College of Agriculture, Engineering
and Science (CAES)

Water Wheel Feature Dives into Spatial Ecology of Freshwater Eels in South Africa

Postdoctoral researcher in the School of Life Sciences Dr Céline Hanzen’s work on the diversity, distribution and spatial ecology of freshwater eels in South Africa and the implications for their conservation was featured in the November/December edition of the Water Research Commission’s Water Wheel magazine.

Working in the Centre for Functional Biodiversity, Hanzen focuses on the spatial ecology of African freshwater eels and their associated fisheries. This is part of a multi-country project funded by the Western Indian Ocean Marine Science Association. She is also the recipient of a postdoctoral fellowship from the Oppenheimer Memorial Trust, and is one of 100 female scientists participating in the global Homeward Bound initiative promoting female leadership in Science, Technology, Engineering, Mathematics and Medicine.

With more than a decade’s experience in terrestrial and aquatic ecology and conservation, Hanzen’s work has taken her across Europe and Africa where she is now contributing to the implementation of projects relating to fish migration and river connectivity. With colleagues, she has contributed to research that resulted in the downgrading of the conservation status of the African Longfin Eel.

In the magazine feature, Hanzen noted that there is a dearth of knowledge on freshwater eels – a migratory species affected by changing land use and altered or interrupted water courses – and highlighted that eel species are declining rapidly.

Research by Hanzen on this topic was published in the Hydrobiologia journal. She and her co-authors were the first to measure the home range and quantify the habitat use of freshwater eels in African freshwater habitats. This work also featured in Hanzen’s PhD research.

She focused on four eel species in the Thukela River, part of KwaZulu-Natal’s largest water catchment.

Hanzen recounted the effort of capturing the slippery Anguillids to weigh, measure, photograph and tag them before re-release. By clipping a small part of their fins, the researchers were able to barcode the creatures’ DNA to provide information about the species, particularly those being harvested and traded.

Hanzen and her colleagues tracked the eels’ movement for almost a year, using the data to analyse their home range, spatial overlap and habitat preferences. Unexpected results included seasonal changes in home range, core area and habitat use, with small home ranges in winter and a lack of territoriality.

The changes in habitat preferences across seasons and between species call for river management that considers the varying habitat requirements of threatened eel species throughout the year; however, this is a challenge in South Africa’s water-stressed river systems.

Freshwater eels in Africa have long, complex lifespans, utilising different aquatic environments throughout their lives, spawning in the ocean then making their way to riverine systems before returning to the ocean at the end of their lives to breed. They are difficult to separate into different species based on their form and structure, making the development of targeted conservation strategies challenging.

Hanzen said the eels’ long-distance migration and widespread distribution make them useful indicators of the health of ecosystems, but more action is required to conserve them in the face of habitat loss and fragmentation, pollution, overexploitation, environmental and climate change, diseases and parasites and barriers to their migration.

Significant declines in recent years, coupled with increased export of the species from Africa, mean that more data that catalogues Anguillids’ contributions to sustainable ecosystems is needed to promote their sustainable use and conservation, as well as better informed river connectivity and fish migration management practices.

Words: Christine Cuénod

Photograph: Supplied