Hostname: page-component-78c5997874-lj6df Total loading time: 0 Render date: 2024-11-05T08:01:04.608Z Has data issue: false hasContentIssue false
  • English
  • Français

Fishes and freshwater in southern African estuaries – A review

Published online by Cambridge University Press:  15 November 2005

Alan K. Whitfield
Alan K. Whitfield*
Affiliation:
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa
*
[email protected]
Get access

Abstract

The functioning of estuaries relies on a natural dynamism imposed on these systems by riverine and marine influences. The increasing abstraction of fresh water from both large and small river catchments in southern Africa has had the effect of forcing some estuaries into artificial cycles, i.e. natural successions now have human imposed trajectories that are changing estuarine variability and forcing some systems into extreme states. The ichthyofauna has responded to these changes in a variety of ways. Where river flow has declined considerably, or ceased altogether for extended periods, fish recruitment has shown a considerable decrease. This can be related to the collapse in planktonic productivity which negatively affects zooplanktivorous fishes, as well as decreased amounts of olfactory cues entering the sea for the attraction of larval and juvenile marine fishes into these estuaries. Hypersaline conditions can result in both a reduced species diversity and abundance. However, where estuaries lose their normal estuarine salinity gradient and become “arms” of the sea, there is often an increase in fish species diversity due to stenohaline marine taxa entering the estuary. Unfortunately the gain in small numbers of marine stragglers is insufficient to compensate for the decline in estuarine dependent fishes that usually dominate these systems. Conversely, major river flooding often causes temporary decreases in both species diversity and abundance due to a rapid decline in salinity, increased suspended sediments, reduced dissolved oxygen levels, and a collapse in the availability of pelagic and benthic food resources. However, the “resetting” of estuaries by episodic events is part of the essential cycle that maintains and enhances estuarine productivity and habitat diversity. Recovery by estuary associated fishes from such events is usually rapid and linked to a variety of factors, especially estuary morphometry which has a direct influence on the flushing or retention of estuarine biota. Freshwater flows interact directly and indirectly with the fishes that inhabit estuaries, e.g. river floods directly influence estuarine morphometry, water temperature, salinity, pH, turbidity, nutrient status, organic inputs, dissolved oxygen concentrations and olfactory cues; and indirectly affect mouth status, tidal prism, habitat diversity, primary and secondary productivity, fish recruitment, food availability and competition. Depletion or removal of components of river flow to an estuary have major short and long-term negative impacts on the ichthyofauna, some of which can be ameliorated by the provision of an environmental freshwater allocation that is appropriate to that particular system.

Keywords

River flowSalinityFishEstuarySouth Africa
Type
Research Article
Information
Aquatic Living Resources , Volume 18 , Issue 3 , July 2005 , pp. 275 - 289
Copyright
© EDP Sciences, IFREMER, IRD, 2005

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Adams, J.B., Bate, G.C., Harrison, T.D., Huizinga, P., Taljaard, S., van Niekerk, L., Plumstead, E.E., Whitfield, A.K., Wooldridge, T.H., 2002, A method to assess the freshwater inflow requirements of estuaries and application to the Mtata Estuary, South Africa. Estuaries 25, 1382-1393. CrossRef
Adams, J.B., Bate, G.C., Knoop, W.T., 1992, The distribution of estuarine macrophytes in relation to freshwater. Bot. Mar. 35, 215-226.
Adams, J.B., Talbot, M.M., 1992, The influence of river impoundment on the estuarine seagrass Zostera capensis Setchell. Bot. Mar. 35, 69-75.
Allanson, B.R., Boltt, R.E., Hill, B.J., Schultz, V., 1966, An estuarine fauna in a freshwater lake in South Africa. Nature 209, 532-533. CrossRef
Allanson, B.R., Grange, N., Maree, B., 2000, An introduction to the chemistry of the water column of the Knysna Estuary with particular reference to nutrients and suspended solids. Trans. R. Soc. S. Afr. 55, 141-162. CrossRef
Allanson B.R., Read G.H.L., 1987, The response of estuaries along the south eastern coast of southern Africa to marked variation in freshwater inflow. Inst. Freshw. Stud. Rep. 2/87, 1-40.
Allanson, B.R., Read, G.H.L., 1995, Further comment on the response of Eastern Cape Province estuaries to variable freshwater flows. S. Afr. J. Aquat. Sci. 21, 56-70.
Allanson B.R., Winter D., 1999, Chemistry. In: Allanson B.R., Baird D. (Eds.), Estuaries of South Africa, pp. 53-89. Cambridge University Press, Cambridge.
Baird, D., Heymans, J.J., 1996, Assessment of ecosystem changes in response to freshwater inflow of the Kromme River Estuary, St Francis Bay, South Africa: a network analysis approach. Water SA 22, 307-318.
Baird, D., Ulanowicz, R.E., 1993, Comparative study on the trophic structure, cycling and ecosystem properties of four tidal estuaries. Mar. Ecol. Prog. Ser. 99, 221-237. CrossRef
Barletta, M., Barletta-Bergen, A., Saint-Paul, U., Hubold, G., 2005, The role of salinity in structuring the fish assemblages in a tropical estuary. J. Fish Biol. 66, 45-72. CrossRef
Bass, A.J., D'Aubrey, J.D., Kistnasamy, N., 1973, Sharks of the east coast of southern Africa. 1. The genus Carcharhinus (Carcharhindae). Investigat. Rep. Oceanogr. Res. Inst. 33, 1-168.
Bate, G.C., Whitfield, A.K., Adams, J.B., Huizinga, P., Wooldridge, T.H., 2002, The importance of the river-estuary interface zone in estuaries. Water SA 28, 271-279. CrossRef
Begg, G.W., 1978, The estuaries of Natal. Natal Town and Regional Planning Report 41, 657.
Bennett, B.A., 1985, A mass mortality of fish associated with low salinity conditions in the Bot River estuary. Trans. R. Soc. S. Afr. 45, 437-448. CrossRef
Bennett, B.A., 1994, The fish community of the Berg River estuary and an assessment of the likely effects of reduced freshwater inflows. S. Afr. J. Zool. 29, 118-125. CrossRef
Bennett, B.A., Branch, G.M., Hamman, K.C.D., Thorne, S., 1985, Changes in the fish fauna of the Bot River estuary in relation to opening and closure of the estuary mouth. Trans. R. Soc. S. Afr. 45, 449-464.
Bickerton, I.B., Pierce, S.M., 1988, Report No. 33: Krom (CMS 45), Seekoei (CMS 46) and Kabeljous (CMS 47). In: Estuaries of the Cape. Part 2. Synopses of available information on individual systems. CSIR Res. Rep. 432, 1-109.
Blaber, S.J.M., 1973, Temperature and salinity tolerance of juvenile Rhabdosargus holubi (Steindachner) (Teleostei: Sparidae). J. Fish Biol. 5, 593-598. CrossRef
Blaber, S.J.M., 1974, Osmoregulation in juvenile Rhabdosargus holubi (Steindachner) (Teleostei: Sparidae). J. Fish Biol. 6, 797-800. CrossRef
Blaber, S.J.M., 1979, The biology of filter feeding teleosts in Lake St Lucia, Zululand. J. Fish Biol. 15, 37-59. CrossRef
Blaber, S.J.M., 1981, An unusual mass mortality of Clarias gariepinus in the Mkuze River at Lake St Lucia. Lammergeyer 31, 43.
Blaber, S.J.M., Whitfield, A.K., 1976, Large scale mortality of fish at St Lucia. S. Afr. J. Sci. 72, 218.
Bok, A.H., 1979, The distribution and ecology of two mullet species in some freshwater rivers in the eastern Cape, South Africa. J. Limnol. Soc. S. Afr. 5, 97-102.
Boltt, R.E., 1975, The benthos of some southern African lakes. Part 5: The recovery of the benthic fauna of St Lucia following a period of excessively high salinity. Trans. R. Soc. S. Afr. 41, 295-323.
Brown, A.C., 1958, The ecology of South African estuaries. Part 9: Notes on the estuary of the Orange River. Trans. R. Soc. S. Afr. 35, 463-473.
Bruton M.N., Bok A.H., Davies M.T.T., 1987, Life history styles of diadromous fishes in inland waters of southern Africa. Am. Fish. Soc. Symp.1, 104-121.
Campbell, E.E., Knoop, W.T., Bate, G.C., 1991, A comparison of phytoplankton biomass and primary production in three Eastern Cape estuaries, South Africa. S. Afr. J. Sci. 87, 259-264.
Cooper, J.A.G., 1989, Fairweather versus flood sedimentation in Mhlanga lagoon, Natal: implications for environmental management. S. Afr. J. Geol. 92, 279-294.
Cooper, J.A.G., 1993, Sedimentary processes in the river-dominated Mvoti estuary, South Africa. Geomorphology 9, 271-300. CrossRef
Cooper J.A.G., 1994, Lagoons and microtidal coasts. In: Carter R.W.G., Woodroffe C. (Ed.), Coastal Evolution, pp. 219-265. Cambridge University Press, Cambridge.
Cyrus, D.P., 1991, The biology of Solea bleekeri (Teleostei) in Lake St Lucia on the south east coast of Africa. Neth. J. Sea Res. 27, 209-216. CrossRef
Davies B.R., Day J.H., 1986, The Biology and Conservation of South Africa Vanishing Waters. University of Cape Town, Rondebosch.
Davies B.R., O'Keefe J.H., Snadden C.D., 1993, A synthesis of ecological functioning, conservation and management of South African river ecosystems. Water Res. Comm. Rep. TT62/93.
Day J.H., 1981a, Summaries of current knowledge of 43 estuaries in southern Africa. In: Day J.H. (Ed.), Estuarine Ecology with Particular Reference to Southern Africa, pp. 251-330. A.A. Balkema, Cape Town.
Day J.H., 1981b, Estuarine currents, salinities and temperatures. In: Estuarine Ecology With Particular Reference to Southern Africa (Ed. J.H.Day), pp. 27-44. A.A. Balkema, Cape Town.
Day J.H., Morgans J.F.C., 1956, The ecology of South African estuaries. Part 7: The biology of Durban Bay. Ann. Natal Mus.13, 259-312.
Department of Water Affairs and Forestry 1986. Management of the Water Resources of the Republic of South Africa. Government Printer, Pretoria.
Drinkwater, K.F., Frank, K.T., 1994, Effects of river regulation and diversion on marine fish and invertebrates. Aquat. Conserv. Mar. Freshw. Ecosyst. 4, 135-151. CrossRef
Dye, P., Poulter, A., 1995, Clearing invasive trees in riparian zones increases streamflow. Environ. Planning Manage. 6, 13-15.
Emmerson, W.D., Erasmus, T., 1987, The nutrient status of the Kromme River estuary, South Africa. Hydrobiologia 148, 87-96. CrossRef
Forbes, A.T., Benfield, M.C., 1986, Tidal behaviour of postlarval penaeid prawns (Crustacea: Decapoda: Penaeidae) in a southeast African estuary. J. Exp. Mar. Biol. Ecol. 102, 23-34. CrossRef
Forbes, A.T., Cyrus, D.P., 1993, Biological effects of salinity gradient reversals in a southeast African estuarine lake. Neth. J. Aquat. Ecol. 27, 265-272. CrossRef
Garcia, A.M., Vieira, J.P., Winemiller, K.O., 2003, Effects of the 1997-1998 El Niño on the dynamics of the shallow-water fish assemblage of the Patos Lagoon estuary (Brazil). Estuar. Coast. Shelf Sci. 57, 489-500. CrossRef
Garcia, A.M., Vieira, J.P., Winemiller, K.O., Grimm, A.M., 2004, Comparison of 1982-1983 and 1997-1998 El Niño effects on the shallow-water fish assemblage of the Patos Lagoon Estuary. Estuaries 27, 905-914. CrossRef
Gillanders, B.M., Kingsford, M.J., 2002, Impact of changes in flow of freshwater on estuarine and open coastal habitats and the associated organisms. Oceanogr. Mar. Biol. Ann. Rev. 40, 233-309.
Grange N., 1992, The influence of contrasting freshwater inflows on the feeding ecology and food resources of zooplankton in two Eastern Cape estuaries, South Africa. PhD thesis, Rhodes University, Grahamstown.
Grange, N., Allanson, B.R., 1995, The influence of freshwater inflow on the nature, amount and distribution of seston in estuaries of the Eastern Cape, South Africa. Estuar. Coast. Shelf Sci. 40, 403-420. CrossRef
Grange N., Whitfield A.K., de Villiers C.J., Allanson B.R., 2000, The response of two South African east coast estuaries to altered river flow regimes. Aquat. Conserv. Mar. Freshw. Ecosyst.10, 155-177.
Grimes, C.B., Kingsford, M.J., 1996, How do river plumes of different sizes influence fish larvae: do they enhance recruitment? Mar. Freshw. Res. 47, 191-208. CrossRef
Grindley, J.R., 1964, Effect of low-salinity water on the vertical migration of estuarine plankton. Nature 203, 781-782. CrossRef
Hanekom, N., 1989, A note on the effects of a flood of medium intensity on macrobenthos of soft substrata in the Swartkops estuary, South Africa. S. Afr. J. Mar. Sci. 8, 349-355. CrossRef
Hanekom N., Baird D., 1984, Fish community structures in Zostera and non-Zostera regions of the Kromme estuary, St Francis Bay. S. Afr. J. Zool.19, 295-301.
Hara T.J., 1992, Overview and introduction. In: Hara T.J. (Ed.), Fish Chemoreception pp. 1-12. Chapman and Hall, London.
Harrison, T.D., 2004, Physico-chemical characteristics of South African estuaries in relation to the zoogeography of the region. Estuar. Coast. Shelf Sci. 61, 73-87. CrossRef
Harrison, T.D., Whitfield, A.K., 1995, Fish community structure in three temporarily open/closed estuaries on the Natal coast. Ichthyol. Bull. Smith Inst. Ichthyol. 64, 1-80.
Hedgpeth J.W., 1967, Ecological aspects of the Laguna Madre, a hypersaline estuary. In: Lauff G.H. (Ed.), Estuaries pp. 408-419. Am. Assoc. Advancem. Sci., Washington, DC.
Harris, S.A., Cyrus, D.P., 1999, Composition, abundance and seasonality of fish larvae in the mouth of Durban Harbour, KwaZulu-Natal, South Africa. S. Afr. J. Mar. Sci. 21, 19-39. CrossRef
Hill, B.J., 1975, The origin of southern African coastal lakes. Trans. R. Soc. S. Afr. 41, 225-240. CrossRef
Hill B.J., 1981, Adaptations to temperature and salinity stress in southern African estuaries. In: Day J.H. (Ed.), Estuarine Ecology with Particular Reference to Southern Africa, pp. 187-196. A.A. Balkema, Cape Town.
Hilmer, T., Bate, G.C., 1991, Vertical migration of a flagellate-dominated bloom in a shallow South African estuary. Bot. Mar. 34, 113-121. CrossRef
Howard-Williams, C., 1977, The distribution of nutrients in Swartvlei, a southern Cape coastal lake. Water SA 3, 213-217.
Huizinga P., van Niekerk L., 1997, The hydrodynamics of the Thukela Estuary. CSIR Rep., Stellenbosch.
Hurst, T.P., McKown, K.A., Conover, D.O., 2004, Interannual and long-term variation in the nearshore fish community of the mesohaline Hudson River Estuary. Estuaries 27, 659-669. CrossRef
Hutchison, I.P.G., 1977, Lake St Lucia - the computer points the way. Afr. Wildl. 31, 25-27.
Hutchison, I.P.G., Midgley, D.C., 1978, Modelling the water and salt balance in a shallow lake. Ecol. Model. 4, 211-235. CrossRef
Jezewski, W.A., Roberts, C.P.R., 1986, Estuarine and lake freshwater requirements. Dep. Water Affairs Tech. Rep. 129, 1-36.
Kok, H.M., Whitfield, A.K., 1986, The influence of open and closed mouth phases on the marine fish fauna of the Swartvlei estuary. S. Afr. J. Zool. 21, 613-617.
Kyle, R., 1989, A mass mortality of fish at Kosi Bay. Lammergeyer 40, 39.
Largier, J.L., Attwood, C., Harcourt-Baldwin, J.-L., 2000, The hydrographic character of the Knysna Estuary. Trans. R. Soc. S. Afr. 55, 107-122. CrossRef
Mann, B.Q., James, N.C., Beckley, L.E., 2002, An assessment of the recreational fishery in the St Lucia estuarine system, KwaZulu-Natal, South Africa. S. Afr. J. Mar. Sci. 24, 263-279. CrossRef
Marais J.F.K., 1982, The effects of river flooding on the fish populations of two Eastern Cape estuaries. S. Afr. J. Zool.17, 96-104.
Marais J.F.K., 1983, Fish abundance and distribution in the Gamtoos estuary with notes on the effects of floods. S. Afr. J. Zool.18, 103-109.
Marais, J.F.K., 1988, Some factors that influence fish abundance in South African estuaries. S. Afr. J. Mar. Sci. 6, 67-77. CrossRef
Martin, T.J., 1988, Interaction of salinity and temperature as a mechanism for spatial separation of three coexisting species of Ambassidae (Cuvier) (Teleostei) in estuaries on the southeast coast of Africa. J. Fish Biol. 33, 9-15. CrossRef
Martin, T.J., Cyrus, D.P., Forbes, A.T., 1992, Episodic events: the effects of cyclonic flushing on the ichthyoplankton of St Lucia estuary on the southeast coast of Africa. Netherlands J. Sea Res. 30, 273-278. CrossRef
McLachlan, A., Grindley, J.R., 1974, Distribution of macrobenthic fauna of soft substrata in Swartkops estuary with observations on the effects of floods. Zool. Afr. 9, 147-160.
Mehl, J.A.P., 1973, Ecology, osmoregulation and reproductive biology of the white steenbras Lithognathus lithognathus (Teleostei: Sparidae). Zool. Afr. 8, 157-230. CrossRef
Millard, N.A.H., Broekhuysen, G.J., 1970, The ecology of South African estuaries. Part 10. St Lucia. A second report. Zool. Afr. 5, 277-307.
Mires, D., Shak, Y., Shilo, S., 1974, Further observations on the effect of salinity and temperature changes on Mugil capito and Mugil cephalus fry. Bamidgeh 26, 104-109.
Panikkar, N.K., 1960, Physiological aspects of adaptation to estuarine conditions. Aust. Fish. Counc. Proc. 32, 168-175.
Paterson, A.W., 1995, Preliminary observations on the ecology of the blackspotted electric ray. The Naturalist 39, 32-34.
Paterson, A.W., Whitfield, A.K., 1997, A stable carbon isotope study of the food-web in a freshwater-deprived South African estuary, with particular emphasis on the ichthyofauna. Estuar. Coast. Shelf Sci. 45, 705-715. CrossRef
Perry J.E., 1989, The impact of the September 1987 floods on the estuaries of Natal/Kwazulu; a hydro-photographic perspective. CSIR Res. Rep. 640, 1-29.
Pooley, A.C., 1975, New fish records for Ndumu Game Reserve. Lammergeyer 22, 50-51.
Prins J.G., 1990, Assessment of environmental water requirement of the Orange River mouth. Department of Water Affairs Report V/D400/01/E001, Pretoria.
Ratte T.H., 1989, Population structure, production, growth, reproduction and the ecology of Atherina breviceps Valenciennes, 1935 (Pisces: Atherinidae) and Gilchristella Aestuaria (Gilchrist, 1914) (Pisces: Clupeidae), from two southern Cape coastal lakes. PhD thesis, University of Port Elizabeth, Port Elizabeth.
Read, G.H.L., 1983, The effect of a dry and wet summer on the thermal and salinity structure of the middle and upper reaches of the Keiskamma estuary, Ciskei. Trans. R. Soc. S. Afr. 45, 45-62. CrossRef
Read, G.H.L., 1985, Factors affecting the distribution and abundance of Macrobranchium petersi (Hilgendorf) in the Keiskamma River and estuary, South Africa. Estuar. Coast. Shelf Sci. 21, 313-324. CrossRef
Reavell, P.E., Cyrus, D.P., 1989, Preliminary observations on the macrocrustacea of coastal lakes in the vicinity of Richards Bay, South Africa. S. Afr. J. Aquat. Sci. 15, 103-128.
Reddering, J.S.V., 1988, Prediction of the effects of reduced river discharge of the estuaries of the southeastern Cape Province, South Africa. S. Afr. J. Aquat. Sci. 84, 726-730.
Reddering, J.S.V., Esterhuysen, K., 1987, The effects of river floods on sediment dispersal in small estuaries: a case study from East London. S. Afr. J. Geol. 90, 458-470.
Reddering, J.S.V., Rust, I.C., 1990, Historical changes and sedimentary characteristics of southern African estuaries. S. Afr. J. Aquat. Sci. 86, 425-428.
Robarts, R.D., 1976, Primary productivity of the upper reaches of a South African estuary (Swartvlei). J. Exp. Mar. Biol. Ecol. 24, 93102. CrossRef
Russell, I.A., 1996, Water quality in the Knysna estuary. Koedoe 39, 1-8. CrossRef
Scharler U.M., 2000, Response of nutrient status and biotic communities to variable freshwater input regimes in Eastern Cape estuaries, South Africa, including a network analysis approach. PhD Thesis, University of Port Elizabeth, Port Elizabeth.
Schlacher, T.A., Wooldridge, T.H., 1996a, Ecological responses to reductions in freshwater supply and quality in South Africa's estuaries: lessons for management and conservation. J. Coast. Conserv. 2, 115-130. CrossRef
Schlacher, T.A., Wooldridge, T.H., 1996b, Axial zonation patterns of subtidal macrozoobenthos in the Gamtoos estuary, South Africa. Estuaries 19, 680-696. CrossRef
Schumann, E.H., Pearce, M.W., 1997, Freshwater inflow and estuarine variability in the Gamtoos estuary, South Africa. Estuaries 20, 124-133. CrossRef
Sinclair, S.A., Lane, S.B., Grindley, J.R., 1986, Report No. 32: Verlorenvlei (CW 13). In: Estuaries of the Cape. Part 2. Synopses of available information on individual systems. CSIR Res. Rep. 431, 1-95.
Slinger, J.H., Breen, C.M., 1995, Integrated research into estuarine management. Water Sci. Technol. 32, 79-86.
Stabell O.B., 1992, Olfactory control of homing behaviour in salmonids. In: Hara T.J. (Ed.) Fish Chemoreception. Chapman and Hall, London.
Strydom, N.A., 2003, Occurrence of larval and early juvenile fishes in the surf zone adjacent to two intermittently open estuaries, S. Afr. Environ. Biol. Fishes 66, 349-359. CrossRef
Strydom, N.A., Whitfield, A.K., Paterson, A.W., 2002, The influence of altered freshwater flow regimes on larval and juvenile Gilchristella aestuaria (Pisces: Clupeidae) abundance in the upper reaches of two South African estuaries. Mar. Freshw. Res. 53, 431-438. CrossRef
Sylvester, J.R., Nash, C.E., Emberson, C.R., 1975, Salinity and oxygen tolerances of eggs and larvae of Hawaiian striped mullet, Mugil cephalus L. J. Fish Biol. 7, 621-629. CrossRef
Talbot, M.M.B., Knoop, W.T., Bate, G.C., 1990, The dynamics of estuarine macrophytes in relation to flood/siltation cycles. Bot. Mar. 33, 159-164. CrossRef
Ter Morshuizen, L.D., Whitfield, A.K., 1994, The distribution of littoral fish associated with eelgrass Zostera capensis in the Kariega estuary, a southern African system with a reversed salinity gradient. S. Afr. J. Mar. Sci. 14, 95-105. CrossRef
Ter Morshuizen, L.D., Whitfield, A.K., Paterson, A.W., 1996, Influence of freshwater flow regime on fish assemblages in the Great Fish River and estuary. S. Afr. J. Aquat. Sci. 22, 52-61.
Ter Morshuizen, L.D., Whitfield, A.K., Paterson, A.W., 1997, Distribution patterns of fishes in an Eastern Cape estuary and river with particular emphasis on the ebb and flow region. Trans. R. Soc. S. Afr. 51, 257-280. CrossRef
van der Elst R.P., Blaber S.J.M., Wallace J.H., Whitfield A.K., 1976, The fish fauna of Lake St Lucia under different salinity regimes. In: Heydorn A.E.F. (Ed.), St Lucia Scientific Advisory Council Workshop Meeting - Charters Creek 15-17 Feb. 1976, Appendix 1. Natal Parks, Game and Fish Preservation Board, Pietermaritzburg.
van Heerden, I.L., 1986, Fluvial sedimentation in the ebb dominated Orange estuary. S. Afr. J. Aquat. Sci. 82, 141-147.
Vorwerk, P.D., Whitfield, A.K., Cowley, P.D., Paterson, A.W., 2003, The influence of selected environmental variables on fish assemblage structure in a range of southeast African estuaries. Environ. Biol. Fishes 66, 237-247. CrossRef
Wallace, J.H., 1975, The estuarine fishes of the east coast of South Africa. Part 1. Species composition and length distribution in the estuarine and marine environments. Part 2. Seasonal abundance and migrations. Investig. Rep. Oceanogr. Res. Inst. 40, 1-72.
Whitfield, A.K., 1977, The future of aquatic birds at Lake St Lucia. Bokmakierie 29, 24-25.
Whitfield A.K., 1980, A checklist of fish species recorded from Maputaland estuarine systems. In: Bruton M.N., Cooper K.H. (Ed.), Studies on the Ecology of Maputaland, pp. 204-209. Rhodes University, Grahamstown.
Whitfield, A.K., 1989, Paradise lagoon or paradise lost? Ichthos 22, 2-3.
Whitfield, A.K., 1992, A characterization of Southern African estuarine systems. S. Afr. J. Aquat. Sci. 18, 89-103.
Whitfield, A.K., 1994, Abundance of larval and 0+ juvenile marine fishes in the lower reaches of three southern African estuaries with differing freshwater inputs. Mar. Ecol. Prog. Ser. 105, 257-267. CrossRef
Whitfield, A.K., 1995a, Mass mortalities of fish in South African estuaries. S. Afr. J. Aquat. Sci. 21, 29-34.
Whitfield, A.K., 1995b, Threatened fishes of the world: Syngnathus watermeyeri Smith,1963 (Syngnathidae). Environ. Biol. Fishes 43, 152. CrossRef
Whitfield, A.K., 1998, Biology and ecology of fishes in southern African estuaries. Ichthyological Monogr. Smith Inst. Ichthyol. 2, 1-223.
Whitfield, A.K., Blaber, S.J.M., Cyrus, D.P., 1981, Salinity ranges of some southern African fish species occurring in estuaries. S. Afr. J. Zool. 16, 151-155. CrossRef
Whitfield A.K., Bruton M.N., 1989. Some biological implications of reduced fresh water inflow into eastern Cape estuaries: a preliminary assessment. S. Afr. J. Sci. 85, 691-695.
Whitfield, A.K., Harrison, T.D., 2003, River flow and fish abundance in a South African estuary. J. Fish Biol. 62, 1467-1472. CrossRef
Whitfield, A.K., Harrison, T.D., 1996, Gilchristella aestuaria (Pisces: Clupeidae) biomass and consumption of zooplankton in the Sundays Estuary. S. Afr. J. Mar. Sci. 17, 49-53. CrossRef
Whitfield, A.K., Paterson, A.W., 1995, Flood-associated mass mortality of fishes in the Sundays estuary. Water SA 21, 385-389.
Whitfield, A.K., Paterson, A.W., 2003, Distribution patterns of fishes in a freshwater deprived Eastern Cape estuary, with particular emphasis on the geographical headwater region. Water SA 29, 61-67.
Whitfield, A.K., Paterson, A.W., Bok, A.H., Kok, H.M., 1994, A comparison of the ichthyofaunas in two permanently open eastern Cape estuaries. S. Afr. J. Zool. 29, 175-185. CrossRef
Whitfield A.K., Wood A.D. (Ed.), 2003, Studies on the river-estuary interface region of selected Eastern Cape estuaries. Water Research Commission Report 756/1/03, 1-313.
Whitfield A.K., Wooldridge T.H., 1994, Changes in freshwater supplies to southern African estuaries: some theoretical and practical considerations. In: Dyer K.R, Orth R.J. (Ed.), Changes in Fluxes in Estuaries: Implications From Science to Management, pp. 41-50. Olsen, Olsen, Fredensborg.
Wooldridge, T.H., 1991, Exchange of two species of decapod larvae across an estuarine mouth inlet and implications of anthropogenic changes in the frequency and duration of mouth closure. S. Afr. J. Aquat. Sci. 87, 519-525.
Wooldridge T.H., 1999, Estuarine zooplankton community structure and dynamics. In: Allanson B.R., Baird D. (Eds.), Estuaries of South Africa. pp. 141-166. Cambridge University Press, Cambridge.
Wooldridge, T.H., Melville-Smith, R., 1979, Copepod succession in two South African estuaries. J. Plankton Res. 1, 329-341. CrossRef