Life-stage and environmental influences on the recruitment of African freshwater eels into the uThukela River, South Africa.

Anguillid eel recruitment into east-flowing rivers along the east coast of Africa is poorly understood. The few harvest records of anguillid eels from South Africa have highlighted anthropogenically derived environmental stressors as risks for further decline. Our study aimed to determine environmental conditions and elver development associated with eel recruitment in the uThukela River, KwaZulu-Natal, South Africa. Our study was conducted between November 2021 and September 2022 and compared the effect of high- and low-flow conditions and the associated environmental variables on eel recruitment. We captured 519 eels and identified 220 (42%) which were classified into three species (Anguilla bengalensis n = 51, Anguilla marmorata n = 60 and Anguilla mossambica n = 120). We captured glass eels (n = 461) and elvers (n = 36), and included transitioning individuals (n = 22) between the stages. All eels were caught in high-water-flow conditions, which supports the hypothesis that eels prefer high water flow for recruitment, which usually occurs in rainy, warm austral summer months. We found a significant difference between the body lengths of the three identified species. We found a significant difference between the life stages present, which was primarily between glass eel and elver, with the transitional phase grouping in body length relative to glass eel body length. Our results highlighted the need to improve field identification of glass eels. In addition, an in-depth understanding of the recruitment trends for African freshwater eels in east-flowing rivers is needed.