The value of Nabugabo lakes in the conservation of Oreochromis esculentus

The wide-spread impact of exotic fishes especially Oreochromis niloticus and Lates niloticus together with over fishing in the Victoria and Kyoga lake basins during the 1950s and 1960s, caused endemic species such as the previously most important Oreochromis esculentus to become virtually extinct in the two lakes by the 1970s. Based on reports of presence of this native species in some satellite lakes within the two lake basins, a set of satellite lakes in the Victoria basin (Nabugabo lakes: Kayanja and Kayugi), were sampled between 1997-2002 with an objective of assessing their value as conservation sites for O. esculentus. Other satellite lakes (Mburo and Kachera) also in the Victoria basin, and Lemwa, Kawi and Nabisojjo, in the Kyoga basin, were sampled for comparison. Among the Nabugabo lakes, O. esculentus was more abundant in Lake Kayanja (20.1 %) ofthe total fish catch by weight compared to Lake Kayugi (1.4 %). The largest fish examined (38.7 cm TL) was caught in Lake Kayugi, (also the largest in all satellite lakes sampled), while the smallest (6.6 cm TL) was from Lake Kayanja. Fish from Lake Kayugi had a higher condition factor K (1.89± 0.02) than that from Lake Kayanja (1.53±0.0I), which was the second highest (compared with other satellite lakes) to Lake Kawi (1.92±0.2). Diatoms, especially Aulacoseira, which were previously known to be the best food for O. esculentus in Lake Victoria were mostly encountered (93.2 %) in fish stomachs from Lake Kayugi. In Lake Kayanja the dominant food item was the blue green algae (Planktolyngbya) while Microcystis was the most abundant diet item in fish from other satellite lakes. There were more male than female fish (ratio 1:0.91 and 1: 0.79 in lakes Kayugi and Kayanja respectively). This is comparable to the situation in Lake Victoria before the species got depleted. The highest mean fecundity was (771±218 eggs) recorded in Lake Kayugi compared to Lake Kayanja (399±143). Based on the results from Lake Kayugi, where diatoms dominated the diet of O. esculentus and where the largest, most fecund and healthy fish were found, this lake would be a most valuable site for the conservation of O. esculentus and the best source of fish, for restocking and for captive-propagation. This lake is therefore recommended for protection from over exploitation and misuse.

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.

Aspects of the fishery and biology of the African catfish Clarias gariepinus (Burchell, 1822) amidst environmental changes in Lake Wamala (Uganda)

Environmental changes are some of the factors that affect fisheries and biological characteristics of fishes. The African catfish Clarias gariepinus (Burchell, 1822) has biological characteristics that enable it to persist under various stressful environmental conditions. However, few studies have examined how the African catfish responds to conditions created by a changing climate. The study examined some of the fishery and biological characteristics of African catfish in Lake Wamala (Uganda) to provide an understanding of their response to changing climatic conditions using data for the period 1950 - 2013. Temperature around the lake increased by 0.02ºC/year since 1980, commensurate with the regional trend, while rainfall was above average since 1996, except in 2004 and 2008. Lake depth was strongly positively correlated with rainfall (r =0.83, n= 6, p<0.05) up to 2000, after which, lake depth decreased amidst increase in rainfall. The contribution of African catfish increased from 20% to 85% and 17% to 78% respectively to commercial and experimental catches respectively between 1975 and 2013 despite the decrease in lake depth. The modal total length, condition factor, food, and fecundity did not change. Only size at first maturity decreased from 37.5 to 30 cm TL in females and 39.5 to 34.2 cm TL in males between 1999/2000 and 2012/2013. The biological characteristics of the African catfish were comparable with those of the same species in other lakes and remained relatively stable. The results suggested that the African catfish has the capacity to persist and/or adjust appropriately under conditions created by climate variability and change, and if properly managed, can sustain the fisheries of Lake Wamala.

Etude de la chaine de commercialisation du poisson: Lac Ntomba, section du fleuve Congo (Ngombe) et marchés de Mbandaka et Kinshasa

Cette étude a été réalisée par le WorldFish Center dans le cadre de sa collaboration avec le WWF et le projet CARPE de l’USAID. La chaîne de commercialisation du poisson a été suivie des zones de production jusqu’au principal marché final. La région au centre de cette étude est le lac Ntomba ainsi qu’une partie du fleuve Congo. Ceci correspond à la partie nord de la section du Paysage Lac Télé - Lac Tumba de la République Démocratique du Congo. Toutes les étapes de la chaîne de commercialisation du poisson ont été prises en compte dans cette étude. Les stratégies des acteurs présents à chaque étape ainsi que les dynamiques les associant à la chaîne ont été utilisées pour refléter le fonctionnement de la chaîne de commercialisation du poisson et identifier ses spécificités. La pêche est une activité saisonnière de grande importance dans la région du lac Ntomba et la partie proche du fleuve Congo. La majorité des habitants de la région constituent leurs moyens d’existence d’un panachage d’activités, dont la séquence semble être rythmée essentiellement par l’opportunité et le climat. Presque aucun service n’est offert dans cette région où les activités économiques sont réduites et n’ont le plus souvent qu’une faible productivité. Cependant, la chaîne de commercialisation du poisson supporte un large éventail d’acteurs différents et représente un secteur d’une grande importance pour la région. Cette région périphérique est reliée au reste de l’économie nationale par une série de marchés et de nombreux différents types d’acteurs. Assurer ce lien représente de sérieuses difficultés et comporte des risques importants tandis que les marges de profits sont le plus souvent minces. Cependant, il semblerait que, de manière générale, le marché se développe et les liens se renforcent, même si cette évolution est plus discrète dans les lieux les plus isolés.