The ecology and relative abundance of clarias species in relation to land use change in the M Mpologoma riverine wetland, Uganda

Abstract

Land use change influences wetland’s services through effects on structure, physicochemical environment and the biota. This consequently affects the ecology and relative abundance of individuals or populations of certain fish species. This calls for concerted efforts to understand the wetlands’ response to land use change impacts if a sustainable balance between demand and wetland resources is to be achieved. The ecology and relative abundance of the endemic small Clarias species in relation to land use change were examined at selected sites in the Mpologoma riverine wetland. The main objective of the study was to investigate the small Clarias species’ life history biometrics, movement patterns, wetland fishery production and its socio economics at different sites in relation to land use. Four sites exposed to different disturbance levels ranging from intact wetland, least disturbed, moderately and highly disturbed were identified. Selected physico-chemical parameters were determined to differentiate the sites further. Field sampling for fish habitat attributes, wetland fish biometrics and catch, and a socioeconomic survey were done in 2012. Land use, water quality and fish catch models were used to predict land use and the fishery production change with time. Water conductivity was significantly higher at the highly disturbed site than less disturbed sites (one way ANOVA and Tukey’s HSD test; p < 0.05). The total phosphorus content was higher at the least disturbed sites. Two small Clarias species were identified. Mean total length and weight of Clarias liocephalus (Boulenger 1902), the most abundant species (66%), were 16.81 ± 4.03 cm and 33.77 ± 19.63 g, respectively, whilst those for Clarias alluaudi (Boulenger, 1906) (34%) were 17.83 ± 4.49 cm and 39.94 ± 22.99 g, respectively. The total length, weight and fecundity of both species were significantly higher at the highly disturbed sites than at the least disturbed sites (between the weight of C. alluaudi at less disturbed and highly disturbed sites with ANOVA and Tukey’s HSD test at p = 0.003, and between weight of C. liocephalus at less disturbed and highly disturbed sites at p = 0.013). The fish weight positively correlated with conductivity (R2 = 0.22; p = 0.001) and negatively related to total phosphorus (R2 = -0.357; p = 0.001). The female individuals of the both species matured faster at the highly disturbed Nsango site than at the less disturbed sites. The small Clarias fish associated more with habitats of 0.5 m depth and their prey items were dominated by chironomid larvae at the highly disturbed sites and adult insects at the less disturbed sites. Their movement pattern did not significantly vary with sites but moved downstream in dry season. The small scale wetland fishery was dominated by Clarias gariepinus (Burchell, 1815) and Protopterus aethiopicus (Heckel, 1851) with higher catch at the less disturbed sites than at highly disturbed sites, accounting for 91.5% of total wetland fish production. As the wetland cover was changing to other land uses, an increasing trend of catch per unit effort of the small clariids was predicted at the highly disturbed sites with subsequent increase from 516 to 1114 g/trap/night. The findings were mainly attributed to habitat disturbance that provided population-level benefits and pollution tolerance of the small Clarias species. Wetland disturbance negatively impacted the large wetland fish species ecology given the observed significant decline in the weight of C. gariepinus and P. aethiopicus at the highly disturbed site (ANOVA and Tukey’s test; p < 0.05). Clarias fishery resource was important to the livelihoods of the riparian communities as major bait for the large wetland fish species and a cheap fish source, contributing to poverty allievation in the area. However, Mpologoma riverine wetland was undervalued by policy makers, there was no management strategy associated to it. The information generated illustrated that there is need to formulate appropriate wetland specific and small scale fisheries management strategies for the Mpologoma riverine wetland in order to maintain its relevance to riparian community and the region at large.