Ichthyofaunal Community of the Anthropogenically Altered Seekoei Estuary in Warm Temperate, South Africa

• Published in: Estuaries and coasts 2023-12, Vol.46 (8), p.2159-2174
• Main Authors: Mpinga, Mfundo S., Kisten, Yanasivan, Bornman, Eugin, Perissinotto, Renzo, Strydom, Nadine A.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Brackishwater environment; Catch per unit effort; Causeway; Causeways; Coastal Sciences; Earth and Environmental Science; Ecological function; Ecology; Environment; Environmental Management; Estuaries; Estuarine dynamics; Fish; Fish conservation; Fish migration; Freshwater; Freshwater & Marine Ecology; Human influences; Impoundments; Inflow; Inland water environment; Marine fishes; Mass mortality; Migrations; Seine nets; Special Issue: Low Inflow Estuaries; Species richness; Water and Health; Water inflow
• ISSN: 1559-2723; 1559-2731
• DOI: 10.1007/s12237-022-01150-1

The temporarily open-closed (TOCE) Seekoei Estuary, on the warm temperate coast of South Africa, has been subject to various anthropogenic modifications such as impoundments, water abstraction, causeway construction, and artificial breaches that have impacted its estuarine functioning. To determine the impact of these combined factors on the fish community, the Seekoei Estuary was sampled twice per season over 2 years, which included a hypersaline phase. A total of 92,026 fishes, comprising 12 families and 25 species, were caught from five different habitat types using a 30 m × 1.7 m seine net (10-mm mesh aperture). The catches were dominated by the exclusively estuarine species Gilchristella aestuaria (81.0%) (Clupeidae), followed by the estuarine and marine Atherina breviceps (11.4%) (Atherinidae) and the marine estuarine-dependent Rhabdosargus holubi (5.1%) (Sparidae). Fish catch-per-unit effort (CPUE) were similar among seasons and sites; however, species richness was highest ( d  = 1.24) at the site directly below an obstructing causeway hindering fish migration. Additionally, reoccurring hypersaline conditions due to low freshwater inflow and artificial breaching have resulted in frequent fish kills of mainly marine origin species, creating an anthropogenically mediated ecological trap. The current anthropogenic alterations require amelioration for the conservation of the fish and the ecological functioning of this estuary. Rehabilitation to restore functioning is important for estuaries globally, especially estuaries with low inflow.