Uilkraals Situation Assessment - Anchor Environmental

Estuaries are typically shallow and sheltered habitats that provide a refuge from the action ofwaves that are characteristic of the South African coastline, making them ideal nurseryhabitats for juvenile fish species, many of which are of commercial importance (Wallace et al.1984). While estuaries are widely accepted as being among the most biologically productiveecosystems on earth (Kennish 2002), estuaries in the region where the Uilkraals is located arefed by oligotrophic (nutrient‐poor) rivers, and are thus not particularly productive.There are about 431 000 recreational fishers and well over 21 000 commercial fishers active inthe inshore marine environment in South Africa. Commercial net fisheries (beach seine and gillnet) on the south coast are likely to be the fisheries that benefit most from the UilkraalsEstuary. The commercial line fishery, recreational shore angling and recreational boat anglingfisheries could also benefit to a small extent.Nursery areas are breeding habitat for populations that reside elsewhere. Estuaries providenursery areas and habitat for numerous species of fishes which are exploited by recreationaland commercial harvesting in the inshore marine environment. Different species aredependent on estuaries to different degrees for stages of their development and growth.Freshwater flow and the frequency and duration of estuary mouth openings are major factorsaffecting estuarine biota (Turpie & Clark 2007), and particularly the juveniles of marineorganisms that use them as nursery grounds (Whitfield 1994, Strydom et al. 2003) eitherdirectly through habitat availability, or indirectly through their impact on estuarineproductivity (Gillanders & Kingsford 2002). Factors that make estuaries suitable nursery areasare increased food, higher temperature, turbid waters and lower salinities, all of which can bechanged by the variation in freshwater input (GiIlanders & Kingsford 2002, Turpie & Clark2007). The nursery function of the Uilkraals Estuary is considered to be relatively important, inthat some marine species caught in the surrounding marine fisheries are dependent onestuaries as nursery areas. With high macrophyte diversity and a large area of submergedmacrophytes within the estuary, nursery areas and refugia are important. However, thenursery areas may have been reduced or possibly eliminated as a result of the changes infunctioning and mouth dynamics brought about by the upstream dams.As per the ichthyological survey carried out in 2006, three of the species found within theUilkraals Estuary breed in the estuary, one species is completely dependent on the estuary forthe first year of its life and five species are partially dependent on the estuary. The nurseryvalue is derived from the amount of fish caught which fall under I, III and IV in terms of theirdependence on estuaries (Table 1). Of particular importance in calculating the value isCategory II species for which management of estuaries plays a crucial role in inshore fisheries.Turpie & Clark (2007) estimated the total nursery value of all the estuaries within South Africafrom the Orange River to Kosi Bay to be in the order of R773 million per annum, ranging fromR900 to R167 million per estuary. The majority of estuaries were estimated to have a nurseryvalue in the range of R100 000 to R10 million per annum. The Uilkraals Estuary theoreticallyfalls within this category (Turpie & Clark 2007), but it is unlikely that this value is realised nowdue to the closure of the estuary to the sea for such an extended period of time, and thereduction in freshwater flow.Uilkraals Estuary Situation Assessment37Anchor Environmental