| dc.description.abstract | Globally, riverine fishes are important in supplementing lacustrine fish production. In Uganda, Upper Victoria Nile (UVN) is considered as a critical habitat to fish species reproduction, feeding, shelter and as source of food to the community. Yet information on population dynamics of resident fish species, biological integrity of riverine ecosystem, habitat quality is not known and catch rates of fish species in UVN are scanty. Further, information of the species Mormyrus kannume on growth patterns and exploitation is unknown. The main objective of the study was to determine habitat characteristics and population structure of the fishes of UVN. Specific objectives were: i) To characterise habitat quality in relation to physico-chemical parameters and fish community structure in UVN; ii) To determine the population dynamics of fish in UVN; iii) To determine trends in fishing effort and fish catches in UVN; and iv) To determine spatial and temporal abundance of bait fishery in UVN. The study covered twelve stations distributed between station 1 (ST1) to ST12. Out of twelve sampling stations, three were for catch assessment and effort data, while nine were for collection of fisheries, limnology, and ecosystem integrity datasets. Data were collected biannually from April 2014 to September 2019. Physico-chemical variables of water were measured using HacH HQ40d multi probe. Water samples were obtained in duplicate using 500mm borosilicate bottles prewashed with distilled water and nutrient analysis in laboratory was done following standard methods. Principle Component Analysis was used in water quality analysis. Nine-habitat metrics estimated habitat quality index (HQI). Fish biodiversity indices were estimated using occurrence and fish-based index of biotic integrity (FIBI) methods. Counts of exotic/indigenous and tolerant/intolerant species were recorded to generate species richness. Generated measurements were used to develop 12 metrics FIBI by summing up scores. Duplicate samples of fish were obtained using experimental gillnets of mesh sizes ranging from 25.4-203.2 mm. Fish Stock Assessment Tool (FISAT) and IBM SPSS Statistic Version 20 were used in data analysis of population structure. The study mainly focused on population structure, sexual maturity, food and feeding habits, growth parameters, growth performance indices, mortality rates, and yield per recruit.
Population dynamics characteristics of fish exhibited a lower size at sexual maturity (L50) for males and females. For example, L. niloticus, O. niloticus and M. kannume (L50) for males and females; 30.1 & 40.3 cm TL; 24.5 and 17.5 cm FL respectively. Fish community structure recorded5,202 fish specimens comprising 67 species belonging to 8 families. Species recorded, Lates niloticus13.82%, M. kannume 1.8%; Oreochromis niloticus0.54%,Bagrus docmac 0.41%and other including the haplochromines72%.Trophic guilds recorded omnivores (62.7%),carnivores (22.4%) and detrivores (14.9%). Mean HQI, (25.86-32.89), total fish catch and FIBI, (1.8-3.5) varied among stations that showed fair biodiversity that needed proper conservation measures of habitat type. The observed changes in annual changes were attributed to increased fishing effort along with gear changes from legal to illegal such as traps, nets below 5 inches based on Fishing rule (2010). The growth and morality parameters for commercial fishes such as L.niloticus,O.niloticus,M. kannume, O. variabilis recorded; length at infinity in centimetre total length and maximum age in years at 90.3, 8.1; 47.3,4.1 and 36.75;6.4 respectively. Total morality (Z) and exploitation rate (E) for same fish species were;Z=1.71 per year (yr-1), E=0.62; Z=2.80 yr-1, E=0.50; Z=1.74 yr-1, E=0.5 yr-1 respectively. That exhibited a decrease in population characteristics thus environmental stress. Annual fish production recorded> 70 percent low sized fishes that earned low market value. Estimated production showed high regeneration rates and often dynamic that needed regular monitoring to provide adequate information to inform management decisions. M. kannume recorded increase in annual catches and value of 40 tonnes (t) to 300 t in 2014 to 2019 respectively; though maturing at small sizes of male and females at 24.5 and 17.5 cm FL. That requires scientific attention on sustainability of the resources to avoid depletion and eventual collapse. | en_US |
