Slippery customers for conservation: Distribution and decline of anguillid eels in South Africa

Abstract

These catadromous fishes face multiple stressors, including habitat alteration and deterioration, barriers to migration, pollution and the adverse impacts of alien species, but knowledge of eel species occurrence, abundance and ecology in Africa remains poor.2. This study investigated the present and historical distribution of anguillid eels and the potential associated drivers of declines at the southern extremities of their ranges in South Africa. Data analysed included sampling conducted in KwaZulu-Natal and Eastern Cape between 2015 and 2020, and secondary data extracted from databases, museums and local management agencies.3. The median extent of inland penetration increased as follows: 22 km for A. bicolor, 29 km for A. marmorata, 94 km for A. bengalensis and 293 km for A. mossambica.

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

“…However, we stress that African eels are no longer abundant and that they are experiencing a dramatic decline in their range distribution in KwaZulu-Natal Province, South Africa (Pike et al, 2019). The abundance of the three eel species at Zingela was greater than at most other sites in KwaZulu-Natal Province, surveyed by similar means by the lead author during 2017-2019 (Hanzen, 2020). The relatively small sample size is a common issue when studying vertebrates of conservation concern, but telemetry does offer a powerful method of collecting a large amount of relevant ecological data per individual in such cases (Cooke et al, 2012).…”

“…The biology of most of these tropical eel species is poorly known, and most are probably undervalued ecologically and commercially. Tropical eel species may be at risk of endangerment if the present trends of habitat deterioration and fragmentation (Hanzen et al, 2019), and biological exploitation (Jacoby et al, 2015;Hanzen et al, 2019), continue.…”

“…Four eel species occur in the Western Indian Ocean Region; the African longfin eel Anguilla mossambica (Peters, 1852), the African mottled eel A. bengalensis (Gray, 1831), the shortfin eel A. bicolor McClelland, 1844 and the giant mottled eel A. marmorata Quoy & Gaimard, 1824 (Skelton, 2001;Hanzen et al, 2019). African river systems are increasingly threatened by anthropogenic habitat degradation, pollution, damming and water diversion (Mantel et al, 2017;O'Brien et al, 2019).…”

“…Of particular concern is the case of the African endemic A. mossambica, the conservation status of which was recently changed from "Least concern" to "Near threatened", partly because of the worrying decline in range distribution in KwaZulu-Natal, South Africa (Pike et al, 2019). Information is urgently needed on these species' habitat use and behaviour, including the extent to which they may share habitats, to develop sustainable water management practices and conserve remaining eel populations (Hanzen et al, 2019).…”

“…In riverine environments, the four tropical African eel species exhibit a degree of longitudinal zonation at the catchment scale, with A. mossambica being the most ubiquitous species found throughout catchments (Hanzen et al, 2019). Differences in longitudinal distribution translate into putative differences in habitat use for the four species, with A. bicolor usually found in coastal swamps, the lower reaches of rivers and coastal lakes, while the other species occur in all available riverine habitats (Jubb, 1961).…”