey. From 1995 there was a decrease in the number of shoreline fisherfolk and a decrease in the number of transport canoes, the number of engines remained the same. During the 1996 survey, a total number of 18,655 gill nets, 1,560 drift nets, 753 beach seines, 5,548 cast nets, 7,400 longlines and 36,979 traps were recorded. The concentration of the gears (number per km shoreline) was highest in substrata 06 and 08. The total number of gill nets increased from 17,680 in 1995 to 18,655 in 1996. For the remaining 5 gear types a decrease in number was observed. Despite increasing numbers of gears on the lake, of concern is the decline recorded in all the fishing methods of the number of gears owned by individual entrepreneurs. This was most notable in the gill net and longline fisheries. These two fisheries have the lowest daily catch values and coupled with the problem of gear theft on the lake, ownership in future, may be expected to fall further. The number of larger fishing units also declined as did the number of gears new entrants enter the fishery with. The decline is particularly worrying for the beach seine fishery where diversification into other fishing methods would be beneficial in light of the present ban on seines. The group of not active fishing entrepreneurs (those who do not themselves participate in fishing activities) had the highest ownership of gears whilst the new entrants into the fishery had the lowest. There was evidence that these new entrants into the fishery were using cast nets which is worrying given the trend of using smaller mesh size of this gear. (PDF contains 44 pages)