Anthropogenic Impacts on Distribution and Abundance of Mountain Catfish (Amphilias Uranoscopus, Pfeffer, 1889) and Other Fishes, in the Sagana and Thego Streams, Nyeri, Kenya
Odhiambo, Charles Oduor
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The clearance of forest for agriculture, settlement and grazing has had some of the most widespread human impacts on natural ecosystems globally. In Kenya large tracks of indigenous forests continue to be cleared to give way for human settlement and exotic tree plantations. The catchment on the slopes of Mt. Kenya has experienced such major losses that have affected the aquatic ecosystem. The objective of this study was therefore to document the extent of impact of anthropogenic activities on the distribution, abundance and population sizes of the mountain catfish (Amphilius uranoscopus Pfeffer, 1889) and other fish species along two second order tropical forested streams, Sagana and Thego on the slopes of Mt. Kenya. This study was done from June 2016 through May 2017. Fish samples were caught using an electrofisher and recorded for distribution, population sizes, reproductive strategies and feeding habits. Water samples for physiochemical parameters were determined in situ and a socio-economic survey of the riparian community carried out using a structured questionnaire. The smallest sized catfish were caught in November 2016 at the Thego station T2 midstream while the largest specimen electrofished was a I9.0 cm fork length (92.19 female caught in the downstream station (T3) of the Thego. There was a significant difference (t-test, t : - 3.35; p:0.007) in the mean number of catfish caught per hour of electrofishing between the Thego stations (T2 and T3). A comparison between Catch per unit effort (CPUE) in Sagana and Thego (ANOVA, F : 6.82; p : 0.004) showed a significant difference in catches between the two streams. Results from this study shows that there have been major significant changes in the distribution patterns of both the native species as well as the salmonid species in the two streams and that the mountain catfish has expanded its territory while the introduced salmonid species zones have shrank or become thin. Catfish exhibited a wider food base overlapping with those of the other species such as rainbow trout, brown trout and barbus. The occurrence of the mountain catfish (Amphilius uranoscopus), Barbus sp. and Labeo sp. inthe midstream of the Thego and downstream of the Sagana and Thego, the absence of rainbow trout in the midstream of the Thego and the restriction of the brown trout to the near pristine reaches of the Sagana at an altitude above 2150 metres are some of the changes that have occurred since 1960s due to the impact of human settlement in the watersheds of streams in the slopes of Mt. Kenya. Major factors associated with the variation in catfish distribution and abundance among the study stations included increased temperatures, elevated stream water conductivity and decline in water discharge. These clearly show that the catfish population is likely to move fuither upstream in Thego than in Sagana unless urgent measures to control human related anthropogenic activities in Thego catchment area are adopted. This study supports the hypothesis that the mountain catfish distributional range will continue to expand at the expense of other fish species unless corrective measures are considered to control anthropogenic human driven settlement activities in the watershed of the Sagana and Thego. Management strategies should focus on the values of the society and recognize that the continuous expansion of mountain catfish home range is an indicator of environmental perturbation arising from change in landuse and increase in human activities.