CONTRIBUTION OF ANGUILLIDS TO FISH CONSERVATION VALUE AT TWO KENYAN EAST FLOWING RIVERS

Abstract

Global eel declines attributed to habitat fragmentation, pollution, and overexploitation have driven existing management, but the contribution of habitat conservation value remains poorly described. Habitat conservation values, incorporating fish diversity, migratory lifestyle, endemism, and IUCN status singly or in combination, have been reported. This study monitored eels and sympatric fish obtained using fyke nets from Athi and Ramisi rivers between April and October 2021. Fish occurrence and diversity data were combined with Likert scale scored published data on fish migration, IUCN status, endemism and used to derive composite conservation values, and compared. Results indicate higher fish diversity (1.15±0.23) at Athi than (0.92± 0.24) at Ramisi. Eel diversity was recorded higher in downstream locations; Sabaki (0.52±0.18), Taliani (0.28±0.28) with dissimilarity between eel and sympatric at Athi and Ramisi rivers (ANOSIM; P<0.05). Differences were attributed to occurrence of eels (78%) Anguilla bengalensis (55%), A. mossambica (23%), and sympatric taxa (37%); Oreochromis niloticus (20%) and Glossogobius giuris (17%). Higher eel biomass (1166±981g.d^-1) but lower density (0.79+0.38 ind. sampling^-1) occurred at Athi compared to Ramisi (1034±328g.d^-1) and higher density (3.15+1.09 ind. Sampling-¹), dominated by migratory A. bengalensis, especially at upstream locations. Higher IUCN ranking of fish at upstream of Athi (2.1±0.07), were attributed to the prevalence of critically endangered Oreochromis variabililis and threatened eels. The highest fish migration scores were recorded at Ramisi downstream location (3.5±0.06), due to prevalence of amphidromous species (45%). Additionally, downstream sites at Ramisi (1.9±0.1) and Athi (1.35±0.04) recorded the highest endemism scores, due to prevalence of endemic A. mossambica and O. spilurus. The highest composite conservation value was subsequently obtained for the downstream location of Athi (1.2±0.2), both sites at Ramisi had intermediate values (0.991±0.3; 0.901±0.12), while the lowest was recorded at upper Athi (0.87± 0.2). Thus, fish endemism, migratory fish, and eel prevalence are critical to the conservation status of Kenyan rivers.