Uilkraals Situation Assessment - Anchor Environmental

3.6 FishEstuaries provide an extremely important habitat for fish in southern Africa. The vast majorityof coastal habitat in southern Africa is directly exposed to the open ocean, and as such issubject to intensive wave action throughout the year (Field & Griffiths 1991). Estuaries insouthern Africa are thus disproportionately important relative to other parts of the world, inthat they constitute the bulk of the sheltered, shallow water inshore habitat in the region.Juveniles of many marine fish species in southern Africa have adapted to take advantage ofthis situation, and have developed the necessary adaptations to enable them to persist inestuaries for at least part of their life cycles. There are at least 100 species that show a clearassociation with estuaries in South Africa (Whitfield 1998). Most of these are juveniles ofmarine species that enter estuaries as juveniles, remain there for a year or more beforereturning to the marine environment as adults or sub‐adults where they spawn, completingthe cycles. Several other species also use estuaries in southern Africa, including some that areable to complete their entire life cycles in these systems, and a range of salt tolerantfreshwater species and euryhaline marine species. Whitfield (1994) has developed a detailedclassification system of estuary associated fishes in southern Africa. He recognized five majorcategories of estuary associated fish species and several subcategories (Table 1).Table 1. Classification of South African fish fauna according to their dependence on estuaries (Whitfield1994)CategoryIIaIbIIIIaIIbIIcIIIIVVDescriptionTruly estuarine species, which breed in southern African estuaries; subdivided as follows:Resident species which have not been recorded breeding in the freshwater or marineenvironmentResident species which have marine or freshwater breeding populationsEuryhaline marine species which usually breed at sea with the juveniles showing varyingdegrees of dependence on southern African estuaries; subdivided as follows:Juveniles dependant of estuaries as nursery areasJuveniles occur mainly in estuaries, but are also found at seaJuveniles occur in estuaries but are more abundant at seaMarine species which occur in estuaries in small numbers but are not dependant onthese systemsEuryhaline freshwater species that can penetrate estuaries depending on salinitytolerance. Includes some species which may breed in both freshwater and estuarinesystemsObligate catadromous species which use estuaries as transit routes between the marineand freshwater environmentsFish species in categories I, II, and V as defined by Whitfield (1994) are all wholly or largelydependent on estuaries for their survival and are hence the most important from an estuaryconservation perspective. These species need to receive most attention from a managementperspective.Uilkraals Estuary Situation Assessment26Anchor Environmental