Abstract
Freshwater and marine-spawned fishes were sampled from the Baakens River, a small urban river that runs through the city of Port Elizabeth in the Eastern Cape of South Africa. Using fyke nets, 8 sites were sampled along the river course over a 4-month period (January – April 2014). Catches were comprised of indigenous freshwater, marine migrant and alien fishes. Marine migrant fishes, including catadromous species dependent on freshwater for early life-history strategies, were significantly affected by instream barriers which prohibited upstream migration of all species except Anguilla mossambica. The freshwater fish fauna was dominated by Tilapia sparrmanii and Pseudocrenilabrus philander, species that are alien to the Baakens River. While indigenous Barbus pallidus and Sandelia capensis were both abundant and widely distributed in the river, only two Pseudobarbus afer were sampled from one survey site. The low abundance and narrow distribution of this endangered species is of concern and human-mediated impacts on this species require urgent evaluation and mitigation. Keywords : Baakens River, migration barrier, weir, alien fish, endangered fish
Highlights
South Africa is a water-stressed country and rivers and lakes are critical for providing freshwater for human use (Mukheibir and Sparks, 2003)
Human-mediated impacts on rivers in South Africa include habitat alteration, freshwater abstraction and the introduction of alien species which have been identified as primary contributors to the decline in native fish populations, in the Cape Fold ecoregion in South Africa where endemic species have limited distribution ranges (Darwall et al, 2009)
The primary aim of the current study was to determine the composition, abundance and distribution of fishes currently resident in the Baakens River and to determine the extent of migration restriction by instream barriers for marine-spawned fishes
Summary
South Africa is a water-stressed country and rivers and lakes are critical for providing freshwater for human use (Mukheibir and Sparks, 2003). Freshwater fishes are entirely dependent on these habitats for their existence and survival and their dependence renders them extremely vulnerable to anthropogenic influence in the form of habitat alteration, degradation of water quality and barriers (Skelton et al, 1995). The fragmentation of river systems has been suggested as the primary factor leading to the decline in migratory fish populations (Masters et al, 2006). Human-mediated impacts on rivers in South Africa include habitat alteration, freshwater abstraction and the introduction of alien species which have been identified as primary contributors to the decline in native fish populations, in the Cape Fold ecoregion in South Africa where endemic species have limited distribution ranges (Darwall et al, 2009). Urban rivers are vulnerable to this suite of anthropogenically-induced threats
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