Assessment of the Ecological Health of Afrotropical Rivers Using Fish Assemblages: A Case Study of Selected Rivers in the Lake Victoria Basin, Kenya

Abstract

Streams and rivers are globally threatened ecosystems because of increasing levels of exploitation, habitat degradation and other anthropogenic pressures. In the Lake Victoria Basin (LVB) in East Africa, these threats are mostly caused by unsustainable land use; however, the monitoring of ecological integrity of river systems has been hampered by a lack of locally developed indices. This study assessed the health of four rivers (Nzoia, Nyando, Sondu–Miriu and Mara) on the Kenyan side of the LVB using physicochemical water quality parameters and a fish-based index of biotic integrity (IBI). Fish tolerance ranking was derived from principal component analysis of water quality parameters, and the concept of niche breadth (NB). The relationship between fish species and water quality parameters was examined with canonical correspondence analysis, whereas community metrics and stressors were evaluated through Pearson network correlation analysis. Fish species richness, trophic structures, taxonomic composition and species tolerance were used to generate the metrics for fish-based IBI. NB showed that most of the fish species were moderately tolerant to poor water. Moderately tolerant and intolerant fish species were negatively correlated with a high level of organic loading in the Mara River. Fish-based IBI scores for the rivers ranged from 26 to 34, with Sondu–Miriu scoring the lowest. Our results show that the cumulative effect of stressors can adequately rank fish species tolerance according to the disturbance gradients and further develop regional metrics to assess river health. Despite the fact that fish communities are declining, continual management and enforcement of environmental regulations are important, with conservation and management of headwaters and low-order streams being essential while they are still species rich.

Reproductive Biology of Ripon Barbel (Labeobarbus Altianalis) In River Kuja-Migori Basin, Kenya

“…On the other hand, the shorter period of breeding happening from October to December is due to shorter rains occurring later every year (Kizza et al, 2009). Whereas breeding for this species follows specific pattern, there are chances that this is affected by anthropogenic activities on the river catchments such as direct disposal of organic and inorganic wastes particularly from agriculture and other development activities (Achieng et al, 2021;Aura et al, 2020).…”

“…It is among fish species that can sustain commercial riverine fishery in the basin (Masese et al, 2020). In Kenya it's found in rivers Nzoia, Nyando, Yala, Sondu, Kuja-Migori and Mara among others (Achieng et al, 2021;Chemoiwa et al, 2017). Although, L. altianalis is considered a species of less concern, the indigenous stocks face a serious threat due to degradation of their habitats (Ondhoro et al, 2017;Chemoiwa et al, 2013).…”

“…Commercial fishery in major rivers in Kenya was once lucrative but has declined over time (Balirwa et al, 2003). The decline in commercial riverine fishery is attributable to pollution, degradation of fish habitats (Achieng et al, 2021), use of illegal gears which target egg laden females at the river mouths at the time of reproduction and introduction of alien species into Lake Victoria basin (Ogutu-Ohwayo, 1990). Most studies have focused on Lake Victoria fish communities but little has been done on riverine fish species.…”

Using the Biological Condition Gradient Model as a Bioassessment Framework to Support Rehabilitation and Restoration of the Upper Tana River Watershed in Kenya

“…The availability of this huge body of literature offers opportunities to strengthen the use of BCG, especially overcoming problems of determining undisturbed ecological conditions as well as the knowledge needed during pre-and post-status of ecosystems during rehabilitation programs. Only a few studies exist on fish bioassessment (Raburu and Masese, 2012;Achieng et al, 2021), and we recommend their continued promotion because they are sensitive to effects of poor agricultural practices and deforestation, which cause sedimentation and loss of habitat diversity and heterogeneity (Hocutt et al, 1994;Ganasan and Hughes, 1998;Toham and Teugels, 1999). Similarly, the use of diatoms in bioassessment of rivers is still at a nascent stage in Kenya (Ndiritu et al, 2006;Triest et al, 2012); however, findings of this study found them to be very reliable in assessing river conditions, especially the effects of climate on water quality.…”

Ecological River Health Assessment Using Multi-Metric Models in an Asian Temperate Region with Land Use/Land Cover as the Primary Factor Regulating Nutrients, Organic Matter, and Fish Composition

“…Rapid urban expansion and industrial developments worldwide, as well as intensive farming, have contributed to the deterioration of chemical water quality and alterations of physical habitats in rivers and streams [ 6 , 7 ]. Such modifications influence the aquatic biota composition and trophic interactions throughout the food chain, thereby damaging the overall river health and shifting the community structures of low- to high-level trophic biota [ 8 , 9 ]. Concomitant modifications are more intricate in riverine ecosystems, particularly in Asian temperate river systems that are primarily regulated by the seasonal monsoon [ 10 ].…”