Slippery customers for conservation: Freshwater eels (Anguilla spp.) range distribution, decline and associated drivers in South Africa

Abstract

Freshwater eels are important ecological and socio-economical components of the aquatic ecosystems in which they occur. The level of understanding regarding their occurrence, abundance, diversity and ecology in Africa remains relatively poor. Four freshwater eel (Anguilla)species occur in South Africa: Anguilla mossambica, A. bengalensis,A. marmorataand A. bicolor. These catadromous migratory fishes face multiple stressors, including habitat alteration and deterioration, barriers to migration, pollution, and adverse impacts by alien species. We investigated their present and historical distributions and associated drivers of declines in South Africa, particularly in KwaZulu-Natal and Eastern Cape Provinces. Over 1000 geographic location data points were collected in South Africa since the end of the 19^thcentury from historical records and our sampling. We also evaluated the altitudinal and longitudinal distribution of Anguillaspp. across catchments in South Africa.Extent of Occurrence (EOO) analyses, following the guidelines of IUCN red list assessment, were carried out at the regional level in KwaZulu-Natal. Our extensive sampling over the last 4 years showed significant declines in the EOOs of the four eel species in KwaZulu-Natal, ranging between 31% and 48% in the last 30 years and between 35% and 82% since the 1950s.We highlight the effects of altered catchment morphology, ecological connectivity impairment, habitat characteristics and water quality on Anguilla spp.  abundance and distribution across South Africa. Conservation action is an urgent requirement to mitigate against the further decline of the four Anguilla spp.in South Africa.