Fishes and salinities in the St Lucia estuarine system—a review

• Published in: Reviews in fish biology and fisheries Vol. 16; no. 1; pp. 1 - 20
• Main Authors: Whitfield, Alan K, Taylor, Ricky H, Fox, Caroline, Cyrus, Digby P
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01-02-2006
• Subjects: Aquatic plants; Brackish; Detritus; Estuaries; Fish; Food resources; Freshwater fish; High temperature; Lakes; Marine fish; Oreochromis mossambicus; Salinity; Surface area; Taxa; Water temperature; World Heritage Areas; Zoobenthos; ISW, Mozambique; ASW, Lesser Antilles, St. Lucia
• ISSN: 0960-3166; 1573-5184
• DOI: 10.1007/s11160-006-0003-x

The recorded salinity ranges of freshwater, estuarine and marine fish species in Lake St Lucia, a Ramsar and World Heritage Site, are documented. The freshwater group is most diverse and abundant under oligohaline conditions, although the Mozambique tilapia (Oreochromis mossambicus) was common under all salinity regimes. Estuary resident species also favoured oligohaline conditions but, in contrast to the freshwater taxa, were well represented in salinities up to 40 [per thousand]. The marine group was most diverse and abundant within the salinity range 10-40 [per thousand], but a large number of species could also be found in salinities up to 70 [per thousand]. Very few fish species were able to tolerate salinities between 70 [per thousand] and 110 [per thousand], with only O. mossambicus surviving for extended periods in salinities above 110 [per thousand]. All the aquatic macrophytes and most of the zoobenthos within the lake appear to die out within the salinity range of 50-60 [per thousand], thus creating additional stress to those fish present under such conditions. The food resources least affected by extreme hypersalinity are the microphytobenthos and detritus food chains, with detritivorous fishes being dominant when the lake is in this state. Mass mortalities of fishes in Lake St Lucia have been recorded under both low (<5 [per thousand]) and high salinity (>70 [per thousand]) conditions. The fish kills are often triggered by exceptionally low or high water temperatures which affect the osmoregulatory abilities of these species. Hypersaline conditions and fish mortalities under the most recent closed estuary mouth conditions (2002-2005) are reviewed. If the surface area of St Lucia (35,000 ha) is compared to the total surface area of all South African estuaries (approximately 70,000 ha), then the possibility exists that the loss of the Lake St Lucia nursery area for estuary-associated marine fish species over the past few years may cause significant short-term declines in the future abundance of these taxa on both a local and regional scale.[PUBLICATION ABSTRACT]