Spatial ecology of freshwater eels in South Africa: implications for conservation

Four freshwater eel species (Anguilla spp.) occur in southern African rivers that are increasingly anthropogenically modified. Information on movements, habitat use and overlap by African eels is needed for their conservation. We carried out a preliminary investigation of the spatial ecology of three eel species in the Thukela River, South Africa, using radio-telemetry. Nineteen yellow-stage eels were surgically implanted with radio-tags, comprising A. mossambica (n = 2), A. bengalensis (n = 9) and A. marmorata (n = 8), and tracked from October 2018 to August 2019. Tagged eels exhibited high individual variability in space use. We recorded very small home ranges in winter for all species. A lack of apparent territoriality at inter- and intra-specific levels was observed. Eel species tended to use similar mesohabitats, especially glides, but habitat preference changed across seasons, and between species, suggesting fine-scale spatial and temporal niche partitioning. Given the breadth of flow typologies used by Thukela eels across the seasons, conservation of these long-lived species indicates that management of river flows needs to be sensitive to their habitat requirements all year round, but in many water-stressed South African rivers, this may be unlikely. Maintaining good habitat connectivity for these migrant species must be prioritised.